ABSTRACT

Two surface stratigraphic cross sections of Lower Cretaceous rocks in West Texas contain four depositional systems: coastal plain, carbonate shelf, platform-shelf margin, and shelf basin. These systems consist of lithofacies, megafossil paleocommunities, and palynomorph assemblages that represent specific environments. The vertical succession of deeper and shallower, or low - and high-energy facies indicates depocenter cycles of subsidence and progradation. The diversity and abundance of palynomorph morphotypes seem to be reliable environmental tools because they vary with other environmental indicators.

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These depositional systems comprise depositional sequences, which are transgressive-regressive stratigraphic units bounded at least in part by unconformities: the Trinity, Fredericksburg, lower Washita, and the Upper Cretaceous upper Washita sequences. Some of the sequence boundaries are synchronous within the limits of a paleontologic zone, but others are clearly time-transgressive. These sequences can be correlated in cross sections from a detailed measured section at Fort Stockton to Big Bend National Park and to the Southern Quitman Mountains.

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