NOAA/WDS Paleoclimatology - Western Kentucky LGM Peoria Loess Gastropod Data and July Temperature

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 5 cm 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 ~23C at 30 cal ka, cooling to ~18C by 26 cal ka; about 3-8C cooler than today (~26C). Superimposed on this cooling trend are multi-centennial variations in detrital carbonate, fossil shell concentrations, palaeotemperature estimates, and oxygen isotope values (Vertigo, Discus, Helicodiscus). The finer-scale variations imply relatively synchronous fluctuations in glacial sediment supply, loess sedimentation, and climate.

位于未受冰川作用影响的肯塔基州西部的罗克斯黄土剖面，为末次冰盛期起始阶段提供了高分辨率环境记录。厚度达9米的佩奥里亚粉砂层（Peoria Silt）内含26种陆生腹足类物种，在单个5厘米的地层间隔内最多可出现15个物种。基于壳体或木炭测得的13组放射性碳年代数据，年代范围介于30至24.5校准千年（cal ka）之间；较年轻的黄土层已遭受淋溶或侵蚀。腹足类组合的地层学偏移指示了显著的降温过程，尤其是在约27校准千年时——彼时太阳辐射照度持续下降，南部劳伦泰德冰盖快速推进。中西部至南部分布的物种（如Anguispira kochi、Gastrocopta pentodon、Hawaii miniscula、Helicodiscus parallelus、Vallonia perspectiva）仅见于佩奥里亚粉砂层的最下部（约30~27校准千年）。与之相反，耐寒物种（Columella alticola、Vertigo modesta、Vallonia gracilicosta）仅出现在全冰期阶段的佩奥里亚粉砂层中（27~24.5校准千年）。基于互气候区间法推算的七月平均气温，从30校准千年时的约23℃降至26校准千年时的约18℃，较现今（约26℃）低3~8℃。在这一降温趋势之上，还叠加了碎屑碳酸盐、化石壳体丰度、古温度估算值以及腹足类（Vertigo、Discus、Helicodiscus）的氧同位素值所记录的百年尺度波动。这些更精细的波动指示了冰川沉积物供给、黄土沉积作用与气候的相对同步波动。