Seismic expression of a late Palaeozoic drift and implications for paleo‐basin currents: Midland Basin, West Texas, USA

ABSTRACT Bottom current influence and drift deposits are rarely defined in ancient systems, particularly in onshore basins. In the northern Midland Basin, the eastern sub‐basin of the greater Permian Basin, three‐dimensional seismic data reveal the presence and growth history of a mixed carbonate‐siliciclastic drift formed from bottom current‐driven sedimentation initiated from the San Simon Channel. The drift reaches up to 600 m thick and displays strike and dip dimensions of up to 50 × 50 km. The accumulation is best described as a modified delta drift displaying a three‐stage growth history: (1) initiation of the drift as a radially distributive sediment wedge. The drift progrades to the east, being formed by expanding outflow undercurrents, and generates a mounded, convex‐up profile in both strike and dip view. (2) Transition to asymmetric northward growth. The drift builds oblique/perpendicular to depositional dip with significant erosional truncation and non‐deposition at the eastern edge of the drift by a deeper competing basinal current. The top also contains continuous, well‐developed flat‐lying seismic reflectors, possibly representing a contourite terrace. (3) Demise of the drift driven by weakening or shifting currents. The drift becomes ornamented with gravitational deposits and terminal lobes to develop distal of channels where bottom current truncation previously occurred. The drift accumulation influences carbonate slope and platform geometries as accretion of the drift along the slope alters platform to basin relief locally, driving a decrease in slope height and subsequent rapid asymmetric platform progradation. This delta drift is the first drift interpreted in the Midland Basin, and the second study to highlight drifts in the greater Permian Basin. As such, it further highlights the overlooked influence of bottom currents in the region, but also the potential overlooked influence in other ancient basins.