Diagenesis and provenance of Silurian quartz arenites in south-eastern New York State
Résumé
Combined scanning electron microscopy — cathodoluminescence and optical microscopy (SEM-CL/OM) of single quartz grains was used to determine the diagenetic history and provenance of framework grains in quartz arenites of the Silurian Shawangunk Conglomerate and Binnewater Sandstone in south-eastern New York State. Most sand-sized sedimentary rocks of these two units experienced compaction and quartz cementation after deposition, except for those with high matrix or pseudomatrix content. No primary porosity is left today and secondary porosity is insignificant, leaving the Shawangunk Conglomerate and Binnewater Sandstone with poor reservoir qualities. The medium to coarse sand fraction of the Shawangunk Conglomerate and Binnewater Sandstone is dominated by quartz of plutonic origin. Of these usually sub-rounded to rounded grains, 10–15% carry remnants of inherited quartz cement, indicating recycling from a sedimentary source such as quartz-rich sedimentary rocks of the former Iapetus passive margin. In contrast, polycrystalline vein quartz pebbles in the Shawangunk Conglomerate were most likely derived from a proximal crystalline source in the Taconic orogen to the east. Formation of the Shawangunk Conglomerate and Binnewater Sandstone quartz arenites was likely supported by subtropical climatic conditions, given the latitudinal position of eastern North America during the Silurian, with relatively high mean annual temperatures and high precipitation rates, which accelerated the breakdown of unstable grains.