USGS - science for a changing world

Data Series 999


Sedimentologic Characteristics of Recent Washover Deposits From Assateague Island, Maryland

Skip Links

Citation Page
Abstract
Introduction
Field Data Collection
Laboratory Methods and Analyses
Results
Data Downloads
References Cited
Abbreviations
 

Results

Sediments from non-vegetated sand flats along the control transect 2 consisted of moderately well to well sorted (1.45 ± 0.04 μm), medium-grained sand (mean grain size 378.95 ± 26.92 μm; number of samples [N] = 37). Internal structure was mostly massive, with a few laminations or deformed horizons visible in these cores. In contrast, sediments from a single transect 2 back-barrier marsh core (14CTB-321W) consisted of organic-rich, very poorly sorted (5.50 ± 1.02 μm), coarsening downward sandy mud and muddy sand (mean grain size 55.53 ± 28.82 μm; N = 4) overlying moderately to moderately well sorted (1.63 ± 0.14 μm), medium-grained sand (mean grain size 411.32 ± 61.58 μm; N = 4). Similarly, sand augers collected at back-barrier marsh sites along the overwash transects contained organic-rich, very poorly sorted (5.12 ± 0.75 μm) sandy mud to muddy sand (mean grain size 49.24 ± 71.47 μm; N = 4) overlying moderately well sorted (1.50 ± 0.08 μm), medium-grained sand (mean grain size 431.55 ± 79.78 μm; N = 7). Thicknesses of extant marsh sediments ranged from 3 to 9 cm. The textural characteristics of the sand auger cores collected from back-barrier marshes are similar to those described from marsh push and peat auger cores at unprotected back-barrier sites on Assateague Island (Smith and others, 2015).

Washover sediments in cores collected from transect 1 consisted of massive to laminated, moderately well to well sorted (1.44 ± 0.09 μm) medium-grained sand (mean grain size 377.14 ± 60.15 μm; N = 104). Where the transect 1 cores penetrated an organic-rich pre-overwash deposit (for example, see fig. 6), the texture of those sediments varied substantially, ranging from very poorly sorted, sandy mud to moderately well sorted, medium-grained sand (average sorting 3.28 ± 1.88 μm; mean grain size 191.68 ± 134.73 μm; N = 14). The buried organic-rich sediments were generally thin (2 to 7 cm), overlying moderately well sorted (1.44 ± 0.10 μm), medium-grained sand (mean grain size 335.66 ± 55.35 μm). Sediments recovered in cores collected from transect 4 were on average slightly coarser than sediments collected from transect 1. Transect 4 washover sediments consisted of massive to laminated, moderately well to well sorted (1.45 ± 0.07 μm), medium- to coarse-grained sand (mean grain size 446.23 ± 87.46 μm; N = 168). Where penetrated, buried organic-rich sediments (2 to 6 cm thick) varied from very poorly sorted, sandy mud to moderately well sorted, medium-grained sand (average sorting 3.26 ± 1.83 μm; mean grain size 264.14 ± 147.91 μm; N = 24), overlying moderately well sorted (1.57 ± 0.22 μm), medium- to coarse-grained sand (mean grain size 416.73 ± 79.45 μm; N = 23).

In cores from the overwash zones at transects 1 (N = 7) and 4 (N = 7), sediment thicknesses overlying the pre-Hurricane Sandy wetland surface ranged from 14 to 44 cm. At core sites where multiple overwash events since 1989 could be inferred from image analysis, observed sediment thicknesses above the pre-overwash vegetated surface were as much as 97 cm and 74 cm at transects 1 (N = 11) and 4 (N = 12), respectively. Stratigraphic and sedimentologic data will be integrated with GPR (Zaremba and others, 2016) and geomorphic change data to quantify the spatial and temporal variability of event-related depositional processes along this barrier-island system.

Accessibility FOIA Privacy Policies and Notices

USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/ds/0999/ds999_results.html
Page Contact Information: Contact USGS
Page Last Modified: Monday, November 28, 2016, 08:49:52 PM