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AAPG Bulletin

Abstract

AAPG Bulletin, V. 99, No. 3 (March 2015), P. 389ndash401.

Copyright copy2015. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/06301413006

Neoformed magnetic minerals as an indicator of moderate burial: The key example of middle Paleozoic sedimentary rocks, West Virginia

Myriam Kars,1 Charles Aubourg,2 and Isabel Suárez-Ruiz3

1Laboratoire des Fluides Complexes et leurs Réservoirs, Université de Pau et des Pays de l’Adour, UMR 5150 CNRS TOTAL, Avenue de l’université, 64013 Pau cedex, France; present address: Kochi University, Center for Advanced Marine Core Research, B200 Monobe, Nankoku, 783-8502, Japan; [email protected]
2Laboratoire des Fluides Complexes et leurs Réservoirs, Université de Pau et des Pays de l’Adour, UMR 5150 CNRS TOTAL, Avenue de l’université, 64013 Pau cedex, France; [email protected]
3Instituto Nacional del Carbón (INCAR-CSIC), Francisco Pintado Fe 26, 33011 Oviedo, Spain; [email protected]

ABSTRACT

In order to help unravel the thermal history of middle Paleozoic sedimentary rocks in West Virginia, a rock magnetic study was conducted with a focus on the Marcellus Shale. Vitrinite reflectance, fluid inclusions microthermometry and conodont alteration index data yield contradictory burial temperature within the range 150–250°C (302–482°F). The characterization of magnetite and pyrrhotite may be used as an index to track burial temperature around 200°C (392°F). Low-temperature and room-temperature magnetic measurements were performed in order to determine the magnetic assemblage. Three magnetic assemblages were identified that were stratigraphically distributed. The goethite and nanosized magnetite (A1) assemblage is mainly found in the Clinton Group–Oriskany Sandstone stratigraphic interval (Silurian–Lower Devonian). Nanosized fraction of magnetite and probably pyrrhotite (A3) assemblage essentially constitutes the Marcellus Shale–Chemung Formation sequence (Devonian). Microsized pyrrhotite is the typical mineral for A2 that is only identified near the Alleghenian structural front. Overall, the rare occurrence of micron pyrrhotite in our samples suggests that the study area has not experienced burial temperatures higher than 200°C (392°F).

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