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Wan Yang1
(1) Wichita State University, Wichita, KS

Abstract: Carbonate Sedimentation Rates in Mixed Siliciclastic and Carbonate Cycles, Cisco Group (Virgilian and Wolfcampian), Eastern Shelf, Texas

Marine and nonmarine carbonates and siliciclastics comprise meter-scale transgressive-regressive cycles of the Cisco Group on a shallow shelf. Carbonates are 0.1-5 m thick, thickening basinward. Gamma analysis of Kominz and Bond (1990) was used to calculate relative sedimentation rates of component facies in 18 sections in a 50x100 km2 area. The rates are converted into absolute rates through Milankovitch calibration of Cisco spectra. The rates are facies dependent and do not include stratal hiatuses of missing cycles.

Carbonate sedimentation rate varies systematically along depositional dip: (1) It is ~10-15 cm/ky in the up-dip part where siliciclastic influx was large, (2) it increases to ~20-30 cm/ky 10-20 km down dip where siliciclastic influence diminished, (3) it decreases to ~10-20 cm/ky 10-20 km farther down dip where lagoonal conditions dominated, and (4) 15-20 km farther down dip, the rate increases by several cm/ky, but in one case, by 20 cm/ky, depending on the proximity to shelf-margin carbonate bank. The rate is consistent along strike for ~40 km. Upsection the rate varies similarly to the dip trend because of systematic aggradation and progradation of the platform. Transgressive and regressive limestones are not differentiated although they are different in depositional dynamics and some environmental factors. Regional topography, siliciclastic influx, proximity to shelf-margin carbonate bank, and depositional dynamics determined carbonate facies mosaic and sedimentation rate, whereas eustasy, climate, clastic supply pattern, and subsidence determined regional transgression and regression and, thus, the occurrence of carbonate deposition.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana