Geology of the Castle Hayne Limestone in the Onslow Quarry, Richlands, NC

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Craig Simms (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: The Eocene age Castle Hayne Limestone Formation on the coastal plain of North Carolina is found throughout Onslow County and is mined at the Onslow quarry south of Richlands. This study characterizes the geology of the rock units present at the quarry, which is located in the western end of the range for the Castle Hayne Formation. The site has a variable thickness of sandy clay overburden ranging from less than five feet to almost sixty feet. Limestone immediately underlies the overburden and varies in thickness from approximately two feet to greater than one hundred feet. In areas where the limestone is thin, usually less than 10 feet, there is a poorly indurated wackestone (marl) layer. This layer thickens from east to west and its greatest thickness, over fifty feet, is in the north and northwest. The marl is rich in siliciclastics and contains fossils of bryozoans. The limestone is divided into several distinct layers and in some areas there are interbedded layers of very loosely consolidated carbonate sand. Some of the limestone layers consist of porous grainstone and packstone while others are dense wackestone. Structural features evident in the limestone layers include cross-beds, lamination and graded bedding. The limestones contain a variety of fossils including bryozoans, echinoderms, gastropods, foraminifera and a few coral fragments. Below approximately 120 and 140 feet below land surface the limestone is replaced by either sand or marl possibly signifying the base of the Castle Hayne Formation. The limestone layers correspond to the inner and mid-ramp zones of a homoclinal carbonate ramp facies model. Depositional sequences were identified that indicate successive flooding and shallowing upward events. The specific sequences include the inner ramp shoal, inner ramp restricted/open marine and inner ramp open marine facies. The mechanism may be either change in relative sea level or migration of near shore sediments. Diagenetic features in the rocks include cavities of dissolved bivalve shells, replacement of original shell material, neomorphism of micrite with microspar and spar, syntaxial overgrowths on echinoderms, filling of molds and voids with micrite, microspar and spar, micritic rims, authigenic pyrite and breakage of bioclasts. The diagenetic features change with depth\; there is more dissolution of micritic matrix with depth. Strontium isotope ratios of bivalve shell samples indicate an age for the shells between 48.25 and 49.83 Ma.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

Geology;Sedimentary geology;Castle Hayne limestone;Diagenesis;Eocene;Sequence;Stratigraphy;Strontium isotope analysis

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