UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre

The US Cordillera

Excursion 2015

Edited by Henrik Åslund

Contributors Erik Alsteryd, Diana Carlsson, Sandra Davidsson, Anders Eurenius, Eric Floberg, Susanna Gelin, Alexandra Glommé, Rickard Haeggman, Annelie Helmfrid,

Jimmy Jakobsson, Filip Johansson, Andreas Karlsson, Aron Kindbom Jonsson, Emma Kruse, Sara Kullberg, Lorenz Lindroth, Camilla Lindström, Caroline Lundell,

Christoffer Åkesson, Henrik Åslund

ISSN 1400-383X C122 Report Göteborg 2016

Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN The US Cordillera Excursion 2015

Contents

Foreword ...... viii Contributors ...... viii Part I: Introduction ...... ix Preface ...... 1 Field stops...... 2 Part II: Road logs ...... 3 5 October – Picking up the mini-vans in Denver and arriving in Golden – Erik Alsteryd ...... 4 6 October – Red Rocks – Aron Kindbom Jonsson ...... 4 7 October – Golden to Steamboat Springs – Sandra Davidsson ...... 5 8 October – Steamboat Springs to Dinosaur National Monument – Sandra Davidsson ...... 6 9 October – Dinosaur National Monument – Sara Kullberg ...... 7 10 October – Rock Springs – SLC – Caroline Lundell ...... 7 11 October – Salt Lake and Wendover – Henrik Åslund ...... 8 12 October – the Robinson Mine – Lorenz Lindroth ...... 10 13 October – Zion National Park – Alexandra Glommé ...... 10 14 October – The Navajo Bridge – Rickard Haeggman ...... 11 15 October – The Descent of Grand Canyon – Anders Eurenius ...... 11 16 October – Grand Canyon to Las Vegas – Camilla Lindström ...... 13 17 October – Las Vegas to Red Rock Canyon – Henrik Åslund ...... 14 18 October – Red Rock Canyon Campground, Utah to Furnace Creek Campground, Nevada – Eric Floberg ...... 14 19 October – Furnace Creek Campground to Motel 6 Mammoth Lake, CA – Annelie Helmfrid ...... 15 20 October – Mammoth Lakes – Filip Johansson ...... 16 21 October – Från Yosemite till Sierra Nevada – Christoffer Åkesson...... 17 22 October – San Francisco – Andreas Karlsson ...... 17 23 October – Return of the Geeks – Jimmy Jakobsson ...... 18 Part III: Essays ...... 19 1 The Unclear Origin of the Ancestral Rocky Mountains ...... 20 Alexandra Glommé

Abstract ...... 20

i

The US Cordillera Excursion 2015

Introduction ...... 20 Theories ...... 22 Summary ...... 23 References ...... 24 2 The Dakota Formation and its Associated Flora and Fauna ...... 25 Sandra Davidsson

Introduction ...... 25 The Dakota Formation ...... 25 Flora ...... 28 Fauna ...... 29 Climate ...... 31 Conclusions ...... 32 References ...... 32 3 The Morrison Formation of Late Jurassic age: An Overview of the Paleontology, Paleoenvironment and Paleoclimate During Deposition ...... 35 Camilla Lindström

Introduction ...... 35 Geology and Tectonic Setting ...... 36 Paleoclimate Overview ...... 38 Paleontology Overview ...... 38 Conclusions ...... 41 References ...... 41 4 The Yavapai Province, Crustal Growth and Metamorphic Development ...... 43 Diana Carlsson

Abstract ...... 43 Introduction ...... 43 The Yavapai Province ...... 43 The Yavapai orogen and metamorphic development ...... 45 Summary ...... 47 References ...... 48 5 Western Interior Seaway - Sedimentology and Stratigraphy in Relation to the Sevier Orogenic Belt ...... 49 Anders Eurenius

ii

The US Cordillera Excursion 2015

The Western Interior Seaway ...... 49 The Sevier orogeny ...... 50 Environments and lateral extent of the Western Interior Seaway ...... 50 Sediment from the Sevier ...... 51 Tectonic effects on subsidence and sedimentation ...... 52 Summary ...... 53 References ...... 54 6 Sierra Nevada-Batoliten ...... 55 Sara Kullberg

Abstrakt ...... 55 Introduktion ...... 55 Tektonisk utveckling ...... 56 Sierra Nevada-batoliten ...... 57 Plutoner och sviter ...... 57 Kemiska trender ...... 57 Ursprung ...... 58 Platsproblemet ...... 58 Mineraliseringar ...... 59 Sammanfattning ...... 59 Referenser ...... 60 7 The Colorado Plateau and the development of the Grand Canyon ...... 61 Christoffer Åkesson

Introduction ...... 61 Stratigrapfy ...... 61 Geologic history of the Colorado Plateau ...... 63 Conclusions ...... 64 References ...... 65 8 Post-Laramide Development of Relief in the Rocky Mountains and Foothills ...... 66 Henrik Åslund

Introduction ...... 66 Endogenous processes ...... 67 Exogenous processes ...... 68 Topographic history ...... 68

iii

The US Cordillera Excursion 2015

Controversy ...... 70 Conclusion ...... 70 References ...... 71 9 Glaciation in the Sierra Nevada, CA: Chronology and Climate Susceptibility of an Alpine Ice Field...... 72 Filip Johansson

Introduction ...... 72 Regional setting ...... 72 Pleistocene glaciations ...... 73 Dansgaard-Oeschger events in the Sierra Nevada ...... 74 Heinrich events in the Sierra Nevada ...... 75 Holocene glacial fluctuations ...... 76 Conclusions ...... 78 References ...... 78 10 Sandstone Hosted Uranium Deposits of the Roll-Front Type in the Western Cordillera, USA 80 Jimmy Jakobsson

Occurrence and classification ...... 80 Host rock ...... 81 Source rock and mechanism of transport ...... 82 Morphology ...... 84 Mining...... 84 References ...... 85 11 Basins of the Green River Formation ...... 87 Erik Alsteryd

Introduction ...... 87 Stratigraphy ...... 88 Uinta Basin ...... 88 Green River Basin ...... 90 Washakie Basin...... 90 Piceance Basin ...... 90 Oil and Gas ...... 91 Mineral resources...... 92

iv

The US Cordillera Excursion 2015

Summary ...... 92 References ...... 92 12 Sedimentological and Tectonic Relations of Neoproterozoic Rift Basins: Uinta Mountain Group, Big Cottonwood Formation, Chuar Group and Pahrump Group ...... 94 Lorenz Lindroth

Introduction ...... 94 Uinta Mountain Group ...... 94 Big Cottonwood Formation ...... 97 Chuar Group ...... 98 Pahrump Group ...... 99 References ...... 100 13 Earthscope ...... 102 Richard Haeggman

USArrays ...... 102 Farallon ...... 103 San Andreas Fault Observatory at Depth ...... 105 Plate Boundary Observatory ...... 106 Conclusion ...... 106 References ...... 106 14 Lake Bonneville: The Development of the Largest Pluvial Lake in North America During the Late Pleistocene ...... 108 Eric Floberg

Introduction ...... 108 General geology of the Lake Bonneville area ...... 108 The development of Lake Bonneville ...... 110 The transgressive period ...... 110 The overflowing period ...... 110 The regressive period ...... 111 Isostacy ...... 111 Summary ...... 111 References ...... 112 15 Risks of Earthquakes in the Western USA: The Basin and Range Province ...... 114 Emma Kruse

v

The US Cordillera Excursion 2015

Introduction ...... 114 Basin and Range and its seismic activity and geologic history ...... 114 Basic fact of the Basin and Range ...... 117 Seismicity ...... 118 Hurricane fault ...... 119 Earthquake data from USGS ...... 120 Conclusions ...... 122 References ...... 122 16 Gold, Copper and Related Sulphide Mineralizations in Nevada ...... 124 Caroline Lundell

Introduction ...... 124 Carlin-type deposits ...... 125 Genetic models ...... 125 Tectonics...... 125 Where is the gold? ...... 127 Alteration...... 127 Additional ore deposits in Nevada ...... 128 Discussion ...... 128 References ...... 128 17 The California Gold Rush ...... 130 Aron Kindbom Jonsson

Introduction ...... 130 The discovery and the initiation of the California Gold Rush ...... 130 Society and economics ...... 130 The miners and their methods ...... 131 Mother lode ...... 134 References ...... 135 18 Dissemination of Metals from Abandoned Mines in the United States ...... 137 Annelie Helmfrid

Introduction ...... 137 EPA's Superfund ...... 137 Examples of contaminated mining areas – Leviathan Mine, California ...... 137 The Gold King Mine, Colorado ...... 138

vi

The US Cordillera Excursion 2015

Discussion ...... 140 Dissemination and long-term effects ...... 140 Risk of contamination...... 141 Measures to prevent AMD and mining-related disasters ...... 141 Summary ...... 141 References ...... 142 19 California Drought: The Golden State Goes Brown ...... 143 Susanna Gelin

Introduction ...... 143 Questions at issue ...... 143 Climate in California ...... 143 The current drought in California ...... 144 Droughts in the past ...... 145 Causes and predictability ...... 145 Climate change in California...... 145 El Niño’s influence on California drought ...... 146 Impacts of the ongoing drought in California ...... 146 Water management and groundwater legislation...... 148 Mono Lake ...... 150 Discussion ...... 150 References ...... 151 20 On the Exotic High-Grade Metamorphic Blocks in a Subduction Mélange from the Franciscan Complex, CA ...... 154 Andreas Karlsson

Introduction ...... 154 General geological background of the high grade blocks of the Franciscan ...... 155 Tectonic and temporal models of Franciscan subduction ...... 158 New insights into the P-T-t-paths of the high-grade blocks ...... 159 References ...... 161

vii

The US Cordillera Excursion 2015

Foreword As a geologist it is important to get out in the field to test and push one’s understanding of the subject and improve one’s field skills as often as the opportunity presents itself. Associate Professor Lennart Björklund1 enabled us to do just that as he guided us through this adventure in the “tectonic penthouse” that is the western USA. Lennart also went out of his way to share valuable insights in American culture throughout this journey as they randomly presented themselves on our journey and as he presented lectures. Therefore, would we like to dedicate this foreword as an acknowledgement to show our warmest gratitude to Lennart and his wife and associate Professor Piret Plink- Björklund3 who together developed and perfected this field trip over the years. Piret also set the bar for this journey as she presented valuable lectures in the field at the very beginning of the journey at the Red Rocks Amphitheatre, Colorado.

– The students

Edited by

Henrik Åslund1

Contributors

Erik Alsteryd1, Diana Carlsson1, Sandra Davidsson1, Anders Eurenius1, Eric Floberg1, Susanna Gelin1, Alexandra Glommé2, Rickard Haeggman1, Annelie Helmfrid1, Jimmy Jakobsson1, Filip Johansson1, Andreas Karlsson1, Aron Kindbom Jonsson1, Emma Kruse1, Sara Kullberg2, Lorenz Lindroth1, Camilla Lindström1, Caroline Lundell1, Christoffer Åkesson1, Henrik Åslund1

1University of Gothenburg, SE 405 30 Göteborg, Sweden 2Lund University, SE 221 00 Lund, Sweden. 3Colorado School of Mines, Golden, CO 80401, USA.

viii

The US Cordillera Excursion 2015

Part I: Introduction Part I:

Introduction

ix

The US Cordillera Excursion 2015

Preface

This report is part of the course non-Nordic geology, GV6000, the course is available at the University of Gothenburg during every other fall semester, from October to December. GV6000 is comprised of two parts, an excursion to the US that took place from 5- 24 October 2015 and this report, which is the result of a joint effort from all the participants of the course.

This report is made up of three parts: I. Introduction II. Road logs III. Essays

Every student has written a short essay on a subject of their own choosing. These were written in American and British English except essay 6 which was written in Swedish. The students also presented their subjects in the field at a suitable location connected with each subject. The Essays in part III are thus ordered primarily after the order in which they were presented in the field, secondly after similarity with other essay and thirdly after the geologic time of relevant events. A map of the route for the field stops is also included in the introduction. A road log was written for each day and these logs are chiefly written in the Swedish language. This report aims to give an overview over everything that we saw and learned in the US, since the geology there is dramatically different from that in Sweden. The excursion started just outside Denver, Colorado and ended in San Francisco about three weeks later. 20 students, as well as our Professor Lennart Björklund, were divided over three cars and one bus. We spent most nights camping, once even in freezing temperatures, and cooked a lot of our own food over gas stoves. The excursion took us through the dramatic and geologically young (compared to Sweden) landscape of the southwest US. Some highlights on the trip were the Rocky Mountains in Colorado, the Dinosaur National Monument on the border between Colorado and Utah, Zion National Park in Utah, Grand Canyon in Arizona and Yosemite in California, just to mention a few places. The field trip took us through 12 different orogenic periods. The Rocky Mountains in Colorado have been raised during three orogenic events; the Ancestral Rockies Orogen, the Laramide Orogen and the Sevier Orogen. The excursion also took us over the relatively undeformed Colorado Plateau which extends over Colorado, Utah, Arizona and New Mexico. The Basin and Range in Nevada is a good example on Neogene crustal extension and the Sierra Nevada in California consists of Jurassic-Cretaceous magmatic arc rocks. The Great Valley in California is very important agriculturally and is really a forearc basin unit, one of few forearc basins that are not submerged below the sea. The Coast Ranges in California are subduction-related and have been accreted from Jurassic to Paleogene, ophiolites and blueschist are found in this area.

Sandra Davidsson Henrik Åslund

1

The US Cordillera Excursion 2015

Field stops

Weather conditions were good throughout the excursion, consequently only a few modifications were made to the planed travel route. Stops and their corresponding dates are shown in Figure A.

Emma Kruse

Figure A. Field stops shown as colour coded dots according to date visited.

2

The US Cordillera Excursion 2015

Part II: Road logs Part II:

Road logs

3

The US Cordillera Excursion 2015

5 October – Picking up the mini-vans in Denver and arriving in Golden – Erik Alsteryd The day started as usual with a bathroom visit followed by an “American” breakfast at the motel in Denver. Eric, Erik and Christoffer got to the breakfast a little bit later than the others which were already in the process of stuffing themselves with the sweets that Americans eats for breakfast. After the breakfast everyone or almost everyone went to the shopping mall for a day of window shopping. The lunch was consumed at the malls lunch area and Eric, Erik and Christoffer ate a Philly cheesesteak sandwich which was very subpar. After the tour around the mall Lennart came to the motel and picked up those who wanted to drive (and those who didn’t want to drive but was over 25) in order to go to the rental place which was located next to the airport. Next to the airport apparently is 10km away. Andreas and Erik were the supposed to drive one of the cars and after a lot of talking to those who rented out the cars we finally got to choose a car. There were two Nissan and one Toyota. We obviously took the Toyota since Nissan is Nissan. The Toyota had the most space for packing and it had a cool map that was sadly only working within larger cities. The car also had automatic doors in the back which made it easier for the children; Aron, Jimmy and Filip to get out and in from the backseat. We also found a button to control the AC for the kids in the back. Lorenz and Rickard drove one of the Nissans and Caroline and Christoffer drove the other car. Since we were first out from the rental area, we decided to stay and wait for the others on the shoulder on the road. The road was 10m wide, with 5m wide gravel shoulders and there hardly was any traffic on it. But apparently the Americans that also rented cars and passed us wanted us to have our hazard lights on. Maybe the 10m wide road wasn’t enough to safely pass a parked vehicle that. On the return trip home Lennart left us alone since he had to pick up a passenger at the airport. There was a lot of traffic and really slow traffic on the way home because someone decided to drive faster the others in front and tried to pass a car straight through which obviously didn’t work out very well. We also noticed in the evening that the markings on the road are impossible to see if it’s dark and raining. There is no reflective paint on the road markings which made someone, maybe Erik, drive between two-three lanes. Anyhow we survived the beer run and made it back to the motel safely, with the beer intact. The day ended with the usual bathroom visit.

6 October – Red Rocks – Aron Kindbom Jonsson 06:00~09:00. Breakfast consisting of banana cupcakes, Danish pastries with severe frosting and a large amount of toasts. 08:00~12:00. Acquiring of supplies for the coming three days such as food, refreshments and camping equipment from REI. Some people used their extensive social skills in combination with the use of puppy eyes in order to get a pretty good discount on some of the camping equipment. 13:00~15:00. Lennart Björklund’s wife, Piret, is handling the education at Red Rocks Amphitheatre. After observations, discussions within the group and a brusque reminder from Lennart Björklund about reverse faults we come to the conclusion that the depositional environment for the Red Rocks is an alluvial fan.

4

The US Cordillera Excursion 2015

15:00~18:00. Looking at fossils and dinosaur tracks in mudrock. Sandra Davidsson holds presentation on the local flora and fauna at 100 Ma. ~18:00. Dinner at Woody’s Pizza. All you can eat for 11,97$ which is a fair price as the pizza and salad buffet was pretty good. Our 24 pairs of muddy shoes and boots result in frantic vacuuming by the staff. I and the people at my table did not realise the reason for this vacuuming until it was too late and we were already leaving. Other events: *Annelie Helmfrid was unable to receive her luggage at the airport on arrival and it has still not been found. * There is apparently a crucial difference between credit and debit on the American card payment devices. Pressing “credit” results in a smooth purchase without difficulties while pressing “debit” denies the transaction and gives the user a short sense of panic as the user assumes that their card will be useless in the United States or that the card and account information has been compromised. * In the Alsteryd Car some of us are educating the rest in how to operate the automatic doors.

7 October – Golden to Steamboat Springs – Sandra Davidsson We had to take a different path than planned over the Rocky Mountains due to snowfall during the night, this meant that some roads were closed. As Lennart so nicely put it: "The Americans cannot drive at all, they only press the gas pedal in their automatic cars and then hit the brakes and drive off the road." So now we take a road that does not go as high up and is located a little further south. We will see much Precambrian rocks today, first we will cross the Front Range, followed by flat terrain in tertiary rocks where the Rio Grande rift also goes. Then we go into the next mountain range, the Park Range, before ending the day in Steamboat Springs where we will be camping for the first time during this trip. Unfortunately, Annelie’s bags didn’t arrive together with her, somehow the luggage seems to have been left in London. The Americans have been surprisingly incompetent when trying to solve the problem, everyone Annelie has talked to have said different things. Sometimes, they have not had any idea where the bag is located, the next person said they know exactly which bag Annelie is talking about and that it would soon arrive at the hotel. Then the bag was lost again. The last I heard was that it had arrived to Steamboat Springs last night and was waiting for her there. The first stop of the day was close to Golden around Lookout Mountain, here we saw subvolcanic intrusions that were heavily fragmented due to sporadic uplift. Light felsic gneiss with biotite and isoclinal folds, there were also occasional thin layers with amphibolite in between. This is presumably due to bimodal volcanism. Diana had her presentation here. The next stop was at Berthoud pass. There we could see two types of topography. Topography 1 is rounded while topography 2 is sharper and cut through topography 1, this is caused by two different tectonic events and uplifts. Here we could also see meandering rivers despite the fact that we were at a high altitude, this is because the rivers were here before the rapid uplift and this has led to steep V-shaped valleys. It is unusual for such a steep uplift as the one we see here. Henrik and Philip had their talks here. Because we could not take the path Lennart had planned over the Rocky Mountains, we took the backway up, the sun had taken care of any leftover snow during the day. We did not come all the way to the highest point due to limited time, but it was be fun

5

The US Cordillera Excursion 2015 to drive on the paved road that is situated at the highest altitude in the US. The next stop of the day was in Rocky Mountain National Park. Higher up from our vantage point, we could see the same two types of topography as at Berthoud pass. We also saw a tertiary ignimbrite, composed of felsic and gas-rich magma. On the way down we stopped at a tuff outcrop. The tuff probably has the same age as the ignimbrite we saw on the top, thus early Miocene (ca. 25 Ma). Our fourth stop was just after Kremling and was in the northern part of the Rio Grande Basin. Lacolites were seen as round "blopps" here. The lacolites had lifted tertiary sediments from below. The magma was so ductile that it would rather lift the overlying sediment layers than flow out to the sides. Our last stop of the day was in the Park West Range. A reverse fault makes the Precambrian rocks lie above the Cretaceous rocks here. And not to forget, we also saw a very small and a very cute little squirrel here, too.

8 October – Steamboat Springs to Dinosaur National Monument – Sandra Davidsson We arrived to Steamboat Springs in the dark the night before, we were still at a high altitude so it was cold and we had to struggle a while rising our new tent. During the night we had a visit in the form of a fox with large ears and a long tail, it seemed quite at home and obviously went around looking for scraps of food. The night was cold, certainly below 0°C, and poor Annelie had still not received her bag, even though it should have been waiting for her in Steamboat Springs, luckily Jimmy had an extra sleeping bag that Annelie could borrow. Fortunately, the bag was delivered this morning as we were about to leave, a joyous and very relieved Annelie could at last relax and start to enjoy the trip. Unfortunately, she later discovered that the bag had been searched through and everything had been torn up and then just pressed into the bag again, so shampoo and sunscreen had leaked its content all over the bag. At the first stop of the day were at the Black Sulphur Springs in Steamboat Springs, the pungent smell of hydrogen sulphide led the way. It’s usually more water in the springs than it was today, the dark and cloying surface was now exposed to the air with just some lukewarm water in the bottom of the spring. Then we stopped at an outcrop of the Mesaverde group. Honeycomb weathering is common in some parts of the Mesaverde group, as well as cross-bedding – here we saw trough cross-beds. The next stop was in the Maybell area and here we saw large cross-beds, of eolian origin, deposited around Uinta. At the next stop close to the Colorado/Utah border we saw lots of what I think is prairie dogs, they are at least quite abundant here in Colorado and Utah. Here we saw older rock types lying above younger rocks. We also saw Weber sandstone from Perm lying below Triassic shale and Jurassic Navajo sandstone. At the fifth stop we saw petroglyphs in Navajo sandstone at Dinosaur National Monument. Traces of human settlements in this area is reaching back at least 10 000 years. However, the Indians that left these petroglyphs lived here about 400-500 A.D. and belonged to the Fremont culture. The last stop of the day was at Josie Bassett’s home, in Box Canyon. We walked into a canyon composed of Weber sandstone were we saw soft sediment deformation. Josie Bassett lived here during the early 20th century, she used Box Canyon to lock up her animals at night so the predators wouldn’t get to them. She was also famous for her love affairs and associations with infamous people such as Butch Cassidy’s Wild Bunch.

6

The US Cordillera Excursion 2015

9 October – Dinosaur National Monument – Sara Kullberg Dagen fick en spännande start med ett fynd av en Svarta Änkan i en av Filips skor. Folk blev lite upprymda, det var ju trots allt första gången vi fick se något farligt (tur bara att ingen kom till skada). Efter att vi hade packat ihop oss satte vi oss och njöt av utsikten över campingplatsen som var belägen vid en liten oas vid Green River mitt ute i öknen. Utöver en geologiredogörelse berättade Lennart även om Buffalo Bill och indianernas tro att geologer var galna då de talade med berg. Ett av dagens första stopp var i Dinosaur National Monument Museum vilken befinner sig mitt i Morrisson-formationen (155–148 Ma). Morrisson-formationen representerar en varierande lakustrin/fluvial miljö med en stor mångfald. Här fick vi även tid att shoppa loss! Därpå körde vi vidare och gjorde stopp vid bland annat Steinaker Dam and Reservoir och en del vägstopp utan exakt benämning för att kolla på stratigrafin i Green River-bassängen samt lunchstopp vid en fosfatgruva belägen i Fosforia-formationen (270– 250 Ma). När dagen närmade sig sitt slut begav vi oss till Flaming Gorge vilket jag tror gav alla en wow-upplevelse och en försmak inför Gran Canyon. Bergen har fått sitt namn efter sitt eldiga utseende. Den planerade campingen för kvällen uteblev på grund av ogästvänlig campingplats och natten fick istället tillbringas inne på ett motell i Rock Springs.

10 October – Rock Springs – SLC – Caroline Lundell Natten tillbringades på Motel 6 i Rock Springs och såg ut som ett urtypiskt motell taget ur en filmscen. De flesta var nog lyckliga för att ha kunnat duscha och sova i en riktig säng. Frukost åt vi på Denny’s Diner där de amerikanska klichéerna fortsatte. Jag åt en riktig amerikansk frukost med ägg, bacon och pannkakor. Lyckan var total! Efter frukosten åkte vi och handlade och fyllde upp matförråden. På parkeringen utanför mataffären hade Lennart lite introduktion för dagen, där han pratade om Green River bassängen och att det finns olja där. Längs bilfärden höll vi utkik efter pipelines. Vi körde längs I80 där första stoppet gjordes vid Little America, vid den här platsen finns slutet för Green River avsättningarna och Erik Alsteryd berättade lite om Green River bassängen. Längs nästa körsträcka kunde vi se att Sevier Fronten står upp i det flacka landskapet. Färden fortsatte längs I80 och nästa stopp gjordes vid gränsen för Sevier vid Hogsback thrust. Olja kan hittas i ”fault propagation folds” och för första gången på alla år som Lennart haft den här exkursionen kunde vi se att provborrningar har påbörjats på den här platsen. Nästa stopp längs I80 skedde på en okänd plats där vi kunde bland annat se avsättningar av molassetyp. Det blev ett ganska sent lunchstopp eftersom de flesta av oss stod oss bra på den rejäla frukosten. Lunchstoppet var vid något ställe som de lokala använde som skjutbana, vilket de även gjorde denna lördag. Det var en rätt obskyr känsla för oss svenskar som inte är vana vid såhär liberala vapenlagar. Vi satt och njöt av vår lunch och bredvid fanns några som övade prickskytte. Medan vi åt kollade vi på berget och kunde se en kanal av grovklastiskt material och en ”coarsening-upward” sekvens. När alla ätit upp höll Anders sin presentation om Western Interior Seaway. Klockan började springa ifrån oss och vi packade in oss i bilarna och for iväg, lyckliga att alla kom därifrån levande. Nästa stopp gjorde vi i närheten av Coalville, där vi kunde se konglomerat och metasediment, bland annat kvartsit. Det fanns en prefererad orientering av klasternas längsaxlar, åt vilket håll rådde det lite delade meningar om. Sista stoppet för dagen var i Salt Lake City och där stod vi i solnedgången och tittade ut över staden och såg solens sista strålar träffa de vackra bergen. Salt Lake City ligger precis där Basin & Range börjar. Det finns

7

The US Cordillera Excursion 2015 en postglacialförkastning som avgränsar Basin & Range från öst. Vi kunde se en horisontell vit linje i bergen som är en gammal strandlinje. Bakom oss finns Bingham Copper Mine där vi kunde se gigantiska dumphögar torna upp sig. Bingham är ett dagbrott där de bryter porfyrkoppar, de utvinner även bly, guld och molybden. Efter solnedgången kom vi fram till campingen där vi skulle spendera natten i tält. Det första Christoffer sa när han fick syn på campingen var ”vilken osexig camping, det är som att tälta i Slottsskogen”. När tälten var uppsatta njöt vi i goda vänners lag av lite mat och öl. Vissa (nämner inga namn) drack även whiskey ur diskade konservburkar. Precis när vi tryckt i oss vår burkmat som den här dagen skulle föreställa köttgryta kom ett pizzabud och frågade om vi hade beställt pizza. Jag tror att vi alla funderade på att svara ja på den frågan. Dessvärre var det inte någon i vår grupp. Med facit i hand var campingen bra, duscharna var fräscha och det fanns till och med möjlighet att diska gasköken. Definitionen av lyx förändras efter några dagar i fält. Däremot stördes nattsömnen kontinuerligt av tutande tåg och det var nog ingen som vaknade utvilad.

11 October – Salt Lake and Wendover – Henrik Åslund I woke up refreshed after a superb and full night’s sleep at the KOA camping ground, SLC. The familiar sounds probably sent me fast asleep virtually straight away as I had recently visited SLC the days before I met up with everyone else in Golden. The time was a few minutes after 7 am and I could hear some of the other students outside the tent I shared with Christoffer, Eric and Erik. We had breakfast in the relatively comfortable and covered kitchen area, which transitioned into a morning meeting at ca 8:45. Lennart starts out with a map called “Colorado Plateau and its drainage” which shows the topography west of the Rockies and he continues to explains Sevier, Basin and Range and continues to talk about the ophiolites accreted from Farallon in the Sierra Nevada and subsequent inherited rivers and topography. Then it is time for Rickard to speak about Earthscope.org which seems to be a database and a system of seismic arrays. We make several stops around the Salt Lake, one of which is relatively close to one of the salt factories. I want to take up my drone but it is too windy when we get to the stop around the lake where Eric has his presentation about Lake Bonneville. I regretfully miss out of some of his presentation as I have not properly closed the door to the Mothership (Lennart’s mini-bus) and I notice this and have to turn back to close it as it otherwise might get broken due to the respectable wind speeds at this time. I guess it was I who failed the most this particular day. I finally get to take my drone up in western Wendover, which is a town with a view over the Salt Lake and is famous for the Wendover Army Air field which was a training base for the pilots and crew of the B-29 Superfortress bomber Enola Gay, who dropped the atomic bomb on Hiroshima. Here we ascended the spectacularly exposed granitic intrusion in rust like brown colour with a flowing foliation pattern. I missed out most of the presentation because I was piloting the drone which filmed everyone (Figure B) as they ascended and enjoyed the view over the Salt Lake. We made several other stops in the area locking at outcrops with dolomite and Mississippian carbonate rock. Most interesting was however the pumice rock at the last stop at about 7 pm that had pebble sized quartz grains in it which had been deposited as acidic pyroclastic flow with loose material which rained down on top of it. 8

The US Cordillera Excursion 2015

Figure B. Aerial photo of the Wendover intrusion with the Salt Lake in the background. If you look closely at the path leading up the hill it is possible to see the excursion members as they ascend.

In the evening we arrived at Shell, Creek Nevada. A very exotic place where there is a motel that is now abandoned (Lorenz explains this in detail in the next Road log entry). We set up camp at the on the field behind the motel. Luckily we bought a footprint for our tent because there are sharp bushes and other hostile little plants here that could easily rip a tent. At night time we sit on the ground and have a couple of beers. I have not actually bought any but Diana lets me share hers and most students take the opportunity to get to know each other better. What is absolutely brilliant, literary at this time is the night sky. The stars are incredibly bright out here in the semi desert. We can see the “spine” of the Milky way (Figure C) in such a way that makes it worthy of its name. Noteworthy is that in the early hours of the next day I am awakened by a group of howling coyotes that pass a couple of hundred meters from our tents.

Figure C. Photo of the starry night sky in Shell Creek. (photo: Filip Johansson) 9

The US Cordillera Excursion 2015

12 October – the Robinson Mine – Lorenz Lindroth We woke up at dawn after camping behind an abandoned motel in the middle of nowhere (Schell Creek, Nevada). We called it ”Bate’s Motel”. Schell Creek used to be a Pony Express station back in the 19th century, with legends such as Buffalo Bill passing through. We started the day by going to Schell Creek range, which was nearby, to check out some basaltic-rhyolitic magma-mingling and rhyolites near a dirt road. Next stop was the Robinson Mine where gold and silver had been mined since the 1800’s. It was now owned by a Polish company. Later on we stopped for lunch by some old charcoal ovens built in 1870 by Italian immigrants. The ovens weren’t active for very long and was afterwards used as hideouts for cowboys and bandits. The next few road-stops we checked out some slates and ignimbrites and after that we arrived to an old boomtown called Pioche, which literally blew up in 1871. We visited the towns’ old cemetery (1800’s); a long row of wooden crosses with stories about how the persons had died engraved on them. Next stop we saw some more ignimbrites and tuffs and then we crossed the Utah state line for the third time since we left Colorado. After a long, long drive in the dark we stopped by the side of the road and then trespassed to check out a magnetite quarry which was no longer exploited. After that we drove to Cedar City to set up camp for the night. On the way there we had to be extremely careful not to hit deer and other wildlife which stood by the side of the road in great numbers (or lay dead upon it). The camping in Cedar City turned out to be really nice. It had been a long day and the evening beers were much appreciated.

13 October – Zion National Park – Alexandra Glommé The day started at the campsite in Cedar City Utah where Emma talked about seismic events and active areas in the US. Then we hit the road and stopped to look at some pillar basalts, and even this early it was obvious that it was going to be a cloudless scolding hot day. At this stop we found a big yellow butterfly, which after some research turned out to be a two tailed swallowtail butterfly and is Arizona’s state butterfly. One of the main stops today were supposed to be a walk up a cinder cone volcano, but when we started to come close we saw that there was extensive road work being carried out so they had closed the road. This meant that we could add one more thing to the list of things that went wrong on this trip. During lunchtime we parked the cars in such a way that we were able to sit in the shade and eat otherwise it would have been too warm! As we didn’t go up the volcano it meant that we had more time in Zion nt. Park, which was nice as it was a breathtaking place to be. After some souvenir shopping we drove through the park and looked at the beautiful scenery of cross-bedded sandstones. We also got to see the famous chessboard cliff which is found in many geological textbooks. Leaving the park we saw some of the buffalos that survived extinction after Buffalo Bills rampaging, discussing how it would be nice to try the meat to see how it tasted. We finished the day and camped in Kanab known as little Hollywood. It’s a famous city because a lot of western movies were filmed here such as the lone ranger, planet of the apes and El Dorado. The city is Located in the grand circle area as its located centrally between Grand Canyon, Zion nt. Park, Bryce Canyon nt. Park, Vermillion Cliffs nt.

10

The US Cordillera Excursion 2015

Monument amongst others. It’s also one of only two places where the endangered Kanab ambersnail can be found in its natural habitat.

14 October – The Navajo Bridge – Rickard Haeggman Thoughts are spinning through the mind: Where are those rattle snakes hiding? How will we find them? Why Haven’t we seen them? Why haven’t we heard them? We’ve been looking everywhere. We’ve been looking under shady rocks, in dark corners and yet they are nowhere to be found. Where would I hide if I were a rattle snake? Perhaps there are no snakes? Perhaps rattle snakes only was something Lenny B came up with to scare poor, innocent students like us? I bet we will never find out… It is a fine day. Sun protection is the best of friends during a hot desert day like this. We’re all excited, because we know that today is the big day. The day we will see Grand Canyon. We’re standing on a big ledge before another giant valley with flat, never ending roads. We’re not alone on the ledge. Some local Indians are selling souvenirs to the many tourists at the parking lot. They sell anything from hand crafted bear statues to hand made earrings and necklaces. The day continues. We’re driving on a long and lonesome road in a hot valley with the tunes of Creedence Clearwater Revival booming from the speakers. Of course this don't keep the people in the back of the car from falling into a deep and cozy slumber. The Kaibab limestone, Chinle sandstone, Moenkopi sandstone and Kayenta sandstone formations are brightening up our view to the left. In the middle of nowhere arrives a small little community. We encounter the first circulation spot in the traffic on the whole trip in a small community in the middle of nowhere with almost no cars. It might seem unnecessary to place such a safety measures in a friendly little neighbourhood like this, but awkward accidents do occur as seen in Figure D.

Figure D. The wall on a gas station in front of a parking lot.

We continue our trip to see the first really amazing thing this day. We arrive at the Navajo bridge which is crossing the green river. It is the valley and river that soon is going to be Grand Canyon. We know that we are close.

15 October – The Descent of Grand Canyon – Anders Eurenius Dawn was breaking in the Grand Canyon National Park and the sharp smell of pines filled the chill morning air. What had previously been a quiet space around the campground, had now been occupied with a local flock of large black ravens. They had taken it upon themselves, the task of waking their fellow inhabitants, the campers, by strutting 11

The US Cordillera Excursion 2015 around and noisily croaking outside their tents. As one of these campers, I was not pleased. I turned in my sleeping bag so that the small opening at my head faced downward. Soundproof. For a while I had managed to ignore the birds, but soon the camp filled with the clanking sound of pots and pans, and the opening and closing of car doors, as people began preparing for breakfast. When the alarm of my cell phone eventually began ringing, I realised, as I sleepily peeked my head out of the sleeping bag, that the new day was an irreversible fact. After the regular morning routines, and a quick breakfast consisting of an American style sugary-sludge-porridge, we were seated in the cars, heading toward the Bright Angel Lodge on the edge of the Grand Canyon. Once there, a short introductory lecture was held by our excursion leader Lennart, and we were divided into groups for the purpose of logging the stratigraphy on our way down. After deciding upon meeting up with the other groups at one o’ clock at the Indian Gardens; Lorenz, Andreas and myself eagerly began making our way down the mule-piss stinking path they call the Bright Angel Trail. Despite that the sun had risen high above the horizon, large parts of the valley were still in the shade, it was cool and the hike was easy. We passed through the Permian deposits of the Kaibab limestone that make up the top layer of the Grand Canyon. Eventually we ran in to the Toroweap formation, with the magnificent cross beds of the Coconino sandstone and the muddy deposits of the Hermit shale at the bottom. It was not until we had passed through the greater part of the Supai Group with its nearshore marine deposits, that we finally found the Watahomi formation, where our stratigraphic log was supposed to start. We had little time, and the logging through the Watahomi formation and the subsequent Surprise Canyon formation was complicated, faults and rubble didn’t exactly make things easier. After some time of frustration over having to go back up along the trail from where we had come, we were finally done and could continue logging the underlying Redwall limestone. From here on the logging was easy, one hundred and fifty meters of homogenous, massive limestone, followed by the Temple Butte formation, which was completely covered by rubble, and could therefore not be logged at all. As a result of this, we arrived at the bottom of the valley sooner than we had planned. On our way down, the temperature had increased considerably, it was dry, hot and dusty, and we could finally allow ourselves some well needed rest, in the shade of the verdant Indian Gardens. During our descent, we had also passed the Muav limestone and the Bright Angel shale, and we were now heading out to Plateau Point, at the edge of a large cliff overlooking the Colorado River. The plateau was made up of the Tapeats sandstone, which at the overlook, was so dark that it was almost black. The shade was in short supply; only those who arrived first were able to save themselves from the unrelenting sun. It was here that fatigue, thirst and hunger made itself felt through the Tapeats sandstone; the dark stone surface cooked our brains like hot kebab. After a short discussion of the remaining stratigraphy, containing Shinumo quartzite, Hakatau shale, Bass limestone and the metamorphic rocks in the Vishnu Group, we decided that lunch is better had in the shade at the Indian Gardens. After thirty minutes of walking along the hot plateau, back to the Indian Gardens, we had developed a large appetite. Food and liquid were greedily ingested by everyone, and the air filled with the sweet, sour scent of hot feet being released from captivity. The influence of food coma was a fact; as half-hearted displays of the stratigraphic logs were presented to the rest of the groups.

12

The US Cordillera Excursion 2015

The thought of trudging back up the trail the same way I had come, had so far, somehow eluded me; it now hit me with the full realization. Gravity is a bitch. Despite my sudden insight into the laws of nature, it felt good, as me and Lorenz began making our way back up. It was certainly easier for my knees, and we made a more comfortable pace. Although, it wasn’t long before the one hundred and fifty meters of Redwall limestone started to feel like a thousand, and what was previously the beautiful cross beds of the Coconino sandstone, now stared down at me with cruel contempt. The seemingly endless Kaibab limestone felt like it became steeper and steeper the closer we came to reaching top of the canyon. The promise of cold beer that had loomed ahead all day, as a reward for our conviction, felt closer now more than ever. At last, tired and exhausted, we stepped into the Bright Angel Lodge, and headed with delightful determination to the bar at the back of the building. As I sat down, I felt that the sludge of sweat and dust that had accumulated on my face, were so thick that it could have been scraped off like an icy crust on the windshield of a car in winter. Dirty or smelly, it did not matter, as a large, misty glass of steaming cold beer was put into my hands. I was pleased.

16 October – Grand Canyon to Las Vegas – Camilla Lindström Vi lämnar Mather Campground, Grand Canyon, som vanligt strax efter 8:30, efter att ha spenderat två nätter här. Alla är lite stela och slitna efter gårdagens strapatser upp och ner för Black Angel Trail i Grand Canyon. Vi åker idag mot Las Vegas, där lla ser fram emot en natt i en vanlig säng efter 6 raka nätter i tält. Vädret har skiftat från soligt och 80 F grader till mulet och 60 F grader. Efter ett par kilometer i bilarna stöter vi på de första regndropparna sen Golden, Co. Men efter regn kommer solsken lovar Lennart. Strax norr om Williams kör vi fram till en cindercone, vilken har agerat grustag tidigare. Idag verkar området mest agera kohage och skjutbana där valfria elektronikprylar kan skjutas glatt på. Henrik vill ta med sig en lavabomb hem från denna lokal, men Carro tvekar på om tullen gillar bomber... Vi kör sen genom Williams (Historic Route 66!) och tar I-40 västerut – mot Las Vegas. Längs vägen stannar vi vid en vägskärning med ”oroligt tjafs”; typ Ignimbrit. Sista stoppet för dagen innan ankomst blir Hoover Dam, en spänndam av betong byggd i en blåsrik ignimbrit, uppförd under ”The Great Depression” på gränsen mellan Arizona och Nevada. Vi kör sedan längs med ett oväder med ösregn och blixtar sista biten fram till Las Vegas. Väl där blir det svårt att hålla ihop vår fyra-bilars karavan i sökandet efter vårt hotell, sagoslottet ”Excalibur”. Väl framme släpper Lennart oss fria fram till kl14 dagen därpå. Efter dusch och återhämtning/tur på stan samlas alla för ”förfest” på ett av hotellrummen. De flesta ger sig sen efter lite mat ut på ”strippen” och promenerar, bortåt Bellagio, Ceasars Palace, osv, undantaget Susanna och Emma som letar upp ett dansgolv istället. Ett gäng börjar bli ”torra i strupen” så en bar letas upp inne på Ceasars Palace, medan andra kikar på fontänerna utanför bl a. Aron och Filip hamnar direkt i sällskap med två äldre systrar och den enes man. De bjuds på varsin öl, varefter Filips ”sällskap” blir väldigt glad och närgången... Även Erik Floberg blir bjuden på sin öl då han anses söt, men han drar sig sen rutinerat undan. Även Sandra bjuds på drink i baren, dock av en mer jämnårig kille... Under kvällens gång är det några som spelar bort lite småsedlar i spelautomaterna. Christoffer var en av få som vann något större; satsade 1$ - vann 31,75$! Richard håller sitt löfte/sin önskan om att spela 100$ på rött – och vinner! Dubblar därmed sin insats. Dom flesta drar sig sedan tillbaka till hotellet och kommer i säng runt 3-tiden.

13

The US Cordillera Excursion 2015

17 October – Las Vegas to Red Rock Canyon – Henrik Åslund Erikarna, Christoffer och jag går upp vid normal tid trots att vi var in på småtimmarna under natten. Vi hade tänkt gå till skjutbana för att få ta del av den amerikanska kulturen. Men dessa ligger något utanför strippen där vi bor. Istället går vi och kollar in Luxor hotellet som vi inte hann med kvällen innan. Här spelades filmen Mars Attacks! in och det ligger granne med vårat hotell. Sedan går vi iväg till strippen och strosar runt bland klädbutikerna. Vi hade fått höra att vi skulle bada i swimming pool dagen efter och ingen av oss hade väl egentligen packat ner några badbyxor. På eftermiddagen blir det uppsittning i ”Mothership” och resterande ”Cruisers” och vi beger oss med siktet mot och Red Rock Canyon samt Blue Diamond Mine som är en av världens största gipsgruvor.

18 October – Red Rock Canyon Campground, Utah to Furnace Creek Campground, Nevada – Eric Floberg Effekten av 2015 års El Niño gjorde att väderförhållandena på flera platser på exkursionen var något avvikande från det normala. Detta innebar för tältarna på Red Rock Canyon Campground en ganska regning natt och morgon med mycket nederbörd, men eftersom campingen erbjöd tältplatser med tak (som vi givetvis knep) så drabbades vi egentligen inte av detta alls. Campingen lämnades i sedvanlig ordning strax innan kl 09:00 med sikte på Death Valley. I staden Pahrump, där somliga hade hoppats att få syn på en Rat Rod eller två, tankades bilarna upp innan det bar iväg mot dagens första riktiga stopp som var en welded tuff med ett relativt tjockt lager av obsidian centralt lokaliserat. När bilarna sedan rullade vidare mot Death Valley upptäcktes det att vägen vi skulle ha tagit var stängd p.g.a. att regnet hade orsakat ett ras som blockerade vägbanan. I slutändan var nog ingen speciellt bitter över detta då den nya vägen vi tvingades ta tog oss till Dante’s View (Figur E), en plats med helt magisk utsikt över Death Valley! Efter ett kort stopp vid Zabriskie Point var det dags för lunch. Denna intogs i skuggan bakom Furnace Creek Visitor Centre där vi först hade fått en överskådlig bild av hur Death Valley National Park ser ut från en interaktiv 3D-modell som fanns inne på turistbyrån. Temperaturen vid lunchtid låg på omkring 100˚F (ca 40˚C) i solen. Efter en lång, varm och dammig dag väntade ett utlovat och efterlängtat bad i en pool inte långt från campingen. Ett kraftigt oväder var dock på ingång över Death Valley och blixtarna kunde vid tidpunkten skådas långt bort i fjärran. Detta fick till följd att vi inte hann mer än att hoppa i poolen innan världens förmodligen vresigaste badvakt gav order på att samtliga badgäster skulle befinna sig utanför poolområdet inom 5 minuter. Tydligen kunde ovädret (som aldrig nådde fram till platsen där vi befann oss) vara ett hot mot eventuella badgäster. Better safe than sorry, right?

14

The US Cordillera Excursion 2015

Figur E. Utsikt över Death Valley från Dante's View

19 October – Furnace Creek Campground to Motel 6 Mammoth Lake, CA – Annelie Helmfrid Vi vaknade upp på Furnace Creek Campground i Death Valley, Kalifornien glada över att ovädret som skådades på andra sidan berget kvällen innan aldrig tog sig över och därmed slapp vi vakna upp i en lervälling. Några av oss ville gärna se blixtrarna på nära håll, men fick nöja oss med att se en vacker ljusshow på håll. Personerna som åkte i bussen hade svårt att komma in i bussen eftersom de trodde att de hade låst in bilnycklarna. Ingen visste vem som hade nycklarna. Det visade sig att nycklarna hade ramlat ur ett hål i Lennarts ficka och hamnat i fodret på jackan. Efter en genomgång av Death Valley och ignimbriter åkte vi bort till ranchen för att försöka få tillbaka pengarna från gårdagens bad som mest blev en dyr dusch. Vi fick tillbaka 50 % av kostnaderna. Sedan bar det av mot bergen som vi kunde se från campingen och enligt Lennart skulle vägarna vara som en bergodalbana. Upp högt i bergen och djupt ner i dalarna. Det första stoppet för dagen var vid Mesquite Flat Sand Dunes som är stora vindavsatta sanddyner i öknen några kilometer från Furnace Creek Campground. Bilfärden fortsatte i Death Valley National Park till Mosaik Canyon där Lorenz Lindroth pratade om Pahrump group. Sedan vandrade och klättrade vi omkring på de häftiga klipporna. Lennart berättade om bildningsprocessen och vi studerade mineralogin och strukturerna i berget. Bilfärden fortsatte förbi Panamint Springs i en bergodalbana till Father Crawly Look out där vi tog lunch. Vid lunchstoppet fick vi se ett Top Gun-flygplan långt ner i dalen som såg ut som en vit pick. Precis innan färden gick vidare kom det vi alla hade väntat på, ett Top Gun- flygplan på nära håll. Det flög i dalen nedanför oss och la sig 90 grader, på sidan mot bergväggen.

15

The US Cordillera Excursion 2015

Vi rullade ner för berget, ner i dalen och såg Sierra Nevada framför oss. Vi gjorde ett snabbstopp längsmed vägen för att titta på normalförkastningar med basalter som har kommit upp mellan förkastningarna. Vi passerade Big Pine och Bishop, två små städer i dalen med Sierra Nevada i väster och fortsatte till Long Valley Caldera. Long Valley Caldera är en av världens största caldera. Vi tittade på Bishop tuff som är en welded tuff och som bildades av ryolitiska pyroklastiska flöden när Long Valley Caldera hade sitt utbrott. Vidare gick färden ner i calderan till sjön South Tufa, där vi kunde se ändmorän i området och alluvialkoner från Sierra Nevada. Sista stoppet för dagen var vid Hot Springs, där vulkanisk aktvitet pågår och det är mitt i calderan (Figur F). Det kommer upp svavelhaltiga gaser och det är 100 grader på vissa ställen i bäcken. Förut kunde man bada i bäcken, men nu har temperaturen stigit och därför är det avstängt. Färden gick vidare till Mammoth Lakes, där vi checkade in på Motel 6. Bilarna tömdes på precis allt för att inte någon björn skulle bryta sig in i bilarna och leta efter mat. På grund av de stora höjdskillnaderna förändrades temperaturen från 35º C i Death Valley till 7º C i Mammoth Lakes på bara en dag. Kvällen avslutades på Johns Pizza Works för de flesta och några andra gick till Angels restaurang. Det sägs att filmen Dantes Peak spelades in i baren på Angels restaurang.

Figur F. Vy över Hot Springs, Kalifornien (foto: Eric Floberg)

20 October – Mammoth Lakes – Filip Johansson Vi lämnar Mammoth Lakes utan några inbrott av svartbjörnar på jakt efter tandkräm. Efter att ha yrat runt ett tag följandes spanska vägbeskrivningar åkte vi upp till ’obsidian dome’ med dess hög viskösa obsidian (förkastningsrelaterat utbrott). Dagens andra stopp blev Mono Lake med dess kalk tuffs, vilka blivit exponerade från sjöns antropogent sänkta vattennivå, då sjön agerar vattenreservoar för Los

16

The US Cordillera Excursion 2015

Angeles. Susanna redogör om dessa samhällsorsakade miljöproblem. Sjön har även ett vulkaniskt center, markerat av en ö av basalt. Därefter körde vi till Parom Crater, vilket är kratern kvarlämnat efter en mindre vulkan för ca 600 år sedan, en så kallad cynder cone. Från denna kratern kunde man även se moränavlämningar från Sierra Nevadas glaciärer som kontinuerligt dragit sig tillbaka sedan lilla istiden. Strax innan Tioga pass kollar vi på kontaktmetamorfos av metasediment från intrusiv granit. Dessa bergarter utgör viktiga sulfidmalmer och ibland även guldmalmer, där sura lösningar mobiliserar guld vilket sedan fälls ut och således anrikas. Här klargör även Aron om guldruschen och de skäggiga gubbarna som led genom svält och kvicksilverförgiftning i jakten på rikedomar. Efter ett kort snöbollskrig och lunchpaus körde vi in i Yosemite, där första stoppet var Lambert Dome, en så kallad Rouche Moutonneé, alltså en glacial landform där en lä och stötsida eroderas fram på en större berghäll av isen. Graniterna har stora fältslags fenokryster. Här redogör Sara för Sierra Nevada batoliten; skapad av mesozoisk magmatism och flertalet plutoner, vilka blir successivt yngre och felsiska österut (p.g.a. den tjockare skorpan). Batoliten har sitt ursprung från extensions tektonism. På väg ned mot the valley kollade vi på fler hällar och de stora fältspat fenokrysterna som ofta var zonerade. Innan vi skulle gå och kolla på jätte sequoias stannade vi för att Aron skulle pudra näsan, vilket han inte klarade av under den tryckande tidspressen. Tältplatsen blev nere i the valley, där vi i vanlig manér slog upp tälten i mörkret varefter vi inmundigade öl.

21 October – Från Yosemite till Sierra Nevada – Christoffer Åkesson Yosemite camping bjöd inte på något björnmöte men några hörde skott under natten för att skrämma iväg björnarna. Första stoppet på dagen var Yosemite general store för att köpa souvenirer och färdkost alltså godis. Sedan kollade vi på El Capitan och på dess klättrare. Luften var alldeles rökig pga. av de kontrollerade skogsbränderna vilket med solen skapade effektfulla ljusstrimmor och gav därmed typiskt fina bilder. Vi åkte vidare och passerade Sierra Nevada batholiterna och stannade till vid The Shoo Fly complex. Vi fick åka en omväg då vägen var täckt av ca 10m rasmassor. Resan fortsätter och vi stannar vid Smartville ofioliten där Aron pratar om guldrushen. Resan fortsätter och vi i ”Dessert Storm-bilen” har hunnit bli ordentligt hungriga men vi håller ut med snacks och godis tills det efterlängtade lunchstoppet kommer. Efter lunchen pratar Susanna om torkan i området, vilket också märktes. Det var varm och torrt och det fanns skyltar med texten ”Pray for rain” vid åkrarna som även hade en och annan ”Dust Devil”. Resan går på och vi filosoferar i vår bil om att kullarna ser ut som sammet. Vi passerar en skylt som säger ”6 for 1 dollar”, vilket misstolkas lite lätt, kort efter vänder vi och kör in på Lovers Lane vilket spär på misstolkningarna och ger några sköna skratt. Resan fortsätter och första bilen även kallad Huston tar ledningen följt av Cockoo’s nest (eller gökboet), Black Hawk och sist men inte minst Dessert Storm. Vi stannar till vid en bensinstation men pumpen strular och vi får värdelös service, en gubbe som ska tanka gas blir svinsur för att vi står i vägen. Frustrationen över servicen, gubben och att solen håller på att gå ned struntar vi i alltihopa och drar kvickt till stranden för att avnjuta solnedgången.

22 October – San Francisco – Andreas Karlsson Natten mellan den 21/10 och 22/10 bodde vi över på Lombard Plaza Motel, som naturligt nog låg på Lombard Street, vi börjar morgonen med att inhandla frukost på närmaste mataffär, där enbart ”organisk” mat (vad det nu är) kunde inhandlas. Vi sätter oss sedan i bilarna för att åka mot Baker beach via Presidio, efter lite felkörningar där Lennart

17

The US Cordillera Excursion 2015 modigt kör mot enkelriktat (de andra ekipagen föredrar att följa trafikreglerna), så småningom når vi Baker Beach och går ner till stranden och tittar på serpentiniter i svarta skiffrar plus ett häftigt olistostrom. Efter detta beger vi oss mot Marin Headlands via Golden gate-bron, vi stannar sedan på sydspetsen av Marin Headlands halvön för att titta på chert samt att få en förträffande vy över Golden gate-bron samt San Francisco. Efter detta beger vi oss mot Rodeo Beach för att titta på pillow-basalter, vi tar fel väg ner till stranden, men kommer fram till pillow-basalaterna, vissa tar sig ett dopp i Stilla Havet, andra äter lunch. Efter lunch är det dags att bege sig mot dagens höjdpunkt: Tiburon Peninsula och Ring Mountain, på väg dit kör vi fel i ett bostadsområde i hipstermeckat Sausolito men hittar snart rätt igen. Väl framme vid Ring Mountain på Tiburon Peninsula så parkerar vi vid en kyrka och börjar traska uppåt på Ring Mountain. Vandringen uppåt var lite småsvettig då den kaliforniska solen steker på bra framåt eftermiddagen. När vi väl kommer så förklarar Andreas den rådande mineralogin i blåskiffrarna och den generella geologiska utvecklingen. Lennarts karta över var de mest exotiska blocken finns lämnar mycket att önska och vi hittar inte de utlovade eklogiterna, men oavsett redogör Andreas vid vilket djup eklogiterna kommer ifrån samt de mekanismer som tagit de till ytan. Från Ring Mountain är det en slående utsikt över San Francisco, efter detta beger vi oss till bilarna och återvänder mot San Francisco via Golden Gate-bron igen, där det råder en trafikstockning av gigantiska proportioner. Vi styr bilarna mot Fishermans Wharf för att boka bord på en fisk-restaurang för kvällens aktiviter, vi kommer ifrån Lennart och yrar omkring i cirklar för att hitta rätt parkeringshus, det är fortfarande ytterst oklart varför vi behövde vara alla tjugoen för att boka bordet. Oavsett vilket så åker vi tillbaks till motellet och gör oss redo, framåt kvällningen promenerar vi och åker buss till Fishermans Wharf för att äta middag, väl där äter de flesta restaurangenlig mat. Vi tackar Lennart för en under omständigheter väl genomförd exkursion och överlämnar en flaska whiskey som tack. Lennart tackar oss i sin tur för vi varit relativt medgörliga. Efter maten så beger vi oss till första bästa pub för att inmundiga maltdrycker. Kvällen avslutas lite olika men det blir nog ganska sent för de flesta.

23 October – Return of the Geeks – Jimmy Jakobsson Dagen inleddes med att en något stressad Lennart och ett antal lakejer körde bilarna till flygplatsen. Detta markerade det definitiva slutet på exkursionen och sällskapet kunde börja fragmenteras. För oss i rum 204 som valde att boka en extra natt innebar det här sovmorgon (för alla utom Andreas som fick lämna tillbaka bilen på flygplatsen). I rum 204 rådde f.ö. ett inferno av överpackade väskor, smutstvätt och stuffer som naivt och girigt packats ned under exkursionens tidigare delar. Här kan flera rejäla bitar fossiliserat trä samt en 8 kilos magnetitskiva nämnas. Separationsångesten var svår. Läget förvärrades av att misstaget att solidariskt låta även Erik & Co förvara sin packning på detta rum under dagen. Moralen fick sig dessutom en törn sedan det stod klart att Aron stuckit till Sverige med ett av korten till rummet. Med Andreas tillbaka vid 11-tiden kunde jag, han och Filip inleda en välbehövlig och totalt geologilös dag av konventionellt turistande. Rent konkret innebar detta runt 7 timmars planlöst strosande i Chinatown, finanskvarteren och Fishermans Wharf, då och då avbrutet av sporadiska sammanstötningar med andra fragment av exkursionsgruppen. Kvällen avslutades med något av en utekväll för stora delar av det kvarvarande exkursionssällskapet. Undertecknad valde dock att slöa på rummet istället.

18

The US Cordillera Excursion 2015

Part III: Essays Part III:

Essays

19

The US Cordillera Excursion 2015

1 The Unclear Origin of the Ancestral Rocky Mountains

Alexandra Glommé Lund University

Abstract The Ancestral Rocky Mountains is a precursor to the modern Rocky Mountains as they were located in the same area as the ones we can go and visit today but roughly 300 million years ago. But as it’s an old orogen the origin and evolution of the Ancestral Rocky Mountains is not entirely solved. It’s hard to conclude how it all started and evolved as not much remains other than the sediments they left behind and some other clues that can help in the investigation. Many theories have developed over the years and some are more similar than others but no final answer have yet been found to the origin of the Ancestral Rockies.

Introduction Looking back in time there are several orogens that’s named the Rocky Mountains, the one we can see today and one older that is known as the Ancestral Rocky Mountains. In this paper the focus will be on the older of the two and a closer look at the different theories of its origin, as there are several (Kluth and Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003, Björklund & Plink-Björklund 2015).

Figure 1-1. Showing the formation of Pangaea as the results of continental collisions and tectonically active period of Carboniferous and Permian. From Marshak 2008.

20

The US Cordillera Excursion 2015

The mountains formed during a period of extensive deformation in the carboniferous, in both the Pennsylvanian and Mississippian time. The uplift and deformation of the Midwestern parts of what are the modern Rockies was not uniform. The area of maximum deformation and uplift shifted as the orogeny went on but was slowing down in early Permian in most areas. The tectonically active period ended in the formation of the supercontinent Pangea in the Permian period (Björklund & Plink-Björklund 2015) which is illustrated in Figure 1-1. The core of the Ancestral Rocky Mountain uplift was the pre-Cambrian crystalline rock. As the craton was uplifted deep troughs was formed, as the Uinta and Williston basins amongst others. They were later filled with enormous amounts of sediments when the mountains started to be eroded down (Björklund & Plink-Björklund 2015, Kluth and Coney 1981, Marshak et al. 2000). The Ancestral Rockies evolution was quick and the uplift of the mountains reached maximal distribution in the middle of Pennsylvanian, and already at this time filling the close basins with thick sedimentary sequences (Kluth & Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003), as shown in Figure 1-2 and Figure 1-3. The evidence that can be found for the existence of the Ancestral Rocky Mountains, are the massive layers of sedimentary rock that is now uplifted in the modern Rocky Mountains (Kluth and Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003, Björklund & Plink-Björklund 2015).

Figure 1-2. An illustration of the North American continent in the middle Pennsylvanian. It shows the Gondwana and Laurassia continent collision, which is located in the lower parts of the picture the Appalachian Mountains can also be seen in the east of the craton (Marshak 2008).

21

The US Cordillera Excursion 2015

The reason for the uplift and start of the orogen is debated and there are several theories about what started the orogen. It coincides with the formation of the Ouachita Mountains in the south, but some suggest that its deformation after left-slip truncation in the south west that started it all (Kluth and Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003, Björklund & Plink-Björklund 2015). The reason it’s not yet solved how it started is because of the tricky position of the area compared to the active plate boundary of the time. The location of the Ancestral Rockies was far inside the stable craton and this is the reason there are still so many questions left to be answered (Kluth and Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003, Björklund & Plink-Björklund 2015).

Figure 1-3. This is an illustration and a close up of the Ancestral Rocky Mountains and the connecting basins. (Modified after web link- Ron Blakey, NAU Geology).

Theories Kluth and Coney (1981) argue that the craton uplift in late Carboniferous to early Permian period is related to the continent-continent collision between what is now North America and South America together with parts of Africa. This is the collision that resulted in the Ouachita-Marathon orogeny. This collision is also related to the Alleghenian orogeny which formed the Appalachian on the east coast of the US. They compare the formation of the Ancestral Rocky Mountains to the modern intraplate deformation in India from the collision with Asia. The connection to the Ouachita-Maraton orogeny is complex as the uplifted area is located so far inside the craton and is explained by suturing and deep and complex fault systems. They suggest that the Ancestral Rockies formed from the suturing and block uplift. The deformation got more intense over time to the end of the Pennsylvanian period and then started to die out. But it’s still questionable since the mountains are located so far from the tectonically active plate boundary (Kluth & Coney 1981). The intense deformation from the carboniferous continued into the Permian, but lost some of its initial intensity compared to when it was at its maximum. This was probably because of the movement of the active area, as it moved in the suture zone and the activity also decreased in general all over the area. The now slower uplift together with 22

The US Cordillera Excursion 2015 the subsidence started to fill the basins with sediment for a long time after the orogen had stopped. Ye et al. (1996) argue that the formation of the Ancestral Rocky Mountains is coeval with subduction on the coast of North America and the Ouachita-Marathon orogenic belt. But again the hard question to answer is how the mountains could form so far in the craton? They suggest that the late Paleozoic Andean margin along the southwest part of North America, with its volcanic arcs, subduction and overthurusting of basement rocks is the start of the Ancestral Rocky Mountains, similar to some of the other existing theories (Kluth & Coney 1981, Dickinson & Lawton 2003). Marshak et al. (2000) suggest that the Ancestral Rocky Mountains and the associated structures formed by reactivation of stress fractures, fault- and rift systems. The reactivation would be concentrated to areas that were already weak in the earth crust. Why they would be reactivated could be because of a number of reasons but they propose it’s because of stress in the crust from continental collisions, break ups of supercontinents during the Phanerozoic (Marshak et al. 2000). These major events in earth evolution would make the crust permanently weak in these areas so that they can be reactivated at a later time by the same processes. The deformation responsible for the Ancestral Rockies would be from inversion of these extensional features in the crust, to be more precise the collision on the southern part of the North American craton (Marshak et al. 2000). Dickinson & Lawton 2003 suggests a similar theory to both Kluth & Coney (1981) and Ye et al. (1996) but with some differences. They say that the deformation and stress in the inner part of the craton is because of the active plate boundary and suture line in the Ouachita belt, how the active area moves along the suture and the subduction of Gondwana under Laurentia. The subduction continued in the Ouachita belt even though the continents were already sutured together in the in the eastern parts of the craton. They suggest that it’s the subduction that is more responsible for the forming of the Ancestral Rockies than the continent-continent collision itself. They argue that the evidence lies in the time and place of the other orogenys in what is now North America.No other orogeny than the Ouachita fits both in timing and place and can be responsible for the Ancestral Rockies (Dickinson & Lawton 2003). As the deformation and stress in the mountains were not even throughout the formation the Ancestral Rockies the Marathon segment in the Ouachita was the last to close as it’s the furthest to the south west. This means that the north east reached a maximal deformation before the more southern parts. This is seen in the sediments in the basins around the mountains (Figure 1-3) and the different sedimentary sequences. The evolution of the area is also seen in the subsidence variation in the Midwest and the thickness of the sediments in question, as some basins hade more time to fill up than others (Dickinson & Lawton 2003).

Summary After going through books and articles it was clear that not everyone agreed on one origin for the Ancestral Rocky Mountains. The reason for this disagreement is that the Ancestral Rocky Mountain is an old mountain range so it’s hard to decide about its origin, since there is not that much left of it that can be studied. During the years several theories have developed but it’s still not clear on exactly how the orogen started. If it’s the continent collision between modern North America and South America in a Himalayan style mountain range, the subduction of

23

The US Cordillera Excursion 2015

Gondwana under Laurentia or a combination of the two (Kluth and Coney 1981, Marshak et al. 2000, Dickinson & Lawton 2003, Björklund & Plink-Björklund 2015). Today it’s hard to say where this discussion will end as it depends on what clues scientist will discover in the future and if there are tools to analyze the findings. This is always the case when it comes to older mountain ranges that have been eroded, overprinted and is highly affected by metamorphism. Some clues might lie in the modern mountain range and the uplift of the sediments that once was the great Ancestral Rocky Mountains.

References

Dickinson., W.R. & Lawton., T.F. (2003): Sequential intercontinental suturing as the ultimate control for Pennsylvanian Ancestral Rocky Mountains deformation. Geology, vol. 31, 609–612. Kluth., C.F. & Coney., P.J. (1981): Plate tectonics of the Ancestral Rocky Mountains. Geology, vol. 9, pp. 10¬ – 15. Marshak., S., Karlstrom., K. & Timmons., M.J. (2000): Inversion of the Proterozoic extension faults: An explanation for the pattern of Laramide and Ancestral Rockies intracratonic deformation, United States. Geology, vol.28, pp. 735–738. Ye., H., Royden., L., Burchfiel., C. & Schuepbach., M. (1996): Late Paleozoic deformation of interior North America: the greater Ancestral Rocky Mountain. American Association of Petroleum Geologists Bulletin. vol. 10, pp. 1397–1432. Marshak. S. (2008): Portrait of a planet third edition. W.W Norton & Company, Inc. pp. 832. Share, Jack (2011, March 28) Written in stone...seen through my lense [blog article] Retreived from: http://written-in-stone-seen-through-my- lens.blogspot.se/2011/02/ancestral-rocky-mountains-and-their.html

24

The US Cordillera Excursion 2015

2 The Dakota Formation and its Associated Flora and Fauna

Sandra Davidsson University of Gothenburg

Introduction The Cretaceous is usually referred to as a warm period in the earth’s history. The global sea level was between 150-200 m higher than today and a huge inland sea, the Western Interior Seaway (WIS), divided the North America. During mid-Cretaceous (late Albian-Cenomanian) the Dakota Formation was deposited along the eastern margin of WIS. Studies show that the temperatures were between 6-8°C higher than today and wetlands, swamps and floodplains covered a large part of the land. Braided streams, anastomosed river system, floodplains, estuaries, lagoons, offshore and shoreface deposits dominated the environment as the Dakota Formation was deposited, recording a number of relative sea- level fluctuations. Angiosperms exploded in diversity during this period and started to compete with gymnosperms and ferns. Dinosaurs such as ornithopods and theropods migrated along the coast, leaving footprints behind that can still be admired today. Apart from the impressive dinosaurs, fossils from birds, crocodilians, therian mammals and insects from the Dakota Formation has been found and studied through the 19th, 20th and 21th century.

The Dakota Formation The Dakota Formation was deposited during mid-Cretaceous along the eastern margin of the Western Interior Seaway (WIS) (Figure 2-1). The break-up of the Gondwana in the early Mesozoic led to a major marine transgression of about 150-200 m and during the Cretaceous the tectonic plates underwent substantial redistribution. After a regression during the mid-Cretaceous the world oceans reached their maximum sea level in the upper Cretaceous (Drehobl, 2013). By late Albian a huge inland sea, WIS (Figure 2-1), extended from the Gulf of Mexico in the south to the Arctic in the north, covering much of the North America continent (Hu, 2006). When the sea level was at its highest the WIS in the US extended from central Utah to Minnesota, a distance of about 1600 km (Wang, 2002). WIS was bordered on the west by the Cordilleran thrust belt and on the east by the tectonically inactive cratonic platform (Hu, 2006). During the Sevier orogeny, low-angle thrust sheets loaded the lithosphere, creating the Western Interior foreland basin through flexural subsidence where the Dakota Formation later deposited (Ulicny, 1999). The foreland basin was asymmetric, with the deepest part on the western side of the basin. This resulted in processes such as sediment

25

The US Cordillera Excursion 2015 accumulation, subsidence, uplift, and erosion being less obvious on the eastern side of the basin (Wang, 2002). Witzke and Ludvigson (1994) and Brenner et al. (2000) subdivided the Dakota Formation in western Iowa into two members; the Nishnabotna Member and the Woodbury Member. Brenner et al. also defined three unconformity surfaces, D0, D1 and D2 (Figure 2-2). The Nishnabotna Member is sandstone-dominated with coarse-grained and conglomeratic facies while the Woodbury Member is mudstone-dominated with sandstone channel bodies and lignites. Witzke and Ludvigson (1994) date the Woodbury Member to be of Cenomanian age (100.5-93.9 Ma), the age of the Nishnabotna Member is less certain, but they believe it to be deposited during Albian (113-100.5 Ma). However, am Ende (1991) states that the Dakota Formation in southern Utah is neither older nor younger than Cenomanian.

Figure 2-1. Overview of the Western Interior Seaway (WIS) during the latest Albian. Modified from Brenner et al. (2000). Witzke and Ludvigson (1994) studied the type area of the Dakota Formation (Figure 2-2), in the eastern margin of the Western Interior Seaway, which today encompasses the central and western Iowa as well as eastern Nebraska. Witzke and Ludvigson (1994) discourage from using the term Dakota formation for western-derived sedimentary sequences in the Rocky Mountains. “Dakota Formation” is used as a lithostratigraphic unit across a vast area of central and west-central North America and the name is often used without consideration of the relationship to the type Dakota Formation. This means that the age and lithology in the western margin is probably not the same as the age and lithology of the eastern margin of the Western Interior Seaway (Hu, 2006). Ludvigson et al. (2010) submit evidence that marine-influenced deposition in the Dakota Formation was more common and abundant than previous thought. Ever since the Dakota Formation first was defined by Meek and Hayden (1862) the Formation has been considered to be of mostly fluvial origin. Witzke et al. (1983) and Witzke and Ludvigson (1994) confirm the presence of marine deposition earlier than Ludvigson et al. (2010). However, evidence for older Albian and early Cenomanian marine influence in the Dakota type area was not recognized in those reports. Ludvigson et al. (2010) recognised three major cycles of marine-influenced deposition in the Dakota Formation in Iowa, Nebraska,

26

The US Cordillera Excursion 2015 and Kansas. The first is the late Albian Kiowa-Skull Creek Cycle, the second is the latest Albian “Muddy-Mowry Cycle” and the third is the Cenomanian lower Greenhorn Cycle. Peterson (1969) studied the Dakota Formation in the Kaiparowits Plateau region, south-central Utah, he divided the Dakota Formation into a lower, middle and upper

Figure 2-2. An example on the regional stratigraphy in the type area of the Dakota Formation, D0, D1 and D2 is marked in the figure. Modified from Brenner et al. (2000). member. In this area the lower member consists mainly of chert-pebble conglomerate, pebbly sandstone or sandstone. The middle member of the Dakota Formation consists of interbedded sandstone, mudstone, carbonaceous mudstone, and coal, while the upper member consists of sandstone, mudstone and shale, together with smaller amounts of carbonaceous mudstone and coal. Ulicny (1999) describes the part of the Dakota Formation in southern Utah (Kaiparowits Plateau region) that was deposited during Cenomanian. He divided the Dakota Formation into 8 units (1-6B). Unit 1 (oldest) consists mainly of conglomerate that fines upward and is thought to be deposited in braided streams. Unit 2 is dominated by mudstones, with minor amounts of sandstone and coal, unit 2 represents an anastomosed river system, together with floodplains and swamp deposits. Units 3A and 3B consists of crossbedded sandstone, heterolithic sandstone/mudstone laminates that fine upwards into silty mudstones. The units show signs of tidal influence and brackish waters. Units 4-6B represents the upper member of the Dakota Formation. The units are generally coarsening upwards and Ulicny (1999) interprets this as offshore to shoreface deposits. In summary the Dakota Formation is a succession of fluvial through shallow marine facies that records a number of relative sea-level fluctuations at this location in southern Utah.

27

The US Cordillera Excursion 2015

Flora Angiosperms (Figure 2-3) are flowering plants and first appeared in the lower Cretaceous. They are the most evolved of plants and are distinguished by producing seeds that are enclosed by fruits (Allard, 2008). The angiosperms started to spread out during mid- Cretaceous and this time period was therefore important for the evolution of the angiosperms. The oldest found angiosperm pollen fossil originates from a carbonaceous shale in the Helez Formation (in Israel) and was deposited during late Valanginian (139.8- 132.9 Ma) to Hauterivian (132.9-129.4 Ma) (Drehobl, 2013). Angiosperm megafossils are abundant in the Dakota Formation giving important information on unique depositional settings and have been studied since the 19th century (Figure 2-2) (Wang, 2002).

Figure 2-3. An example of leaf megafossils from the Dakota Formation, all belongs to the species Eoplatanus serrata. Modified from Wang (2002). Ever since angiosperms were introduced in Cretaceous they have thrived and competed out many gymnosperms and other plant groups. Angiosperms have many advantages when competing with other plants due to several innovations that angiosperm has developed, such as longer length of vessels, greater vein density that led to higher transpiration rates and a more flexible photosynthetic mechanism. With the exception of northern alpine forests, nearly all modern biomes are dominated by angiosperms (Drehobl, 2013). Another reason why angiosperm prevailed over other plant clades may be because of co-evolution with insects (Drehobl, 2013). Pollination by insect is thought to be the most important pollination technique for angiosperms during Cretaceous, up to 77 % of the pollen was insect pollinated. However wind pollination may have been more important than first thought, constituting about 23 % of the pollination (Hu, 2006). Wang (2002) investigated the angiosperm fauna in 6 locations in Minnesota, Kansas, Nebraska, and Iowa and estimated that approximately 150-200 angiosperm species were present (Wang, 2002).

28

The US Cordillera Excursion 2015

Gymnosperms are a seed plant where the ovules are carried naked on the cone scales. They first appeared in the Carboniferous and dominated the floras of the world until the Cretaceous, after that they have been more and more replaced with angiosperms (Allard, 2008). Palynomorphs are microfossils and are made from an organic substance that is resistant to chemical attack. Palynomorphs include groups such as dinoflagellate cysts, acritarchs, spores, pollen, fungi, scolecodonts, arthropod organs, chitinozoans and microforams (Allard, 2008). The palynoflora in the Dakota Formation is one of the most diverse and abundant known in the world, reflecting the blossoming and explosive radiation of the angiosperms during this period, a very important part in the evolution of life on earth (Ludvigson et al., 2010). am Ende (1991) found approximately equal percentages of spores, gymnosperm pollen, and angiosperm pollen in the Dakota Formation. Apart from angiosperms and gymnosperms Ludvigson et al. (2010) found pteridophytes (e.g. club mosses and ferns), lycophytes (lycopods and selaginellaceans), bryophytes (mosses and liverworts) as well as algae, fungi and other palynomorphs. Skog and Dilcher (1994) studied vascular plants in the Dakota Formation. They found that ferns were most likely undergrowth in conifer-dominated forests or swamps, they also suggest that some ferns were common and dominated in some environments such as thickets or fern prairies. Wang and Dilcher (2006) states that the presence of a number of aquatic angiosperms and ferns in the Dakota Formation indicate that the diversity of the wetlands plants were high during the Cretaceous, implying that the aquatic angiosperms played an important role in the wetland vegetation during this time.

Fauna The Dakota Formation contains few fossils like bones and teeth but holds abundant information of the mid-Cretaceous fauna in the form of tracksites. These tracksites are popularly referred to as the “Dinosaur Freeway” and comprise an extensively trampled tract of coastal plain sediments, which may represent an ancient migration route (Lockley et al., 1992). Lockley et al. (1992) also writes about 25 known tracksites in the Dakota Formation at localities in Colorado and New Mexico, containing over 1300 individual tracks, comprising a minimum of 210 trackways. The tracks seems to be dominated by ornithopods, theropods (including coelurosaurs) (Figure 2-4), crocodilians and birds, they left tracks over a minimum area of about eighty thousand square kilometres of coastal plain (Phillips et al, 2007; Lockley et al., 1992). Ornithopods (Figure 2-4) were a diverse and abundant group of land living herbivorous ornithischians (bird-hipped dinosaurs). Many ornithopods were probably bipedal, with strong hind legs, even though they also had strong arms that may have been used for walking. They lived over most of the earth during the Jurassic and Cretaceous periods. The ornithopds included many species, but perhaps the most important were the iguanodonts and hadrosaurs that lived during the Cretaceous (Kricher & Morrison, 1999). Theropods (Figure 2-4) are a suborder to the saurischian dinosaurs, they are exclusively bipedal and carnivorous and existed from Triassic to the Cretaceous (Allaby, 2008). Coelurosaurs are a suborder to theropods, they lived from Triassic to Cretaceous, were bipedal and carnivorous (Allaby, 2008). Coelurosaurs were usually small and agile hunters, the largest found was 3 m long, although most were much smaller (Allaby, 2008; Brusatte & Benton, 2008). Modern birds evolved in this group so all coelurosaurs were

29

The US Cordillera Excursion 2015 probably feathered, some could fly and some even slept, ate and reproduced like birds (Brusatte & Benton, 2008). Apart from dinosaurs, a diverse therian fauna has been found in the Dakota Formation, including species such as a pediomyd-like taxa, a Alphadon-like genera, Alphadontidae and Stagodontidaes. Classification and identification is manly based on fossilized teeth (Eaton, 1993). Mcallister (1989) identified subaqueous tracks from tetrapods in the Dakota Formation as well.

Figure 2-4. At the top: Rhabdodon priscus (Omithopod, Iguanodontidae), length: 7 m. At the bottom: Variraptor mechinorum (Theropod, Dromaeosauridae), length: 1.5 m. Modified from Laurent (2001).

Therian mammals are a subclass to mammals, which includes the groups marsupial and placenta mammals (Merriam-webster.com, 2015). Pediomyids are a diverse group of small- to medium-sized marsupials, during the late Cretaceous the pediomyids comprised a large portion of the mammal fauna in North America (Davis, 2007). Alphadon was a member of the Metatheria, a group that includes modern marsupials, it is thought to appear and behave similarly as living opossums (didelphids). They were probably small and mouse-like, adapted to live in trees and usually lived in environments such as rivers, deltas and marshes (BBC Earth, 2015). Alphadontidae is a kind of Cretaceous marsupial that first appeared in Cenomanian and is extinct today. It was one of the most diverse families of marsupials, the different species ranged in size from a shrew to a squirrel and was presumably insectivorous to omnivorous (Kielan-Jaworowska et al., 2013). Stagodontidaes are a type of marsupials (Scott & Fox, 2015). Tetrapods are vertebrate animals with four limbs and include the amphibians, reptilians, aves and mammals (Allaby, 2008). At the same time as the angiosperm radiation during the mid-Cretaceous there were several pollinating insect groups that diversified as well. These include Diptera (flies) and Hymenoptera (bees and wasps), which first appeared in the Triassic, and Lepidoptera (moths and butterflies), which also underwent a major radiation during the Cretaceous (Drehobl, 2013).

30

The US Cordillera Excursion 2015

Climate The mid-Cretaceous is often considered to be a warm and humid period with higher CO2-concentrations which resulted in a global mean annual temperature up to ~6°C (Drehobl, 2013) or even 8°C (White et al., 2001) higher than today. White et al. (2001) also writes that “the late Albian seaway’s eastern margin was subject to average precipitation rates ranging from ~2500 to 4100 mm/yr.” Reconstructed steady-state surface salinity during the early Turonian (93.9-89.8 Ma) in the central part of the WIS gives a value of 37.0 psu (White et al., 2001). Dilcher et al. (2005) reconstructed mean annual temperature and mean annual precipitation in several locations in Kansas, Minnesota and Nebraska. They found that the mean annual temperature fluctuated between 14.9-21.1°C and that the mean annual precipitation varied between 7.9-12.7 cm rainfall based on leaf average area. Several studies (Ludvigson et al., 2010; Wang, 2002; am Ende, 1991) show that the climate during the mid-Cretaceous was warm and humid. am Ende (1991) writes that palynological evidence from the Dakota Formation indicate that the climate was subtropical to tropical. Wang (2002) mean that morphological characters of angiosperm leaves indicate a warm, wet paleoclimate with high humidity and possible seasonality on the eastern margin of the WIS. At a locality in Minnesota the leaf assemblage indicate that the mean annual temperature was about 22°C (Wang, 2002). Ludvigson et al. (2010) argues that the floral composition and sedimentary character indicate a humid subtropical to warm temperate climate during this time period. Mosses, lycophytes and algal spores found in the Dakota Formation all indicates a wet habitat with abundant wetlands, swamps and ponds. There are also several sedimentary features, such as sideritic paleosols (saturated wetland soils), kaolinitic mudstones (indicative of humid weathering), and abundant lignites and carbonaceous shale (swampy wetlands) that indicates a warm and wet climate (Ludvigson et al., 2010). During the mid-Cretaceous many plants and nannofossils (such as coral reefs and floral provinces) extended their habitat up to 15° poleward, further supporting the idea that the mid-Cretaceous was substantially warmer than today. Furthermore, records of oxygen isotopes (δ18O) shows that the intermediate-deep waters during this time period were about 15°C warmer than present (Wang, 2002). There are however, a few uncertainties concerning the climate during this time period. One uncertainty is whether the ice was present over the year, or if the warmth was year-round. Ice-rafted deposits have been found in both the Northern and Southern Hemispheres, suggesting that there were indeed seasonally cold conditions. Deciduous plants have also been found in Alaska (paleo-latitude 70° to 80°), which is another evidence for seasonality. Ludvigson et al. (2010) found evidence for seasonality in paleosols and tree rings, probably indicating changes between wet and dry seasons. Wang (2002) also writes that “Seasonality at this time is implied by the presence of deciduous angiosperm species.” However, White et al. (2001) writes that seasonal effects were minor during the mid- Cretaceous and that rainfall was evenly distributed over the year. Another uncertainty is the sea surface temperature (SST) for low latitudes during the mid-Cretaceous. The SST for the subtropical North Atlantic has been reconstructed, resulting in a SST between 30-31°C, but there is still not sufficient data to reconstruct the equatorial SST during the mid-Cretaceous (Wang, 2002). The Dakota Formation records an environment that encompassed brackish water lagoons, coastal swamps, freshwater lakes, and river channels along broad floodplains (Drehobl, 2013). The climate was warm and wet while the environment probably was

31

The US Cordillera Excursion 2015 characterized by heavily vegetated, moist to swampy forests covering much of the eastern margin of the WIS. The forest probably consisted of both gymnosperm and angiosperm plants (both small and large trees, shrubs and vines) with dense undergrowth made up by ferns (Ludvigson et al., 2010).

Conclusions The Dakota Formation was deposited in the North America in the mid- Cretaceous, probably during the late Albian to Cenomanian. The Dakota Formation was deposited along the eastern margin of the Western Interior Seaway that divided the North America during the Cretaceous. It is usually divided into two members; the lower sandstone- dominated Nishnabotna member and the upper mudstone-dominated Woodbury member. It is mostly a fluvial deposition. However, three individual marine-influenced cycles has been identified in the Formation. The Mid-Cretaceous was an important time period for the evolution of angiosperms (flowering plants) and they started to replace gymnosperms more and more during this time period. Apart from angiosperms and gymnosperm, different kinds of ferns, mosses and algae have been found, supporting the idea of a wet and swampy environment. Apart from a diverse fauna of dinosaurs such as ornithopods, theropods and coelurosaurs, the mid-Cretaceous also had a rich fauna of birds, insects, crocodilians and therian mammals. The mid-Cretaceous was a warm and humid period, between 6°-8°C warmer on average than today. The precipitation was plentiful as well, between 2500-4100 mm/yr is thought to have fallen on average. In conclusion, the Dakota Formation records an environment that encompassed brackish water lagoons, coastal swamps, freshwater lakes, and river channels along broad floodplains. The climate was warm and wet while the environment probably was characterized by heavily vegetated, moist to swampy forests.

References

Allaby, M. (2008). A dictionary of earth sciences. Oxford: Oxford University Press. am Ende, B. A. (1991). Depositional environments, palynology, and age of the Dakota Formation, south-central Utah. Geological Society of America Special Papers, 260, 65- 84. BBC Earth,. (2015). Walking with Dinosaurs: Prehistoric Planet 3D | BBC Earth | Movies | BBC Earth. Retrieved 1 December 2015, from http://www.bbcearth.com/prehistoricplanet/modal/alphadon/ Brenner, R. L., Ludvigson, G. A., Witzke, B. J., Zawistoski, A. N., Kvale, E. P., Ravn, R. L., & Joeckel, R. M. (2000). Late Albian Kiowa-skull creek marine transgression, lower Dakota Formation, eastern margin of Western Interior Seaway, USA. Journal of Sedimentary Research, 70(4). Brusatte, S., & Benton, M. (2008). Dinosaurs. London: Quercus. Davis, B. M. (2007). A revision of" pediomyid" marsupials from the Late Cretaceous of North America. Acta Palaeontologica Polonica, 52(2), 217. Dilcher, D. L., Wang, H., & Kowalski, E. (2005, May). Dakota Formation paleoclimate estimates from Late Albian angiosperm leaves. In Geological Society of America Abstracts (Vol. 37, No. 5, pp. 85-86).

32

The US Cordillera Excursion 2015

Drehobl, M. B. (2013). Paleoecological reconstruction of Mid Cretaceous plant communities from the Dakota Formation of Iowa, USA. MS (Master of Science) thesis, University of Iowa. Eaton, J. G. (1993). Therian mammals from the Cenomanian (Upper Cretaceous) Dakota Formation, southwestern Utah. Journal of Vertebrate Paleontology, 13(1), 105-124. Hu, S. (2006). Palynomorphs and selected mesofossils from the Cretaceous Dakota Formation, Minnesota, USA (Doctoral dissertation, University of Florida). Kielan-Jaworowska, Z., Cifelli, R., & Luo, Z. X. (2013). Mammals from the age of dinosaurs: origins, evolution, and structure. Columbia University Press. Kricher, J. C., & Morrison, G. (1999). Peterson first guide to dinosaurs. Houghton Mifflin Harcourt. Laurent, Y., Le Loeuff, J., Bilotte, M., Buffetaut, E., & Odin, G. S. (2001). Campanian- Maastrichtian continental-marine connection in the Aquitaine-Pyrenees-Provence area (S France). D10, 694-711. Lockley, M., Hunt, A., Holbrook, J., Matsukawa, M., & Meyer, C. (1992). The dinosaur freeway: a preliminary report on the Cretaceous megatracksite, Dakota Group, Rocky Mountain Front Range, and High Plains, Colorado, Oklahoma and New Mexico. Rocky Mountain Section (SEPM). Ludvigson, G. A., Witzke, B. J., Joeckel, R. M., Ravn, R. L., Phillips, P. L., González, L. A., & Brenner, R. L. (2010). New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation in Kansas--Nebraska--Iowa from a Decade of Sponsored Research Activity. Kansas Geological Survey. McAllister, J. A. (1989). Dakota Formation tracks from Kansas: implications for the recognition of tetrapod subaqueous traces. Dinosaur tracks and traces, 343-348. Meek, F. B., & Hayden, F. V. (1862). Descriptions of New Cretaceous Fossils from Nebraska Territory, Collected by the Expedition Sent out by the Government under the Command of Lieut. John Mullan, US Topographical Engineers, for the Location and Construction of a Wagon Road from the Sources of the Missouri to the Pacific Ocean. Proceedings of the Academy of Natural Sciences of Philadelphia, 21-28. Merriam-webster.com,. (2015). therian | any of a subclass (Theria) of mammals comprising the marsupials and the placental mammals. Retrieved 1 December 2015, from http://www.merriam-webster.com/dictionary/therian. Peterson, F. (1969). Cretaceous sedimentation and tectonism in the southeastern Kaiparowits region, Utah (No. 69-202). US Geological Survey],. Phillips, P. L., Ludvigson, G. A., Joeckel, R. M., González, L. A., Brenner, R. L., & Witzke, B. J. (2007). Sequence stratigraphic controls on synsedimentary cementation and preservation of dinosaur tracks: Example from the lower Cretaceous,(Upper Albian) Dakota Formation, Southeastern Nebraska, USA.Palaeogeography, Palaeoclimatology, Palaeoecology, 246(2), 367-389. Scott, C. S., & Fox, R. C. (2015). Review of Stagodontidae (Mammalia, Marsupialia) from the Judithian (Late Cretaceous) Belly River Group of southeastern Alberta, Canada 1. Canadian Journal of Earth Sciences, 52(8), 682-695. Skog, J. E., & Dilcher, D. L. (1994). Lower vascular plants of the Dakota Formation in Kansas and Nebraska, USA. Review of Palaeobotany and Palynology, 80(1), 1-18. Wang, H. (2002). Diversity of angiosperm leaf megafossils from the Dakota Formation (Cenomanian, Cretaceous), north Western Interior, USA (Doctoral dissertation, University of Florida).

33

The US Cordillera Excursion 2015

Wang, H., & Dilcher, D. L. (2006). Aquatic angiosperms from the Dakota Formation (Albian, Lower Cretaceous), Hoisington III Locality, Kansas, USA.International Journal of Plant Sciences, 167(2), 385-401. White, T., González, L., Ludvigson, G., & Poulsen, C. (2001). Middle Cretaceous greenhouse hydrologic cycle of North America. Geology, 29(4), 363-366. Witzke, B. J., Ludvigson, G. A., Ravn, R. L., and Poppe, J. R., 1983, Cretaceous paleogeography along the eastern margin of the Western Interior seaway, Iowa, southern Minnesota, and eastern Nebraska and South Dakota; in, Mesozoic Paleogeography of the West- Central United States, M. W. Reynolds and E. D. Dolly, eds.: Rocky Mountain Paleogeography Symposium 2, Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section, Denver, p. 225-252. Witzke, B. J., & Ludvigson, G. A. (1994). The Dakota Formation in Iowa and the type area. SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA, 43-43.

34

The US Cordillera Excursion 2015

3 The Morrison Formation of Late Jurassic age: An Overview of the Paleontology, Paleoenvironment and Paleoclimate During Deposition

Camilla Lindström University of Gothenburg

Introduction The Morrison Formation of Late Jurassic age is a deposit of mainly terrestrial sedimentary rocks, present over an extensive area of the Western Interior region of the United States (Figure 3-1), famous mostly for the extensive and diverse findings of vertebrate fossils in the formation. Outcrops can be found throughout the Rocky Mountain area, in Utah, Colorado, Wyoming, Montana, New Mexico, north-eastern Arizona, western Oklahoma panhandle, and western South Dakota (Foster, 2003). The name Morrison Formation was assigned by Cross (1894) to exposures of the formation found near the town of Morrison, Co. Eldridge (1896) later described the formation more extensively.

Figure 3-1. Map of the United States, dashed line indicating the extent of the Morrison Formation in outcrop and subsurface (Foster, 2003).

35

The US Cordillera Excursion 2015

The Morrison Formation has been intensively studied for over 100 years, mostly for its remarkable abundance of dinosaur fossils (Chure et al, 2006), but also for its uranium resources as well as its smaller portions of fossil mammals and fossil plants, trace fossils, and track sites. The fossil findings of large varieties of animals and plants together represent a huge range of environments and geographic areas possibly present throughout the time and place of the Morrison depositional basin. The time of deposition was 148-155 Ma, Kimmeridgian to Tithonian of age (e.g. Litwin et al., 1998; Schudack et al., 1998), and during these 7 million years the ecosystem of the depositional area likely shifted dramatically through time, and the same can therefore be assumed for the abundance and geographical extent of the flora and fauna (Foster, 2003). The paleoclimate in the Western Interior during the deposition of the Morrison Formation has long been a controversial matter however. Climatic models and geologic evidence, such as the sedimentology of the formation, indicates a seasonal and dry climate (Turner and Fisherman, 1991; Demko et al., 2004), theories that have been challenged by studies of the Morrison fossil flora, which in contrary is believed to indicate a non-seasonal and humid climate (Tidwell, 1990a) during the time of deposition. Over the last few decades, the discussions have almost exclusively followed the line of evidence given from the sedimentology of the formation, implying of a semi-arid and seasonal climate much like the modern day savannah (Farlow et al., 1995; Foster, 2003; Turner and Peterson, 2004).

Geology and Tectonic Setting The Morrison Formation is found to be 25-300 m thick, thinning out from the southwest to the northeast, and consists mostly of interbedded sandstones, multicolored mudstones, and limestones, together with occasional volcanic ash beds, conglomerate, and evaporites (Foster, 2003). Stratigraphically, the formation is most well known in the Colorado Plateau region, where ten formal members have been recognized. Apart from this region, the Morrison Formation is largely undifferentiated or recognized by informally named members north and east from the Plateau region (Turner and Peterson, 2004). The strata of the formation were almost exclusively deposited in terrestrial environments, with the exception marginal marine beds in the northern parts of the formation (Turner and Peterson, 2004). Turner and Peterson (2004) considers the best vertical section representative of the formation to be located at the Four Corners, where Utah, Colorado, Arizona and New Mexico join corners. Here, the following members are recognized, generally from oldest to youngest: Tidwell, Bluff Sandstone, Junction Creek Sandstone, Salt Wash, Recapture, Westwater Canyon, and Brushy Basin. Turner and Peterson (2004) therefore produced facies sections of the Morrison Formation at this location, to give an idea of the interfingering strata that is the Morrison Formation (Figure 3-2 and Figure 3-3). The strata in the Morrison Formation were deposited in a mosaic of predominantly terrestrial environments in a large and unique system of alluvial plains (e.g. Demko et al., 2004; Turner and Peterson, 2004), including large fluvial complexes, eolian deposits, coal swamp and marsh environments, as well as overbank, lacustrine and minor fluvial environments (Turner and Peterson, 2004). Hence, the landscape can be said to have developed mainly in response to the availability of water, in turn dependant upon tectonic setting and of course climate.

36

The US Cordillera Excursion 2015

Figure 3-2. South-to-northeast facies section of the Morrison Formation in the Western Interior basin (Turner and Peterson, 2004).

Figure 3-3. South-to-north facies section of the Morrison Formation in the Western Interior basin (Turner and Peterson, 2004).

37

The US Cordillera Excursion 2015

Determining the tectonic framework of the region of deposition is essential for pinpointing the source of the huge volumes of sediment that today constitutes the Morrison formation, as well as the abundant volcanic ashes incorporated into it. The Morrison depositional basin, given its position inboard a magmatic arc developing along the western edge of Laurasia (Figure 3-4) (Dickinson, 2001), was able to record detailed paleoclimatic changes by means of the extensive amount of sediment filling the basin over a relatively short period of time (Demko and Parrish, 1998). Provenance and paleocurrent studies of the formation (e.g. Craig et al., 1955; Cadigan, 1967; Martinez, 1979; Turner-Peterson, 1986) reveal that rift shoulders and uplifts in the back arc region, elevated southwest of the depositional basin by thermotectonic processes, was a significant source of sediment through most of the time of deposition (Turner and Peterson, 2004).

Paleoclimate Overview During the time of deposition, the Morrison basin was located between 30⁰N and 40⁰N latitude, some 5⁰N south of today’s equivalent position of the US. The depositional area has been modeled to lie within a belt of subtropical westerly winds, and together with the elevated rift shoulders to the west, this created a rain shadow effect over the Morrison basin (Foster, 2003). This adds to the evidence indicating dry conditions with low amounts of precipitation, at least seasonally. The Morrison Formation also contains a number of sedimentary paleoclimatic indicators, such as eolian sandstones, calcareous paleosols, evaporite deposits, and playa/saline, alkaline lake deposits, most of which are indicative of a dry climate with periodic and/or seasonal precipitation (Demko and Parrish, 1998). Water of course played a huge roll in the defining of habitats and evolving of environments in the depositional basin. The main source of water to the basin is thought to be groundwater and surface water, often with contributions from the upland regions to the west, with very little input by meteoric water (Turner and Peterson, 2004).

Paleontology Overview Although famous mostly for its abundant and diverse dinosaur fossils, as well as its remarkable uranium resources, the Morrison Formation contains many additional faunal and floral elements, together representing a diverse biota acting as clues to the prevailing paleoenvironment and paleoclimate during time of deposition. Given the scarce availability of water, either seasonally or periodically, the majority of the flora and fauna in the Morrison basin was likely concentrated and in some matter restricted to riparian environments where water was more likely available, such as near streams, lakes och other water bodies (Turner and Peterson, 2004).

38

The US Cordillera Excursion 2015

Figure 3-4. Map of the suggested tectonic setting in the vicinity of the Morrison depositional basin during Late Jurassic time in the western US. 1, Chihuahua trough; 2, Mar Mexicano; 3, Remnant of Middle Jurassic arc graben depression; 4, Remnant of Middle Jurassic Toiyabe uplift (?). Modified by Turner and Perterson (2004) after Saleeby and Busby-Spera (1992, pl. 5F) and Lucas et al. (2001).

As mentioned, the controversy concerning the paleoclimate depends much on fossil plant findings, with over 35 genera of plants represented in the Morrison Formation by macrofossils of logs of large trees, leaves, stems and fruiting bodies of conifers, ginkgoes, cycads, ferns, and horsetails, together with charophytes and a diverse palynoflora (references in Engelmann et al., 2004). The plants are, or were, by some thought to reflect humid conditions throughout the depositional basin (e.g. Ash and Tidwell, 1998), leading to others pointing out that the fossil plants only represent an environment limited in time and space (Demko and Parrish, 1998; Parrish et al., 2004), e.g. conditions during the wet season or areas supplied with water from distant sources, such as riparian environments. Vertebrates such as ostracods, gastropods and bivalve mollusks all indicate that water was available, e.g. as standing bodies of freshwater or perennial streams, either seasonally or for periods of years (Engelmann et al., 2004). Trace fossils have been located as well, revealing a diverse arthropod fauna comprising ants, termites, and other insects and crayfish (Hasiotis, 2004). Insects do not provide much clue to the paleoclimate as they have

39

The US Cordillera Excursion 2015 the ability to adapt to many different climates, but they have been seen to be successful in adapting to arid environments. Lower vertebrates are also represented in the fossil fauna, by different types of fish (Kirkland, 1998) as well as frogs, salamanders, turtles, crocodilians, and lizards (Henrici, 1998; Evans and Chure, 1999). Mammals were also present, the largest ones equivalent to the modern day ground squirrel. The dinosaur assemblage of the Morrison Formation contained more than 20 genera (Figure 3-5), but was dominated by Sauropods, size-wise as well as diversity-wise, as they made up more than half of the herbivorous dinosaurs in the ecosystem (Engelmann et al., 2004). Studies of the dentation of different findings of sauropod body fossils show that they was probably some kind of resource partitioning going on when it comes to food and other resources (Fiorillo, 1998). This may be one of many reasons to why the sauropods were so dominant. However, the sauropods size may seem disadvantageous in an ecosystem with limited resources. Owen-Smith (1988) means that large herbivores can survive on lower quality forage as well as survive longer periods of starvation, as cannot smaller animals. Schmidt-Nielsen (1984) points out that large size comes with increased energy efficiency of transport, which would allow the giant sauropods to travel long distances between resource patches. Smaller, herbivorous and carnivorous dinosaurs are not as abundant in the Morrison fossil record, but still present and were likely restricted to areas of sufficient food and water resources (Engelmann et al., 2004).

Figure 3-5. (Left column): Examples of common Morrison Formation dinosaurs. A. Allosaurus; B. Stegosaurus; C. Dryosaurus; D. Camptosaurus. Scale bars = 1 m (A, D); 50 cm (B, C). Skeletal reconstructions by Greg Paul. (Foster, 2003). (Right column): Examples of Morrison Formation Sauropod dinosaurs. A. Brachiosaurus; B. Camarasaurus; C. Diplodocus; D. Apatosaurus; E. Barosaurus. All scale bars = 2 m. Skeletal reconstructions by Greg Paul. (Foster, 2003)

40

The US Cordillera Excursion 2015

Conclusions There is a huge amount of research regarding the Morrison formation and the paleoclimate, paleontology and paleoenvironment of its time. Still, there are many uncertainties surrounding them all. What can be concluded to this day is that the sedimentary deposits Morrison Formation is thought to have been deposited in a complex mosaic of mostly terrestrial environments, in a warm and dry climate with only seasonal or perhaps periodic input of precipitation. Water was added to the system by groundwater or surface water, mainly from the elevated shoulders of the magmatic arc to the west. The flora and fauna of the ecosystem was very diverse and abundant, but probably concentrated and restricted in some matter in riparian environments, near streams, lakes or other water bodies. Although the fossil flora and fauna are not the best indicators of paleoclimate in this case, given its great diversity, they still offer clues to what kind of environment they lived and died in. The remarkable diversity is more likely an evidence of the great variation of environments in time and space during the deposition of the Morrison Formation.

References

Ash, S. R., & Tidwell, W. D. (1998). 4. Palynology and paleobotany-plant megafossils from the brushy basin member of the morrison formation near montezuma creek trading post, southeastern Utah. Modern geology, 22(1), 321-340. Cadigan, R. A. (1967). Petrology of the Morrison Formation in the Colorado Plateau Region. U.S. Geol. Survey Professional Paper, 556, 113. Chure, D. J., Litwin, R., Hasiotis, S. T., Evanoff, E., & Carpenter, K. (2006). The fauna and flora of the Morrison Formation: 2006. New Mexico Museum of Natural History and Science Bulletin, 36, 233-249. Craig, L. C., Holmes, C. N., Cadigan, R. A., Freeman, V. L., Mullens, T. E. & Weir, G. W. (1955). Stratigraphy of the Morrison and related formations, Colorado Plateau region; a preliminary report. U.S. Geol. Survey Bulletin, 1009-E, 125–168. Cross, C. W. (1894). Pike’s Peak Colorado: Geological Atlas Folio 1894. US Geol. Survey, 8p. Demko, T. M. & Parrish, J. T. (1998). Paleoclimatic setting of the Upper Jurassic Morrison formation. Modern Geology, 22, 283-296. Demko, T. M., Currie, B. S. & Nicoll, K. A. (2004). Regional paleoclimatic and stratigraphic implications of paleosols and fluvial-overbank architecture in the Morrison Formation (Upper Jurassic), Western Interior, U.S.A. Sedimentary Geology, 167, 117 – 137. Dickinson, W. R. (2001). Tectonic setting of the Great Basin through geologic time: implications for metallogeny. In: Shaddrick, D. R., Zbinden, E. A., Mathewson, D. C., Prenn, C. (Eds.), Regional Tectonics and Structural Control of Ore: The Major Gold Trends of Northern Nevada. Special Publication Geological Society of Nevada, 2001 Spring Field Conference vol. 33 Geological Society of Nevada, Reno, NV, 27– 53. Eldridge, G. H. (1896). Geology of the Denver Basin in Colorado. US Geol. Survey Mon, 27, 556. Engelmann, G. F., Chure, D. J., & Fiorillo, A. R. (2004). The implications of a dry climate for the paleoecology of the fauna of the Upper Jurassic Morrison Formation. Sedimentary Geology, 167(3), 297-308. Evans, S. E., & Chure, D. J. (1999). Upper Jurassic lizards from the Morrison Formation of Dinosaur National Monument, Utah. Vertebrate Paleontology in Utah, 99(1), 151. Farlow, J. O., Dodson, P. & Chinsamy, A. (1995). Dinosaur biology. Annual Review of Ecology

41

The US Cordillera Excursion 2015

and Systematics, 445-471. Fiorillo, A. R. (1998b). Dental microwear patterns of sauropod dinosaurs Camarasaurus and Diplodocus: evidence for resource partitioning in the Late Jurassic of north America. Historical Biology, 13, 1-16. (nv) Foster, J. R. (2003). Paleoecological analysis of the vertebrate fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain region, USA. New Mexico Museum of Natural History and Science Bulletin, 23, 1-95. Hasiotis, S. T. (2004). Reconnaissance of Upper Jurassic Morrison Formation ichnofossils, Rocky Mountain Region, USA: paleoenvironmental, stratigraphic, and paleoclimatic significance of terrestrial and freshwater ichnocoenoses. Sedimentary Geology, 167(3), 177-268. Henrici, A. C. (1998). A new pipoid anuran from the late Jurassic Morrison Formation at Dinosaur National Monument, Utah. Journal of Vertebrate Paleontology, 18(2), 321- 332. Kirkland, J. I. (1998). Morrison fishes. Modern Geology, 22/1/1–4, 503– 533. Litwin, R. J., Turner, C. E., Peterson, F. (1998). Palynological evidence on the age of the Morrison Formation, Western Interior U.S. Modern Geology, 22/1–4, 297– 319. Martinez, R. (1979). Provenance study of the Westwater Canyon and Brushy Basin Members of the Morrison Formation between Gallup and Laguna, New Mexico. PhD dissertation. University of New Mexico, Albuquerque, 79. Owen-Smith, R. N. (1988). Megaherbivores: The Influence of Very Large Body Size on Ecology. Cambridge Univ. Press, London, 369 pp. Parrish, J. T., Peterson, F., Turner, C. E. (2004). Jurassic ‘‘savannah’’— Plant taphonomy and climate of the Morrison Formation (Jurassic, western U.S.A.). Sedimentary Geology, 167, 139–164. Schmidt-Nielsen, K. (1984). Scaling: Why is Animal Size so Important? Cambridge Univ. Press, London, 241 pp. Schudack, M. E., Turner, C. E. & Peterson, F. (1998). Biostratigraphy, paleoecology and biogeography of charophytes and ostracods from the Upper Jurassic Morrison Formation, Western Interior, USA. Modern Geology, 22/1/1– 4, 379– 414. Tidwell, W. D. (1990a) Preliminary report on the megafossil flora of the Upper Jurassic Morrison Formation, Utah, USA. Hunteria, 2, no. 8, 1-12. Turner, C. E. & Fishman, N. S. (1991). Jurassic Lake T’oo’dichi’: a large alkaline, saline lake, Morrison Formation, eastern Colorado Plateau. Geological Society of America Bulletin 103/4, 538–558. Turner, C. E. & Peterson, F. (2004). Reconstruction of the Upper Jurassic Morrison Formation extinct ecosystem—a synthesis. Sedimentary Geology,167(3), 309-355. Turner-Peterson, C. E. (1986). Fluvial sedimentology of a major uranium-bearing sandstone—A study of the Westwater Canyon Member of the Morrison Formation, San Juan basin, New Mexico. In: Turner-Peterson, C. E., Santos, E. S., Fishman, N. S. (Eds.), A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico. American Association of Petroleum Geologists Studies in Geology, 22, 47– 75.

42

The US Cordillera Excursion 2015

4 The Yavapai Province, Crustal Growth and Metamorphic Development

Diana Carlsson University of Gothenburg

Abstract The 1.76-1.72 Ga old Yavapai Province consists of Archean aged oceanic arc terranes that were accreted during subduction to the North American continent. It consists of felsic to mafic volcanic rocks, intermediate plutonic rocks, volcanogenic sedimentary rocks and their metamorphosed equivalents. Metamorphism occurred contemporary with the Yavapai Orogen between 1.71 and 1.68 Ga and the Province shows poly-metamorphic events with a clockwise PT-path, where metamorphism ranges between amphibolite to greenschist facies. Isobaric conditions due to large pluton intrusions are thought to have contributed to granulite facies conditions in the transitional zones between the Yavapai Province and the Mazatzal and Mojave Provinces.

Introduction The North American core was initiated by plate collisions between Archean aged continents and continental fragments between 2.0 and 1.8 Ga (Whitmeyer and Karlström 2007). This resulted in the Trans-Hudson orogeny, comparable to the modern Himalayas, which is seen today as reworked Archean crust and remnants of juvenile volcanic belts. Laruentia continued to grow in the south by possible subduction related accretion of oceanic and volcanic terranes and arcs during the Yavapai orogeny. Further to the south and southeast, this convergent plate margin gave rise to volcanic arcs and back-arc successions, followed by extensive plutonic magmatism during the Mazatzal orogeny. Terrane sutures are seen as shear zones that have been reactivated several times between the Provinces. The North American lithosphere was stabilized with no major events during early Mesoproterozoic and accretion was resumed after 1.55 Ga. Juvenile terrain and arc accretion along the south and south eastern margin of the Mazatzal Province contributed to the Granite-Rhyolite Province with ages between 1.55 and 1.35 Ga. This Province was further sutured to Laurentia by plutonic magmatism during the later end of the same time interval (Figure 4-1).

The Yavapai Province The Yavapai Province is found as a NE-SW trending belt over the south western USA. It is bordered in the north by the Trans-Hudson orogeny, in the North West by the Mojave Province that is interpreted as an old convergent margin, and to the south by the Mazatzal Province, interpreted as an old divergent margin. Transition zones are found

43

The US Cordillera Excursion 2015 towards the Mojave and Mazatzal Provinces (Figure 4-2) and are defined by Nd and Pb isotope signatures as well as geochronological data (Holland et al. 2015).

Figure 4-1.Whitmeyer and Karlström (2007

The Yavapai Province consists of accreted oceanic arc terranes with Nd model ages of about 1.8-1.76 Ga, and possible Archean aged, based on inherited zircons (Karlström and Bowring, 1988, Bennet and DePaolo, 1987). Accretion is thought to have occurred between 1.76 and 1.72 Ga through a northerly subduction and has been compared to present day Banda Sea region (Whitmeyer and Karlström, 2007). The accretion was followed by voluminous intrusion of granitoids between 1.72 and 1.68 Ga, contemporary to the Yavapai orogeny, making the final attachment of the Yavapai Province to the Northern Laurentia. Bimodal igneous suites are common in the Province and have been interpreted, by Bickford and Hill (2007), based on Nd, Hf and Pb isotopic data, to have a crustal source. Bickford and Hill (2007) suggested that these could have intruded due to intracontinental rifting around 1.80 Ga and that the accretion model by Karlström and Bowring (1993) is oversimplified. Quartzite deposits, 1.70 Ga, are found in larger basins in the Yavapai Province, and are considered to have deposited in an extensional environment due to slab roll back during the subduction present at this time. The extensional tectonism ended shortly afterwards when the Mazatzal orogenic event contributed to crustal shortening and burial, 5-15 km below the crust, of these quartzite deposits. During the time for both accretion and intrusive magmatism, the Yavapai Orogen contributed to the metamorphic overprint seen today. Magmatism in the Yavapai Province ended with large plutonic intrusions of granitoids during the Mesoproterozoic Era between 1.48 and 1.40 Ga.

44

The US Cordillera Excursion 2015

Figure 4-2. Holland et al. (2015)

The Yavapai orogen and metamorphic development The peak of the Yavapai orogen is thought to have occurred at about 1.71-1.68 Ga. This orogenic event gave rise to poly-metamorphic overprint, consistent with a clockwise PT-path, where burial is considered up to 10-20 km due to thrusting, recumbent folding and crustal thickening. Metamorphosed Archean aged rocks are rather uncommon in the Yavapai Province and are characterised by high deformation with extensive faulting and later metamorphism and plutonic inference. Such rocks can be found in in the north western Wyoming, in northern Colorado (Sims et al. 2001) and the Owiyukuts Complex in the Uinta Mountains (Sears et al. 1982). Metamorphism of Proterozoic aged rocks are more widespread in the Province and can be found in the Colorado Plateau. The Vishnu Group is one example and contains metamorphosed crystalline rocks and sediments, probably deposited in an ancient marine setting with volcanic intrusions (Tweto and Ogden 1987). This group is considered to lie along the suture between the Mojave and Yavapai Province and was deposited either in the

45

The US Cordillera Excursion 2015 trench where the Yavapai subducted to the todays west under the Mojave, or in a back-arc basin that occurred along the suture after the Mojave and Yavapai had accreted. The sediments were deposited between 1.75 and 1.74 Ga and was followed by folding and faulting due to initiated (reactivated?) subduction to the west between 1.74 and 1.71 Ga. Metamorphism was contemporary with the Yavapai orogen at 1.71 and 1.68 Ga (Holland et al. 2015).

Figure 4-3. Levin, H.L. (2006)

Whitmeyer and Karlström (2007) argue that isobaric conditions with pressures up to 6 kbar have contributed to the metamorphic overprint seen in the Vishnu Group rather than subduction related metamorphism and juxtaposition of the crust. The Vishnu Group, belonging to the Grand Canyon Supergroup, is overlaid by several sedimentary and metamorphosed formations, which have been deposited in marine, transitional and terrestrial environments. The Grand Canyon Supergroup is found under the Great Unconformity and are followed by Cambrian aged rocks (Figure 4-3). The area has experience several later events with major plutonic intrusions and is highly deformed. Early Proterozoic aged crystalline rocks, contemporary with the Vishnu Schist, and their metamorphosed equivalents are found along the border between Nevada and California. Later Proterozoic sedimentary rocks are exposed in the Mojave Desert and in Death Valley national park, known as the Pahrump Group (USGS). Metamorphism ranges between greenschist to amphibolite facies in the Yavapai Province, and PT-estimates for amphibolite facies rocks in the Park Range area have yielded temperatures between 550°-700° C and a pressure between 4 and 6 kbar for Proterozoic metasedimentary rocks (Foster et al. 1999). Prograde metamorphism is also found in metasedimentary alumina rich conglomerates with staurolite and kyanite overprinted by sillimanite. This confirms a setting with high pressure and is thought to have been an earlier event than the amphibolite overprint found in the Park Range. The metasedimentary sequences are overlying older bimodal volcanic intrusions that also have been highly metamorphosed and deformed. Later rehydration and uplift have contributed to a greenschist facies overprint in some regions where andalusite have been found by Snyder (1988) in the Park Range. Low-pressure metamorphism of metasedimentary rocks with staurolite, andalusite, cordierite and garnet porphyroblasts have also been seen in the Front Range by Shaw et al. (1999) (Figure 4-4). Poly-metamorphism of the Paleoproterozoic rocks in Front Range seems to have its last Precambrian metamorphic event during Mesoproterozoic time and could be pluton inferred. The metamorphic grade seems to

46

The US Cordillera Excursion 2015 decrease towards the north and the accretionary suture that the Cheyenne belt is thought to constitute between the Yavapai Province and the Wyoming craton. In the Park Range area two shear zones are found. One is between the Soda Creek and the Fish Creek and the other is found between the Farwell and Lester mountains. These are thought to be major suture zones between the larger terranes in the Park Range area and are characterised by plutonic intrusions and a widely changing metamorphic facies over short distances (Foster et al. 1999). One of the most well studied plutonic intrusions in the area is the Mount Ethel pluton with an age of 1.4 Ga, making it one of the youngest intrusions in the area.

Figure 4-4. Shaw et al. (1999).

Summary The origin of the Yavapai Province is still being debated, where the bimodal igneous suites together with the diffuse transitional zones between the Mojave and Mazatzal might hold an answer to the magma source and the Proterozoic tectonic history of the area. Metamorphism seems to have overall been within the Amphibolite to Greenschist facies, with steep metamorphic gradient found along shear zones and plutonic intrusions. More studies of the metamorphic overprint along the transition zones could also contribute to a better understanding of the tectonic history of the area.

47

The US Cordillera Excursion 2015

References

BENNET, V.C., DEPAOLO, D.J., (1987), Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping, Geologic Society of America Bulletin, vol. 99, ppp. 674 – 685 BICKFORD, M.E., HILL, B.M., (2007), Does the arc accretion model adequately explain the Paleoproterozoic evolution of southern Laurentia? An expanded interpretation, Geology, vol. 35, pp. 167-170 FOSTER, C.T, REAGAN, M.K., KENNEDY, S.G., SMITH, G.A., WHITE, C.A., EILER, J.E., ROUGVIE, J.R., (1999), Insight into the Proterozoic geology of Park Range, Colorado, Rocky Mountain Geology, vol. 34, no. 1, pp. 7-20 HEWETT, D.F., (1956), Geology and mineral resources of the Ivanpah Quadrangle, California and Nevada, U.S. Geological Survey Professional Paper, vol. 275, pp. 172 (cited from USGS) HOLLAND, M.E., KARLSTRÖM, K.E., DOE, M.F., GEHRELS, G.E., PECHA, M., SHUFELDT, O.P., BEGG, G., GRIFFIN, W.I., BELUSOVA, E., (2015), An Imbricated midcrustal suture zone: The Mojave-Yavapai Province boundary in Grand Canyon, Arizona, GSA Bulletin, vol. 127, no. 9/10, pp. 1391-1410 KARLSTRÖM, K.E., BOWRING, S.A., (1988), Early Proterozoic assembly of tectonostratigraphic terranes in southwestern North America, Journal of Geology, vol. 96, pp. 561-576 SEARS, J.W., GRAFF, P.J., HOLDEN, G.S., (1982), Tectonic evolution of lower Proterozoic rocks, Uinta Mountains, Utah and Colorado, Geological Society of America Bulletin, vol. 93, no. 10, pp. 990-997, (cited from USGS) SHAW, C.A., SNEE, W., SELVERSTONE, J., REED JR., J.C., (1999), 40Ar/39Ar Thermochronology of Mesoproterozoic Metamorphism in the Colorado Front Range, The Journal of Geology, col. 107, pp. 49-67 SIMS, P.K., BANKEY, V., FINN, C.A., (2001), Preliminary Precambrian basement map of Colorado-A geologic interpretation of an aeromagnetic anomoly map, U.S. Geological Survey Open-File Report 01-0364 (cited from USGS) TWETO, O., (1987), Rock units of the Precambrian basement in Colorado, IN Geology of the Precambrian basement in Colorado, U.S. Geological Survey Professional Paper, vol. 1321-A, pp. A1-A54, (incl. geologic map, scale 1:1,000,000), (cited from USGS) WHITMEYER, S.J., KARLSTRÖM, K.E., (2007), Tectonic model for the Proterozoic growth of North America, Geosphere, vol. 3, no. 4, pp. 220-259 LEVIN, H.L., (2006), The Earth Through Time, Eight edition, ISBN-13: 978-1118254677 USGS (January 20, 2015), Precambrian Basement Rocks of the Colorado Plateau. Retreived from: http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/precambrian.htm

48

The US Cordillera Excursion 2015

5 Western Interior Seaway - Sedimentology and Stratigraphy in Relation to the Sevier Orogenic Belt

Anders Euenius University of Gothenburg

The Western Interior Seaway The Cretaceous Inner Seaway, or commonly referred to as the Western Interior Seaway was an epicontinental sea covering a large extent of north America (Figure 5-1B) during the Jurassic and Cretaceous, approximately at 172 Ma to 65 Ma as seen in Figure 5-1 (Blakey, 2014). Western Interior Seaway formed as the sea transgressed into the western interior basin, which was created as a result of mantle flow-effects related to the subduction of the Farallon plate (Liu et al., 2011). During its largest (Figure 5-1B), the seaway stretched from the Tethys ocean in the south to the Panthalassa sea in the northwest, dividing north America into Laramidia to the west and Appalachia to the east (Blakey, 2014).

Figure 5-1. Western Interior Seaway during (A) the Middle Jurassic (172-170 Ma), (B) middle Coniacian (87,9 Ma) and (C) the K/T boundary (65 Ma). From Blakey (2014).

49

The US Cordillera Excursion 2015

The sediments deposited in and around the Western Interior Seaway are partly visible today in places such as Park Range, Front Range, Uinta Mountains and Rock Springs (Figure 5-2). This is due to the regional uplift that occurred during the Laramide orogeny, a mountain building event that followed, and over overlapped with Sevier in some places. Sediments from the Western Interior Basin have been previously well studied, age constraints consist largely of bio stratigraphic dating combined with radiometric dating of metamorphic-, structural-, volcanic-plutonic events and bentonites (Blakey, 2014; Utah Geological Survey, 2015).

Figure 5-2. Regional overview of the Sevier orogenic front and the Laramide uplift in the Western Interior Basin. Structural cross sections, A-A and B-B. Stratigraphic cross sections, I-I and II-II. From Liu et al. (2011).

The Sevier orogeny According to the Utah Geological Survey (2015), the Sevier orogeny was a mountain building event that occurred between 170-40 Ma and stretched as far as from Alaska to Mexico, where the part located in and around Utah is referred to as the Sevier thrust-system. It was characterized mainly by thin-skinned tectonics, and display the typical structure commonly related with thrust systems. In the west there was a foreland fold and thrust belt which progressively migrated toward the east, which consisted of a foredeep basin followed by a back-bulge high. In the thrust-system in Utah, individual thrust-sheet measure up to 50000 feet in thickness, several of these thrust-sheets constitute large stacks that made up mountains of considerable size, comparable to the Andes today (Utah Geological Survey, 2015; Moores & Twiss, 1995).

Environments and lateral extent of the Western Interior Seaway The history of Western Interior Seaway begins even before the Sevier orogeny begin, and the sedimentary record display a great variety of environments (Figure 5-1). Blakey (2014) show that in the middle of the Jurassic, the Western Interior Seaway consisted of a narrow sea (Gypsum Seaway, 172-170 Ma) with an opening to the Panthalassa sea to

50

The US Cordillera Excursion 2015 the northwest. After a brief transgression (Carmel-Twin Creek Seaway, 170-168 Ma), this was followed by a sharp regression which lead to the Western Interior Seaway retreating northward (Swift Upper Sundance Seaway, 161-156 Ma) and is replaced by the Morrison fluvial system (150-148 Ma). Through a major transgression in the early Cretaceous, Western Interior Seaway goes from being a small inlet of the sea, toward becoming a large epicontinental sea during the Albian (105-102 Ma). After a brief regression that leads to the Mowry Seaway (99- 98.5 Ma), Western Interior Seaway reaches its peak in the Turonian (93.2 Ma), during this time the seaway extends continuously from the Tethys Sea to the south Panthalassa in the north (Blakey, 2014). Blakey (2014) suggest that a series of short transgressions and regressions occurs during the late Cretaceous, which lead to a gradual decrease in size. Eventually during the Campanian/Maastrichtian (70.8 Ma), seaway is closed in its connection to Tethys to the south. The final termination of the seaway is at the end of Palaeocene (65-60 Ma), where the subsidence is replaced by the beginning of the Laramide uplift.

Sediment from the Sevier The sediments from the Western Interior Seaway have been studied widely, both well log data and outcrops, which are available to us today thanks to the Laramide uplift. Moores & Twiss (1995) describes the Western Interior Basin as a classic example of a foreland basin, also known as molasse basins from the French terminology. The basin was situated between the main orogenic belt of Sevier to the west and the undeformed crust to the east, which result in different modes of sedimentation at each side. As seen in Figure 5-3, the sediments on the east side of the basin consist of a generally thin sequence of shallow marine sediments, predominantly limestone and shale. Little variation signifies that this was a much more stable environment than the western side. The western side commonly contains a sediment thickness of over 3 km and is dominated by the interfingering of marine and terrestrial sediments (Utah Geological Survey, 2015; Moores & Twiss, 1995).

Figure 5-3. Schematic view of the sediments in the Western Interior Basin. From Moores & Twiss (1995).

51

The US Cordillera Excursion 2015

This interfingering is described by Moores & Twiss (1995) as a result of the migration of the orogenic front of Sevier. This means that as the most recent thrust-sheets are eroded, they supply new material that is later dumped in the basin. This can be seen as a general trend of periods of abrupt eastern lateral displacement of the shoreline sedimentation, as well as an increase of coarse sediment near the orogenic front (Figure 5-3).

Tectonic effects on subsidence and sedimentation The accommodation through the continuous subsidence across the Western Interior Basin have had great importance both for sedimentation and the preserving of the sedimentary sequence (Liu et al. 2011; Blakey 2014). It is implied by Liu et al. (2014) that it is the subsidence that is the major controlling factor of sedimentation in the basin. It has previously been suggested that the subsidence is mainly driven by thickening of crust due to the stacking of thrust-sheets in the Sevier orogeny (Liu et al. (2014). This hypothesis was rejected in a study by Pang & Nummedal (1995), where they showed that the influence of stacked thrust-sheets on subsidence, only affected a small portion of the basin, a narrow band of around 120 km. Liu et al. (2014) has further studied historic subsidence of the Western Interior Basin by investigating structural and stratigraphic cross sections in Utah, Wyoming and Colorado. Figure 5-2 show the cross sections from the orogenic front of Sevier, eastward into the Western Interior Basin. They argue that the eastward migrating depo-center in the basin (Figure 5-3) is related to an also migrating zone of maximum subsidence. It is also suggested that this is due to the opening of the Atlantic, which caused north America to be pushed over the distinct crest of the shallow subducting Farallon plate. According to Liu et al. (2011), and as seen in Figure 5-4, between approximately 98 Ma 90 Ma the dynamic pull of the Farallon plate stayed stable at the western margin of the basin and caused a high rate of subsidence. The effect of subsidence on the eastern part of the basin was very low, due to the depth of the subducting slab below it. Liu et al. (2011) further argue that after 90 Ma the Farallon plate moves eastward relative to north America, and by 84 Ma the crest is situated below Utah and Wyoming, in which it starts affecting the whole basin (Figure 5-4). At this time the viscous pull above the slab crest was at its maximum. At around 80 Ma the center of subsidence moved further eastward to western Colorado where the subsidence rate continued to increase. After 80 Ma the direction in which north America was pushed over the Farallon plate changed, resulting in a change to a northeastward relative motion on the Farallon plate. At the time the viscous pull had started to decrease due to the slab sinking further into the mantle, which brought an end to the high rates of subsidence in the region. Liu et al. (2011) conclude that the type of trough-shaped subsidence profiles that their study shows, suggest that the primary driver for the subsidence in the Western Interior Basin was the dynamic pull of the sinking Farallon plate.

52

The US Cordillera Excursion 2015

Figure 5-4. (A) Shows the restored cross section I-I, as seen in figure 2. (B) Shows the eastward migration of the zone of maximum subsidence from 98,8 Ma to 75 Ma. From Liu et al. (2011).

Summary The events as described by Moores & Twiss (1995), Utah Geological Survey (2015), and in studies of Blakey (2014), Liu et al. (2011) and Pang & Nummedal (1995), suggest that the Western Interior Seaway and the basin in which it lay, has a long history that begins even before the major events of the Sevier orogeny. In the beginning, the Western Interior Seaway went from being a narrow inlet of the sea from the Panthalassa, to a fluvial system, to growing to its maximum during the major subsidence of the Cretaceous, connecting the Panthalassa and the Tethys ocean from north to south. During the Sevier orogeny, syn-tectonic erosion material from the eastward migrating front of thrust-sheets appear to give rise a trend in prograding shoreline as well as coarser sediment, outward into the Western Interior Basin. These events have been recorded in the sedimentary archive due to the high rate of subsidence in the western part of the basin, caused by viscous pull of the subducting Farallon plate. The depo-center of the basin can be seen to shift slowly eastward as a result of an eastward migrating zone of maximum subsidence, as north America is pushed westward over the subducting Farallon plate. The Western Interior Seaway is finally terminated as the Farallon plate sinks further, decreasing the viscous pull and therefore the subsidence of the region. Eventually, the sediments of the basin are subject to unroofing through the uplift of the Laramide orogeny, which give us the sedimentary sequences seen in outcrops across the western Cordillera today.

53

The US Cordillera Excursion 2015

References

Moores, E., Twiss, R. (1995). Tectonics. W. H. Freeman Company, New York. Pang, M., and Nummedal, D. (1995), Flexural subsidence and basement tectonics of the Cretaceous Western Interior basin, United States, Geology, 23, 173–176. Liu, S.F., Nummedal, D., Liu, L.J. (2011). Migration of dynamic subsidence across the Late Cretaceous United States Western Interior Basin in response to Farallon plate subduction. Geology 39, 555–558. Blakey, R. (2014). Paleogeography and Paleotectonics of the Western Interior Seaway, Jurassic-Cretaceous of North America. Search and Discovery Article #30392. (2015-11- 19) at: http://cpgeosystems.com/paleomaps.html Utah Geological Survey (2015-11-19) at: http://geology.utah.gov/map-pub/survey- notes/knowledge-of-utah-thrust-system-pushes-forward/

54

The US Cordillera Excursion 2015

6 Sierra Nevada-Batoliten

Sara Kullberg Lund University

Abstrakt Sierra Nevada-batoliten är en av de mest välexponerade batoliterna i världen och därmed också en av de mest välstuderade. Batoliten, vilken i stort är en granitoid, har sitt ursprung i subduktionen av Farallon-plattan under främst kretaseisk tid. Kemiska trender visar på att den kontinentala trenden blir mer utpräglad österut samtidigt som åldersdateringar visar att den samtidigt blir yngre. Detta tros bero på en kombination av variationer i skorpans sammansättning samt en förändring av subduktionsvinkel under Sevier-orogenesen.

Introduktion Ordet batolit är en storleksterm som beskriver en pluton, eller en samling plutoner som täcker in en yta på 100 km2 eller mer. Sierra Nevada-batoliten sträcker sig cirka 600 km i nord-nordvästlig riktning och täcker samtidigt in 35000 km2 och uppfyller därmed kriterierna för en batolit (Figure 6-1) (Lackey et al. 2008, Marshak 2010). I början trodde man att hela komplexet utgjordes av en enda intrusion men denna hypotes förkastades snabbt när man började studera batolitens kemiska sammansättning och strukturella egenskaper mer ingående (Huber, 1987), något som kommer att förklaras mer detaljerat nedan.

Figure 6-1. figuren visas västra delen av USA. Sierra Nevada-batoliten är markerad i rött. Huvuddelen av batoliten befinner sig i Kalifornien men vissa plutoner kan hittas längre österut i Nevada (www1).

55

The US Cordillera Excursion 2015

En av anledningarna till att Sierra Nevadabatoliten har fått så stor uppmärksamhet är tack vare John Muir. Muir var under sent 1800-tal aktiv i Yosemite- området och drev en kamp för att göra området till ett naturreservat, vilket 1890 blev verklighet (www2). John Muir var glaciolog och hans artiklar blev därför startskotten för det vetenskapliga intresset för Yosemite och därmed även Sierra Nevada-batoliten. Denna text ämnar att ge läsaren en överskådlig bild av Sierra Nevada-batoliten gällande den tektoniska utvecklingen, de kemiska- och de åldersmässiga trenderna samt en liten diskussion angående dess ursprung. Slutligen beskrivs det även kort vilka olika sorters ekonomiska mineraliseringar som kan kopplas till batoliten.

Tektonisk utveckling Dagens Sierra Nevada ligger på den västra gränsen av den paleozoiska (542– 251 Ma) Nordamerikanska plattan. Fram till Devon (416–359 Ma) var denna gräns en passiv kontinentalgräns vilken fungerade som en sedimentär bassäng. I den sedimentära bassängen avlagrades enheter vilka kom att bli både en kemisk komponent i Sierra Nevadabatoliten men även bergarterna vilken den intruderade i (Bateman 1992). Under DevonKarbon (416– 299 Ma) ackreterades djuphavsstrata, på grund av den kompressiva miljön som uppstod med Antler-orogenesen, på den västra delen av den Nordamerikanska plattan (Bateman 1992, Marshak 2010). Denna orogenes var startskottet för en tektonisk aktiv miljö vilken kom att prägla utvecklingen av den Nordamerikanska plattan. Därefter följde Sonoma-orogenesen och Nevada-orogenesen vilka båda ackreterade vulkanöar och mikrokontinenter till USA:s västkust som då gradvis växte och blev större. Den förstnämnda orogenesen är enigmatisk och kontroversiell (Ketner 2008), forskare har inte riktigt kunnat enas om hur den egentligen framskred. Den sistnämnda orogenesen övergick sedan i den kretaseiska Sevier-orogenesen, vilken bildades på grund av subduktion av Farallon-plattan (Ducea et al. 2015), varpå en kontinental vulkankedja började att byggas upp (Bateman 1992, Marshak 2010). Denna vulkankedja kom att kallas för Sierran Arc och var mycket lik den vi ser i Sydamerika idag. Dock är det enbart dess rötter som idag finns kvar i form av Sierra Nevada-batoliten (Bateman 1992, Marshak 2010). Sevier-orogenesen övergick så småningom i Laramide-orogenesen vilken hade en helt annan karaktär. Farallon-plattan subducerades med en lägre vinkel och orogenesen övergick i en så kallad deepskinned orogenes vilket innebar att berggrunden lyftes upp i ett böljande mönster och blottlades (Figure 6-2). Vid den här tidpunkten hade den överliggande bergskedjan redan eroderats bort och kvar var stora mjuka former vilket kännetecknar bland annat Yosemite-området idag. Batoliten fortsätter idag att höjas och bli gradvis mer blottlagd i takt med att den Nordamerikanska plattan ständigt höjs. Förklaringen till detta ligger i att Farallon-plattan för 40 miljoner år sedan blev komplett subducerad och tappade fästet varpå den sjönk ner i manteln. Tomrummet som blev efter Farallon ersattes med varm astenosfär. Då varm astenosfär har lägre densitet jämfört med en relativt kall oceanskorpa så lyfter den nordamerikanska plattan (Marshak 2010).

56

The US Cordillera Excursion 2015

Figure 6-2. Figuren är en principiell skiss över hur Laramide-orogenesen påverkade Nordamerikas berggrund. Som det tydliggörs i figuren är förkastningarna djupt gående, de är deepskinned, och verkar så att de trycker upp den djupt liggande berggrunden. Vid erosion av ovanliggande enheter blottläggs en rundad häll (Marshak 2010).

Sierra Nevada-batoliten Rent kemiskt och åldersmässigt är Sierra Nevada-batoliten inte homogen utan raka motsatsen, heterogen. Förklaringen till detta är att intrusionerna som bildade Sierra Nevada-batoliten kom pulsartat i olika episoder. Efter intensivt kemiskt karterande har man idag delat in batoliten i 4 distinkta zoner; (1) 140-115 Ma dioritzon med kvartsdiorit, gabbro, tonalit, (2) 115-100 Ma tonalitzon med lite kvartsdiorit och gabbro, (3) 105-90 Ma granodioritzon med mestadels kvartsdiorit och gabbro och, (4) 90-80 Ma granitiska zonen med granodioriter och graniter (Chapman et al. 2012). Förklaringen i trenden ligger i att den subducerande Farallon-plattan ändrade subduktionsvinkel under kretaseisk tid vilket medförde att magmatismen gradvis ändrade lokus österut, och med det ändrades även sammansättningen (Marshak 2010).

Plutoner och sviter Sierra Nevada batoliten delas in i så kallade sviter där varje svit består av flertalet plutoner. Plutonerna i en svit karaktäriseras av att de är mer eller mindre likåldriga, har liknande kemi och textur (Bateman 1992). Plutonerna i varje svit förekommer i ett systematiskt mönster med de mer mafiska plutonerna i ytterkanterna och de mer felsiska plutonerna i den centrala delen (Figure 6-3). Åldersförhållanden följer samma trend med yngre bergarter omringade av äldre. Förklaringen ligger i att magman har intruderat gradvis. En pluton svalnar från utsidan och in vilket innebär att de centrala, och därmed varma delarna, är en svaghetszon. När en ny intrusion närmar sig underifrån letar den sig till svaghetszonen, tränger in här och kommer på så vis också att tvinga den äldre intrusionen åt sidorna (Figure 6-3), (Huber 1987).

Kemiska trender Som tidigare nämnt finns det en kemisk variation i västöstlig riktning över batoliten, vilken har resulterat i indelningen i 4 zoner (se tidigare i kapitlet). Rent generellt ökar mängden inkompatibla ämnen österut, såsom K2O, U, Th, Rb, Be, Ta och Ba. Det är svårare att se trender för enskilda sällsynta jordartsmetaller men däremot ökar totalmängden av de sällsynta jordartsmetallerna österut (Bateman 1992). Dessutom ökar 87Sr/86Sr österut samtidigt som 143Nd/144Nd minskar vilka båda är tecken på en mer kontinental trend österut. De kombinerade kemiska trenderna visar att batoliten har en allt större kontinental signatur ju längre österut man kommer (Winter 2010). Till varför det är så finns det en del teorier som kommer att diskuteras nedan.

57

The US Cordillera Excursion 2015

Figure 6-3. A-D visar en morfologisk utveckling av en svit där del D är den yngsta. Det röda visar den gradvis yngre magman som intruderar och därmed trycker ut de äldre delarna och ändrar dess utseende.

Ursprung Det är teoretiserat att magman som gav upphov till batoliten härstammar från tre olika källor; sedimentära bergarter med ursprung i den sedimentära bassängen som utvecklades under palaezoisk tid, material från den lägre krustan samt material från en ung och förmodligen urlakad mantel. Dock har man ej kunnat uppskatta hur stor andel varje komponent motsvarar (Lackey et al. 2005). Däremot har man kunnat göra uppskattningar angående vilken komponent som har varit den dominerande. Lackey et al. (2008) studerade variationer i ẟ18O både i det enskilda mineralet zircon men även för hela bergarter, det vill säga whole rock analys, samt variationer i uranisotoper och strontiumisotoper. Resultaten visade på att det finns en variation angående vilken den dominerande källan är. I de västra delarna av batoliten är den krustala komponenten hög där tidigare ackreterade vulkaniska öbågar och mikrokontinenter (med ursprung i Antlerorogenesen samt Sonoma-orogenesen) smälts upp och återvinns. Ju längre österut man kommer desto större blir påverkan av den litosfäriska manteln och lägre krustan samtidigt som kontaminationen av skorpan blir mindre påtaglig (Lackey et al. 2008). Innan dessa resultat blev kända teoretiserades det om vad anledningen till den kemiska trenden kunde vara. Teorierna var att kontaminationen av skorpan och ovanliggande sedimentära enheter skulle öka österut. Detta stödjs av bland annat 87Sr/86Sr och 143Nd/144Nd signaturer vilka visar att skorpan ska vara en större kontaminationskomponent österut. Trenderna skulle även förklaras med att de sedimentära enheterna blev tjockare österut och längre inåt kratonen (Bateman 1992). Detta kan anses dock vara orimligt då det generellt är så att en sedimentär bassäng minskar i tjocklek ju längre inåt kratonen man kommer (Miall 2008). Det är då mer troligt att den kemiska trenden är ett resultat av en mer berikad mantel och lägre skorpa ju längre österut man kommer i Sierra Nevada (Lackey et al. 2008).

Platsproblemet När en batolit av denna magnitud intruderar uppstår det så kallade platsproblemet; var ska allt material ta vägen? Enligt Bateman (1992) har flertalet processer samverkat för att ge plats åt Sierra Nevada-batoliten. 1. En del av materialet härstammar från skorpan. Uppsmällt material därifrån tar således inte mer plats. 2. Stopning innebär att den intruderande magman spräcker upp moderbergarten på grund av sin värme och fyller därefter ut sprickorna som uppstår. På grund av densitetskontraster mellan moderbergarten och den intruderande magman så

58

The US Cordillera Excursion 2015 antingen sjunker eller flyter blocken moderbergartsblocken. Denna process finns beskriven i Sierra Nevada-batoliten men anses vara en process som har påverkat med mindre betydelse. 3. Marginellt med plats bildas när omkringliggande bergarter deformeras och trycks undan av den intruderande batoliten. 4. Allra mest plats bildades då miljön, trots den kompressiva orogenesen, faktiskt var extentionell. Upptäckten av att miljön var extentionell stödjs av flertalet bevis; dels har man hittat likåldriga jurassiska intrusioner på vardera sida av en yngre kretaseisk intrusion, och dels av det faktum att Independence Dyke Swarm skär delar av batoliten. Mafiska gångar, såsom Independence Dyke Swarm, hör hemma i en extentionell miljö; om miljön hade varit kompressiv hade intrusionen antagligen ej kunnat intrudera lika smärtfritt utan legat kvar i skorpan längre och därmed blivit mer kontaminerade och således mer felsisk (Bateman 1992, Carl & Glazner 2002).

Mineraliseringar Kopplat till intrusionen finns även en del mineraliseringar och malmfyndigheter. Den stora majoriteten av fyndigheterna härstammar dock inte rent kemiskt från Sierra Nevadabatoliten i sig utan från moderbergarten. Det är värmen från intrusionen som katalyserade reaktioner i omkringliggande sedimentära enheter som sedan gav upphov till malmbildning. Enda undantaget är fyndigheter av tungsten (W) som faktiskt har sitt ursprung i magmatiska fluider. Fluiderna reagerade med kalksten och tungstenbärande mineral, såsom scheelite (CaWO4), kunde fällas ut. Dessutom gäller sambandet; ju renare kalksten, desto högre blir koncentrationen av tungstenmineraliseringar (Bateman 1992, Rinehart & Ross 1964). Majoriteten av all tungstenbrytning i USA kommer just från Sierra Nevada- batoliten, huvudsakligen från Pine Creek Mine (Lemmon, 1941). Man hittar tungsten i kontaktmetamorfa skarner vilka kan variera från någon centimeter i storlek till att vara några meter tjocka och sträcka sig hundratals meter. Dessa fyndigheter är koncentrerade till den östra delen av Sierra Nevada-batoliten för det är just här som det finns kontakter till stora enheter av kalksten (Bateman 1992, Rinehart & Ross 1964). Förutom tungsten är området kring Sierra Nevada-batoliten även rik på guld, koppar, bly, silver och molybden. Bildningssätten för dessa skiljer sig inte mycket från det för tungsten. Mineraliseringarna hittar man i kvartsgångar som är bildade genom metasomatism. Guldet finns antingen i ren fas eller i olika sulfidfaser såsom pyrit (Rinehart & Ross 1964).

Sammanfattning Sammanfattningsvis kan Sierra Nevada-batoliten beskrivas som en av världens mest studerade, men ändå mest svårförstådda batoliter. Batoliten är uppdelad i hundratals sviter och plutoner vilka alla följer en trend mot mer felsisk och berikad kemi österut, samtidigt som den blir yngre österut. Förklaringen i trenden ligger i att den subducerande Farallon-plattan ändrade subduktionsvinkel under kretaseisk tid vilket medförde att magmatismen gradvis ändrade lokus österut. Rent kemiskt har man ännu inte riktigt kunnat förklara batoliten. Frågor som berör batolitens ursprungskällor, och variationen av dem, återstår att besvaras.

59

The US Cordillera Excursion 2015

Referenser

Bateman, P.C., 1992: Plutonism in the central part of the Sierra Nevada Batholith, California. U.S. Geological survey professional paper 1483, 186 s. Carl, B.S. & Glazner, A.F., 2002: Extent and significance of the Independence dike swarm, eastern California. Geological Society of America Memoir 195, 117–128 sid. Chapman, A.D, Saleeby, J.B., Wood, D.J., Piasecki, A., Kidder, S., Ducea, M.N. & Farley, K.A., 2012: Late Cretaceous gravitational collapse of the Southern Sierra Nevada batholith, California. Geosphere 8(2), 314–341 sid. Ducea, M.N., Saleeby, J.B. & Bergantz, G., 2015: The Architecture, Chemistry, and Evolution of Continental Magmatic Arcs. Annual Review of Earth and Planetary Sciences 43, 299– 331 sid. Huber, N.K. 1987: The Geologic History of Yosemite National Park. US Geological Survey Bulletin 1595, 84 s. Ketner, K.B., 2008: The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern Nevada – An Interrelated Paleozoic Assemblage in the Home of the Sonoma Orogeny. U.S. Geological Survey Professional Paper 1757, 21 sid. Lackey, J.D., Valley, J.W., Chen, J.H. & Stockli, D.F., 2008: Dynamic Magma Systems, Crustal Recycling, and Alteration in the Central Sierra Nevada Batholith: the Oxygen Isotope Record. Journal of Petrology 49, 1397–1426 s. Lackey, J.D., Valley, J.W. & Saleeby, J.B., 2005: Supracrustal input to magmas in the deep crust of Sierra Nevada batholith: Evidence from high- ẟ18O zircon. Earth and planetary science letters 235, 315–330 sid. Lemmon, D.M., 1941: Tungsten Deposits in the Sierra Nevada near Bishop Californa: a preliminary report. Strategic Minerals Investigations, 79–104 sid. Marshak, S., 2008: Earth, Portrait of a Planet (3rd ed.). W.W. Norton & Company. 832 s. Miall, A.D., 2008: The Paleozoic Western Craton Margin. Sedimentary Basins of the World, kapitel 5. Rinehart, C.D. & Ross, D.C., 1964: Geology and Mineral Deposits of the Mount Morrison Quadrangle Sierra Nevada, California. Geological Survey Proffesional Paper 385, 112 sid. Winter, J.D. (ed.) 2010: Principles of Igneous and Metamorphic Petrology (2a ed.). Prentice Hall 702 sid. www1: History of the Sierra Nevada (2015-10-30) Retried from: https://pangea.stanford.edu/research/groups/structure/gfx/fig1ed.jpg www2: National Park Service (2015-10-30). Retrieved from: http://www.nps.gov/yose/learn/historyculture/muir.htm wwwx: National Park Service (2015-10-30). Retrived from: http://www.nps.gov/yose/learn/nature/granite.htm

60

The US Cordillera Excursion 2015

7 The Colorado Plateau and the development of the Grand Canyon

Christoffer Åkesson University of Gothenburg

Introduction The Colorado River is cutting down into the Colorado Plateau, which is being uplifted, and makes up the Grand Canyon. The Canyon is 277 mile long (~446km) and wriggles through the landscape (Ranney, 2005). Incision of the plateau is exposing rock as old as 1840 Ma and makes it possible to study the Stratigraphy. The Stratigraphy is important in the understanding of the development of the landscape. The Colorado Plateau has today been uplifted to an average of 2000 m.a.s.l. and during the uplift the Colorado River has been carving the Grand Canyon (Karlstrom, 2012). The uplift has occurred 70 million years, from the day the plateau was at sea level. However the Grand Canyons development is argued but the most recent hypothesis suggests an incision of just a couple of million years. One of the hypothesis are made by Karlstrom et al ,2008, which suggest an incision in 6 million years. The Colorado plateau’s high location, average 2000 is partly due to the delamination of the lithosphere and the dynamic mantel convection that transfer warm mantle under the plateau which causes isostatic uplift. This is all a consequence of the sinking Farallon plate.

Stratigrapfy Colorado Plateau consist of a series of rock that are divided into three sets, Layered Paleozoic Rocks, Grand Canyon Supergroup Rocks and Vishnu Basement Rock. These Groups are then divided into formation and the youngest one are the Kaibab, deposited 270 Ma, which are a member of the Paleoszoic Rocks as can be seen in Figure 7-1 (Mathis & Bowman, 2006). Mathis and Bowman (2006) means that the Ages for the Layered Paleozoic Rocks is quite difficult to determine. They explain that the ages rely on fossil correlation, index fossils and relative age relationships which give the ages 525-270 Ma for the deposition. This is however sediment that has been deposited during a period of time and the ages can’t be exact but this doesn’t make the ages less importance (Mathis & Bowman, 2006). Between the Layered Paleozoic Rocks and the Supergroup the Great Unconformity can be found. The unconformities time gap ranging from 220 Ma to 1.2 Ga which are due to the angle of older sediment (Mathis & Bowman, 2006). Peters and Gaines (2012) explains that unconformity separates the shallow marine sediment with the

61

The US Cordillera Excursion 2015 underlying metamorphosed rock in this area but that the unconformity is global. They explain that it can be traced across Laurentia, Gondwana, Baltica, Avalonia and Siberia which makes it “the most widely recognized and distinctive stratigraphic surface in the rock record” (p. 363). There are also several more unconformities in the stratigraphy that not are mention in this article.

Figure 7-1. Stratigraphy of the Grand Canyon (Mathis and Bowman, 2006)

The Supergroup are deposited, at about sea level, 1200-750 Ma in a tectonically active basin. Today the group are tilted 10 degrees which occurred during and after deposition, during the faulting there also was faulting. This processes made it possible for high accumulation of sediment. (Mathis & Bowman, 2006) According to Mathis and Bowman (2006) the Grand Canyon Supergroup is hard to date due to the lack of fossils and are there not assigned numeric age based of index fossils. Instead the aging depends on dating basalt, few ashlayers and zircons. At the bottom of the Grand Canyon can the Vishnu Basement Rock be found which consist of Precambrian, mostly formed between 1750 Ma and 1680 Ma, metamorphic and igneous rocks (Mathis & Bowman, 2006). The youngest are 1680 Ma and the oldest rock is 1840 Ma and is called the Elves Chasm Gneiss. Mathis and bowman (2006) says that the origin of the Gneiss is unclear so it doesn’t have to be a member of the “basement for the basement” but a fragment of older continental crust.

62

The US Cordillera Excursion 2015

Geologic history of the Colorado Plateau The Colorado River runs through the Colorado Plateau and has carved its way through the landscape to the shape it has today. However it is not just the river in itself that have shaped the landscape. The denudation of the mountain has made it possible for erosional forces to work. The alternating stronger and weaker rock makes it possible to erode the sides faster and the eroded material is carried away by the river. The weaker rock is eroded faster than the stronger, undermining the stronger rock which also can cause “stair steps” shape of the walls (Marshack, 2008). This had lead to a width up to 24 km in some parts of the Canyon. Liu and Gurnmis (2010) means that the uplift of the southwest Utah and northwest Arizona started to rise 85 Ma which seems to be the start of the Laramide uplift. According to Liu and Gurnmis (2010) model of mantel convection, the Colorado plateau was tilted downward to the northeast which indicates that the water was flowing in the opposite direction. They mean that the cause of this is a “northeast-trending subduction of the Farallon slab” and the tilt is the largest 75Ma. According to their model the tilting is changing direction 15Ma which they mean is “consistent with the southwest carving of the Grand Canyon during the neogene (Karlstrom et al., 2008)”. According to Karlstrom et al. (2008) the carving of the canyon are suggested to have occurred in the past 6 Ma and that the evidence for it are strong. Karlstrom et al. (2008) mainly have three arguments for it, the arguments are: “(1) The sedimentary record shows that there are no Colorado River sediments in the 13–6 Ma Muddy Creek Formation that now blankets the Grand Wash trough at the mouth of the Grand Canyon (Lucchitta, 1972; Faulds et al., 2001). (2) The first sediments containing distinctive sand composition and detrital zircons that can be traced to Rocky Mountain sources reached the newly opened Gulf of California at 5.3 Ma (Dorsey et al., 2007; Kimbrough et al., 2007). (3) Gravels on top of the 6 Ma Hualapai Limestone and beneath the 4.4 Ma Sandy Point basalt show that the river became established in its present course between 6 and 4.4 Ma (Howard and Bohannan, 2001).” (p. 835) Karlstrom et al. (2008) also argue that there has been a semi-steady incision for the last 3-4 Ma. They also talking of an astenospheric flow that has driven a ~700m uplift of a block in the eastern part of the Colorado plateau in the last 6 Ma. The rates of incision are therefore different in the eastern (175-250 m/Ma) and the western parts of the plateau (50- 80 m/Ma), details show in Karlstroms et al. (2008) model in Figure 7-2. This astenospheric flow is a consequence of the Farallon plate.

63

The US Cordillera Excursion 2015

Figure 7-2. Part of a model showing the rate of incision and uplift. (Karlstrom et al., 2008)

According to Levander et al 2011 there is evidence that suggesting periods of uplift during Laramide, mid-Cenozoic and late Cenozoic. The driving forces are the Farallon plate that has been flat-slabed subducted underneath the Colorado Plateau. The Subduction causing weakening of the overriding plate and are believed to have removed the North American lithosphere deeper than 120-150km (Levander et al, 2011). Levander et al. (2011) also means that the plate is “cooling down the remainder from conductive heating and thermal expansion and a small-scale convective removal of the Colorado plateau lithospheric mantel”. The Farallon flat-slab subduction effects the North American lithosphere by hydrating which weakening the lithosphere (Levander et al., 2011). According to Levander there is also refertilizing of the lithosphere due to melt infiltration, which means a small but important density increase, that also weakening the lithosphere thermally. This sums up in a foundering of the lithosphere and delamination (Levander et al., 2011). The Colorado plateau is being weighed down by the North Americas lithosphere and are therefore uplifted when the lithosphere are being delaminated.

Conclusions Colorado Plateau has a stratigraphy going back to 1840 Ma including the globally Great Unconformity. The Colorado Plateau has been uplifted since 85 Ma when the tilt of the plateau was at northeast. Since 15 Ma the plateau has gone from no tilt to the tilt it has today in rates of 0.01 to 0.02 °/Ma (Crow et al., 2014). However the Colorado River did not established its path until somewhere between 6 and 4.4 Ma. The Grand Canyon had therefore been carved in less than 6 Ma.

64

The US Cordillera Excursion 2015

References

Mathis, A., & Bowman, C. (2006). The Grand Age of Rocks: The Numeric Ages for Rocks Exposed within Grand Canyon. Retrieved from: http://www2.nature.nps.gov/geology/parks/grca/age/index.cfm Peters, S. E., & Gaines, R. R. (2012). Formation of the 'great unconformity' as a trigger for the cambrian explosion. Nature, 484(7394), 363. doi:10.1038/nature10969 Karlstrom, K. E., Crow, R., Crossey, L. J., Coblentz, D., & Van Wijk, J. W. (2008). Model for tectonically driven incision of the younger than 6 Ma Grand Canyon. Geology, 36(11), 835-838. Karlstrom, K. E., Coblentz, D., Dueker, K., Ouimet, W., Kirby, E., Van Wijk, J., ... & CREST Working Group. (2012). Mantle-driven dynamic uplift of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified hypothesis. Lithosphere, 4(1), 3-22. Karlstrom, K. E., & Timmons, J. M. (2012). Faulting and uplift in the Grand Cany on region. Geological Society of America Special Papers, 489, 93-107. Levander, A., Schmandt, B., Miller, M. S., Liu, K., Karlstrom, K. E., Crow, R. S., ... & Humphreys, E. D. (2011). Continuing Colorado plateau uplift by delamination-style convective lithospheric downwelling. Nature, 472(7344), 461-465. Liu, L., & Gurnis, M. (2010). Dynamic subsidence and uplift of the Colorado Plateau. Geology, 38(7), 663-666. Mathis, A., & Bowman, C. (2006). The Grand Age of Rocks: The Numeric Ages for Rocks Exposed within Grand Canyon. Retrieved from: http://www2.nature.nps.gov/geology/parks/grca/age/index.cfm Peters, S. E., & Gaines, R. R. (2012). Formation of the 'great unconformity' as a trigger for the cambrian explosion. Nature, 484(7394), 363. doi:10.1038/nature10969

65

The US Cordillera Excursion 2015

8 Post-Laramide Development of Relief in the Rocky Mountains and Foothills

Henrik Åslund University of Gothenburg

Introduction Estes Park, Colorado (Figure 8-1.) encompasses an area of 1,955 square miles which lies south of the Laramie Mountains and spans the Front Range uplift of the southern Rocky Mountains and the westernmost part of the Colorado Piedmont (Cole & Braddock, 2009). The Laramie Mountains spans the central Rocky Mountains which together with the Southern Rocky Mountains make up the Rocky Mountain orogenic plateau. This plateau has a mean altitude over 2 km above sea level and has a relief that spans from 30 m in the river valleys in the Great Planes to more than 1.6 km in the deep basins of Rocky Mountains and Colorado Plateau (McMillan, Heller, & Wing, 2006). The Continental divide of the Rocky mountain traces north to south along the glaciated crest of Estes Park with summits that exceed 3,600 m elevation. The eastern margin of the Front Range is marked by a narrow and linear foothill zone consisting of hogback ridges formed by upturned sedimentary strata and most of the eastern slope is rolling forested upland. The valleys in the north are northwest-trading (fault controlled) which segment the Front Range and break up the hogback ridges into en échelon segments that step progressively eastward. The middle zone of the Front Range is characterized by gently rolling upland block of Proterozoic rocks and has elevations between 2000 to 2750 meters. These summits decline gently eastward with narrow steep canyons due to their deep incisions. The highest zone is the glaciated highland terrain above ca 2750 m that is marked by steeper than the incised upland zone to the east. The westernmost zone of the Front Range is the steep, western slope that declines rapidly to about 2450 m elevation in the fault controlled north-south valley of the upper Colorado River, and the sedimentary- basin lowlands surrounding Granby. Several other major rivers also have headwaters along the Continental Divide within Estes park such as the Colorado Rivers which flows westward between the Never Summer Mountains to the east and the Front Range on the east. (Cole & Braddock, 2009). What is striking about the Rocky Mountains landscape as a whole and the Front Range in particular is that there are parts which are bevelled by remarkably even summit topography. This even summit surface is known as the Flattop Surface (at ca 4000 m) and the extensive piedmont surface (Figure 8-2) is known as Sherman erosion surface (Eggler et al., 1969).

66

The US Cordillera Excursion 2015

Figure 8-1. Map showing zones of the Estes Park quadrangle (i.e., rectangle) and adjoining areas. Taken from Cole & Braddock (2009).

Endogenous processes Mantle-surface interactions are important drivers for topographic change in continental settings, additionally to earthquakes and plate tectonics (Karlstrom et al., 2012; McMillan et al., 2006). Uplift can be generated by buoyancy changes in the mantle which are derived either by density changes in the mantle or by and mantle dynamics and flow. Mantle dynamics are divided into lithospheric and asthenospheric dynamics which are believed to affect the topography in different ways. Buoyancy changes in the asthenosphere (i.e., beneath the lithosphere) are thought to generate longer wavelength topographic effects and consequently cover a larger geographic region compared to lithospheric dynamics which are thought to be of shorter wavelengths and consequently affecting topography on a subregional scale. Mantle flow is tectonically driven mantle convection, which in a similar manner can cause differential pressures at the base of the lithosphere that result in uplift (Karlstrom et al., 2012 and references therein).

67

The US Cordillera Excursion 2015

Exogenous processes Rivers (see also chapter 7, this volume) and glacial systems (chapter 9) are often climate related and are well known to affect topography. Glacial systems are mainly temperature controlled (for a more detailed review see chapter 9). River systems on the other hand are controlled by the abundance of water in relation to sediment supply, additionally to topographic effects (e.g., gradient). Consequently, are uplift and subsidence generally followed by erosion and basin fill, respectively (McMillan et al., 2006). The evolution of river systems studied through paleodrainage or incision measurements have been used to understand the uplift mechanics of the Rockies and the Colorado Plateau (Dickinson et al., 1988; Karlstrom et al., 2012). Isostatic rebound is caused by the exhumation (chiefly by river incision) and by retreating glaciers (chapter 9), which both can also generate knickpoints (i.e., abrupt change in slope) in the valleys where they flowed (McMillan et al., 2006). Mass wasting events are landslides and debris flows that flow into river canyons and are frequent in the Front Range area and are related to periods of intense rainfall. A recent study (Coe et al., 2014) also related them to flows initiated in canyons and hogbacks at elevation lower than a wide spread erosion surface of low slope and relief (<2600 m) with flows running on steep slopes facing south and east. They could furthermore relate the flows to colluvial soils formed on sedimentary rocks (rather than crystalline rock).

Topographic history The North American Cordillera has been made possible through the proximity to the west of the North America tectonic plate by a large oceanic realm known as the Pacific-Panthalassa system. This ocean has remained a large basin through immense periods of geologic time and evolved into the present Pacific Ocean basin. Such a large oceanic realm is made possible through the rapid circuit of spreading at the mid-ocean ridge corresponding subduction of the oceanic plate at the continental margin (Frisch, Meschede, & Blakey, 2010). Today the Pacific Ocean is on top of the Pacific Plate but during the Mesozoic it was underlain by the Farallon Plate. The Farallon plate has over the past 200 Ma transported terrains onto the North American continental margin (Frisch, Meschede, & Blakey, 2010). The Laramide orogeny was preceded by the Nevadan and Sevier orogenies. These orogenies and their relationship to the subduction of the Farallon plate are explained in chapter 6 (this volume). Uplift generated by the end of the Laramide orogeny due to the mid-Cenozoic removal of the Farallon plate ca 35 Ma (20-40 Ma) and subsequent heating of the lithosphere and isostatic uplift (Roy, Jordan, & Pederson, 2009). This elevation as well as topographies created at in the middle Oligocene at ca 28 Ma are due to igneous activities with ignimbrite aggradation throughout the much of the whole of the Rockies. Locally in the Front Range, Estes Park area, this is exposed today as the Braddock Peak intrusive complex in the Never Summer Mountains which include preserved volcanic ejecta such as, andesitic, dacitic, rhyolitic lavas and welded tuffs that all blanketed the landscape at that time (Cole & Braddock, 2009). Intrusions during this time is believed to have made the lithosphere weaker to better allow extension later on (Morgan, Seager, & Golombek, 1986). Much of these topographic changes in the Rockies area were however almost completely denudated, additionally to negated by sedimentation which was recorded by the basal Troublesome Formation in the Granby area, Estes Park starting during the Oligocene

68

The US Cordillera Excursion 2015 but its upper part may be as young as Late Miocene, 11 Ma (Cole & Braddock, 2009 and references therein). This erosion and sedimentation could have been due to a long time increase of moisture due to mid-Cenozoic cooling (28-16 Ma) (Dickinson et al., 1988; Karlstrom et al., 2012). The foothills-hogbacks belt is a product of erosion during the last 5 Ma (Cole & Braddock, 2009). Continued erosion on the eastern slope of the Front Range produced east trending fluvial channels with a westward facing apron across the Laramide front, with broad meandering paths developed by low gradient streams derived from renewed uplift during the Pliocene. Continued global cooling during the Pliocene enabled glaciation during the Quaternary. The Pliocene uplift also accentuated the topographic relief across the Continental Divide with continued erosion during the Pliestocene at which time erosion made incisions in the High Planes at the eastern mountain front (Cole & Braddock, 2009).

Figure 8-2. Planulation surfaces of the Front Range. 1: Laramide tectonic front; 2: extentsional faulting related to the Rio Grande rift; 3: Flattop surface; 4: Sherman surface; 5: Upper Miocene Ogalalla formation (alluvial); 6 Site of the Palegenoe Florissant Flora. Taken from Calvet et al. (2015) which is redrawn from references therein.

69

The US Cordillera Excursion 2015

Controversy There are studies that suggest the elevation in the Front Range was mainly created in the pre-Neogene (Sjostrom et al., 2006), or just additionally suggest that the following uplift was isostatic by emphasising on climatic forced incision based exhumation during this period (Gregory & Chase, 1992, 1994). That some workers seem to favour this could be due to that the Rockies stand relatively remote from any active plate boundary. That said, most workers seem to agree that uplift during the late Cenozoic is mostly responsible for the elevation and subsequent topography (McMillan et al., 2006; Roy et al., 2009; Karlstrom et al., 2012; Calvet et al., 2015). Cather et al. (2012) recognise three diachronous uplifts following the Laramide orogeny during the Cenozoic. (1) Late Eocene uplift ca 42-37 Ma which they argue was caused by erosion in response to epeirogenic uplift related to the Farallon plate (chapter 6). (2) Late Oligocene-early Miocene deep erosion, ca 27-15 Ma which they relate to endogenous processes related to concurrent volcanism. (3) Late Miocene-Holocene uplift at ca 6-0 Ma which they mostly related to both mantle related uplift and fluvial erosion. There are mainly two competing hypotheses for late Miocene uplift which may not be mutually exclusive. The first could be described as exogenous and is based on the previously mentioned cooling phase at this period which increases fluvial (and possibly glacial) incision into an already elevated plateau which leads to erosion of the Rockies and exhumation of the basin fill (Small & Anderson, 1998; Riihimaki et al., 2007). The second hypothesis is based on endogenous processes and focuses on epeirogenic (i.e., long wave length, austenospheric derived) uplift (Eaton, 2008; Cather et al., 2012). The problem that the first hypothesis faces is that only the last uplift mentioned by Cather et al., (2012) at ca 6 Ma can be temporally correlated with climatic change and the rest of the episodes can be explained by expected natural denudation or exhumation and basin fill cycles as the region stayed relatively close to sea-level during the end of each of these erosion cycles. Furthermore was the a broad area of the southwestern North America uplifted at the 6 Ma time frame at the initiation of the opening of the Rio Grande rift and related mantle dynamics (Calvet et al., 2015 and references therein), additionally (McMillan et al., 2006) relates this to hot lithospheric mantle and thus shorter wavelength regional doming of thin crust. Karlstrom et al. (2012) additionally argues that the Rocky Mountains had a relative uplift compared to the Colorado Plateau between 6-10 Ma due to mantle flow. The Flattop and Sherman erosion surfaces could be remains of a single Eocene surface that was later offset by faulting. This can be argued from the overlying volcanic rocks which cover it as well as lacustrine beds containing both the upper Eocene to lower Oligocene (34 Ma) (Calvet et al., 2015). There is also evidence of tilting western Great Plains which is based on the anomalously steep Ogalalla-related (Figure 8-2) stream gradient in the piedmont, which indicate ongoing uplift. Calvet et al. (2015) argues that this further weakens the case for uplift due to climatic forcing during the Miocene-Pliocene.

Conclusion The main driver behind the Rocky Mountain elevation in the Front Range is most likely due to endogenous processes in the mantle. Incision and exhumation based isostatic uplift seem to be important but still secondary to mantle processes when it comes to elevation and relief. Landscape and topographic features however have been heavily influenced by exogenous processes e.g., river incision.

70

The US Cordillera Excursion 2015

References

Calvet, M., Gunnell, Y., & Farines, B. (2015). Flat-topped mountain ranges: Their global distribution and value for understanding the evolution of mountain topography. Geomorphology, 241, 255–291. http://doi.org/10.1016/j.geomorph.2015.04.015 Cather, S. M., Chapin, C. E., & Kelley, S. A. (2012). Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry. Geosphere, 8(6), 1177–1206. Coe, J. A., Kean, J. W., Godt, J. W., Baum, R. L., Jones, E. S., Gochis, D. J., & Anderson, G. S. (2014). New insights into debris-flow hazards from an extraordinary event in the Colorado Front Range. GSA Today, 24(10), 4–10. Cole, J. C., & Braddock, W. A. (2009). Geologic Map of the Estes Park 30ʹ X 60ʹ Quadrangle, North-central Colorado. US Geological Survey. Eaton, G. P. (2008). Epeirogeny in the Southern Rocky Mountains region: Evidence and origin. Geosphere, 4(5), 764–784. Eggler, D. H., Larson, E. E., & Bradley, W. C. (1969). Granites, grusses, and the Sherman erosion surface, southern Laramie Range, Colorado-Wyoming. American Journal of Science, 267(4), 510–522. Karlstrom, K. E., Coblentz, D., Dueker, K., Ouimet, W., Kirby, E., Van Wijk, J., … Crossey, L. J. (2012). Mantle-driven dynamic uplift of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified hypothesis. Lithosphere, 4(1), 3–22. McMillan, M. E., Heller, P. L., & Wing, S. L. (2006). History and causes of post-Laramide relief in the Rocky Mountain orogenic plateau. Geological Society of America Bulletin, 118(3- 4), 393–405. Riihimaki, C. A., Anderson, R. S., & Safran, E. B. (2007). Impact of rock uplift on rates of late Cenozoic Rocky Mountain river incision. Journal of Geophysical Research: Earth Surface (2003–2012), 112(F3). Roy, M., Jordan, T. H., & Pederson, J. (2009). Colorado Plateau magmatism and uplift by warming of heterogeneous lithosphere. Nature, 459(7249), 978–982. Retrieved from http://dx.doi.org/10.1038/nature08052 Sjostrom, D. J., Hren, M. T., Horton, T. W., Waldbauer, J. R., & Chamberlain, C. P. (2006). Stable isotopic evidence for a pre–late Miocene elevation gradient in the Great Plains– Rocky Mountain region, USA. Geological Society of America Special Papers, 398, 309– 319. Small, E. E., & Anderson, R. S. (1998). Pleistocene relief production in Laramide mountain ranges, western United States. Geology, 26(2), 123–126.

71

The US Cordillera Excursion 2015

9 Glaciation in the Sierra Nevada, CA: Chronology and Climate Susceptibility of an Alpine Ice Field

Filip Johansson University of Gothenburg

Introduction The Sierra Nevada (CA, USA) mountain range (40-36°N) hosts a landscape sculpted by alpine glacial presence, where waxing and waning of an alpine ice field during the Pleistocene has significantly lowered ridge crest elevation and created relief in the headwalls by glacial erosion (Brocklehurst et al. 2008). The mountain range also hosts multiple U-shaped valleys, such as the renowned Yosemite Valley with its notorious vertical walls of polished granite. Valley morphology of the Sierra Nevada tells a tale of multiple glacial pulses throughout the Pleistocene, however glacial fingerprints such as moraines and trimlines only date back to MIS 6 (Rood et al. 2011), and are generally skewed in abundance and prominence towards the present. This limits spatial reconstructions of the Sierra Nevada ice field to MIS 6, a time span comprising 3 major glacial cycles following the northern hemispheric glaciations with some temporal lag (Rood et al. 2011). High resolution glacial chronologies and spatial reconstructions is crucial to accurately model glacial response to future climate forcing. Currently glaciers and ice caps are the dominant contributor to eustatic sea level rise for the 21th century, amounting to 60% of global ice loss (Meier et al. 2007, Radic & Hock 2010). Alpine glaciers’ mass balance is especially sensitive to climate fluctuations, even on short time scales, which makes the alpine glaciated landscape an excellent archive for regional paleoclimate reconstructions. Improved chronologies are needed to successfully compare impacts of climate variability on global scales, identify regional climate patterns, and so explicate a holistic account of Pleistocene climate forcings and associated regional responses.

Regional setting The Sierra Nevada is today located in a temperate climate zone, but significant climate gradients within the range exists due to its 700 km N-S alignment and orographic effects by its altitude (> 4000 m a.s.l.). Annual precipitation ranges between 100 cm/yr at the western side to about 15 cm/yr at the eastern (Owen’s valley). Precipitation in general is dominated by winter storms delivered by the Pacific jet stream. In recent years California has experienced one of the most severe droughts in anthropologic history, which in part from presenting an agricultural crisis also affect the mass balance of the remaining glaciers in Sierra Nevada negatively (Basagic & Fountain, 2011). 72

The US Cordillera Excursion 2015

Pleistocene glaciations Climate reconstructions for the glaciated Sierra Nevada are model based, where glacier growth variables are modeled to fit to glacial chronological and geomorphological constraints, pinpointing the necessity of high resolution spatial and chronological glacial reconstructions. Simulations yield that annual precipitation must have been around 200 cm/yr (about twice the modern) and mean annual temperature was lowered about 5.6°C. This would result in a lowering of the Equilibrium Line Altitude (ELA) by about 700 meters. This is believed to have been caused by a southward deflection of the Pacific jet stream by the Laurentide ice sheet anticyclone. This would intensify the winter storm tracks which brings the precipitation, and the lowering of mean annual temperature shortened the ablation season as well. From atmospheric modeling it suggested that the Sierra Nevada ice field’s mass balance was more sensitive to precipitation than the alpine ice fields and caps further east (e.g. Rocky Mountains) since it was located more distally from the Laurentide ice sheet anticyclone, where the westerlies dominate the atmospheric circulation (Hostetler & Clark, 1997).

Figure 9-1 . Last Glacial Maximum (LGM) extent of glaciers in Sierra Nevada from cosmogenic nuclide data (10Be) (left image). As seen the east side has a more extensive proxy record than the western slopes of the range. This ice cap has waxed and waned throughout the Pleistocene, shaping the valleys into characteristic U-valleys and actively lowered crest ridge elevation. The prominent glacial landscape shows occupancy of warm based, actively eroding glaciers. The right map shows present day glacier extent marked in red. From: Rood et al. 2011 (left) and Basagic & Fountain 2011 (right).

The oldest known evidence of glaciation in the Sierras dates back to 2.7 Ma, comprised by a till unit overlain by a latite (yielding a minimum age). However, little else evidence that can yield chronological constraints on glacial variability remains prior to the MIS 6. The main archives producing reliable glacial chronologies of the Sierra Nevada are

73

The US Cordillera Excursion 2015 down-glacier lake sediment cores, and dating of landforms such as terminal moraines by cosmogenic nuclides and radiocarbon ages. 10Be surface exposure ages on terminal moraines dates the Last Glacial Maximum (LGM), known as the Tioga glaciation in the Sierra Nevada to 18.8±1.9 ka. Little is known of the glacial dynamics prior to and in between the (penultimate) MIS 6 (~145 ka) and (LGM) MIS 2 (~25 ka) stadials since these dominate the geomorphological fingerprints preserved throughout the Pleistocene, and CND cluster only around these stadials (Figure 9-2) (Rood et al. 2011). The lacustrine record is more continuous (Figure 9-2). A possible MIS 4 stadial is represented by an increased supply of rock flour (Na2O) and decrease in authigenic carbonate between 65-85 ka in Owens Lake, signaling glacial erosion up-valley (Bischoff et al. 1997, re-calibrated by Litwin et al. 1999). Based on the lacustrine proxy records, the entire MIS 5 saw little glacial activity (Bischoff et al. 1997), but the latter part of the last 100 kyr glacial cycle experienced waxing and waning of glaciers in the Sierra Nevada. Organic carbon and magnetic susceptibility from Owens Lake sediment cores signals 19 glacial pulses with ~1500 year cyclicality, between 52,500 and 23,500 years B.P. These were significantly more severe 52,500-40,000 years B.P. and became less severe prior to the Tioga glaciation (Benton et al. 1996). This points out the necessity of multi-proxy assessments in paleoclimate reconstructions, where the complete story rarely is reflected in a single proxy and archive. Although cosmogenic nuclide exposure ages provide an excellent tool for reconstructing deglaciation ages, the obliterate overlap has to be matched with other archives such as lacustrine sedimentation.

Dansgaard-Oeschger events in the Sierra Nevada Dansgaard-Oeschger (D-O) events (Figure 9-3) were enigmatic millennia-scale climate oscillations that prevailed during the last glacial cycle. These were characterized by an abrupt increase in annual average surface temperature of about 5°C (interstades) on the Greenland ice sheet, followed by a gradual cooling back to minima surface temperatures (stades). From ice cores recovered from the Greenland ice sheet, 24 D-O events can be recognized from the last glacial cycle (Dansgaard et al. 1993). These millennia scale fluctuations are believed to originate from disturbances in the salinity driven deep water formation in the North Atlantic, which deflected the Atlantic Meridional Overturning Circulation (AMOC) north-south generating warmer/colder conditions over Greenland respectively (Broecker et al. 1990). Evidence from the Great Basin lakes show oscillatory fluctuations in the hydrologic cycle, that correlates in time with the Dansgaard-Oeschger events. Stades were characterized by especially cold and dry conditions while interstades were marked by relatively warm and wet conditions. These alternating climatological conditions’ direct influence over the glacial mass balance in the Sierra Nevada have not been established, but it’s clear that the glacier volume paced these millennial scale events (Benton et al. 2003). These climatological fluctuations were probably caused by a deflection of the Pacific jet stream and, as pointed out by Benton et al. (2003) the explanatory model for D-O events must also be able to explain the deflection of the jet stream. The D-O events is also reflected in the intensity of the East Asian monsoon (Wang et al. 2001), which further supports the idea that D-O events were hemispheric in extent.

74

The US Cordillera Excursion 2015

Heinrich events in the Sierra Nevada The terminations of each D-O events culminated in minima temperatures and were at multiple times associated with the release of giant iceberg armadas from the eastern side of the Laurentide ice sheet into the North Atlantic, speculated to result from a surge-like behavior from a size induced collapse of the ice sheet (Clark et al. 1995). These are evident in the deep sea sediment record from high contents of ice rafted debris, interlaying the deep marine deposits (Broecker et al. 1992). By evidence from the Pleistocene mountain ice fields in the Rocky Mountains and the Sierra Nevada, it is apparent that growth and decay of these ice fields paced the frequency of 5-10 ka with multiple Heinrich events (Clark et al. 1995). Phillips et al. (1996) investigated 36Cl exposure ages on moraines combined with the Owens Lake record and found the glacial pulses between about 50 ka and the LGM correlated well with Heinrich events H5, H3, H2 and H1, where each glacial advance slightly preceded the Heinrich event. How North Atlantic climate oscillators so directly propagates to the western US is still somewhat debated, but atmospheric teleconnections offers one of the most probable explanations. This theory links each collapse of the Laurentide Ice Sheet with a displacement of the Pacific Jet stream, which as mentioned before governed the precipitation patterns in the western US during the Pleistocene (Clark et al. 1995). Thus the internal ice sheet oscillations of the Laurentide ice sheet were super-imposed on the orbital forcings, and summer insolation minima combined with growth of the Laurentide ice sheet, and intensification the anticyclone, would promote and amplify glacial growth in the mountainous western US prior to each collapse and iceberg discharge (Clark et al. 1995).

Figure 9-2. Multi-proxy assessment of the last 200 kyr in the Sierra Nevada in relation to GISP2 oxygen record. Lowermost is the 10Be exposure age clusters from erratic boulders on terminal moraines, where two clusters are apparent while no dates cluster throughout MIS 3-5. Rock flour content in the lacustrine record from Owens Lake is more continuous and signals glaciation between about 85-65 ka. MIS 5 experienced sparse glacial volume. The millennial-scale see-saw pattern in the oxygen isotope record of GISP2 reflects the Dansgaard-Oeschger events

75

The US Cordillera Excursion 2015

Holocene glacial fluctuations Alpine glaciers provide an important archive for regional climate variability on shorter time scales due to their fast response time and climate susceptible mass balance, which tends to be closely equilibrated with the locally prevailing climate (Phillips et al. 1996). Climate variability is known to have induced significant growth and decay in glacial volume in the Sierras throughout the Holocene, with average summer temperature and winter precipitation being the main factors driving mass balance of these mid-latitude glaciers (Leonard, 1989). Recess peak was a glacial advance preceding the onset of the Holocene (11,700 yr B.P.), but since it was more similar in dynamics and forcings to the Holocene than the larger Pleistocene glacial pulses it will be discussed here. The Recess Peak was the largest glacial advance since the LGM (Figure 9-3), and glaciers had retreated from this maximum by 14-15 cal. Ka. Thus the Recess Peak glacial advance predates the Younger Dryas (YD) stadial. Absence of any deposits between this advance and the Little ice age strongly suggests that a possible YD advance was limited, if existing, and not as extensive as the Little ice age advance (Clark & Gilliespiere, 1997). By studying lateral moraines from the Recess Peak advance, an ELA ~250 m lower than today has been reconstructed. ELA based modeling of paleoclimates suggests summer temperatures of 1.7-2.8 °C lower and winter precipitation of 22-34 cm s.w.e. higher than modern (Bowerman & Clark, 2011). Although never as extensive as the full scale Pleistocene glaciations, there’s 5 known glacial maxima evident in the lake sediment record from the late-Holocene at 2800, 2200, 1600, 700 and 250-170 cal. years BP. The last one, known as the Matthes represents the Little Ice Age (LIA) glacial advance and was also the most extensive advance since the Recess Peak (Figure 9-2). From the lake sediment record (Figure 9-2d), it is inferred that the Sierra Nevada was glacier free throughout the early Holocene (10,500-3200 cal. yr BP), with a possible smaller re-advance 5400-4800 cal. yr BP (Rood et al. 2011). The regional lowering of the Matthes ELA have been estimated to ~90 m, inferring a temperature 0.2-2°C lower than modern and a winter precipitation increase of 3-26 cm s.w.e. Lateral moraines have been identified as the most reliable ELA proxy available in alpine settings due to the effect of localrography has on snow accumulation and ablation (by hill shading in the cirques) (Bowerman & Clark, 2011). In general the glacier’s ELA coupling to regional climate increases with glacier size, where topographic influence on accumulation and ablation is more significant on smaller cirque glaciers (Graf, 1976). Hence altitudinal based ELA reconstructions such as accumulation-area ratios and toe-head altitude ratios may prove inaccurate for alpine glacial settings. This should also be considered when evaluating ELA based climate reconstructions; single glacier ELA reconstructions may not be fully representative of regional climate patterns, rather one has to consider the large scale ELA altitudes across the region. The role of debris cover on glaciers should also be considered when making snowline and climate reconstructions in alpine areas such as the Sierra Nevada. The insulation factor accompanied by a ~1 m debris cover will decrease the ablation rate by an order of magnitude, making the paleo-ELA non representative of the prevailing climate during the glacier’s existence (Clark et al. 1994). Ice cored moraines from the Matthes advance (LIA) occur in the Sierra Nevada, testifying that thick debris covers existed on some glaciers during the Holocene advances (Clark et al. 1994).

76

The US Cordillera Excursion 2015

Figure 9-3. Up-left: Holocene glacier growth in the John Muir wilderness area in the Sierra Nevada. Geomorphologic evidence in form of trimlines and moraines have been used to reconstruct the extent of the Recess Peak (red lines, 14.1-12.5 ka) and Matthes (blue lines, LIA) glacial advances. Up-right & down-left: ELA reconstructions for the Matthes and Recess advances based on lateral moraines. From ELA lowering climate reconstructions for the region can be made, thus utilizing glaciers as a climate proxy. Downright: sediment core from First lake (visible in upper-right map, marked 30367). Sediment cores are an important glaciological proxy since they are more likely to preserve a continuous record, even of less severe advances. As seen there was little to non glacial influence until the 2.8 ka advance, Sierra Nevada might have been ice free during this period. Data, figures and maps from Bowman & Clark 2011

77

The US Cordillera Excursion 2015

Conclusions The Sierra Nevada has seen the waxing and waning of an alpine ice field at multiple times throughout the Pleistocene, which has left fingerprints in geomorphologic and lacustrine archives. By combining proxies and archives, a more complete story of the Sierra Nevada Pleistocene glacial dynamics can be unrevealed. Glacial reconstructions may be utilized as spatial and temporal constraints to model past climate variability. This is also essential for predicting future glaciers’ susceptibility to a warming climate. For modern times mountain glaciers and ice caps are the dominant contributor to eustatic sea level, and are predicted to remain so for the rest of the century (Meier et al. 2007). Hence there is a crucial need for understanding their response to abrupt external forcing. The glaciation history of the Sierra Nevada also serves as an important archive for how the mid-latitude western US responded to Quaternary climate events, and ultimately how globally extensive and synchronous these events were. The displacement of the Pacfic jet stream has played a crucial role over the mass balance on Sierra Nevada glaciers, amplifying the winter storms that bring precipitation during the accumulation seasons (Rood et al. 2011). The last 100 kyr glacial cycle was extremely dynamic and 19 glacial advances have been identified 52,500-23,500 years B.P. At the end of this period the Sierra Nevada locked in to a full glacial mode, similar to the rest of the northern hemisphere (Benson et al. 1996). Following the last glacial maximum was the Recess Peak re-advance which preceded the Holocene. The Matthes advance coincides with the Little Ice Age and was the most severe re-advance since throughout the entire Holocene (Bowerman & Clark, 2011).

References

Benson, L., Lund, S., Negrini, R., Linsley, B., & Zic, M. (2003). Response of north American Great basin lakes to Dansgaard–Oeschger oscillations. Quaternary Scienqce Reviews, 22(21), 2239-2251. Bischoff, J. L., Menking, K. M., Fitts, J. P., & Fitzpatrick, J. A. (1997). Climatic oscillations 10,000–155,000 yr BP at Owens Lake, California reflected in glacial rock flour abundance and lake salinity in core OL-92. Quaternary Research, 48(3), 313-325. Bowerman, N. D., & Clark, D. H. (2011). Holocene glaciation of the central Sierra Nevada, California. Quaternary Science Reviews, 30(9), 1067-1085. Broecker, W. S. (1994). Massive iceberg discharges as triggers for global climate change. Nature, 372, 421-424. Broecker, W. S., Bond, G., Klas, M., Bonani, G., & Wolfli, W. (1990). A salt oscillator in the glacial Atlantic? 1. The concept. Paleoceanography, 5(4), 469-477. Broecker, W., Bond, G., Klas, M., Clark, E., & McManus, J. (1992). Origin of the northern Atlantic's Heinrich events. Climate Dynamics, 6(3-4), 265-273. Clark, D. H., & Gillespie, A. R. (1997). Timing and significance of late-glacial and Holocene cirque glaciation in the Sierra Nevada, California. Quaternary International, 38, 21-38. Clark, P. U., & Bartlein, P. J. (1995). Correlation of late Pleistocene glaciation in the western United States with North Atlantic Heinrich events. Geology, 23(6), 483-486. Clark, P. U., Dyke, A. S., Shakun, J. D., Carlson, A. E., Clark, J., Wohlfarth, B., ... & McCabe, A. M. (2009). The last glacial maximum. science, 325(5941), 710-714. Dansgaard, W., Johnsen, S. J., Clausen, H. B., Dahl-Jensen, D., Gundestrup, N. S., Hammer, C.

78

The US Cordillera Excursion 2015

U., ... & Bond, G. (1993). Evidence for general instability of past climate from a 250-kyr ice-core record. Nature, 364(6434), 218-220. Hostetler, S. W., & Clark, P. U. (1997). Climatic controls of western US glaciers at the last glacial maximum. Quaternary Science Reviews, 16(6), 505-511. Leonard, E. M. (1989). Climatic change in the Colorado Rocky Mountains: estimates based on modern climate at late Pleistocene equilibrium lines. Arctic and Alpine Research, 245- 255. Litwin, R. J., Smoot, J. P., Durika, N. J., & Smith, G. I. (1999). Calibrating Late Quaternary terrestrial climate signals: radiometrically dated pollen evidence from the southern Sierra Nevada, USA. Quaternary Science Reviews, 18(10), 1151-1171. Meier, M. F., Dyurgerov, M. B., Rick, U. K., O'Neel, S., Pfeffer, W. T., Anderson, R. S., ... & Glazovsky, A. F. (2007). Glaciers dominate eustatic sea-level rise in the 21st century. Science, 317(5841), 1064-1067. Phillips, F. M., Zreda, M. G., Benson, L., Plummer, M. A., Elmore, D., & Sharma, P. (1996). Chronology for fluctuations in late Pleistocene Sierra Nevada glaciers and lakes. Radić, V., & Hock, R. (2011). Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise. Nature Geoscience, 4(2), 91-94. Rood, D. H., Burbank, D. W., & Finkel, R. C. (2011). Chronology of glaciations in the Sierra Nevada, California, from 10 Be surface exposure dating. Quaternary Science Reviews, 30(5), 646-661.

79

The US Cordillera Excursion 2015

10 Sandstone Hosted Uranium Deposits of the Roll-Front Type in the Western Cordillera, USA

Jimmy Jakobsson University of Gothenburg

A roll-front is a sandstone-hosted hydrothermal epigenetic uranium ore deposit of economic importance. Most occur in mid-Paleozoic continental sandstones of lacustrine or fluvial origin. Roll-fronts form by the leaching of uraniferous rocks such as felsic extrusives by meteoric water which in turn infiltrates a permeable would-be host rock where uranium precipitation can occur. Often, such host rocks are essentially confined aquifers and the ore morphology reflects the local hydrological regime. Mobilization and precipitation is controlled by redox-reactions and uranium precipitation occurs at the oxidized-reduced interface within the host rock. Successive recharge of oxidized water will move the front further. Roll-fronts, along with other sandstone hosted uranium deposits are globally widespread, with significant reserves located in the western US.

Occurrence and classification Sandstone-hosted uranium deposits are widespread globally and regions with significant reserves include China, Kazakhstan, Australia, Central Europe and USA. Uranium deposits in the USA (Figure 10-1) are, with a few notable exceptions, concentrated in the Western Cordillera. The most prominent sandstone-hosted uranium ores located in the Colorado Plateau, the Wyoming basins and the Texas Gulf Coastal Plain. Sandstone-hosted uranium deposits are generally classified into three main types; tabular, roll-front and tectonic-lithologic (Dahlkamp, 2010). These share similar characteristics and depositional environments. Roll-front deposits are distinct from the other two in that the ore is epigenetic rather than synsedimentary. The deposition-mechanism for tabular and tectonic- lithologic ores is similar with the main difference being that the fluid percolation of the latter is strongly influenced by the presence of faults (Curey, 2009). The focus of this article will be the roll-front type.

80

The US Cordillera Excursion 2015

Figure 10-1. Uranium deposits of the United States of America (Dahlkamp, 2010).

Host rock Arkosic to sub-arkosic sandstones are the typical host rocks for roll-front deposits, reflecting the tectonic, and by extension erosional and hydrological, setting favorable for the formation of such deposits, but also the physical characteristics (e.g. porosity and permeability) of the sandstones themselves (Harshman & Adams, 1980; Finch & Davis, 1985). Age-wise, most host rocks are younger than the Ordovician and they are typically continental (fluvial or lacustrine) (Cuney, 2009). Most deposits in the US occur in structural basins with adjacent Precambrian terranes (Dahlkamp, 2010) but similar deposits are known in areas (e.g. China) with younger crust (Dahlkamp, 2009). Roll-fronts in near- shore marine sediments, including sandstones interlayered with mud rocks also occur (Cuney, 2009). One such example is the Texas Gulf Coastal Plain (Dahlkamp, 2010). Roll- fronts are epigenetic and typically form long after the ore host rock has been deposited and undergone diagenesis (Cuney, 2009). Essentially, the host rock is in many cases a confined aquifer, over- and underlain by aquitards such as shales (Taylor et al, 2004).

81

The US Cordillera Excursion 2015

Figure 10-2. Schematic diagram illustrating the relationship between uraniferous instrusives and associated depositional basins. (IAEA, 1988).

Source rock and mechanism of transport Sources of uranium include a variety of rocks (two examples in Figure 9-3), usually felsic in chemistry. In the reduced aquifer case the source of uranium is typically much younger (often tertiary in age) superimposed felsic volcanics (Harshman & Adams, 1980). In some cases however, the uranium source may actually be interlayered volcanic ash inside the host rock (Harshman & Adams, 1980; Cuney, 2009). At low temperatures redox-state is the most important factor controlling the mobility of U (Figure 10-3). While oxidized uranium (U6+) is significantly more soluble in reduced state (U4+), uranium itself is insufficiently abundant to influence the general redox state of a solution. The main oxidizing agents are oxygen and sulfate, the latter being derived either from oxidized pyrite or from the atmosphere, whereas the reducing agents are organic carbon and reduced sulfur such as pyrite and sulfide derived from reduction of

82

The US Cordillera Excursion 2015 sulfate in organic matter. As oxidized rain water enters the source rock, uranium is leached and carried into the host rock where the uranium will precipitate once it encounters sufficiently reducing agents (e.g. organic matter), forming the front. Successive rainwater recharge will result in re-mobilization of U and the front will thus move further into the sandstone layer. (Spirakis, 1996). While organic matter plays an important role as a reductant, the conventional view is that the reaction itself is inorganic. However, more recent studies suggest that several species of Fe3+-reducing microorganisms may play an active role by enzymatically reduce U6+ to U4+. As such, thermodynamics alone is insufficient to fully explain uranium reduction (Min et al., 2005; Suzuki & Suko, 2006). The major carrier of uranium is thought to be uranyl (UO2+) carbonate complexes (Spirakis, 1996; Cuney, 2009). Apart from carbonates, the highly mobile uranyl ion can bond with hydroxyl, sulfate, chloride, phosphate, fluoride and silicate anions, being able to form more than 40 known complexes (Cuney, 2009). Leaching, transport and deposition of uranium in roll-front deposits have little effect on REE-abundances. REE- patterns instead mimic that of the host rock, making it possible to deduce the origin of a deposit (Mercadier et al., 2011).

Figure 10-3. Pourbaix-diagram for the uranium system in water at 25 ‘C. The redox-potential (eH) is the most important factor in influencing the solubility of U. Also evident is the effect of pH on which complexes form. (from Lisboa et al., 2013)

83

The US Cordillera Excursion 2015

Morphology The front is typically sinuous-shaped (Figure 10-4) along the front’s interface and exhibit a crescent shape in cross section. Size-wise, a roll-front may extent laterally for hundreds of meters (Cuney, 2009). The shape and its direction reflect the hydrological regime of the host rock, which in turn is controlled by the environment of deposition. As such, unconformities and sedimentary features like channel fills may complicate the morphology of the deposit (Harshman & Adams, 1980). In terms of alteration, a red oxidized hematite-rich tail is typically found behind the front, resulting in a sharp contrast between the oxidized and unaltered parts of the host rock (Harshman & Adams, 1980; Finch & Davis, 1985; Spirakis, 1996). The oxidized tail can sometimes be traced up-dip all the way to the uraniferous source rock located several kilometers away (Hostetler & Garrels, 1962). Sometimes, a bleached, greenish to yellowish, area is found between the iron-rich tail and the front itself. The cause for this is the presence of limonite or goethite-stained sands (Harshman & Adams, 1980). Primary minerals are few with the most common uranium bearing ones being uraninite, UO2+x, and coffinite, UO2(SiO4)1-x(OH)4x (Hostetler & Garrels, 1962; Spirakis, 1996). Non-uranium bearing phases typically include montroseite, vanadium silicates, pyrite, chalcopyrite, bornite, chalcocite, calcite, quartz and gypsum (Hostetler & Garrels, 1962).

Figure 10-4. Schematic illustration of a roll-front deposit in a confined aquifer seen in cross-section with I) and II) representing early and later development of the oxidized tongue (Dahlkamp, 2010).

Mining While uranium mining is documented as far back as 1872, large scale exploration and production took off in 1943 when the development of nuclear weapons drastically increased demand. Until the 1980s when uranium prices fell, the USA was one of the leading countries in uranium production. Uranium mining in the US has historically been characterized by many, but small operations (Dahlkamp, 2010).

84

The US Cordillera Excursion 2015

One of the most commonly used methods for extracting sandstone-hosted uranium ores is in situ leach (ISL) a.k.a. solution mining. This method has been used extensively in the US and in Eastern Europe since the 1960s (Mudd, 2001; Taylor et al., 2004). ISL takes advantage of the permeable nature of the host rock and involves dissolving the ore in situ and then extracting it by pumping. As such, it involves little to no conventional mining of surrounding or overlying host rock. Reagents, which can be acidic or alkaline, are introduced to the ore body through holes drilled from the surface (injection wells). The solution is then either extracted through another borehole (recovery well) (Taylor et al., 2004) or allowed to drain along zones of weaknesses such as bedding planes or fissure zones into a suitable basin (Gardner & Malcolm, 1967; Mudd, 2001). The reagent used is recycled during processing for further extraction use (Taylor et al., 2004). Historically, two types of reagents have been used; acidic and alkaline. Apart from environmental concerns and local legislation, ore zone chemistry is the single most important factor in choosing solvent. Acidic solvents are generally more efficient unless the orebody is carbonate rich in which case alkaline solvents are more suitable. An acidic solvent is more efficient in extracting uranium but requires more expensive corrosion resistant equipment and poses a greater challenge in terms of groundwater restoration (Taylor et al., 2004). Acid ISL has never been approved on a commercial scale in the USA because groundwater restoration has effectively proved to be impossible (Mudd, 2001). In comparison, acid ISL was used extensively in the eastern bloc with little regard to environmental consequences causing problems persisting to this day (e.g. Konigstein, Germany and Straz, Czech Republic) (Taylor et al., 2004). Alkaline reagents include ones based on sodium-carbonate, carbon-dioxide and ammonia. The latter was phased out during the early 1980s due to the difficulty in restoring ammonia-based sites (Mudd, 2001). As of 2014, there are two conventional and eight ISL-operations in the USA (US Department of Energy, U.S Energy Information Administration, 2015) and the share of mining operations that utilize the ISL-method is predicted to increase in the future (Dahlkamp, 2010).

References

Cuney, M. (2009). The extreme diversity of uranium deposits. Mineralium Deposita, 44(1), 3- 9 Dahlkamp, F. J. (2009). Uranium deposits of the world: Asia. Springer Science & Business Media. Dahlkamp, F. J. (2010). Uranium deposits of the world (Vol. 2). Springer Science & Business Media. Gardner, J., & Malcolm, R. (1967). U.S. Patent No. 3,309,140. Washington, DC: U.S. Patent and Trademark Office. Harshman, E. N., & Adams, S. S. (1980). Geology and recognition criteria for roll-type uranium deposits in continental sandstones: US Department of Energy. GJBX-I (81). Hostetler, P.B. & Garrels, R.M. (1962) Transportation and precipitation of uranium and vanadium at low temperatures, with special reference to sandstone-type uranium deposits. Economic Geology, 57(2), 137-167. International atomic energy agency (1988) Report of an Advisory Group Meeting held in Vienna, 13-16 December 1988. IAEA-TECDOC-583. Retrieved from: http://www- pub.iaea.org/MTCD/publications/PDF/te_0583.pdf

85

The US Cordillera Excursion 2015

International Atomic Energy Agency. Working Group on Uranium Geology, Finch, W. I., & Davis, J. F. (1985). Geological Environments of Sandstone-type Uranium Deposits: Report of the Working Group on Uranium Geology Organized by the International Atomic Energy Agency. The Agency. Lisboa, J., Cifuentes, G., Marin, J., & Mieres, E. (2013). Use of electrodeposition of nickel in the manufacture of LEU annular targets. Journal of the Chilean Chemical Society, 58(4), 2102-2105. Mercadier, J., Cuney, M., Lach, P., Boiron, M. C., Bonhoure, J., Richard, A., ... & Kister, P. (2011). Origin of uranium deposits revealed by their rare earth element signature. Terra Nova, 23(4), 264-269. Min, M., Xu, H., Chen, J., & Fayek, M. (2005). Evidence of uranium biomineralization in sandstone-hosted roll-front uranium deposits, northwestern China. Ore Geology Reviews, 26(3), 198-206 Mudd, G. M. (2001). Critical review of acid in situ leach uranium mining: 1. USA and Australia. Environmental Geology, 41(3-4), 390-403. Spirakis, C.S. (1995) The roles of organic matter in the formation of uranium in sedimentary rocks. Ore geology review, 11, 53-69. Suzuki, Y., & Suko, T. (2006). Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium- contaminated sites. Journal of Mineralogical and Petrological Sciences, 101(6), 299-307. Taylor, G., Farrington, V., Woods, P., Ring, R., & Molloy, R. (2004). Review of environmental impacts of the acid in-situ leach uranium mining process. In CSIRO Land and Water Client Report (p. 60). CSIRO Clayton, Victoria. US Department of Energy, U.S Energy Information Administration (2015). 2014 Domestric Uranium Production Report. Retrieved from: https://www.eia.gov/uranium/production/annual/pdf/dupr.pdf

86

The US Cordillera Excursion 2015

11 Basins of the Green River Formation

Erik Alsteryd University of Gothenburg

Introduction The Green River Formation is an oil and gas bearing formation located in four sedimentary basins around the Uinta Mountains in the United States. The Green River Formation was formed during early Eocene, ~52Ma. It consists mainly of lacustrine sedimentary rocks deposited in intermontane basins created adjacent to the uplift of the Uinta Mountains (Smith & Carrol, 2015). There are four main basins that contain the Green River Formation; the Green River Basin, the Washakie Basin, the Uinta Basin and the Piceance Basin. These four basins are located around the Uinta Mountain which spans next to the state border between Wyoming, Colorado and Utah (Figure 11-1). As seen in Figure 11-1, the Green River Basin and the Washakie basin are situated in southwestern Wyoming, the Uinta Basin in northeastern Utah and the Piceance Basin in northwestern Colorado.

Figure 11-1. Location of the four main basins containing the Green River Formation (GRF), Map created with ArcGIS, data for GRF collected from USGS energy and basemap from Esri ArcGIS.

The size of the Green River Formation basins varies in size, depth and slightly in composition, however they are generally interpreted to have similar depositional

87

The US Cordillera Excursion 2015 environments because of how they were created and later filled with sediment. The basins were created during the uplift of the Uinta Mountains, which led to a series of adjacent depressions that were later filled with water and after that successively filled with sediment over a few million years (12 million for the Uinta Basin). The Green River Basin and the Uinta Basin are the largest and the Washakie Basin and the Piceance Basin is smaller, however, not insignificant in size and oil resources (Johnson, Mercier, Brownfield, & Self, 2010).

Stratigraphy In general the Green River Formation have finer sediment in the lower parts and coarser in the upper parts. The lower parts of the Green River Formation are dominated by clay, silt and shale. With more sediment being filled in the water regressed and this created a successively more turbulent depositional environment leading to more sand being deposited in the upper parts of the Green River Formation. Figure 11-2 shows the stratigraphy of the four basins containing the Green River Formation. The Green River Basin and the Washakie Basin is sometimes referred as the Greater Green River Basin.

Figure 11-2. Stratigraphy of the formations in the Uinta Basin, the Piceance Basin and the Greater Green River Basin (the Green River Basin and the Washakie Basin), modified from two figures (Smith & Carrol, 2015)

Uinta Basin The Uinta Basin has yielded and is still yielding the most oil, over 500 million barrels has been extracted from the lower and middle part of the Green River Formation (Burton, Woolf, & Sullivan, 2014). The Green River Formation was deposited in early Eocene in Lake Uinta that was formed by the depression that was created when the Uinta Mountains uplifted. The lake was later filled with sediment for 12 million years, 52ma- 40ma. According to Burton et al. there are five main depositional environments for the lower and middle part of the Green River Formation; Deep Lacustrine, Shallow Lacustrine, Lacustrine delta, Lacustrine Coastal Plain and Alluvial Plain (Burton, Woolf, & Sullivan, 2014). The sediment deposited in these environments varies with the different processes that occur when the water level changes. As seen below in Figure 11-3, the finer

88

The US Cordillera Excursion 2015 fraction is dominated in the early depositional environments leading to a higher sandstone fraction when the water depth is lower in Lacustrine Delta and forward (Burton, Woolf, & Sullivan, 2014).

Figure 11-3 Rough overview of the facies percentage of the five depositional environments in Uinta Basin (Burton, Woolf, & Sullivan, 2014).

The first of the depositional environments is Deep Lacustrine which resulted in the formation of laminated black shales and laminated micrites (lime mud). There are also indications of very little turbulence and that there was an oxygen free bottom environment which leads to good preservation of the organic content. Up to 15% total organic carbon can be found in the black shale (Burton, Woolf, & Sullivan, 2014). Shallow Lacustrine is the following depositional environment. This environment formed laminated calcareous mudstone, laminated carbonate mudstones and sparsely frequent sandstones. The shallower water depth results in slightly coarser sediment and more oxygenated bottom environment. (Burton, Woolf, & Sullivan, 2014). Lacustrine Delta is the third depositional environment Burton et al. brings up. This environment has an even shallower water depth which gives coarser sediment. It formed mudstones, siltstones and sandstones, with sequences of coarsening upward structures, mudstone towards sandstone. This coarsening upward sequence is interpreted to be a prograding delta (Burton, Woolf, & Sullivan, 2014). Lacustrine Coastal Plain usually follows the Lacustrine Delta and Shallow Lacustrine environments. It mainly formed thick mud- and siltstones with traces of roots and plants. The finer grained sediments, mud and siltstone, are usually overlain by fine grained sandstone. Structures in the sandstone are either cross-beds or ripples which is a strong indication of a coastal environment (Burton, Woolf, & Sullivan, 2014).

89

The US Cordillera Excursion 2015

The last depositional environment characterizing the Uinta Basin is Alluvial Plain. It formed red mudstones which are sequentially cut off by thinner sandstones. It’s the sequence of the mudstones and thin sandstone strings that is interpreted to be an alluvial plain environment. There are four main members of the Green River Formation in the Uinta Basin; the Parachute Creek member, the Douglas Creek member, the Garden Gulch member and the Evacuation Creek member. However, they are quite debated and questioned if they are correctly interpreted, especially the Evacuation Creek member (Johnson, Mercier, Brownfield, & Self, 2010).

Green River Basin The Green River Basin is the largest of the four basins. The lake in which the Green River Formation was deposited in is called Lake Gosiute and was formed the same way as Lake Uinta (Self, Ryder, Johnson, Brownfield, & Mercier, 2011). There are four main members that subdivide the Green River Formation in the Green River Basin (Figure 11-4), the oldest one is the Tipton Shale Member, overlain by the Wilkins Peak Member, followed by the LaClede Bed of Laney Member and the youngest one is the Hartt Cabin Bed of Laney Member. The Tipton Shale Member as the name suggest is mainly built up by shale. The Wilkins Peak Member which is the thickest of the four and it’s dominated by shale with interbedded sand- and mudstones. Above this, the LaClede Bed of Laney Member is found and it’s the thinnest of the four members in Green River Basin and is mainly built up by shale with interbedded siltstones (Self, Ryder, Johnson, Brownfield, & Mercier, 2011).

Washakie Basin The Washakie Basin is smaller in lateral and vertical extent than the other basins. It is divided into the same members as the Green River Formation in the Green River Basin. However, the LaClede Bed of Laney Member is a lot thicker in this basin than that of the Green River Basin (figure 4). Also, another difference between the two basins is that the LaClede Bed of Laney Member and the Wilkins Peak Member is truncated by another formation, namely the Wasatch Formation (Self, Ryder, Johnson, Brownfield, & Mercier, 2011).

Piceance Basin The Piceance Basin is situated east of the Uinta Basin. However, the Piceance Basin is sometimes included into the Uinta Basin since they were formed in the same lake (Figure 11-2). The Green River Formation in the Piceance Basin is slightly thinner than the Green River Formation in the Uinta Basin (Self, Johnson, Brownfield, & Mercier, 2010).

90

The US Cordillera Excursion 2015

Figure 11-4. Cross section of the Green River Formation in the Green River Basin and the Washakie Basin (USGS, 2011)

Oil and Gas The Green River Formation is rich in oil and gas. The source rock in the Green River Formation is mainly the black shale formed by the deep lacustrine depositional environment. The organic content percentage and the preserving conditions in this environment were ideal for the creation of oil and gas. For most parts of the Green River Formation, the oil either stayed in the source rock or migrated towards the edges of the basins where there is more sandstone, which is the primary reservoir rock in the Green River Formation (Burton, Woolf, & Sullivan, 2014). The oil traps over the reservoir rocks are mainly

91

The US Cordillera Excursion 2015 stratigraphic traps like impermeable mudstones and fine-grained carbonates (Burton, Woolf, & Sullivan, 2014). The Greater Green River Basin, including the Washakie Basin, is the largest of the Green River Formation basins. However, it does not contain the most oil since the grade is quite low. The Piceance basin is considered to be the richest oil shale deposit in the world but then it is four times smaller than Greater Green River Basin and three times smaller than the Uinta Basin. The Piceance is estimated to contain about 1.53 trillion barrels of oil in the shale compared to the Uinta Basin which is estimated to contain 1.32 trillion barrels and the Greater Green River Basin which contain 1.44 trillion barrels. The three oil bearing members in the Greater Green River Basin are; the Tipton Shale Member, the Wilkins Peak Member and the LaClede Bed of Laney Member (Johnson, Mercier, Brownfield, & Self, 2010).

Mineral resources The climate at these basins during Eocene was subtropical and warm temperate with highly saline waters are optimum conditions for the formation of sodium carbonates. Mineral resources in the Green River Formation mainly consist out of two sodium carbonates. Trona (Na2CO3*NaHCO3*2H2O) in the Green River Basin and nacholite (NaHCO3) in the Piceance Basin. The Green River Basin and the Piceance Basin is some of the largest known deposits of these two minerals. The other two basins, the Washakie Basin and the Uinta Basin, contain less sodium carbonate minerals and are today not economically recoverable (Brownfield, Johnson, & Dyni, 2010).

Summary The Green River Formation is rich in shale oil and natural gas in the four basins. Usually the reservoir rock is the outlying sandstones with stratigraphic traps. The source of the oil and gas is the black shale that was formed early during the formation of the Green River Formation when the water level was high and anoxic conditions prevailed. In total the Green River Formation contains about 4.3 trillion barrels of oil with varying grade over the four basins. How much oil is recoverable out of these 4.3 trillion barrels is yet to be determined.

References

Brownfield, M., Johnson, R., & Dyni, J. (2010). Sodium Carbonate Resources of the Eocene Green River Formation, Uinta Basin, Utah and Colorado. Virginia: U.S. Geological Survey. Burton, D., Woolf, K., & Sullivan, B. (2014). Lacustrine depositional environments in the Green River Formation, Uinta Basin: Expression in outcrop and wireline logs. AAPG Bulletin. Johnson, R., Mercier, T., Brownfield, M. E., & Self, J. (2010). Assessment of In-Place Oil Shale Resources in the Eocene Green River Formation, Uinta Basin, Utah and Colorado. Virginia: U.S Geological Survey. Self, J., Johnson, R., Brownfield, M., & Mercier, T. (2010). Stratigraphic Cross Sections of the Eocene Green River Formation in the Piceance Basin, Northwestern Colorado. Virginia: U.S. Geolocial Survey. Self, J., Ryder, R., Johnson, R., Brownfield, M., & Mercier, T. (2011). Stratigraphic Cross Sections of the Eocene Green River Formation in the Green River Basin, Southwestern 92

The US Cordillera Excursion 2015

Wyoming, Northwestern Colorado, and Northeastern Utah. Virginia: U.S. Geological Survey. Smith, M. E., & Carrol, A. R. (2015). Introduction to the Green River Formation. In M. E. Smith, & A. R. Carrol, Stratigraphy and Paleolimnology of the Green River Formation, Western USA, Syntheses in Limnology. Springer. Smith, M. E., & Carrol, A. R. (2015). Stratigraphy and Paleolimnology of the Green River Formation, Western USA. Springer. US Department of Energy, U.S Energy Information Administration (2015). 2014 Domestric Uranium Production Report. Retrieved from: https://www.eia.gov/uranium/production/annual/pdf/dupr.pdf

93

The US Cordillera Excursion 2015

12 Sedimentological and Tectonic Relations of Neoproterozoic Rift Basins: Uinta Mountain Group, Big Cottonwood Formation, Chuar Group and Pahrump Group

Lorenz Lindroth University of Gothenburg

Introduction The Uinta Mountain Group (UMG) and Big Cottonwood Formation (BCF), located in northeastern and northern Utah respectively, the Chuar Group (CG) in the Grand Canyon of Arizona, and the Pahrump Group (PG) in Death Valley, California, are approximately coeval and were deposited in intracratonic rift basins during the Neoproterozoic ( 1000̴ -543 Ma) (figure 12-1). They were deposited in or near epicontinental seas in southwestern Laurentia (the Western Laurentian Seaway), which were created as a result of the breakup of the supercontinent Rodinia ( 700̴ Ma ago). The lithologies of these groups are varied; shale, sandstone, conglomerate, diamictite and dolomite formed in different sedimentological settings within the rift basins. Provenance studies that have been made indicate different sources for the infilling material. The four groups have been correlated by means of micro- and macrofossils, provenance similarities, C-isotopes and facies interpretations.

Uinta Mountain Group The Uinta Mountain Group is an east-west trending mountain range situated in northeastern Utah (Figure 12-2). It is composed of a massive red siliciclastic succession of chiefly marine and fluviomarine strata, up to 7 km thick, about 4 km on average (Condie et al., 2001; Kingsbury-Stewart et al., 2013). Furthermore, the UMG basin lies on a suture zone which separates the Archean Wyoming craton in the north and the accreted Paleoproterozoic arc terranes in the south (Condie et al., 2001). The western lobe of the Uinta Mountains thickens northward and its southern boundary is somewhat unclear. This (along with other indices) suggests asymmetric subsidence of the UMG basin due to normal faulting along its northern margin (Ball & Lang Farmer, 1998). Hence, deposition occurred in a half-graben with an active northern margin (Kingsbury-Stewart et al., 2013).

94

The US Cordillera Excursion 2015

Figure 12-1. Late Proterozoic (650-600 Ma) paleotectonic map of western North America. 1. UMG. 2. BCF. 3. CG. 4. PG. Retrieved and modified from http://cpgeosystems.com/images/WNA_600-650_Late_Proter_Tect-sm.jpg (November 2015).

Figure 12-2. Regional geologic map of the Uinta mountains. From Kingsbury-Stewart et al., 2013.

95

The US Cordillera Excursion 2015

As is shown in Figure 12-3, the stratigraphies in the west and east are different. Only the Hades Pass Formation is present in both columns. The Red Pine Shale is possibly also found in the east, however, it is much thinner there. The Red Pine Shale (western Uinta) is 1̴ km thick and thought to be 740̴ Ma. This shale is fossiliferous and organic- rich and was deposited in a restricted environment in a marine deltaic setting. The underlying formations are mainly composed of orthoquartzite and sandstone and were deposited in a fluviomarine setting (Dehler et al., 2005). The eastern UMG comprises arkosic sandstones, interbedded shales and quartzites. The lowermost formations also contain conglomerate and breccia. The interpreted depositional setting for these sediments is braided fluvial systems flowing to the southwest (Ibid). Nd-isotope provenance studies reveal two different signatures for the origin of UMG basin infilling material. One from the Archean Wyoming Province in the north and another Proterozoic from the Colorado Province in the east (Ball & Lang Farmer, 1998). This concurs with the paleotectonic reconstruction map included in Kingsbury-Stewart et al. (2013), showing the south-flowing Red Castle River draining the Neoarchean Province in the north and the west-flowing Laurentian River draining the Proterozoic Yavapai and Mazatzal provinces and the Grenville orogenic belt in the east.

Figure 12-3. Generalized stratigraphic columns from eastern and western Uinta Mountains. From Kingsbury-Stewart et al., 2013.

96

The US Cordillera Excursion 2015

Studies that were made in the middle UMG revealed several composite depositional sequences which show long-term eustatic transgressions at 770-740 Ma. These transgressions were driven by the breakup of supercontinent Rodinia that started around 780 Ma. Laurentia, in turn, started rifting in a “zipper-like” manner at 750̴ Ma. Paleomagnetic studies indicate near-equatorial paleolatitudes for southwestern Laurentia during the mid-Neoproterozoic (Kingsbury-Stewart et al., 2013).

Big Cottonwood Formation The Big Cottonwood Formation is part of the Wasatch Mountain Range in northern Utah, located between Salt Lake City in the west and the Uinta Mountains in the east. The BCF was deposited in the same intracratonic basin as the UMG, but further west. It consists of almost 5 km of interbedded quartz arenite, siltite and shale which were deposited in a shallow marine environment (Condie et al., 2001). Moreover, five different lithofacies have been distinguished; two quartz arenites containing e.g. dune cross-bedding, showing flow to the west, and three argillites containing tidal structures such as heterolithic rhythmites, clay-draped reactivation surfaces and flaser bedding. These structures have led to the interpretation that the BCF was deposited in a tide-dominated estuary (Ehlers & Chan, 1999). As can be seen in ure 12-4, the UMG, BCF, CG and PG can be broadly correlated. The Chuar Group and Uinta Mountain Group have been correlated based upon C-isotope and fossil data sets but also provenance data, the Big Cottonwood Formation by sandstone composition similarities and the Pahrump Group by C-isotope and fossil data sets (Dehler et al., 2005).

Figure 12-4. Regional correlation between the Uinta Mountain Group, Big Cottonwood Formation, Chuar Group and Pahrump Group. Modified from Dehler et al., 2005.

97

The US Cordillera Excursion 2015

Chuar Group The Chuar Group, part of the Grand Canyon Supergroup Rocks (no. 13, Figure 12-5), is a 1600 m thick succession exposed only in the eastern parts of the Grand Canyon, Arizona. It is bounded by the Butte fault zone in the east and mainly by the Great Unconformity and Cambrian Tapeats Sandstone in the remaining directions (Dehler et al., 2001). Composed of two formations (Galeros Fm. and Kwagunt Fm.) which hold seven members, the CG sits on top of the Nankoweap Fm. and is overlain by the Sixtymile Fm. The top of the CG has been dated to 742̴ Ma by U-Pb zircon dating from an ash bed. The age at the bottom of the CG has been set to 1070̴ Ma by whole-rock dating of the Cardenas Basalt, which cuts through the underlying Unkar Group (Ibid).

Figure 12-5. Stratigraphy of the Grand Canyon. Retrieved from https://www.grandcanyon.org/sites/default/files/public/document_learn_facts_geology_crosssection1.pdf (November 2015).

However, results from paleomagnetic correlations and biostratigraphic studies (stromatolites and microfossils) indicate that the CG was deposited between 850̴ -740 Ma in the mid-Neoproterozoic at paleolatitudes 5-20° north of the equator (Ibid). The Chuar Group is primarily composed of mudrock with secondary meter- scale beds of sandstone and dolomite. The interpreted depositional environment is a marine setting, influenced by tides and waves. Marine, because of marine fossils and high pyrite content, and tidal, because of characteristic tidal structures such as herringbone cross-beds and mudcracked and mud-draped symmetric ripples. Approximately 320 different meter- scale cycles with basal mudrock (20-150 m thick), capped with either sandstone or dolomite (1-20 m thick) are present within all seven members of the group. The mudrock facies were 98

The US Cordillera Excursion 2015 deposited at subtidal water depths whereas the sandstone and dolomite facies were deposited at shallow water depths (Ibid). The cycles of the lower to middle CG are thought to represent low-amplitude sea-level changes during global greenhouse climates. In contrast, the middle to upper CG cycles contain thicker non-cyclic intervals and fewer peritidal cycles, and are therefore thought to reflect moderate-amplitude sea-level changes during greenhouse-icehouse transition climates. This change indicates a growth of the continental ice volume and hence a global climate change ultimately leading to the Sturtian Ice Age (Snowball Earth) (Ibid).

Pahrump Group The Pahrump Group is situated in the Death Valley region of eastern California, where it crops out in several of the ranges (e.g. Panamint Range and Black Mountains). With an average thickness of 3̴ km, it contains sediments from both the Meso- and Neoproterozoic ( 1300̴ -650 Ma). It also contains an unconformity representing a 300̴ Ma hiatus between 1080-787 Ma. The PG is composed of four formations, unconformably underlain by metamorphic crystalline basement and overlain by the Noonday Dolomite (Figure 12-6) (Mahon et al., 2014). The lowermost Crystal Spring Formation is divided into a lower and middle member. The lower member includes a basal conglomerate fining upwards into arkose, followed by mudstone and dolomitic limestone. The top of the member is a diabase sill. The depositional setting has been interpreted as alluvial fans, followed by fluvial and marine. The middle member is dominated by algal and dolomitic limestone, representing a carbonate shelf, minor siliciclastic material and a diabase sill. The Horse Thief Springs Formation is composed of six units of marine siliciclastic material covered with dolostone. These units range from 10s to 100s of meters in thickness and are interpreted as shoreline to offshore shoreface deposits covered by transgressive carbonate facies. The overlying Beck Spring Dolomite is chiefly dominated by carbonate but also includes siliciclastic components. Containing stromatolitic and microbial laminations, giant oolites and oncolitic beds, the depositional environment is interpreted as a shallow platform. Syn-depositional normal faults and seismically induced soft-sediment deformation structures are present in both the Horse Thief Springs Formation and Beck Spring Dolomite and suggest extensional tectonism and seismicity during deposition. The almost 1800 m thick heterolithic Kingston Peak Formation comprises four members (KP 1-4) which are divided by internal unconformities. The KP1 member is probably related to the underlying formation as it contains calcareous siltstone and fine sand. KP 2-4 are composed of sandstone, siltstone and cobble-boulder diamictite. The diamictite has been interpreted to be of glacial or glaciomarine origin due to dropstones, striated clasts and ice-rafted debris. Furthermore, these members presumably represent the 710̴ -635 Ma, Sturtian and Marinoan Snowball Earth intervals (Ibid).

99

The US Cordillera Excursion 2015

Figure 12-6. Generalized stratigraphy of the Mesoproterozoic to Lower Camrian sedimentary sequence in the Death Valley region. From Mahon et al., 2014.

References

Ball, T. T., Lang Farmer, G. 1998. Infilling history of a Neoproterozoic intracratonic basin: Nd isotope provenance studies of the Uinta Mountain Group, Western United States. Precambrian Research 87 (1998) pp. 1-18. Condie, K. C., Lee, D., Lang Farmer, G. 2001. Tectonic setting and provenance of the Neoproterozoic Uinta Mountain and Big Cottonwood groups, northern Utah: constraints from geochemistry, Nd isotopes, and detrital modes. Sedimentary Geology 141-142 (2001) pp. 443-464. Dehler, C. M., Elrick, M., Karlstrom, K. E., Smith, G. A., Crossey, L. J., Timmons, J. M. 2001. Neoproterozoic Chuar Group ( ̴ 800-742 Ma), Grand Canyon: a record of cyclic marine deposition during global cooling and supercontinent rifting. Sedimentary Geology 141- 142 (2001) pp. 465-499.

100

The US Cordillera Excursion 2015

Dehler, C. M., Sprinkel, D. A., Porter, S. M. 2005. Neoproterozoic Uinta Mountain Group of northeastern Utah: Pre-Sturtian geographic, tectonic, and biologic evolution. Geological Society of America. Field Guide 6 (2005). Ehlers, T. A., Chan, M. A. 1999. Tidal Sedimentology and Estuarine Deposition of the Proterozoic Big Cottonwood Formation, Utah. Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies. Vol 69 (1999) No. 6. (November), pp. 1169-1180 Kingsbury-Stewart, E. M., Osterhout, S. L., Link, P. L., Dehler, C. M. 2013. Sequence stratigraphy and formalization of the Middle Uinta Mountain Group (Neoproterozoic), central Uinta Mountains, Utah: A closer look at the western Laurentian Seaway at ca. 750 Ma. Precambrian Research 236 (2013) pp. 65-84. Mahon, R. C., Dehler, C. M., Link, P. K., Karlstrom, K. E., Gehrels, G. E. 2014. Detrital zircon provenance and paleogeography of the Pahrump Group and overlying strata, Death Valley, California. Precambrian Research 251 (2014) pp. 102-117.

101

The US Cordillera Excursion 2015

13 Earthscope

Rickard Haeggman University of Gothenburg

Earthscope is a collaborative scientific project initiated in 2004 in the USA. It is an open database consisting of several kinds of geological and metrological data gathered from over 1000 measuring stations across the USA. The data is open for the public in order to stimulate research, education and to raise the interest in nature science. While being funded by the National Science Foundation (NSF) it is operated by organizations like the Incorporated Research Institutions for Seismology (IRIS), UNAVCO, the National Aeronautics and Space Administration (NASA) and the United States Geological Survey (USGS). (www.earthscope.org). By using Northern America as a natural laboratory the earthscope project aims to study geological processes on and within the earth (Long, Levander & Shearer, 2014). There are many advantages with an open database. For instance, when studying tectonics, data is often needed for large areas and often need long time series to provide useful information. By using information from the earthscope project there is no need to spend vast amounts of money and time to gather data. This stimulates the scientific progress since everyone with the proper knowledge is provided with sufficient data and is thus able to perform their research being less constrained by for example getting funding for research. While several projects are running in the Earthscope program, The USArray, San Andreas Fault Observation at Depth (SAFOD) and the Plate Boundary Observation (PBO) are considered to be the major ones (www.earthscope.org). This review aims to provide a summary of what the earthscope is, mainly focusing on the USArrays, SAFOD and PBO, as well as to demonstrate a few examples of what has been achieved by the project.

USArrays One of the three major components of the earthscope project is called the USArrays. The USArrays use seismographs that measure the natural energy produced by earthquakes to study tectonic processes like the movements of tectonic plates and volcanic activity as well as the rheology of the lithosphere and the mantle. North America is used as a “Natural Laboratory” to study processes occurring beneath the earth’s surface. The USArrays can be further subdivided into four components (Figure 13-1). The first are called seismic Transportable Arrays (TA) which measure seismic activity. Between 2006 and 2013, 400 TAs were deployed in a 70 km grid in the west. They were stationed, doing measurements for two years, and were then moved in the grid towards the east (Long et al., 2014). Ultimately a 3D image of the lithosphere and the mantle from the whole country (It now covers 48 states) has been achieved (www.earthscope.org, www.usarray.org, Long et al., 2014). Currently the TAs are being deployed in Alaska (www.usarray.org). Studies of the mantle

102

The US Cordillera Excursion 2015 below the United States have been done prior to the deployment of the USArrays. However, many of these studies used two-dimensional transects and the models were produced accordingly. Deploying the USArrays in a uniform grid provides the advantage of getting a three-dimensional view of the mantle. The second component is the Seismic reference network which serves as reference points for the TAs. The reference network consists of roughly 100 stationary seismographs positioned in a 300km grid. Another component is the Magnetotelluric TA. These have been used to study the two rifts of the Northwest Pacific and the Mid-Continent. This data has produced some of the earliest 3D-models displaying conductivity from the mantle and lithosphere (www.earthscope.org). The last component is the Flexible Arrays which are mainly operated by individual researchers to study certain places of interest (www.earthscope.org).

Figure 13-1. Map showing distribution of the four main components of the USArrays. Map is borrowed and modified from Long, Levander & Shearer (2014).

Farallon The probably most relevant topic concerning the USArrays is the geometry and history of the Farallon plate. A major problem regarding the investigations of the subducted tectonic plate has been that the most models produced were made using 2D data. Simplifying a 3D system into a 2D model is bound to cause misconceptions. Due to the deployment of the TAs there are more data available and models are no longer constrained to a 2D view. As a result, more articles providing 3D models with new insights have been published regarding the subject. An example is the article by Pavlis, Sigloch, Burdick, Fouch and Vernon (2012). Using TA data they compare seismic images visualized in 3D and, at times, 4D. Their principal goal is to use the data to say as much as they can about the Farallon plate. It is worth to mention that they provide all the used data as well as the software, programming and calculations required to replicate and their models. Thus other researchers are able to criticize and further develop the models. The study has given many indications about the Farallon plate. It seems that the Farallon plate subducted as a coherent slab underneath

103

The US Cordillera Excursion 2015

North America. It can be tracked from the trench to where its subducted remnant is believed to be lying beneath the Atlantic Ocean and the Eastern parts of the United States. The dip is gentle between the trench and the volcanic arc. The dip increases after the volcanic arc. It flattens out into a gentle dip when it approaches the 410 km discontinuity. The size of the subducted material is believed to be similar to the size of the Pacific Plate. Data indicates on there being a “slab gap” beneath Oregon. It is seen as a hole in the central USA where there does not seem to be traces of the plate. The cause of the hole is yet to be determined. An interpretation is that the Yellowstone hotspot provides a “blowtorch effect” which warms the slab, which in turn let seismic waves travel faster. The authors urge other people not to see all these statements as complete facts but subjects to focus further studies. A research by Liu and Stegman (2011) focuses on the subduction of the Farallon and Juan de Fuca plates during last 40 Ma (Figure 13-2). Using USArray data together with previously known plate motion history, paleo-ages of the sea floor as well as paleo geography they make a model in order to simulate the late subduction of the two plates. They state that the subduction is up to 60° between 40 and 25 Ma. The subduction rate during this time interval ranges between 5 and 10 cm/yr. When the slab reaches the 410km discontinuity it starts to break and spread. At 20 to 15 Ma areas of basin and range type are forming. Contemporaneously, the trench’s westward movement increases from 2 to 6 cm/yr. The effect is that the subduction trench is pushed westward which makes the subduction roll back dominated.

Figure 13-2. The evolution of the Farallon and Juan de Fuca slabs from 40 Ma until present. The trench is located under the black arrow. The green line marks where the slab is located today. The Yellow lines mark the American continent. The orange lines mark the 410 km and 660 km discontinuities. The figures to the right serve as references from previous studies. Figure borrowed from Liu & Stegman (2011).

They deduce that the Farallon slab breaks loose from the Juan de Fuca slab at the same time. Since the force of the slab pull decreased, the subduction rate of the remaining plate decreased to 2 cm/y. The dipping angle of the subduction is reduced to 30°. Today the remains of the Farallon slab would be lying slightly beneath the 660 km discontinuity while the Juan de Fuca slab would be above the same discontinuity. They analyze a previously known horseshoe shaped fast seismic anomaly that lies under Nevada and Utah. It has, among other theories, been thought to be lithospheric drip. Liu and 104

The US Cordillera Excursion 2015

Stegman argue that it is a part of the Farallon slab that broke loose at 15 Ma which has been curled by Toroidal mantle flow.

San Andreas Fault Observatory at Depth The San Andreas Fault is located in western California. It is a strike slip type fault that serves as the limit between the North American Plate and the Pacific Plate. The Pacific Plate moves northwestwards relative to the North American Plate. Strong earthquakes, usually around 6 on the Richter scale, are coming from the fault around every 20 years (www.earthscope.org). The last one had a magnitude of M6 and occurred at August 24th, 2014 in Napa Valley (www.usgs.gov). The SAFOD is a project to study the processes affecting the San Andreas Fault. It consists of a 3.2 km deep hole (Figure 13-3) down in the fault where chemical and physical measurements are performed. The hole is located in Parkfield, approximately 1.8 km from the fault. It goes straight down to a certain depth, and then turns towards the fault, thus intersecting the fault. Drilling cores have been extracted from the hole, along with various measurements to directly measure physical and chemical properties of the famous fault zone.

Figure 13-3. Principal image of the SAFOD drilling hole The hole goes in a vertical direction and is located 1.8 km from the actual fault. It then turns to intercept the fault at roughly 3.2 km depth. Image from earthscope.org.

Due to the new advantages from the SAFOD project new kinds subjects are being analyzed. An example is one done by Warr, Wojatschke, Carpenter, Marone, Schleicher & Van der Pluijm (2014). Parts of the fault creeps roughly 25 mm/yr without being exposed to any apparent high tectonic pressure affecting the location. Their study aims to find out why. Having collected clay from the fault zone in the cracks between the plates at a depth around 2.7 km they investigate the physical properties of the clay in order to determine if it affects the movements of the fault. The study area is victim to earthquakes up to 6M about every 20 year. Smaller, earthquakes, M>3, occur at a more regular basis. Warr et al. presents a three-phased model of how the aseismic creep is possible. The initiating phase involves the earthquakes. The earthquakes generate cracks in shales and

105

The US Cordillera Excursion 2015 serpentinitic rocks. The effect is a shear fractured network with cavities where fluids can enter. This leads to metasomatism of the rocks which form smectite. During the second phase, the smectite forms low friction layers that coats the fault surface, eventually leading to a small creep. During the last phase the movement of the creep mechanically erodes loose grains in the fault, eventually forming even more clay minerals. Grains get rounded, lowering the friction even more. They conclude that if this model is correct aseismic creep can form wherever there are occurs small earthquakes at regular basis and they encourage the model to be tested at more locations (Warr et al., 2014).

Plate Boundary Observatory the Plate Boundary Observatory is a part of the earthscope project which mainly focus on gathering geodetic data to analyze the boundary between the North American and the Pacific tectonic plates. It collects data from several sources. A set of 1100 GPSs have been distributed across the land. They can measure both vertical and lateral movements giving them the possibility to get an accurate view of how the tectonic plates are moving as well as developments of volcanic activity and how the magmatic situation in Yellowstone is evolving. Different kinds of strain meters have been deployed along the fault to measure the movement of the fault and at what velocity it is moving. Tilt meters are used to measure changes in the inclination of a surface. It measures vertical movements with high precision and is commonly used in tectonic and volcanic studies. The gathered information is used to view the active boundary in a 3D spectrum and with a well-defined time frame (www.earthscope.org). The project has several purposes. The most prominent being to determine properties of the plate boundary like what forces are behind the tectonic movements, the spatial distribution of the deformation caused by the movements and how the plate boundary have evolved through time and space. There is also a big focus concerning seismicity. The PBO tries to determine the spatial and temporal distribution of earthquakes, how their epicenters are formed and also what factors are controlling volcanic activity. To be able to reduce risks from earthquakes and eruptions is a final purpose (www.earthscope.org).

Conclusion The Earthscope has already provided lots of advances in earth science. By providing public data anyone with the ability can contribute to science without having to worry about spending time and funding to obtain the vast amounts of data that is necessary for conducting geologic science at larger scale. Earthscope is a vast pool of geologic data which is still growing. Since the advent of earthscope, several kinds of scientific feats have been achieved and it is very likely that more is to come.

References

Liu, L., & Stegman, D. R. (2011). Segmentation of the Farallon slab. Earth and Planetary Science Letters, 311, 1-10. Long, M. D., Levander, A., & Shearer, P. M. (2014). An introduction to the special issue of Earth and Planetary Science Letters on USArray science. Earth and Planetary Science Letters, 402, 1-5. Pavlis, P. L., Sigloch, K., Burdick, S., Fouch, M. J., Vernon, F. L. (2012). Unraveling the 106

The US Cordillera Excursion 2015

geometry of the Farallon plate: Synthesis of three-dimensional imaging results from USArray. Tectonophysics, 532-535, 82-102. Warr, L. N., Wojatschke, J., Carpenter, B. M., Marone, C., Schleicher, A. M., Van der Pluijm, B. A. (2014). A “Slice-and-view” (FIB-SEM) study of clay gouge from the SAFOD creeping section of the San Andreas Fault at ~2.7 km depth. Journal of Structural Geology, 69, 234-244. www.eartscope.org. Retrieved November 11, 2015. www.usarray.org. Retrieved November 30, 2015. www.earthquake.usgs.gov/research/napa2014/, Retrieved November 30, 2015

107

The US Cordillera Excursion 2015

14 Lake Bonneville: The Development of the Largest Pluvial Lake in North America During the Late Pleistocene

Eric Floberg University of Gothenburg

Introduction Lake Bonneville was a pluvial lake during the later stages of the Pleistocene epoch, existing between approximately 30 ka cal to 12 ka cal (Oviatt et al., 1990; Oviatt et al., 1992; Benson et al., 2011; Oviatt, 2015). It was located mainly in the north-western Utah, but extended into both Nevada and Idaho as well (Figure 14-1). Present-day Great Salt Lake is a remnant of the ancient Lake Bonneville and covers about 9% of the 55500 km2 that Lake Bonneville occupied at its greatest extent during late Marine Isotope Stage 2 (Nishizawa et al., 2013). The water level during Lake Bonneville’s evolution has been oscillating back and forth a lot, and defined shorelines have developed each time the water level has been stable enough during a longer period of time. The Lake Bonneville history can be divided into three primary periods: the transgressive phase, the overflowing phase and the regressive phase. These phases will be explained in detail in a later section in this report. The first publication about Lake Bonneville was authored by Grove Karl Gilbert in the late 19th century. Gilbert (1882, 1890) was very early with understanding that the water level had oscillated back and forth by studying the various shorelines present at the walls around the Great Salt Lake. His work contains a relatively comprehensive interpretation of Lake Bonneville’s history, which is impressive since it is so early. Ever since Gilberts work in the 19th century countless of articles and reports have been published regarding Lake Bonneville. The resulting hydrograph is considered one of the best in the world (Miller et al., 2013) and the detailed knowledge of the different water levels in the lake has helped a lot with understanding paleoclimate.

General geology of the Lake Bonneville area Lake Bonneville was located in the extensional-tectonic basin, today occupied by the Great Salt Lake, in the eastern Great Basin of western United States. This area, called the Basin and Range Province, has been exposed to severe extensional tectonics for some 16 million years (Snow and Wernicke, 2000). Wernicke (1992) suggests that western Utah and eastern Nevada alone has been subjected to horizontal surface extensions of up to 150 km. Note that the Basin and Range Province thus is a great example showing that the lithosphere can withstand great extensional stress without breaking up to form a new ocean basin. As a result of experiencing extensional stress for such a long time, the topography of the

108

The US Cordillera Excursion 2015 landscape shows the typical characteristics of an extensional-tectonic basin: mountain ranges alternating with flat valleys. The Lake Bonneville basin was filled up with water from both the Great Salt Lake basin via the Bear, Weber and Provo rivers and from the Sevier basin via the Beaver and Sevier rivers (Figure 14-1). The lake itself was not hydrographically connected to the Laurentide or Cordilleran ice sheets (Oviatt, 2015). However, the Laurentide ice sheet did have an impact on the climate which is believed to have contributed to the formation of Lake Bonneville. The Laurentide Ice Sheet (LIS) covered a large area of North America, mainly present day Canada, at the time of Lake Bonneville’s formation. Antevs (1948) suggested that the size of the LIS, in combination with the permanent high- pressure area above it, pushed the storm tracks associated with the polar jet stream (PJS) southward. Benson and Thompson (1987) proposed that as the PJS was pushed southward over the Bonneville basin, enough thermal instability was created to induce lake-effect precipitation resulting in an increase in lake size and degree of glaciations. Later, Hostetler et al. (1994) showed with modeling that lake-generated precipitation was an important factor that contributed to the water budget of Lake Bonneville 18 ka.

Figure 14-1. Map showing the extent of Lake Bonneville at its maximum just prior to the Bonneville Flood at about 18 ka. Red Rock pass, where the unconsolidated sediments collapsed causing the Bonneville Flood, can be seen in the northeastern part of Lake Bonneville. All the major rivers (Bear River, Weber River, Provo River, Sevier River and Beaver river) feeding the lake with water are marked on the map. Map edited from Oviatt (2015).

109

The US Cordillera Excursion 2015

The development of Lake Bonneville The history of Lake Bonneville can furthermore be divided into three major periods (the transgressive phase, the overflowing phase and the regressive phase) in which the properties of the lake basin, the climatic situation and thus also the water level in Lake Bonneville (that was controlled mainly by climate) varied significantly. Depending on how long the lake level was stable at a specific elevation, shorelines would develop around the lake. With radiocarbon dating, it has been possible to date the shorelines by collecting sediment cores from around the Bonneville basin. The radiocarbon dating has helped acquiring a rather precise timescale on the evolution of Lake Bonneville. The exact time span for when the three periods occurred varies from literature to literature and depends on how the dating was done and what samples were dated.

The transgressive period The transgressive phase of the lake was initiated at about 30 ka. At the same time as the water in the lake started rising, the Hansel Valley basaltic ash was erupted and deposited in the area. This ash has been found in several cores and outcrops around Lake Bonneville (Miller et al., 2008) and the best dating available for the Hansel Valley ash shows an age of 30.5 ka (Thompson et al., 1990). Additionally, the Hansel Valley ash has been found on altitudes ranging between 1252 m and 1340 m suggesting a rapid 88 m rise in water level during a rather short period of time (Oviatt, 2015). The transgressive phase was characterized by a hydrographically closed lake basin, which means that all the water that entered the lake from precipitation, river runoff and groundwater exited the system as evaporation and not via a river. Reheis et al. (2014) suggested that the rapid rise in water level of more than 80 m could be explained by a diversion of the upper Bear River into the Bonneville basin. The Bonneville shoreline developed at an altitude of about 1552 m at around 18 ka (Oviatt, 2015) and marks the highest water elevation of Lake Bonneville. Furthermore, the water level oscillated a lot during this phase since the system was so sensible to climatic variations that had a direct impact on the amount of evaporation (Currey, 1983; Oviatt et al., 1990). Understanding the connection between the prevailing climatic situation and the response in lake-level elevation has proven to be important when it comes to understanding paleoclimate. Stratigraphic records exist for the fluctuations during the transgressive phase, but the dating of these events is highly uncertain. The most commonly known oscillation is probably the Stansbury oscillation, which also is the best dated (approximately 25 ka) one during this time, but the chronology can still be improved (Oviatt, 2015).

The overflowing period The transgressive phase exceeded into the overflowing phase at around 18 ka. The overflowing phase was initiated with a collapse of a natural dam, consisting of alluvial- fan gravel and other unconsolidated sediments, in the close proximity of Red Rock Pass (Figure 14-1). This collapse resulted in the Bonneville Flood (Gilbert, 1890), a catastrophic event that caused huge amounts of water from Lake Bonneville to rush out into Snake River, Idaho. The water level in Lake Bonneville dropped with about 130 meters (Gilbert, 1890; Currey; 1982; Miller et al., 2013) over the course of, most likely, less than a year (Gilbert, 1890). After the collapse at Red Rock Pass the water level in Lake Bonneville remained rather stable for almost 3000 years. During this period the Provo shoreline developed (Miller et al., 2013). Oviatt (2015) has been able to give a time constraint on when the lake reached its

110

The US Cordillera Excursion 2015 maximum and when the lake dropped to the Provo shoreline. Three samples from two different sites, both sites being just below the Bonneville shoreline, limits the age of when the lake reached its maximum to after about 18.4 ka. Radiocarbon ages from tufa samples collected from the Tabernacle Hill basalt flow (which erupted after the Bonneville Flood) gives a minimum age of about 18.6 to 17.1 ka. The ages acquired from the tufa samples are the best available that gives a minimum age for the flood event (Oviatt, 2015). These radiocarbon ages are considered to be good temporal constraints on the Bonneville Flood.

The regressive period The age that marks the overflowing of the Provo shoreline and the initiation of the regressive phase has still not been determined and definitely needs more work. Godsey et al. (2011) suggests an age of about 15 ka, while Miller et al. (2013) mentions an age of about 16.7 ka. Howbeit, during the regressive phase the lake basin returned to being hydrographically closed like in the transgressive phase. At a certain point during this period the lake level was drastically reduced once again, this time to levels comparable to modern- day Great Salt Lake (Benson et al., 1992; Benson et al., 2011). However, this loss of water was not caused by an overflowing event but rather from a drastic change in climate in the area. Dating of organic materials in post-Bonneville wetlands gives an age to this event of about 13 ka (Oviatt, 2015).

Isostacy The weight of the vast amount of water in the Bonneville Basin was sufficient enough to isostatically push down the crust of the Earth. As the water from the lake was removed, the crust slowly rebounded to its original position (Bills and May, 1987; Bills et al., 1994, Bills et al., 2002). This has resulted in the shorelines around the Bonneville basin being slightly bow-shaped, with the Bonneville shoreline being the most notable one with a rebound of up to 74 m (Currey, 1990) to the west of Great Salt Lake where the water load was the greatest. The previously mentioned radiocarbon ages were adjusted in consideration of the isostatic depression of the crust during the time when the dated sediments were deposited (Oviatt, 2015). Furthermore, the altitude of the unrebounded lowest point in the Bonneville basin and the unrebounded Bonneville shoreline at the lake maximum is assumed to have been 1200 m and 1552 m respectively (Oviatt, 2015). This gives a maximum lake depth of about 352 m.

Summary The understanding of Lake Bonneville’s formation and demise is an extremely studied and rather well understood topic as scientists have been working on the subject for almost 150 years. The circumstances that led up to Lake Bonneville formation was a combination of the Basin and Range tectonics, the prevailing climate conditions caused by the huge LIS covering a large part of the continent and the geology of the Bonneville Basin with a mainly hydrographically closed basin. Work that can still be improved is more precise dating of the different events, i.e. the oscillations and different lake level stages that have occurred during Lake Bonneville’s evolution.

111

The US Cordillera Excursion 2015

References

Antevs, E. (1948). The Great Basin, with Emphasis on Glacial and Postglacial Times: Climatic Changes and Pre-white Man. III. University of Utah. Benson, L. V., & Thompson, R. S. (1987). Lake-level variation in the Lahontan Basin for the past 50,000 years. Quaternary Research, 28(1), 69-85. Benson, L., Currey, D., Lao, Y., & Hostetler, S. (1992). Lake-size variations in the Lahontan and Bonneville basins between 13,000 and 9000 14 C yr BP. Palaeogeography, Palaeoclimatology, Palaeoecology, 95(1), 19-32. Benson, L. V., Lund, S. P., Smoot, J. P., Rhode, D. E., Spencer, R. J., Verosub, K. L., ... & Negrini, R. M. (2011). The rise and fall of Lake Bonneville between 45 and 10.5 ka. Quaternary International, 235(1), 57-69. Bills, B. G., & May, G. M. (1987). Lake Bonneville-Constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of Bonneville, Provo, and Gilbertstage shorelines. Journal of Geophysical Research Atmospheres. Bills, B. G., De Silva, S. L., Currey, D. R., Emenger, R. S., Lillquist, K. D., Donnellan, A., & Worden, B. (1994). Hydro‐isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines. Geophysical Research Letters, 21(4), 293-296. Bills, B. G., Wambeam, T. J., & Currey, D. R. (2002). Geodynamics of Lake Bonneville. Great Salt Lake: An Overview of Change, Utah Department of Natural Resources Special Publication, Salt Lake City, 7-32. Currey, D. R. (1983). Lake Bonneville; selected features of relevance to neotectonic analysis (No. 82-1070). US Geological Survey. Currey, D. R. (1990). Quaternary palaeolakes in the evolution of semidesert basins, with special emphasis on Lake Bonneville and the Great Basin, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 76(3), 189-214. Gilbert, G. K. (1882). Contributions to the history of Lake Bonneville. Department of the Interior, US Geological Survey. Gilbert, C. H. (1890). A preliminary report on the fishes collected by the steamer Albatross on the Pacific coast of North America during the year 1889, with descriptions of twelve new genera and ninety-two new species. Proc. US Natl. Mus., 13, 49-126. Godsey, H. S., Oviatt, C. G., Miller, D. M., & Chan, M. A. (2011). Stratigraphy and chronology of offshore to nearshore deposits associated with the Provo shoreline, Pleistocene Lake Bonneville, Utah. Palaeogeography, Palaeoclimatology, Palaeoecology, 310(3), 442-450. Hostetler, S. W., Giorgi, F., Bates, G. T., & Bartlein, P. J. (1994). Lake-atmosphere feedbacks associated with Paleolakes Bonneville and Lahontan. Science, 263(5147), 665-668. Miller, D. M., Oviatt, C. G., & Nash, B. P. (2008). Late Pleistocene Hansel Valley basaltic ash, northern Lake Bonneville, Utah, USA. Quaternary International, 178(1), 238-245. Miller, D. M., Oviatt, C. G., & Mcgeehin, J. P. (2013). Stratigraphy and chronology of Provo shoreline deposits and lake‐level implications, Late Pleistocene Lake Bonneville, eastern Great Basin, USA. Boreas, 42(2), 342-361. Nishizawa, S., Currey, D. R., Brunelle, A., & Sack, D. (2013). Bonneville basin shoreline records of large lake intervals during Marine Isotope Stage 3 and the Last Glacial Maximum. Palaeogeography, Palaeoclimatology, Palaeoecology, 386, 374-391. Oviatt, C. G., Currey, D. R., & Miller, D. M. (1990). Age and paleoclimatic significance of the Stansbury shoreline of Lake Bonneville, northeastern Great Basin. Quaternary Research,

112

The US Cordillera Excursion 2015

33(3), 291-305. Oviatt, C. G., Currey, D. R., & Sack, D. (1992). Radiocarbon chronology of Lake Bonneville, eastern Great Basin, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 99(3), 225-241. Oviatt, C. G. (2015). Chronology of Lake Bonneville, 30,000 to 10,000 yr BP. Quaternary Science Reviews, 110, 166-171. Reheis, M. C., Adams, K. D., Oviatt, C. G., & Bacon, S. N. (2014). Pluvial lakes in the Great Basin of the western United States—a view from the outcrop. Quaternary Science Reviews, 97, 33-57. Snow, J. K., & Wernicke, B. P. (2000). Cenozoic tectonism, in the central Basin and Range: magnitude, rate, and distribution of upper crustal strain. American Journal of Science, 300(9), 659. Thompson, R. S., Toolin, L. J., Forester, R. M., & Spencer, R. J. (1990). Accelerator-mass spectrometer (AMS) radiocarbon dating of Pleistocene lake sediments in the Great Basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 78(3), 301-313. Wernicke, B. P. (1992). Cenozoic extensional tectonics of the US Cordillera. The Geology of North America, 3, 553-581.

113

The US Cordillera Excursion 2015

15 Risks of Earthquakes in the Western USA: The Basin and Range Province

Emma Kruse University of Gothenburg

Introduction The western part of the USA has a high seismicity and lots of earthquakes each year. It’s known that it is one of the most seismic places in the world and have one part in the ring of fire. The most know fault in the area is the San Andreas fault. The fault is 800 miles (1300 km) long and starts in the northern California, San Francisco, and goes down to the gulf of California in the south. The San Andreas fault is a transform boundary between the north American plate and the pacific plate, it’s called a strike-slip fault (Britannica academic, 2015). There are very many active faults and folds in the western USA, but in this report the focus will in the area of basin and range. The basin and range is a province in the western USA that have an active continental rifting with several active faults (IRIS, 2015) which results in earthquakes. An earthquake takes place when the blocks slip in a fault and the stress will become higher than the friction between the blocks (USGS, 2015). The earthquakes that reaches the surface and that we actually can feel are more unusual then the smaller ones. If the magnitude is under 6 or if the epic centrum is very deep in to the ground it will be harder for the seismic waves to reach the surface (USGS, 2015). But when they reach the surface and we feel them is the most dangerous part. Earthquakes is something that can be caused by extension, which they mostly do in this province. The report will focus on understanding how and where earthquakes and faulting happens in the Basin and Rang province in the western USA. It will be easier to understand why earthquakes happened if we understand the geological history and some other basic information about the province.

Basin and Range and its seismic activity and geologic history Basin and range is a province in the western United States (Figure 15-1). The province is known for its wide continental rifting followed by faulting and earthquakes. There have been two types of extensions in the geological history, of the Basin and Range. Youngest in time are the creation of high angle block faulting. The oldest event is the creation of high extended areas, as the metamorphic core complexes. This means that the area has gone through erosion, uplifting, exposed rocks and highlighted low-angle normal faults. This older type of extension where mostly in the northern part of the province and were created under Eocene.

114

The US Cordillera Excursion 2015

Figure 15-1. The Basin and Range province (earthscope Voyager, 2015).

The metamorphic core complexes are known as highly extended areas but cannot all be recognized as that in this province. But they are large-magnitude extensions together with areas where the extension is not that high (Parsons, 1995). Low-angle faults were created in high extended Great Basin (eastern Nevada, central Basin and Range) under Oligocene. These may have been a result of intra- or back-arc setting that were localized on the North American continental edge from Proterozoic. Under the late Oligocene the first steps of the extension history began, but the first strong one were in the beginning of the Miocene. This strong extension took place in Mexico and reacted large existing normal faults and created metamorphic core complexes. This metamorphic core complexes were created along the Colorado River (between Arizona and California) and also on the southern edge of the Colorado Plateau (Parsons, 1995).

115

The US Cordillera Excursion 2015

Figure 15-2. map over the Basin and Range province in the western USA. The light colored areas with dots is the Basin and Range (modified from T. Parsons, 1992).

In the central Basin and Range there was an ongoing extension, between south Colorado Plateau and south Sierra Nevada, in the early Miocene and also late Oligocene. In this place is it possible to find some of the later created metamorphic core complexes (Parsons, 1995). In the middle of the Miocene epoch, 10 and 13 Ma, the widest form of extension took place. This stretching was localized in the southern and northern part of the province. Under this time the basin-range structure was created by steep normal faults activated by later stages of low magnitude extension. The event that occurred at this time in the geological history gave the province its name (Parsons, 1995).

116

The US Cordillera Excursion 2015

Under the Pliocene and Quaternary there were ongoing rifting in the Jalisco block, in the southern rim of Sierra Madre Occidental in Mexico, were also eruptions occurred together with the rifting. These event could suggest that the direction of the grooving Basin and Range province is going to the south. That the continental rifting is still active today can be told by the seismicity and the large magnitude of the earthquakes that is occurring in the whole province (Parsons, 1995).

Basic fact of the Basin and Range The continental rifting that is stretching the basin and range is one of the largest active continental rift systems of today. The extension has been between 50-100%, some areas under 10 % and other areas up to 300 %. It also contains over 100 of basins that has different age, depths and orientation. These basins are going over 100 of km far and the ranges has a ratio from 4:1 to 8:1 for the length and width. These basins and ranges can easy be seen on a topographic map (Figure 15-3) (Parsons, 1995).

Figure 15-3.Topographic map over basin and range (Parsons, 1995)

It’s hard to understand how the extension behave in the area because of its differences in behaving in the area. Even doe the composition and thickness of the crus is the same in the north and the south, there are differences in the elevation. In the north the elevation stands 1 km higher than in the south. This can be a result from regional differences of the mantel in the province (Parsons, 1995). The thickness of the continental crust in the area indicate that is must have been thick before the extension or the thickness has been build up by lower crystal flows from outside the Basin and Range or by crustal materials of magmatism from extension. If it

117

The US Cordillera Excursion 2015 started as thick it would have to have been between 45-60 km thick or thicker (Parsons, 1995).

Seismicity As mentioned before there is active seismicity and many earthquakes occurring in the Basin and Range (Parsons, 1995). The province is nearly as big as Europe and contains over 100 active faults (Machette) and there have been almost as many hazardous earthquakes (M=7) there as in the San Andreas Fault (Parsons, 1995). The seismicity is outspread along the boundaries of the Basin and Range province (Figure 15-4 and Figure 15-5). In these boundaries most of the earthquakes take place (Figure 15-4) and they have a maximum depth of 15 Km. The most common fault types are normal fault slip, but there are some strike-slips too. Mostly the seismicity act in episodes. It happens often than an area that is quiet and undisturbed can get an episode of high seismicity and then afterwards go back to its tranquility again. As seen in the Figure 15-5, there are different zones of seismicity divided in with different names (Parsons, 1995).

Figure 15-4. (Left): Seismic activity in the basin and range province, under 1700-1995 with a magnitude over 3.5 (parson, 1995).

Figure 15-5. (Right): Seismic zones in the basin and range province (Parsons, 1995).

The intermountain seismic belt is one of the most active belts in the province. It reaches from western Montana, through Utah, eastern Idaho and along eastern edge of Colorado Plateau. This seismic belt is one indicator to that the edge of the Colorado Plateau, that usually is stable, are going towards collapse from the extension. Between the Ba sin and Range and the Rockies the Wasatch front lies, it’s a seismic zone inside the intermountain seismic belt. Wasatch has mostly north to south striking subparallel faults. North of this zone is the Yellowstone caldera hotspot. In this zone there are more magmatism and shallow depth earthquakes. In the edge of this arc the Snake River Plain lies. The east side of the Snake River Plain is aseismic. This can be because of some sort of magmatic strain accommodation that keeps the larger earthquakes away. The central Nevada seismic belt has mostly extensional earthquakes and the walker line has mostly right-lateral slip (Parsons, 1995).

118

The US Cordillera Excursion 2015

Hurricane fault The hurricane cliff and the hurricane fault are two worlds witch is easy to confuse. The hurricane cliff is the sharp edge of the hurricane fault and are therefore not really the same thing (Biek, 2015). The hurricane fault is the largest active faults in the southern Utah and were formed with continuously earthquakes eruptions in different times. It has been active and uplifted under 850 000 years. After every earthquake it has been moved about 5-10 feet (Biek, 2015). The length of the fault is around 250 Km and the stratigraphic separation goes up to 2520 m in south western Utah (Davis, 1999).

Figure 15-6. Map over Hurricane fault (Raucci, 2005).

Over a blind thrust fault the Kanarra anticline where formed. Parts of this fault has been again reactivated do to the hurricane fault. This older anticline where created under Sevier and is tilted to the east. The hurricane fault has some of the oldest exposed rocks in Utah. Its build up by light yellow to brown sandstone and gray limestone that where deposited in warm, subtropical ocean. The limestone belong to the Toroweap and kaibab formation (Biek, 2015).

119

The US Cordillera Excursion 2015

Figure 15-7. Map over Hurricane fault (Raucci, 2005)

Earthquakes in the area can reach up to high scales of magnitude, such as 7. It had a big eruption in 1992 with an earthquake with a magnitude of 5.2 (Biek, 2015). It’s not clear when the basin and range faulting begun in the hurricane fault, but it is possible that it begun in later Miocene, 15-12 Ma, because of the relations between regional tectonics. The hurricane fault is also a part of the Wasatch line (Davis, 1999).

Earthquake data from USGS There are earthquakes under a magnitude of 2.5 that is occurring in the province every day (Figure 15-8). Also earthquakes with a magnitude of 2.5-4.4 are recorded almost every day (Figure 15-9). 4.5 magnitude earthquakes and higher are more unusual in the province with a span of 30 days. In these past 30 days there have been no earthquake over 4.4 (USGS, 2015).

120

The US Cordillera Excursion 2015

Figure 15-8. Earthquakes recorded 2015-12-02 with all magnitudes, no one is over 2.5. The colors indicate witch depth the earthquakes had (USGS, 2015).

Figure 15-9. Earthquakes recorded 2015-12-02 for the last 7 days. Magnitudes in between 2.5-4.4. The colors indicate witch depth the earthquakes had (USGS, 2015).

121

The US Cordillera Excursion 2015

Figure 15-10. Fault in the western USA in red (USGS, 2015).

Conclusions There are earthquakes that occurs every day, but they have a very low magnitude. The bigger earthquakes are more unusually but do also occur in the area, but it’s often years in between them. Because of the recorded small earthquakes it’s true to say that the rifting in basin and range is still active and both large and small earthquakes can happen every second. Almost all of the earthquakes is occurring in the edges of the basin and range province, in the seismic zones.

References

Biek, R. F. (den 02 12 2015). silver reef utah. Hämtat från silver reef utah: http://www.silverreefutah.org/HURRICANE-FAULT.html Britannica academic. (den 02 12 2015). Britannica academic. Hämtat från Britannica academic: http://academic.eb.com.ezproxy.its.uu.se/EBchecked/topic/520930/San- Andreas-Fault). Davis, G. H. (1999). Hurricane fault. i G. H. Davis, Structural Geology of the Colorado Plateau Region of Southern Utah (ss. 20-21). Arizona: University of Arizona. IRIS. (den 02 12 2015). IRIS. Hämtat från IRIS: https://www.iris.edu/hq/files/programs/education_and_outreach/aotm/15/BasinRang e_Background.pdf Parsons, T. (1995). The Basin and Range Province. USGS. Raucci, L. A. (2005). paleoseismology and geomorphology of the hurricane fault and escarpment. i J. L. Dehler, Interior Western United States. the geological society of america. USGS. (den 02 12 2015). USGS. Hämtat från U.S. Geological Survey:

122

The US Cordillera Excursion 2015

http://www.usgs.gov/faq/categories/9827/3343 USGS. (den 02 12 2015). USGS. Hämtat från USGS: http://earthquake.usgs.gov/earthquakes/map/#%7B%22feed%22%3A%221day_all%22 %2C%22search%22%3Anull%2C%22listFormat%22%3A%22default%22%2C%22sort%22 %3A%22newest%22%2C%22basemap%22%3A%22grayscale%22%2C%22autoUpdate%2 2%3Atrue%2C%22restrictListToMap%22%3Atrue%2C USGS. (den 02 12 2015). USGS. Hämtat från U.S. Geological Survey: http://www.usgs.gov/faq/categories/9838/3435

123

The US Cordillera Excursion 2015

16 Gold, Copper and Related Sulphide Mineralizations in Nevada

Caroline Lundell University of Gothenburg

Introduction The sulphide deposits in Nevada are of Carlin-type ore, which are estimated to contain approximately 6000 tons of gold and have the second largest concentration of gold in the world. The United States are the fourth largest producer of gold since the deposits accounts for approximately 6 percent of the annual worldwide production. The four largest clusters of Carlin-type deposits in the area are Carlin Trend, Cortez, Getchell and Jerritt Canyon, see Figure 16-1 (Muntean et al., 2011). Expansion of exploration drilling has led to enlarged mining districts. This together with modern and developed mines led to the understanding that the deposits occur in linear groups (trends) or as clusters (Cline et al., 2005).

Figure 16-1 The four largest clusters of Carlin-type deposits and their locations in northern Nevada. Min = age of mineralization. Mag = age of associated magmatism (Muntean et al., 2011).

124

The US Cordillera Excursion 2015

Carlin-type deposits In 1961 a new deposit type was recognized after the discovery of the Carlin deposit and was called Carlin-type deposits. Although, some deposits had been mined since the beginning of the 1900s (Cline et al., 2005). Mineralizations of Carlin-type are similar to orogenic deposits (compressional processes), but are classified separately since they formed after subduction-related processes. Extensional forces are the major cause to the formation of Carlin-type deposits (Robb, 2005). They are replacement bodies with dominantly decarbonatization of silty carbonate rocks (Cline et al., 2005). In Nevada, USA the Carlin-type deposits formed between 42-30 Ma, which is a relatively short period of time. This makes the deposits unique, although similar ores are located in China they are not as big as those in Nevada. Fluids associated with Carlin-type deposits have a low salinity, an intermediate acidity and gold is transported as Au(HS)2- or Au(HS) in reduced H2O-CO2 solutions. Carlin-type deposits are epigenetic and epithermal with fluid temperatures between 150-200oC which has led to the discussion if they have a meteoric origin instead of a hydrothermal (Robb, 2005). Carlin-type gold deposits contain gold in solid solution or as disseminated grains in pyrite or marcasite (Cline et al., 2005).

Genetic models There are two genetic models regarding the origin of the gold in Carlin-type deposits. The first one is a magmatic-hydrothermal model – where gold is derived from magma and the second one is an amagmatic model – where gold is derived from meteoric or metamorphic water from the crust (Muntean et al., 2011). Hydrogen (H) and oxygen (O) isotope data collected from fluid inclusions show mixtures between meteoric- and magmatic fluids (Cline et al., 2005; Muntean et al., 2011). Kesler et al. (2005) argues that arsenian pyrite was formed from fluids of magmatic origin and that sulphur contamination was caused by sedimentary wall rocks. Magmatic assimilation or hydrothermal leaching of sulphur from sedimentary rocks can be the cause to the meteoric water. Ilchik and Barton (1997) suggest an amagmatic origin and they have made geochemical models which indicate that a deep meteoric fluid circulation was driven by extensional processes in the Basin and Range. However, recent research indicates a magmatic-hydrothermal origin and Muntean et al. (2011) claim to have found strong indications due to new Laser-Ablation-Inductively-Coupled-Plasma-Mass- Spectrometer (LA-ICP-MS) analyses and electron-probe microanalyses. Analyses on ore- stage pyrite prove that it contains gold (Au) together with arsenic (As), mercury (Hg), thallium (Tl), tellurium (Te), copper (Cu) and antimony (Sb). This elemental sequence is consistent with transportation of magmatic fluids.

Tectonics The theory presented here is a summary of more recent research and is based on the magmatic-hydrothermal model. During the assembly of Rodinia in the Mesoproterozoic (1600-1000 Ma) and during the rifting of western North America in the Neoproterozoic (1000-541 Ma) perfect conditions were created for gold deposits of Carlin-type. A carbonate shelf was created along the margin after the rifting. Faults in the basement were reactivated and formed basins where carbonate debris could settle and create breccias, which are important host rocks for Carlin-type deposits (Muntean et al., 2011). During late Devon to early Mississippian (385-345 ma) a sequence of compressive events started - the Antler Orogeny

125

The US Cordillera Excursion 2015 and during Perm to Triassic (299-199.6 Ma) the Sonoma Orogeny (Emsbo et al., 2006). During these periods siliciclastic- and basaltic rocks were thrust over the carbonate shelf and created the Roberts Mountain thrust. Fractured carbonate rocks were located on top of the thrust faults linked to the deep rifts in the crust and uppermost siliciclastic material could be found as an impermeable layer (Muntean et al., 2011).

Figure 16-2. Series of events shown in cross-section, which are likely to have formed the Carlin-type gold deposits (Muntean et al., 2011).

As seen in Figure 16-2, the Farallon slab started to subduct (dipping to east) in the middle Triassic (246-229 Ma) along western North America. Back-arc magmatism in Nevada occurred during middle- to late Jurassic (175-145.5 Ma) and ended at 65 Ma when the dip of the Farallon slab became shallow. During these years of magmatism and dehydration of the slab the mantle wedge under the Great Basin was hydrated and metasomatized with metals like As, Sb, Tl, Pb, Cu and possibly Au. Early magmas may have fractionated a restite rich in Au during the formation of the subcontinental lithospheric

126

The US Cordillera Excursion 2015 mantle (SCLM). Between 65-45 Ma shallow subduction followed and the base of the SCLM became further hydrated and metasomatized of fluids from the subducting slab (Muntean et al., 2011). Rollback and delamination of the shallow subducting Farallon slab associated with the Laramide orogeny (Emsbo et al., 2006) caused further magmatism at 45 Ma and the metasomatized base at SCLM experienced hot asthenosphere. This resulted in huge amounts of hydrated basaltic magma, which contained sulphur (S) and gold (Au). The basaltic magma underplated and started to melt the overlying continental crust and created an intermediate S- and Au-bearing magma. The ore fluids separated to an immiscible brine and vapour during the ascent along faults from the magma chamber. Au, Cu, As, Sb and S can be transported as vapour, while Fe, Pb and Ag preferentially partition into brine. The gold-bearing vapour has most likely incorporated meteoric water during its ascent through the upper crust. The mixture with the cold water may have caused faster cooling and led to a phase change where vapour precipitated into liquid (Muntean et al., 2011). The acid ore fluids probably infiltrated the fractured carbonate rocks at a depth less than 3 kilometres, which then were dissolved by the fluids. The dissolved carbonate rocks buffered the acid ore fluids and made it possible for the sulphides to precipitate (Muntean et al., 2011). Although, argillic alteration, silicification and sulfidization probably contributed to the ore-forming process as well (Robb, 2005). The dissolution of the carbonate rocks led to increased permeability and made it possible for the ore fluids to react with surrounding bedrocks and the siliciclastic rocks captured the mineralizations (Muntean et al., 2011).

Where is the gold? The gold can be found in arsenian pyrite [Fe(As,S)2] (Deditius et al., 2008) and in trace element rich pyrite in hydrothermally altered bedrocks. Gold-bearing deposition of arsenian pyrite is rare, which indicates that fluid-bedrock reactions have caused the ore deposition (Muntean et al., 2011). Gold-bearing pyrite occur as rims on pyrite that formed before the ore and as disseminated micrometre-sized grains. Gold can also be found in arsenopyrite and in marcasite (Robb, 2005).

Alteration As mentioned earlier carbonate rocks are dissolved in most deposits and around ore zones. Jasperoid formed due to quartz replacing carbonates. Breccias collapsed in some deposits due to comprehensive decarbonatization. Argillization is minimal in pure carbonate rocks, but igneous rocks are strongly argillized. Moderately acidic fluids reacted with older alumina-silicate minerals in the wall rocks and formed kaolinite ± dickite ± illite assemblages. Studies have shown crystalline illite close to ore, which suggests a genetic association. Illite and muscovite have provided a wide range of ages, some are older than the gold. This is another controversy in the enigma of the genesis of Carlin-type deposits. Illite and muscovite older than the ore indicate that they stayed stable during most of the alteration and did not alter until the most intense phase (Cline et al., 2005). Jasperoid is an indication of silicification which occur in some gold deposits. Another silicification feature which occur are vugs coated with quartz druses. More uncommon in these deposits are ore-stage quartz veins. The quartz druses line vugs are a characteristic feature of Carlin-type deposits and they are formed due to decarbonatization or in collapse breccias. The lacking of matched quartz and gold together with the low

127

The US Cordillera Excursion 2015 abundance of ore-stage quartz can be a result of ore formation during low temperatures. For indication of temperatures and depth of formation jasperoid textures can be used. Minerals that primarily replaced carbonate minerals tend to be inherited in jasperoid textures. The jasperoids typical found in Carlin-type deposits usually have reticulate or xenomorphic textures. This is due to carbonates being replaced by quartz at temperatures >180oC and at greater depths. It seems to be more likely that high temperature jasperoid is related to gold deposition in Carlin-type deposits. However, low-temperature forms of silica, such as opaline or amorphous usually appears as jigsaw or chalcedony textures in jasperoid. These textures have been seen in some Carlin-type deposits. Observed textures suggest that precipitation occurred at shallow depths and from depleted ore fluids or fluids unconnected to the Carlin system. (Cline et al., 2005).

Additional ore deposits in Nevada SEDEX (Sedimentary Exhalative deposits) barite, porphyry Cu-Mo-W-Au and epithermal Ag-Au deposits are all mineral deposits aligned with the Carlin- and Getchell Trend in Nevada. This is thought to be due to the deep reactivated basement faults along SCLM. SEDEX gold ore in the Devonian Upper Mud Member belonging to the Popovich Formation, is stratiform and related to minerals like Zn, Cd, V, Se, Ni, Cu, Hg and Sb unlike Carlin-type ore (Emsbo et al., 2006) Several intrusion-related gold deposits formed when calc-alkaline granitoids intruded during Eocene. These intrusions have been used as evidence of magmatism in the genesis of the Carlin-type deposits. However, a genetic relationship cannot be linked. The provided heat from the intrusions during crustal extension is more likely to have contributed to hydrothermal circulation (Emsbo et al., 2006).

Discussion A lot of controversies have raised the question of the genesis of Carlin-type deposits. New and improved analytical instruments and methods may have led to some clues. More and more scientists seem to agree that one genetic model cannot solve the mystery. In the deposits there are magmatic mineral assemblages and both low- and high- temperature textures in minerals. Isotopes indicate both a magmatic and meteoric origin. Crystalline illite close to the ore indicate a genetic relationship, but show a range of ages, where some are older than the gold. Carlin-type deposits have been found in China, but they are much smaller with a slighter ore concentration. The question still remains, what circumstances caused the Carlin-type deposits in Nevada to have such a high-grade ore-concentration? Most likely a lot of different events and coincidences worked together. The Farallon slab with the shallow subduction and later on roll-back and delamination. The magmatic intrusions which could contribute with heat. The “cold” meteoric water which cooled the vapour and led to a phase change. The carbonate rocks which could buffer the acid fluids and the impermeable siliciclastic rocks above the carbonates which caught the fluids and preserved the ore.

References

Cline, J.S., Hofstra, A.H., Muntean, J.L., Tosdal, R.M., Hickey, K.A. (2005) Carlin-Type Gold Deposits in Nevada: Critical Geologic Characteristics and Viable Models. Economic Geology 100th Anniversary Volume. pp. 451–484. 128

The US Cordillera Excursion 2015

Deditius, A.P., Utsunomiya, S., Renock, D., Ewing, R.C., Ramana, C.V., Becker, U., Kesler, S.E. (2008) A proposed new type pf arsenian pyrite: Composition, nanostructure and geological significance. Geochimica et Cosmochimica Acta 72. pp.2919–2933. Emsbo, P., Groves, D.I., Hofstra, A.H., Bierlein, F.P. (2006) The giant Carlin gold province: a protracted interplay of orogenic, basinal, and hydrothermal processes above a lithospheric boundary. Miner Deposita. vol. 40. pp. 517-525. Ilchik, R.P. & Barton, M.D. (1997) An amagmatic origin of Carlin-type gold deposits. Economic Geology. vol.92. pp.269-288. Kesler, S.E., Riciputi, L.C., Ye, Z. (2005) Evidence for a magmatic origin for Carlin-type gold deposits: isotopic composition of sulfur in the Betze-Post-Screamer Deposit, Nevada, USA. Mineralium Deposita. vol.40. pp. 127-136. Muntean, J.L., Cline, J.S., Simon, A.C., Longo, A.A. (2011) Magmatic-hydrothermal origin of Nevada’s Carlin-type gold deposits. Nature Geoscience. vol.4. pp.122-127. Robb, L. (2005) Introduction to ore-forming processes. Blackwell Publishing.

129

The US Cordillera Excursion 2015

17 The California Gold Rush

Aron Kindbom Jonsson University of Gothenburg

Introduction The 1849 Gold rush of California had a great impact on the United States and especially the west coast. The promise of gold and hopes of getting rich fast created a massive migration event compared to the actual population of the California area back in 1848. This paper will discuss partly American history and society development as well as the geological processes behind the gold ores and where it was found and why it was there.

The discovery and the initiation of the California Gold Rush The California Gold Rush began in January 1848 at John Sutter’s Mill north of present day Sacramento, where James Marshall, the foreman of a mill construction found some yellow, glimmering mineral grains in the American River. Marshall took the samples to John Sutter and they identified the samples as gold (Clay & Jones, 2008). Marshall and especially John Sutter was not at all excited about the discovery as Sutter feared that all the workers on his farm would quit their job to look for gold instead. The news however, reached San Francisco in May 1848 as Samuell Brannan, a shop owner and newspaper publisher apparently ran through the streets yelling “Gold! Gold! Gold from the American river” (Cutter, 1949). In addition to his running and yelling in the streets Brannan advertised the discovery of gold in his newspaper The California Star. He then proceeded to purchase as much mining equipment as possible in order to resell later, which he did with huge profit. By the end of 1848 there were between 4000-5000 gold- miners at work. By early 1849 a special edition on the newly found gold was published in Brannan’s The California Star and the news of gold reached New York and from there, the rest of the world (Holliday, 1999; Clay & Jones, 2008; Holliday, 2015).

Society and economics California was not an actual state when Marshall found the first pieces of gold, in fact it was hardly a part of the United States. A war between the United States and Mexico had broken out in 1846. The war was a result of the two nation’s inability to conclude on a common border and the US annexation of Texas and parts of present day California (Bauer, 1974). However the finding of gold and the rapid migration of fortune seekers from mainly the United States quickly americanized California in general and (what would be) San Francisco in particular (Rohrbough, 1997). San Francisco was populated by some 1000 people in 1848 and by December 1849 the population had risen to between 25,000 and 30,000 people. And the state itself saw between 100,000 and 200,000 new arrivals (Bauer, 1974). Since California was a province of the United States rather than a state there was

130

The US Cordillera Excursion 2015 almost a complete lack of centralized government or any form of law enforcement (Holliday, 2015). This resulted in a lawless society driven by hopes and greed. “There is a good deal of sin & wickedness going on here, stealing, lying, swearing, drinking, gambling & murdering” (Mr. Sheldon Shuffelt in Holliday, 1999) Sheldon Shuffelt was a miner who arrived in San Francisco in 1849 (Holliday, 1999), who in letters to his cousin describes the life as a goldminer during the peak years of the California Gold Rush. Mr. Shuffelt further writes “Almost every public house is a place for gambling, & this appears to be the greatest evil that prevails here”. According to Mr. Shuffelt men win or lose thousands of dollars’ worth of gold in one evening and that young boys might bet 5- 10 $ (between 100 and 200 $ today) and if they lose they go out the next day to find more. Furthermore, Mr. Shuffelt states that there are attempts of trying to create a system for law and order but it will be hard to execute (Holliday, 1999). I choose to believe that Mr. Shuffelt is not altering his experiences in the letters as he is highlighting the terrible downsides of in the gold fields. Most people embellished the life in the gold fields either to impress or not to worry loved ones back home. Mr. Shuffelt on the other hand, does not. He does indeed confirm that the gold is plentiful, however the sudden riches takes the sense out of otherwise good people. Studies show that traders like Samuell Brannan got much wealthier than the actual miners. In fact Samuell Brannan was the richest man during the early days of the California Gold Rush. Many of early miners usually manage to make a profit in the end and some even got quit wealthy. Those arriving in 1855 and later often could not make enough money to cover the most basic of expense such as food or a place to stay and some could not even afford to go home again (Clay & Jones, 2008; Holliday, 1999). It is important to note that not all shopkeepers and the like were successful either. When a new dig site was discovered it was common that not only miners were drawn to the area but other businessmen as well. Mining camps evolved into small settlements as people moved in with hopes to strike rich either by finding gold or other means like commerce or lodging. If the new dig site was not as rich as it seemed the settlement was abandoned. Some had invested all their assets in, for instance opening a shop or a saloon and thus went completely bankrupt when the site was forsaken (Clay & Jones 2008).

The miners and their methods The gold found by Marshall and during the most part of early the gold rush was taken from placer deposits i.e eroded sediments mostly in rivers (Sutherland, 1985). The gold was initially so plentiful that no actual skill in prospecting or mining was needed to extract gold from the river banks. The distinct colour and massive density was more than enough to separate the gold from sand and gravel either by panning or simply picking the gold by hand. Although it was possible to get the gold without tools it was by far more common to use some sort of gold pan. The very first miners were not necessarily the typical gold seeker with pan, pick and shovel but rather local residents of California. And not only the men, in fact whole families, women and children were often involved in the process. The typical “forty-niner” (Figure 17-1) became the common gold miner in 1849 when the migration had become nationwide.

131

The US Cordillera Excursion 2015

Figure 17-1. (Left) Illustration of 49er with typical basic equipment for small scale gold mining. (www.bbc.co.uk). (Right) Miner with gold nugget (www.ushistory.org)

The gold pan was the most basic tool for small scale gold recovery (Silva, 1986). One simply wash an appropriate amount of sediment in the pan repeatedly until most of the lighter minerals such as quartz is washed away leaving only the heavy minerals in the pan such as magnetite, hematite and of course gold. Gold is very easy to distinguish from the other darker, heavy minerals even when the grain size is very small (Figure 17-2).

Figure 17-2. Concentrate of heavy mineral sand containing a large amount of gold. Note that even the fine grained gold is easily distinguished from the other heavy minerals.

Another tool for small scale mining that was often used was the rocker (Figure 17-3) which allowed for a larger amount of material to be processed during a work day. The material is placed in the hopper where it is washed through a screen where the coarser

132

The US Cordillera Excursion 2015 material is caught and gold nuggets easily distinguished. Beneath the screen is an apron with a pocket on it lower end in which the heavy minerals are concentrated (Silva, 1986).

Figure 17-3. Basic rocker. Coarse material is caught in the screen and the finer in the apron below (Silva, 1986).

Some miners created sluices in order which redirected water flow to further increase the amount of material processed. The larger or denser particles tumble through the channel rather than being suspended and get trapped at riffles on the bottom of the sluice bottom of the sluice (Figure 17-4). This was done on large and small scale but the principle remains the same. Figure 17-5 shows several people working on a medium scale sluice box. When done on larger scales it sometimes involved redirecting the flow of natural rivers and brooks which could limit the water supply to homesteads, farms or settlements (Silva, 1986).

Figure 17-4. Close-up on how the mass separation in the sluice works (Silva, 1986).

133

The US Cordillera Excursion 2015

Figure 17-5. Several people working in the same sluice (Silva, 1986).

The last method of placer gold recovering that will be mentioned is hydraulic mining. The reason I mention it is the severe environmental damage that it has caused. Water cannons or Monitors was used to jet water on placer beds in gravel pits. The mix of sediment and water was directed to sluices were the gold was collected (Thrush, 1968) and the remaining sediments and water was discharged into nearby rivers. This method sets massive amounts of sediments in motion. The large amount of sediment and water that entered the natural water systems from the mining pits was often enough to cut off, redirect or overflow the river which was devastating to both local and distant residents who depended on the river for fresh water (Alpers et. al, 2005). Such sudden and significant changes to the landscape also threatens flora and fauna that is not used to sudden changes in the ecology.

Mother lode All the gold that got concentrated in placer ore deposits had to have a bedrock origin. Many miners thought the same and expected mountains of solid gold. The truth is that gold indeed are in great abundance in the bed rock or mother lode, however it is not nearly as concentrated as the placer ores. This means that the average solitary miners or small groups of miners rarely were able to actually mine any profitable abundances of gold in the mother lode (Rohrbough, 1997). The Mother Lode Gold District of California is an area 225 km long located in the western part of the Sierra Nevada (Figure 17-6). The actual gold usually appears incorporated in quartz veins and carbonate rocks. The carbonate rocks and the quartz veins is a result of hydrothermal fluids of temperatures between 250 and 325oC which react with the surrounding greenschist facies metamorphic and-metasedimentary rocks (Savage et al., 2000). During tertiary uplift the gold bearing rocks got exposed and soon eroded. The eroded marital ran down the mountain side and settled in the placers that millions of years later got hundreds of thousand people moving.

134

The US Cordillera Excursion 2015

Figure 17-6. Map displaying lode gold mines in the foothills of Sierra Nevada (Savage et.al, 2000).

References

Alpers, C. N., Hunerlach, M. P., May, J. T., & Hothem, R. L. (2005). Mercury contamination from historical gold mining in California. Bauer, K. J. (1974). The Mexican War, 1846-1848. U of Nebraska Press. BBC, www.bbc.co.uk/schools/gcsebitesize (2015-11-10) Clay, K., & Jones, R. (2008). Migrating to riches? Evidence from the California gold rush. Journal of Economic History, 68(04), 997-1027. Cutter, D. C., & Sacramento Club of Printing House Craftsmen. (1949). The discovery of gold in California. Sacramento Club of Printing House Craftsmen. Holliday, J. S. (1999). Rush for riches: gold fever and the making of California. Univ of

135

The US Cordillera Excursion 2015

California Press. A letter from a gold miner, Placerville, California, March, 1850; Holliday, J.S. Rush for Riches: Gold Fever and the Making of California (1999). Holliday, J. S. (2015). The world rushed in: The California gold rush experience. University of Oklahoma Press "James W. Marshall's account of the first discovery of the Gold". www.malakoff.com. Retrieved 30 March 2012 .Rohrbough, M. J. (1997). Days of gold: The California gold rush and the American nation. Univ of California Press. Savage, K. S., Bird, D. K., & Ashley, R. P. (2000). Legacy of the California Gold Rush: Environmental geochemistry of arsenic in the southern Mother Lode gold district. International Geology Review, 42(5), 385-415. Silva, M. A. (1986). Placer gold recovery methods (No. 87). Division of Mines and Geology. Thrush, P. W. (1968). A Dictionary of Mining, Mineral and Related Terms. www.ushistory.com (2015-11-13) Wiley, P. B. (2000). National Trust Guide/San Francisco: America's Guide for Architecture and History Travelers. John Wiley & Sons.

136

The US Cordillera Excursion 2015

18 Dissemination of Metals from Abandoned Mines in the United States

Annelie Helmfrid University of Gothenburg

Introduction There are over 500,000 abandoned mines In the United States and EPA (Environmental Protection Agency) has estimated the recovery cost to 50 billion US dollars. About 40 percent of the western US rivers are polluted by mining operations. This because many mines have problems with Acid Mine Drainage (AMD) (Pagel, 2015). AMD is coupled to the mining of a particular type of mineral such as, gold, copper and nickel. The pollutants are spread in rivers and can cause a long-term impairment to waterways and biodiversity. AMD contain high levels of toxic substances such as heavy metals and cyanides, which pose a potential risk to the environment and human health. AMD is formed from various types of sulfide minerals of iron, which is the most common mineral producing AMD. It is a natural process where the mineral, when in contact with oxygen and water, oxidizes and forms an acidic sulfur solution. The type and amount of sulfide minerals oxidized and the type of gangue minerals present in the rock affect the metal contamination associated with AMD. The AMD production rate depends on humidity, the supply of oxygen, the minerals found in the rock and the presence of bacteria. Naturally occurring bacteria have an ability to accelerate the production of AMD (Akcil and Koldas 2006).

EPA's Superfund Within the EPA a program called Superfund is responsible for cleaning up America's most polluted areas to protect the environment and human health. The focus is on making visible and long-term solutions in contaminated areas (EPA 2015a). EPA has a National Priorities List of America's most polluted areas which must be decontaminated. Many of the mines on EPA's National Priorities List are disused (EPA 2015b).

Examples of contaminated mining areas – Leviathan Mine, California Leviathan Mine is an abandoned open-pit sulfur mine (Figure 18-1) located on the eastern slope of the Sierra Nevada, Alpine County in California. The mine was a copper mine from 1860s, but most of the environmental problems are derived from the open-pit sulphur mining, between the years 1951 to 1962. AMD has contaminated a nine-mile stretch of mountain creeks, which is devastating for aquatic life in creeks downstream the source. This AMD is containing high levels of arsenic, copper, nickel, zinc, chromium, aluminum and iron. The leakage from the mine is greatest during snowmelt in spring. Investigations have

137

The US Cordillera Excursion 2015 been carried out for a long time in order to identify the pollution situation before an extensive clean-up (EPA 2015c).

Figure 18-1. Map of Southwestern United States. The Leviathan Mine in California is highlighted in red (Modified from EPA 2015c).

The Gold King Mine, Colorado One of the United States worst hard rock-mining-related disasters in decades was in the abandoned Gold King Mine, near Silverton, Colorado (Figure 18-2) (Pagel 2015). When a team from EPA conducted a survey of the mine in August 5th, 2015 there was an accident. The excavation in the soil of the mine during the investigation made the plugged hatch in the mine tunnel to break due to high water pressure (EPA 2015d). The result was that about three million gallons of acidic water were spilled into Cement Creek, a tributary of the Animas River, and on to San Juan River and the Colorado River. The water was mustard colored and contained high levels of arsenic, lead, cadmium, aluminum, and copper (Figure 18-3) (Chief et al. 2015). This released from the mine at a rate of 600 gallons per minute (EPA 2015e). Lab analysis from the plume of contamination in Animas River in Durango area showed that the concentrations of arsenic and lead were much higher than background levels; 300 times higher for arsenic and 3500 times higher for lead. These levels declined after the plume of contamination moved downstream (Garrison 2015).

138

The US Cordillera Excursion 2015

Figure 18-2. Map of Southwestern United States. The Gold King Mine in Colorado is highlighted in red (Modified from ©Google Maps 2015).

Figure 18-3. Mustard-colored water in Animas River from the Gold King Mine (McBride 2015).

139

The US Cordillera Excursion 2015

The leakage from the mine is now under control. EPA has contact with experts to analyze what the possible effects of the leakage had on the drinking water and human and animal health. They have not seen any acute toxic effects on the aquatic life from the plume of contamination (EPA 2015d). EPA is currently focusing on that people in the area have access to safe drinking water. Their goal is that the contaminated water should not have any impact on aquatic organisms and to prevent contaminated water leaking from the mine. Another goal is that the water from the leakage should not have any adverse effect on human health in long- term period. In the current situation we do not know if there could be long-term effects, more research is necessary. Surveys on crops must also be made to assess the risk from eating. Durango is a city close to the Gold King Mine and most of the drinking water comes from the Animas River. Samples of tap water and groundwater have shown that it has returned to a normal level (EPA 2015e).

Discussion Leviathan Mine and the Gold King Mine is different from each other because of what happened in the Gold King Mine was a disaster which released large amounts of AMD for a short time and Leviathan Mine has been leaking for a long time. However, the Gold King Mine has long been known to be one of America's most polluted mines and has leaked contaminated water over a long period (Pagel, 2015). The composition of AMD in these mines can be compared with each other with respect to arsenic, copper and aluminum, where mainly arsenic may pose a potential risk to the environment and human health. AMD from the Gold King Mine also contains lead and cadmium, which are also toxic metals. The toxic heavy metals in the Gold King Mine and the large amount of AMD that were released during the disaster means that the situation there is far more serious than the one at the Leviathan Mine. Despite differences in pollution situation extent can the long-term effects from the two mines to be similar, but probably not as extensive effects in the Leviathan Mine.

Dissemination and long-term effects Several studies show that mining has a negative long-term impact on water quality and aquatic ecosystems. This is because the metals bind to the sediment particles and sediments transported by and stored in flood plains. The biggest impact is upstream, closest to the mine. Studies on contaminated sediments from the mining areas show that the concentration of metals decrease downstream. The highest concentrations of the metals in sediments can be linked to when the mining was most intense. The recent sedimentation after mining has ended, showing that the concentrations of metals are lower than they were during mining operations. The pollution in the older sediments mobilized mainly through bank erosion (Lecce and Pavlowsky 2014). Long-term effects depend primarily on how metals bind to sediment. There is a risk that the metals end up in suspension at high water events or recreation jobs (Chief et al. 2015). Arsenic and lead are disperse mainly through transport of sediments, since the metals are bound to sediment particles. The largest transport takes place during storm events. The metals transported by surface runoff and follow the gradient. The mainly transport of arsenic and lead during wet season is adsorption on soil particles surface. If a very heavy storm or several smaller storms over a short period would occur, arsenic and lead pose a threat to nearby lakes. (Sims and bottom Berg 2008).

140

The US Cordillera Excursion 2015

The spatial dispersion of metals usually follows the speed of groundwater in soil (Miao et al. 2013).

Risk of contamination There is a risk that the fish ingests high levels of metals if they eat plants that grow in the sediments. The metals may disperse to surface water and groundwater and thus affect drinking water quality. If the contaminated sediments in the river margin dry up, it can be dispersed by the wind and contaminate the surrounding soil. People and animals can be exposed to contaminated soil through inhalation, soil on hands and crops, but also through irrigation with contaminated water. In order to assess the long term effects several investigations are required including sediment, water and aquatic organisms that may form the basis for environmental and health risk assessments (Chief et al. 2015). Studies on a gold mine in southwestern Nigeria with high levels of lead in the soil show that high levels of lead had an acute toxic effect, killing 400 children. The dominant exposure pathways were hand- mouth transmission and inhalation of soil particles. Consumption of contaminated food and water was a lesser but significant pathway. The most affected are small children, but also pregnant women, nursing mothers and older children. This study shows that a similar poisoning disaster may occur in other places in the world that have similar mines (Plumlee et al. 2013). One study investigated the link between mining related pollution in river sediments and its presence in nestling ospreys. These are top predators and the survey was done primarily on chicks because they mainly eat fish from the polluted area. In the most polluted part of the river chicks had a significantly higher content of heavy metals. In a year with heavier runoff than normal and more suspended sediment was significantly elevated levels of heavy metals in the chicks blood measured (Langner et al. 2012).

Measures to prevent AMD and mining-related disasters The composition of AMD differ from place to place in various mines, and therefore there is no standardized method that can be applied to all mines. What methods should be used to avoid problems with AMD must thus be adapted for each mine. Mine planner and manager must investigate what type of AMD that is in the mine and predict possible pathways. It is also important to develop appropriate and safe technique to control AMD in order to avoid a similar accident as in the Gold King Mine. One way to try to treat AMD is to raise the pH to the threshold required for the iron bacteria are not going to produce sulfuric acid. By raising the alkalinity will not as many heavy metals to precipitate. In addition, oxidation is slower in alkaline environments. Another way to prevent the producing of AMD is to build dams that can bind heavy metals so that they are not likely to disperse. By trying to prevent rainwater from entering the mine the producing of AMD can be reduced (Akcil and Koldas 2006).

Summary Abandoned mines have a major negative impact on the environment and human health. Therefore, it is important to prevent leaks and clean up already polluted mines. Mines disperse heavy metals in rivers and can also contaminate the surrounding soil. At investigations and remediation of contaminated mining areas, there are important to use precautions to prevent serious accidents like a severe leakage.

141

The US Cordillera Excursion 2015

References

Akcil, A., Koldas, S., 2006: Acid Mine Drainage (AMD): causes, treatment and case studies. Journal of Cleaner Production 14:1139-1145. Chief, K., Artiola, J.F., Wilkinson, S.T., Beamer, P., Maier, R.M., 2015: Understanding the Gold King Mine Spill. Superfund Research Program, The University of Arizona. 11 pp. EPA, 2015a: Superfund. Retrieved 2015-10-03, from http://www2.epa.gov/superfund EPA, 2015b: Abandoned Mine Lands. Retrieved 2015-11-20, from http://www2.epa.gov/superfund/abandoned-mine-lands EPA, 2015c: Leviathan Mine. Retrieved 2015-11-20, from http://yosemite.epa.gov/r9/sfund/r9sfdocw.nsf/ViewByEPAID/CAD980673685 EPA, 2015d: Emergency Response to August 2015 Release from Gold King Mine. Retrieved 2015-12-01, from http://www2.epa.gov/goldkingmine EPA, 2015e: Frequent Questions Related to Gold King Mine Response. Retrieved 2015-12-01, from http://www2.epa.gov/goldkingmine/frequent-questions-related-gold-king-mine- response Garrison, S., 2015: EPA says 3 million gallons of contaminated water released into Animas River. The Daily Times. Retrieved 2015-10-03, from http://archive.daily- times.com/ci_28611665 Langner, H.W., Greene, E., Domenech, R., Staats, M.F., 2012: Mercury and Other Mining- Related Contaminants in Ospreys Along the Upper Clark Fork River, Montana, USA. Arch Environ Contam Toxicol 62:681–695. Lecce, S.A., Pavlowsky, R.T., 2014: Floodplain storage of sediment contaminated by mercury and copper from historic gold mining at Gold Hill, North Carolina, USA. Geomorphology 206 122-132. McBride, J., 2015: Photos: Mine Waste Spill Pollutes Animas River. The Durango Herald/AP Retrieved 2015-12-01, from http://www.usnews.com/news/photos/2015/08/11/photos-mine-waste-spill-pollutes- animas-river Miao, Z., Carrol, K.C. Brusseau, M.L., 2013: Characterization and quantification of groundwater sulfate sources at a mining site in an arid climate: The Monument Valley site in Arizona, USA. Journal of Hydrology 504 207-215. Pagel, L., 2015: The real culprit in the Animas River spill. CNN. Retrieved 2015-10-03, from http://edition.cnn.com/2015/08/12/opinions/pagel-animas-river-pollution/ Plumlee, G.S., Durant, J.T., Morman, S.A., Neri, A., Wolf, R.E., Dooyema, C.A., Hageman, P.L., Lowers, H.A., Fernette, G.L., Meeker, G.P., Benzel, W.M., Driscoll, R.L., Berry, C.J., Crock, J.G., Goldstein, H.L., Adams, M., Bartrem, C.L., Tirima, S., Behbod, B., von Lindern, I., Brown, M-J., 2013: Linking Geological and Health Science to Assess Childhood Lead Poisoning from Artisanal Gold Mining in Nigeria. Environ Health Perspect 121:744-750. Sims, D.B., Bottenberg, B.C., 2008: Arsenic and Lead Contamination in wash sediments at historic Three Kids Mine- Henderson, Nevada: The Environmental Hazards Associated with Historic Mining Sites and Their Possible Impact on Water Quality. Journal of the Arizona-Nevada Academy of Science 40(1):16-19.

142

The US Cordillera Excursion 2015

19 California Drought: The Golden State Goes Brown

Susanna Gelin University of Gothenburg

Introduction Drought can be defined in many ways. Some ways can be quantified, such as meteorological drought (period of below normal precipitation) or hydrologic drought (period of below average runoff), others are more qualitative in nature such as shortage of water. There is no universal definition of when a drought begins or ends, it is a gradual phenomenon. Impacts of drought are typically felt first by those most dependent on annual rainfall, such as farmers engaged in dryland grazing or rural residents relying on wells in low- yield rock formations. Drought impacts increase with the length of a drought, as reservoirs are depleted and water levels in ground water basins decline (DWR 2012). Droughts in California are not unusual and often extend several years. However, the current episode, which began in late 2011, may turn out to be the worst ever experienced by the state in terms of environmental and economic impacts. As a result of several years of severe drought, numerous industries in the state, including the agriculture, water resource and fishery sector are experiencing major impacts and competing for water, while communities are experiencing increasing impacts on employment, tourism, health and daily life (Sullivan 2014).

Questions at issue • What has caused the ongoing drought in California? • How has the current drought affected California? • What is El Niño’s influence to the drought in California?

Climate in California California, the Golden state, experiences a distinct dry season every year. It usually sets in between mid to late May and ends sometimes between late September and early October. This natural dry season with characteristics of a Mediterranean climate with little precipitation is unique for the United States. Topography plays a large role in precipitation distribution. The windward side of the Sierra Nevada, in the northern and central California, catches much of the precipitation (up to ten times the state average) from storm systems coming in from the Pacific Ocean. The desert regions mainly have local showers and thunderstorms. The state’s wet season kicks off when the main storm track for many West Coast storms typically dips southward in autumn. The wet season becomes more robust in November and December as storm systems become more numerous and often tap

143

The US Cordillera Excursion 2015 more moisture. Most of the annual precipitation across California falls between December and Mars. Recent research has shown that a significant percentage of wintertime precipitation falls in only a handful of large events. Missing even just one or two of these storms can mean big deficits to the snow pack and annual precipitation. Much of California has adapted to the natural dry period by utilizing its reservoirs to store water for consumption, irrigation, wildlife management and other uses. During periods of extended drought, groundwater has been used as substitute for the lack of surface water (Sullivan 2014).

The current drought in California The current drought in California started in early 2011 and was exacerbated in 2014. This drought is the worst experienced for the state in terms of consequences for the environment, economy, health, agriculture and the tourism industry. The reservoirs have come close to or exceeded “all-time record lows” (Figure 18-2). Even where water exists, the continued dry weather also threatened the supply held in storage. The main reason for this drought is less precipitation than normal and above normal temperatures. A drop in snowpack winter 2013/14 resulted in reduced river flow (Sullivan 2014, Seager et al. 2014). Evapotranspiration is a concern, in some areas it accounts for the major part of water loss. The latest U.S. Drought Monitor report (Figure 18-1) released November 24, 2015, indicates that large areas (approximately 45 %) still remains at the D4 – Exceptional Drought Intensity Rating. Approximately 92 % of the state remains at a level D2 – Severe Drought or higher.

Figure 19-1. Map of California showing drought conditions at five intensity levels for November 24th 2015. Area percentage at each intensity level can be seen in the table. http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.aspx?CA 144

The US Cordillera Excursion 2015

Droughts in the past The current drought in California is not only the worst in modern history it is the worst in half a millennium. But the current drought is just one of many dry periods over the last 5 000 years. Sequences of drier than average years repeat every few decades. The geological records reveal that during periods of climatic warmth droughts lasted much longer than a decade in the western parts of America. During the Medieval Climate Anomaly (between 900 and 1400 AD) two 100-year long droughts descended, causing large lakes to shrink or dry out completely and more frequent wildfires with consequences for the native populations. The number of people had grown large during wetter periods, leaving them more vulnerable to the megadrought that followed. Prolonged droughts have led to native population being forced to mass migration from the parched Great Basin to the Californian coast, in history sometimes leading to societies collapsing. Our modern society experienced rapid population growth during the relatively wet 20th century. Today California has 38 million people, a number that may double by 2050. This was possible due to the use of all available sources of water, including underground aquifers that took thousands of years to accumulate (Ingram 2014).

Causes and predictability According to National Oceanic and Atmospheric Administration (NOAA) Climate Division Data, the November through April winter precipitation season 2013/14 was the sixth driest for the state of California since records began in 1895. The three-year period 2011/14 were the second driest period regarding average precipitation for California since 1895. 2011/12 and 2012/13 winter seasons were also dry. Several years of drought, has left California’s water resources in a severely depleted state. Conditions were exacerbated by warm temperatures with November-April 2013/14 being the warmest winter half-year on record. Warming increases evaporative loss, raises water demand and reduces snow pack (Seager et al. 2014). Since the end of the 1990s, droughts has been afflicting much of southwestern U.S. and the ongoing drought lies within this large scale context (Seager 2007; Weiss et al. 2009; Hoerling et al. 2010; Cayan et al. 2010; Seager and Vecchi 2010; Seager and Hoerling 2014). The current drought, though extreme, is not outside the range of California hydro-climate variability and similar events have occurred before. There has been a drying trend in California winters since the late 1970s, but when considering the full observational record since 1895 no trends can be determined (Seager et al. 2014). The climate models examined by Seager et al. 2014 forced with sea surface temperature (SST) anomalies found up to a third of winter precipitation variance driven by SST anomalies. It could not alone explain the cumulative deficit of California precipitation 2011/14, but also internal atmospheric variability. In the future an enhanced understanding of SST forcing (from the Pacific and possibly other ocean basins) could have great potential to improve seasonal prediction in the region.

Climate change in California Concerns for future water supply are intensified by projections from climate models. In southern California, but not northern, projections indicate rising temperatures and declining winter precipitation reducing water availability in coming decades due to higher concentration of greenhouse gases (Seager et al. 2007, 2013; Maloney et al. 2014; 145

The US Cordillera Excursion 2015

Vano et al. 2014). IPCC (2007) projects a warming of 2-3°C until 2100. A study by Swain et al. (2014) concluded that global warming was increasing the likelihood of a weather pattern similar to that observed during the recent drought, however the connections remained uncertain. Vulnerability to extended droughts are increasing across North America as population growth and economic development create more demands from agricultural, municipal and industrial uses, resulting in frequent over-allocation of water resources. Consequences of the over-allocation include saltwater intrusion, and increased groundwater and surface water pollution (IPCC 2014, Marshak 2008).

El Niño’s influence on California drought El Niño-Southern Oscillation (ENSO) is a well-studied climate phenomena and during certain conditions it provides some predictive guidance in parts of the U.S. ENSO is characterized by year-to-year fluctuations in sea surface temperatures along the Equator in the eastern Pacific Ocean, and associated fluctuations in sea level air pressures between Tahiti and Darwin, Australia. The ENSO cycle is expressed as three states: neutral conditions, El Niño (warm ocean phase) and La Niña (cold ocean phase) (de Blij, Muller and Williams 2004). Dry winters are often caused by a ridge of high pressure of the south west cost of U.S. Wet California winters that tend to occur when a trough (low pressure) is established in eastern North Pacific. However, the connection to El Niño events is not strong and not all wet California winters are during El Niño-events. Since the late 1990s a shift to more La Niña- like conditions is likely to have caused a drying trend in California. Research of today show that variation in ENSO cannot alone cause a drought or interrupt an ongoing drought (Seager et al. 2014).

Impacts of the ongoing drought in California California is the nation’s leading agricultural producer and one of the major agricultural regions of the world. Agriculture is the state’s largest water supply user, consuming about 80 % of the state’s total. Throughout the current drought, members of the agricultural community have taken extreme measures to irrigate croplands, feed livestock and maintain livelihoods. Decrease in precipitation and water availability for irrigation are being largely offset by increased groundwater pumping, an unsustainable situation for the state. During 2013 it has cost California $2.2 billion in damage and 17 000 agricultural jobs. 60-70 % of the livestock have been sold or shipped out of the country during 2014. Countrywide production during 2015 was 47 % of average, which threats the country’s economy. In a dry year groundwater account for over 60 % of California’s water supply compared to about 40 % in an average year (DWR 2014). To keep 770 ha of crops alive, a farmer need to pump about 125 liters per second, which is about 11 000 m3 a day, enough water to provide a dozen family homes with all the water they need for a year. There are thousands of pumps like this, pulling water from deep underground up and down the San Joaquin Valley around the clock. Increasing drought conditions are likely to reduce yields in the next two decades and could have a substantial impact on global food security (Brown and Funk 2008). Current drought impacts on fisheries are widespread, with low river flows, limited storage in reservoirs and associated cold pools affecting threatened and endangered fish populations. Other ecosystems and wildlife are stressed by the decrease in water

146

The US Cordillera Excursion 2015 availability and will continue so due to climate change, growing water demand and water transfers to urban- and industrial areas (IPCC 2007). In 2015 (January 1 through November 21), CAL FIRE has responded to 6181 fires, 307 560 acres burned. California’s forests and rangeland in combination with its climate and topography creates a “world class” fire environment, with fires as a natural part of the ecosystem’s health. In wildland areas, more than 8 million people live and have their businesses. As a result, fires that once burned as part of a natural process now threaten lives, property and valuable resources. The ongoing drought have promoted increased frequency and duration, and longer wildfire seasons (CAL FIRE 2015). All tree species have been adversely affected by the drought causing widespread tree mortality throughout the state and the country (IPCC 2014). One of the most endangered native forests in the world have been devastated by the drought. The dead trees serve as fuel, when moisture content is low in the trees, fire starts easily and will spread rapidly. The warming climate is favorable for bark beetles. If drought lasts more than one year, tree defenses begin to weaken and pests gain an upper hand. As bark beetle numbers increase, tree mortality increases resulting in increased risk for wildfire (USDA 2015). Climate change poses an increased risk for wildfire activity, including fire season length and area burned due to dry soils and warm temperatures in the western U.S (IPCC 2014). The Department of Water Resources released during the summer of 2015 with a NASA report measuring surface subsidence from satellite images (Figure 19-2). Land in the San Joaquin Valley is sinking faster than ever before, nearly 5 cm per month in some locations. The increased pumping has resulted in record low groundwater levels (30 m below previous records) causing the land to sink more rapidly than ever before, putting nearby infrastructure at greater risk of costly damage. The long-term subsidence has already destroyed public and private groundwater well casings. Over time, subsidence can permanently reduce the underground aquifer’s water storage capacity and lead to new equilibrium groundwaters levels (Dale et al. 2013, NASA 2015).

Figure 19-2. Total subsidence in California's San Joaquin Valley for the period May 3, 2014 to Jan. 22, 2015, as measured by Canada's Radarsat-2 satellite. Two large subsidence bowls are evident, centered on Corcoran and south of El Nido. Credit: Canadian Space Agency/NASA/JPL-Caltech. http://www.jpl.nasa.gov/news/news.php?release=2015-273 147

The US Cordillera Excursion 2015

Water management and groundwater legislation Water is scarce throughout most of the western U.S., a vast area of mountain ranges, deserts, canyons and grasslands. Because of its very nature, water has always been a difficult resource to manage. The complexities of water law, policies, institutions and investments are a reflection of the resource itself. In western U.S., the 17 states, are often separated by actual rivers and watersheds. The borders complicate management of waters challenging policy makers and water professionals. Water moves, upstream communities are fighting downstream communities and vice versa over water quality and quantity. Competing states, tribes, industries, hydropower, environmental groups, laws and navigation lobbies are all fighting over the precious resource. Preparing for climate change and its impacts is therefore a complex and slow process (Fahlund et al. 2014). The water supply in California consists of a complex and geographically expansive network of lakes, rivers, reservoirs, aqueducts and channels that store and move water from one area to another. The local availability of water is determined by weather conditions hundreds of miles away. At the same time, in areas that depend on groundwater for water supply, the local weather and run off patterns play a leading role in water availability (Sullivan 2014). California’s extensive system of water supply infrastructure mitigates the effect of statewide short-term dry periods. However, the system does not address circumstances on a local scale e.g. individual water storage, water-trading and declined groundwater levels. Although California’s water supply infrastructure provide means to mitigate impacts for some water users, other types of impacts remain e.g. increased wildfire risk, stress on vegetation and wildlife (DWR 2012).

Figure 19-3. Current reservoir conditions for California November 27, 2015. All reservoirs have exceeded all-times record low levels. http://cdec.water.ca.gov/cdecapp/resapp/getResGraphsMain.action

148

The US Cordillera Excursion 2015

Farmers turn to groundwater where available to sustain fields and orchards through the 2014 growing season. Increased pumping this year will add further strain to basins already experiencing depleted groundwater levels. The groundwater will keep many farmers from devastating losses today, but without sufficient recharge the use is not sustainable in the long term. The pumping affects the state’s economy, due to high costs and energy usage. The electricity needed to pump groundwater now is about 5 % of the state’s total energy use. Even more importantly pumping is accelerating depletion of the regions groundwater basins and land subsidence. The subsidence has economic consequences through damaged wells and water conveyance facilities such as canals and flood channels (ACWA 2014). An April 2014 the Department of Water Resources (DWR) confirmed that groundwater levels are experiencing record lows in most areas of the state (Figure 19-3 and Figure 19-5). The state of California has very few regulations of groundwater usage. People can pump their wells as hard as they want and use as much water as they please, regardless of the effects to their surroundings and neighbours. Right now California is pumping out groundwater faster than it can recharge. Emptying aquifer’s pose a risk for a water scarce future and it could also decrease the amount of water that may be available to recharge springs and streams and nourish ecosystems. It will take at least 50 years for the Central Velley’s aquifers to naturally refill. The water now being pumped is 20 000 years old. Farmers and landowners who no longer have access to surface water spend millions of dollars to dig increasingly deep wells. The depths of the wells increase every year and most wells today are 800-1200 feet (244-366 m). One 1000 feet (300 m) well, installed, tested and fitted with pumps, costs up to $400 000. The California drought spurs a groundwater drilling boom in Central Valley, but complications have aroused within the drilling sector. The work is hard and dangerous with companies fighting to keep workers, since the competition will show up on spot offering workers more money. Competition from out of state crews, may charge two to three times the normal prices as they do not have to follow California’s air quality standards for their equipment. Farmers are worried about a future state regulation of groundwater since they are dependent of their wells. Without a well, they can’t grow crops and they will be forced to lay people off, followed by unpaid cars and houses. As one farmer expressed himself “They’ll do what they have to do to feed their families, even if it’s wrong” (NG 2014). During November 2015 a new California law takes shape and for the first time in more than a century trying to regulate groundwater pumping to achieve a sustainable system of groundwater use. The legislation will include, by 2017, establishing a groundwater sustainability agency and, by 2020, draw up sustainability plans. Those plans should put groundwater basins on a path to sustainability by 2040. The legislation will be a protracted process, predicted to last for decades (Sacbee 2015). Many questions have raised among the farmers, such as; who is responsible for what? How will it be founded? How much groundwater can be drawn? How will the water be divided between people? Who decide what crop should be planted? Will the government pick winners and losers? Should local politicians really shape the regulations? Is the congress to blame for this dust bowl? Who is going to sue who? How is groundwater tracked? How are violators punished? The regulation will be even more difficult, since the Democrats and the Republicans are not united in this water issue (Sacbee 2015).

149

The US Cordillera Excursion 2015

Mono Lake Mono lake is one example of what increasing demand for water, unplanned land use, changeable politics, increasing recreational use, underfunded management agencies and climate change could mean for the environment and the people of California. Mono Lake is situated nestled at the edge of the arid Great Basin and the snowy Sierra Nevada Mountains in California (Figure 19-4). Mono Lake is an ancient saline lake (salinity is two to three times salter than the oceans) that covers over 180 square kilometers and supports a unique chemistry and productive ecosystem. The lake is at least 760 000 years but probably 1-3 million years old, and thereby one of the oldest lakes in North America. Between the years 1941 to 1990 the Los Angeles Department of Water and Power (DWP) diverted extensive amounts of water from Mono Basin streams. Mono Lake dropped 15 meter, lost half its volume and doubled in salinity, all to meet the growing water demands of Los Angeles. Due to the rapid drop, the ecosystems was unable to adapt and began to collapse. Obviously, that was devastating for an earlier ecological rich region. The lake is California’s richest environmental areas and it contains 14 ecological zones. The lake has no fish, instead it is home to trillions of alkali flies and brine shrimps. The ecosystems also contain 1000 plant species and 400 vertebrates, including millions of migratory birds that visit the lake each year. The Mono Lake Committee, founded in 1978, has led the fight to save the lake and its environment with cooperative solutions. In 1994, after over a decade of litigation, the California State Water Resources Control Board ordered DWP to allow Mono Lake to rise to a healthy level again and is now rising towards this goal.

Figure 19-4. Mono Lake, California. In the background the Sierra Nevada mountains

Discussion The climate in California is mainly dry. Natural variations lead to drought conditions on a regular basis ranging over a few years to decades. Population growth during the 20th to 21st centuries has led to an increased demand for water supply. The impacts of droughts have increased accordingly. The ongoing drought has caused large impacts on the

150

The US Cordillera Excursion 2015 environment and growing water conflicts. Droughts are hard to predict as of today, but we can be sure that this is not the last. Rising temperatures due to Climate change is likely to increase the water shortage in the future. Sustainable groundwater water management is crucial in order to handle future droughts. Measures are needed very soon since groundwater depletion and aquifer destruction combined with population growth will severely aggravate California’s ability to cope with coming droughts. The golden state is up for a great challenge, if they do not embrace it parts of the state may go brown permanently.

Figure 19-5. View upstream from Hoover Dam in the Black Canyon of the Colorado River, on the border between the U.S states of Nevada and Arizona. Lake Mead has dropped, leaving a with ring mark around its shores

References

Association of California Water Agencies (ACWA) (2014). 2014 Drought – impacts and strategies for resilience. Available at: https://cwc.ca.gov/Documents/2014/06_June/June2014_Agenda_Item_9_Attach_2_ACWA DroughtReport.pdf Brown, M. E., and Funk, C. C. (2008). Food security under climate change. CALL FIRE. (2015). California Fire Plan. Available at: http://www.calfire.ca.gov/communications/downloads/fact_sheets/FirePlan.pdf CALL FIRE. (2015). Incident Information. Available at: http://cdfdata.fire.ca.gov/incidents/incidents_current California Department of Water Resources (DWR), Natural Resources Agency, State of California (2012). Drought in California. Available at: http://www.water.ca.gov/wateruseefficiency/docs/2014/021114_Kent_Drought2012.pdf Cayan, D., T. Das, D. Pierce, T. Barnett, M. Tyree, and A. Gershunova. (2010). Future dry- ness in the southwest United States and the hydrology of the early 21st Century drought. Proc. Nat. Acad. Sci., 107, 21 271–21 276. Dale, L. L., Dogrul, E. C., Brush, C. F., Kadir, T. N., Chung, F. I., Miller, N. L., & Vicuna, S. D. (2013). Simulating the impact of drought on California’s central valley hydrology, groundwater and cropping. British Journal of Environment and Climate Change, 3(3), 271-291. Available at:

151

The US Cordillera Excursion 2015

http://baydeltaoffice.water.ca.gov/modeling/hydrology/IWFM/Publications/downloada bles/Articles/Dale_et_al_2013.pdf De Blij, H. J., Muller, P. O., and Williams, R. S. (2004). Physical geography: the global environment Third edition. Oxford University Press. Department of Water Resources (DWR) and the Resources Agency, State of California. Brown, B. J., Laird, J. and Cowin, M.W. (2014). Public Update for Drought Response. Groundwater Basins with Potential Water Shortages and Gaps in Groundwater Monitoring. Fahlund, A., Choy, M. L. J., & Szeptycki, L. (2014). Water in the West. California Journal of Politics and Policy, 6(1), 61-102. Field, C.B., L.D. Mortsch, M. Brklacich, D.L. Forbes, P. Kovacs, J.A. Patz, S.W. Running and M.J. Scott. (2007). North America. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernment Panel on Climate Change, M.L Parry, O.F. Canziani, J.P. Palutikop, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 617- 652. Hoerling, M. P., J. Eischeid, and J. Perlwitz. (2010). Regional precipitation trends: Distinguishing natural variability from anthropogenic forcing. J. Climate., 23, 2131– 2145. Howard, C.H. National Geographic (NG) (2014). California Drought Spurs Groundwater Drilling Boom in Central Valley. Available at: http://news.nationalgeographic.com/news/2014/08/140815-central-valley-california- drilling-boom-groundwater-drought-wells/ Ingram, B. L. (2014). California needs to begin a serious and comprehensive plan to adapt to what may be a very long drought. USAPP. Available at: http://blogs.lse.ac.uk/usappblog/2014/09/02/california-needs-to-begin-a-serious-and- comprehensive-plan-to-adapt-to-what-may-be-a-very-long-drought/ Maloney, E. D., et al. (2014). North American climate in CMIP5 experiments: Part III: Assessment of 21st century projections. J. Climate, 27, 2230–2270. Marshak, S. (2008). Earth: portrait of a planet. WW Norton. p. 675-681. NASA. (2015). Drought Causing Valley Land to Sink. Retrieved from: http://www.water.ca.gov/news/newsreleases/2015/081915.pdf Full report retrieved from: http://www.water.ca.gov/groundwater/docs/NASA_REPORT.pdf Romero-Lankao, P., J.B. Smith, D.J. Davidson, N.S. Diffenbaugh, P.L. Kinney, P. Kirshen, P. Kovacs, and L. Villers Ruiz. (2014). North America. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L.White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1439-1498. Seager, R. (2007). The turn-of-the-century North American drought: dynamics, global context and prior analogues. J. Climate, 20, 5527–5552. Seager, R. and G. A. Vecchi. (2010). Greenhouse warming and the 21st Century hydroclimate of southwestern North America. Proc. Nat. Acad. Sci., 107, 21 277–21 282. Seager, R. and M. P. Hoerling. (2014). Atmosphere and ocean origins of North American

152

The US Cordillera Excursion 2015

drought. J. Climate, 27, 4581–4606. Seager, R., Ting, M., Held, I., Kushnir, Y., Lu, J., Vecchi, G. and Naik, N. (2007). Model projections of an imminent transition to a more arid climate in southwestern North America. Science, 316(5828), 1181-1184. Seager, R., Hoerling, M., Schubert, S., Wang, H., Lyon, B., Kumar, A., Nakamura, J., and Henderson, N. (2014a). Causes and Predictability of the 2011 to 2014 California Drought. Available at: cpo. noaa. gov/ClimatePrograms/ModelingAnalysisPredictionsandProjections/MAPPTaskForces. Seager, R., M. Ting, C. Li, N. Naik, B. Cook, J. Nakamura, and H. Liu. (2013). Projections of declining surface water availability for the southwestern U.S. Nature Climate Change, 3, 482-486. Sullivan, D. K. (2014). California Drought, 2014 Service Assessment. National Oceanic and Atmospheric Administration, NOAA. Available at: http://www.nws.noaa.gov/om/assessments/pdfs/drought_ca14.pdf Swain, D., M. Tsiang, M. Haughen, D. Singh, A. Charland, B. Rajarthan, and N. S. Diffenbaugh. (2014). The extraordinary California drought of 2013/14: Character, context and the role of climate change. (In Explaining Extremes of 2013 from a Climate Perspective). Bull. Amer. Meteor. Soc., 95, S3–S6. The Sacramento Bee (Sacbee) (2015). Tension, threats as California’s new groundwater law takes shape. Available at: http://www.sacbee.com/news/state/california/water-and-drought/article45802360.html United States Department of Agriculture. (USDA) (2015). Bark beetles in California conifers. Available at: http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5384837.pdf Vano, J. A., Udall, B., Cayan, D. R., Overpeck, J. T., Brekke, L. D., Das, T., and Lettenmaier, D. P. (2014). Understanding uncertainties in future Colorado River streamflow. Bulletin of the American Meteorological Society, 95(1), 59-78. Weiss, J. L., C. L. Castro, and J. T. Overpeck. (2009). Distinguishing pronounced droughts in the southwestern United States: Seasonality and effects of warmer temperatures. J. Climate, 22, 5918–5932.

153

The US Cordillera Excursion 2015

20 On the Exotic High-Grade Metamorphic Blocks in a Subduction Mélange from the Franciscan Complex, CA

Andreas Karlsson University of Gothenburg

Introduction The Franciscan Complex (part of the California Coast Ranges) is and has throughout history been a well-studied area to acquire insights into subduction mechanisms, and is a classic locality of low-temperature and high-pressure subduction. It is well documented that the eclogite in the broad sense, in the case of the Tiburion Peninsula, the eclogites have undergone retrograde metamorphism but preserve some of the eclogite mineralogy and blueschist blocks. These high-grade blocks of the Franciscan Complex occur as half a meter to several meter scale exotic blocks in a surrounding shale matrix or serpentinite mélange (Figure 20-1) (Coleman et al., 1965; Coleman & Lanphere, 1971; Wakabayashi, 1992; Ernst, 1993; Wakabayashi, 2011; Wakabayashi; 2012).

Figure 20-1. Photograph showing a serpentinite-mélange block (in greenschist facies) with exotic slices of Blueschist from the Franciscan complex, Ring Mountain, Tiburon Peninsula, CA. This high-grade block is present in the map in figure 4 marked with ba (close to the 70 dip marker in the middle of the map). The blue color can be attributed to either Lawsonite or Glaucophane. Scale: Roughly 1.5 meters across

154

The US Cordillera Excursion 2015

The eclogites from the Franciscan Complex has previously been interpreted to have formed below the reaction: albite = jadeite + quartz but Tsujimori et al. (2006a) demonstrated that the eclogites must have experienced much higher pressure, probably just below the higher pressure reaction of paragonite = kyanite + jadeite. The albite was consequently formed during retrograde metamorphism. It has been known for long that the Franciscan complex was accreted during late Jurassic to the early Cretaceous, but Anczkiewicz et al. (2004) has since updated the geochronology of the high-temperature metamorphism (the eclogites, turns out to be older then the blueschist). The ages span from 169 to 153 Ma based on 40Ar-39Ar on hornblende and 176Lu-176Hf on garnet. The blueschist ages range from 159 to 138 Ma based on 40K-40Ar on hornblende and actinolite and 40Ar-39Ar on hornblende (Marayama & Liou, 1988; Wakabayashi, 1999). The suture is structurally bounded by the Coast Range Ophiolite that is slightly older (172 – 165 Ma) than the high- grade blocks. In contrast with the low grade blocks (the serpentinites) the high grade blocks have a geochemistry of a nascent volcanic arc compared to the lower grade blocks which has a MORB or OIB geochemistry (Shervais, 1987). Additionally the Tiburon Peninsula is renowned for being the type locality for lawsonite, a blue to white sorosilicate with the chemical formula CaAl2(Si2O7)(OH)2 · H2O, similar to the epidote – clino-zoisite group in mineral structure. Lawsonite is also the parent name for a whole range of sorosilicates with similar chemical composition which in parts are all in solid-solution amongst each other called the Lawsonite group (Ransome, 1894; Crawford & Fyfe, 1965). Furthermore, lawsonite is an index mineral of the blueschist and in special cases of eclogite-facies; lawsonite is stable in the lower eclogite facies sometimes referred to as lawsonite-eclogite-facies (Tsujimori et al., 2006b)

General geological background of the high grade blocks of the Franciscan In general the highest grade metamorphic blocks of the Franciscan complex are coarse-grained amphibolites, blueschists and eclogites that occur as tectonic blocks in a serpentinite or shale matrix mélange, in total the high-grade blocks make up less than 1% of the high-grade metamorphic Franciscan rocks (Greenschist is by far the most dominating metamorphic facies). As seen in Figure 20-2. The Franciscan complex crops out (and in the San Francisco bay area) in an N-NE striking direction overlain to the east by the more recent Central Valley sedimentary rocks, and in the west it’s bounded towards the Salinian block of Cretaceous age (Wakabayashi & Moores, 1988). On the Tiburon Peninsula there are several outcrops of both serpentinite and serpentinite matrix mélange (in Figure 20-3 marked with dark gray), further south on the peninsula intact blueschist-facies rocks, which are primarily composed of the protoliths: greywacke, basalt and minor chert (in Figure 20-3 marked in dashed gray). Ring Mountain itself is the structurally highest nappe in the Franciscan complex, and high grade blocks sits in a matrix mélange of serpentinite, this unit is in turn surrounded by a much less metamorphosed shale matrix mélange (in Figure 20-2. Light gray).

155

The US Cordillera Excursion 2015

Figure 20-2. Metamorphic facies map of Northern California, the Franciscan complex is marked in 3 different shades of gray which contains the high grade blocks. There is a general trend that the population density of high-grade blocks increases towards the west in the Franciscan block. From Wakabayashi (1999)

On top of Ring Mountain there are several hundreds of blocks that show a high grade of metamorphism, notably: eclogites, blueschists, garnet-blueschists, amphibolites, epidote-amphibolites and garnet- amphibolites, there is also several lower-grade blocks such as chert and felsic metavolcanics (a detailed map of the block locations shown in Figure 20-4). Since the range in different lithologies of the exotic blocks of Ring Mountain varies greatly, this reflects varying the metamorphic P-T conditions. Discussed in this work are primarily the highest grade blocks such as the amphibolites, blueschists and eclogites, as they form the maximum limit in P-T space from where these blocks were exhumed (Wakabayashi, 1992; Wakabayashi, 1999; Tsujimori et al., 2006a).

156

The US Cordillera Excursion 2015

Figure 20-3. Geological map of the Tiburon Peninsula (after Wakabayashi, 1990). The points (A, B, C) situated on Ring Mountain represent sample localities from Tsujimori et al. (2006a) where he sampled 3 different exotic eclogite blocks.

Figure 20-4. Detailed map showing the different blocks and the type of the subduction matrix on Ring Mountain (after Wakabayashi, 2012). 157

The US Cordillera Excursion 2015

Tectonic and temporal models of Franciscan subduction Figure 20-5 (a) Prior to 175 Ma subduction of the Farallon plate is initiated (see fig. 4), this is responsible for some of the magmatism further into the North American plate and the subduction of an Andean Type arc is structurally bound by the Coast Range Ophiolite (CRO) (Wakabayashi 1999; Ernst 2015). Figure 20-5 (b) At roughly 150 Ma to 140 Ma the high-grade meta-basalts migrate upwards between the down going Farallon plate and the overriding North American plate (see Figure 20-4). The high grade blocks were probably transported in more buoyant serpentinized harzburgites; this is evident from rims of actinolite in the high grade blocks, clearly indicating that the high grade blocks were in contact with the hydrated mantle wedge (Shervais, 2011; Ernst 2015). Figure 20-6 (a & b) Around 90 Ma (late cretaceous) the subduction changes from a steep angle to a shallow angle. This causes more extensive volcanism in the Sierra Nevada and high-grade blocks are scraped of the old plate (CRO) and returned to the surface via serpentinite diapirism or mud-matrix diapirs. When these high-grade blocks reached the surface, erosion weathered these blocks and these high-grade metamafic rocks were subsequently transported as conglomerates and olistostromes into the Franciscan trench. This way the older Jurassic high-grade blocks end up situated as exotic xenoliths in the cretaceous sedimentary and metasedimentary units (Wakabayashi, 2012; Ernst 2015).

Figure 20-5. (a & b). Tectonic and temporal model of Franciscan subduction from roughly 165Ma in (a), and around 150 to 140 Ma in (b). Figure from Ernst, 2015.

158

The US Cordillera Excursion 2015

Figure 20-6.(a & b). At 90 Ma the subduction changes angle (from steep to shallow). Dehydration melting and that the subducting plate comes in contact with hot asthenosphere causes igneous activity inland (Sierran flare-up). In the subduction channel return flow scrapes of the high-grade metamafic rocks and erosion puts them in the younger sedimentary/metasedimentary rocks in the subduction trench. Figure from Ernst, 2015.

New insights into the P-T-t-paths of the high-grade blocks The mineralogy of three eclogites (labeled A, B and C in Figure 20-3) from Ring Mountain were studied in detail by Tsujimori et al. (2006a) and their mineralogy varies substantially. All high-grade blocks studied show significant changes in mineralogy that can be linked to deformation and/or replacement textures. Sample A is a garnet-amphibolite with some eclogitic mineral assemblages and a later blueschist-facies overprinting (see Figure 20-7). The garnets in sample A are partially chloritized and have a compositional zoning where modal percentage of Mg in the garnet increases towards the rim, but are mostly of almandine composition. Furthermore sample B is a less retrograded eclogite that contain considerably more modal volume of omphacite and some phengite (a compositional variety of muscovite with the chemical formula K(AlMg)2(Si,Al)4O10(OH)2) (Ahn et al., 1985; Tsujimori et al., 2006a). Garnets in sample B show wider spread in Mg contents from rim to core, and both sample A and B show a high Si per unit formula (p.u.f) at about 3.39 to 3.47 Si. Sample C is a garnet blueschist with relict omphacite and contains mostly glaucophane and chloritized garnet. The most almandine rich garnets are found in sample C and the matrix-phengite have a Si p.u.f of c. 3.27, however phengites as inclusions in garnet show as high Si p.u.f as in sample A or B) (Tsujimori et al., 2006a).

159

The US Cordillera Excursion 2015

Figure 20-7. Photomicrographs of the samples investigated in the study by Tsujimori et al. (2006a). For example, he highlights that sample A (in subpicture d) has omphacite present at the same time as garnet and hornblende, and that the hornblende-rich matrix is foliated from sample A (subpicture b) which supports the theory that these rocks have seen amphibolite facies before eclogite facies previously postulated by Wakabayashi (1990).

Tsujimori et al. (2006a) further looked into major element composition of the mineral phases and additionally obtained new K-Ar ages on phengite and hornblende from sample A. These ages: 153±3.3 Ma for phengite and 153±7.5 Ma for hornblende agree well with the previously established peak metamorphic age of 153±0.6 Ma from Lu-Hf on garnet from the same block (Anczkiewicz et al., 2004). Tsujimori et al. (2006a) interprets the modelling of the P-T conditions (from the major element mineral chemistry on garnet, clinopyroxene and phengite, see Figure 20-8) that the pressure for the peak eclogite stage must have been between 2.3 to 2.6 GPa in all three samples at 550 - 620 °C using the thermobarometric relationships established by Krogh et al. (2004). Furthermore, Tsujimori et al. (2006a) estimated the P-T conditions with the aid of THERMOCALC applied to the Grt+Omp+Hbl+Ep+Phe+Pg system, these calculations yielded very similar results, and are limited towards higher pressure by the Paragonite = Jadeite + Kyanite + H2O reaction. Blueschist-facies overprint is characterized by Chl+Gln±Ab and THERMOCALC calculations on this assemblage constrain the P to 0.8 GPa at around 350 °C. These estimations on P-T conditions coupled to age information of both the eclogite-facies (153.4 Ma) and blueschist-facies (146.7 Ma) suggest that these high-grade blocks must have been exhumed at a rate of about 34km in 6 Ma, which is a rate of about 5 km/Ma, rates that are similar to ultra-high-pressure terranes. Mechanisms behind such a high exhumation rate are poorly understood but forearc serpentinite mud volcanism could be one such mechanism (Fryer et al., 2000; Tsujimori et al., 2006a).

160

The US Cordillera Excursion 2015

Figure 20-8. P-T diagram showing the eclogite-facies conditions for the three samples from THERMOCALC, the gray arrows indicate older studies from Wakabayashi (1999). Figure from Tsujimori et al. (2006a)

References

Ahn, J. H., Peacor, D. R., & Essene, E. J. (1985). Coexisting paragonite-phengite in blueschist eclogite; a TEM study. American Mineralogist, 70(11-12), 1193-1204. Anczkiewicz, R., Platt, J. P., Thirlwall, M. F., & Wakabayashi, J. (2004). Franciscan subduction off to a slow start: evidence from high-precision Lu–Hf garnet ages on high grade- blocks. Earth and Planetary Science Letters, 225(1), 147-161. Coleman, R. G., & Lanphere, M. A. (1971). Distribution and age of high-grade blueschists, associated eclogites, and amphibolites from Oregon and California. Geological Society of America Bulletin, 82(9), 2397-2412. Coleman, R. G., Lee, D. E., Beatty, L. B., & Brannock, W. W. (1965). Eclogites and eclogites: their differences and similarities. Geological Society of America Bulletin, 76(5), 483-508. Crawford, W. A., & Fyfe, W. S. (1965). Lawsonite equilibria. American Journal of Science, 263(3), 262-270. Ernst, W. G. (1993). Metamorphism of Franciscan tectonostratigraphic assemblage, Pacheco Pass area, east-central Diablo Range, California coast ranges. Geological Society of America Bulletin, 105(5), 618-636. Ernst, W. G. (2015). Franciscan geologic history constrained by tectonic/olistostromal high- grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex. American Mineralogist, 100(1), 6-13. Fryer, P., Lockwood, J. P., Becker, N., Phipps, S., & Todd, C. S. (2000). Significance of serpentine mud volcanism in convergent margins. SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA, 35-52. Krogh Ravna, E. J., & Terry, M. P. (2004). Geothermobarometry of UHP and HP eclogites and schists–an evaluation of equilibria among garnet–clinopyroxene–kyanite–phengite– 161

The US Cordillera Excursion 2015

coesite/quartz. Journal of metamorphic Geology, 22(6), 579-592. Maruyama, S., & Liou, J. G. (1988). Petrology of Franciscan metabasites along the jadeite- glaucophane type facies series, Cazadero, California. Journal of Petrology, 29(1), 1-37. Ransome, F.L. (1894) On lawsonite, a new rock forming mineral from the Tiburon Peninsula, Marin County, California. Univ California Dept Geol Sci Bull 1, 301-312 Shervais, J. W. (1987). Island arc and ocean crust ophiolites; contrasts in the petrology, geochemistry and tectonic style of ophiolite assemblages in the California Coast Ranges. In Ophiolites: oceanic crustal analogues. Proc Symp Troodos (pp. 507-520). Shervais, J. W., Choi, S. H., Sharp, W. D., Ross, J., Zoglman-Schuman, M., & Mukasa, S. B. (2011). Serpentinite matrix mélange: Implications of mixed provenance for mélange formation. Geological Society of America Special Papers, 480, 1-30. Tsujimori, T., Matsumoto, K., Wakabayashi, J., & Liou, J. G. (2006a). Franciscan eclogite revisited: Reevaluation of the P–T evolution of tectonic blocks from Tiburon Peninsula, California, USA. Mineralogy and Petrology, 88(1-2), 243-267. Tsujimori, T., Sisson, V. B., Liou, J. G., Harlow, G. E., & Sorensen, S. S. (2006b). Petrologic characterization of Guatemalan lawsonite eclogite: Eclogitization of subducted oceanic crust in a cold subduction zone. Geological Society of America Special Papers, 403, 147- 168. Wakabayashi, J. (1990). Counterclockwise PTt paths from amphibolites, Franciscan Complex, California: Relics from the early stages of subduction zone metamorphism. The Journal of Geology, 657-680. Wakabayashi, J. (1992). Nappes, tectonics of oblique plate convergence, and metamorphic evolution related to 140 million years of continuous subduction, Franciscan Complex, California. The Journal of Geology, 19-40. Wakabayashi, J. (1999). Subduction and the rock record: Concepts developed in the Franciscan Complex, California. Classic Cordilleran concepts: A view from California: Geological Society of America Special Paper, 338, 123-133. Wakabayashi, J. (2011). Mélanges of the Franciscan Complex, California: Diverse structural settings, evidence for sedimentary mixing, and their connection to subduction processes. Geological Society of America Special Papers, 480, 117-141. Wakabayashi, J. (2012). Subducted sedimentary serpentinite mélanges: Record of multiple burial–exhumation cycles and subduction erosion. Tectonophysics, 568, 230-247. Wakabayashi, J., & Moores, E. M. (1988). Evidence for the collision of the Salinian block with the Franciscan subduction zone, California. The Journal of Geology, 245-253.

162