Submarine intrareef pisoliths and the origin of Silurian carbonate clinothems, northcentral Indiana
- Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Geological Sciences
Evaluation of the relative importance of biological versus physical processes during the deposition of midwestern Silurian carbonate buildups has resulted in three generally incompatible scenarios: (1) that bioherms consist largely of autochthonous debris generated and deposited in deep shelf settings; (2) that most carbonate was generated in reefal settings, but styles of accumulation evolved from primarily core accretion to dominantly flank bed progradation with upward growth to shallower depths, and (3) that larger Silurian buildups are neither reefs nor bioherms in that they consist almost entirely of allochthonous biotic debris derived from high-energy wave-swept benches. Vertical tension fractures that crosscut proximal flank beds in the Pipe Creek Junior quarry of northcentral Indiana formed during compaction of underlying interreef muds and are commonly filled with well-sorted pisolitic grainstone. Pisolith cortices are petrologically indistinguishable from marine cement between pisoliths, from marine cement lining tension fractures, and from marine cement in surrounding grainstone. Isotopic signatures and trace element concentrations for these components are identical. In addition, the pisolitic grainstone commonly exhibits lateral grading, with pisolith size increasing toward fracture interiors. These features demonstrate that pisoliths are submarine cave pearls that formed from Silurian seawater within synsedimentary tension cracks during flank bed deposition and progradation. This origin supports an interpretation that present exposure levels at Pipe Creek Junior are generally coincident with the Silurian depositional top of the buildup, as minimum current energies necessary for the formation of large coated grains require high-energy, shallow-water conditions.
- OSTI ID:
- 6137132
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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