Fluvial and coastal depositional environments may have been quite different before
the development of land plants in the late Silurian. Rapid drainage of terrestrial surfaces,
flashy rivers with poorly stabilized banks, coarse sediment loads supplied to coasts from
landscapes dominated by physical weathering, and the prevalence of epicontinental seas
are expected to have altered depositional patterns and associated preserved Facies.
Quarries in the Upper Cambrian Hickory Sandstone located in central Texas provide an
exceptional opportunity to examine the sedimentology of deposits of this age in order to
interpret sedimentary environments. During quarrying, vertical walls, one half-kilometer
long and several tens of meters high, are blasted back a few tens of meters at a time and
then the rubble excavated, exposing successive outcrops in walls that are perpendicular
to the regional paleocurrent direction. The deposits are characterized by sheet-like
bedsets dominated by unidirectional cross-stratified sandstones interpreted to have
formed in coastal areas fed by bedload dominated rivers. Thinner heterolithic and clay
beds locally separating cross-stratified bedsets are commonly bioturbated by marine
organisms. Presence of tidal features, such as abundant mud drapes, concave-upward cross-stratification and sparse herringbone cross-stratification, also suggests marine
influence during deposition. Detailed mapping of stratal geometry and Facies across
these exposures shows a complex internal architecture that can be interpreted in terms of
growth and superposition of bars within shallow fluvial channels and adjacent shallow
marine areas along the coast. Detailed 3D reconstruction of bars and channels reveals a
range of processes including growth, coalescence, and erosion of bars during channel
migration, switching and filling of channel segments, and mouth bar growth as
channelised flows decelerated seaward. Sedimentary Facies, stratal geometry and
ichnofossils suggest that these deposits were formed in a braid-delta system fed by lowsinuosity
bedload-dominated rivers. Basinal processes were controlled by the shallow
epicontinental sea, dissipating wave action and strengthening tidal currents.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1522 |
| Date | 15 May 2009 |
| Creators | Perez Teran, Isaac Antonio |
| Contributors | Bouma, Arnold, Willis, Brian J |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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