Correlation of hierarchal Upper Silurian stacking patterns generated by Milankovitch orbital forcing
- Temple Univ., Philadelphia, PA (United States). Dept. of Geology
The Upper Silurian Wills Creek Formation in Pennsylvania and Maryland is entirely divisible into meter-scale allocycles. Stacking patterns of these allocycles reveal a hierarchy consistent with predictions based on the Milankovitch model of orbital forcing. Asymmetrical Sixth-Order cycles (PACs), bounded by surfaces produced by precessional sea-level rises, are divisible into a lower highstand portion and an upper lowstand portion separated by a sharp sea-level fall surface produced by a rapid sea-level drop within the precessional cycle. Sixth-Order cycles may be genetically grouped into Fifth-Order (100 ky.) and subsequently, Fourth-Order (400 ky.) cycles, each of which exhibits a distinct internal symmetry. Fifth-Order cycles, on average three to four meters in thickness, are composed of a basal transgressive portion consisting of two PACs followed by two or three successively regressive PACs. Four Fifth-Order cycles constitute a complete Fourth-Order cycle, in which the second Fifth-Order cycle contains facies representing the deepest or least restricted paleoenvironments. In each case, the fundamental Sixth-Order cycles were generated by the precessional signal modulated by orbital eccentricity variations. Over distances in excess of 100 km, Wills Creek facies change laterally from nearshore marine to fluvial coastal plain. Stacking patterns in these distinct facies are identical, and thus correlative, indicating the basin-wide extent of the stratigraphic events which produced these patterns. These correlations demonstrate that Milankovitch-driven eustatic sea-level fluctuations were occurring during the Late Silurian.
- OSTI ID:
- 5640091
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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