Depositonal Environments of the Catahoula Formation, Walker County, East Texas

Fluvial sedimentary rocks of the Oligocene-Early Miocene Catahoula Formation crop out at a flooded rock quarry northwest of Huntsville in Walker County, East Texas. The fluvial architecture consists of multistory channel bodies. Key architectural elements recognized from the fluvial deposits are lateral and downstream accretion, interchannel lacustrine fill, overbank, and abandoned channel deposits. Eleven lithofacies described from these elements display a variety of sedimentary structures which include trough and tabular cross-stratification, planar stratification, and ripple-drift lamination. The channel deposits are composed of fine- to very coarse-grained quartzarenites which are silica-cemented. Differential silica cementation occurs at different stratigraphic levels within the channel. The reason may be due to the interplay between the geochemistry of the circulating groundwater and permeability variations due to facies changes. The lacustrine facies is dominated by thick to thinly bedded claystones and clayey siltstones. The clay appears to have been formed by the alteration of volcanic ash in response to pedogenesis or shallow burial diagenesis.

Paleocurrent analyses from cross strata reveals a primary southeast paleoflow direction and a subordinate northeast component due to lateral migration of the fluvial channel. Channel avulsion resulted in the deposition of abandoned channel facies. The fluvial architectural elements and paleocurrent analysis indicates that deposition occurred within a single-thread meandering river system. Maximum bankfull depth (estimated from cross-set thicknesses) is about 5 m, and the minimum channel width is about 60 m.

Previously unrecognized faulting has significantly altered the distribution of these lithofacies. The mined-out portion of the quarry is in a NNW-trending graben in which the quartzarenite was preferentially preserved. The graben is offset by several smaller E-W trending faults. The cause of faulting remains uncertain; however the faults do not appear to be syndepositional.