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Stratigraphy, diagenesis, and provenance of Upper Paleozoic eolian limestones, western Grand Canyon and southern Nevada
Abstract
Calcareous dunes and eolian limestones are considered by many to be genetically related to rapid glacio-eustatic fluctuations of sea level. However, while these deposits are widespread along Pleistocene and Holocene low-latitude coasts, older analogs are either extremely rare, or misinterpreted as subaqueous in origin. Medium- to large-scale crossbedded arenaceous limestones of the Pennsylvanian Callville Limestone of southern Nevada, and the correlative Manakacha and Wescogame Formations (Supai Group) and the Permian Pakoon Limestone of western Grand Canyon, although considered marine by earlier workers, contain several diagnostic structures indicative of an eolian origin. They are composed chiefly of thin, inverse-graded laminae produced by the migration and climb of wind ripples. Many are bimodal with the coarse mode never exceeding two millimeters. Sets of cross-strata commonly have irregular upper surfaces produced by differential wind erosion of damp or lightly cemented laminae. Southward-dipping cross-strata in these rocks are the earliest record of a paleowind system that persisted in this region well into Jurassic time. Marine beds that are cyclically interbedded with the eolian deposits did not undergo early lithification. Petrographic evidence includes mechanical breakage of shells, fitted fabrics, and microstylolites. Field evidence includes load casts, desiccation cracks, and deflation lags at the contacts between wackestones and eolian grainstones. Where marine units underwent extensive early lithification, there are no interbedded eolian deposits. The marine units are interpreted as the source of the sediment comprising the eolianites. During eustatic highstands, onshore winds drove beach sediments landward. In contrast to Quaternary examples, the eolian deposits of this study do not cap shallowing upward sequences; beach facies are generally absent. During low-stands, most quartz-rich beach facies were removed by deflation; that material too coarse to be wind-transported accumulated as laterally-persistent gravel lags. Deflation was facilitated by the lack of widespread sea floor cementation (hardgrounds), and an arid paleoclimate which limited the extent of meteoric diagenesis.
Subject Area
Geology
Recommended Citation
Rice, Jonathan Aaron, "Stratigraphy, diagenesis, and provenance of Upper Paleozoic eolian limestones, western Grand Canyon and southern Nevada" (1990). ETD collection for University of Nebraska-Lincoln. AAI9030148.
https://digitalcommons.unl.edu/dissertations/AAI9030148