Carbonate platform margin facies on an evolving suspect terrane: Wallowa Mountains, Oregon
In the Wallowa Mountains of eastern Oregon late Triassic (Karnian-Norian) limestones or the Martin Bridge formation were deposited within a complex island arc system which was accreted to North America in mid- to late-Jurassic time. In the northern Wallowas and Hells' Canyon shallow water carbonate platform facies include intertidal cryptalgal laminites, open platform packstones and fossiliferous grainstones, and platform margin shoal deposits. Reef development was limited to local mounds and isolated patch reefs. At the type locality along Eagle Creek in the southern Wallowas, Martin Bridge facies are indicative of deposition in deeper water beyond the platform margin. These facies include three end member types: (1) hemipelagic slope deposits that are thinly bedded, show abundant slump features, are often nodular, and contain a rich fauna of pelagic bivalves; (2) platform-derived conglomeratic carbonate debris sheets; and (3) well bedded proximal and distal carbonate turbidites. The hemipelagic facies represents the normal background carbonate sedimentation on the slope and base of slope, while the latter two facies represent gravity flow deposits generated by periodic slumping at the shelf edge. Alteration between these allochthonous facies is most likely a function of the varying degree of submarine cementation and lithification of carbonate source sediments along the platform margin. Martin Bridge limestones interfinger basinward in the southern Wallowas with argillites and minor carbonates of the Hurwal Formation. Regional paleogeography suggests that the Martin Bridge represents an asymmetric carbonate platform built out from a volcanic archipelago into a sediment-starved forearc (.) basin during a period of volcanic quiescence in Karnian and Norian time.
- Research Organization:
- Harvard Univ., Cambridge, MA (USA)
- OSTI ID:
- 6652630
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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