HIGH-RESOLUTION STRATIGRAPHY AND SEDIMENTOLOGY OF LATE MIOCENE-PLIOCENE PALEOLACUSTRINE STRATA DEPOSITED IN PALEOSINKHOLE SETTINGS, EASTERN U.S

The Late Tertiary was a time of major climatic change, but unfortunately there are currently few identified sites from the eastern half of the U.S., and information about Tertiary climate is scarce. Three recently discovered sites provide a rare opportunity to examine depositional processes and paleoclimate recorded by high-resolution lacustrine sediments deposited within doline-type karst paleoenvironments. All sites are late Tertiary (based on diverse vertebrate fossil assemblages preserved within each); the stratigraphy and geomorphology vary at each location, but all three karst environments progressed through similar phases that included: 1) corrosion of the host carbonate bedrock, 2) doline collapse into a steep-sided and open basin, and 3) a lacustrine phase, which included accumulation of lake sediment. Each location included multiple basins of close spatial and temporal proximity. The ~2.5 Ma Haile 7G site is located in north-central Florida and represents a small, steep-sided basin that filled with an apparently continuous Late Pliocene lacustrine record. Clean eolian sand is interbedded with mottled lacustrine sediment near the top of the stratigraphic section, and this phase characterizes the transition from a lacustrine environment to subaerial exposure. The 4.5-7 Ma Gray Fossil site (GFS) is located in northeastern Tennessee; the lacustrine stratigraphy consists of both graded beds and organic-rich rhythmites, and contains an abrupt facies shift that records major climate change, which is capped by multiple paleosols. The ~4-5 Ma Pipe Creek site (PCS) is located in north-central Indiana, and PCS deposits consist of oxidized cave sediments overlain by a thin lacustrine layer, which suggests that the site was a cave that opened into a small, ephemeral pond environment. A mature yellow-colored paleosol that developed from the pedogenic alteration of the cave sediments indicates that the basin was open for a substantial period of time prior to the lacustrine phase.