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AAPG Bulletin

Abstract


Volume: 39 (1955)

Issue: 10. (October)

First Page: 2020

Last Page: 2037

Title: Brackish Water and its Structural Implications in Great Carolina Ridge, North Carolina

Author(s): H. E. LeGrand (2)

Abstract:

The finding of surficial brackish water in Bladen County, North Carolina, has led to a study of the Great Carolina ridge, known heretofore merely as a wide southeast-trending uplift of Cretaceous strata of the Atlantic Coastal Plain. The brackish water is unusual because of its surficial occurrence in the hinterland and because, as its chemical character proves, it represents artesian water rising to the ground surface presumably along a fault, through breached clay beds and unconsolidated sands. The fault, trending slightly east of north, marks the west border of a broad, domed area of brackish ground water west of Wilmington. The area is elongate northeastward, indicating that northeast-trending structures form a barrier of low permeability which has retarded the flushi g of salty water from the artesian beds.

Microfaunal analysis of cuttings from four wells reaching basement, on a line extending from Conway, South Carolina, through Wilmington to the vicinity of Jacksonville, North Carolina, indicates that the Tuscaloosa formation, which crops out at the base of the Coastal Plain formations along the Fall Line at the west, is absent. It is inferred from this anomaly that a landmass was present along this line in Tuscaloosa time, and that a basin of undetermined proportions lies at the west. An ecologic study of Foraminifera of the outcropping Peedee formation reveals the existence of both a littoral and an outer neritic facies. The presence of the two distinct facies in juxtaposition near the area of surficial brackish water suggests faulting rather than rapid deepening of sediments.

All lines of evidence, including published results of a magnetic survey, support the existence of complex northeast-trending structures. The writer believes that, contrary to general opinion, the Carolina ridge, containing an undrilled area of 8,000 square miles, has structures that deserve attention if oil-prospecting becomes more active on the Atlantic Coast.

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