2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 3
Presentation Time: 8:50 AM


TURNER, Christine E., U.S. Geol Survey, M.S. 939, Federal Center, Box 25046, Denver, CO 80225, FISHMAN, Neil S., US Geological Survey, Box 25046 MS 939, Denver, CO 80225 and PETERSON, Fred, U. S. Geol Survey, Federal Center M.S. 939, Box 25046, Denver, CO 80225, cturner@usgs.gov

Dick Hay, with his considerable expertise and generosity of spirit, contributed greatly to our discovery and delineation of ancient Lake T'oo'dichi' in the Upper Jurassic Morrison Formation, Colorado Plateau. Our field observations and reports of analcime and clinoptilolite had indicated a possible lacustrine origin for fine-grained deposits previously interpreted as overbank deposits. The hint of zeolites intrigued Dick and lured him to New Mexico to see if our hunch was correct. At the first outcrop Dick exclaimed “This is a ‘Green River' story that has not been touched!” Thus began a productive collaboration. Dick provided students and his own expertise to help us delineate an ancient lacustrine complex that contains a concentric zonation of authigenic minerals, characteristic of alteration of silicic volcanic ash in alkaline, saline lakes. With Dick's encouragement, we used the Morrison as a natural laboratory to challenge several paradigms, including the conditions for the formation of authigenic albite and illitic mixed layer I/S clays. This led to the first documentation of a low-temperature, synsedimentary origin for both minerals.

Recently recognized ground-water-fed wetland deposits (including those of Lake T'oo'dichi') in the Morrison Formation reflect greater understanding of the role of ground water in semiarid basins. These new understandings resulted in large part from the recent work in wetland deposits by Jay Quade, a student of Thure Cerling, himself a former Dick Hay student. Appreciation of the wetland deposits was key to reinterpreting the Morrison in the context of an integrated climatic/hydrologic framework. Extensive subaqueous charophyte meadows that inhabited the distal wetlands were a probable food source for herbivorous dinosaurs common in the Morrison. Thus, a study that began with a hint of zeolites has serendipitously taken us on a journey in companionship with Dick Hay and others he inspired, and has led to new advances in sedimentary geology.