T234 Impact Cratering from the Microscopic to the Planetary Scale II

Wednesday, 21 October 2009
8:00 AM - 12:00 PM
A106

SEISMIC AND BOREHOLE EVIDENCE FOR NUMEROUS IMPACT, TECTONIC, AND COMPACTION FAULTS ACROSS THE SOUTHERN HALF OF THE SALISBURY EMBAYMENT, VIRGINIA AND MARYLAND

Paper number: T234-11
Program: Technical Sessions
Time: 10:40 AM – 10:55 AM

Authors

Abstract

Compilation of seismic, core, and borehole data across the Virginia and Maryland Coastal Plain reveals numerous faults that offset (tectonic up to 80 m offset; impact up to 100 m offset) the top of the crystalline basement and most of the overlying unconsolidated sediments. The impact that created the Chesapeake Bay impact structure (CBIS) generated reverse and normal faults out to ~27 km beyond the outer rim and form a concentric pattern. Seismic data from in and around the central crater reveal a complexly faulted basement that includes faults beneath the crater floor. Some of the collapse structures documented within syn- and post-impact deposits are rooted in deeper, impact-related faults and have a concentric multi-ring configuration. Only a few radial faults have been documented, including a radial graben with 183 m of relief on top of the Cretaceous deposits near Gloucester, Virginia. Differential loading and the variable nature of the syn-impact deposits in the CBIS have created numerous compaction faults, some of which displace Pleistocene sediments or have been traced to the base of the Holocene bay mud.

Seismic and borehole data document numerous Cretaceous and Cenozoic high-angle reverse and normal faults, and folds that are rooted in early Mesozoic and/or Paleozoic NE-trending fault systems that underlie the Coastal Plain. Marine seismic data along the Potomac River (PR) and across the Chesapeake Bay reveal numerous faults with similar styles and displacements from west of the mouth of the PR to the Fall Zone. East of the PR, these faults decrease in apparent density and amount of offset across a gravity low interpreted as a granite pluton. Most of these tectonic faults strike NE, and dip NW, and produce horst and graben structures across the southern half of the Salisbury Embayment that demonstrate prolonged reactivation of Mesozoic and Paleozoic fault systems. A few faults strike NW, such as the James River structural zone that is up to the SW. These faults were active during the Cretaceous, relatively inactive during the Paleocene and early Eocene, and reactivated by the late Eocene impact. These faults strongly affected the distribution of stratigraphic units and have modern geomorphic surficial expression.