Last glacial maximum ecology and climate from terrestrial gastropod assemblages in Peoria loess, western Kentucky

Abstract

The Rocks loess section, in unglaciated western Kentucky, provides a high resolution environmental record during the last glacial maximum onset. The Peoria Silt (9 m thick) contains 26 terrestrial gastropod species, with up to 15 species within a single 5cm interval. Thirteen radiocarbon ages, using shells or charcoal, range between 30 and 24.5 cal ka; younger loess has been leached or eroded. Stratigraphic shifts in gastropod assemblages imply significant cooling, particularly ~ 27 cal ka, as solar insolation was decreasing and the southern Laurentide Ice Sheet rapidly advancing. Midwestern to southern species (e.g., Anguispira kochi, Gastrocopta pentodon, Hawaii miniscula, Helicodiscus parallelus, Vallonia perspectiva) occur only in the lowermost Peoria Silt (~30-27 cal ka). In contrast, cold-tolerant species (Columella alticola, Vertigo modesta, Vallonia gracilicosta) occur only in full glacial Peoria Silt (27-24.5 cal ka). Inferred mean July temperatures, from mutual climatic range methods, range from ~23°C at 30 cal ka, cooling to ~18°C by 26 cal ka, about 3-8°C cooler than today (~26°C). Superimposed on this cooling trend are multi-centennial variations in detrital carbonate, fossil shell concentrations, paleotemperature estimates, and oxygen isotope values (Vertigo, Discus, Helicodiscus). The finer-scale variations imply relatively synchronous fluctuations in glacial sediment supply, loess sedimentation, and climate.

Oxygen isotopes in terrestrial gastropod shells track Quaternary climate change in the American Southwest

“…Future work should focus on improving the temporal resolution of gastropod shell records by targeting known paleowetland sedimentary sequences that exhibit extremely high rates of sedimentation (e.g., Springer et al, 2015, 2018; Pigati et al, 2019). An additional depositional setting suitable for gastropod shell δ 18 O investigations is the thick packages of terrestrial shell-rich glacial age loess, which occur in the midwestern and south-central U.S. (Pigati et al, 2013, 2015; Nash et al, 2018; Grimley et al, 2020). Together, these deposits could provide gastropod shell isotopic records that span large portions of North America.…”

“…Gastropods are one of the most abundant fossil groups in the terrestrial geologic record and their shells are preserved in a wide variety of depositional settings, including loess, eolian sand, alluvial and fluvial sequences, and geologic deposits associated with desert wetland ecosystems. Their abundance, preservation, and broad spatial and temporal coverage make fossil gastropod shells a potentially important archive of past environmental and climatic conditions in the terrestrial realm, provided the isotopic system is well constrained (Goodfriend and Ellis, 2002; Yanes et al, 2009; Nash et al, 2018; Grimley et al, 2020).…”

Updated chronology for Peoria Silt (loess) accumulation in Illinois and western Indiana from radiocarbon dating of terrestrial gastropod shells

“…Significantly, these loess deposits serve as the parent material for some of the most productive agricultural soils in North America (Fehrenbacher et al, 1986;Catt, 2001). A more precise understanding of the chronology of Peoria Silt deposition, along meltwater valleys segments with contrasting glacial history, is important for providing context to studies of paleoclimate (Muhs et al, 2013;Conroy et al, 2019), terrestrial gastropod fossils (Baker, 1936;Leonard and Frye, 1960;Grimley et al, 2020), mammalian fossils (Treworgy et al, 2007;Saunders et al, 2010), loess-stratigraphy correlations (Frye et al, 1968;Mason et al, 2007), soil genesis (Ruhe, 1984;Muhs et al, 2001), archaeology (Van Nest, 1993), and soil chronosequences (Schumacher et al, 1987). Geochronology can also help determine the extent to which loess deposition is connected with the geologic history and fluctuations of sediment-rich glacial lobes of the southern Laurentide Ice Sheet (Curry, 1998;Grimley, 2000;Ullman et al, 2015;Curry et al, 2018;Heath et al, 2018;Dendy et al, 2021) or to what extent loess accumulation is driven directly by climatic change (Wang et al, 2000;Muhs et al, 2013).…”

“…In last glacial palustrine (former wetland) sediments of central Indiana, comparisons of radiocarbon ages from terrestrial gastropods (Succineidae, Discus) with those from plant macrofossils in the same stratigraphic layers show good correspondence (Loope et al, 2018;this study). Terrestrial gastropods are locally abundant in thick last glacial loess deposits (>5 m), proximal to the valley bluffs of major river valleys in the central United States such as the Illinois Valley, Ohio Valley, and Mississippi Valley (Baker, 1936;Leonard and Frye, 1960;Nash et al, 2018;Grimley et al, 2020). Based on two recent studies, loess accumulation rates average ∼1 mm/yr or more in loess zones that have complete (identifiable) gastropod shells preserved (Nash et al, 2018;Grimley et al, 2020).…”

“…Terrestrial gastropods are locally abundant in thick last glacial loess deposits (>5 m), proximal to the valley bluffs of major river valleys in the central United States such as the Illinois Valley, Ohio Valley, and Mississippi Valley (Baker, 1936;Leonard and Frye, 1960;Nash et al, 2018;Grimley et al, 2020). Based on two recent studies, loess accumulation rates average ∼1 mm/yr or more in loess zones that have complete (identifiable) gastropod shells preserved (Nash et al, 2018;Grimley et al, 2020). In loess with accumulation rates ≤0.5 mm/yr, the shells are probably not buried quickly enough to be fully protected from carbonate dissolution or leaching processes.…”