Abstract

Recent studies of ancient depositional systems indicate that braided streams were quite common in pre-Cretaceous times due to the lack of wide areal distribution of vegetational cover. For this reason modern braided streams and rivers should be studied in order to find criteria which are useful for recognition of these deposits in the geologic record.

The South Canadian River in panhandle Texas and western Oklahoma exhibits several features which are important in understanding and recognizing braided channel deposits. Trenches through longitudinal and transverse bars in the active part of the river channel revealed the occurrence of relatively few sedimentary structure types. Within an individual flood sequence the only bedding types usually observed were parallel bedding, tabular cross-beds, and small ripple cross-laminations. Individual flood sequences were punctuated by thin clay drapes which represent the settling out of fine material during waning flood conditions. Flood sequences were laterally discontinuous downstream.

Overall river valley patterns in the Canadian and other braided streams are reasonably straight rather than sinuous. The anastomosing pattern of channels associated with braided streams is an internal feature of the sand body which has been deposited in the river valley by various sequences of aggradation. In the geologic record the Canadian River sediments would be preserved as a thin (150 feet or less) lateral sand body with remnants of numerous overlapping channel sequences.

The study of daily discharge data reveals that the major aggradational and degradational features observed in the active portions of the Canadian River valley are the result of less than 40 days of catastrophic flooding in the last 32 years. Sediments preserved in braided stream deposits are the result of extremely high flow conditions over a short period of time.