Controls on Deposition of an Organic-Rich Mudstone in a Cretaceous High-Latitude Basin: ~35 Million Years of Enhanced Organic Carbon Burial in the Colville Basin, Northern Alaska

The late Aptian–Cenomanian gamma ray zone (GRZ) of the Hue Shale, deposited throughout the nascent Colville foreland basin, is widely known as a major Cretaceous source rock across northern Alaska. The Colville basin was filled axially from the west and south throughout much of the Cretaceous via large-scale clinothem deposition. Recent field studies and volcanic ash dates demonstrate that additional younger (late Cenomanian–Campanian), organic carbon-rich mudstone units of the Hue Shale were deposited in the distal, eastern part of the Colville foreland basin. These units predominantly comprise argillaceous mudstones with lenticular fabric and common volcanic ash beds. Total organic carbon values for thermally immature sections of the Hue Shale reach 26 wt.%, with an average of 7 wt.%, suggesting that significant marine organic carbon burial occurred throughout much of the Cretaceous in this basin. Inorganic carbon occurs infrequently as diagenetic cement and Inoceramid shell beds.

Several factors likely played important roles in the deposition and preservation of organic matter in the Aptian–Campanian: 1) sediment-gravity flows transported sediment with entrained organic matter across the distal toes of clinoforms, thereby delivering organic matter to the deep, distal basinal setting, 2) common to abundant Arctic volcanism potentially increased the availability of nutrients in surface waters, as well as added to atmospheric CO2 levels, together driving increased primary production, and 3) the high latitude setting and relatively cooler temperatures of the Arctic may have inhibited inorganic carbon precipitation and slowed microbial remineralization of organic matter.