A Paradigm Change: Late Devonian onset of Gondwana glaciation and its proxies

ISAACSON, P.; GRADER, G.; DI PASQUO, M.M.

Moscow

Encuentro; GSA 68th Annual Meeting; 2016

University of Idaho

(Moscow, 18?19 May 2016) - T7. Late Paleozoic Ice Age: Gondwana Systems and Proxies in the U.S. Cordillera, Abstract #275805. The Late Devonian through Carboniferous was an important period in Earth?s history for it recorded widespread Gondwanan glaciations (Frakes et al., 1992; Crowell, 1999; Isaacson et al, 1999, 2008). The timing and mode of initiation of Gondwanan glaciation, and its mechanistic link to eustatic fluctuations, changes in continental weathering rates, and paleoceanographic and climatic conditions remain poorly resolved. This reflects in part the disparity between various proxy records, the problem of accurately dating Gondwana diamictites (as either part of ice advance or retreat). Onset of the glaciation is believed to have occurred in the latest Famennian epoch at 360.7 Ma (Kauffman, 2006) or earliest Tournaisian 358.9 Ma (Becker et al., 2012). Recent cyclostratigraphic study of carbonate, medium-fine grained siliciclastic and black shale sedimentary rocks, and stable isotopic study of latest Devonian marine strata further support a rapid deterioration of Late Devonian paleoclimate that initiated Gondwana and Laurentian glaciation in the Famennian epoch (Cecil et al., 2004; Brezinski et al., 2010). To what degree the Late Devonian glacial episode was short-lived (Caputo,1985; Caputo et al., 2008; Streel, et al., 2000; De Vleeschower et al., 2013; Kaiser et al., 2015), events heralding the onset of the main phase of widespread glaciation later in the Mississippian, or whether they are evidence of earlier initiation of main-stage glaciation remains a topic of debate. We hypothesize that the changes in sea level, continental weathering patterns, and oceanographic and paleoclimatic conditions that would have accompanied the significant change in ice-sheet dynamics associated with either onset of glaciation or potentially intermittent deglaciation during the Devonian-Carboniferous (D-C) boundary interval should be recorded in the sedimentologic and biostratigraphic records of late Famennian and early Tournaisian sedimentary rocks. We further hypothesize that each of the two aforementioned scenarios would have imparted, on the D-C boundary deposits, a unique set of stratigraphic and geochemical signatures that can be used to place quantitative constraints on the hypothesized evolutionary paths of glaciation and its low-latitude proxies during the Late Devonian and Early Mississippian.