The Late Cenozoic lacustrine and fine-grained sediments from the south-central United States should contain abundant, well-preserved pollen assemblages; unfortunately, many are entirely devoid of pollen, while others contain only corroded pollen in low concentrations. The absence of pollen in the southern Great Plains is widespread, encompassing many lacustrine and alluvial deposits. This absence or poor preservation of pollen and other organic matter within these materials is probably the result of post-depositional biotic or chemical oxidation, perhaps related to drying out of the deposits and subsequent movement of meteoric or ground water through the sediments. Among southern Plains localities barren of pollen are the type sections of the Clarendonian, Hemphillian, and Blancan North American Land Mammal ages in Texas. Other localities barren of pollen or containing low concentrations of poorly preserved grains include the Laverne (Miocene), Camp Rice (early Pleistocene), and Tule (early-middle Pleistocene) formations, sediments below the Pearlette O ("Lava Creek B") and Bishop ashes (middle Pleistocene), the Slaton (Illinoian), Easley Ranch (Sangamon), Quiteque, Jones, Howard Ranch (Wisconsinan), Clovis, Lubbock Lake, and Plainview sites (late Wisconsin-Holocene), and several early Holocene lacustrine and alluvial localities. Only a few localities in the region have provided reliable pollen records. The Rita Blanca beds in the Texas Panhandle have yielded the only Pliocene pollen record in the region; it indicates a cool-climate sagebrush grassland vegetation. The only pre-Illinoian Pleistocene pollen record is Hansen Bluff, south-central Colorado, which shows local shifts from sagebrush grassland to forest vegetation. Illinoian-age pollen assemblages from north-western Oklahoma and southwestern Kansas indicate a sagebrush grassland with significant percentages of pine and spruce, possibly signaling the presence of pine and spruce populations in the central Plains. Well-preserved Wisconsin-age pollen assemblages also document a full-glacial sagebrush grassland on the southern High Plains.

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