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Abstract: Mudstone Facies of the Upper Brushy Canyon Formation and Getaway Limestone: Insights Into Depositional Processes and Stratigraphic Distribution

WEGNER, MARYBETH, UW-Madison, Department of Geology and Geophysics; KEVIN M. BOHACS and DAVID PEVEAR, Exxon Production Research Company; J.A. (TONI) SIMO, AND ALAN CARROLL, UW. Madison, Department of Geology and Geophysics

Integration of physical, chemical, and biological aspects of mudstone and sandstone character, within a sequence stratigraphic framework, reveals a variety of significant depositional processes important in the accumulation of deep-water strata in the upper Brushy Canyon and lowermost Getaway Limestone (U. Permian, west Texas). We have recognized three main mudrock facies in the outcrop. 1) Graded siltstone-organic mudstone facies containing silts grading into organic-rich mudstones on scoured, loaded bases, mixed quartz and carbonate clasts, diverse macrofossils, and abundant woody/coaly organic matter. This facies occurs as lenses, mostly interbedded with channel and sheet sandstones and at channel margins, and interpreted to be strongly influenced by turbidity currents. 2) Scattered silt-discontinuous organic mudstone fades characterized by “wispy” bedding, abundant and diverse zooplanktonic fetal pellets, radiolarians, sparse macrofossils, and abundant amorphous organic matter. This facies forms in small- and large-scale laterally extensive mudstone intervals, interpreted to be strongly influenced by pelagic/hemipelagic processes during abandonment. 3) Lamina-scale beds containing aligned and scattered silts with clay-size organic matter, bimodal clast size and composition of quartz and carbonate, some graded beds, occasional macrofossil fragments, radiolarians, and zooplanktonic fecal pellets, and mixed woody/coaly and amorphous organic matter. This fades occurs in drapes on master erosional channel bases, representing a mixture of pelagic and turbidite processes, and bypass. Recognition of these facies in core could improve the interpretation of the sequence stratigraphy of deep-water sandstones.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah