The Sedimentology, Depositional Environments, and Correlation of the Eagle Ford Group (Boquillas Formation) in West Texas from Big Bend National Park to Maverick Basin

Abstract

Abstract

The sequence stratigraphic framework of the Eagle Ford Group, defined previously from Lozier Canyon (Terrell County, Texas), is correlated to Hot Springs, Big Bend National Park (Brewster County, Texas) and the Maverick Basin (Webb County, Texas). This correlation relies on sedimentology, stratigraphy, and hand-held spectral gammaray (SGR) scintillometer profiles that define distinctive units.

Hummocky cross-stratification (HCS), swaley cross-stratification (SCS), wave ripples, gutter casts, and well-sorted molluscan shell lags all indicate that the depositional environment of the Eagle Ford Group is a flooded, storm-dominated carbonate ramp/ shelf (Comanche Platform) at the southern end of the Cretaceous epicontinental seaway.

There was minimal terrrigenous input in this area, except for volcanic ash. We argue that most of the deposits previously interpreted as debris flows in the Eagle Ford Group were produced by reverse density gradients that failed by seismic shaking or cyclic loading. Furthermore few deposits in the study area have characteristics of turbidites or debrites,

Overall, the depositional conditions at the Hot Springs section, similar to those in the Maverick Basin, were in deeper water than at Lozier Canyon but still on the Comanche Platform, based on the increase of current ripples, smaller wave ripples, fewer HCS, and smaller soft-sediment deformation zones. The gamma ray log data and outcrop features suggest that the Scott Ranch Member (mostly Turonian) at the Hot Springs is more complete because it has at least two shallowing-upward trends, unlike Lozier Canyon which does not record one complete shallowing-upward sequence.

AAPG Datapages/Search and Discovery Article #90196 © 2014 GCAGS, Lafayette, Louisiana, October 5-7, 2014