Chronology, time averaging, and oxygen isotope composition of harvested marine mollusk assemblages from Ifri Oudadane, northeast Morocco

2021 ◽  
pp. 1-15
Author(s):  
William Sanchez ◽  
Yurena Yanes ◽  
Jörg Linstädter ◽  
Rainer Hutterer
Keyword(s):  
Oxygen Isotopes ◽  
Food Production ◽  
Isotope Composition ◽  
Archaeological Site ◽  
High Temporal Resolution ◽  
Time Averaging ◽  
Marine Mollusk ◽  
Mode Of Life ◽  
Deposition Processes ◽  
Work First

Abstract The archaeological site of Ifri Oudadane, NE Morocco, contains well-preserved marine mollusk concentrations throughout the Epipaleolithic (hunting-gathering) and Neolithic (food production) cultural phases, useful to test hypotheses driving such transition. However, the chronology and stratigraphy of harvested shells is complex due to the confluence of human activity and natural deposition processes. This work first quantifies the age and degree of time averaging of archaeological shells and then estimates sea-surface temperatures (SSTs) from the oxygen isotopes of selected specimens. Thirty-four radiocarbon-dated shells exhibited significant time averaging between 310 to 1170 yr that could not be explained by analytical error alone. This finding illustrates the need for individually dating shells in future paleoclimate investigations aiming for high temporal resolution. Nine isotopically analyzed shells dated to the Neolithic phase, between 5700 and 7600 cal yr BP, indicate that assuming constant oxygen isotopes of seawater, SSTs remained consistently warm, between 20°C and 22°C, that is, 2°C–4°C warmer than today. Results point to warmer conditions during the Neolithic, supporting the hypothesis that the rise of a food production mode of life in NE Morocco could have in part been triggered by warming conditions following the colder 8.2 event.

scholarly journals The stable isotope composition of water vapour above Corsica during the HyMeX SOP1: insight into vertical mixing processes from lower-tropospheric survey flights

2016 ◽  
Author(s):  
Harald Sodemann ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Mark Bitter ◽  
Ulrich Corsmeier ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Isotope ◽  
Water Vapour ◽  
Isotope Composition ◽  
Water Isotopes ◽  
High Temporal Resolution ◽  
Stable Isotope Composition ◽  
Stable Water Isotopes ◽  
Mixing Processes ◽  
Strong Inversion

Abstract. Stable water isotopes are powerful indicators of meteorological processes on a broad range of scales, reflecting evaporation, condensation, and airmass mixing processes. With the recent advent of fast laser-based spectroscopic methods it has become possible to measure the stable isotopic composition of atmospheric water vapour in situ at high temporal resolution, enabling to tremendously extend the measurement data base in space and time. Here we present the first set of airborne spectroscopic stable water isotopes measurements over the western Mediterranean. Measurements have been acquired by a customised Picarro L2130-i cavity-ring down spectrometer deployed onboard of the Dornier 128 D-IBUF aircraft together with a meteorological flux measurement package during the HyMeX SOP1 field campaign in Corsica, France during September and October 2012. Taking into account memory effects of the air inlet pipe, the typical time resolution of the measurements was about 15–30 s, resulting in an average horizontal resolution of about 1–2 km. Cross-calibration of the water vapour measurements from all humidity sensors showed good agreement in most flight conditions but the most turbulent ones. In total 21 successful stable isotope flights with 59 flight hours have been performed. Our data provide quasi-climatological autumn average conditions of the stable isotope parameters δD, δ18O and d-excess during the study period. A time-averaged perspective of the vertical stable isotope composition reveals for the first time the mean vertical structure of stable water isotopes over the Mediterranean at high resolution. A d-excess minimum in the overall average profile is reached in the region of the boundary layer top due to precipitation evaporation, bracketed by higher d-excess values near the surface due to non-equilibrium fractionation and above the boundary layer due to the non-linearity of the d-excess definition. Repeated flights along the same pattern reveals pronounced day-to-day variability due to changes in the large-scale circulation. During a period marked by a strong inversion at the top of the marine boundary layer, vertical gradients in stable isotopes reached up to 25.4 ‰ 100 m−1 for δD.

scholarly journals Potential Reference Materials for Hematite Oxygen Isotope Analysis

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 987
Author(s):  
Lianjun Feng ◽  
Hongwei Li ◽  
Tiejun Li
Keyword(s):  
Oxygen Isotope ◽  
Iron Oxides ◽  
Oxygen Isotopes ◽  
Reference Materials ◽  
Isotope Composition ◽  
Isotope Analysis ◽  
Isotope Ratios ◽  
Bulk Rock ◽  
Accurate Analysis ◽  
Oxygen Isotope Ratios

Hematite is a potential mineral for reconstructing the oxygen isotope composition and paleotemperature of paleowater. A highly accurate analysis of oxygen isotopes is essential. However, relative to other oxygenated minerals, we lack hematite reference materials that allow for internationally comparable analyses between different laboratories. To address this issue, we attempted to perform bulk rock oxygen isotope analysis on five hematite reference materials (GBW07223a, GBW07825, YSBC28740-95, YSBC28756-2008, Harvard 92649). Meanwhile, the oxygen isotope ratios of iron oxides (GBW07223a, GBW07825, YSBC28740-95, YSBC28756-2008) were obtained by mass balance involving other oxygen-bearing minerals such as quartz and silicates. In addition, the oxygen isotope ratios of iron oxides in an oolitic hematite (ca. 1.65 billion years ago) are consistent with the results of previous analyses of this class of minerals.

An Oxygen Isotope Study of Seasonal Trends in Jinxiuchuan River of Jinan South Mountain

2014 ◽  
Vol 522-524 ◽  
pp. 954-957 ◽  
Author(s):  
Yong Sen Wang ◽  
Zheng He Xu ◽  
Si Fang Dong
Keyword(s):  
Stable Isotope ◽  
Oxygen Isotope ◽  
River Water ◽  
Oxygen Isotopes ◽  
Water Cycle ◽  
Climatic Factors ◽  
Isotope Composition ◽  
Stable Isotope Composition ◽  
Isotope Study ◽  
Isotopic Variations

The stable isotope composition of river water contains some information of water cycle and climatic factors, such as precipitation, evaporation and temperature. Oxygen isotopes in river water were monitored at one site in Jinxiuchuang basin of Jinan southern mountain.δ18O values of river water show a variation from-7.82 on July 6 to-9.98 on June 6. The result reveals that the river water was mainly supplied by the precipitation. The isotopic variations at Jinxiuchuan river have strong precipitation patterns owning to different rainfall in summer.

scholarly journals Trace elements and oxygen isotopes of gem spinels in marble from the Luc Yen - An Phu areas, Yen Bai province, North Vietnam

2018 ◽  
Vol 40 (2) ◽  
pp. 165-177 ◽  
Author(s):  
Pham Van Long ◽  
Gaston Giuliani ◽  
Anthony E. Fallick ◽  
Andrian J. Boyce ◽  
Vincent Pardieu
Keyword(s):  
Trace Elements ◽  
Stable Isotope ◽  
Oxygen Isotopes ◽  
Genetic Model ◽  
Chemical Elements ◽  
Isotope Geochemistry ◽  
Isotope Composition ◽  
Stable Isotope Geochemistry ◽  
Oxygen Isotopic ◽  
North Vietnam

Trace elements investigated by electron microprobe analysis (EMPA) have been combined with oxygen isotopic composition of pink, red and other colored spinels (blue, purple, brown, orange, lavender) hosted by marbles and found in placers from Luc Yen and An Phu deposits, Yen Bai province, North Vietnam. The deposits are those from Nuoc Ngap, Cong Troi, Bai Son and different placers from the An Phu area. Trace elements such as Fe-Zn-Cr-V in red and pink gem spinels permit to separate those from Cong Troi and those from the others deposits of the An Phu area. Spinels from Cong Troi have low to extremely low Zn (< 500 ppm) and high Fe contents (3,000 to 16,000 ppm) while those from An Phu area are Zn-rich (up to 11,000 ppm). Iron is the dominant element for the other colored spinels whereas Zn, Cr and V contents are extremely variable. The Bai Son blue spinel is Fe-rich (5,000 to 7,200 ppm) with some V (950 to 1,830 ppm), Cr (270 to 480 ppm), Co (240 to 400 ppm) and Ni (550 to 950 ppm). The O-isotope composition of the whole spinels ranges between 12.1 and 24.2‰ (n = 25). Within each deposit, the range of δ18O values for red, pink and colored spinels is usually similar. However, the red and pink spinels from An Phu present two distinct sets of δ18O values, respectively between  13.2 to 17.0‰  (n = 7) and 22.5< δ18O < 24.2 (n = 5). Those from Cong Troi are from 14.8 to 17.7‰ (n = 3) and their range overlaps that of An Phu. The use of O-isotopes is not useful for distinguishing between the deposits, but the low to extremely low Zn content of the Cong Trois spinels is a discriminant. The variation of δ18O values (12.1 <δ18O < 24.2‰) of the whole spinels indicates that the oxygen isotopic compositions of the metamorphic fluids were probably buffered by the local δ18O values of the impure host marbles.ReferencesChauviré B., Rondeau B., Fritsch E., Ressigeac Ph., Devidal J.-L., 2015. Blue spinel from the Luc Yen district of Vietnam. Gems & Gemology, 51, 2-17.D'Ippolito V., Andreozzi G.B., Hålenius H., Skogby H., Hametner K., Günther D., 2015. Colour mechanisms in spinel: cobalt and iron interplay for the blue colour. Physics and Chemistry of Minerals, 42, 431-439.Garnier V., 2003. Les gisements de rubis associés aux marbres de l’Asie Centrale et du Sud-est: genèse et caractérisation isotopique. PhD thesis INPL, Nancy, France, 373p.Garnier, V., Ohnenstetter, D., Giuliani, G., Maluski, H., Deloule, E., Phan Trong Trinh, Pham Van Long, Hoang Quang Vinh, 2005. Age and significance of ruby-bearing marbles from the Red River shear zone, northern Vietnam. The Canadian Mineralogist, 43, 1315-1329.Garnier V., Giuliani G., Ohnenstetter D., Fallick A.E., Dubessy J., Banks D., Hoang Quang Vinh, Lhomme Th., Maluski H., Pêcher A., Bakhsh K.A., Pham Van Long, Phan Trong Trinh, Schwarz D., 2008. Marble-hosted ruby deposits from central and Southeast Asia: towards a new genetic model. Ore Geology Reviews, 34, 169-191.Giuliani G., Fallick A.E., Garnier V., France-Lanord Ch., Ohnenstetter D., Schwarz D., 2005. Oxygen isotope composition as a tracer for the origins of rubies and sapphires. Geology, 33(4), 249-252.Giuliani G., Fallick A.E., Boyce A.J., Pardieu V., Pham Van Long, 2017. Pink and red spinels in marble: trace elements, oxygen isotopes, and sources. The Canadian Mineralogist, 55, 743-761.Hauzenberger C.A., Häeger T., Baumgartner L.P., Hofmeister W., 2001. High-grade metamorphism and stable isotope geochemistry of N-Vietnamese gem-bearing rocks. In: Proceedings of the Workshop on gems and minerals of Vietnam, Hanoi, 124-138.Hauzenberger C.A., Bagola C., Häeger T., Muellen C., Nguyen Ngoc Khoi, Le Thi Thu Huong, 2014. Mineralogy and petrology of the An Phu marble hosted spinel and corundum deposit, Luc Yen, N-Vietnam. In Proceedings of the 4th International Gem and Jewelry Conference, Chiang Mai, Thailand, 76-78.Kleišmantas A., Daukšyte A., 2016. The influence of Vietnam and Sri Lanka spinel mineral chemical elements on colour. Chemija, 27, 45-51.Kretz R., 1983. Symbols for rock-forming minerals. American Mineralogist, 68, 277-279.Le Thi Thu Huong, Häeger T., Hofmeister W., Hauzenberger C., Schwarz D., Pham Van Long, Wehmeister U., Nguyen Ngoc Khoi, Nguy Tuyet Nhung, 2012. Gemstones from Vietnam: An update. Gems & Gemology, 48, 158-176.Malsy A., Klemm L., 2010. Distinction of gem spinels from the Himalayan mountain belt. Chimia, 64(10), 741-746.Malsy A., Karampelas S., Schwarz D., Klemm L., Armbruster T., Tuan Do Anh, 2012. Orangey-red to orangey-pink gem spinels from a new deposit at Lang Chap (Tan Huong - Truc Lau), Vietnam. The Journal of Gemmology, 33, 19-27.Pham Van Long, Hoang Quang Vinh, Garnier V., Giuliani G., Ohnenstetter D., Lhomme,T., Schwarz D., Fallick A.E., Dubessy J., Phan Trong Trinh, 2004. Gem corundum deposits in Vietnam. Journal of Gemmology, 29, 129-147.Pham Van Long, Pardieu V., Giuliani G., Nguy Tuyet Nhung, Pham Thi Thanh Hien, Pham Duc Anh, Nguyen Ngoc Khoi, Hoang Quang Vinh, 2014. Gemmological characteristics of spinel from Luc Yen, Yen Bai. Journal of Geology, 340, 29-36.Pham Van Long, Pardieu V., Giuliani G., 2014. Update on gemstone mining in Luc Yen, Vietnam. Gems & Gemology, 49, 233-245.Pouchou J.L., Pichoir F., 1991. Quantitative analysis of homogeneous or stratified microvolumes applying "PAP" In Electron Probe Quantification (K.F.J. Heinrich & D.E. Newbury eds.). Plenum Press, New York, USA, 31-75.Valley J.W., 1986. Stable isotope geochemistry of metamorphic rocks. Reviews in Mineralogy, 16, 445-481.Yui T.F., Khin Zaw, Wu C.-M., 2008. A preliminary stable isotope study on Mogok ruby, Myanmar. Ore Geology Reviews, 34, 182-199.

scholarly journals New insights into the climatic signal from firn cores at the northern Antarctic Peninsula

2017 ◽  
Author(s):  
Francisco Fernandoy ◽  
Dieter Tetzner ◽  
Hanno Meyer ◽  
Guisella Gacitúa ◽  
Kirstin Hoffmann ◽  
...  
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
Isotope Composition ◽  
Accumulation Rate ◽  
Regional Scale ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
High Temporal Resolution ◽  
Near Surface ◽  
The Antarctic

Abstract. The Antarctic Peninsula is one of the most challenging regions of Antarctica from a climatological perspective, owing to the recent atmospheric and oceanic warming. The steep topography and a lack of long–term and in situ meteorological observations complicate extrapolation of existing climate models to the sub-regional scale. Here, we present new evidence from the northern Antarctic Peninsula to demonstrate how stable water isotopes of firn cores and recent precipitation samples can reveal climatic processes related to nearby oceanic and atmospheric conditions. A noticeable effect of the sea ice cover on local temperatures and atmospheric modes, in particular the Southern Annular Mode (SAM), is demonstrated. In years with large sea ice extension in winter (negative SAM anomaly), an inversion layer in the lower troposphere develops at the coastal zone. Therefore, an isotope–temperature relationship valid for all seasons cannot be concluded. The δ–T relationship rather depends on seasonal variability of oceanic conditions. Transitional seasons (autumn and spring) are both stable seasons with an isotope–temperature gradient of +0.69 ‰ °C−1. The firn stable isotope composition reveals that the near–surface temperature at the Antarctic Peninsula shows a decreasing trend (−0.33 °C y−1) between 2008 and 2014. Moreover, the deuterium excess (dexcess) has been demonstrated to be a reliable indicator of seasonal oceanic conditions, and therefore suitable to improve a firn age model based on seasonal dexcess variability. The annual accumulation rate in this region is highly variable, ranging between 1060 kg m−2 y−1 and 2470 kg m−2 y−1 from 2008 to 2014. The combination of isotopic and meteorological data is key for reconstructing recent climatic conditions with a high temporal resolution in polar regions where no direct observation exists

scholarly journals Bothersome burrowers: tracking gopher (Thomomys bottae) time-averaging in a late-Holocene site in California

2021 ◽  
Author(s):  
Maria Viteri ◽  
Elizabeth Hadly
Keyword(s):  
Small Mammals ◽  
Late Holocene ◽  
Archaeological Site ◽  
Skeletal Remains ◽  
Time Averaging ◽  
Faunal Remains ◽  
Pocket Gophers ◽  
Thomomys Bottae ◽  
Sediment Layers ◽  
Shed Light

Understanding the taphonomic biases affecting fossil deposits is necessary in order to extract their true ecological signals. In terrestrial sites, the mixing of fossil material by mammalian bioturbators can substantially increase time-averaging, obscuring or even erasing stratification. In particular, pocket gophers (Thomomys sp.) are known to burrow in Holocene sites and thereby complicate the contextualization of faunal remains. Not only is it unclear if bones have been transported vertically by gophers, but the gophers themselves have the potential to die in their burrows, adding young skeletal remains to older deposits. We establish the degree of bias introduced by gopher remains in a late-Holocene archaeological site in Woodside, California by radiocarbon dating skeletal remains of Thomomys bottae and non-fossorial small mammals from the same stratigraphic units. The ages of T. bottae bones are younger overall, and span a wider range, than the distribution of ages from other small mammals from the same site and sediment layers. This suggests that a significant number of gopher remains have been introduced after the site’s deposition as a consequence of burrowing. These results shed light on a common taphonomic process that affects archaeological and paleontological sites, and may prompt reevaluation of faunal community reconstructions from fossil deposits impacted by gophers and other fossorial mammals.

Neotropical Ostracodes as Indicator for Paleo-Hurricanes - High-temporal Calcification Periods traced by Oxygen Isotopes

2021 ◽  
Author(s):  
Claudia Wrozyna ◽  
Thomas C. Brachert ◽  
Martin Dietzel ◽  
Stefan Geyer ◽  
Markus Reuter ◽  
...  
Keyword(s):  
Life Cycle ◽  
Oxygen Isotope ◽  
Temporal Resolution ◽  
Lake Water ◽  
Environmental Control ◽  
Isotope Composition ◽  
Coastal Lagoons ◽  
Climatic Conditions ◽  
High Temporal Resolution ◽  
Precipitation Seasonality

&lt;p&gt;Overwash deposits in coastal lagoons are most commonly utilized for the identification of past hurricane landfalls. These deposits have a small spatial distribution and a limited preservation potential. Thus, geochemical approaches to indicate palaeo-hurricanes, such as &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O signatures of carbonate deposits, are rare besides most archives do not provide the requested high temporal resolution. Ostracodes are ideally suited for the application of paleo-hurricanes since they calcify new valves within hours to few days &amp;#8211; fast enough to document a rainstorm event. But, information on the ostracode life cycle and influences on modern oxygen isotope compositions are limited, especially in tropical regions.&amp;#160;&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;This study investigates the relationship between hydrochemistry, climate, and valve geochemistry (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) of living populations of the common Neotropical ostracode &lt;em&gt;Cytheridella &lt;/em&gt;on a large geographical range. Since most of the regions in the Neotropics are sparsely covered by hydrochemical data, especially with respect to stable isotopes (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C), the present approach is based on estimation of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;eq&lt;/sub&gt; values calcites at isotope equilibrium as references for the interpretation of oxygen isotope distribution of ostracodes.&lt;/p&gt;&lt;p&gt;As postulated in other studies &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;precipitation&lt;/sub&gt; and temperature are the most important controls on lake water and, consequently, ostracode &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O.&lt;/p&gt;&lt;p&gt;Oxygen isotope composition reveals inferences to be drawn on calcification periods of &lt;em&gt;Cytheridella &lt;/em&gt;within its geographical distribution. Offsets between &lt;em&gt;Cytheridella &lt;/em&gt;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;eq&lt;/sub&gt; values vary throughout the year and coincide only during spring (April/May) and autumn (October) which indicates that &lt;em&gt;Cytheridella &lt;/em&gt;calcifies seasonally in all investigated regions. This implies a synchronous life cycle of &lt;em&gt;Cytheridella &lt;/em&gt;in all investigated regions. Since the regions differ in climatic conditions (i.e., precipitation seasonality and amounts, temperature gradients) an environmental control on Cytheridella&amp;#180;s life cycle can be excluded.&lt;/p&gt;&lt;p&gt;The above approach yields in an improved understanding of geochemical (i.e., &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) signatures of ostracode valves on a seasonal basis especially in regions where few information on lake water hydrochemistry is available and points to &amp;#948;18O values of ostracode species to be used for the identification of hurricane-related precipitation extremes by their high-temporal resolution of seasonal calcification.&lt;/p&gt;

Summer air temperature, reconstructions from the last glacial stage based on rodents from the site Taillis-des-Coteaux (Vienne), Western France

2014 ◽  
Vol 82 (2) ◽  
pp. 420-429 ◽  
Author(s):  
Aurélien Royer ◽  
Christophe Lécuyer ◽  
Sophie Montuire ◽  
Jérôme Primault ◽  
François Fourel ◽  
...  
Keyword(s):  
Tooth Enamel ◽  
Isotope Composition ◽  
Archaeological Site ◽  
Sedimentary Sequence ◽  
Human Occupation ◽  
Tooth Formation ◽  
Climatic Fluctuations ◽  
Last Glacial ◽  
Air Temperatures ◽  
The Last Glacial

AbstractThe oxygen isotope composition of phosphate from tooth enamel of rodents (δ18Op) constitutes a valuable proxy to reconstruct past air temperatures in continental environments. This method has been applied to rodent dental remains from three genera, Arvicola sp., Microtus sp. and Dicrostonyx sp., coming from Taillis-des-Coteaux, Vienne, France. This archaeological site contains an exceptionally preserved sedimentary sequence spanning almost the whole Upper Palaeolithic, including seven stratigraphic layers dated from 35 to 17 cal ka BP. The abundant presence of rodent remains offers the opportunity to quantify the climatic fluctuations coeval of the various stages of human occupation of the site. Differences between δ18Op values of Arvicola sp. and Microtus sp. teeth are interpreted as the result of heterochrony in tooth formation as well as differences in ecology. Mean δ18Op values of Microtus sp. are preferentially used to reconstruct summer air temperatures, which range from 16.0 ± 3.7 to 19.1 ± 3.1°C throughout the sedimentary sequence; however, the highest variability is observed during the last glacial maximum.

Paleoenvironment of the Folsom archaeological site, New Mexico, USA, approximately 10,500 14C yr B.P. as inferred from the stable isotope composition of fossil land snail shells

2005 ◽  
Vol 63 (1) ◽  
pp. 31-44 ◽  
Author(s):  
Meena Balakrishnan ◽  
Crayton J. Yapp ◽  
David J. Meltzer ◽  
James L. Theler
Keyword(s):  
New Mexico ◽  
Stable Isotope ◽  
Relative Humidity ◽  
Isotope Composition ◽  
Younger Dryas ◽  
Archaeological Site ◽  
Land Snail ◽  
Climatic Changes ◽  
Stable Isotope Composition ◽  
The Times

Well-preserved aragonitic land snail shells (Vallonia) from late Pleistocene Eolian sediment in the Folsom archaeological site in New Mexico exhibit an overall decrease of δ18OPDB from maximum values of +2.7‰ (more positive than modern) to younger samples with lower average values of about −3.6‰ (within the modern range). The age of the samples (approximately 10,500 14C yr B.P.) suggests that the decrease in δ18O may manifest climatic changes associated with the Younger Dryas. Some combination of increased relative humidity and cooler temperatures with decreased δ18O of precipitation during the times of snail activity can explain the decrease in shell δ18O. A well-known Paleoindian bison kill occurred at the Folsom site during this inferred environmental transition.Average δ13C values of the aragonite shells of the fossil Vallonia range from −7.3 to −6.0‰ among different archaeological levels and are not as negative as modern values. This suggests that the proportion of C4 vegetation at the Folsom site approximately 10,500 14C yr B.P. was greater than at present; a result which is consistent with other evidence for higher proportions of C4 plants in the region at that time.

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