DEPOSITIONAL CONTROLS AND SEQUENCE STRATIGRAPHY OF LACUSTRINE TO MARINE TRANSGRESSIVE DEPOSITS IN AN ACTIVE RIFT BASIN, CRETACEOUS BLUFF MESA, INDIO MOUNTAINS, WEST TEXAS
The Lower Cretaceous Bluff Mesa Formation was deposited on the eastern margin of the Chihuahuan Trough failed rift and is exposed within multiple Laramide-age thrust panels in the Indio Mountains of West Texas. The mixed carbonate-siliciclastic system thins from 360m to 220m across the study area and contains 9 fourth-order sequences that record the transition from fluvio-lacustrine to shallow marine deposition. Sequences 1-4 are characterized by lacustrine siltstones or thin marine wackestones during highstands and fluvial sandstones during lowstands. Sequences 5-9 are characterized by thick ooid grainstones and fossiliferous packstones during highstands and shoreface to shelfal sands during lowstands. The presence of thin marine limestones in sequences 1-4 suggest that marine incursion occurred during highstands but the basin was still primarily a rift lake. A significant rise in base level occurred during sequence 5 marking the onset of continuous marine deposition. The observed succession of mixed terrestrial-marine sequences suggests transgression of rift basins involves multiple pulses.