27 Undergraduate Research – Structure, Tectonics, Geophysics and Remote Sensing (Posters)

CLASSIFICATION OF FOLDS AT THE PADDY CREEK SECTION OF THE MARTIN BRIDGE LIMESTONE, SOUTHERN, WALLOWA MOUNTAINS, OREGON

Paper number: 27-4
Program: Technical Sessions
Time: 1:00 PM – 4:30 PM

Authors

Abstract

The Triassic Martin Bridge Limestone of the Wallowa Mountains has been pervasively folded and faulted by multiple deformational events. Avé Lallemant (1995) classified folding in the northern Wallowa Mountains as being Ramsay class 2 (similar folding). Recent work in the southern Wallowas indicates that folding, at least near the type section of the Martin Bridge Formation along Paddy Creek, belongs to Ramsay class 1b (parallel folds) and 1c with associated cleavages (S2) poorly developed.

In some instances, progressive deformation of the folds produced northwest-verging thrust faults. Work in the southern Wallowas indicates that this event corresponds to the first local deformation, but is regionally correlated to a D2 event. The location of these fold measurements, at the confluence of Paddy Creek with Eagle Creek, is also near the syntaxis of folding for a later regional deformational event, D3, so folding styles may have been modified through interference. From measurements of folding and estimates in the displacements along faults, we have estimated the minimum shortening and compression directions responsible for this event.