DOCSLIB.ORG

Quantifying Rock Uplift Rates Using Channel Steepness and Cosmogenic Nuclide–Determined Erosion Rates: Examples from Northern and Southern Italy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Quantifying Rock Uplift Rates Using Channel Steepness and Cosmogenic Nuclide–Determined Erosion Rates: Examples from Northern and Southern Italy Quantifying rock uplift rates using channel steepness and cosmogenic nuclide–determined erosion rates: Examples from northern and southern Italy Andrew J. Cyr1,†, Darryl E. Granger1, Valerio Olivetti2, and Paola Molin2 1DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES, PURDUE UNIVERSITY, 550 STADIUM MALL DRIVE, WEST LAFAYETTE, INDIANA 47907, USA 2DIPARTIMENTO DI SCIENZE GEOLOGICHE, UNIVERSITÀ DEGLI STUDI “ROMA TRE,” LARGO SAN LEONARDO MURIALDO 1, 00146 ROME, ITALY ABSTRACT Rock uplift rates can be diffi cult to measure over 103–105 yr time scales. If, however, a landscape approaches steady state, where hillslope erosion and rock uplift rates are steady and locally similar, then it should be possible to quantify rock uplift rates from hillslope erosion rates. Here, we test this prediction by comparing channel steepness index values and 10Be catchment-averaged erosion rates to well-constrained rock uplift rates in two landscapes in Italy. The fi rst fi eld area is the Romagna Apennines, northern Italy, where rock uplift rates are relatively uniform, between 0.2 and 0.5 mm/yr (regional mean 0.40 ± 0.15 [SE] mm/yr), and have been steady since 0.9 Ma. The second area is the region around northeastern Sicily and the southernmost Italian peninsula, where rock uplift rates are higher and exhibit a strong spatial gradient, from ~0.7 to ~1.6 mm/yr (regional mean 1.09 ± 0.13 [SE] mm/yr). In both regions, channel steepness indices and 10Be erosion rates vary directly with rock uplift rates. Although there is considerable variability in erosion rates, regionally averaged rates in both the northern (0.46 ± 0.04 [SE] mm/yr) and southern (1.21 ± 0.24 [SE] mm/yr) areas accurately measure rock uplift rates. Although channel steepness indi- ces do not quantify rock uplift rates, they are useful for (1) identifying regional patterns of rock uplift, (2) identifying areas where uplift rates might be expected to be uniform, and (3) informing 10Be sampling strategies. This study demonstrates that, together, channel steepness and hillslope erosion rates can provide a powerful tool for determining rock uplift rates. LITHOSPHERE; v. 2; no. 3; p. 188–198, Data Repository 2010137. doi: 10.1130/L96.1 INTRODUCTION races require the assumption that river incision cators of rock uplift rates in a place where uplift is equilibrated with rock uplift, yet strath forma- rates are known independently. Knowing the distribution of rock uplift tion is often attributed to climatic fl uctuations, In the following section, we briefl y intro- rates across a landscape is important for iden- making it diffi cult to distinguish climatic from duce the use of channel steepness index and tifying and understanding active tectonic struc- tectonic causes of river incision (e.g., Pazza- erosion rate to determine rock uplift rates, with tures, and for establishing the pace and pattern glia and Gardner, 1993; Merritts et al., 1994; an emphasis on the assumptions and conditions of mountain growth. Rock uplift rates can be Hancock et al., 1999; Wegmann and Pazzaglia, necessary for their success. Channel steepness determined geodetically over short (100–102 yr) 2002; Pan et al., 2003). index is a measure of stream-channel gradi- time scales, or inferred from thermochrono- Alternative methods for inferring local- to ent normalized to drainage area (see Wobus et meters over much longer (106 yr) time scales. regional-scale rock uplift rates, such as stream- al., 2006), and it has been shown to be directly Over intermediate (103–105 yr) time scales, channel morphometry and catchment-averaged proportional to rock uplift rates in a variety of rock uplift rates can be inferred from uplifted erosion rates, have become increasingly used to landscapes (e.g., Snyder et al., 2000; Lague and geomorphic markers such as marine or fl uvial measure relative differences in rock uplift rates Davy, 2003; Duvall et al., 2004). We measured terraces, provided that their ages can be deter- across a region (Lague et al., 2000; Kirby and erosion rates using cosmogenic 10Be in quartz, mined. Each of these methods provides impor- Whipple, 2001; Kobor and Roering, 2004; Fer- which is produced in proportion to the residence tant constraints but also suffers from limitations. rier et al., 2005; Wobus et al., 2005, 2006; Kirby time of mineral grains in the uppermost few Geodetic measurements only incorporate a frac- et al., 2007). These methods are widely applica- meters of Earth’s surface. We then applied both tion of the seismic cycle and are limited to sites ble; however, they implicitly assume a landscape of these methods to two different landscapes in with existing surveys and where uplift rates are in steady state or dynamic equilibrium, in which Italy, where rock uplift rates are known indepen- rapid enough to be measured precisely. Thermo- erosion and river incision are equal to rock uplift. dently from marine terrace stratigraphy. chronology indicates the time taken to exhume This assumption is diffi cult to test. Nevertheless, rocks by kilometers and cannot typically resolve both channel steepness index, a proxy for river Channel Steepness Index shorter-term patterns. Uplifted fl uvial strath ter- incision rate, and cosmogenic nuclide–deter- mined erosion rates have become widely used Bedrock river channel steepness index can †Present address: U.S. Geological Survey, 345 with at least qualitative success. What remains be used to infer relative differences in rock uplift Middlefi eld Road, Menlo Park, California 94025, USA; to be demonstrated is a quantitative test of both rates across a landscape, given uniform lithol- e-mail: [email protected]. channel steepness index and erosion rate as indi- ogy and climatic forcing. River incision, E, is 188 For permission to copy, contact [email protected] | |Volume © 2010 2 Geological | Number Society3 | LITHOSPHERE of America Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/2/3/188/3044578/188.pdf by guest on 02 October 2021 Quantifying rock uplift rates using channel steepness and erosion rates | RESEARCH often cast as a function of basal shear stress, and 1999) and empirical (Howard and Kerby, 1983; ~80% of rock uplift, and in an orogen main- can be expressed as (Howard and Kerby, 1983; Tarboton et al., 1991; Snyder et al., 2000) argu- taining a constant elevation, erosion must equal Howard et al., 1994), ments, their ratio (θ) should be between 0.35 rock uplift (Molnar and England, 1990). In these and 0.6. cases, a measure of spatially averaged erosion E = KAmn S , (1) Channel steepness index can be obtained by rates over time scales of 103 to 105 yr should either surveying stream channels or by regres- closely correspond to the regionally averaged where S is local channel slope, A is the contrib- sion of local channel slopes and drainage areas rock uplift rate. uting drainage area that serves as a proxy for obtained from digital elevation models (e.g., Spatially averaged erosion rates can be esti- local discharge, K is a variable that incorpo- Wobus et al., 2006). Provided that K and n are mated using cosmogenic nuclides such as 10Be rates incision process–, substrate-, climate-, and uniform across the region of interest, then varia- in quartz-bearing alluvial sediment (Brown et hydrology-dependent variables (see Whipple, tions in ks among channels or channel segments al., 1995; Bierman and Steig, 1996; Granger et 2004), and m and n are positive constants that will track variations in uplift rate (Whipple and al., 1996). Beryllium-10 accumulates in quartz are functions of basin hydrology, channel geom- Tucker, 1999; Snyder et al., 2000). It is diffi cult near Earth’s surface proportional to its local etry, and specifi c incision process (Howard et to solve for rock uplift rates directly, because K production rate and inversely proportional to the al., 1994; Whipple and Tucker, 1999; Whipple is poorly constrained. For example, Stock and surface erosion rate. The cosmogenic nuclide et al., 2000a). Montgomery (1999) suggested that K may vary method averages erosion rates over the time The change in channel bed elevation at any over several orders of magnitude due to spatial required to erode a catchment by about one point along the longitudinal profi le with respect differences in rock properties, as well as due to secondary cosmic-ray penetration length, or to time, dz/dt, refl ects a competition between the frequency of discharge events signifi cant ~60 cm in rock of density 2.6 g/cm3 (Masarik the rates of rock uplift and channel incision with enough to initiate bedrock incision. Addition- and Reedy, 1995). In most landscapes, this is 3 5 respect to base level. This can be expressed as, ally, in order for ks to indicate relative changes in anywhere from 10 to 10 yr. rock uplift rates, the channel longitudinal profi le Several conditions must be met for cosmo- dz =−=− mn dt UEUKAS, (2) must be in steady state and refl ect the current genic nuclides to accurately indicate catch- climatic and tectonic conditions. Both U and K ment-averaged erosion rates. Quartz must be where U is the rock uplift rate. For a steady-state must be uniform along the entire channel length. distributed evenly throughout the catchment, landscape, where river incision rate is equal to Empirical support for a correlation between or else erosion rates will be biased to areas of the rock uplift rate, dz/dt = 0, and Equation 2 can channel steepness index and rock uplift rates higher quartz content. Sediment samples must be solved for equilibrium channel slope, S, at a is emerging from multiple landscapes around be representative of the entire watershed, rather given drainage area, A, the globe. In two regions of coastal Califor- than be dominated by a single landslide.
Load more

Recommended publications
  • The Rock Cycle Compressed and Cemented to Form What the Original Rocks on Earth Were Like
    | The Rock Cycle compressed and cemented to form what the original rocks on Earth were like. sedimentary rock, such as sandstone. IMMG has some excellent examples of Soluble material can be precipitated from these extraterrestrial visitors in our The continual set of processes affecting water to form sedimentary rocks such as meteorite exhibit. rocks is called the rock cycle. All existing limestone and gypsum. Sedimentary rocks rocks on Earth have been changed over can also be exposed at the surface and Various examples of the three different time by various geologic processes. Earth undergo erosion, providing materials for types of rocks are listed below. Specimens was formed about 4.6 billion years ago, and future sedimentary rocks. of some of these rocks can be found the oldest known rock unit is found in throughout the museum. Canada, dated at just over 4 billion years If sedimentary rocks become buried deep old. This rock material was altered by heat within the crust, they can be subjected to How many can you find? and pressure into the metamorphic rock high heat and pressure along with physical gneiss. stresses such as compression or extension, Igneous which transforms them into metamorphic rocks such as schist or gneiss Originally all of Earth’s crustal rocks had Basalt Gabbro Diorite an igneous origin. They start as semi- (“metamorphic” simply means “changed molten magma in the upper mantle and form”). Sometimes igneous rocks can be Rhyolite Syenite Andesite either rise to the surface as extrusive lava metamorphosed by similar processes (like Granite Granodiorite Obsidian (like basalt) in volcanoes and oceanic rifts, granite into gneiss).
    [Show full text]
  • Exhumation Processes
    Exhumation processes UWE RING1, MARK T. BRANDON2, SEAN D. WILLETT3 & GORDON S. LISTER4 1Institut fur Geowissenschaften,Johannes Gutenberg-Universitiit,55099 Mainz, Germany 2Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA 3Department of Geosciences, Pennsylvania State University, University Park, PA I 6802, USA Present address: Department of Geological Sciences, University of Washington, Seattle, WA 98125, USA 4Department of Earth Sciences, Monash University, Clayton, Victoria VIC 3168,Australia Abstract: Deep-seated metamorphic rocks are commonly found in the interior of many divergent and convergent orogens. Plate tectonics can account for high-pressure meta­ morphism by subduction and crustal thickening, but the return of these metamorphosed crustal rocks back to the surface is a more complicated problem. In particular, we seek to know how various processes, such as normal faulting, ductile thinning, and erosion, con­ tribute to the exhumation of metamorphic rocks, and what evidence can be used to distin­ guish between these different exhumation processes. In this paper, we provide a selective overview of the issues associated with the exhuma­ tion problem. We start with a discussion of the terms exhumation, denudation and erosion, and follow with a summary of relevant tectonic parameters. Then, we review the charac­ teristics of exhumation in differenttectonic settings. For instance, continental rifts, such as the severely extended Basin-and-Range province, appear to exhume only middle and upper crustal rocks, whereas continental collision zones expose rocks from 125 km and greater. Mantle rocks are locally exhumed in oceanic rifts and transform zones, probably due to the relatively thin crust associated with oceanic lithosphere.
    [Show full text]
  • Sedimentological Constraints on the Initial Uplift of the West Bogda Mountains in Mid-Permian
    www.nature.com/scientificreports OPEN Sedimentological constraints on the initial uplift of the West Bogda Mountains in Mid-Permian Received: 14 August 2017 Jian Wang1,2, Ying-chang Cao1,2, Xin-tong Wang1, Ke-yu Liu1,3, Zhu-kun Wang1 & Qi-song Xu1 Accepted: 9 January 2018 The Late Paleozoic is considered to be an important stage in the evolution of the Central Asian Orogenic Published: xx xx xxxx Belt (CAOB). The Bogda Mountains, a northeastern branch of the Tianshan Mountains, record the complete Paleozoic history of the Tianshan orogenic belt. The tectonic and sedimentary evolution of the west Bogda area and the timing of initial uplift of the West Bogda Mountains were investigated based on detailed sedimentological study of outcrops, including lithology, sedimentary structures, rock and isotopic compositions and paleocurrent directions. At the end of the Early Permian, the West Bogda Trough was closed and an island arc was formed. The sedimentary and subsidence center of the Middle Permian inherited that of the Early Permian. The west Bogda area became an inherited catchment area, and developed a widespread shallow, deep and then shallow lacustrine succession during the Mid- Permian. At the end of the Mid-Permian, strong intracontinental collision caused the initial uplift of the West Bogda Mountains. Sedimentological evidence further confrmed that the West Bogda Mountains was a rift basin in the Carboniferous-Early Permian, and subsequently entered the Late Paleozoic large- scale intracontinental orogeny in the region. The Central Asia Orogenic Belt (CAOB) is the largest accretionary orogen on Earth, which was formed by the amalgamation of multiple micro-continents, island arcs and accretionary wedges1–5.
    [Show full text]
  • Layer Cake Geology
    LAYER CAKE GEOLOGY John R. Wagner Department of Earth Sciences Clemson University Clemson, S.C. 29634-1908 Level: Grades 4 - 6 Can be modified for use with Grades 2 - 3. Estimated Time Required: 50 - 60 minutes Anticipated Learning Outcomes • Students will understand the mechanisms by which folds and faults occur within the earth's crust. • Students will recognize the difference in behavior between brittle and ductile rocks. • Students will predict the structure likely to result from application of various forces to layered rocks. • Students will interpret "core samples" to determine rock structures beneath the land surface. • Students will learn the meaning of the following geologic terms: fold, fault, brittle, ductile, fracture, and core samples. Background No prior knowledge of geology is required. However, the teacher should introduce the two basic concepts of layered rock: superposition (oldest layer at bottom, youngest at top) and original horizontality (sediments deposited in horizontal layers until some force changes their tilt or orientation). Materials • Multiple-layer cake prepared according to the following instructions: 1. Use moist pound cake (or other dense, coherent cake) mix. (One mix is sufficient for whole class activity if layers are made thin enough.) 2. Bake four to six thin cakes, (each between 0.5 and 2.0 cm thick), each a different color (mix in food coloring before baking). Use square or rectangular pans. 3. Stack the cakes in any order. Apply icing (of any kind) between the layers but not on the top or sides of the cake. • Knife for cutting cake • Three transparent plastic tubes (diameter between 1 and 2 centimeters) at least as long as the cake is high.
    [Show full text]
  • Gober Paleoclimatology Presentation.Pptx
    3/8/15 Objective Uplift of Tibetan Plateau v Use Paleoarchives from the Tibetan Plateau to support the uplift weathering hypothesis for global cooling as Active Driver for over the last 50 million years Cenozoic Climate Change v Hypothesis: The uplift of the Tibetan Plateau is an active driver for global cooling of the Cenozoic period By Roslyn Gober 11 February 2015 onebigphoto.com/stunning-dolomites-mountains-italy/ Cenozoic Period Cenozoic: CO2 & Climate Change Global Atmospheric Cooling CO Levels 2 v Atmospheric CO2 and global temperature decline Uplift Weathering Hypothesis v Clear relationship between climate and atmospheric CO Tibetan 2 Plateau v Need to identify driver of atmospheric CO2 removal Extensive Physical Chemical High Terrain Weathering Weathering (Beerling, 2011) 1 3/8/15 Cenozoic: Icehouse Climate Uplift Weathering Hypothesis v Benthic foraminifera Uplift is the cause of large-scale climate changes, δ18O measurements through both direct physical impacts and indirect over last 70 Myr biochemical effects v Trend toward more v Proposed by Maureen Raymo in the late 1980’s positive values of δ18O v Physical impact v Progressive cooling of deep ocean v Changes in circulation of atmosphere and ocean v Continental ice sheet v Chemical impact growth v Drawdown of atmospheric CO2 is a result of chemical weathering of silicate rocks (Raymo, 1992) (Ruddiman, 1997) Uplift Weathering Hypothesis Uplift Weathering Hypothesis Positive Feedback Negative Feedback (Ruddiman, 2014) (Ruddiman, 2014) 2 3/8/15 Criteria for Uplift Weathering Extensive High Terrain: Tibetan Plateau 1) Extensive High Terrain v Collision between India v Must be proven to be uniquely high compared to past and Asia created most geologic eras extensive plateau on Earth v 55 Myr ago 2) Unusual Physical Weathering v 2.5 million km2 v High terrain must be causing large amounts of rock fragmentation v Avg.
    [Show full text]
  • Geochemical and Tectonic Uplift Controls on Rock Nitrogen Inputs
    PUBLICATIONS Global Biogeochemical Cycles RESEARCH ARTICLE Geochemical and tectonic uplift controls on rock 10.1002/2015GB005283 nitrogen inputs across terrestrial ecosystems Key Points: Scott L. Morford1, Benjamin Z. Houlton1, and Randy A. Dahlgren1 • Surficial sedimentary and metasedimentary rocks host large N 1Department of Land, Air and Water Resources, University of California, Davis, California, USA reservoirs • Lithology and tectonics strongly fl in uence rock N erosion and input > ’ rates in terrestrial ecosystems Abstract Rock contains 99% of Earth s reactive nitrogen (N), but questions remain over the direct • Rock N fluxes can exceed atmospheric importance of rock N weathering inputs to terrestrial biogeochemical cycling. Here we investigate the factors N inputs among denuding landscapes that regulate rock N abundance and develop a new model for quantifying rock N mobilization fluxes across desert to temperate rainforest ecosystems in California, USA. We analyzed the N content of 968 rock samples Supporting Information: from 531 locations and compiled 178 cosmogenically derived denudation estimates from across the region to • Data Set S1 identify landscapes and ecosystems where rocks account for a significant fraction of terrestrial N inputs. • Figure S1 and Tables S1–S5 Strong coherence between rock N content and geophysical factors, such as protolith, (i.e. parent rock), grain Correspondence to: size, and thermal history, are observed. A spatial model that combines rock geochemistry with lithology and À À S. L. Morford, topography demonstrates that average rock N reservoirs range from 0.18 to 1.2 kg N m 3 (80 to 534 mg N kg 1) À [email protected] across the nine geomorphic provinces of California and estimates a rock N denudation flux of 20–92 Gg yr 1 À across the entire study area (natural atmospheric inputs ~ 140 Gg yr 1).
    [Show full text]
  • Sedimentology, Petrography, and Tectonic Significance of Cretaceous to Lower Tertiary Deposits in the Tingri -Gyangtse Area, Southern Tibet
    University at Albany, State University of New York Scholars Archive Geology Theses and Dissertations Atmospheric and Environmental Sciences 2003 Sedimentology, petrography, and tectonic significance of Cretaceous to Lower Tertiary deposits in the Tingri -Gyangtse area, southern Tibet Bin Zhu University at Albany, State University of New York Follow this and additional works at: https://scholarsarchive.library.albany.edu/cas_daes_geology_etd Recommended Citation Zhu, Bin, "Sedimentology, petrography, and tectonic significance of Cretaceous to Lower Tertiary deposits in the Tingri -Gyangtse area, southern Tibet" (2003). Geology Theses and Dissertations. 114. https://scholarsarchive.library.albany.edu/cas_daes_geology_etd/114 This Dissertation is brought to you for free and open access by the Atmospheric and Environmental Sciences at Scholars Archive. It has been accepted for inclusion in Geology Theses and Dissertations by an authorized administrator of Scholars Archive. For more information, please contact [email protected]. SEDIMENTOLOGY, PETROGRAPHY, AND TECTONIC SIGNIFICANCE OF CRETACEOUS TO LOWER TERTIARY DEPOSITS IN THE TINGRI-GYANGTSE AREA, SOUTHERN TIBET By Bin Zhu A Dissertation Submitted to the University at Albany, State University of New York in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy College of Arts & Sciences Department of Earth & Atmospheric Sciences 2003 Abstract Cretaceous and Lower Tertiary sedimentary rocks are well exposed in the Tingri- Gyangtse area, tectonically belonging to the central Tibetan Himalayas, to the south of the Indus-Yarlung-Zangbo suture. The Cretaceous Tianba flysch in the Tianba-Jiabula region is correlative with the Giumal Group sandstone in Zanskar, northwestern Himalayas. There are significant amounts of chrome-rich spinels in turbiditic sandstones from the upper part of Tianba Flysch, which might suggest ophiolite derivation and a Cretaceous ophiolite obduction event on the northern Indian continental margin in southern Tibet.
    [Show full text]
  • Crustal Uplift and Subsidence Due to the Interaction Between Tectonic and Surface Processes – an Integrated 3D Numerical Approach for Spatial Quantification
    Crustal uplift and subsidence due to the interaction between tectonic and surface processes – an integrated 3D numerical approach for spatial quantification Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN von der Fakult¨at fur¨ Physik der Universit¨at Karlsruhe (TH) genehmigte DISSERTATION von Diplom-Physiker Daniel Kurfeß aus Karlsruhe Tag der mundlichen¨ Prufung:¨ 5. Dezember 2008 Referent: Prof. Dr. Friedemann Wenzel Korreferent: Prof. Dr. Karl Fuchs Crustal uplift and subsidence due to the interaction between tectonic and surface processes – an integrated 3D numerical approach for spatial quantification by Daniel Kurfeß (E-mail: [email protected]) Geophysikalisches Institut, Universit¨at Karlsruhe (TH) 5 Contents Abstract 9 1 Introduction 11 1.1 Motivation.............................. 11 1.2 Objectivesofthisthesis . 13 2 Theoretical foundations 17 2.1 Upliftandsubsidence. 17 2.1.1 Feedback between tectonic and surface processes . 18 2.1.2 Orders of crustal displacement rates . 19 2.1.3 Definition of “uplift” and “subsidence” . 20 2.2 Isostasyanderosion......................... 21 2.2.1 Simpleerosionmodels . 21 2.2.2 Localisostasy ........................ 22 2.2.3 Regional isostasy . 23 2.3 Numerical landscape evolution modeling . 25 2.3.1 FE modeling with ABAQUS/StandardTM ........ 27 2.3.2 Surfaceprocessesmodeling. 30 6 CONTENTS 3 Coupled simulation integrating surface processes modeling and geomechanical FE modeling 35 3.1 Technique .............................. 35 3.2 Benchmarkmodels ......................... 39 3.2.1 ModelA(flexure). 39 3.2.2 ModelB(feedback). 42 3.3 Discussion.............................. 46 3.3.1 Limitations ......................... 47 3.3.2 Capabilities ......................... 47 4 Feedback process study 49 4.1 Impact of isostatic tectonic response . 49 4.2 Modelsetup............................. 50 4.3 Resultsanddiscussion ......................
    [Show full text]
  • Strong Tectonic and Weak Climatic Control of Long-Term Chemical Weathering Rates
    Strong tectonic and weak climatic control of long-term chemical weathering rates Clifford S. Riebe* James W. Kirchner Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA Darryl E. Granger Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, USA Robert C. Finkel Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94551, USA ABSTRACT The relationships among climate, physical erosion, and chemical weathering have remained uncertain, because long-term chemical weathering rates have been dif®cult to measure. Here we show that long-term chemical weathering rates can be measured by combining physical erosion rates, inferred from cosmogenic nuclides, with dissolution loss- es, inferred from the rock-to-soil enrichment of insoluble elements. We used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates. Chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate, implying that, by reg- ulating erosion rates, tectonic uplift may signi®cantly accelerate chemical weathering rates in granitic landscapes. Keywords: geochemical mass balance, cosmogenic nuclides, chemical weathering rates, climate. INTRODUCTION AND METHODOLOGY and soil erosion can be assumed to be negligible, long-term chemical Physical erosion and chemical weathering are interrelated pro- weathering rates can be measured using soil mass-balance techniques cesses (Stallard and Edmond, 1983) that together regulate soil depth (April et al., 1986). According to the mass-balance approach, as the and development, deliver sediment and solutes to aquatic habitats, and relatively soluble minerals in soils dissolve away, the more immobile shape mountainous landscapes.
    [Show full text]
  • How Erosion Builds Mountains
    How Erosion Builds Mountains An understanding of how tectonic, erosional and climatic forces interact to shape mountains permits clearer insights into the earth’s history Nicholas Pinter and Mark T. Brandon ountains are far more erosion. In particular, the interactions for earth science. To a geologist, the massive than all human between tectonic, climatic and erosional earth’s plains, canyons and, especially, M structures combined and processes exert strong control over the mountains reveal the outline of the plan- are sculpted in greater detail than a Ba- shape and maximum height of moun- et’s development over hundreds of mil- roque palace. The world’s tallest pinna- tains as well as the amount of time nec- lions of years. In this sprawling history, cle—Mount Everest in the Himalayas— essary to build—or destroy—a mountain mountains indicate where events in or reaches 8,848 meters, or about 15 times range. Paradoxically, the shaping of just below the earth’s crust, such as the higher than anything people have ever mountains seems to depend as much on collisions of the tectonic plates, have built. Not surprisingly, such spectacular the destructive forces of erosion as on thrust this surface layer skyward. Thus, topography has evoked awe and in- the constructive power of tectonics. In mountains are the most visible manifes- spired artists and adventurers through- fact, after 100 years of viewing erosion tation of the powerful tectonic forces at out human existence. as the weak sister of tectonics, many ge- work and the vast time spans over which Recent research has led to important ologists now believe erosion actually those forces have operated.
    [Show full text]
  • Early to Mid-Cretaceous Tectonics and Unconformities of the Wessex Basin (Southern England)
    Journal of the Geological Society, London, Vol. 149, 1992, pp. 443454, 12 figs. Printed in Northern Ireland Early to mid-Cretaceous tectonics and unconformities of the Wessex Basin (southern England) A. H. RUFFELL Department of Geology, Queen’s University, Belfast, Northern Ireland BT7 INN, UK Abstract: Sediment distribution patterns, time-subsidence plots, seismic data and outcropanalysis of the Lower Cretaceous (?Ryazanian-Albian) of the Wessex Basin, southern England, suggest that a number of unconformablehorizons exist and that there is no single ‘late Cimmerian unconformity’ surface. A tectonic change, from areally restricted deposition in the Weald and Channel sub-basins to extensive sedimentation across the whole of southern England, began in the mid-Aptian. This change ended with transgression of basement ‘highs’ in the early Albian of the Dorset area,and later Albian of the Devon and London Platform basin margin areas: its onset can be linked to the Austrian tectonic phase of Europe. The onset of marine deposition in the Aptian is coincident with periodic transgression of the margins of the Wessex Basin throughout the Aptian-Albian. Mid-late Aptian and early/mid-Albian transgressions were preceded by periods of erosion. The Aptian-Albian Lower Greensand is characterized by transgressive- regressive phases, suggesting a short-term controlling process (third-order eustatic changes or intra-plate mechanisms). Tectonic changes in the mid-Aptian include uplift followed by widespread subsidence. This change coincides with a time of plate reorganization in the European and North Atlantic areas. The Mesozoic Wessex Basin of southern England is a structur- (Drummond 1970; Stoneley 1982). Thus structures such as the ally complexbasin (Whittaker 1985), where a predominant ‘mid-Dorset Swell’ (Drummond 1970, 1982) may also be re- east-west pattern of extensional faults is cut by a seriesof lated to basement faults.
    [Show full text]
  • Uplift and Deformation of Marine Terraces Along the San Andreas Fault; Duncan's Landing to Fort Ross, California Breanyn Macin
    Uplift and Deformation of Marine Terraces Along the San Andreas Fault; Duncan’s Landing to Fort Ross, California Breanyn MacInnes Senior Integrative Exercise March 10, 2004 Submitted in partial fulfillment of the requirements for a Bachelor of Arts degree from Carleton College, Northfield, Minnesota. Table of Contents Abstract Keywords Introduction 1 Figure 1 2 Geological Setting 3 Generation of Marine Terraces 3 Preservation of Marine Terraces 5 Figure 2 6 Figure 3 7 Mapping Marine Terraces ________________________ 8 Figure 4 9 Terrace Identification 10 Figure 5 11 Age Assignment and Uplift Rate 12 Figure 6 13 Figure 7 14 Figure 8 16 Discussion 17 Figure 9 18 Conclusion 20 Acknowledgements 20 References Cited 21 Uplift and Deformation of Marine Terraces Along the San Andreas Fault; Duncan’s Landing to Fort Ross, California Breanyn MacInnes March 10, 2004 Faculty advisors: Dorothy Merritts, Franklin and Marshall College Cameron Davidson, Carleton College Abstract Marine terraces between Fort Ross and Duncan’s Landing, California were used to evaluate uplift and deformation of the coast. Six terraces were mapped using Global Positioning System equipment to record position and elevation. Terraces found at elevations of 25-30 m, 40-50 m, 50-70 m, 90-110 m, 100-120 m, and 150-170 m correlate respectively with 83, 108, 122, 194, 305, and 330 ka sea-level highstands. These results give uplift rates between 0.4 and 0.6 mm/yr along the coast. Because of the variation in uplift rates, originally horizontal terraces now appear to tilt down towards the north. Offset terrace inner edges at the San Andreas Fault indicate that the tilting is due to differential uplift on the fault and offset terrace inner edges at the Russian River suggest that there is an unmapped fault along the river channel.
    [Show full text]