# Castle Hayne Limestone

Canonical page: https://lithomap.app/resources/geologic-formations/united-states/castle-hayne-limestone
Last reviewed: September 17, 2026
Page purpose: Comprehensive United States geologic formation reference for human readers, search systems, and language models.
Major region: Gulf / Atlantic
Regional setting: North Carolina Atlantic Coastal Plain
Age: Middle to late Eocene
Age detail: Mainly middle Eocene, with broad age limits reported for some subsurface sections
Depositional setting: Warm shallow shelf with shell and bryozoan banks
Rock types: Fossiliferous limestone, Calcarenite, Calcirudite, Marl
States in recognized usage: North Carolina

## Summary

The Castle Hayne Limestone is a highly fossiliferous Eocene carbonate of eastern North Carolina, formed from shell, bryozoan, and lime sediment on the Atlantic shelf.

## Distribution

Castle Hayne strata occur in eastern North Carolina and are best known from quarries and river exposures near the type area. The formation thins toward its western margin and continues beneath younger Coastal Plain deposits.

Members include contrasting phosphatic basal material and younger bryozoan- or mollusk-rich limestone. Exposure is discontinuous, so subsurface logs are important to regional mapping.

## Geological history

Skeletal debris accumulated in warm, shallow marine water, producing coarse bioclastic limestone and finer calcareous sediment. Currents reworked shells and bryozoan fragments into banks and lenses.

Calcite cement lithified the deposits, while silica, glauconite, and phosphate entered certain beds. Erosion separated the formation from younger and older units by regional unconformities.

## Fossil record

Mollusks, bryozoans, foraminifera, echinoids, shark and ray teeth, and occasional vertebrate bone occur. Fossil assemblages differ among the New Hanover, Comfort, and Spring Garden members.

Molds may remain where shells dissolved, and quarry weathering can free specimens from carbonate matrix. Fossil presence never overrides quarry access rules.

## Minerals and geological resources

Calcite is dominant, with quartz, glauconite, phosphate, and silica in selected beds. Iron oxides stain weathered surfaces, and secondary calcite may line pores or fractures.

Limestone is a major aggregate resource and an aquifer material. Quarrying and groundwater flow depend on solution features, porosity, and overburden.

## Field context

- Active and inactive quarries can contain unstable highwalls, deep water, and restricted property.
- Fossil-rich float may have moved from its original member.
- Use member-level information when comparing phosphate, fossils, or texture.

## Connected field guides

- Limestone (rock; Named rock type and mineral context) — https://lithomap.app/resources/rock-identification/limestone
- Calcite (mineral; Mineral discussed in this formation) — https://lithomap.app/resources/mineral-identification/calcite
- Quartz (mineral; Mineral discussed in this formation) — https://lithomap.app/resources/mineral-identification/quartz

Mapped location and formation context support an identification but cannot establish one. Compare several physical properties and use laboratory analysis when the material remains ambiguous.

## Connected state geology guides

- No directly overlapping state guide is currently published.

## Authoritative sources

- Geolex Castle Hayne references — U.S. Geological Survey: https://ngmdb.usgs.gov/Geolex/UnitRefs/CastleHayneRefs_915.html
- Geolex Spring Garden Member — U.S. Geological Survey: https://ngmdb.usgs.gov/Geolex/UnitRefs/SpringGardenRefs_3920.html

## Formation photograph

- Image: https://lithomap.app/_delivery/formations/castle-hayne-limestone.webp
- Description: Historic photograph of a fossil-bearing Castle Hayne Limestone locality in North Carolina
- Creator: UNC Sea Grant College Program
- License: No known copyright restrictions — https://commons.wikimedia.org/wiki/Commons:Copyright_tags#No_known_copyright_restrictions
- Source record: https://commons.wikimedia.org/wiki/File:Coast_watch_(1979)_(20472080678).jpg

Formation-level information does not prove that a fossil or mineral occurs at a specific coordinate. It also does not establish ownership, access, collecting permission, present conditions, or specimen identity.