New Estimations on the Magnitude and Timing of Cenozoic Exhumation for the Eastern Barents Sea

Peter Sobolev

New results on magnitude and timing of the regional Cenozoic exhumation for the Russian part of the Barents Sea are presented. They were obtained in the framework of current multi-client international project “Basin analysis and petroleum systems modeling of the Eastern Barents Sea”. Several kinds of data and methods were applied to estimate uplift/erosion magnitude. The first approach is based on the comparison of normal compaction trends for the upper part of section (>3 km). Interpretation of offshore well logs has been performed, generalized porosity-depth curves were compiled for different lithogies, and anomalous intervals were removed. Generally, normal compaction trends are close to exponential, the vertical shift of curves depends on relative changes of exhumation magnitude. Vitrinite reflectance measurements were used to estimate absolute values of uplift/erosion; according the data, exhumation value of 500 m has been accepted for the Shtokmanovskaya area. The results of total exhumation values for 25 wells were interpolated over the whole East Barents Basin Province using seismic velocity model of sedimentary cover. The model was compiled from both stacking velocity data (pseudo wells velocity values obtained during common-depth point seismic reflection surveys) and vertical seismic profiling velocity data for offshore wells. Results of reinterpretation of regional seismic reflection profiles were also included into the velocity model. The previous point assessments of the regional Cenozoic exhumation magnitude were significantly improved. Differential exhumation throughout the province has occurred. The least uplift and erosion (400-500 m) occur in the depocenters of South and North Barents Sea Basins. Fission-track dating of apatite was undertaken in order to reconstruct the thermal history and evaluate the timing of uplift within the Fersmanovskaya-1 well. Apatite grains from 13 core samples were analyzed using the LA-ICP-MS method. AFT ages from samples above ~2100 m were all greater than 100 Ma, with some equal to the original Jurassic depositional age for the unit, suggesting that this part of the section had not been exposed to significantly high paleotemperatures following deposition. The AFT ages from samples collected below ~2100 m (Triassic rocks) were all less than ~60 Ma, suggesting that the ages from these samples had been significantly reduced or reset since deposition. Based on preliminary modeling of the results using HeFTy, the fission-track data from the Fersmanovskaya-1 well suggest the Lower Triassic – Lower Jurassic section was buried to maximum (or near maximum) paleotemperatures during the Late Cretaceous. As a result, the section below ~2100 m was exposed to elevated paleotemperatures sufficient to totally reset the AFT ages for the samples, whereas the shallower samples were only partially reset. The entire section then experienced rapid cooling (exhumation) during the early Tertiary at about 60 Ma.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013