Abstract
A hitherto unrecognized Paleogene outcrop has been discovered at Sylfjellet, a mountain located at the northern side of Isfjorden, Svalbard. The strata, which cover an area of 0.8 km2, have until now been assigned to the Lower Cretaceous succession of the Adventdalen Group. In this study, the Sylfjellet site was studied in detail to provide an updated structural and sedimentological description of strata and lithostratigraphy. The age and burial history of the investigated succession were constrained by absolute (U/PB) and relative dating methods in addition to vitrinite reflectance analyses of coal seams. The results show a Paleogene age of the deposits, which is supported by the occurrence of an angiosperm pollen grain, plant macrofossils, and a tephra layer of early Selandian age (61.53 Ma). The 250 m-thick succession of Sylfjellet is assigned to the Firkanten, Basilika and Grumantbyen formations. This succession unconformably overlies the Lower Cretaceous Helvetiafjellet Formation. Sylfjellet is incorporated into the West Spitsbergen Fold-and-Thrust Belt and interpreted to be a fourth structural outlier of the Van Mijenfjorden Group. Vitrinite reflectance data indicate that at least 2000 m overburden has been eroded above the Sylfjellet coal seams, and that maximum burial of the strata predates folding and thrusting in the area.
Highlights
The mountain Sylfjellet is incorporated into the West Spitsbergen Fold-and-Thrust Belt (WSFTB; [1]) on central to western Spitsbergen, the largest island of the SvalbardElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.In one of the first geological maps of Spitsbergen, the topmost strata at Sylfjellet are assigned to the Jurassic [2]
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)
Based on detailed structural mapping, sedimentological descriptions, as well as relative and absolute age analyses of strata exposed on the mountain of Sylfjellet, we conclude the following:. Both micro- and macrofossil content and absolute dating of a tephra layer located at the base of the succession show that the summit region of Sylfjellet consists of Paleogene sedimentary rocks
Summary
The mountain Sylfjellet is incorporated into the West Spitsbergen Fold-and-Thrust Belt (WSFTB; [1]) on central to western Spitsbergen, the largest island of the Svalbard. In one of the first geological maps of Spitsbergen, the topmost strata at Sylfjellet are assigned to the Jurassic [2]. All subsequently published geological maps assign the strata. In 2015, during fieldwork targeting the Lower Cretaceous strata, doubt arose concerning the age of this succession and initiated this study. The strata at Sylfjellet, here informally referred to as the Sylfjellet succession, are re-visited and new findings from recent fieldwork reported. The objective of this paper is to describe the structural and sedimentological character of the stratigraphic succession at Sylfjellet, with an overall aim at revising its age and lithostratigraphic affinity
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