Regional Paleosol Variability on a Dissected Alluvial/Coastal Plain: A Proposal to Develop an Empirical Paleosol-Landscape Model for Nonmarine Sequence Stratigraphy

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Regional Paleosol Variability on a Dissected Alluvial/Coastal Plain:A Proposal to Develop an Empirical Paleosol-Landscape ModelFor Nonmarine Sequence Stratigraphy and Terrestrial Basin AnalysisPaul McCarthyEAR-0229196 The use of paleosols (fossil soils) for partitioning continental rocks and understanding changing sedimentation rates in terrestrial sedimentary basins is now firmly established. Early successes in applying paleopedological techniques to the recognition and correlation of terrestrial unconformities (sequence boundaries) have built largely upon paleosol-landscape models that were developed primarily from aggradational basin settings. In contrast, relatively little attention has been paid to paleosol variability in an alluvial/coastal plain undergoing dissection during the falling stage on the relative sea level curve. This research will document the spatial variability of paleosols across a single interfluve surface in the Cretaceous (Cenomanian) Dunvegan Fm. with respect to distance from associated valley margins and the coeval paleo-shoreline. The Dunvegan Fm. is ideally suited for this study because it is both spatially extensive and stratigraphically well understood; because coeval shallow marine and shoreline environments can be confidently correlated with nonmarine deposits updip; and because paleo-valley deposits have been mapped in detail and the distance from any interfluve paleosol to the valley margin can be fairly accurately determined. Ten paleosols will be sampled from a single interfluve at distances from less than 1 km to more than 20 km from adjacent valley margins along a transect extending more than 250 km updip from the coeval shoreline. Paleosols will be described in the field and analyzed for micromorphological features, geochemistry and mineralogy. Micromorphological features will be quantified and paleosols will be objectively compared using a soil micromorphology index. These paleopedological data will be used to reconstruct the pedosedimentary histories of these paleosols, to develop a paleosol-landscape model for dissected alluvial/coastal plain settings, and to assess the value of the soil micromorphology index for objective description and comparison of paleosols both within and between basins.