Abstract A new method for recognizing hydrocarbon seepage and migration in exploration wells is documented from the Immiugak A-06 exploration well that drilled through a hydrocarbon-related diagenetic zone (HRDZ). The HRDZ is seismically conspicuous as part of a gas chimney on a shale-cored anticline in the Tertiary of the Beaufort-Mackenzie Basin, Arctic Canada. The HRDZ contains classic diagenetic minerals, notably greigite (Fe 3 S 4 ) and calcite with δ 34 S and δ 13 C values diagnostic of hydrocarbon-related, sulfate-reducing, microbial activity. The HRDZ also contains exceptionally preserved calcareous benthic foraminifera with conspicuous bitumen-filled chambers and agglutinated foraminifera with bitumen and diagenetic silica with bound particles. Silica was highly mobile within the seepage or migration system and was precipitated and dissolved extensively in the agglutinated foraminifera. Seismic profiles, resistivity anomalies, diagenetic minerals, and altered foraminifera all suggest that significant hydrocarbons migrated or seeped through sandy Oligocene and Miocene strata at the crest of a shale-cored anticline in response to late Miocene tectonism. Hydrocarbon-related diagenesis can be distinguished from standard burial diagenesis using the foraminiferal coloration index (FCI). Foraminiferal coloration within the HRDZ was controlled by silicification in a bitumen-rich environment. The FCI values in the HRDZ are much higher than predicted for normal burial and show abnormal variance caused by variable dissolution of foraminiferal silica. The FCI values from agglutinated foraminifera outside the HRDZ show a uniform linear trend increasing with depth. The extent of hydrocarbon-related diagenesis observed in foraminifera can be used to assess the relative magnitude of hydrocarbon seepage in the Beaufort-Mackenzie Basin and potentially other petroleum basins.

ABSTRACT Fifty-three new species of benthic foraminifers and four new genera have been formally named from the Cenomanian to Miocene sequences of the Beaufort-Mackenzie Basin of Arctic Canada. The new species consist of 36 agglutinated walled foraminifers and 17 calcareous. The new taxa belong to the families Haplophragmoididae, Discamminidae, Cyclamminidae, Trochamminidae, Verneuilinidae, Globotextulariidae, Spiroloculinidae, Hauerinidae, Bolivinidae, Turrilinidae, Stainforthiidae, Siphogenerinoididae, Bagginidae, Parrelloididae, Epistomariidae, Asterigerinatidae, Nonionidae, Heterolepidae, and Elphidiidae. The Beaufort-Mackenzie Basin is located on the cratonic margin of North America bordering the Arctic Ocean and contains 12 to 16 km of Upper Cretaceous to Cenozoic terrigenous clastic sediments. Planktonic foraminifers are absent through the entire section, and therefore benthic foraminifers have added significance for biostratigraphic analysis. Fifteen interval zones, defined from the last occurrences of benthic foraminifers, have been recognized in these strata. Ten of the new taxa are indices in this interval zonation and new names replace the open nomenclature that was previously used. All 53 new species are significant for biostratigraphic zonation, depositional sequence analysis, and other basinal studies in the Beaufort-Mackenzie and neighbouring Arctic regions. Many of the species have restricted environmental ranges and are important for paleoenvironmental reconstruction.