ABSTRACT

Superior Stone Quarry near New Bern exposes 9.2 meters of Eocene Castle Hayne Limestone that is disconformably overlain by 2 meters of an unnamed Oligocene carbonate unit. Both form part of the most important aquifer system in eastern North Carolina.

The Eocene, Castle Hayne strata are divisible into two massively bedded facies: A. sandy, pelecypod-mold biomicrudite with micro- and pseudospar matrix, and B. sandy, pelecypod-mold biosparite and biosparrudite, which grade westward into calcareous quartz sand. Facies A consists of unabraded pelecypod valves (dominantly molds of aragonite Macrocallista shells) and 20 volume percent moderately well sorted, fine quartz sand that are set in microspar and pseudospar. Facies B consists of pelecypod valves (chiefly molds of worn, fragmented, and unabraded Macrocallista) and 27 percent well sorted, fine quartz sand. Sparry calcite forms 41 percent of this facies. Subordinate allochems in both facies are gastropods, foraminifers, bryozoans, echinoderms, ostracodes, intraclasts, peloids, glauconite, and bone. Facies A is a low energy, shallow marine bank deposit that accumulated seaward of Facies B, which was deposited in a higher energy nearshore environment.

The Oligocene stratum is a sandy, molluscan-mold biomicrudite consisting of pelecypods, turritellid and naticid gastropods, and scaphopods (all as molds of unabraded aragonite shells) that are set in micrite. Fine, moderately well sorted quartz sand forms 3 percent of the unit. Other allochems are echinoderms, foraminifers, peloids, ostracodes, and bone. This is an inner or middle shelf deposit that accumulated below wave base.

Upon subaerial exposure, the following diagenetic changes occurred: 1. high-Mg calcite skeletons, mainly echinoderms, recrystallized to low-Mg calcite, 2. most aragonite skeletons dissolved to form molds, and the carbonate precipitated nearby as low-Mg calcite cement, while some neomorphed to spar, 3. molds and other voids were reduced or filled with low-Mg spar, and 4. micrite and pelmicrite aggraded to microspar and pseudospar. The fast two stages did not appreciably affect the Oligocene unit.