Shell Dates Research Articles

Racemization of isoleucine in fossil molluscs from Indian middens and interglacial terraces in southern California

The amino acid racemization dating technique is applied to the West Coast mollusc Chione from interglacial terrace deposits and Indian midden sites. The racemization kinetics of isoleucine were studied in Total hydrolysates and in the non-dialyzable Protein fraction from Chione shell. The reliability of the isoleucine dates was evaluated by (1) comparison with ages determined by radiocarbon and uranium disequilibrium dating, (2) species effects, and (3) reproducibility. Isoleucine dates for the interglacial terrace shell were found to be more reliable than the midden shell dates. A radiocarbon analysis of amino acids extracted from Del Mar midden shell was performed in order to resolve the discrepancies between the racemization ages and the 14 C dates on shell carbonate.

Late-Wisconsin marine environments of the Champlain Valley (New York, Quebec)

The Champlain Sea occupied the Champlain Valley from about 12,500 to 10,000 yr BP. Following an initial maximum limit of inundation, isostatic crustal rebound caused the sea's gradual regression, which is documented by the parallel alignment of tilted shoreline features at successively low elevations along a north-south profile. Two new radiocarbon shell dates, 11,665 ± 175 (QC 200), elevation 95 m, and 10,300 ± 180 (QC 199), elevation 47 m, date early and late Champlain Sea deposits, respectively. From the elevation (ASL) and invertebrate fauna of littoral deposits, three environmentally distinct phases of the sea were recognized. Early Champlain Sea Transitional phase deposits at high elevations are characterized by a mixed association of fresh and euryhaline marine ostracodes. Frigid-subfrigid climates and fluctuating salinities of this period possibly reflect intermixing of the fresh waters of Lake Vermont with incoming marine waters. Hiatella arctica phase faunas indicate similar climatic conditions but significantly higher salinities (polyhaline). Deposits from the final phase of the sea, the Mya arenaria phase, were found at low elevations just above the present level of Lake Champlain. A predominantly cold-temperate, mesohaline fauna characterizes this period. The influences of Lake Algonquin drainage, warm Gulf Stream water and perhaps the retreating Laurentide Ice Sheet are discussed as possible causes for the observed faunal and environmental changes.

Fréquence des datations Au 14C de faunes marines post-glaciaires de l'est du Canada et variations paléoclimatiques

A statistical analysis of radiocarbon dates for 365 samples associated with postglacial marine deposits of Eastern Canada and New England, U.S.A., yield a non-random statistical distribution. This distribution pattern is explained by two principal controls (that are partly interdependent): (1) secondary eustatic fluctuations, creating relative stabilizations of the sea level with an uplifting land; and (2) more generally the climatic variations. Other factors involved may include: (1) limitations of 14C dating method; (2) non-statistical sampling methodology adopted by the Quaternary geologists; (3) lack of intensive study of some of the marine basins; and (4) incidence of rapidly changing paleogeographic events (opening and shoaling of marine basins, glacial re-advances and changes in the ice flow). The statistical appraisal of errors in published 14C dates and the standard deviation, calculated with sliding means, enable us to screen out the influence of most of the non-climatic factors. With this technique, we are also able to draw a curve based on a general synthesis of all variations in 14C dates distribution. In this way, the irregularities observed in the synthesis curve are now correlated with paleoclimatic and paleogeographic events that took place in Eastern Canada between 15,000 years B.P. to present. That curve shows a close correlation during the Holocene with other climatic indicators and gives some original informations concerning the period 15,000–10,000 B.P. No attempt has been made to adjust radiocarbon years to calendar years for two reasons: (1) lack of agreement between comparative curves prior to 7,000 B.P.; and (2) lack of information concerning the effect of “old waters” on shell dates.

Radiocarbon dating of shells from marine Holocene deposits in the Disko Bugt area, West Greenland

Shells were collected from marine sediments in the area youth of Disko Bugt from various altitudes up to 50 m. Radiocarbon dates showed that only some of the shells were from sands and gravels formed at or near sea level and could be used to date the land/sea level changes. The shell dates show a regression from about 43 m at 7000 B.P. to about 8 m at 4000 B.P. All sediments with shells are Holocene in age, the oldest date being nearly 9000 B.P. The date of the Fjord Stage moraine in Orpigsoq is estimated at about 8000 B.P. on the basis of the altitude of the marine limit at 62 m. Extrapolations dated the older marine limits, falling from an altitude of 130 m to 80 m, at about 11,000 B.P. to 9000 B.P. These are approximate dates for the deglaciation of the area outside the Fjord Stage moraine. The distribution of shells in the sediments was shown to be largely dependent on habitat and water depth. At least some changes ill fauna were caused by a decrease of water depth due to the relative uplift of land. No tilting or warping of the land surface could he detected in the at‐ea about 100 km long from the coast towards the Inland Ice.

Late Quaternary Marine Invasion in Maine: Its Chronology and Associated Crustal Movement

Research Article| January 01, 1975 Late Quaternary Marine Invasion in Maine: Its Chronology and Associated Crustal Movement MINZE STUIVER; MINZE STUIVER 1Departments of Geological Sciences and Zoology and Quaternary Research Center, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar HAROLD W. BORNS, JR. HAROLD W. BORNS, JR. 2Department of Geological Sciences and Institute for Quaternary Studies, University of Maine at Orono, Orono, Maine 04473 Search for other works by this author on: GSW Google Scholar Author and Article Information MINZE STUIVER 1Departments of Geological Sciences and Zoology and Quaternary Research Center, University of Washington, Seattle, Washington 98195 HAROLD W. BORNS, JR. 2Department of Geological Sciences and Institute for Quaternary Studies, University of Maine at Orono, Orono, Maine 04473 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (1): 99–104. https://doi.org/10.1130/0016-7606(1975)86<99:LQMIIM>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MINZE STUIVER, HAROLD W. BORNS; Late Quaternary Marine Invasion in Maine: Its Chronology and Associated Crustal Movement. GSA Bulletin 1975;; 86 (1): 99–104. doi: https://doi.org/10.1130/0016-7606(1975)86<99:LQMIIM>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Recession of the ice margin at a rate of 0.3 km/yr or more in coastal areas in central Maine between 13,000 and 12,700 yr B.P. resulted in a large-scale marine submergence of this region. Isostatic uplift brought the region above sea level by 12,100 yr B.P. Model calculations show the existence of an inland sea in the later stages of emergence. The chronology of these events is given by 14C dates on shells and seaweed from the Presumpscot Formation. Several criteria applied indicate age reliability of the shell dates within a few hundred years. 14C ages of the earliest grown organic material in kettles often lag behind the time of deglaciation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Radiocarbon dating of marine shells, including a discussion of apparent age of Recent shells from Norway

General problems in determining and interpreting shell C14 dates are discussed: calculation methods, factors influencing primary activity (apparent age), and determination of contamination. It is concluded that shell dates are reliable when handled carefully. Measurements on ten shells, collected between 1898 and 1923 on the Norwegian coast, gave apparent ages from 340±75 to 550±80 years, indicating that apparent age is not a significant problem in dating of Norwegian shells.

The Age of the Ågård Interstadial and the Fjärås Stadial

Abstract Marine shell dates from the Kattegatt region give evidence of a climatic amelioration called the Ågård Interstadial, which is older than the Bölling Interstadial and younger than the Susaca Interstadial. The Ågård and Bölling Interstadials are separated by the Fjärås Stadial. Re-examination of available radiocarbon dates and correction of an earlier mistake lead to the following corrected chronology: 12,700 B. P.=onset of the Ågård Interstadial (no change), 12,400 B. P. = Ågård/Fjärås boundary (earlier 12,300-12,350 B. P.) and 12,350 B. P. = end of Fjärås Stadial (earlier 12,250-12,300 B. P.).

Postglacial crustal movements in southwestern British Columbia and adjacent Washington state

Records of former land–sea relationships in southwestern British Columbia and adjacent Washington State have been established in considerable detail by terrestrial and marine stratigraphy, by terrestrial and littoral landforms, and by archeological remains, aided by radiocarbon dating of shells, wood, peat, and charcoal from critical sites. These records indicate submergent conditions at the time of retreat of the Vashon ice sheet, 13 000 y ago, followed by an unusually quick emergence of several hundred feet by about 12 000 y ago. In the north-east and north of the area studied, this emergence was followed by a submergence of some hundreds of feet during the next half millennium preceding the Sumas ice advance. During and following this ice advance, land again became emergent, and during the period 9 000 to 6 000 y ago sea level stood approximately 35 ft (10 m) below the present shore in some parts of the area. The shore has stood close to its present level for the last 5 500 y in all parts of the area.Early movements were dominantly isostatic. The pre-Sumas submergence is of problematical origin. Sea level shifts since 8 000 y ago appear to be dominantly eustatic; isostatic movements were evidently essentially complete by this time. In historic time very small changes shown by tide gauges and precise levelling may be tectonic.

Validity of Radiocarbon Dates on Terrestrial Snail Shells

AbstractRadiocarbon dating of terrestrial snail shells is examined. Three groups of samples, two from archaeological sites of Venezuela and one from the state of Texas, were taken as examples. The true ages were determined from radiocarbon dates on associated charcoal, and measurements on the snail shells allowed the errors to be determined. The groups showed completely different characteristics: 15 samples from Texas all had ages falsely old, 12 specimens of one Venezuelan group produced all correct dates, and another Venezuelan type with five samples gave dates all too recent. This study defines the directions and extents of errors for each group of snail shells, permitting them to be used as relatively reliable datable objectives in excavations where better materials are not available.The possibility of correcting the radiocarbon dates using carbon-13 concentrations is considered, and 24 measurements are presented. It is concluded that more than one factor can influence the stable isotope concentrations in each case, and, therefore, carbon-13 is not useful for the improvement of the accuracy of snail shell dates.

A radiocarbon-dated marine algal bed of the Champlain Sea episode near Ottawa, Ontario

A bed of marine algae (seaweed) in a sand pit in Champlain Sea sediments southwest of Ottawa, Ontario, was dated by the radiocarbon method and gave an age of 10 800 ± 150 years (GSC-570). Marine shells from above and below the algal bed gave radiocarbon ages of 10 620 ± 200 years (GSC-587) and 10 880 ± 160 years (GSC-588) respectively.The algae and underlying shells have been excellently preserved as a result of rapid burial following deposition and remaining beneath a high water table. The similarity of the radiocarbon dates on the algae and on the shells above and below, and with previous dates on shells from other Champlain Sea deposits indicates the reliability of these shell dates.

Possible Late Pleistocene Uplift Chesapeake Bay Entrance

Paleontological and lithological studies of engineering borings and boring logs indicate that a buried, subaerial erosion surface of Pliocene (?)-Pleistocene age cuts across clastic sediments of pre-Yorktownian Miocene age in the subsurface and subbottom of the lower Chesapeake Bay area. When the bore-hole data are coupled with the results of subbottom echo profiling and piledriving records, it is possible to construct accurate cross sections of the buried Miocene-Pleistocene contact. The cross sections show "lows" in the erosion surface that may be correlated with the buried channels of the Pleistocene Elizabeth, James, York, and Susquehanna river valleys. Probable channel depths below mean low water at control points are: 100 feet (Elizabeth River, beneath Tunnel no. 1), 155 feet (James River, at Hampton Roads Tunnel), 120 feet (York River, at Yorktown), 158 feet (Susquehanna River, off Cape Charles City), and 160 feet (Susquehanna River, at Fisherman Island, Cape Charles). The channel depths of what is...