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| Sangamonian Stage | |
|---|---|
| Name | Sangamonian Stage |
| Period | Pleistocene |
| Namedfor | Sangamon River |
| Type | Interglacial stage |
| Time start | ~125 ka |
| Time end | ~71 ka |
| Chronology methods | Oxygen isotope stratigraphy, radiometric dating, luminescence dating |
Sangamonian Stage The Sangamonian Stage is a late Pleistocene interglacial interval recognized primarily in North America and correlated with global marine oxygen isotope stages. It is framed by glacial and stadial deposits and is used in correlation with marine isotope stage records, terrestrial stratigraphy, and archaeological assemblages involving Late Pleistocene cultures.
The Sangamonian Stage is defined as the last major interglacial before the Last Glacial Maximum and is commonly correlated with Marine Isotope Stage 5e, Marine Isotope Stage 5c, and Marine Isotope Stage 5a in marine stratigraphy, with proposed duration approximately from ~125,000 to ~71,000 years before present. Key chronological frameworks derive from correlations to the Eemian, the British Ipswichian Stage, and the European Last Interglacial sequence, aligning North American facies with global records such as the LR04 benthic stack and the Greenland ice cores chronology. Important stratigraphic markers include the Sangamon Soil developed on glacial tills and correlation to paleosol horizons in Midwestern loess profiles evaluated alongside sequences from the Mississippi River, Ohio River, and Hudson River basins.
Sangamonian stratigraphy involves soil development atop deposits from the Illinoian glaciation and beneath tills and loess of the Wisconsin Glaciation. Correlations use the Loess Plateau analogs, Midwestern loess units such as the Peoria Loess, and terraces along the Missouri River and Mississippi River systems. Key sections include stratotypes in Illinois near the Sangamon River valley, fluvial terraces at Cahokia Mounds peripheries, and exposures in the Great Lakes region. Correlative frameworks connect to European stratigraphic schemes like the Holstein interglacial and to African sequences including deposits in the Kakira Basin and Omo Kibish contexts where interglacial proxies align temporally.
Paleoclimate reconstructions for the Sangamonian use proxies from Greenland ice cores, Coral reef terraces in the Caribbean and Atlantic, pollen sequences from lacustrine records at Lake Michigan and Lake Huron, and faunal assemblages from cave sites such as Crawford Cave. Isotope analyses from marine cores off the Mid-Atlantic Bight and Pacific cores near California indicate warmer-than-glacial temperatures, higher sea levels inferred from submerged terraces near Florida and the Bahamas, and expanded temperate biomes across the Midwestern United States. Palynological records from the Appalachian Mountains and prairie sequences across the Great Plains yield evidence for mixed temperate forest and grassland mosaics, while speleothem records in the Mammoth Cave National Park region provide hydroclimatic detail.
Megafaunal and floral assemblages during the Sangamonian include taxa recorded in faunal lists from sites like Rancho La Brea analogues and northeastern cave deposits such as Bear Cave. Faunal indicators include temperate species analogous to those in the Eemian faunal complexes—deer, elk, and small mammals recorded in Midwestern sites—and extirpations evident prior to the Younger Dryas sequence. Pollen records show expansions of deciduous genera such as Quercus, Carya, and Acer in eastern North America, with prairie taxa like Andropogon and Bouteloua prominent in Great Plains pollen assemblages. Marine faunas, documented in coral and mollusk terraces along Florida Keys and Atlantic coastlines, reflect higher sea levels and warmer SSTs contemporaneous with the Sangamonian.
Regional expression of the Sangamonian varies between the Midwest United States, the Northeastern United States, the Southeast United States coastal plain, and the Great Plains. In the Midwest, the Sangamon Soil atop Illinoian till is a prominent marker, whereas in the Southeast sandy coastal deposits and shell middens in Florida and the Carolinas provide marine-terrestrial interfaces. In the Great Lakes region, erosional unconformities and lacustrine deposits from Lake Erie and Lake Ontario margins complicate boundary delineation. Western correlations into the Rocky Mountains and Pacific Northwest rely on alpine moraine sequences and lacustrine records from basins like Great Salt Lake and Lake Bonneville.
Dating of Sangamonian deposits employs multiple techniques including uranium-thorium dating used on speleothems from Carlsbad Caverns analogues, optically stimulated luminescence (OSL) on loess from Loess Hills sections, radiocarbon for late-stage deposits (when within range), and amino acid racemization in marine mollusks from Florida terraces. Discrepancies arise between OSL, uranium-series, and correlations to Marine Isotope Stage curves, leading to debates over the Sangamonian's exact onset and termination. Controversies also involve whether the Sangamonian should be equated strictly with MIS 5e or include subsequent substages, and how to reconcile regional stratigraphic nomenclature such as the Brimfield Interstadial and the local Sangamon Soil terminologies.
Archaeological contexts potentially contemporaneous with Sangamonian deposits include open-air sites on river terraces and lithic assemblages in the Midwest linked to Late Pleistocene technologies. Stone tool typologies recovered from terrace contexts near Cahokia Mounds peripheries and in the Ohio River Valley have been evaluated against chronologies established by OSL and tephrochronology where available. Human-environment interactions are inferred from faunal processing evidence at fluvial sites, shell middens along the Atlantic Seaboard, and possible seasonal campsite indicators in upland lacustrine margins. Ongoing debates concern preservation biases, stratigraphic mixing, and the resolution of chronological controls needed to definitively associate specific archaeological materials with the Sangamonian interval.
Category:Pleistocene stages