Open File Report 1990-01

Author(s) Date 1989-12-31

Palynology supported study of the Jurassic-Lower Cretaceous boundary strata indicates that the main hydrocarbon-producing zone of the Niton field - here informally called the 'Niton B' unit - is of Upper Jurassic age and shallow - marine in origin.

Formerly considered as a part of a continental to transitional Lower Cretaceous (Lower Mannville Ellerslie) succession, or as the uppermost part of the marine Middle Jurassic Rock Creek Member, this distinct lithostratigraphic unit is built up of sandstones, siltstones and rare shales containing Oxfordian-Kimmeridgian palynofloral assemblages, and unconformably overlies marine sediments of the Rock Creek Member which are characterized by Bajocian palynoflora.

Above the Niton B unit, impersistent shales corresponding to the 'Upper Fernie' also contain Oxfordian-Kimmeridgian palynofloral relics and are succeeded by the Lower Mannville Ellerslie strata. The latter lack diagnostic fossils and flora and fill erosional valleys carved into the Jurassic units (lower Ellerslie), or blanket larger areas (upper Ellerslie).

The areal limits of the Niton B unit reflect 1) lateral facies changes illustrated by silting and shaling-out of the reservoir-quality sandstones at the periphery of the unit, and 2) post-depositional erosion which removed the sandstones in pre-Ellerslie valleys cut into the unit, and also truncated the unit at the regional unconformity surface close to its updip depositional edge.

Hydrocarbon reservoirs in the Niton field are associated with sandstones of the Rock Creek Member, with sandstones of the Niton B unit and with sandstones present in the upper part of the Ellerslie. Oil and gas which are stratigraphically trapped in the Niton B unit are the most important source of hydrocarbons in the Niton field

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Losert, J. (1990): The Jurassic-Cretaceous boundary units and associated hydrocarbon pools in the Niton field, west-central Alberta; Alberta Research Council, ARC/AGS Open File Report 1990-01, 43 p.