An introduction to structures and stratigraphy in the proximal portion of the Middle Devonian Marcellus and Burket/Geneseo black shales in the Central Appalachian Valley and Ridge

Abstract

A Marcellus-Burket/Geneseo fi eld trip in the Appalachian Valley and Ridge features both brittle and ductile structures. The degree to which these structures have developed depends on both lithology, which is a function of the stratigraphic architecture of the Devonian Appalachian Basin and position relative to the foreland during the Alleghanian Orogeny. Joints are best developed in the black shales and the units immediately above with the J 2 joint set most prominent in the Brallier Formation just above the Burket/Geneseo Formation. Faults are seen in the form of cleavage duplexes and bedding-parallel slip accompanying fl exural-slip folding. Cleavage duplexes are found in the Marcellus whereas bedding-parallel slip is more common in the overlying Mahantango Formation and further up the section in the Brallier Formation. Layer-parallel shortening decreases from greater than 50% to approximately 10% when crossing the Jacks Mountain-Berwick Anticline structural front from the hinterland portion to the foreland portion of the Valley and Ridge. Disjunctive cleavage, the primary mechanism for layer-parallel shortening, is best developed in carbonates whereas pencil cleavage is best developed in shales.

How Particle Size Influences Oxidation of Ancient Organic Matter during Weathering of Black Shale

“…Both sites, 30 km apart from each other, are located in the Valley and Ridge provinces in the Appalachian Mountain region. The quarry exposes an outcrop in the lower Union Springs Member of the Middle Devonian Marcellus Formation . This member is known to have some of the highest contents of total organic carbon (TOC) in the formation.…”

“…The base of the unit is terminated by the underlying Onondaga limestone. 34 The quarry was used to sample saprock, i.e., partially weathered and fractured but largely intact rock material. Given that the hillside of the quarry was excavated, leaving the outcrop under the ridgeline of the hill, we inferred that most of the weathering of the samples had occurred by downward weathering from the land surface prior to quarrying.…”

“…This member is known to have some of the highest contents of total organic carbon (TOC) in the formation. The base of the unit is terminated by the underlying Onondaga limestone …”

Revisiting the Hubbert–Rubey pore pressure model for overthrust faulting: Inferences from bedding-parallel detachment surfaces within Middle Devonian gas shale, the Appalachian Basin, USA

“…A number of structures are a manifestation of elevated pore pressure in the Appalachian Basin including natural hydraulic fracturing in several black shale units ranging from the Middle Devonian Marcellus to the Upper Devonian DunkirkeHuron (Engelder et al, 2009;Lacazette and Engelder, 1992;McConaughy and Engelder, 1999;Sheldon, 1912), slickensides arising from bedparallel slip through these same shales (CliffsMinerals, 1982;Evans, 1994), cleavage duplexes, particularly in the Marcellus (Bosworth, 1984;Engelder et al, 2011;Kepferle et al, 1981;Nickelsen, 1986;Wheeler, 1978), fibrous veins including beef and cone-in-cone structures (Gilman and Metzger, 1967;Taber, 1918) and other detachment surfaces found cutting several shales (Hatcher et al, 1989). To examine whether the HubberteRubey model operated in shale of the foreland portion of the Appalachian foldethrust belt because of maturation-related detachment, we document the distribution of detachment surfaces at two scales based on thickness and slip magnitude.…”

Advocacy-Based Science

“…I best understand the geology of the Marcellus gas shale and my conclusions about Smythe's agenda are based purely on his assertions concerning the Marcellus (Engelder et al, 2009;Engelder et al, 2011;Kohl et al, 2014;Lash and Engelder, 2007;Lash and Engelder, 2011). The general premise of Smythe's paper is that there is risk of groundwater contamination by flow along faults during or after unconventional resource appraisal and development.…”