Stratigraphy and palaeosol profiles of the Upper Triassic Isfjorden Member, Svalbard

Abstract

The Isfjorden Member forms the upper part of the De Geerdalen Formation in Svalbard and is well exposed throughout central and eastern Spitsbergen, including the island of Wilhelmøya. We examine palaeosol profiles identified in the Isfjorden Member and compare these to profiles seen in the remainder of the De Geerdalen Formation. In addition, we address the nuances of the Isfjorden Member, its practicality as a stratigraphic interval and attempt to constrain the unit's presence, as well as the nature of its lower boundary throughout outcrops in Svalbard. The Isfjorden Member is easily recognised by its conspicuous beds of alternating red and green coloured palaeosols, occasional caliche profiles and bivalve coquina beds. These beds have commonly been used to identify the unit in outcrop and we explore their relevance to the formal stratigraphic definition. The lower boundary is typically difficult to identify, especially when using the original definition; however, we find that placing it at the top of the last major sandstone in the De Geerdalen Formation is a practical solution. The boundary is conformable throughout Spitsbergen with no obvious erosion or break in sedimentation observed.The abundance, thickness and maturity of palaeosols increases upwards through the De Geerdalen Formation. Mature palaeosol and occasional caliche horizons are found to dominate within the Isfjorden Member. Immature palaeosols are in general constrained to the strata below. The position of palaeosols in relation to sedimentary successions is typically restricted to floodplain and interdistributary bay deposits, or atop upper shoreface deposits. The transition from immature palaeosols with common histosols to mature palaeosols and caliche reflects the development of the delta plain from a dynamic paralic setting to a more stable proximal system.

Stratigraphy and palaeosol profiles of the Upper Triassic Isfjorden Member, Svalbard

“…The Hopen Member, defined by Lord et al (2014a), is not present at any of the localities visited in this study -nor are the characteristic facies of the Isfjorden Member present on the island of Hopen.…”

“…The stratigraphy and sedimentology of the Upper Triassic succession in Svalbard can largely be considered as well studied. Early works by Buchan et al (1965), Worsley (1973), Smith (1975), Smith et al (1975), Lock et al (1978), Pčelina (1980Pčelina ( , 1983 and Mørk et al (1982Mørk et al ( , 1999Mørk et al ( , 2013 conducted primary mapping studies and identified the first Triassic stratigraphic units, whilst Mørk et al (1982), Anell et al (2014Anell et al ( , 2016Anell et al ( , 2020, Klausen & Mørk (2014), Klausen et al (2015Klausen et al ( , 2016Klausen et al ( , 2019, Rød et al (2014), Lord et al (2014aLord et al ( , b, 2017 focused on the nuances of facies studies and correlation of Upper Triassic sequences throughout Svalbard and the Barents Sea. The Longyearbyen CO 2 Lab Dh4 well and the diagenetic properties of a proposed Upper Triassic to Lower Jurassic reservoir interval were investigated by Mørk (2013).…”

“…The Hopen Member is described as a marine equivalent to the Isfjorden Member, with the lateral facies transition between the two being enigmatic due to erosion of the upper part of the De Geerdalen Formation throughout eastern areas of Svalbard (Lundschien et al, 2014;Lord et al, 2014aLord et al, , 2017.…”

Svalbard Composite Tectono-Sedimentary Element, Barents Sea

“…The well-preserved fluvial channel fill sandstone bodies are prominently exposed in the steep cliff sides of the island. Whilst these are relatively isolated in their stratigraphic position and encased in a highly heterolithic succession they clearly indicate the presence of relatively good reservoir quality rocks in the region (Lord et al, 2014(Lord et al, : 2017.…”

“…Local highs throughout the eastern part of the SCTSE existed with the Induan part of the succession missing in many places (Mørk et al, 1999;Lord et al, 2017;Vigran et al, 2014).The prodeltaic part of this delta system is represented by the Tschermakfjellet Formation (Ladinian/early Carnian), whereas the overlying De Geerdalen Formation (Carnian to early Norian) represent delta slope to delta front and delta plain depositional environment (Fig. 4) (Klausen and Mørk 2013;Lord et al, 2014;2017;Rød et al, 2014). On Edgeøya, fluvial, tidal and delta front deposits are documented in the De Geerdalen Formation, with thick sandstone intervals featuring a lobate geometry found in many parts of the strata (Rød et al, 2014).…”