TY - JOUR
T1 - Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas
AU - Lehman, Thomas
AU - Chatterjee, Sankar
PY - 2005/6
Y1 - 2005/6
N2 - 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.
AB - 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.
KW - Dockum
KW - Sedimentology
KW - Texas
KW - Triassic
KW - Vertebrate biostratigraphy
UR - http://www.scopus.com/inward/record.url?scp=22144434855&partnerID=8YFLogxK
U2 - 10.1007/BF02702953
DO - 10.1007/BF02702953
M3 - Review article
AN - SCOPUS:22144434855
SN - 0253-4126
VL - 114
SP - 325
EP - 351
JO - Journal of Earth System Science
JF - Journal of Earth System Science
IS - 3
ER -