DIFFENDAL, R. F., JR, University of Nebraska, Lincoln, NE, and A. LOWRIE,* Consultant, Picayune, MS
ABSTRACT: Application of Sea Level Stratigraphy to Neogene Great Plains
Absolute-dated high-frequency (Milankovitch cycles) marine climate-sea level oscillatory stratigraphy can be correlated with emerging absolute continental stratigraphies. Improvements in absolute dating of Neogene formations across the North American Great Plains make this a candidate area in which to correlate marine and continental stratigraphies. Midlatitude continental areas respond directly to climate variations. During glaciated/cold weather, sea level lowering results in steepened river gradients with increased erosion all along the river channel and larger stress-bed loads. This, combined with glacial catastrophic flooding, produces greater cut-and-fill sequences along river systems, then crevasse splays along the emergent coastal plain, deltas along the shelf, and submarine f ns on the slope. Eustatic sea level oscillations for the Tertiary are accepted as driven by glacial accumulations on the continents, with even greater seasonality, aridity, and general cooling.
A Great Plains Neogene section contains conglomerate, grading upward to sandstone, and topped by caliches. The conglomerate is residue left after glacial flooding that created cut-and-fill, all with climatic cooling and maxima. Sandstone is deposited with waning of cooling. In interglacials, calcium carbonate-rich caliches formed. This sequence may represent fourth-order deposition, and certainly third-order cycles. Correlation of Neogene Great Plains stratigraphy with recognized eustatic curves permits more detailed understanding of depositional mechanisms and sediment type along southern and offshore Louisiana.
AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.