Pennsylvanian-Permian rocks of the North American Mid-continent were deposited on a near-equatorial epeiric platform during a time of global icehouse conditions. High-frequency, high-amplitude eustatic and climatic changes, analogous to those of the late Neogene, are recorded as a hierarchy of metre-scale stratigraphic cycles packaged into composite sequences. Cycles dominated by nearshore facies are depositional sequences with pedogenesis and incision at their boundaries, carbonate-dominated transgressive systems tracts and siliciclastic-dominated highstand systems tracts lacking condensation associated with their maximum flooding surfaces; lowstand systems tracts are preserved as valley fills. Offshore facies cycles have carbonate-dominated transgressive systems tracts and siliciclastic-dominated highstand systems tracts separated by a maximum flooding surface associated with stratigraphic condensation. Offshore cycles do not have distinct lowstand systems tracts or evidence of subaerial exposure; the carbonate transgressive systems tracts record and (evaporitic) conditions, whereas the siliciclastic highstand systems tracts reflect humid (coal-bearing) conditions. These reflect an alternation of climatic regimes reflecting and eustatic lows and humid eustatic highs explained by glacial-interglacial changes in the summertime position of the intertropical convergence zone (ITCZ). Based on analogy with the Neogene, the ITCZ did not extend as far north into Pangea during lowstand and transgression (i.e., glacial conditions) as it did during highstand and fall (i.e., interglacial conditions). During glacial times, the ITCZ was blocked from carrying equatorial moisture into the continental interior by the Appalachian-Variscan mountains, leading to and conditions in the Mid-continent. During interglacial times, the ITCZ swung farther north, bypassing the high mountains and providing the moisture needed for deposition under humid conditions in the continental interior.
|Original language||English (US)|
|Number of pages||17|
|Journal||Special Paper - Geological Association of Canada|
|State||Published - Dec 1 2008|
All Science Journal Classification (ASJC) codes
- Fuel Technology
- Geochemistry and Petrology