From terrestrial to shallow-marine depositional environments: reconstruction of the depositional environments during the Late Carboniferous transgression of the Lomfjorden Trough in NE Spitsbergen (Malte Brunfjellet Formation)

Sedimentary rocks of the Upper Carboniferous Malte Brunfjellet Formation are investigated in five sections, located on a N–S-oriented transect along the Lomfjorden Fault Zone in eastern Spitsbergen. Results of facies and microfacies analysis led to a redefinition of the Malte Brunfjellet Formation, and formerly unspecified Carboniferous sedimentary rocks in the investigated area are now assigned to this formation. In the northern part of the Lomfjorden Trough, the Malte Brunfjellet Formation consists of a 41 m-thick, cyclic succession with variegated shales at the base and tidal flat sandstones or dolomites at the top. They are conformably deposited on gray, siliciclastic deposits of the Billefjorden Group, and in turn conformably overlain by the limestone succession of the Wordiekammen Formation. The cyclicity and overall sedimentary development of the mixed clastic/ carbonate succession indicate coastal plain to sabkha environments controlled by high-frequency sea-level fluctuations. In the southern Lomfjorden Trough, the Malte Brunfjellet strata, resting unconformably on Neoproterozoic basement rocks, comprise a basal, 13 m-thick, siliciclastic interbedding of distinct red shales, siltstones and sandstones, reflecting alluvial to fluvial environments under warm, semi-arid climatic conditions. The redbed succession is separated by a 32 m-thick scree-covered interval from a 15 m-thick, cyclic intercalation of grayish sandstones, caliche horizons, and shallow-marine, near-shore limestones, forming the upper part of the formation. The deposits reflect a development into a coastal plain controlled by sea-level fluctuations and an overall rising sea level. This lateral facies variation with shallow-marine environments in the north and alluvial to near-shore environments in the south reflect a successive transgression of the Lomfjorden Trough from northerly directions. Biostratigraphy of smaller foraminfers and cyclostratigraphy indicate a Bashkirian age for the marine sediments deposited in the upper part of the Malte Brunfjellet Formation. The marine sediments in the Lomfjorden Trough are contemporaneous with shallow-marine deposits in the Billefjorden and the St. Jonsfjorden troughs in central and western Spitsbergen. They mark the first, nearly Spitsbergen-wide, transgression, which resulted in the Svalbardwide deposition of the shallow-marine carbonates of the Wordiekammen Formation.

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