Remagnetization of Marcellus Formation in the Plateau Province of the Appalachian Basin

Abstract

An integrated paleomagnetic, magnetic fabric, and petrographic study of two cores (EC, oriented; DB, unoriented) in the Devonian Marcellus Formation from the Plateau Province (PA) indicates the presence of chemical remanent magnetizations (CRMs) and extensive diagenetic alteration. Anisotropy of magnetic susceptibility results indicate a predominately oblate fabric. Some specimens contain a prolate fabric that is interpreted as diagenetically altered. A well-developed viscous magnetization, possibly contaminated by a drilling induced component, is not present in either core, and cannot be used for orientation. An intermediate temperature component (ITN) with steep down inclinations is removed in both cores below ∼300 • C. Specimens in DB also contain a component with steep up inclinations (ITR) that is removed between 300 and 440 • C. The ITN is interpreted to reside in magnetite and/or possibly pyrrhotite, and the ITR resides in magnetite. The ITN could be a reversal of ITR, acquired in the Cretaceous to Cenozoic based on a comparison with the expected inclinations. Alternatively, the ITN could be a contaminated by a Brunhes viscous magnetization. Specimens from both cores contain a characteristic remanent magnetization (ChRM) with shallow inclinations that is removed by 500 • C in DB and 460 • C in EC, and is interpreted to reside in magnetite. The DB ChRM has an inclination of −9.0 • , which corresponds to a range of ages between 310 and 225 Ma based on the expected inclinations. The ChRM in EC has streaked declinations, which may have been caused by core barrel rotation. Shallow inclinations (−3.7 • ) in this core suggest a range of acquisition from 305 to 230 Ma. Rock magnetic data are consistent with the presence of magnetite but provide conflicting evidence for pyrrhotite. The ChRM in DB is interpreted as a CRM whereas the ChRM in EC could be thermoviscous in origin. Diagenetic studies indicate a complex paragenesis with authigenic minerals such as barite, sphalerite, baroque dolomite, and sylvite suggestive of alteration by external fluids. The presence of the CRM in highly altered zones suggests it is related to alteration by external fluids, although its presence in other facies suggests that burial diagenetic processes could also be a cause of remagnetization.

Unraveling the complex burial history of the Antrim formation in Michigan basin using paleomagnetism, rock magnetism and geochemistry

“…Paleomagnetic studies of Devonian shales in North America have provided key insights regarding the timing of paleofluid activity in sedimentary basins (e.g., Dennie et al, 2012;Manning and Elmore, 2015;Elmore, 2017, Roberts et al, 2019;Steullet et al, 2019). The Antrim Formation represents one such shale deposited within the vast eastern interior seaway which separated the North American craton.…”

Burial Diagenesis and Tectonism Inferred From Paleomagnetism and Magnetic Fabrics in the Wolfcamp Shale, Midland Basin, Texas, USA

“…In addition to obtaining the timing of burial events, the chemical and physical processes shaping rock fabrics are key to understanding the evolution of sedimentary basins. Anisotropy of magnetic susceptibility (AMS) has been effectively utilized in this capacity and can document incipient compression, fingerprint tectonic domains in foreland systems, measure paleocurrent directions, quantify petrofabrics, identify diagenetically altered zones, and quantify mechanical compaction (Almqvist & Koyi, 2018; Aubourg et al, 1991; Heij & Elmore, 2019; Schieber & Ellwood, 1993; Schwehr et al, 2006; Steullet et al, 2019). AMS studies can also compliment paleomagnetic studies by determining possible deformation‐induced and compaction deflections in natural remanent magnetizations (NRMs; e.g., Parés & Van der Pluijm, 2004).…”

“…AMS studies can also compliment paleomagnetic studies by determining possible deformation‐induced and compaction deflections in natural remanent magnetizations (NRMs; e.g., Parés & Van der Pluijm, 2004). Valid interpretation of both AMS and paleomagnetic data from cores hinge upon precisely oriented samples to determine paleomagnetic pole positions and evaluate stress fields or paleocurrents; however, precise orientation of specimens has proven to be challenging in previous core‐based studies (e.g., Dennie et al, 2012; Steullet et al, 2019). With the advent of borehole imaging, specifically the resistivity‐based formation image logging tool, it is now possible to reorient AMS and paleomagnetic specimens relative to subvertical natural fractures that can be traced from the image log to its corresponding fractures in core slabs (e.g., MacLeod et al, 1994).…”