Ordovician Stratigraphy in Marathon Folded Belt, West Texas

Abstract

Stratigraphic study of little known Ordovician exposures south and east of the Marathon uplift, West Texas, shows that a facies change exists from predominantly shaly beds of the Marathon region to more arenaceous beds in the Solitario and Dove Mountain quadrangle areas. Discovery of graptolites in a few incomplete measured sections indicates that probably Dagger Flat type of sandstone rises in the stratigraphic sequence to replace, in part, the lower Marathon limestone and shale. The upper Marathon and Alsate shale formations of the Marathon anticlinorium are represented, in the exposures considered, by sandy laminated limestones and possibly by overlying beds of massive quartzite. Typical Fort Pena and Woods Hollow formations (Middle Ordovician) of the Marathon uplift a e also present in the Solitario and Dove Mountain areas. The Maravillas is present but thin, and is overlain by about 25-40 feet of shale, probably of Late Ordovician age; the latter is here named the Persimmon Gap formation. Regional correlation shows close similarity between the sections studied and the McCurtain County, Oklahoma, exposures which also contain Early Ordovician sandy beds at approximately the same stratigraphic position. The Ordovician section of the interior (southeasternmost) folds of the Ouachita-Marathon system suggests that orogenic activity occurred in the system in Ordovician time and that this long enduring mobile belt may be considered an early and middle Paleozoic geosyncline despite its comparatively thin stratigraphic sequence.