19 Sediments and Stratigraphy (Posters)

Thursday, 19 March 2015
1:00 PM - 5:00 PM
Ballroom

HEAVY MINERAL CONSTRAINTS ON DETRITAL HISTORY OF THE CONGLOMERATE MAGNAFACIES IN SOUTHERN CAHABA SYNCLINORIUM, ALABAMA

Paper number: 19-1
Program: Technical Sessions
Time: 1:00 PM – 5:00 PM

Authors

Abstract

The conglomerate magnafacies, which forms the top of the Lower Pennsylvanian Pottsville Formation in the Cahaba synclinorium of the southern Appalachians, was deposited in a series of stacked braidplain-anastomosed cycles, possibly at the distal fringes of giant piedmont fans of the Alleghanian orogen. Lithoclasts within the upper Pottsville conglomerate units consist mainly of chert, sedimentary and metamorphic lithic fragments, and lesser amounts of volcanic grains. Heavy mineral analysis of sandstone in and around the conglomerate beds revealed the detrital history of these sediments.

Sandstones within the conglomerate measures have a low abundance of heavy minerals. (0.2%- 1.2% of total sample weight), most of which are concentrated in the fine sand fraction. Heavy minerals consist of a high proportion of ultrastable minerals, e.g., zircon, tourmaline, rutile and garnet, including abundant opaque minerals and chlorite.

The low abundance of heavy minerals and dominance of ultra-stable minerals in the fine fractions reflect intense chemical weathering and recycling during deposition of these sediments. The presence of rutile and garnet further suggests a medium- to high-grade regionally metamorphosed source in the Alleghanian orogen. Ongoing research on the chemistry of selected heavy minerals will provide additional information on provenance.