| The lower member platform facies of the Noonday Formation (Neoproterozoic, California) is primarily a domal dolomite containing laminates interspersed with pockets of fine-grained material. This material comes in many forms—layers, irregular pockets, and distinctive tubular structures. These structures have formerly been interpreted as stromatolites, bioturbation, out-gassing tubes, and many other types of structures. This study employed field, petrographic, and geochemical methods to elucidate the nature of these structures; and the previous suggestions of stromatolites, root casts, Skolithos , out-gassing tubes, selective diagenetic alteration, and post depositional fluid flow have been eliminated. The collected evidence indicates that these fabrics are the result of a balance between microbial mat growth and contemporaneous abiotic sedimentation. Data also confirmed an interpretation of the Noonday as a Marinoan-type cap carbonate. |
