--> Abstract: Devonian-Carboniferous Passive to Foreland Basin Buildup-Rich Carbonates in Idaho: Significant Subsidence and Eustacy Events, by Peter E. Isaacson, George W. Grader, Liselle Batt, Michael C. Pope, Isabel Montanez, and Bonny Archuleta; #90039 (2005)

Datapages, Inc.Print this page

Devonian-Carboniferous Passive to Foreland Basin Buildup-Rich Carbonates in Idaho: Significant Subsidence and Eustacy Events

Peter E. Isaacson1, George W. Grader1, Liselle Batt1, Michael C. Pope2, Isabel Montanez3, and Bonny Archuleta2
1 University of Idaho, Moscow, ID
2 Washington State University, Pullman, WA
3 University of California, Davis, CA

Idaho's mid- and late Paleozoic margin had a history of anomalous subsidence (relative to adjacent BC/Alberta and Nevada) combined with several organic buildups in downslope and eustacy-influenced foreland basin settings. Classic “Alberta” style buildups and many rare Palaeoaplysina - phylloid algal mounds are found in a very thick carbonate-dominated succession. Overall, Devonian through Early Permian sediments comprise 7 km thickness. Idaho's margin began as a passive one in Middle Devonian time, yielding to a significant foreland basin with large accommodation events in the Carboniferous. Starting with the Jefferson Formation (Middle and Late Devonian, over 2 km), downslope rhythmites pass upward into a Nisku-type downslope buildup with stromatoporoids (showing ecophenotypic growth forms) and disphyllid corals. A drowning event occurs, with eustatic lowstand following, subjecting the buildup to subaerial exposure. The abrupt sealevel change is a consequence of coeval glaciation in Gondwana. Coincident with the first Late Devonian/Early Carboniferous tectonic loading event, the resulting foreland basin received western-derived flysch with a 3 km carbonate progradation event following. It is represented by changes from mudstone through packstone, with horizons of pelletal and ooid grainstones. A second tectonic adjustment from sediment loading provided accommodation for a second progradational carbonate package in Bashkirian time. Late Carboniferous carbonates show cyclic development of phylloid algal and hydrozoan(?) buildups, which show an ecologic succession from pelmatozoans (sediment stabilizers), colonial rugosans (colonizers), and diverse shelly faunas and phylloid algae (diversification) and Palaeoaplysina (domination). Buildups show termination by salinity rise (dolomites), siliciclastic suffocation (sands and silts), and brief subaerial exposure.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005