Southwestern Barents Sea margin: late Mesozoic sedimentary basins and crustal extension

The deep sedimentary basins of the southwestern Barents Sea were formed in response to several late Mesozoic-early Cenozoic tectonic events within the North Atlantic rift zone, which culminated with continental breakup and formation of a mainly sheared margin in early Tertiary times. Due to deteriorating data quality, the development of the margin-bordering Sorvestsnaget Basin is not well known. To improve on this, we use both seismic interpretation and gravity modelling to estimate the depth to the Middle Jurassic (MJ) sequence boundary, which marks the onset of Mesozoic rifting. The horizon represents a first-order contrast in seismic velocity and density, and the gravity field correlates well with its depth of burial. Only one seismic line enables tracing of the MJ from surrounding areas into the Sorvestsnaget Basin, down to a depth of at least 17 km in the northeastern part of the basin. The deep basin is reflected in a general thinning of the crust from 30-36 km within the Barents Sea to 20-24 km in the margin area. The gravity modelling show that the Middle Jurassic-Lower Cretaceous sequences are of comparable thicknesses in the Tromso and Sorvestsnaget Basins. However, adjacent to the rifted margin segment the deep northern part of the Sorvestsnaget Basin is affected by additional large Late Cretaceous normal faulting and subsidence. These faults also caused additional structuring of the intrabasinal Veslemoy High. Post-Middle Jurassic crustal thinning in the southwestern Barents Sea shows maximum cumulative beta-values exceeding 4 within the Tromso and the northern Sorvestsnaget Basins. The corresponding crustal extension is estimated to 70-85 km in a west to northwest direction. There is no uniform increase in crustal thinning toward the continent-ocean boundary, which we attribute to the transform origin of the margin. However, there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached. (C) 1998 Elsevier Science B.V. All rights reserved.