ROCK MAGNETIC FABRICS AND PALEOMAGNETIC VECTORS OF THE MARCELLUS FM, SUNBURY PA

We present magnetic fabrics and paleomagnetic directions of the Devonian Marcellus FM measured from a core extracted near Sunbury, PA. Anisotropy of Magnetic Susceptibility (AMS) and Anisotropy of Magnetic Remanence (AAR) were measured to characterize the orientation and anisotropy of paramagnetic clay and silt particles and ferromagnetic minerals. Paleomagnetic directions were measured to create a high-resolution magnetostratigraphy. Paleomagnetic directions obtained using alternating field (AF) demagnetization demonstrate a high coercivity remanence (>35 mT) with a south and shallow direction (D= 183.4 I=-14.7). This result is consistent with previous studies of Devonian formations in North America and indicates a Devonian age for the magnetization. Thermal demagnetization experiments demonstrate a similar magnetization removed by temperatures between 250 °C and 350 °C, however, continued heating results in the acquisition of strong, inconsistent magnetizations likely the result of oxidizing iron sulfides. Thermal demagnetization of orthogonal partial ARMs demonstrates that a low coercivity (50mT) pARM is removed by 400 °C and a high coercivity (100mT) pARM is removed by 600 °C, behavior that is characteristic of low coercivity Fe sulfides and high coercivity magnetite. AMS fabrics consistently demonstrate a nearly triaxial fabric with maximum principal axes clustering east-west and horizontal in geographic coordinates, nearly parallel to the direction of bedding strike. AMS minimum principal axes cluster near the pole to the bedding plane. Anisotropy of anhysteretic remanence (AAR) applied with a 100 mT peak field demonstrates a markedly different fabric, with maximum principal axis clustering north-south and horizontal in geographic coordinates. Minimum principal axes of AAR cluster steeply (~60˚-70˚) to the west. AMS likely indicates an intact depositional fabric carried by paramagnetic minerals.