| Description |
Upper Cambrian strata in the Great Basin of western Utah are dominated by marine carbonate facies. The Hellnmaria Member of the Notch Peak Formation in the southern House Range and the Upper Carbonate Member of the St. Charles Formation in the northern South Lakeside Mountains are correlative Upper Cambrian strata. At both localities, the correlative carbonate units preserve cyanobacterical stromatolite facies containing burrows. The Hellnmaria Member and the Upper Carbonate Member both contain smooth walled cylindrical burrows inside and surrounding the stromatolites. The burrows exhibit a branching morphology, and they have a coarser grain fill that is different in texture from surrounding sediments. The branching geometry of the burrow tunnels is irregular and constricted. These are assigned to the trace fossil Thalassinoides paradoxicus. Thalassinoides paradoxicus is a deep infaunal deposit feeding trace fossil (fodinichnion) constructed by burrowing organisms of unknown identity. The probable burrowers mined shallow marine muds for food as well as seeking protection in the complex web of burrows. The Thalassinoides of this study are far too old to have been created by decapod crustaceans, which are the primary creators of such trace fossils in the Mesozoic and Cenozoic, so the identity of the Cambrian trace makers remains unknown. Many of the Thalassinoides burrows have been replaced with chert, which appears to be early diagenetic in origin when the burrows were still porous enough for the silica to find favorable nucleation sites on the burrow surface. Many of the burrows are over-silicified due to growth of the microcrystalline chert nodules extending beyond the boundaries of the original trace fossil. The Hellnmaria and Upper Carbonate members represent a shallow, tropical, quiet water paleoenvironment on an open marine platform. This interpretation is due to the presence of stromatolites and Thalassinoides burrows, both of which flourished in this paleoenvironment. This study demonstrates the importance of trace fossils in the interpretation of paleoecology, paleoclimate, and paleoenvironment of the ancient carbonate strata during the Late Cambrian in the Great Basin. This is particularly useful, because much of the strata of this age in this region lack a substantial body fossil record. |
