The middle sandstone member of the Upper Triassic Chinle Formation in northeastern New Mexico consists of ephemeral-stream deposits adjacent to the Ancestral Rocky Mountain uplift and perennial braided-stream deposits on the plains to the east. The two fluvial systems were contemporaneous with the ephemeral rivers existing as transverse tributaries to a perennial trunk system flowing from north to south.
Proximal ephemeral-stream deposits are characterized by 60-80 m thick sequences of coarse-grained sediments deposited principally by overbank sheetflooding processes. Facies associations are dominated by horizontally-stratified, medium-grained sandstone with subordinate sets of tabular-tangential and trough cross-stratified medium-grained sandstone. Streamflooding events are indicated by basal conglomeratic channelized deposits and single-story massive and trough cross-stratified channel sandstones. Uppermost portions of proximal ephemeral-stream sequences contain 0. 5 to 1. 0 m-thick units of trough cross-laminated, fine-grained sandstone and siltstone. Distal ephemeral-stream deposits are distinguished by their lenticular geometries, thicknesses of 20 to 30 m and sedimentary structures indicative of lower flow-regime streamflooding processes. Channelized conglomerates and trough cross-stratified and parallel-stratified sands~ones are capped by tabular and wedge cross-stratified, trough cross-laminated and subordinate horizontally-stratified sandstones.
Facies associations in the deposits of the trunk system are comparable to those of the Platte and South Saskatchewan braided rivers (Miall, 1977). Sets and cosets of tabular-tangential or trough cross-stratified medium-grained sandstone are separated by variable thicknesses of horizontally-stratified medium-grained sandstone; these dominate 10 to 30 m-thick, sheet-like sandstones which are traceable laterally for tens of kilometers. The sheet-like sandstones are separated by equivalent or lesser thicknesses of red mudstones.
Effects of the allocyclic controls of tectonics and climate are recognizable in sedimentary architectures of individual members or of the whole formation. In contrast, the effects of autocyclic controls can be recognized when internal geometries of individual members are focussed upon. The concept of base level is helpful in realizing the time dependency of controls on sedimentation because allocyclic controls determine the position of base level and base level determines which autocyclic controls operate. / M.S.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106090 |
| Date | January 1986 |
| Creators | DeLuca, James L. |
| Contributors | Geology |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | ix, 157 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 15062651 |
Page generated in 0.0018 seconds