Abstract
The Aptian deposits on Spitsbergen Island are poorly studied. Moreover, there were no published data on fossil distribution in the Aptian and Albian in the vicinity of the town of Longyearbyen. This article provides new data on ammonite-based biostratigraphy of the Carolinefjellet Formation, indicating the presence of Beds with Tropaeum arcticum (middle Aptian) and Beds with Grantziceras (lower Albian). The age of the formation was verified and the presence of lower Albian strata was justified. The results of microscopic and isotope studies of five samples of glendonites collected from the middle Aptian of the Carolinefjellet Formation section are presented. Glendonites from the Carolinefjellet Formation are composed of three calcite phases: ikaite-derived calcite and two successive types of cement, which fill cavities and develop partially after the first-phase calcite. The O and C isotope compositions of glendonites were measured in five bulk samples from the middle Aptian interval of the section. The δ18O isotope composition of glendonites is significantly different from that of seawater, indicating the input of diagenetic fluids; the δ13C values are characteristic of sedimentary organic matter and methanotrophy. For the first time, findings of ammonites allowed us to clarify the stratigraphic intervals of glendonite occurrence and associated cold-climate episodes and prove the early Albian age of glendonites from the top of the Carolinefjellet Formation.
Highlights
Compared to other stages of the Lower Cretaceous, the biostratigraphy of Aptian deposits of Spitsbergen Island is poorly studied
The only Tropaeum arcticum “Zone,” which is included in the Boreal Zonal Standard, is distinguished in the middle Aptian sediments of Spitsbergen (Baraboshkin, 2004; Baraboshkin and Guzhikov, 2018)
The complete specimens of T. (T.) arcticum that we have found are close to specimens from the type series of this species from Spitsbergen (Stolley, 1912, p. 16) and to those from Northern Germany (Gaida et al, 1978; Kemper, 1982, 1995)
Summary
Compared to other stages of the Lower Cretaceous, the biostratigraphy of Aptian deposits of Spitsbergen Island is poorly studied. There are only scarce data on the distribution of bivalve mollusks, ammonites, and dinocysts in this stratigraphic interval. No data on the distribution of ammonites in any section were published. The only Tropaeum arcticum “Zone,” which is included in the Boreal Zonal Standard, is distinguished in the middle Aptian sediments of Spitsbergen (Baraboshkin, 2004; Baraboshkin and Guzhikov, 2018). Given that this zone is underlain and overlain by thick strata, which are not characterized by findings of ammonites, it would be correct to call this stratigraphic unit “Beds with T. arcticum” (Ershova, 1983). The stratigraphic distribution of an index species of these beds and other taxa is still not clear
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