Sequence boundaries in uppermost Proterozoic mixed siliciclastic-carbonate rocks: Deep Spring Formation, southern Basin and Range

The authors propose that a sequence boundary lies at the top of the Reed Dolomite and another at the top of the lower member of the overlying Deep Spring Formation. These boundaries should be useful in correlating critical pre-trilobite Neoproterozoic rocks across the southern Basin and Range Province. Furthermore, the mixed siliciclastic-carbonate rocks between these boundaries reflect an intimate interplay between subsidences, sea-level change and the different rates at which siliciclastic and carbonate sediments accumulate. The Type 2 sequence boundary at the top of the Reed Dolomite is marked in outcrop near Bishop, California by minor channelization and dissolution surfaces that resulted from subaerial exposure of the carbonate platform. This sea level low stand is recorded in the lower Deep Spring Formation, 150 km northwest, by carbonate sediment-gravity-flow deposits. With initiation of transgression, siliciclastics buried the eroded platform and carbonate sedimentation continued in the northwest. As sea level continued to rise, carbonate deposition occurred across the region. Time of maximum flooding is represented by lagoonal deposits in the southeast and a condensed section to the northwest. The condensed section is characterized by dolomitized limestones containing glauconite and small shelly fossils that are overlain by thinly interbedded shales and siltstones withmore » rare trace fossils. The slower rate of siliciclastic deposition on the rapidly subsiding shelf produced an increase in accommodation space resulting in development of an ooid shoal to the southeast. To the northwest, however, continued submarine deposition produced thinly interbedded limestone turbidities and shales. Ooid accumulation outpaced subsidence and together with sea level fall resulted in extensive subaerial exposure of the oolite. Thus, the top of the lower member of the Deep Spring Formation represents the second Type 2 sequence boundary.« less