Preservation of carbohydrates through sulfurization in a Jurassic euxinic shelf sea: Examination of the Blackstone Band TOC cycle in the Kimmeridge Clay Formation, UK

Abstract

A complete total organic carbon (TOC) cycle in the Upper Jurassic Kimmeridge Clay Formation (KCF) comprising the extremely TOC-rich (34%) Blackstone Band was studied to investigate the controlling factors on TOC accumulation. Compared with the under-and overlying strata, TOC in the Blackstone Band was enriched by a factor of six and, concomitantly, the d 13 C TOC shows a $4& enrichment. Al-normalized TOC values indicated that the enhanced TOC values were probably caused by increased TOC accumulation and not by a decreased dilution with inorganic matter. The amounts of short chain alkylated thiophenes and the sulfur-rich unresolved complex mixture (UCM) in the kerogen pyrolysates, as well as the TOC/Al ratios, correlated linearly with d 13 C TOC for sediments with TOC/Al ratios >1.7. The alkylated thiophenes and sulfur-rich UCM both originate from sulfurized carbohydrate carbon (C carb ), suggesting that the primary cause of the TOC maximum is the enhanced contribution of C carb to TOC. Since carbohydrates can be substantially 13 C-enriched over lipids in biomass, the enhanced contribution of C carb explains the enriched d 13 C TOC values. Compound specific isotope data showed that primary productivity during deposition of the KCF TOC cycle varied little, while a two member isotopic mixing model showed that the preservation of C carb relative to that of the lipid carbon may have increased by a factor of >10 in the Blackstone Band. The enhanced preservation of C carb was most likely caused by more frequent or longer lasting events of photic zone euxinia, as revealed by the concentration of isorenieratene derivatives. Enhanced contributions of C carb have also been observed in other KCF cycles, suggesting that enhanced preservation of C carb , rather than an increase in primary production, exerted direct control on the TOC cycles of the KCF.

C27–C30 neohop-13(18)-enes and their saturated and aromatic derivatives in sediments: Indicators for diagenesis and water column stratification

“…10c). This is consistent with the idea that the C 28 28,30-dinorhopene IV and, thus, its diagenetic derivatives V-VII, can be used as stratification markers since it is well established that the Blackstone Band was deposited in a stratified, euxinic shelf sea (van KaamPeters et al, 1997KaamPeters et al, , 1998van Dongen et al, 2006a) as is also evident from increased levels of isorenieratene derivatives (Fig. 10b).…”

“…The C 24 tetra-aromatic and C 25 triaromatic members of this series were identified in relatively high concentrations in the Messel oil shale (Greiner et al, 1976(Greiner et al, , 1977 and have subsequently been found, together with the C 26 diaromatic and C 27 monoaromatic members (V-VI), in many other, often thermally immature, organic matter-rich sediments (e.g., Barnes et al, 1979;Comet et al, 1981;Simoneit, 1981;Rullkötter et al, 1984;van Kaam Peters et al, 1997;van Dongen et al, 2006a). Their structures suggest a diagenetic sequence of successive aromatization reactions from ring D through rings C, B, and A (Greiner et al, 1976(Greiner et al, , 1997 (Fig.…”

“…(Isaacs et al, 2000) c n.a. = not applicable d n.d. = not determined Cox and Gallois (1981) b data from van Kaam-Peters et al (1998) c data from van Dongen et al (2006a); detail on core in Morgan-Bells et al (2001) all data except for hopenes reported by Schouten et al (2000b) c all data except for hopenes reported by Schouten et al (1997) d all data except for triaromatic hopanoid reported by Schouten et al (2000c) e all data except for hopenes and aromatic hopanoid reported by Sinninghe and Sinninghe Damsté et al (2008) f n.d.=not determined because of low concentration or co-elution with another component g n.a. = not applicable, i.e.…”

Rapid organic matter sulfurization in sinking particles from the Cariaco Basin water column

“…Li et al (2011) found elevated concentrations of organic sulfur in suspended particles near the chemocline in the Cariaco Basin water column and proposed that this indicated early OM sulfurization. Rapid OM sulfurization in particles sinking through the water column was also proposed to explain the high S:C ratios in certain OM-rich rocks (van Dongen et al, 2006;Tribovillard et al, 2004). Support for the feasibility of more rapid OM sulfurization is also provided by laboratory experiments.…”

Carbon- and oxygen-isotope records of palaeoenvironmental and carbonate production changes in shallow-marine carbonates (Kimmeridgian, Swiss Jura)

“…6) in bulk organic matter from the Kimmeridge Clay Formation (KCF) of southern England (Morgans-Bell et al 2001). However, the enhanced δ 13 C TOC values in the KCF mostly correlate with enhanced TOC values that probably result from enhanced preservation of carbohydrates through sulphurization (van Dongen, Schouten & Sinninghe Damste, 2006). They are most likely caused by a longer duration of photic zone euxinia in the depositional environment and do not reflect the overall composition of dissolved inorganic carbon in seawater.…”