Abstract

Newly available fusulinid biostratigraphic data clearly suggest the overall Early Leonardian age and therefore, temporal equivalence of the Tubb platform and Dean basinal sand and associated carbonate sections. The biostratigraphic correlation of the Tubb and Dean are consistent with the complex and seemingly contradictory depositional architectures observed in platform-basin transitional areas in the northern Midland Basin. The Tubb and proximal Dean sections can each be subdivided, on the basis of mechanical log characteristics, into four discrete, correlative siliciclastic units (in descending stratigraphic order these are “A”-“D”) separated by carbonates. Where the Tubb sandstone-carbonate section has stacked vertically on the subjacent Lower Clear Fork shelf edge, the transition into the basin was abrupt and steep. In such areas, sand units “A”-“D” bypassed the upper slope and were deposited in the basin such that the Tubb and Dean are not physically continuous across the slope. In areas of more gradual platform-to-basin transition two different stratigraphic relations are recognized: (1) Tubb sandstone units “A”-“D” grade directly into equivalent Dean units, or; (2) the lower Tubb sandstone unit (“D”) passes into basinal Dean equivalents and is then overlain, owing to progradational offlap, by successive Tubb units “A”-“D”.