ABSTRACT

The 60 foot sequence of sedimentary rocks overlying the Lower Kittanning coal bed in western Pennsylvania consists of a marine-brackish facies both overlain by and laterally intertongued with non-marine strata. The marine-brackish rocks, occupying an east-northeast trending belt some sixty miles wide, compose an excellent, well exposed record of a small Allegheny marine inundation. A temporal sequence of events of the marine invasion--transgression, maximum inundation and regression--can be equated to three major lithic divisions of the marine-brackish strata, and within each of the divisions, spatial distribution of objectively defined genetic rock types provides a basis for re-creation of physical geography and ecology for temporal events. Characteristics of sediments and their rela ionships to fauna in each event as well as comparisons between events suggest that the factors controlling location and character of marine advance and retreat were (1) subsidence of a surface characterized by well defined elevated and depressed areas and (2) variation in volume and type of sediment reaching the area of deposition. This pattern of Allegheny sedimentation is believed to be similar to that of the Recent Mississippi River delta.