31 Leaving Footprints, Changing Landscapes: Advances in Ichnological and Zoogeomorphological Research

Monday, 21 March 2022
1:30 PM - 5:30 PM
Commonwealth Salon 2

TEXTURAL AND MAGNETIC SUSCEPTIBILITY TRENDS IN AEOLIAN RAMP DEPOSITS ASSOCIATED WITH SEA TURTLE NESTING SITES ON THE MID-ATLANTIC COAST

Paper number: 31-7
Program: Theme Sessions
Time: 3:15 PM – 3:35 PM

Authors

Abstract

Sea turtle nests, especially numerous in the past, have profound impact on upper-beach morphology and sediment reworking due to re-use of coastal segments. This study characterizes aeolian ramp sequences at three mid-Atlantic sites to complement high-resolution georadar surveys: a simulated structure (Delaware; sampling depth: 1.48 m), as well as post-emergence Kemp’s-Ridley (0.55 m) and Loggerhead (1.00 m) nests in Virginia. Fifteen samples ranged in mean grain size between 0.88-1.60 φ, sorting 0.68-1.00 φ, and 80% are negatively skewed (-0.02 – -0.19 φ). These granulometric statistics indicate continued winnowing along the lower section of the aeolian ramp, as finer fraction is transported landward into the foredunes. For the entire excavated section, the surface sample at the Delaware site yielded the most positive skewness (0.145 φ), and the two Virginia locations these had the least negative values (-0.015 φ and -0.055 φ, respectively), consistent with aeolian deposition. In situ low-field magnetic susceptibility values range from 6 μSI (quartz-dominated sand) to ~2800 μSI (heavy-mineral concentrations). The latter are typically slightly finer-grained and coarser-skewed than underlying horizons, consistent with density segregation during deposition and aeolian deflation. Mineralogical anomalies provide clear visual indicators of disrupted bedding due to biogenic activity, such as nest excavation and hatchling emergence. Similarly, they aid in correlation with high-amplitude reflections in radargrams and accentuate truncations of otherwise continuous bounding surfaces, thereby facilitating the recognition and quantification of substrate disruption in subsurface images.

Geological Society of America Abstracts with Programs. Vol. 54, No. 3

doi: 10.1130/abs/2022NE-373661

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