SEDIMENTOLOGY OF THE CARDIUM FORMATION LOCHEND FIELD, ALBERTA

Abstract

<p>Examination of 22 cores and over 100 petrophysical logs of the Turonian (Upper Cretaceous) Cardium Formation in the Lochend region permitted the identification of 9 facies which could be arranged into 3 major coarsening-upward cycles.At Lochend, the Burnstick Sequence comprises 5 distinct facies that progressively coarsen upward from a silt laminated mudstone through various bioturbated mud and sand facies into a gravelly conglomerate. There is a sharp return to a dark mud facies.</p> <p>The overlying Raven River sequence in this region is characterized by a double coarsening upwards cycle which can be described in terms of 6 facies. The first cycle coarsens upward from a black laminated mudstone into various bioturbated mud and sand facies. The sands become progressively cleaner upwards before returning to a muddier bioturbated facies which marks the base of the second coarsening upward cycle. This cycle similarly decreases in mud content upwards but never 'cleans' to the extent of the lower cycle.</p> <p>The upper-most "zone" sequence comprises muddy bioturbated facies which coarsen upwards into a 2 cm thick capping of conglomerate. There are no preserved physical sedimentary structures associated with any of the facies. The trace fossil assemblage indicates a sedimentary environment below fair weather wave but above storm wave base. The regional sandstone distribution of all coarsening upward sequences was investigated by cross section correlation of petrophysical logs between Lochend and Crossfield (to the west) and Caroline (to the north).</p>