Regional geologic characterization of the Second Bone Spring Sandstone, Delaware basin, Lea and Eddy Counties, New Mexico

Abstract

The Bone Spring Formation is a series of interbedded siliciclastics and carbonates that were deposited in the Delaware basin during the Leonardian (Early Permian). It consists of the First, Second and Third Carbonate and the First, Second and Third Sandstone, as well as the informally named Avalon Sandstone. The Second Bone Spring Sandstone, the focus of the study, can be subdivided into 4 distinct sand bodies separated by pelagic zones. These sands are designated the A-D Sands. The depositional patterns of the Bone Spring Formation are reflective of the underlying structure that resulted from compression during the Mississippian and Pennsylvanian. The Second Bone Spring Sandstone (specifically the C Sand) is essentially a dolomitic, coarse siltstone that is composed of facies reflective of deposition by turbidity currents in a slope fan environment. The midfan, levee/overbank and hemipelagic environments of deposition identified in the Second Bone Spring Sandstone are consistent with those of the typical slope fan of Walker (1978). The slope fans of the C Sand were confined by north-to-south trending reverse faults, which inhibited lateral migration of both the fans and the channels within them. The A-D Sands are correlatable throughout the study area but thicken in the underlying structural lows. These thicker sands are lobate in plan view and are located adjacent to, rather than directly on top of, underlying thick sands. This is likely a result of differential compaction of underlying sediment which served to further confine the fans. The sediment comprising the Second Bone Spring Sandstone was likely transported through basinward migration of sand dunes in an arid environment during relative sea level lowstands. Periodically, brief rises in sea level choked off sediment supply allowing hemipelagic material to be draped over underlying sands. With sea level fall, sands were again deposited in the tectonic sub-basins.