West Texas
- View of the Franklin Mountains, west Texas. Here, carbonate rocks of the 1.25 Ga Castner Marble are preserved as a roof pendant within a large granitic intrusions. Although metamorphism has destroyed the primary chemistry of Castner carbonates, depositional structures remain well-preserved.
- The lower and middle Castner Marble consists of shallow-water carbonates that contain a number of different stromatolitic forms. In this horizon, small domal stromatolites are interspersed among generally flat-lying carbonate laminae.
- Elsewhere in the lower and middle Castner Marble, densely packed stromatolitic columns coat the sea floor - here seen in plan view.
- • The upper Castner Marble is marked by a transition to deeper-water deposition of carbonate-shale rhythmites. Metamorphism of the carbonate fabrics make grain-size differentiation impossible, but rhythmite patterns suggest deep shelf-to-slope environments.
- Slump features in upper Castner rhythmites give way to thick flat-clast breccias, again suggesting deep shelf-to-slope environments.
- Several hundred kilometers to the east of the Castner Marble lies the similarly-aged Allamoore Formation. These two formations are considered lateral equivalents, in which the Allamoore represents shallow-water shelf environments, here dominated by small bioherms of tightly-packed, branching columnar stromatolites.
Linda Kah
Department of Earth and Planetary Sciences
1412 Circle Drive
Knoxville, TN 37996-1410
Phone: (865) 974-6399
Email: lckah@utk.edu