GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 291-9
Presentation Time: 3:50 PM


MONAMI, Shifat, UDDIN, Ashraf and HAMES, Willis, Department of Geosciences, Auburn University, Auburn, AL 36849

The Lower Pennsylvanian Pottsville Formation in Pennsylvania contain clastic deposits of the Alleghenian foreland basin system that are the focus of this study. These siliciclastic sediments were deposited near the paleo-equator at that time, and consist of predominantly interbedded sandstone, siltstone, conglomerate, conglomeratic sandstone, shale, limestone, and coal beds. A detailed study of sandstone modal composition, heavy mineral analysis, mineral chemistry and 40Ar/39Ar geochronology on detrital muscovite was made on samples collected from both eastern anthracite and western bituminous fields in Pennsylvania. Modal analyses on Pottsville sandstones reveal composition that ranges from quartzarenite to sublitharenite with a mean composition of Qt84F1L15. In contrast, the sandstones from eastern anthracite field are dominated by sublitharenite to litharenite with a mean composition of Qt70F2L29. The sandstones from bituminous fields are texturally and compositionally more mature than the sandstones from eastern anthracite field. Heavy mineral analyses reveal a low to moderate diversity of heavy minerals that are mostly dominated by ultra-stable minerals and opaques. Study of those heavy minerals are characteristic of source terrane(s) dominated by metasedimentary/sedimentary units with low- to medium grade metamorphic, and igneous lithologies. A few grains of chromium and zinc-rich spinels were recovered in heavy mineral separates, and analyzed with an electron microprobe; these may indicate source components including exhumed arc terrane and/or ophiolitic belts with ultramafic igneous rocks. Detrital feldspars show evidence of alteration to kaolinite clays, consistent with weathering and erosion in a warm humid climate during the Pennsylvanian. Detrital muscovite was separated from six sandstone samples for laser 40Ar/39Ar dating; preliminary results for these indicate a preponderance of Middle to Late Ordovician ages among these micas. These initial results are consistent with a dominance of Taconian source terranes for sediments of the Lower Pottsville Formation, as preserved in the Appalachian foreland of Pennsylvania.