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Alternating Fluvial Styles within the Late Paleozoic Maritimes Basin Complex, Atlantic Canada: a Record of Paleoclimate Fluctuation

Allen, Jonathan P.1; Fielding, Christopher 1; Gibling, Martin R.2; Rygel, Michael 3
1 Department of Geosciences, University of Nebraska-Lincoln, Lincoln, NE.
2 Department of Earth Sciences, Dalhousie University, Halifax, NS, Canada.
3 Department of Geology, SUNY Potsdam, Potsdam, NY.

This study utilizes a newly recognized type of fluvial style in order to interpret paleoclimatic changes within the Pennsylvanian-lower Permian succession of Atlantic Canada. This fluvial style is characterized by 1) erosionally based sandstone bodies that display complex and abrupt lateral variations of sandstone and pedogenic mudstones, 2) an abundance of sedimentary structures deposited by high flow conditions such as plane bedding and convex-upward antidune stratification, 3) complex internal stratification produced by plant sediment interactions, and 4) in situ arborescent trees preserved within densely spaced groups that are consistently tilted in a downflow orientation. These characteristics have been interpreted to represent fluvial sandbodies deposited under a seasonal tropical climatic regime characterized by flashy, strongly seasonal discharge. Within the Maritimes Basin, this strongly seasonal fluvial style is restricted to three stratigraphic intervals: the late Visean-early Namurian, late Namurian-Westphalian A, and Westphalian D-early Permian. Fluvial styles characteristic of both humid and arid climates are dominant in other stratigraphic intervals. This pattern of alternating fluvial styles can be correlated across different basins within the basin complex which suggests a regional paleoclimatic signal represented by several pronounced, long-term changes in precipitation and runoff.

This work suggests that the paleoequatorial realm records various scales of climatic variation that may be comparable to the scales of variation observed in Gondwanan records. Intervals that record strongly seasonal paleoclimate are approximately 1-2 m.y. in duration. Within at least one of these intervals, Milankovitch-scale climatic fluctuations are potentially recorded. These intervals within the Maritimes Basin that record strongly seasonal paleoclimate correlate broadly with peak Gondwanan glaciation suggesting synchroneity of global climate shifts in the Late Paloezoic.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009