Paleoenvironment and sea-level change in the early Cretaceous Barents Sea?implications from near-shore marine sapropels

Abstract

The late Volgian (early ''Boreal'' Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottomwater conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by wellpreserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.

Late Jurassic to Early Cretaceous black shale formation and paleoenvironment in high northern latitudes: Examples from the Norwegian‐Greenland Seaway

“…This abnormal (different from modern) relationship is also reported from other Mesozoic sites, e.g., DSDP sites 367, 530 [ Dean et al , 1986], and 603 [ Arthur et al , 1985] which are summarized in Figure 8. This relationship seems to be stronger developed with increasing anoxia, and/or higher northern latitudes [ Langrock et al , 2003].…”

“…However, in many fossil sediments, especially under anoxic conditions, C/N ratios are often reported to show remarkable exceptions from this “rule” [e.g., Rau et al , 1987; Lüniger and Schwark , 2002; Twichell et al , 2002]. Moreover, Langrock et al [2003] demonstrate that in late Jurassic algae‐rich sapropels from the Barents Sea high C/N ratios may indicate a high degree of bottom water anoxia.…”

The Late Mesozoic‐Cenozoic Arctic Ocean Climate and Sea Ice History: A Challenge for Past and Future Scientific Ocean Drilling

“…relationships (cf. Hofmann et al, 2000 ;Lückge et al, 1996), the high concentrations of Mo, and the Re/Mo ratios also support widespread euxinic conditions (Langrock et al, 2003a(Langrock et al, , 2003bLipinski et al, 2003).…”

“…The increasing OC content in the late Volgian section was most likely caused by a combination of increasing preservation by bottom-water anoxia, coupled with periods of increasing primary production as well as a low and decreasing dilution of clastic material, related to a marked rise in sea level (Figure 8; Langrock et al, 2003a). During the Late Jurassic and Early Cretaceous, such anoxic conditions proposed for large parts of the proto-Arctic Ocean, probably extended toward the south into the Norwegian-Greenland Sea as shown in geochemistry and microscopy data sets from black shale sequences recovered in drill cores along the Norwegian shelf ( Figure 8; Langrock et al, 2003b;Langrock & Stein, 2004). The high abundance of autochthonous small-sized pyrite framboids indicative for an anoxic water column (i.e., under euxinic conditions), such as typical for the modern Black Sea (cf.…”

“…The high abundance of autochthonous small‐sized pyrite framboids indicative for an anoxic water column (i.e., under euxinic conditions), such as typical for the modern Black Sea (cf. Wilkin et al, ), the carbon‐sulfur‐iron relationships (cf.Hofmann et al, ; Lückge et al, ), the high concentrations of Mo, and the Re/Mo ratios also support widespread euxinic conditions (Langrock et al, , ; Lipinski et al, ).…”