ABSTRACT

Low meander-belt ridges left by the ancient Brazos River are the most enduring depositional features of the Pleistocene outcrop near Houston, where those on the Beaumont Formation (seaward from Houston) stand out on most early soils maps and aerial photographs. These and the USGS one-foot contour interval topographic sheets of Galveston and Harris counties, surveyed in 1915 - 1929, show that the meander-belt ridges have become the drainage divides between the modern streams, almost none of which occupy former river channels. This transposition of the drainage makes it possible to identify also the pattern of eroded older ridges farther inland.

Five distinct meander-belt ridge systems deflect eastward from successive fluvial terraces along the present Brazos Valley, and repeatedly branch down-slope to the southeast. The inland margin of each is marked by one of the region's longer east-flowing streams, which head just outside the Brazos Valley and flow into the San Jacinto River or Galveston Bay; Cypress Creek is the simplest example and Buffalo Bayou the most complex. These flow almost parallel with the nearest meander-belt ridges on their south side, but the ridges from the north generally approach at high angles and are cut off abruptly by the stream. Each such stream developed along the landward edge of an onlapping, eastward-prograding increment of coastal plain to carry off the blocked drainage from the slightly raised and tilted next-older increment to the north. Thus these long east-flowing streams mark the approximate traces of unconformities along the landward edges of successive stratigraphic sequences.

The meander-belt ridge patterns that distinguish the sequences confirm the utility of the present stratigraphic nomenclature, but suggest very substantial changes in published boundaries and support separation of the Beaumont into Doering's (1956) Oberlin and Eunice Formations. Comparison of the more or less stepwise differences between the five sequences with the Pleistocene high sealevel stages of Beard et al. (1982) implies that the Bentley Formation was deposited during the "conceptual" Aftonian interglacial stage, Lissie (Montgomery) in Yarmouthian, older Beaumont (Oberlin) during Sagamonian, and that two distinct sequences of younger Beaumont (Eunice) strata formed during the Wisconsinan.