Post-Early Devonian thermal constraints on hydrocarbon source rock maturation in the Keele Tectonic Zone, Tulita area, NWT, Canada, from multi-kinetic apatite fission track thermochronology, vitrinite reflectance and shale compaction

Abstract

New thermal maturity (%Ro, Rock-Eval ® pyrolysis), shale compaction and apatite fission track (FT) data were integrated into thermal history models for the East MacKay I-77 petroleum exploration well located approximately 80 km southeast of Norman Wells, Northwest Territories. The study well is in the Keele Tectonic Zone where multiple phases of anomalous Phanerozoic subsidence and uplift have resulted in an Upper Cretaceous-Cenozoic foreland succession resting unconformably on Devonian strata. This major unconformity, which developed during pre-and post-Albian time, displays a thermal maturity discontinuity (0.55-0.75%Ro) and represents approximately 270 m.y. of missing geological record. Linear shale compaction across this unconformity suggests that maximum burial occurred during the Cenozoic, whereas thermal maturity data imply that maximum temperatures were reached sometime between the Devonian and Early Cretaceous. Detrital apatite grains from a single sample from the Upper Devonian Imperial Formation of the I-77 well yielded two FT age populations (90.4±6.1 Ma and 222.2±22.5 Ma; ± one standard deviation) with different thermal annealing properties based on their chlorine content.An inverse multi-kinetic FT annealing model was developed and used to determine thermal histories that are consistent with the FT parameters and other geological constraints. Model results suggest that hydrocarbon generation from Devonian rocks at the I-77 well location occurred during the early Mesozoic prior to the development of Late Cretaceous-Cenozoic structures. Peak FT model temperatures are 124±10ºC within the Early Triassic to Middle Jurassic (250-170 Ma), <75ºC during the Albian (112-100 Ma) and 97±9ºC during the Paleocene-Early Eocene (65-50 Ma). The Cretaceous-Cenozoic thermal history was modelled using a simple burial history with the present geothermal gradient (32ºC/km) held constant; a range of geothermal gradients (31-42ºC/km) and maximum burial depths for the pre-Aptian thermal history fit Devonian maturity data. If maximum burial was during the Cenozoic, then Mesozoic peak maturity was achieved under a higher geothermal gradient than present. Although hydrocarbon generation pre-dates structural trap development near the I-77 well, Devonian source rocks retain significant hydrocarbon potential. Given the complicated geological history of the central Mackenzie Valley, deeper Cenozoic burial elsewhere in the region may have generated hydrocarbons from Cretaceous and reactivated Devonian source rocks. RÉSUMÉUne nouvelle maturité thermique, (%Ro, pyrolyse Rock-Eval ® ), un compactage d'argile litée et des données de trajectoires de fissions apatites (FT) ont été intégrés à des modèles thermiques historiques pour l'exploration pétrolière du puits East MacKay I-77 situé approximativement à 80 km Sud-Est de Norman Wells, dans les Territoires du NordOuest. L'étude du puits se trouve dans la zone tectonique de Keele dans laquelle des phases multiples de subsidences et d'ascendances anomales du Phanérozoïque ont abouti à une...

Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

“…In the Mackenzie Plain, a major regional unconformity exists between the Upper Devonian Imperial Formation and Albian strata. Mesozoic stratigraphic section elsewhere in northern Canada and thermal maturity studies from wells in the Mackenzie Plain indicate that deposition must have continued following the Devonian and been eroded prior to the Albian [ Williams , ; Feinstein et al ., ; Issler et al ., ]. Deposition in the Mackenzie Plain resumed by the Albian, where 750–1700 m of sediment derived from the craton to the east were deposited in a westerly deepening basin [ Yorath and Cook , ; Thomson et al ., ].…”

“…Issler et al . [] integrated borehole organic thermal maturity and a shale compaction profile with apatite fission track (AFT) analysis of the Devonian Imperial Formation to suggest that maximum burial occurred between the Carboniferous and Triassic, where the Imperial Formation was buried to a depth of 2.7 to 3.6 km, compared to the 3 km burial depth in the Paleocene. Thermal histories derived from apatite (U‐Th)/He analysis from the Archean Slave craton to the east suggest that Paleozoic burial reached depths as great as 3.3 km [ Ault et al ., , ] compared to the 1.4 km of Cretaceous material thought to have extended across the shield [ Stasiuk et al ., ].…”

“…[, ] indicates that Phanerozoic burial over the Slave craton reached maximum temperatures in the Carboniferous to Middle Triassic, with unroofing progressing westward from circa 340 Ma in the eastern Slave to circa 225 Ma on its western margin. The fission track modeled thermal history from the Mackenzie Plain [ Issler et al ., ] yields a slightly different result, proposing that Paleozoic burial in the Mackenzie Plain continued into the Mesozoic followed by Early Triassic to Middle Jurassic exhumation. Clearly, more data are required to resolve regional trends and implications for the pre‐Cretaceous evolution of northern Canada.…”

The multi-phase Keele Arch, central Mackenzie Corridor, Northwest Territories

“…Later erosion removed direct evidence regarding depositional thicknesses but Issler et al (2005) has calculated from fission track analysis of Imperial Formation samples taken at East and Mount Cap deposition. The map (Fig.…”

“…deposited across the region. Direct evidence regarding depositional thicknesses was removed by later erosion but fission track analysis has provided an estimated value of about 1 km (Issler et al, 2005). As relative sea level rose, Martin House and younger strata onlapped but failed to completely cover the (pre-existing?)…”