DOCSLIB.ORG

QUATERNARY SEA LEVEL CHANGE in the CARIBBEAN: the IMPLICATIONS for ARCHAEOLOGY Sherri Baker Littman

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
QUATERNARY SEA LEVEL CHANGE in the CARIBBEAN: the IMPLICATIONS for ARCHAEOLOGY Sherri Baker Littman QUATERNARY SEA LEVEL CHANGE IN THE CARIBBEAN: THE IMPLICATIONS FOR ARCHAEOLOGY Sherri Baker Littman ABSTRACT Human habitation of previously subaerial land surfaces is well documented. Geophysical and geological meth­ ods have been applied to elucidate the presence of associated geomorphic features. Records from varved sediments of bottom, anoxic waters yield clues to ancient climate records stored at the bottom of the Cariaco Basin. A sea level curve based upon uranium series (230TH) for Acropora palmata corals off the island of Barbados provides high precision chronology of sea level change since the last glacial maximum. The prograding delta of the Orinoco River has tremendously impacted sites on the island of Trinidad. Tectonic settings, isostasy, coastal hydrodynamics, fluvial and sediment discharge and accumulation rates, along with biostratigraphy and lithos- tratigraphy are necessary to build a valid chronostratigraphy when examining once subaerial archaeological sites. These combined methods provide valuable clues to the "peopling" of the Caribbean and should be employed when searching for prehistoric sites and evaluating settlement models. INTRODUCTION Evidence for Quaternary sea level change has been, at best, tenuous. Since scientific methods for determining sea level change are becoming more widely applied, this scenario is finally beginning to change. Studies show that although sea level has fluctuated eustatically, generalizations regarding specific regions, such as the Caribbean, cannot be made. Hence, this study will briefly examine the regional affects of sea level change on three areas within the Caribbean; the offshore area surrounding the island of Barbados, the Cariaco Basin (offshore Venezuela) and the Orinoco River delta and its affects on the island of Trinidad. Several models used in attempting to gauge sea level have been suc­ cessful, but must be applied on a regional basis. This paper is presented as a model or primer to be used for the purposes of determining the extent of sea level change and what the implications are for prehistoric archaeological sites. The most widely used methods that measure sea level change are varied, but combined, they can help build a valid picture for prehistoric environments. Examining coastal sediment accumula­ tion and erosion is crucial when measuring sea level change. Pollen sampling is another important tool. Marine fossil identification and corals can be used to help build a valid chronostratigraphy, much like dendrochronology. Corals and speleothems exhibit annual growth bands, thus providing calendar year chronologies. However, fossil corals can provide more specific data through C14 and U/TH230 dating. The combination of these methods allows for an accurate reading of sea level trans­ gressions and regressions. Additionally, geophysical methods, such as side scan sonar and sub bot­ tom profiling, can accurately detect prehistoric site locations. The above methods help to 'ground truth' or verify geophysical studies for site localities. 58 It is necessary that local environmental events be considered when predicting the location of archae­ ological sites, which is why regional variations on sea level change are crucial. Global geostrophic events affect gravity, force and pressure on the geoid, thereby resulting in regional variations such as hurricanes, eolian deposition, tectonics, isostasy, subsidence, fluvial sediment accumulation rates and varying ocean currents, such as ENSO (El Nino Southern Oscillation). Since coastal geomorphology throughout the Caribbean varies greatly, a detailed discussion of each regions geologic history is beyond the scope of this paper. Based upon what we do know, both geologically and archaeologically what types of environ­ mental changes occurred that affected island coastlines, resulting in paleoshorelines? What does the location of littoral archaeological sites tell us about sea level, and did sea level fluctuate enough dur­ ing the Quaternary to inundate prehistoric coastal habitation areas? As we can see from present-day settlement patterns, people have always migrated to coastlines. Certainly, during prehistoric periods, an abundance of marine fauna and proximity to waterways were key factors for settlement location. Recent geological and geophysical studies show that that indeed, prehistoric humans settled along now submerged paleo river channels and coastlines. Technically speaking, the late Pleistocene marked the movement of humans into the New World. Recent articles on New World migration suggest that the correlation of radiocarbon dates, cal­ ibrated into calendar years, pushes back earliest settlement date to 13,000 (cal BP). Scientists have retested atmospheric levels of radiocarbon since new evidence has been introduced into the study of paleoclimatology. This new evidence comes from pollen imbedded in Greenland ice cores, in addition to Caribbean corals and sediments from lakebeds that have aided in dating sea level changes. Late Quaternary climate was highly unstable and prone to large, rapid oscillations that occurred with­ in a few decades. This climatic variability was particularly pronounced during the last Ice Age when ice sheets, that covered northern latitudes, led to exposure of the continental shelves. Global climate variations, indicated by Milankovitch and Daansgard/Oescher (D/O) cycles, are primary causes of changes in the geosphere. Additionally, the Great Ocean Conveyor and thermohaline circulation of the North Atlantic cause variations in climate cycles. Milankovitch cycles, confirmed by Greenland ice cores, are gravitational pulls from planets, which have caused subtle changes in the orbit of the Earth. These alterations have resulted in differing intensities of sunlight that lead to dramatic variations in climate. Milankovitch cycles show oscillations in climate roughly every 20, 40 and lOOka and are con­ comitant with glacial and interstadial periods in geologic history. The more obvious intervals are those that occur approximately every lOOka, with the shorter oscillations occurring at 20 and 40ka intervals. Much like Milankovitch cycles that show variations in climate, D/O cycles show warm phas­ es (interstadials). These D/O cycles are punctuated by the cold conditions of the Last Glacial Maximum (LGM) and are demonstrated by their bistable behavior. The Great Ocean Conveyor and thermohaline circulation of the North Atlantic provide valuable data for D/O cycles through the analysis of marine organisms such as benthic formanifiera. These foraminifera show dextral and sinis­ tral coiling of benthic marine organisms (such as N. pachyderma), in response to warming and cool­ ing ocean temperature variations. D/O cycles show that warm, interstadial climates alternated 59 between cool stadial climatic episodes, and resulted in a severely cold Heinrich event approximately 7,200 years ago. These climatic changes do appear to be synchronous between Greenland (shown by ice cores) and the Cariaco Basin off the coast of Venezuela, where annual laminations or varves, can be preserved in both marine and lucustrine sediments. Marine varved chronologies are limited in that they usually only represent fragments of temperature change within the last 80 ka (for example, 9-15 ka ago in the Cariaco Basin). However, lacustrine environments are ideal for preservation for the length of duration of a lakebed. All of these cycles can be used as paleoenvironmental proxies that are vital when attempting to reconstruct and predict the locations of prehistoric archaeological site. METHODS Geophysical methods that help to identify landscapes that were ideal for human settlement involve the use of high resolution acoustic reflection and side scan sonar. Seismic data from these are processed using standard geophysical methods to delineate hard ground surfaces and drainage sys­ tems that were subaerially exposed during the Pleistocene. Side scan sonar is an acoustic technique that records topographic images of the sea floor, thus creating sonogram mosaics. Sonar is a good device for mapping the topography of an area because boulders and rocks are good reflectors. A typical sonar frequency is 100 kHz. However, sonar leaves an acoustic shadow, hence, the need to use an additional method such as sub bottom profiling. This is an acoustic profil­ ing technique (seismic reflection) that is utilized to penetrate the sub-sea floor and then image geo- morphic and geologic features. The technique relies on the contrast of the acoustic impedance of sub- bottom features. For example, sediment layering, outcrops and incised valleys are routinely detected with this method. Most sub-bottom profiling uses a very low frequency, such as 3.5 kHz. The lower the frequency, the better the penetration of the sea floor fades. A higher frequency could give overall accuracy, but would cause rapid attenuation, thus decreasing penetration due to considerable lag time in layers of clay. Basically, the shortest pulse length that does not sacrifice resolution is best. Subsurface investigations of areas presumed to contain cultural deposits can help to determine whether they are allogenic in nature. This is why 'ground truthing' is crucial to any seismic explo­ ration. Coring is the preferred method of 'ground truthing', whether coring is conducted on a terres­ trial landscape or a submerged one. Coring permits the recovery of significant volumes of sediment so that their character can be ascertained without alteration. In addition, coring can isolate
Load more

Recommended publications
  • PHANEROZOIC and PRECAMBRIAN CHRONOSTRATIGRAPHY 2016
    PHANEROZOIC and PRECAMBRIAN CHRONOSTRATIGRAPHY 2016 Series/ Age Series/ Age Erathem/ System/ Age Epoch Stage/Age Ma Epoch Stage/Age Ma Era Period Ma GSSP/ GSSA GSSP GSSP Eonothem Eon Eonothem Erathem Period Eonothem Period Eon Era System System Eon Erathem Era 237.0 541 Anthropocene * Ladinian Ediacaran Middle 241.5 Neo- 635 Upper Anisian Cryogenian 4.2 ka 246.8 proterozoic 720 Holocene Middle Olenekian Tonian 8.2 ka Triassic Lower 249.8 1000 Lower Mesozoic Induan Stenian 11.8 ka 251.9 Meso- 1200 Upper Changhsingian Ectasian 126 ka Lopingian 254.2 proterozoic 1400 “Ionian” Wuchiapingian Calymmian Quaternary Pleisto- 773 ka 259.8 1600 cene Calabrian Capitanian Statherian 1.80 Guada- 265.1 Proterozoic 1800 Gelasian Wordian Paleo- Orosirian 2.58 lupian 268.8 2050 Piacenzian Roadian proterozoic Rhyacian Pliocene 3.60 272.3 2300 Zanclean Kungurian Siderian 5.33 Permian 282.0 2500 Messinian Artinskian Neo- 7.25 Cisuralian 290.1 Tortonian Sakmarian archean 11.63 295.0 2800 Serravallian Asselian Meso- Miocene 13.82 298.9 r e c a m b i n P Neogene Langhian Gzhelian archean 15.97 Upper 303.4 3200 Burdigalian Kasimovian Paleo- C e n o z i c 20.44 306.7 Archean archean Aquitanian Penn- Middle Moscovian 23.03 sylvanian 314.6 3600 Chattian Lower Bashkirian Oligocene 28.1 323.2 Eoarchean Rupelian Upper Serpukhovian 33.9 330.9 4000 Priabonian Middle Visean 38.0 Carboniferous 346.7 Hadean (informal) Missis- Bartonian sippian Lower Tournaisian Eocene 41.0 358.9 ~4560 Lutetian Famennian 47.8 Upper 372.2 Ypresian Frasnian Units of the international Paleogene 56.0 382.7 Thanetian Givetian chronostratigraphic scale with 59.2 Middle 387.7 Paleocene Selandian Eifelian estimated numerical ages.
    [Show full text]
  • A Middle to Late Holocene Record of Arroyo Cut-Fill Events
    A MIDDLE TO LATE HOLOCENE RECORD OF ARROYO CUT-FILL EVENTS IN KITCHEN CORRAL WASH, SOUTHERN UTAH by William M. Huff A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Geology Approved: _________________________ _________________________ Dr. Tammy M. Rittenour Dr. Joel L. Pederson Major Professor Committee Member _________________________ _________________________ Dr. Patrick Belmont Dr. Mark R. McLellan Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2013 ii Copyright © William M. Huff 2013 All Rights Reserved iii ABSTRACT A Middle to Late Holocene Record of Arroyo Cut-Fill Events in Kitchen Corral Wash, Southern Utah by William M. Huff, Master of Science Utah State University, 2013 Major Professor: Dr. Tammy M. Rittenour Department: Geology This study examines middle to late Holocene episodes of arroyo incision and aggradation in the Kitchen Corral Wash (KCW), a tributary of the Paria River in southern Utah. Arroyos are entrenched channels in valley-fill alluvium, and are capable of capturing decadal- to centennial- scale fluctuations in watershed hydrology as evidenced by the Holocene cut-fill stratigraphy recorded within near-vertical arroyo-channel walls. KCW has experienced both historic (ca. 1880-1920 AD) and prehistoric (Holocene) episodes of arroyo cutting and filling. The near- synchronous timing of arroyo cut-fill events between the Paria River and regional drainages over the last ~1 have led some researchers to argue that arroyo development is climatically driven. However, the influence of allogenic (climate-related) or autogenic (geomorphic threshold) forcings on arroyo dynamics are less clear.
    [Show full text]
  • Chronostratigraphy
    Dr. Maha Al-Hasson Stratigraphy Lectures Chronostratigraphy An elements of stratigraphy that deals with the relative time relations and ages of rock bodies. Chronostratigraphic classification: The organization of rocks into units on the basis of their age or time of origin. Inferential UNITS Groups of strata recognized as being formed during a specific interval of geological time .These units are not self-evident nor directly observable; Chronostratigraphic units: Are bodies of rocks(layered orunlayered), that were formed during a specified interval of a geologic time,they are bounded by synchronous horizons. synchronous horizons(chronohorizon):A stratigraphic surface or interface that is chronous, everywhere of the same age. position within chronostratigraphic unit is expressed by adjectives of position such as; basal, lower, middle, upper, etc.; position within a geochronologic unit is expressed by temporal adjectives such as: early, middle, late, etc. e.g.: lower Cambrian strata/Early Cambrian age middle Cambrian strata/ middle Cambrian strata upper Cambrian strata / late Cambrian strata. 1 Dr. Maha Al-Hasson Stratigraphy Lectures Ranks or types (Hierarchy) of inferential stratigraphic units Chronostratigraphic (Time rock) units Geochronologic (geologic time units) Eon Eonotheme Era Eratheme Period System Epoch Series Age Stage Chron Chronozone Many scientists believe systems & series are units of strata bounded by time surfaces. Stage & Age: all rocks that formed during an age.its a lowest rank of chronostratigraphic unit below series.Age: its' equivalent geochronologic unit, represents their times during rock' deposition . Series & Epochs: Series is achronostratigraphic unit ranking above a stage and below a system,subdivition of System,while Epoch its' equivalent geochronologic unit, representstheir times during rock deposition .
    [Show full text]
  • North American Stratigraphic Code1
    NORTH AMERICAN STRATIGRAPHIC CODE1 North American Commission on Stratigraphic Nomenclature FOREWORD TO THE REVISED EDITION FOREWORD TO THE 1983 CODE By design, the North American Stratigraphic Code is The 1983 Code of recommended procedures for clas- meant to be an evolving document, one that requires change sifying and naming stratigraphic and related units was pre- as the field of earth science evolves. The revisions to the pared during a four-year period, by and for North American Code that are included in this 2005 edition encompass a earth scientists, under the auspices of the North American broad spectrum of changes, ranging from a complete revision Commission on Stratigraphic Nomenclature. It represents of the section on Biostratigraphic Units (Articles 48 to 54), the thought and work of scores of persons, and thousands of several wording changes to Article 58 and its remarks con- hours of writing and editing. Opportunities to participate in cerning Allostratigraphic Units, updating of Article 4 to in- and review the work have been provided throughout its corporate changes in publishing methods over the last two development, as cited in the Preamble, to a degree unprece- decades, and a variety of minor wording changes to improve dented during preparation of earlier codes. clarity and self-consistency between different sections of the Publication of the International Stratigraphic Guide in Code. In addition, Figures 1, 4, 5, and 6, as well as Tables 1 1976 made evident some insufficiencies of the American and Tables 2 have been modified. Most of the changes Stratigraphic Codes of 1961 and 1970. The Commission adopted in this revision arose from Notes 60, 63, and 64 of considered whether to discard our codes, patch them over, the Commission, all of which were published in the AAPG or rewrite them fully, and chose the last.
    [Show full text]
  • 2. Late Quaternary Paleomagnetic Secular Variation and Chronostratigraphy from Odp Sites 1233 and 12341
    Tiedemann, R., Mix, A.C., Richter, C., and Ruddiman, W.F. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 202 2. LATE QUATERNARY PALEOMAGNETIC SECULAR VARIATION AND CHRONOSTRATIGRAPHY FROM ODP SITES 1233 AND 12341 Steve P. Lund,2 Joseph Stoner,3 and Frank Lamy4 ABSTRACT During Ocean Drilling Program Leg 202, detailed shipboard paleo- magnetic measurements at Sites 1233 and 1234 identified a reproduc- ible high-resolution record of paleomagnetic secular variation (PSV) at each site. These records also contained evidence for three magnetic 1Lund, S.P., Stoner, J., and Lamy, F., field excursions. This paper summarizes the complete paleomagnetic 2006. Late Quarternary paleomagnetic record from Site 1233 and the paleomagnetic record for the uppermost secular variation and chronostratigraphy from ODP Sites 30 meters from Site 1234. We also establish a detailed PSV correlation 1233 and 1234. In Tiedemann, R., between the two sites, located ~500 km apart. Twenty-seven accelerator Mix, A.C., Richter, C., and Ruddiman, mass spectrometry radiocarbon dates permit us to develop time-depth W.F. (Eds.), Proc. ODP, Sci. Results, 202: plots and detailed PSV time series for the last ~50,000 yr at both sites. College Station, TX (Ocean Drilling Based on our chronostratigraphy, the most recent excursions occur at Program), 1–22. doi:10.2973/ α odp.proc.sr.202.208.2006 ~35,000 cal. yr before present (BP) (Excursion 3 ) and ~41,000 cal. yr BP 2Department of Earth Sciences, (Excursion 3β). The excursions were named for the oxygen isotope University of Southern California, Los stages within which they occur.
    [Show full text]
  • Lithostratigraphic Unit
    E. F. McBride Geo. 420K Spring, 1999 NOTES ON STRATIGRAPHY FOR GEO420K TYPES OF STRATIGRAPHY Lithostratigraphy - Lithostratigraphic unit [Group, Formation, Member] - Lithodemic unit (intrusives, etc.) Pedostratigraphy - Pedostratigraphic unit Biostratigraphy - Zones Chronostratigraphy - Chronostratigraphic units [Period, Epoch, Age] Geochronostratigraphy - Geochronostratigraphic unit [System, Series, Stage] Magnetostratigraphy - Reversals, chrons Chemostratigraphy - Isotope zones Sequence Stratigraphy - Allostratigraphic units [Unconformity-bounded units] IMPORTANT SURFACES & TIME IMPLICATIONS 1) FAULTS, FRACTURES 2) UNCONFORMITIES = Buried erosion surfaces Physical erosion Biological erosion Chemical erosion Hiatus = amount of time record missing Diastem = small amount of rock missing Paraconformity " " " " Non-conformity: sedimentary rocks on top of igneous or metamorphics Disconformity: sediments conformable with sediments Angular unconformity: angular discordance 3) BEDDING Problem: how much time is represented by each bedding plane? FACIES Definitions: 1) Aspects of a rock that characterize it (minerals, fossils, color, etc). 2) Mappable, areally restricted part of a lithostratigraphic body that differs from its coeval equivalents. 3) A distinctive rock type that is characteristic of a particular environment: black shale facies, bioherm facies, channel facies, turbidite facies. 4) A body of rock distinguished on the basis of its fossil content: Ophiomorpha facies, Exogyra texana facies. BIOSTRATIGRAPHY PROCEDURE: plot range of every
    [Show full text]
  • Ch 72 (2009) 16–26
    Quaternary Research 72 (2009) 16–26 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres Evidence of NAO control on subsurface ice accumulation in a 1200 yr old cave-ice sequence, St. Livres ice cave, Switzerland Markus Stoffel a,b,c,⁎, Marc Luetscher d,e, Michelle Bollschweiler b,c, Frédéric Schlatter c a Climatic Change and Climate Impacts Group (C3i), Institute for Environmental Sciences, University of Geneva, Site de Batelle, chemin de Drize 7, CH-1227 Carouge-Geneva, Switzerland b Laboratory of Dendrogeomorphology (Dendrolab.ch), Institute of Geological Sciences, University of Berne, Baltzerstrasse 1+3, CH-3012 Berne, Switzerland c Department of Geosciences, Geography, University of Fribourg, chemin du Musée 4, CH-1700 Fribourg, Switzerland d Geology and Paleontology, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria e Swiss Institute for Speleology and Karst Studies (SISKA), P.O. Box 818, CH-2301 La Chaux-de-Fonds, Switzerland article info abstract Article history: Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially Received 15 September 2008 interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the Available online 16 April 2009 understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees and organic material are Keywords: abundant in the cave-ice deposit, therefore allowing the dating of individual ice layers. The dendrochrono- Cave ice logical analysis of 45 subfossil samples of Norway spruce (Picea abies (L.) Karst.) from the overhanging front of Sporadic permafrost 14 Dendrochronology the ice outcrop as well as the dating of seven wood samples with C dating allowed for a reconstruction of the Radiocarbon dating St.
    [Show full text]
  • Amino Acid Racemization of Planktonic Foraminifera
    AMINO ACID RACEMIZATION OF PLANKTONIC FORAMINIFERA: PRETREATMENT EFFECTS AND TEMPERATURE RECONSTRUCTIONS by Emily Watson A thesis submitted to the Faculty of the University of Delaware in partial fulfillment of the requirements for the degree of Master of Science in Marine Studies Spring 2019 © 2019 Emily Watson All Rights Reserved AMINO ACID RACEMIZATION OF PLANKTONIC FORAMINIFERA: PRETREATMENT EFFECTS AND TEMPERATURE RECONSTRUCTIONS by Emily Watson Approved: __________________________________________________________ Katharina Billups, Ph.D. Professor in charge of thesis on behalf of the Advisory Committee Approved: __________________________________________________________ Mark Moline, Ph.D. Chair of the Department of Marine Science and Policy Approved: __________________________________________________________ Estella Atekwana, Ph.D. Dean of the College of Earth, Ocean, and Environment Approved: __________________________________________________________ Douglas J. Doren, Ph.D. Interim Vice Provost for Graduate and Professional Education ACKNOWLEDGMENTS Very special thanks to my M.S. advisor Dr. Katharina Billups for providing me with this amazing opportunity and giving me her utmost support. Her willingness to give her time so generously has been indispensable during my Masters. She is my ultimate scientific role model. I am grateful for my collaborators from Northern Arizona University, Dr. Darrell Kaufman and Katherine Whitacre, who taught me the cleaning methods for this project and opened up their lab to me in January 2018. I would like to express my appreciation to Dr. Kaufman for his valuable and constructive suggestions during the planning and development of this research work. Data provided by Katherine was very valuable. I would also like to thank Dr. Doug Miller, and Dr. Andrew Wozniak, Dr. John Wehmiller from the University of Delaware for their assistance with this project.
    [Show full text]
  • Doc.Rero.Ch Populated and Industrialized Areas (E.G., Cecil Et Al., 2004)
    Published in "Quaternary Research 72(1): 16-26, 2009" which should be cited to refer to this work. Evidence of NAO control on subsurface ice accumulation in a 1200 yr old cave-ice sequence, St. Livres ice cave, Switzerland Markus Stoffel a,b,c,⁎, Marc Luetscher d,e, Michelle Bollschweiler b,c, Frédéric Schlatter c a Climatic Change and Climate Impacts Group (C3i), Institute for Environmental Sciences, University of Geneva, Site de Batelle, chemin de Drize 7, CH-1227 Carouge-Geneva, Switzerland b Laboratory of Dendrogeomorphology (Dendrolab.ch), Institute of Geological Sciences, University of Berne, Baltzerstrasse 1+3, CH-3012 Berne, Switzerland c Department of Geosciences, Geography, University of Fribourg, chemin du Musée 4, CH-1700 Fribourg, Switzerland d Geology and Paleontology, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria e Swiss Institute for Speleology and Karst Studies (SISKA), P.O. Box 818, CH-2301 La Chaux-de-Fonds, Switzerland Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees and organic material are abundant in the cave-ice deposit, therefore allowing the dating of individual ice layers. The dendrochrono- logical analysis of 45 subfossil samples of Norway spruce (Picea abies (L.) Karst.) from the overhanging front of the ice outcrop as well as the dating of seven wood samples with 14C dating allowed for a reconstruction of the St.
    [Show full text]
  • 1 Forthcoming in Philosophy of Science Calibration, Coherence
    Forthcoming in Philosophy of Science Calibration, Coherence, and Consilience in Radiometric Measures of Geologic Time Alisa Bokulich† Department of Philosophy Boston University [email protected] In 2012 the Geological Time Scale, which sets the temporal framework for studying the timing and tempo of all major geological, biological, and climatic events in Earth's history, had one-quarter of its boundaries moved in a wide-spread revision of radiometric dates. The philosophy of metrology helps us understand this episode, and it, in turn, elucidates the notions of calibration, coherence, and consilience. I argue that coherence testing is a distinct activity preceding calibration and consilience, and highlight the value of discordant evidence and tradeoffs scientists face in calibration. The iterative nature of calibration, moreover, raises the problem of legacy data. 1. Introduction Geochronology is the science of measuring geologic time through the dating of the materials of the Earth. One of the most important dating methods is radioisotope geochronology, which is the investigation of the age of these materials through the radioactive decay of the isotopes they contain. Radiometric methods, which have been around for a hundred years, provide one of most powerful tools for measuring absolute time. There are several different radioactive methods, based on different chemical elements, each with a different half-life, which makes it more or less suitable for measuring particular substances and particular periods of geologic time. The most well- known radiometric method is radiocarbon dating, which is based on the decay of 14C. However, because radiocarbon (14C) has a relatively short half-life, it can only reliably measure dates going back approximately 60,000 years, hardly making a dent in the measurement of geologic time.
    [Show full text]
  • Stratigraphy in the Oil Industry Ken Ratcliffe, Hafren Scientific Ltd., Andy Wilson Chemostrat Australia Ltd
    technology Stratigraphy in the Oil Industry Ken Ratcliffe, Hafren Scientific Ltd., Andy Wilson Chemostrat Australia Ltd. tratigraphy and the oil industry are stratigraphic thinking. The relationship between reduced to the description of innumerable, intricately intertwined, and have been the oil industry and the science of stratigraphy is localised successions of strata without it; an Sso ever since the early days of the a very healthy one and is truly symbiotic. apposite statement about stratigraphy in hydrocarbon exploitation. Stratigraphic the oil gas industry. Characterising single understanding forms the basis for all upstream The aim of this article is not to review stratigraphic well-bores is of little importance, but being activity from basin exploration through field methods, nor to provide a history of stratigraphy able extend that characterisation and place evaluation to reservoir development and in the industry; good quality reviews are available it in a time-context over an oil field or a production. Whilst the subject of stratigraphy elsewhere (e.g. Boggs, 1995; Catuneanu, prospective basin is without doubt the single in itself is fascinating and one that even non- 2006; Slatt, 2007; Ratcliffe and Zaitlin, 2010). most important building block for all later earth scientists will have been in contact Instead, this article examines why stratigraphic studies in hydrocarbon exploration. with when out and about in mountains, techniques that could be considered ‘academic’, on beaches or even driving through road suddenly (at least in geological terms) have “Standard” stratigraphic methods cuts (Figure 1), it is a subject that may well become relatively widely used tools in the oil in the industry have remained firmly bedded in the ivory and gas industry.
    [Show full text]
  • 3. Overview of Stratigraphy and Depositional Systems
    Basic Principles of Stratigraphy and Depositional Systems I. INTRODUCTION A. Stratigraphy: the study of the geologic rock record in the context of geologic time. 1. Geologic Rock Record: analogous to a tape recording in which some historical events are preserved and recorded, others have been erased, and still others were not taped at all a. Referred to as "Stratigraphic Record": originally involved the study of "layered" sedimentary rocks and the fossil record. (1) Advances in sensing techniques (radiometric dating, seismic analysis, paleomagnetism) have expanded the study of stratigraphy and rock record to the realm of igneous and metamorphic rock sequences 2. Geologic Time: abstract concept of continuous linear time from earth's origins to present day (portions of which are preserved in the rock record, and portions of which are not) a. Time record vs. Rock Record 3. The study of Stratigraphy represents an attempt to correlate the relative sequence of observations from the rock record, with that of historical/linear time. B. Historical Geology: Use of the stratigraphic record to derive historical time record and physical/biological evolution of the earth. 1. I.e. examining the rock record to deduce the natural history of the time record. C. Sedimentology: study of the processes and products of the near-surface environment of the earth 1. Sedimentology outgrowth of stratigraphy, historical geology a. Stratigraphy originally based on layered sedimentary rocks and the fossils contained within. b. Sediments accumulate as horizontal layers of particles under the force of gravity, "layer cake" approach to geology and interpretation of the rock record. 20 I.
    [Show full text]