Contrasting Pennsylvanian Carbonate Sedimentation, Southeastern Arizona: ABSTRACT

Abstract

The Horquilla Limestone was deposited on a broad carbonate shelf, the central Arizona shelf, and in a large intracratonic basin, the Pedregosa basin. Shelf sequences of limestone, shale, and sandstone are punctuated by unconformities. These sequences contrast with thicker basinal deposits that are generally unbroken by unconformities. On the northern part of the shelf, local sources of weathered clastic material greatly modified End_Page 517------------------------------ the sedimentary pattern. On the southern part of the shelf, the succession is thinner and has less clastic material. Local tectonic disturbances modified the general pattern of deposition. Marked facies changes and depositional and erosional anomalies are apparent along the southwestern edge of the Pedregosa basin, and many intermediate or transitional facies are not exposed or are missing. Sedimentologic differences were well established by Desmoinesian time and became progressively more marked during the later part of the Pennsylvanian (and Early Permian). The regional Pennsylvanian paleogeography is further complicated by major Late Cretaceous and early Tertiary thrust faulting which moved these sediments about 100 km or farther from their original site of deposition. These faults also may have mixed the relative position of some of the Pennsylvanian outcrops. Reconstruction of the Pennsylvanian stratigraphic successions to their pre-faulted relations, based on estimates of their carbonate facies relations and their structural displacement, suggests that the southwest side of the Pedregosa basin and adjacent shelf margin are buried beneath a series of imbricated thrust sheets containing mostly shallow-shelf sediments. End_of_Article - Last_Page 518------------