Flood tidal delta sedimentation in the Late Cretaceous Menefee Formation (Mesaverde Group), San Juan Basin, northwest New Mexico

Abstract

The Menefee Formation (Mesaverde Group, Late Cretaceous) in the San Juan Basin, northwestern New Mexico, consists largely of deltaic plain and paralic deposits. The deposits were formed along the west coast of the Cretaceous Seaway. The upper part of the Menefee sequence displays isolated sandstone bodies with a Jo bate geometry. The sandstone bodies are embedded in carbonaceous shales of coastal swamp/lagoonal origin. Sedimentary structures include inclined lamination, tabular and wedge-shaped cross-bedding in the lower parts of the sandstone bodies, and trough cross-bedding in the upper parts. The bi po lar distribution of transport directions, as well as the presence of mud drapes on foresets and bottomsets, point to a tidal environment of deposition. The lobate sandstone bodies are thought to have been generated as flood tidal deltas.
Based on theoretica! models for the stacking of tidal delta deposits, an indication is given of the relation between relative rise of sea level and behaviour of the flood tidal del tas and connected tidal inlets on the harrier coast of the Cretaceous Seaway.