ABSTRACT: Lower Claiborne Regional Stratigraphic Architecture: Southeast Texas to East-Central Louisiana

Abstract

Abstract The lower Claiborne section and its units discussed and illustrated here, of Lutetian age - middle Eocene (Figure 1), are recognized as a series of marine shelf, marginal marine, and deltaic-strandline deposits. Regional closely-spaced well-log cross-sections extending for almost 500 miles from south Texas to eastern Louisiana updip of the Claiborne shelf margins clearly show the regional stratigraphic architecture along depositional strike from southeast-central Texas through east-central Louisiana (Ewing, 1994; Ewing and Vincent, 1997). The obvious internal forms when viewing the lower Claiborne at such great scale are large, very-low-angle, sigmoidal clinoform sets delineated by regional flooding surfaces (see Figure 2 below). The flooding surfaces (FS) are depicted as the flat to sigmoidal lines seen in that cross-sectional diagram - major FS's shown by heavier lines; lesser FS's by thin and/or dashed lines. These large downlaps are roughly oriented from NW to SE across coastal Texas and into central Louisiana demonstrating the time-transgressive nature of the entire lower Claiborne - the downlaps proceed from oldest to youngest coming from west to east. (Contrast with Perkins and Hobday, 1980, and Fisher, 1964.) Basin analysis and subsurface exploration rely on the identification of genetic units (or sequences) because they are time-bounded units which unite all of the co-occurring processes and their resulting deposits. Genetic stratigraphic units are defined and bounded by key flooding surfaces which approximate time lines (genetic sequences of Galloway, 1989a, b). These units, combining progradational and transgressive elements, have the advantage of being bounded by surfaces which - on the shelf, at least - are continuous, are easy to recognize, have associated biozonations, and are verifiably correlatable on well logs. Unconformities which may be detectable in up-dip positions in these dynamic basin-margin settings are, for all practical purposes, difficult-to-impossible to find in the down-dip (conformable?) portions of these units and for simplicity's sake are not shown on the accompanying cross-section (Fig. 2).