Orbital forcing of a hierarchy of carbonate allocycles: Devonian Cedar Valley Group, Iowa
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:6860124
- Temple Univ., Philadelphia, PA (United States). Dept. of Geology
Initial results of a study of allocyclicity in the Cedar Valley Group of eastern Iowa indicate that stacking patterns of cycles in the Little Cedar Formation are consistent with the predictions of the Milankovitch model of orbital forcing. The unconformity-bounded Little Cedar Formation, a third-order sequence of approximately 2 million years duration, is divisible into 3 fourth-order sequences (400 k.y.) that correspond to the formal members of the formation: solon, Lower Rapid and Upper Rapid members in southeastern Iowa. One or two fourth-order sequences are missing according to the Milankovitch model, probably as a function of low subsidence rates enhancing the unconformities at the third-order boundaries. Fourth-order sequences consist of 2 to 4 fifth-order sequences (100 k.y.) averaging 2.5 meters in thickness; only the Lower Rapid fourth-order sequence is complete in the sense of containing its full complement of fifth-order sequences. In turn, fifth-order sequences consist of 3 to 6 shallowing-upward sixth-order sequences (PACs, 20 k.y.) averaging less than one meter in thickness. These stacking patterns fit the Milankovitch model of orbital forcing, specifically by precessional and eccentricity cycles. Compared with Silurian and Devonian foreland basin cyclicity, these cratonic carbonate sequences are less complete, and therefore, thinner, at the third, fourth and fifth orders owing to differences in rates of subsidence. Comparable thicknesses of sixth-order cycles in both tectonic settings suggest that subsidence played a minor role in influencing the stratigraphic expression of the precessional signal.
- OSTI ID:
- 6860124
- Report Number(s):
- CONF-9404217--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 26:5
- Country of Publication:
- United States
- Language:
- English
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