The Middle-Upper Devonian clastic wedge of the Franklinian Geosyncline

ABSTRACT Middle-Upper Devonian clastic strata in the Canadian Arctic Islands are present over an area of about 200,000 sq km (75,000 sq mi) and are up to 5,000 m (16,000 ft) thick. The strata comprise a clastic wedge which was deposited in the Franklinian geosyncline prior to Late Devonian - Early Mississippian deformation. The clastic wedge is divided into eleven formations, and six facies are recognized within the strata. The formations and their facies content are: Blackley (submarine fan); Cape de Bray (marine slope); Weatherall (deltaic-marine shelf); Bird Fiord (open-marine shelf and deltaic-marine shelf); Strathcona Fiord (meandering stream); Hecla Bay (braided stream); Fram (meandering stream) (new); Hell Gate (braided stream) (new); Nordstrand Point (meandering stream) (new); Beverley Inlet (meandering stream) (new); and Parry Islands (braided stream, meandering stream and deltaic-marine shelf) (new). Mineralogy, facies distributions, paleocurrent patterns and regional geology all indicate that the source areas of the clastic strata lay to the north and east, and included the Caledonian and Pearya Mountain systems and Precambrian Shield of Greenland. Chert and rock fragments characterize detritus from the Pearya Mountains whereas detritus from the Caledonian Mountains and Precambrian Shield is characterized by a high percentage of monocrystalline quartz. Compositional variations within the clastic wedge indicate that the Pearya Mountains progressively supplied a higher proportion of the detritus throughout wedge development. Paleolatitude estimations, lithologies, fossils and clay mineralogy imply that the clastic wedge was deposited under humid tropical climatic conditions. Lithologic variations in fluvial strata suggest that the climate fluctuated between savanna and very humid. Clastic deposition commenced in the extreme northeast in Eifelian time, and a coastal plain prograded south and west until it covered almost the entire Arctic Islands area by Middle Frasnian. During progradation, submarine fan and marine slope deposits infilled deep basins in the northwest. In Late Frasnian the entire area was uplifted and subjected to erosion. The area was transgressed in latest Frasnian, and a marine shelf was widespread by Early Famennian. In latest Devonian or Early Mississippian the clastic wedge was uplifted and folded to form a "foothills" belt bordering the Pearya Mountains. Sandstone units of delta-front, beach and distributary-channel origin within the Weatherall and Bird Fiord Fms are rated as having the highest potential for petroleum accumulations. The strata may have uranium potential but the meagre data at present available in this regard are not encouraging. End_Page 488------------------------