Regional Extent and Sequence Stratigraphy of the Middle to Upper Triassic Snadd Formation in the Western Barents Sea

Tore Klausen

The Snadd Formation was deposited in a shallow basin facing the Boreal part of Panthalassa. It represents the late stages of a long period of Mesozoic infilling of the basin by a siliclastic wedge prograding from the southeast, with sediments being shed from the Uralide Orogeny. The progradation reached its maximum extent at the level of Spitsbergen which was uplifted in Late Cretaceous and Cenozoic times. Outcrops are exposed as the time-equivalent De Geerdalen Formation. The subsurface Snadd Formation includes depositional environments ranging from offshore shale through shallow marine into fluvial deposits in more or less conformable successions. Channel sandstone bodies are present in the fluvial sections of the formation and these make up the most prominent reservoir rocks. Source rocks are found both in the distal marine shales and in the non-marine coal bearing succession in the upper part of the formation. Five third order sequences have been interpreted within the limits of the study area, divided into two second order sequences split along an Intra Carnian maximum flooding surface. Depositional elements inherent to the sequence stratigraphic framework are interpreted and extrapolated so as to describe the regional distribution of potential reservoir sandstones. Third order sequence stratigraphic evolution can help explain some of the facies distribution. Avulsion of trunk river systems on the delta plain, probably controlled by backwater extent and/or local accommodation, demonstratively played a major role in sediment dispersal and delta lobe evolution. The amount of sand sequestered on this delta plain might preclude major sediment bypass to the basin, and thus also the probability for prodelta turbidite deposits, this implies that the best reservoir rocks are found in the non-marine part of the succession. Decoupling of marine source rocks and the best fluvial reservoir units is a major play risk for the hydrocarbon potential of the formation, as is its complex burial history. However, hydrocarbon reservoirs are proven within the formation in intermediate positions relative to marine source rocks and fluvial trunk river systems in the more proximal parts of this vast delta plain. Regional correlation coupled with detailed depositional environment interpretation has resulted in basin-wide palaeogeographic reconstruction of the Snadd Formation throughout the Norwegian Barents Sea, with implications for understanding reservoir and source rock distribution. Additionally, isopach maps constructed based on the new sequence stratigraphic framework highlight the post depositional erosion of the succession. Keywords: Barents Sea, Snadd Formation, delta plain, fluvial sandstone reservoirs

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