Abstract

The Bay Tree Member of the Cardium Formation (Turonian) was originally defined as a thick conglomerate capping the Cardium in northwestern Alberta and adjacent British Columbia. Stott (1967) considered this member to be a coarse grained facies of the nonmarine Moosehound (= Musreau) Member, and there have been no published interpretations since.

The type locality is found on an escarpment to the south of Bay Tree Alberta (23-78-13W6). Here, up to 2 metres of swaley cross-stratified fine sandstone with thin pebble stringers are abruptly overlain by up to 12 metres of conglomerate with minor (<20%) laminated or crossbedded fine to very coarse sandstone. The top of the conglomerate is not exposed. The conglomerates consist mainly of chert and quartz pebbles, ranging from granules to over 1 centimetre, and are mostly clast-supported. They generally appear massive to crudely bedded, although in places several decimetre thick crossbeds and imbricated pebbles can be seen. The top of the section comprises 3 metres of pebbles interbedded with gently dipping laminated sandstones. These features strongly suggest a beach.

Pebble imbrications in beach strata indicate a northwest-southeast trending shoreline. The crossbedding in the sandstones lower in the section shows a dominant southeast transport direction in response to longshore currents. Pebble imbrication in the lower parts of the section developed in response to either the shore-normal wave approach or the shore-parallel longshore transport. No evidence of deposition in a fluvial environment can be seen here, or elsewhere in the region where the Bay Tree conglomerates are well developed. Wave-formed gravel ripples are present in many of these localities and provide evidence that deposition of these units took place in a shallow marine environment.