THOUGHTS ON LATE PALEOZOIC FLUID MIGRATION IN THE SOUTHERN APPALACHIAN BASIN

Diverse lines of evidence (e.g. fluid inclusion, dates of authigenic K-feldspar, K-Ar dates of diagenetic illite, remagnetization) support the presence of migrating fluids resulting from the Alleghenian Orogeny in the Applachian Basin. While the presence of migrating fluids at the distal margin is not debated, the source and migration process (squeegee, topographic recharge) of the migrating fluids are open questions. Analysis of evidence for fluid migration the proximal basin in the southern Appalachian Basin is one way to identify the source and composition of migrating fluids. The timing and extent of illite-smectite (I-S) formation in Ordovician K-bentonites were studied in the Valley and Ridge Province to address the origin and source of migrating fluids in the southern Appalachian Basin.

The timing of diagenetic I-S (>90% illite layers) ranged from 260 to 310 Ma. The oxygen isotope composition of I-S ranged from 18 to 23‰ SMOW. The oxygen isotope composition of waters in equilibrium with I-S are consistent with I-S being formed from orogenic (saline) waters. The variance of K-Ar dates of I-S basinwide does not correlate with burial depth or conodont alteration index. The variance in K-Ar dates of I-S may reflect the variable time of reaction with migrating fluids, and/or fluid compositions. Upward diffusion of migrating fluids from the base of thick K-bentonites explains concordant dates within thick K-bentonites. The data is consistent with migration of K-rich fluids in the proximal basin. However, the pathways of fluid migration are open questions in this area of the basin.