Thermochronology, denudation and variations in palaeosurface temperature: a case study from the North Slope foreland basin, Alaska

Abstract

Integration of vitrinite reflectance (R o) and apatite fission track (AFT) data from well sequences can provide a direct estimate of the geothermal gradient at the time of maximum palaeotemperatures and the time at which sequences began to cool from maximum palaeotemperatures. These values, plus an understanding of the effects of cooling in response to long-term climatic changes, are particularly important when estimating the amount of denudation experienced by the sequences during cooling from maximum palaeotemperatures. In this case study, AFT data have been generated for subsurface samples from eight wells drilled within the North Slope foreland basin of northern Alaska in an effort to study the thermal history of the basin. The combination of R o and AFT data establish that maximum palaeotemperatures were attained within the North Slope foreland basin prior to cooling beginning in the Palaeocene. Furthermore, they indicate that palaeogeothermal gradients when cooling began were close to the present-day values, and that Cenozoic surface cooling resulted in a significant amount of 'apparent' denudation. These results suggest that heating throughout the basin was largely due to deeper burial, and that cooling was due to both removal of section by denudation and a drop in the mean annual surface temperature. analysis outlined by Bray et al. (1992) and Duddy et al.

Synchronous exhumation events around the Arctic including examples from Barents Sea and Alaska North Slope

“…Examples include Barents Sea (Cavanagh et al 2006), Svalbard (Blythe & Kleinspehn 1998), North Slope Alaska (O'Sullivan et al 1993;O'Sullivan 1996O'Sullivan , 1999, Sverdrup Basin (Arne et al 2002), West Greenland (Japsen et al 2005) and East Greenland (Thomson et al 1999;Hansen et al 2001). Implications for exploration include enhanced maturity levels (compared with assessments that underestimate former burial depths), possible loss of reservoired hydrocarbons as a result of seal breach and spillage, and phase changes due to pressure reduction (see Doré et al 2002, for an extensive review of the influence of exhumation on hydrocarbon systems).…”

Cenozoic tectonic evolution of Liaodong dome, Northeast Liaodong Bay, Bohai, offshore China, constraints from seismic stratigraphy, vitrinite reflectance and apatite fission track data

“…When deposited, detrital apatite may contain fission tracks inherited from their provenance. If sediments have only been heated weakly to moderately after deposition, the AFT age will most likely be older than the depositional age, and the length pattern will reflect a mixture of inherited tracks and those formed post deposition (O'Sullivan, 1999). The AFT ages for the samples 2 (1450 m) and 3 (950 m) are older than the stratigraphic ages (Table 2), which indicate that some of the AFT records are inherited from the provenance.…”

The thermal history of the Sichuan Basin, SW China: Evidence from the deep boreholes

“…There are different approaches to thermal history reconstruction, such as stochastic inversion (Lutz and Omar, 1991;Corrigan, 1991;Gallagher, 1995), paleotemperature gradient based (Buddy et al, 1991;Bray et al, 1992;Feinstein et al, 1996;O'Sullivan, 1999) and paleo-heat flow based methods (Lerche et al, 1984;Hu et al, 2001). Considering that the Paleo-Mesozoic basins experienced multiple episodes of tectonic movement and erosion as well as the complicated thermal history in the Sichuan Basin, the paleotemperature gradient method is employed in this study based on the widely accepted model of vitrinite reflectance called the 'EASYR o % model' (Sweeney and Burnham, 1990).…”