Integrating subsurface and outcrop data of the Middle Jurassic to Lower Cretaceous Agardhfjellet Formation in central Spitsbergen

Abstract

The Longyearbyen CO 2 storage project drilling and coring campaign in central Spitsbergen provided new insights on the shale-dominated Middle Jurassic to Lower Cretaceous Agardhfjellet Formation, which is the onshore counterpart to the Fuglen Formation and the prolific source rocks of the Hekkingen Formation in the Barents Sea. Logs of magnetic susceptibility, organic carbon content, organic carbon isotopes and XRF geochemistry on the cores, together with wireline logs, biostratigraphy and sedimentology, have made it possible to refine the interpretation of the depositional environment and to identify transgressive-regressive (TR) sequences. Several key sequence-stratigraphic surfaces are identified and suggested to be correlative in Central Svalbard, and four of them, although not necessarily chronostratigraphic, also to surfaces in the Barents Sea. Due to the nearly flat-lying thrust faults in the upper décollement zone of the West Spitsbergen Fold and Thrust Belt, there is some concern about the lateral correlation of the sequences within Spitsbergen. However, some of the TR sequence surfaces appear to be of regional importance and are recognised both onshore Svalbard and offshore on the Barents Shelf. The observations suggest a shallow-marine shelf depositional environment within an epicontinental sea with variable dysoxic, anoxic and oxic sea-floor conditions. The majority of the facies vary from outer shelf to transition zone or prodelta and lower shoreface/distal delta front. In one outcrop, proximal facies, i.e., delta front or middle shoreface, are recognised. In our study area the nearly 250 m-thick, fine-grained Agardhfjellet Formation is proposed to represent distal shoreline clinoforms and a precursor to the overlying forward-and southward-stepping wedge of the Valanginian Rurikfjellet Formation and the Barremian to Early Aptian Helvetiafjellet Formation.

Numerical modelling of permafrost spring discharge and open-system pingo formation induced by basal permafrost aggradation

“…Directly below is the ~ 450 m thick Janusfjellet Subgroup (Fig. 2b) that comprises two shale-dominated units, the Rurikfjellet (201-232 m thick, Grundvåg et al, 2019) Agardhfjellet Formations (253-264 m thick, Koevoets et al, 2018). A regional detachment zone with extensive fracturing and swelling clays propagates near the boundary of these two formations (Braathen et al, 2012) and is considered the main seal for the potential of CO2 storage (Olaussen et al, 2020).…”

Facies, palynostratigraphy and sequence stratigraphy of the Wilhelmøya Subgroup (Upper Triassic–Middle Jurassic) in western central Spitsbergen, Svalbard

“…A late Middle Jurassic unconformity and renewed regional transgression marks the onset of rifting in the western Barents shelf (Faleide et al, 2015). Previously exposed platforms and highs became submerged and restricted bottom circulation led to the accumulation of anoxic black shales in Svalbard and the southwestern Barents shelf in the Late Jurassic (e.g., Koevoets et al, 2018). The subsequent geological development of the region was characterised by several phases of uplift and erosion, as well as extensional and strike-slip movements along the western margin of the Barents shelf which culminated with the opening of the Norwegian-Greenland Sea in the Cenozoic (Faleide et al, 1993).…”

Digital Drill Core Models: Structure-from-Motion as a Tool for the Characterisation, Orientation, and Digital Archiving of Drill Core Samples

“…Drill core samples were selected from the interval for which wireline logging (including acoustic televiewer) is available, and are listed in Table 1. This interval covers the lowermost cap rock and uppermost reservoir sequences (approximately 440 to 700 m MD; DH4), represented by the shale-dominated, Late-Jurassic Agardhfjellet Formation [37] and the underlying Norian-Bathonian Wilhelmøya Subgroup [38,39], respectively [29,30]. The samples range from 4.7 cm (Agardhfjellet Fm) to 4.1 cm (Wilhelmøya Subgroup) in diameter ( Figure 1).…”