T193 Coastal Aquifers: Investigations of Submarine and Coastal Groundwater Discharge

Tuesday, 11 October 2022
1:30 PM - 5:30 PM
405

ONSHORE SALTWATER AND OFFSHORE FRESHWATER; A TALE OF TWO GEOLOGIC ENVIRONMENTS

Paper number: T193-11
Program: Technical Sessions
Time: 3:55 PM – 4:10 PM

Authors

Abstract

Within the Bengal Delta, onshore saline water can be found up to 80km onshore of the coastline. This saline water cannot be explained by groundwater pumping. Following the early Holocene transgression, the shoreline of the Bengal Delta migrated oceanward by about 100km due to rapid sediment transport. Measured sedimentation rates were as high as 10 mm/year over the past 10,000 years. We demonstrate using a coupled sediment transport and hydrogeologic model that onshore saline water within the Bengal Delta is the result of rapid shoreline progradation trapping seawater onshore. The presence of confining units accentuates this process. On the Atlantic continental shelf USA, brackish to fresh water can be found in confined aquifers up to 70km offshore. Here, the shoreline migrated 100km oceanward during the last glacial maximum as sea level dropped by up to 120 m followed by the Holocene transgression. However, the maximum Holocene sedimentation rates here are on the order of 0.1 mm/year greatly reducing shoreline progradation. Meteoric recharge and glacial advances onto the continental shelf can account for these offshore freshwater resources. Recent published marine electromagnetic surveys offshore New Jersey and Nantucket Island as well as three-dimensional mathematical modeling indicate that between 1300 to 2800 km3 of brackish to freshwater are sequestered between New Jersey to Maine on the Atlantic continental margin, USA.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378225

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