Abstracts: Storm- and Tide-Controlled Carbonate-Siliciclastic Mixing on a Laterally Variable Open Shelf, Poleta Formation, White Mountains, CA
BUISING, A., A. DEWITT, S. NEWTON, A. SIMMONS, D. SMYTH, L. TAYLOR, R. BOECHE, D. CHEEK, N. ECKMAN, K. LARSON, L. MURPHY, T. SAGER, and C. SMITH
In the central White Mts., eastern CA, the Lower Cambrian Poleta Formation records carbonate-siliciclastic mixing in a range of subtidal shelf environments showing both tidal and storm influences. Poleta shales contain Cruziana-facies trace fossils, and sedimentary structures consistent with deposition in low-energy lower shoreface or upper offshore environments. Carbonate subfacies include: bioturbated subtidal calcarenites; calcarenite tempestites; lenticular and sheetlike, complexly cross-bedded, commonly oolitic bodies interpreted as tidal sand waves; archeocyathid bioherms; and winnowed archeocyathid storm "coquinas." Quartzites probably record storm redeposition of siliciciclastic sand on the outer shelf. Some erosive-based carbonate tempestites grade upward into shale, implying that shale was the background sediment; carbonate tidal sand waves are locally enclosed in shale. Tidal features (e.g., flasers; linsen; calcarenite-shale tidal bedding couplets) occur over the entire stratigraphic thickness of the Poleta; hummocky (plus or minus swaley) cross-stratified units punctuate the section. In our study area, the lower Poleta is carbonate-dominated and the upper is siliciclastic-dominated; overall siliciclastic content increases to the south throughout the section. This stratigraphy differs from the tripartite (carbonate, siliciclastic, carbonate) breakdown described by previous workers elsewhere in the region. The local importance of siliciclastic material in the upper Poleta suggests a point-source, presumably deltaic, siliciclastic influx; strong tides and storms may preclude a rimmed shelf. Thus, mixing probably resulted from tide- and storm-controlled sediment transport between carbonate-dominated and siliciclastic-dominated portions of the laterally variable Poleta coastline. Overall upward coarsening and thickening implies shoaling over Poleta time.
Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California