1 D39. Tectonics/Tectonophysics

Sunday, 4 November 2018
8:00 AM - 12:00 PM
Room 238-239

AGE AND PROVENANCE OF CLASTS IN THE EARLY CRETACEOUS POTOMAC GROUP AT PUDDLEDOCK, VIRGINIA: IMPLICATIONS FOR PASSIVE MARGIN DEVELOPMENT IN EASTERN NORTH AMERICA

Paper number: 1-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

The Early Cretaceous Potomac Formation forms the basal unit of the mid-Atlantic Coastal Plain sedimentary sequence and is well-exposed in the Puddledock quarry near Hopewell, Virginia. At this locality, the Potomac Formation consists of 20 to 30 m of feldspathic sand and polylithic gravel. Sedimentary structures are consistent with fluvial deposition from a western source in a moderate- to high-energy environment. Cobbles and pebbles are sub-rounded to well-rounded, and are primarily vein quartz and well-cemented quartz sandstone with lesser amounts of felsic volcanic, granitic, and gneissic clasts.

Felsic volcanic clasts are a distinctive rhyolitic welded ash-flow tuff (70-83% SiO2) with phenocrysts of K-feldspar, quartz, and relict fiamme in a fine-grained groundmass. The volcanic rocks were variably mylonitized under lower greenschist facies conditions and experienced pervasive K-metasomatism.

A population of 30 zircon grains from clasts of weakly deformed rhyolite yield a U-Pb SIMS age of 540±10 Ma. We interpret the clasts to be sourced from low-grade felsic volcanic rocks in the Roanoke Rapids or Carolina terranes, exposed 20 - 50 km to the west in the Piedmont. However, Puddledock volcanics are 10-20 million years younger than known ages from these terranes, and may represent a younger volcanic sequence that was eroded away during or since the Cretaceous.

Detrital zircons from feldspathic sand have peak age populations at 1100-1000 Ma and ~330 Ma with other broader populations between 460-410 Ma and 575-540 Ma. The population of Grenvillian zircons may have been sourced from the Blue Ridge, derived from recycled zircons in western Piedmont terranes with a Laurentian margin affinity, or sourced from the southern Goochland Terrane. Based on these data, the Early Cretaceous fluvial network was well-established and extended 50 to 150 km into the Appalachian hinterland.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-318085

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.