Print this pageAbstract: Coarse-Grained Deposits by Ephemeral Streams in Carboniferous of Maritime Provinces, Canada
Fining-upward sequences about 7 m thick are common within the lowest 150 m of the Enrage Formation (Namurian) of the Chignecto Bay area. The sequences have markedly eroded bases and grade upward from conglomerates containing pebbles to 10 cm in diameter, to siltstones. The intervening siltstone units comprise up to 55% of the total sequence and contain rootlets and caliche zones. The sandstones and conglomerates are interpreted as fluvial-channel deposits.
Conglomerate units are up to 3 m thick and are trough cross-bedded or horizontally stratified. The absence of planar-tabular sets or any imbricated pebbles suggests that bars were not present although these bedforms normally are common in rivers with such a coarse sediment load.
Thin mud drapes within the coarse sediment have well-developed desiccation cracks and indicate very low-stage periods. The rivers probably were ephemeral and the sediment was moved predominantly during flash floods when large dunes could develop. The high percentage of overbank sediment may be a result of the flash-flood regime.
AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma