John-Paul Zonneveld¹, S. George Pemberton²

(1) University of Calgary, Calgary, AB
(2) University of Alberta, Edmonton, AB

ABSTRACT: Ichnology of the Lower Montney Formation (Lower Triassic), Kahntah River and Ring Border Fields, Northeastern British Columbia, Canada

The Montney Formation in northeastern British Columbia preserves a record of deposition during the recovery period after the terminal Permian extinction. Production from Kahntah River and Ring-Border fields in northeastern British Columbia is primarily from the lowest beds of the this formation.

Production in the Ring-Border area occurs from a coarsening-upwards succession of lower Griesbachian strata (lowest Triassic). Trace fossils are extremely rare in these strata. Lithologies interpreted as offshore transition include isolated specimens of Planolites, Treptichnus and Chondrites in shale and silty sandstone intervals, and rare specimens of Thalassinoides and/or Cruziana on the soles of thin, sharp-based sandstone beds interpreted as tempestites. Trace fossils in lower shoreface very fine-grained sandstone beds consist of extremely rare, isolated Thalassinoides and Conichnus. Trace fossils were not observed within upper shoreface sandstone beds.

Production in the Kahntah River area occurs from slightly younger strata (upper Griesbachian-Dienerian). Pervasive bioturbation has resulted in intermixing of silt and mud laminae into most shoreface sand beds, negatively affecting porosity and permeability. Offshore transition to lower shoreface successions are characterized by gradation from a Cruziana assemblage (Chondrites, Planolites, Rhizocorallium, Teichichnus, Thalassinoides and Cruziana) to a mixed Cruziana-Skolithos assemblage (Cylindrichnus, Diplocraterion, Planolites, Palaeophycus, Skolithos, Thalassinoides and Cruziana). Upper shoreface sandstone beds were characterized by rare, isolated Skolithos. Although ichnotaxonomic diversity is high in the Kahntah River shoreface, most forms are extremely small. The abrupt increase in ichnotaxonomic diversity and abundance is related to faunal recovery from the extinction as well as paleogeographic considerations (deposition in a protected, well-oxygenated setting).

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado