|2009 Portland GSA Annual Meeting (18-21 October 2009)|
|Paper No. 147-8|
|Presentation Time: 10:05 AM-10:20 AM|
CHRONICLES OF VADOSE ZONE DIAGENESIS: CONE-SHAPED IRON OXIDE CONCRETIONS, TRIASSIC TRUJILLO FORMATION, PALO DURO CANYON, TEXAS
DINWIDDIE, Cynthia L.1, CHAN, Marjorie A.2, MCGINNIS, Ronald N. Jr1, and MYERS, James L.1, (1) Geosciences and Engineering Division, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, email@example.com, (2) Department of Geology and Geophysics, University of Utah, 115 South 1460 East, Salt Lake City, UT 84112|
Cone-shaped Fe-oxide concretions occur in the Late Triassic lower fluvial sandstone member of the Trujillo Formation at
Differences in cone-shaped morphologies among three lithofacies suggest that concretion shapes and sizes were affected by host rock sedimentary texture, primary bedding structure and scale, and corresponding paleohydrologic regime. Tall, slender concretions in medium- to coarse-grained sandstone likely resulted from the massive, porous nature of the beds, which permitted fluid to drain freely downwards along advection-dominated, m-scale path lengths. Tortuous, dendritic iron-staining on these concretions is interpreted to have delineated preferred paleo-flow paths in the vadose zone. Short, squat concretions in fine-grained, finely laminated sandstone are attributed to the alignment of platy clays that led to a small-scale permeability structure with a large horizontal-to-vertical permeability ratio that favored lateral fluid displacement in a diffusion-dominated zone of locally reduced permeability. Discoidal concretions in very fine-grained silty sandstone with decimeter-scale bedding planes appear to correspond to an environment intermediate between advection- and diffusion-dominated fluid flow.
The timing of diagenesis and the hydrochemical factors that resulted in the unusual shape of these Trujillo concretions, when fully understood, may provide substantive insight into events that occurred during the 200-m.y. hiatus at a major post-Triassic unconformity of the
2009 Portland GSA Annual Meeting (18-21 October 2009)
General Information for this Meeting
|Session No. 147|
Sediments, Clastic: New Insights to Old Problems
Oregon Convention Center: E145
8:00 AM-12:00 PM, Tuesday, 20 October 2009
Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 393
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