Basin-floor channel stacking and evolution of the Brushy Canyon Formation in the northeastern Delaware Basin

Deep-water depositional systems commonly show two end-member styles of stratigraphic architecture: laterally confined channelized deposits on the slope and more depositional, unconfined distributary channel-lobe deposits on the basin floor. In between, a transitional stratigraphic architecture comprising scours and short-lived, low-sinuosity channels can form. This transitional stratigraphic architecture has been most commonly recognized on the modern seafloor where the components of deep-water depositional systems can be studied in full plan-view display. Outcrops of the Permian Brushy Canyon Formation in the Delaware Basin show weakly confined channel deposits thought to be found in these transition zones. Brushy outcrops have been described as laterally migrating, sandy channel fills up to 500 m wide and 30 m thick deposited in areas of low to moderate gradient. Although outcrops provide high-resolution cross sections of the sedimentology and stacking of deep-water deposits, they lack the larger scale, three-dimensional context of seismic-reflection data and well logs used for basin-framework studies. Here, I integrate a large number of geophysical well logs (1,366) and 3D seismic-reflection data (~30 Hz dominant frequency) covering ~500 km² in the northeastern Delaware Basin, southeastern New Mexico. I created a three-dimensional log-based stratigraphic model of the Brushy Canyon Formation and characterized the depositional architecture within the West Hobbs deep-water depositional system on the basin floor. Generally, the proximal Brushy Canyon Formation consists of lenticular sand bodies interstratified with sheet-like units, and the gamma-ray logs show local blocky, isolated relatively coarse-grained deposits bounded by thicker relatively fine-grained deposits. Downstream, there is a transition to more continuous, sheet-like deposits. I used a spectral decomposition seismic attribute to better visualize the 3D stratigraphic architecture of the system. This revealed a stratigraphic evolution from relatively few, wide isolated channel deposits in the lower Brushy to widespread, narrow channel deposits in the upper Brushy. Both channel architectures show low sinuosity and trend to the south and southwest. The low sinuosity of the channel deposits is interpreted to be a product of frequent channel avulsions. This caused the channels to be short-lived and immature, preventing enough sustained sediment-gravity flow activity to develop significant sinuosity. I interpreted the observed vertical change from isolated, short-lived, weakly confined channels to more numerous, relatively narrow channels, including distributary patterns organized into lobes as reflecting a backstepping of the depositional system. This backstepping stacking pattern has been previously recognized at multiple scales throughout the Brushy Canyon Formation. This is the first time that these patterns have been imaged in 3D seismic-reflection data, mapped in the subsurface, and checked against well log data