Paper No. 5
Presentation Time: 9:00 AM
AN INTEGRATED PALEOMAGNETIC AND DIAGENETIC STUDY OF THE MARCELLUS SHALE, APPALACHIAN VALLEY AND RIDGE PROVINCE, PENNSYLVANIA
A paleomagnetic and rock magnetic study of the Marcellus Subgroup (Oatka Creek [OC] and Union Springs [US] formations) of the Hamilton Group is being conducted as part of an integrated diagenetic study. Due to the fissile nature of the shale, most samples collected were from carbonate beds, however, a few limestone concretions and shales were included. Samples were collected from outcrops of the US in a syncline just to the east of the Broadtop Synclinorium and from the US and OC at other sites in the Valley and Ridge in Pennsylvania. Two southerly and shallow-up components were identified. The two components were removed between 230-330oC and 350-480oC and are interpreted to reside in pyrrhotite and magnetite, respectively. The pyrrhotite component is most common in the east limb where there are numerous mineralized fractures. A stable component was not found in any samples from the OC. Coercivity spectrum analysis of the isothermal remanent magnetization (IRM) acquisition curves, stepwise thermal decay of the triaxial IRM, and thermal demagnetization results indicate that both pyrrhotite and magnetite are present in the specimens. A tilt test indicates that the magnetite component is late syn-tilting. A preliminary tilt test indicates that the pyrrhotite component is syn-tilting. Both components have early Permian paleopoles on the apparent polar wander path. Based on the maximum laboratory unblocking temperatures and conodont color alteration indices data, both are interpreted as chemical remanent magnetizations. NaCl-rich fluid inclusions from quartz in calcite/ saddle dolomite/ quartz filled fractures on the east limb of the syncline have Th values ~200°C with ~12 wt. % NaCl equiv. salinity. The absence of a remagnetization away from the contact between the US and underlying Onondaga suggests a connection between the remagnetization and proximity to the underlying contact. This contact test suggests that Onondaga was a conduit for fluids which locally remagnetized and altered the Marcellus. The pyrrhotite component is hypothesized to have been caused by localized thermochemical sulfate reduction involving hydrothermal fluids.