ABSTRACT: Stratigraphy and Depositional Environments of Catahoula "Formation" Sandstones and Associated Facies in South-Central Mississippi

Christopher P. Cameron, Lee A. Day

Surface and subsurface studies of the Catahoula "Formation" in a seven county area of south-central Mississippi have revealed major problems and misconceptions regarding Neogene stratigraphy and geological mapping in this part of the Gulf basin. The results of these investigations show that the traditional stratigraphic subdivisions of the "up-dip" Neogene section in Mississippi are invalid, and that the fundamental criteria for defining rock stratigraphic units at the formation rank are nonexistent. Although the base of the Neogene section is reasonably well defined by virtue of its relatively continuous contact with the Bucatunna Formation (Oligocene Vicksburg Group), a mappable bounding sequence above the Catahoula-Bucatunna Formation contact does not exist in the stud area.

An overall fine-grained interval (Hattiesburg "Formation"?) above the Catahoula "Formation" appears to wedge out before reaching outcrop. Hence, differentiation between up-dip sandy gravels of the Catahoula and similar facies of the Citronelle "Formation" is difficult (if not impossible). Further complicating the problem of stratigraphic unit discrimination is the discovery of sandy gravels within the Hattiesburg "Formation" interval.

A subsurface analysis in this study area revealed that the Catahoula "Formation," as defined by Day, attains a thickness of 625 ft and has a rough three-tiered stratigraphy: (a) a basal unit (75-140 ft thick) composed of sands and subordinate fine-grained facies; (b) a relatively fine-grained middle unit (250-350 ft thick) composed of silts and clays with recurrent, discontinuous, sand bodies; and (c) an upper unit (175-325 ft thick) composed largely of sand and gravels. This study confirmed that most of these sediments are the product of fluvial channel and

associated floodplain deposition. However, in the basal unit deltaic facies appear to be preserved on outcrop in Smith County and perhaps in a mild structural depression in the southwest portion of the study area.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990