Abstract

Carbonate contourite drifts formed by bottom currents are common on modern sea floors but are rarely defined in the rock record. Regional subsurface well-log mapping in the northern Delaware Basin in southeast New Mexico, USA, reveals early Permian carbonate-dominated elongate, mounded accumulations along the slope of the western margin of the basin. Thickness maps also show possible moats oriented oblique to depositional dip. The thickness variations and moat geometries are hard to explain by deposition from gravity flows but are consistent with deposition from bottom currents with a counterclockwise deflection in the basin. The contourite drift system consists of three large elongate carbonate drifts that form in relation to significant bathymetric irregularities which may alter currents, resulting in localized drift accumulations along the slopes.

These findings highlight the significant role bottom currents play in shaping carbonate margin and slope architecture, rivaling the impact of gravity flows. Furthermore, full-scale assessment of the basin geometry and deposits provide insight into paleo-oceanographic circulation that is inherently difficult to assess. Identification of these large sedimentary bodies requires extensive basin-wide data sets, which were acquired by decades of work in the Permian Basin, as well as comparison with drifts in modern carbonate settings. These new interpretations in one of the most data-rich geologic regions in the world indicate that drift systems may be easily overlooked and are likely more common in the ancient rock record than currently recognized.