A sedimentological study of the Lower Cretaceous Glitrefjellet Member, Svalbard

Abstract

Detailed facies analysis of the Early Cretaceous Helvetiafjellet Formation (Barremian-Aptian) indicates deposition during a long-term transgression. The formation has received a lot of attention in previous published papers, particularly the lowermost Festningen Member has been detailed in numerous papers. However, the uppermost Glitrefjellet Member is typically poorly exposed in outcrops, and consequently difficult to study. There are therefore few available studies that have investigated the Glitrefjellet Member in great detail. This study investigates stratigraphic cores (DH-1 and DH-1A) stored in Longyearbyen, aiming at describing sedimentary facies at a detail not achievable in outcrop. The detailed facies analysis presented in this thesis consequently contributes to the general understanding of the depositional evolution of the Helvetiafjellet Formation in general, and the Glitrefjellet Member in particular. Fourteen facies grouped into nine facies association have been defined. The underlying Rurikfjellet Formation consists of prodelta deposits (FA-1) and is overlain by the Helvetiafjellet Formation. The Festningen Member consists of fluvial braidplain deposits (FA-2). The overlying Glitrefjellet Member encompass a wide range of facies associations. The lowermost part include floodplain deposits (FA-3), crevasse splay deposits (FA-4), fluvial distributary channel deposits (FA-5). The uppermost part of the Glitrefjellet Member includes delta plain deposits (FA-6), delta front deposits (FA-7) and wave-reworked delta deposits (FA-8). The overlying Carolinefjellet Formation consists of offshore transition deposits (FA-9).The results of the facies analysis are compared and correlated to published sections across Svalbard, which has observed an overall thickening towards the south. However, an overall thickening towards the northwest was observed in this thesis. The significant variations in thickness are possibly related to basin subsidence or major fault zones. The depositional model is further compared to some modern analogues to the (Mahakam delta and Pamlico Sound), which is considered to be a close planform. The modern analogues contributes with information with regards to the depositional process and paleogeographic evolution and reconstruction of the Helvetiafjellet Formation shoreline. Of particular interest is the lateral relationship between barrier deposits in Kvalvågen in the east, tidally-influenced estuarine deposits to the west and a transgressive lag documented in the uppermost part of the Glitrefjellet Member to the north in the Adventdalen area. This suggests a large backstepping barrier bar complex.