PALEOMAGNETIC POLARITY AND MAGNETIC MINERALS IN THE EOCENE SANTEE LIMESTONE AND WARLEY HILL FORMATION, CENTRAL SOUTH CAROLINA

Samples of the Warley Hill Fm and from the Moultrie Mbr and Chapel Branch Mbr of the overlying Santee Lms record varied paleomagnetic polarities. Both formations are middle Eocene. The Warley Hill Fm beside the Santee River at Wilson's Landing, just below the Lake Marion dam, records normal polarity. The Moultrie Mbr (middle Eocene) about 3 m above the June 2000 floor of the Martin Marietta Orangeburg quarry records normal polarity. Perhaps 15 m higher in the quarry, the Moultrie Mbr records reverse polarity. About 50 cm above water level at Lake Merion at Santee State Park, the Chapel Branch Mbr records reverse polarity. Calcareous beds of the Warley Hill Fm at Wilson's Landing include the bivalve Cubitostrea lisbonensis and dinoflagellates correlated with calcareous nannofossil zone NP15. Glauconite from beds in the same depositional sequence at Wilson's Landing provided a Rb/Sr date of 42.0±0.5 Ma (Harris and Fullagar, 1987, 1989). The Moultrie Mbr includes the bivalve Cubitostrea sellaeformis and dinoflagellates correlated with calcareous nannofossil zone NP16 and NP17 or both. Glauconite from the neostratotype of the Santee Lms (Ward and others,1979) provided a Rb/Sr isochron date of 37.6± 0.6 Ma (Harris and Fullagar, 1984, 1987). The Chapel Branch Mbr includes the bivalve Cubitostrea sellaeformis and dinoflagellates correlated with calcareous nannofossil zone NP17; regional relationships suggest correlation with the lower part of NP17. Glauconite from the Chapel Branch Mbr at Santee State Park provided a Rb/Sr date of 40.4±0.8 (Harris and Fullagar, 1989). The data suggest assignment of the Warley Hill Fm to Chron C20n. Assignment of the Moultrie Mbr to polarity chrons awaits further developments. Assignment of the Chapel Hill Mbr to Chron C18r (more likely) or C18n-1r was suggested by Liddicoat and others (2000). Isothermal remanent magnetization (IRM) and thermomagnetic laboratory experiments on whole-rock samples from the Warley Hill Fm and from both members of the Santee Lms identify pseudo-single domain magnetite as the carrier of the magnetization.