Angela Jenisch

Unusual distributions of long-chain alkenones and tetrahymanol from the highly alkaline Lake Van, Turkey

Long-chain C37 to C40 alkenones with di-, tri-, and tetra-unsaturation are very abundant in sediment trap material and Holocene to Late Pleistocene core samples from the Earths largest soda lake, Lake Van (Turkey). Thus, the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments. The observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra-unsaturated compounds, especially the C37:4 methyl ketone. Their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation. Using published U37K calibrations, no reliable absolute temperatures were obtained for the Lake Van samples. Accordingly, marine sea surface temperature determinations based on long-chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded. The presence of tetrahymanol and gammacer-3-one in the Lake Van materials is attributed to organic matter contributions of ciliates. The relative abundance of long-chain alkenones and of tetrahymanol/gammacer-3-one is considered to reflect changes in the environmental conditions, in particular in the hydrological setting. We suggest that times of pronounced stagnation are recognised by very high tetrahymanol/gammacer-3-one concentrations together with drastically increased stanol/stenol ratios, and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions.

Structural investigations of sulphur-rich macromolecular oil fractions and a kerogen by sequential chemical degradation

Abstract Structural studies of a sulphur-rich kerogen and macromolecular oil fractions from the Monterey Formation were performed by selective sequential chemical degradation. The method provides low-molecular weight compounds as former building blocks of the network which allow detailed analyses on a molecular level. The degradation sequence is based on three subsequently performed reactions—a selective cleavage of sulphur bonds in the first step carried out with Ni(0)cene/LiAlD 4 , an ether and ester bond cleavage (BCl 3 ), and an oxidation of aromatic entities by ruthenium tetroxide as a final step. Each step of this sequence afforded a considerable amount of low-molecular weight material which was separated chromatographically and studied by GC and GC/MS, while the high-molecular weight or insoluble fractions were subjected to the next reaction step. The chemical degradation products—hydrocarbons and carboxylic acids—are discussed in terms of incorporation into the macromolecular structure, distribution of heteroatomic bridges and the genetic relationships between the different macromolecular crude oil fractions and kerogen. Labelling experiments with deuterium provided evidence for a simultaneous linkage by oxygen and sulphur functionalities or by aromatic units and sulphur bonds of cross-linking macromolecular network constituents. The determination of sulphur positions in the macromolecule suggests early diagenetic sulphur incorporation into the biological precursor compounds and subsequent formation of a cross-linked network.

Mid-chain branched alkanoic acids from living fossil demosponges : a link to ancient sedimentary lipids?

The lipid assemblages of the “living fossil” stromatoporoid Astrosclera willeyana (Great Barrier Reef) and the demosponge Agelas oroides (Mediterranean Sea) were investigated. Large amounts of branched carboxylic acids are present in the sponges studied. These compounds include terminally branched carboxylic acids (iso-/anteiso-) and abundant mid-chain branched carboxylic acids (MBCA) which are characterized by an intriguing variety of structural isomers present in the C15–C25 range. The most prominent MBCA are comprised of isomeric methylhexadecanoic acids and methyloctadecanoic acids. A second cluster of MBCA includes methyldocosanoic acids and methyltetracosanoic acids, but other homologues are also present. Methyl branching points were generally observed between the ω5- and ω9-positions. These complex isomeric mixtures apparently derive from symbiotic bacteria living exclusively in demosponges. Comparison with hydrocarbon compositions of ancient carbonates reveals evidence that the MBCA found are potential lipid precursors of mid-chain branched monomethylalkanes often observed in fossil sediments and oils. As a working hypothesis, we suggest that their bacterial source organisms have been widespread in the geological past, and are found “inherited” in the protective environment of distinctive sponge hosts in recent marine ecosystems. Furthermore, both sponges contain abundant linear, long-chain C24–C26 dienoic “demospongic” acids. The demospongic acid distribution and the presence of phytanic acid in A. willeyana match the patterns found in A. oroides and other members of the Agelasida. These findings confirm the systematic position of A. willeyana within this demosponge taxon.

Microbial carbonate crusts-a key to the environmental analysis of fossil spongiolites?

SummaryMorphological and geochemical comparisons between modern cryptic microbialites from Lizard Island/Great Barrier Reef and fossil counterparts in the Upper Jurassic (Southern Germany, Dobrogea/Romania) and late Lower Cretaceous (Aptian/Albian from Cantabria/Spain) spongiolitic environments show that there are common factors controlling the crust formations mostly independent of light despite of diverging (paleo-) oceanographic positions as well as relationships of competitors. Factors such as increased alkalinity, oligotrophy, and reduced allochthonous deposition are of major importance. Thrombolitic microbialites are interpreted as biologically induced and therefore calcified in isotopic equilibrium with the surrounding sea water. Corresponding with shallowing upward cycles, microbial mats which produce stromatolitic peloidal crusts become more important. Different biomarkers are introduced for the first time extracted and analyzed from spongiolitic limestones of Lower Kimmeridgian age from Southern Germany.

Hydrothermal petroleum generation in Red Sea sediments from the Kebrit and Shaban deeps

Abstract Petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns Red Sea. Biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material. Two organic phases could be distinguished according to their source and maturity. The amounts of n -alkanes show a marked decrease with depth, whereas the concentrations of various branched and cyclic hydrocarbons increase, resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm. Changes in concentrations and distributions of hopanoids in the Kebrit Deep sediments indicate a rapid increase of maturity with depth. The deepest core section (300 cm) and the masive sulfide reveal comparable maturation indices typical for mature oils. By chemical degradation of the polar fractions a series of C 40 -isoprenoids was obtained, which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter. The data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences, superimposes the autochthonous organic substances in the sediments and furthermore, forms asphaltic impregnations in the massive sulfides.

The chemical structure of macromolecular fractions of a sulfur-rich oil

A selective stepwise chemical degradation has been developed for structural studies of highmolecularweight (HMW) fractions of sulfur-rich oils. The degradation steps are: 1. (i) desulfurization 2. (ii) cleavage of oxygen-carbon bonds 3. (iii) oxidation of aromatic structural units. After each step, the remaining macromolecular matter was subjected to the subsequent reaction. This degradation scheme was applied to the asphaltene, the resin and a macromolecular fraction of low polarity (LPMF) of the Rozel Point oil. Total amounts of degraded low-molecular-weight compounds increased progressively in the order asphaltene < resin < LPMF. Desulfurization yielded mainly phytane, steranes and triterpanes. Oxygen-carbon bond cleavage resulted in hydrocarbon fractions predominated by n-alkanes and acyclic isoprenoids. The oxidation step afforded high amounts of linear carboxylic acids in the range of C11 to C33. The released compounds provide a more complete picture of the molecular structure of the oil fractions than previously available. Labelling experiments with deuterium atoms allowed to characterize the site of bonding and the type of linkage for the released compounds. Evidence is presented that subunits of the macromolecular network are attached simultaneously by oxygen and sulfur (n-alkanes, hopanes) or by sulfur and aromatic units (n-alkanes, steranes).

Structural studies of marine and riverine humic matter by chemical degradation

Abstract Selective chemical degradations of humic substances with non-oxidative reagents have revealed high amounts of low-molecular weight soluble material. The compound classes released provide valuable information on the type of material incorporated into the macromolecular matrix. Integral parts of biopolymers can be traced as building blocks of humic substances. Degradations performed with deuterium instead of hydrogen demonstrate characteristic deuterium incorporation into the degradation products. Bonding sites by which the biological precursor compounds are attached to the humic substance matrix can be determined.

Manganese, methane, iron, zinc, and nickel anomalies in hydrothermal plumes from Teahitia and Macdonald volcanoes

Abstract Hydrothermal vents discharging turbid water have recently been discovered at Teahitia and Macdonald seamounts, which are situated at the southeast ends of two South Pacific hotspot systems. Mixtures of the plumes with ambient seawater were sampled during the 1989 CYAPOL cruise and found to contain significant amounts of CH4, Mn, Fe, Zn, and Ni, which are comparable in concentration to those found over hydrothermal fields on the EPR and in megaplumes over the Juan de Fuca Ridge. Above Teahitia volcano, CH4 shows maximum concentrations of 8 nmol/kg, Mn concentrations of 19 nmol/kg, and Fe concentrations of 125 nmol/kg. The concentrations were much higher during an earlier SO-47 cruise in 1987, reaching maximum values of 14 nmol CH4/kg and 60 nmol Mn/kg. By contrast, the Macdonald seamount plume shows an opposite trend reaching very high concentrations of 350 nmol/kg CH4, 250 nmol Mn/kg, and 3920 nmol Fe/kg during the CYAPOL cruise when the volcano was at an eruptive stage with high seismic activity. The Fe Mn ratio of the plume is variable between the two active volcanoes and at different hydrocast stations, reflecting the balance between input and removal of these two elements. Mapping of the element concentrations in the water column shows the plume ceiling, or anomaly maxima, to occur to several hundred metres above the seafloor and up to several kilometres (> 5 km) from the vents on Macdonald seamount. Multiple maxima in hydrocast profiles indicate the presence of several distinct hydrothermal vents at different water depths on Teahitia and on the western flank of Macdonald seamount. REE data from a single hydrocast over the active Macdonald summit indicate a mobility of the REE, which probably results from high-temperature basalt-seawater interaction.

Biomarker indications for microbial contribution to Recent and Late Jurassic carbonate deposits

SummaryBiomarker investigations were applied to the hydrocarbon fractions of three Recent (cyanobacterial mat, Lake Van microbialite and Lake Satonda microbialite) and two Late Jurassic carbonate samples obtained from sponge bioherms. The relative concentrations ofn-alkanes, monomethyl alkanes, acyclic isoprenoids, steroids and hopanoids in these samples are studied and their probable biological precursors are discussed. Normal alkanes with carbon chain lengths ranging from C15 to C34 and monomethyl alkanes ranging from C17 to C21 with a varying methyl branching pattern are found. The major hydrocarbons are low molecular weight (LMW)n-alkanes (C15–C21) with a slight to strong predominance ofn-heptadecane (C17). High molecular weight (HMW)n-alkanes occur in low to moderate relative concentrations showing a preference of odd-carbon numbered compounds with a maximum at C29. Within the acyclic isoprenoids, pristane, phytane/phytene, pentamethyl-eicosane, squalane and lycopane could be identified. Polycyclic terpenoids of the sterane and/or hopane type are present in all carbonate samples. The carbon numbers of these components range from 27 to 29 and 27 to 32, respectively. These organic compounds identified can be attributed to various source organisms such as cyanobacteria, archaebacteria, algae and vascular plants. All hydrocarbon fractions of the samples are characterized by moderate to high relative concentrations of compounds derived from cyanobacteria, signifying the role of these organisms as contributors to the Recent as well as to the Late Jurassic carbonate deposits.

Chemical structural units of macromolecular coal components

Abstract Chemical degradations of coal resins, coal asphaltenes and coal residues have been performed with selective, non-oxidative reagents. The coal comprise samples a rank interval 0.30–1.21 % R m . Degraded low-molecular-weight compounds were analyzed by GC-MS. The distributions of pentacyclic terpanes, isoprenoids, n -alkanes, acids and alcohols obtained as degradation products illustrate a considerable variability between the macromolecular coal fractions. A structural study on the molecular level of the degraded compounds from coal resins and coal asphaltenes show their potential to generate hydrocarbons during coalification process.