Year of Award

2010

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

George Stanley

Commitee Members

Jon Graham, Marc Hendrix

Keywords

Blue Mountain Province, Corals, Olds Ferry, Triassic, Wallowa

Publisher

University of Montana

Abstract

The diversity and abundance of Late Triassic scleractinian corals and carbonate microfacies were analyzed from the Wallowa terrane (southern Wallowa Mountains, Oregon) in order to determine regional and distant paleogeographic relationships during the Late Triassic time. Systematic identification of coral species and depositional environments between two formations in the Wallowa terrane (Summit Point Member of the Martin Bridge Formation and Excelsior Gulch of the Hurwal Formation) and one locality in the adjacent Olds Ferry terrane (Willow Spring of the “Upper” Huntington Formation) were used to analyze similarities between the Tethys realm (Northern Calcareous Alps) and the terranes of the North American Cordillera. The Jaccard and Dice Coefficients were used to determine similarities between the Summit Point Member, Excelsior Gulch conglomerate, and the Willow Spring conglomerate as well as previously studied terranes throughout the Late Triassic world. Results showed strong similarities (p-values less than 0.05) between the Summit Point Member and Excelsior Gulch conglomerate (Wallowa terrane). Statistical similarities between the Wallowa and Olds Ferry terrane were indicated by the Jaccard or Dice Coefficients; however, the co-occurrence of coral species (Cerioheterastraea sp. and Spongiomorpha ramosa) and associated reef biota demonstrate a strong correlation between the Excelsior Gulch conglomerate (Wallowa terrane) and the Willow Spring conglomerate (Olds Ferry terrane). Paleoecological analysis of the Summit Point Member revealed a sequence of in situ stacked patch reefs dominated by scleractinian corals, hypercalcified sponges, and calcareous solenoporacean red algae. Debris produced by physical and biological breakdown of these patch reefs shed voluminous amounts of carbonate remains into the interstitial spaces between the patches creating sediment build-up This debris created mostly massive limestone with concentrations of reef framework mixed with rudstones and bioclastic grainstones, packstones, and wackestones. Summit Point also provides the best source for the limestone clasts of the Excelsior Gulch conglomerate. The behavior of the Summit Point reef is extremely similar to that of the Dachstein Limestone in the Northern Calcareous Alps, Austria. This discovery provides valuable paleogeographic and paleoecologic information for reef build-ups throughout the Late Triassic world.

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© Copyright 2010 Megan Ruth Rosenblatt