14 D1. Sediments, Stratigraphy, and Geomorphology Contributions

Friday, 28 March 2025
1:30 PM - 5:30 PM
170A

INVESTIGATION OF STORM-REWORKED PEAT BALLS, FIRM GROUND RIP-UP CLASTS, NODULES AND CONCRETIONS FROM THE EASTERN SHORE OF VIRGINIA: IMPLICATIONS FOR TIME AVERAGING, SEA LEVEL RISE, AND ENVIRONMENTAL CHANGE

Paper number: 14-8
Program: Technical Sessions
Time: 3:45 PM – 4:05 PM

Authors

Abstract

Over the last 15 years, shoreline mapping has been carried out at NASA’s Wallops Island, Assateague Island, Savage Neck, and other sites on the Delmarva Peninsula. Sediment and shell-bed assemblages have been sampled. Immediately following storms including hurricanes Irene (Sept. 2011), Sandy (Oct. 2012), Hermine (Sept. 2016) & Matthew (Oct. 2016), erosion of barrier island beaches and protected shorelines of Chincoteague Bay, and the Chesapeake resulted in retrogradation of shorelines and the production of a wide range of clast types. These range from small to large peat balls, firm to stiff mud/silt clasts, hardened lithoclasts, cemented steinkerns, encrusted “bryoballs” as well as various nodules and concretions. Intensive storms contributed to exhumation of long-buried marsh and bay sediments. Once broken up, these were incorporated into the shoreface, beach berm, back beach, and overwash deposits. Clasts were found in heavily winnowed shell beds on the beach face and berm, within dune swales, and on the marsh platform. After storm activity ceased, fair weather sedimentation and vegetative growth quickly buried/covered the clasts so few concretions were noted in subsequent surveys. That is until the next significant storm when clasts were once again reworked, re-incorporated into time-averaged assemblages and shell beds. Since Irene, we have noticed an increasing number of specimens with complex sedimentologic and taphonomic history that we now believe includes sunbaking of initially soft lithoclasts. Subsequently, at least some clasts are reworked, moved offshore, and tumbled on the seafloor before being put back onto the beach. Micro and macro borings, encrustation by algae, bryozoans, and other bioimmuring taxa all suggest at least some concretions may experience multiple rounds of exhumation, exposure, colonization, and intermittent reworking to develop a time-averaged assemblage comingled with generations and generations of darkened oyster and scallops shells and heavy minerals. This work provides insights into how complex storm beds and intraformational conglomerates may be generated and has implications for assessing environmental change during transgression.

Geological Society of America Abstracts with Programs. Vol. 57, No. 3

doi: 10.1130/abs/2025NE-409111

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