Multi‐elemental chemostratigraphy of Triassic mudstones in eastern Svalbard: Implications for source rock formation in front of the World’s largest delta plain

Abstract

The Triassic Boreal Ocean was a shallow epicontinental basin and the sink of the World's largest delta plain known to date. Nutrient and freshwater supply from this delta have been regarded as important causes for high productivity and water mass stratification, forming Middle Triassic oil‐prone source rocks. Recent studies attribute upwelling and a productivity‐induced oxygen minimum zone as important factors. A multi‐elemental chemostratigraphic study of a Spathian–Carnian mudstone succession exposed in eastern Svalbard was performed to investigate their formation. This includes 89 samples from three localities, from which 34 elements were acquired using combustion and X‐ray fluorescence analyses. The goal is to provide a correlation framework and infer the role of productivity, redox and water mass restriction on organic matter accumulation and source rock formation. These processes had major impact on the source potential. The Spathian Vendomdalen Member suggests deposition during intermittent benthic euxinia and low productivity, corresponding with a reported deep thermocline that obstructed upwelling. The lower Anisian lower–middle Muen Member shows negligible enrichment in redox‐sensitive elements but in situ phosphate nodules, consistent with developing upwelling and moderate productivity. The middle Anisian upper Muen Member formed during high productivity and phosphogenesis and is linked with basin‐wide upwelling. Productivity, phosphate and redox proxies are all strongly enriched in the upper Anisian–Ladinian Blanknuten Member. In the south‐western Barents Sea, the pro‐deltaic environment of the emerging Triassic Boreal Ocean delta system had terminated these conditions. The upper Ladinian upper Blanknuten Member formed within intermittent euxinic bottom waters due to the shallowing sea level. The Carnian Tschermakfjellet Formation marks the dominance of the prograding delta system and the end of Triassic oil‐prone source rock formation in Svalbard.

Svalbard Composite Tectono-Sedimentary Element, Barents Sea

“…The Botneheia Formation is from 80 to 160 m thick, and contains dominantly kerogen type II in its upper part and type III in its lower part, with TOC values ranging from c. 1-11 wt. % with the Blanknuten Member in the upper part of the formation exhibiting the highest organic content (Mørk & Bjorøy, 1984;Krajewski, 2013;Wesenlund et al, 2021;2022). On northwest Edgeøya and south Barentsøya, this part of the formation is in the oil window (Fig.…”

“…These deposits transition eastward into offshore mudstones of the Lower Triassic Vikinghøgda and the overlying Botneheia formations (Fig. 4) (Mørk et al, 1999;Vigran et al, 2014;Wesenlund et al, 2022).…”

“…Their offshore near time-equivalent counterparts: the Steinkobbe and Hekkingen Formations, respectively, are known to charge both numerous fields in the Norwegian Barents Sea (Henriksen et al, 2011a;Leith et al, 1993;Ohm et al, 2008;Abay et al, 2018). Both the Botneheia and Agardhfjellet formations were deposited in relatively shallow shelf waters, periodically under anoxic sea floor conditions, in distal pro-deltaic settings in front of large, prograding delta systems (Glørstad-Clark et al, 2011;Anell et al, 2014a, b;Koevoets et al, 2018;Wesenlund et al, 2022). Bitumen in Mesozoic sandstones from outcrops and cored boreholes Local intrusive Cretaceous volcanic rocks may influence this trend (Senger et al,.…”

“…This upper member is also typically rich in phosphate, suggesting influence from upwelling and subsequent high rates of primary production, which eventually promoted oxygen deficiency in the water column (Krajewski, 2013;Wesenlund et al, 2021). Integrated geochemical studies by Wesenlund et al (2021;2022) suggests that the lower part of the Botneheia Formation is expected to generate mixed oil and gas (during conditions equivalent to peak oil generation) with relatively greater amounts of saturated versus aromatic hydrocarbons compared to the oil-prone, phosphate-bearing upper part of the unit.…”

Exceptional X-Ray contrast: Radiography imaging of a Middle Triassic mixosaurid from Svalbard

“…Phosphate nodules are found throughout the interval, either dispersed in the shale or as basal lags in the siltstone [ 28 , 38 ]. The early Anisian saw a transgression that led to deep-shelf, anoxic depositional environments throughout the lower Muen Member, before conditions fluctuated more in the Ladinian part of the Blanknuten Member [ 29 , 30 , 36 – 38 ].…”