...Redux

["Jerry D. Harris" <jharris@dixie.edu>]

OK, one more.  Last one, I swear!  Well, until the next one...

Lehman, T., and S. Chatterjee. 2005. Depositional setting and vertebrate 
biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth 
System Science 114(3):325-351.

ABSTRACT: Triassic strata of the Dockum Group in Texas comprise two major 
upward-fining alluvial-lacustrine depositional sequences. The two sequences 
are represented by the (1) Santa Rosa-Tecovas, and (2) Trujillo-Cooper 
Canyon Formations. The second sequence is much thicker than the first, and 
occupies a greater geographic part of the Dockum basin. Each sequence of 
alluvial and lacustrine sediment accumulation is characterized by sediment 
derivation from a different source terrain. The unconformable relationship 
between the two depositional sequences, the change in mineralogical 
composition and presumed source areas between these units, differences in 
paleocurrent orientation between units, and evidence for intervening 
episodes of local deformation indicate that the sequences are of tectonic 
origin. These strata are not the product of a single sediment dispersal 
system, such as the centripetally-drained lacustrine delta complex 
previously envisioned for the Dockum basin. Both Dockum sequences are 
comprised largely of two typical alluvial facies associations; stream 
channel facies, and overbank flood-plain facies, that are similar to those 
described in nearly all fluvial deposits. In addition, the Dockum Group 
contains a peculiar lacustrine facies that accumulated in local flood-plain 
depressions, and probably resulted from subsidence over areas of subsurface 
salt dissolution. Vertebrate fossil assemblages are found in all three 
Dockum facies associations. Five fossiliferous sites in the Dockum are 
discussed in the context of these three depositional settings. The Dockum 
tetrapod diversity is reviewed in a hierarchical phylogeny with remarks on 
the history of collection, stratigraphic distribution of genera, and their 
taxonomic status. The stratigraphic ranges of tetrapod taxa do not support 
the recently proposed successive Otischalkian, Adamanian, Revueltian, and 
Apachean biochrons within the Dockum Group. Instead, a few index fossils 
provide a broad framework for correlation of Late Triassic nonmarine strata 
of the Dockum with the Carnian and Norian Alpine marine stages.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com
http://cactus.dixie.edu/jharris/

"And the role of George W. Bush will
be played by: Ralph Wiggum" -- Conan
O'Brien, during "Earth to America," in
listing the fictitious cast of an upcoming
TV movie about global warming.