Loess is widely distributed across North America. Most of the loess is thin, lacks paleosols, and is temporally related to MIS 2 glacial environments. Thick loess with intercalated paleosols occurs in four distinct regions, providing a terrestrial record of climate and environment extending to the middle Pleistocene in the Mississippi River Valley, Great Plains, and Snake River Plain, while the record likely extends through the entire Pleistocene for the Palouse and interior Alaska and Northwestern Canada. Paleosols were first recognized in loess and glacial deposits of the Mississippi River and its major tributary valleys. Loess deposits are related to glacial advance and are thickest and contain the best paleosol record adjacent to river valleys that drained the Laurentide Ice Sheet. The frequency and spatial distribution of loess and paleosols decrease with increasing age of the loess. Paleosols range from interstadial soils marked by carbonate leaching and organic matter accumulation to interglacial-scale paleosols that formed over one or more glacial cycles and contain thick sola, deep leaching of carbonate minerals, and extensive transformation of primary minerals to clays and oxides. The Great Plains has some of the thickest loess in the western hemisphere and has a temporal and stratigraphic record similar to the Mississippi Valley region, except that much of the loess is derived from nonglacial sources. Loess and paleosols are widespread on the Columbia Plateau of the northwest contiguous USA. In particular, the Palouse region contains a record that may span the Pleistocene, although the late Pleistocene is most extensively studied. Unlike other regions, the loess is deposited during times of deglaciation and slack water sediment accumulation in basins that are later deflated. Soil formation is active continuously, with morphology impacted by rates of loess accumulation, which can bifurcate soil stratigraphic units. Paleosols have dryland morphologies that vary spatially along environmental gradients that enable long-term reconstructions. Interior Alaska and Northwest Canada have some of the oldest loess records, based on tephras dated to the Early Pleistocene. However, scant description and analysis of the earliest paleosols limits environmental interpretations. Late Pleistocene paleosols are very common in loess deposits and are most commonly marked by organic matter accumulation, greater clay content, ground squirrel bioturbation, and cryoturbation features.

Loess-Paleosol Sequences of North America

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发表日期：

2026年

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Peter M. Jacobs

摘要

Loess is widely distributed across North America. Most of the loess is thin, lacks paleosols, and is temporally related to MIS 2 glacial environments. Thick loess with intercalated paleosols occurs in four distinct regions, providing a terrestrial record of climate and environment extending to the middle Pleistocene in the Mississippi River Valley, Great Plains, and Snake River Plain, while the record likely extends through the entire Pleistocene for the Palouse and interior Alaska and Northwestern Canada. Paleosols were first recognized in loess and glacial deposits of the Mississippi River and its major tributary valleys. Loess deposits are related to glacial advance and are thickest and contain the best paleosol record adjacent to river valleys that drained the Laurentide Ice Sheet. The frequency and spatial distribution of loess and paleosols decrease with increasing age of the loess. Paleosols range from interstadial soils marked by carbonate leaching and organic matter accumulation to interglacial-scale paleosols that formed over one or more glacial cycles and contain thick sola, deep leaching of carbonate minerals, and extensive transformation of primary minerals to clays and oxides. The Great Plains has some of the thickest loess in the western hemisphere and has a temporal and stratigraphic record similar to the Mississippi Valley region, except that much of the loess is derived from nonglacial sources. Loess and paleosols are widespread on the Columbia Plateau of the northwest contiguous USA. In particular, the Palouse region contains a record that may span the Pleistocene, although the late Pleistocene is most extensively studied. Unlike other regions, the loess is deposited during times of deglaciation and slack water sediment accumulation in basins that are later deflated. Soil formation is active continuously, with morphology impacted by rates of loess accumulation, which can bifurcate soil stratigraphic units. Paleosols have dryland morphologies that vary spatially along environmental gradients that enable long-term reconstructions. Interior Alaska and Northwest Canada have some of the oldest loess records, based on tephras dated to the Early Pleistocene. However, scant description and analysis of the earliest paleosols limits environmental interpretations. Late Pleistocene paleosols are very common in loess deposits and are most commonly marked by organic matter accumulation, greater clay content, ground squirrel bioturbation, and cryoturbation features.