Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Straeten, C. A. V. Search for Related Content GeoRef GeoRef Citation

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

Charles A. Ver Straeten^,1

¹ New York State Museum, State Education Department, Albany, New York 12230, USA

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 30 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 K-bentonites, 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 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.

Key Words: K-bentonites • Devonian • preservation • marine processes • Acadian orogeny

This article has been cited by other articles:

				Z. Puspoki, M. Kozak, P. Kovacs-Palffy, J. Szepesi, R. McIntosh, P. Konya, L. Vincze, and G. Gyula GEOCHEMICAL RECORDS OF A BENTONITIC ACID-TUFF SUCCESSION RELATED TO A TRANSGRESSIVE SYSTEMS TRACT - INDICATION OF CHANGES IN THE VOLCANIC SEDIMENTATION RATE Clays and Clay Minerals, February 1, 2008; 56(1): 23 - 38. [Abstract] [Full Text] [PDF]

				C. A. Ver Straeten Basinwide stratigraphic synthesis and sequence stratigraphy, upper Pragian, Emsian and Eifelian stages (Lower to Middle Devonian), Appalachian Basin Geological Society, London, Special Publications, January 1, 2007; 278(1): 39 - 81. [Abstract] [Full Text] [PDF]