Sedimentology and palynology of the Lower Cretaceous succession of central Spitsbergen: integration of subsurface and outcrop data

Abstract

The Lower Cretaceous succession in Svalbard is commonly considered as an important analogue to age-equivalent strata on the Barents Shelf which are sporadically targeted by exploration wells. In this study, the stratigraphic and genetic relationship between the Rurikfjellet (open marine), Helvetiafjellet (paralic) and Carolinefjellet (open marine) formations of the Lower Cretaceous succession in Svalbard is evaluated by combining sedimentological outcrop studies with well log and core data across Nordenskiöld Land, central Spitsbergen. Sedimentological characteristics and stratigraphic units are mapped within a refined dinocyst biostratigraphic framework, enabling relatively well-constrained palaeogeographic reconstructions. The Valanginian-lowermost Barremian Rurikfjellet Formation consists of a lower shale-dominated unit of offshore origin which grades upwards into storm-reworked lower shoreface sandstones displaying hummocky cross-stratification. Local occurrences of prodeltaic successions and thick successions of gravity flow deposits containing coal-bearing slump blocks of delta plain origin in some wells, reveal a late Hauterivian progradational pulse which has previously not been recorded in Svalbard. The lower Barremianlower Aptian Helvetiafjellet Formation consists of fluvial braidplain and paralic deposits which rest unconformably on the Rurikfjellet Formation across the entire study area, reflecting regional uplift and widespread subaerial exposure prior to the onset of paralic deposition. The Helvetiafjellet Formation exhibits increased marine influence upwards, and in the investigated cores the uppermost part of the unit consists of wave-reworked mouth-bar deposits which are truncated by a transgressive conglomerate lag dominated by extrabasinal lithic clasts and intraformational siderite clasts. An up to 10 m-thick, regionally extensive, organic-rich (TOC up to 2.1 wt.%) shale unit of early Aptian age marks the base of the overlying Carolinefjellet Formation. The shale accumulated during a regional flooding event which drowned and eventually transformed the Helvetiafjellet Formation coastal plain into a shallow shelf. The organic facies of the shale unit (Type II-III kerogen) and a high Pr/Ph ratio (>2), in combination with abundant long-chained n-alkanes, suggest that the unit was deposited in a suboxic paralic marine environment strongly influenced by input of terrestrial organic matter. The investigated succession exhibits stratigraphic and petrographic resemblance to age-equivalent strata in NE Greenland, suggesting that these successions may have formed part of the same drainage system located on the northwestern margin of the Barents Shelf. Thus, by highlighting the Early Cretaceous palaeogeographic evolution in Svalbard, this study contributes to the regional stratigraphic understanding of the Lower Cretaceous succession on the wider northern Barents Shelf.

Tempestite facies variability and storm‐depositional processes across a wide ramp: Towards a polygenetic model for hummocky cross‐stratification

“…The Kikutodden Member is generally <85 m thick and comprises two clastic wedges (Fig. B) – including: (i) a southern relatively coarse‐sand‐grade clastic wedge of offshore transition to shoreface parasequences (Grundvåg & Olaussen, ); and (ii) a northern comparatively fine‐sand‐grade clastic wedge (Nemec et al ., ; Grundvåg et al ., , ), which is dealt with in this study. The northern wedge is generally characterized by laminated, burrowed or structureless shale, which is intercalated with sandstone exhibiting well‐developed lamination or HCS (Dypvik et al ., 1991b).…”

“…(in press) and data from this study, and modified from Grundvåg et al . (). Mb, formally defined member; mb, informally defined member; R–T trends, regressive–transgressive trends.…”

Sylfjellet: a new outcrop of the Paleogene Van Mijenfjorden Group in Svalbard

“…The outcropping strata cover an area of 0.8 km 2 , and the maximum extent is 1.8 km × 0.7 km. The Sylfjellet succession overlies the c. 25 m-thick cliff-forming sandstones of the Lower (Barremian to Aptian) Festningen Member of the Helvetiafjellet Formation [71][72][73][74][75]. Based on distinct sedimentological and lithological differences, the Sylfjellet succession was subdivided into four units including a coal-bearing unit at the base (Unit 1) overlain by a sandstone-dominated section (Unit 2), which is overlain by dark siltstones (Unit 3), and sandstones on the top (Unit 4).…”

Dinocyst stratigraphy of the Valanginian–Aptian Rurikfjellet and Helvetiafjellet formations on Spitsbergen, Arctic Norway

“…Nøhr-Hansen et al 2019), the Barents Sea (Århus et al 1990;Smelror et al 1998;Smelror & Dypvik, 2005;Smelror & Dypvik, 2006;Kairanov et al 2018), Arctic Norway (Løfaldi & Thusu, 1976;Bjaerke, 1978;Thusu, 1978;Århus et al 1986, 1990Århus, 1991;Grøsfjeld, 1991;Hurum et al 2016b;Smelror & Larssen, 2016;Smelror et al 2018;Hammer et al 2018;Rakociński et al 2018;Grundvåg et al 2019) and Arctic Russia (Smelror, 1986;Lebedeva & Nikitenko, 1999;Riding et al 1999;Pestchevitskaya, 2007;Nikitenko et al 2008;Pestchevitskaya et al 2011). Some early Canadian studies provided dinocyst zonations (e.g.…”

“…S1). The sedimentological profile of the outcrop is provided in Grundvåg et al (2019) and Jelby et al (2020).…”