K-bentonites, volcanic ash preservation, and implications for Early to Middle Devonian volcanism in the Acadian orogen, eastern North America

Abstract

Lower to Middle Devonian marine strata in the Appalachian foreland basin feature up to 80 or more thin K-bentonites that represent ancient volcanic ashes. The time vs. space distribution of K-bentonites through the Lochkovian to Eifelian Stages (representing ϳ30 m.y.) shows a distinct pattern of clustered multiple beds, several scattered beds, and thick intervals with no K-bentonites. Four clusters of 7 to 15 individual, closely spaced layers occur in the middle Lochkovian (Bald Hill K-bentonites, Kalkberg-New Scotland Formations), late Pragian or early Emsian (Sprout Brook Kbentonites, Esopus Formation) and early Eifelian (two clusters, the Tioga middle coarse zone and Tioga A-G K-bentonites, Onondaga Formation).Detailed examination of these Devonian K-bentonites shows that in many cases they do not represent a single eruption. Multilayered beds, fossil layers within beds, authigenic minerals (e.g., glauconite and phosphate nodules), subjacent hardgrounds, and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism. These and other lines of evidence indicate that postdepositional physical, biological, and geochemical processes (e.g., sedimentation rate, event, and background physical processes, burrowing) have modified the primary record of these water-laid ash-fall events. These factors may lead to preservation of primary ash deposits or to † E-mail: cverstra@mail.nysed.gov. their resedimentation and/or partial to complete mixing with background sediments.The preservation potential, and resulting distribution, of the Devonian K-bentonites can be analyzed across a spectrum of preservational magnafacies. In this paper I present a model of ash preservation; the model incorporates environmentally related physical, biological, and chemical processes active in epicontinental seas and marine foreland basins. Conclusions based on the model indicate that the middle Lochkovian, early Emsian, and early Eifelian were times of peak volcanic activity in eastern North America, related to times of increased tectonism in the Acadian orogen.

Microbial proliferation coinciding with volcanism during the Permian–Triassic transition: New, direct evidence from volcanic ashes, South China

“…The good preservation of volcanic ash beds in the PTB successions indicates a high ash-deposition rate and a low water energy, together with weak bioturbation (Ver Straeten, 2004), which may also facilitate the preservation of delicate biofilms in some ash samples. Of all studied sections, the Xinmin, Shangsi, Duanshan sections represent deep-water facies, with deposition depths at ~200-300 m (Shen et al, 2013b).…”

“…Rapid burial typically caused by tremendous amounts of volcanic ashes transported to sedimentary environments during short-timescale volcanic eruptions, generally, is a rather significant factor in the preservation of ash beds, especially glass shards and pumice fragments (Ver Straeten, 2004. During rapid burial processes soon after ash deposition, individual volcanic glass fragments can be readily protected from immediate contact with subaqueous surroundings and prevented from cation exchange.…”

“…Rapidly cooled volcanic glass shards are highly reactive in water and are subsequently converted (Ver Straeten, 2004).…”

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

“…34). ackground: Up to 80 or more Lower and Middle Devonian (Lochkovian to Eifelian) K-bentonites in the Appalachian Basin are distributed through the succession as four major clusters of 8-15 closely spaced beds or as scattered multiple to single beds (ver Straeten, 2004). The most prominent cluster is known as the Tioga A through G ash beds/K-bentonites.…”

Geophysical, stratigraphic, and flow-zone logs of selected wells in Cayuga County, New York, 2001–2011

“…The phosphate nodules produce a characteristic gamma peak that facilitates the identification of the contact between the Onondaga and Manlius Formations, which is a major erosional unconformity. Another significant gamma peak is produced by the Tioga Bentonite, which is a thin volcanic ash deposit at the contact of the Seneca and Moorehouse Members of the Onondaga Limestone (Ver Straeten, 2004).…”