Abstract

Coal company diamond drill core is rarely used in exploration for gas and oil and a tremendous data base is being overlooked. Complete intervals, commonly hundreds of metres in length will be cored throughout, often on a well spacing of 500 metres. The wells are geophysically logged, providing suites of gamma ray, density and sonic logs. There is typically outcrop within a few hundred metres of the well which can provide paleocurrent data and more detailed sedimentological interpretations.

A diamond drill core from the Gates Formation in north eastern British Columbia exhibits an upward coarsening conglomeratic sequence. The facies sequence is non-marine carbonaceous sediment → thin transgressive conglomerate → interbedded sandstone and shale (offshore transitional facies with hummocky cross stratification) → amalgamated hummocky cross stratified sand → swaley cross statification (?) → nearshore conglomerate of storm origin → beach conglomerate → nonmarine carbonaceous sediment. This sequence is laterally equivalent to the subsurface Falher D cycle. It is identical to the Falher A and B cycles. A second core 4 km from the first exhibits an upward coarsening sandstone sequence. There is no conglomerate present. The facies sequence is classical turbidites hummocky cross stratified sandstone → amalgamated hummocky cross stratified sandstone → trough crossbedded and bioturbated sandstone (nearshore with tidal influence) → rooted sandstones (beach) → coal and carbonaceous sandstones. This sequence is laterally equivalent to the subsurface Falher F cycle and identical to some Falher B, C and D cycles. These two zones are interpreted as having been deposited on a wave dominated coast. They typify upward coarsening sequences in much of the Lower Cretaceous of northeastern British Columbia. Similar cycles have been observed in the underlying Gething Formation and overlying Boulder Creek (Paddy - Cadotte) as well as the Notikewin of Alberta. The inference of this is that most Lower Cretaceous shorelines in northeastern British Columbia (and Alberta?) were (storm) wave dominated.