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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 685

Last Page: 685

Title: Depositional Environments in Upper Cambrian Jordan Previous HitSandstoneNext Hit in Wisconsin: ABSTRACT

Author(s): Charles W. Byers, Robert H. Dott, Jr.

Article Type: Meeting abstract

Abstract:

The Upper Cambrian Previous HitsandstoneNext Hit formations of the Upper Midwest are superficially uniform over broad areas. Individual formations are homogeneous in Previous HittextureNext Hit and mineralogy, and several of the Previous HitsandstoneNext Hit units in the sequence are nearly identical in terms of these parameters. However, Previous HittextureNext Hit and Previous HitcompositionNext Hit have been shown to be environmentally ambiguous, whereas sedimentary structures and trace fossils provide definite criteria for interpreting depositional settings and for distinguishing between apparently similar quartzarenites. Major differences exist among the formations in mode of deposition (subtidal marine, eolian, tidal flat, and possibly fluvial environments have been recognized). One formation, the Jordan Previous HitSandstoneTop, is an example of marine depth zonation. The Jorda contains two major facies, based primarily on bedding style: (1) high-angle, trough cross-stratification; and (2) low-angle cross-stratification (hummocky cross-stratification). The high-angle facies is interpreted as shallow subtidal (shoreface depth) in origin, produced by constantly moving dune bed forms in a current-dominated regime. The following criteria suggest this interpretation: festoon bedding, well-defined trough axis modes, and presence of Skolithos without strong bioturbation. The low-angle facies is interpreted as a shoreface to offshore deposit, representing episodic deposition by storm surges--on the basis of dominant hummocky cross-stratification, wide dispersion of trough axis orientations, presence of laterally extensive bedding planes and shale seams, dominance of P anolites-type burrows, and localization of intense bioturbation on tops of cross-sets. Generally, the high-angle facies overlies the low-angle facies, indicating shallowing upward (progradation). However, the facies are intertongued and even lenticular in places; this stratigraphic variability and the lack of beach or nonmarine deposits suggest that no shoreline was present.

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