Depositional facies, petrofacies, and diagenesis of siliciclastics of Morrow and Springer rocks, Anadarko Basin, Oklahoma

Abstract

Investigations of 6,500 ft of core and -100 thin-sectioned core samples from 30 drill holes from the Oklahoma Panhandle to the southeast part of the Anadarko basin, Oklahoma, have led to the recognition of three depositional facies of the Springer and Morrow Formations of Mississippian and Pennsylvanian age, as recognized by geologists working in the subsurface of the Midcontinent region. Lithofacies include (1) fluvial-influenced coastal (FIC), (2) tidal-influenced nearshore (TINS), and (3) mixed, which shows mixed tidal and non-tidal marine influence (MT/NTM). The FIC facies is restricted to down-hole depths of 4,400-8,000 ft; the TINS facies is recognized only between down-hole depths of 4,000 and 18,000 ft. Thin-section study of sandstone indicates that quartz arenite is the most common rock type in both the FIC and TINS facies. Subarkose is present, but not common, in the FIC facies. Sublitharenite is moderately common in the TINS facies. Calcite skeletal fragments, mainly of brachiopods and crinoids, are more abundant in the FJC facies than in the TINS facies. The mixed facies includes quartz arenite, subarkose, and sublitharenite. Iron-bearing carbonate cements are observed in rocks of all three depositional facies. Porosity is typically <10%, and has been reduced by compaction and redistribution of silica, as well as by iron-bearing carbonate cements. Clay cements are less common, but are locally important. Loss of porosity due to mechanical compaction is significant in some samples from depths > 12,000 ft. Thin films of bitumen have inhibited the effects of diagenesis in some samples. Fractures are identified in core samples, but are rare in thin sections. Porosity is due primarily to dissolution of glauconite, clays or clayey matrix, and some framework grains, but many dissolution pores are partly or completely filled with various clays, and only microporosity remains.