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Heavy-mineral analysis of 53 outcrop samples from the Upper Triassic Dockum Group in West Texas and northeastern New Mexico showed a stable heavy-mineral association of zircon, tourmaline, garnet, leucoxene, magnetite-ilmenite, and rutile. An adjacent sedimentary source terrane was suggested by these results.
Previous studies of cross-bedded Dockum sandstones indicated a source for the Upper Triassic at the southeast. Fifteen outcrop samples were therefore examined from sandstones of Pennsylvanian and Permian age in central Texas, the assumed source area. Both heavy minerals and quartz varieties in these rocks were virtually the same in most details as those of the Dockum Group. Comparisons of mineral varieties and their roundness characteristics also indicated close similarities.
It is concluded that: (1) mineralogical comparisons corroborate cross-bedding results of a major source of detritus for the Upper Triassic at the southeast, (2) this source area was the sedimentary terrane consisting of clastics of Pennsylvanian and Permian age in central Texas, (3) more than one sedimentary cycle was involved, and (4) the probable ultimate source was a granitic terrane with minor basic igneous and metamorphic contributions.
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