The Upper Jurassic petroleum system of NE Iraq

Iraq is one of the few countries with significant potential for discovery of major oil and gas fields. Two major petroleum systems occur in Mesozoic strata, the Mid-Upper Jurassic and the Basal Cretaceous. These petroleum systems in Arabia are generally well separated by widespread evaporites of the Hith Fm., its equivalents in central to NE Iraq being the carbonates/anhydrites of the Gotnia Fm. Where missing or replaced by the clastic Barsarin Fm. a differentiation of the two Petroleum Systems becomes difficult. We here report on the Ajeel field of northern Iraq, covering the time interval from the Mid-Jurassic (Aalenian) to the Early Cretaceous (Barremian) to identify source intervals, determine maturity and conduct oil/source rock correlation with Miocene (Euphrates/JeribeFm.) oil reservoirs

Macroecology of methane-oxidizing bacteria: the β-diversity of pmoA genotypes in tropical and subtropical rice paddies

Studies addressing microbial biogeography have increased during the past decade, but research on microbial distribution patterns is still in its infancies, and many aspects are only poorly understood. Here, we compared the methanotroph community in paddy soils sampled in Indonesia, Vietnam, China and Italy, focusing on the distance-decay relationship. We used the pmoA gene as marker for methanotroph diversity in terminal restriction fragment length polymorphism, microarray and pyrosequencing approaches. We could observe a significant increase of -diversity with geographical distance across continents (12000km). Measured environmental parameters explained only a small amount of data variation, and we found no evidence for dispersal limitation. Thus, we propose historical contingencies being responsible for the observed patterns. Furthermore, we performed an in-depth analysis of type II methanotroph pmoA distribution at the sequence level. We used ordination analysis to project sequence dissimilarities into a three-dimensional space (multidimensional scaling). The ordination suggests that type II methanotrophs in paddy fields can be divided into five major groups. However, these groups were found to be distributed in all soils independent of the geographic origin. By including tropical field sites (Indonesia and Vietnam) into the analysis, we further observed the first paddy fields harbouring a methanotroph community depleted in type II methanotrophs

The application of compound-specific sulfur isotopes to the oil–source rock correlation of Kurdistan petroleum

The concentrations and δ34S values of thioaromatic compounds of a suite of oils from several major oil fields in Kurdistan and their corresponding regional Type II-S source rocks have been measured to investigate their source relationship. The oils of three fields (Khabbaz, Jambur, Ajeel) and the bitumen extracted from specific rock formations (Alan, Sargelu, Naokelekan, Chia Gara) showed particularly high abundances of thioaromatics consistent with a carbonate source deposited in a restricted sulfate-rich marine platform setting. The δ34S [V-CDT] values of the major organosulfur compounds (OSCs) in these petroleum samples were measured with a gas chromatograph coupled to a multi-collector inductively coupled plasma mass spectrometer. δ34S values of dibenzothiophenes and methyldibenzothiophenes were consistently in the range −4‰ to −12‰ and −9‰ to −18‰ for the oils and rocks, respectively. Separate groupings of oils and rocks were distinguishable by > 2‰ difference, given an analytical reproducibility of < 0.8‰. OSCs from rocks were consistently ∼2–4‰ depleted than in oils, reflecting a similar trend to previous bulk δ34S studies from which an initial evolution of 34S depleted H2S during diagenesis and thermal maturation had been proposed. Distinctive δ34SOSC data of the oils and rocks with particularly high thioaromatic abundances did suggest several oils–source rock relationships: the Ajeel and Jambur oils and sediments from the Chia Gara formation yielded relatively enriched δ34SOSC values, whereas consistently depleted δ34SOSC values were observed for the Khabbaz oil and Naokelekan source rocks. Results suggest that compound-specific S isotope analysis can help establish oil–source rock relationships of S-rich petroleum

Multiproxy reconstruction of oceanographic conditions in the southern epeiric Kupferschiefer Sea (Late Permian) based on redox-sensitive trace elements, molybdenum isotopes and biomarkers

The key drivers controlling the redox state of seawater and sediment pore waters in low energy environments can be inferred from redox-sensitive trace elements (RSTE), molecular biomarkers and trace metal isotopes. Here, we apply a combination these tools to the Upper Permian Kupferschiefer (T1) from the Thuringian Basin, deposited in the southern part of the semi-enclosed Kupferschiefer Sea. Enrichment patterns of the RSTEs molybdenum (Mo) and uranium (U) as well as biomarker data attest to the rapid development of euxinic conditions in basin settings during early T1 times, which became progressively less extreme during T1 deposition. The evolution of redox conditions in basinal settings, and the associated delay in the onset of euxinia at more shallow marginal sites, can be attributed to the interaction of sea-level change with basin paleogeography. Euxinia in the southern Kupferschiefer Sea did not lead to near-quantitative depletion of aqueous Mo, possibly due to short deepwater renewal times in the Thuringian Basin, low aqueous H2S concentrations, the continuous resupply of RSTE during transgression and declining burial rates of RSTEs throughout T1 times. 30 Drawdown of RSTE is, however, indicated for euxinic lagoon environments. Moreover, admixture of freshwater supplied to these lagoons by rivers strongly impacted on local seawater chemistry. The highest Mo-isotope compositions of ~1.70‰ in basin sediments allows a minimum Kupferschiefer Sea seawater composition of ~2.40‰ to be estimated. This composition is similar to the ~2.30‰ estimate for the Late Permian open ocean, and confirms a strong hydrographic connection between the epeiric Kupferschiefer Sea and the global ocean. The substantial variation in Moisotope signatures is paralleled by diagnostic shifts in biomarkers responding to oxygenation in different parts of the water column. Water column chemistry has been affected by variation in sea level, hydrodynamic restriction, riverine freshwater influx and evaporitic conditions in shallow lagoons. Elucidation of the relative role of each driving factor by a single geochemical proxy is not feasible but the complex scenario can be disentangled by a multiproxy approach

Lipid biomarker signatures as tracers for harmful cyanobacterial blooms in the Baltic Sea

The recent proliferation of harmful cyanobacterial blooms (cyanoHABs) in the Baltic and other marginal seas poses a severe threat for the health of infested ecosystems as e.g. the massive export and decay of cyanobacterial biomass facilitates the spread of bottom water hypoxia. There is evidence that cyanoHABs occurred repeatedly in the Baltic Sea but knowledge of their spatiotemporal distribution and the cyanobacteria that contributed to them is limited. In this study, we examined representatives of the major bloom-forming heterocystous cyanobacteria (i.e. Aphanizomenon, Dolichospermum (formerly Anabaena) and Nodularia) to establish lipid fingerprints that allow tracking these environmentally important diazotrophs in the modern and past Baltic Sea. The distribution of normal and mid-chain branched alkanes, fatty acid methyl esters, bacteriohopanepolyols and heterocyst glycolipids permitted a clear chemotaxonomic separation of the different heterocystous cyanobacteria but also indicated a close phylogenetic relationship between representatives of the genera Aphanizomenon and Dolichospermum. Compared to the discontinuous nature of phytoplankton surveys studies, the distinct lipid profiles reported here will allow obtaining detailed spatiotemporal information on the frequency and intensity of Baltic Sea cyanoHABs as well as their community composition using the time-integrated biomarker signatures recorded in surface and subsurface sediments. As heterocystous cyanobacteria of the genera Aphanizomenon, Dolichospermum and Nodularia are generally known to form massive blooms in many brackish as well as lacustrine systems worldwide, the chemotaxonomic markers introduced in this study may allow investigating cyanoHABs in a great variety of contemporary environments from polar to tropical latitudes.Peer reviewe

Radiolytic alteration of biopolymers in the Mulga Rock (Australia) uranium deposit

We investigated the effect of ionizing radiation on organic matter (OM) in the carbonaceous uranium (U) mineralization at the Mulga Rock deposit, Western Australia. Samples were collected from mineralized layers between 53 and 58.5 m depths in the Ambassador prospect, containing <5300 ppm U. Uranium bears a close spatial relationship with OM, mostly finely interspersed in the attrinite matrix and via enrichments within liptinitic phytoclasts (mainly sporinite and liptodetrinite). Geochemical analyses were conducted to: (i) identify the natural sources of molecular markers, (ii) recognize relationships between molecular markers and U concentrations and (iii) detect radiolysis effects on molecular marker distributions. Carbon to nitrogen ratios between 82 and 153, and Rock–Eval pyrolysis yields of 316–577 mg hydrocarbon/g TOC (HI) and 70–102 mg CO2/g TOC (OI) indicate a predominantly lipid-rich terrigenous plant OM source deposited in a complex shallow swampy wetland or lacustrine environment. Saturated hydrocarbon and ketone fractions reveal molecular distributions co-varying with U concentration. In samples with <1700 ppm U concentrations, long-chain n-alkanes and alkanones (C27–C31) reveal an odd/even carbon preference indicative of extant lipids.Samples with ⩾1700 ppm concentrations contain intermediate-length n-alkanes and alkanones, bearing a keto-group in position 2–10, with no carbon number preference. Such changes in molecular distributions are inconsistent with diagenetic degradation of terrigenous OM in oxic depositional environments and cannot be associated with thermal breakdown due to the relatively low thermal maturity of the deposits (Rr = 0.26%). It is assumed that the intimate spatial association of high U concentrations resulted in breakdown via radiolytic cracking of recalcitrant polyaliphatic macromolecules (spores, pollen, cuticles, or algal cysts) yielding medium chain length n-alkanes (C13–C24). Reactions of n-alkenes with OH− radicals from water hydrolysis produced alcohols that dehydrogenated to alkanones or through carbonylation formed alkanones. Rapid reactions with hydroxyl radicals likely decreased the isomerization of n-alkenes and decreased alkanone diversity, such that the alkan-2-one isomer is predominant. This specific distribution of components generated by natural radiolysis enables their application as “radiolytic molecular markers”. Breaking of C–C bonds through radiolytic cracking at temperatures much lower than the oil window (<50 °C) can have profound implications on initiation of petroleum formation, paleoenvironmental reconstructions, mineral exploration and in tracking radiolysis of OM

Aromatic hydrocarbons provide new insight into carbonate concretion formation and the impact of eogenesis on organic matter

Investigations of aromatic biomarkers extracted from carbonate concretions can contribute to characterization of the enhanced microbial activity that mediates carbonate concretion formation. This microbial footprint can be further inferred from the stable isotopic values of carbonate (δ13C) and pyrite (δ34S). Here, we used a combination of GC–MS and GC × GC-ToF-MS to compare the aromatic fractions of two Toarcian carbonate concretions from the H. falciferum ammonite zone of the Posidonia Shale (SW-Germany) and their host sediment. The results revealed that n-alkylated and phytanyl arenes were enhanced in the concretions, relative to the host sediment. These findings support a very early diagenetic (eogenetic) microbial source for alkylated and phytanyl arenes derived from the microbial ecosystem mediating concretion formation. In contrast, aromatic compounds formed by thermal maturation (e.g. polycyclic aromatic hydrocarbons, aromatic steroids, organic sulphur compounds) remained invariant in host rock and concretion samples. When combined with bulk sediment and concretion properties, the distribution of aromatic compounds indicates that eogenetic microbial activity upon concretion growth does not diminish organic matter quality

Changes of palaeoenvironmental conditions recorded in Late Devonian reef systems from the Canning Basin, Western Australia: A biomarker and stable isotope approach

Although the Late Devonian extinctions were amongst the largest mass extinction events in the Phanerozoic, the causes, nature and timing of these events remain poorly restrained. In addition to the most pronounced biodiversity loss at the Frasnian–Famennian (F–F) boundary and the end Famennian, there were also less extensively studied extinction pulses in the Middle to Late Givetian and the Frasnian. Here we used a combination of palynological, elemental, molecular and stable isotope analyses to investigate a sedimentary record of reef-systems from this time period in the Canning Basin, Western Australia. The acquired data generally showed distinct variations between sediments from (i) the time around the Givetian–Frasnian (G–F) boundary and (ii) later in the Frasnian and indicated a distinct interval of biotic stress, particularly for reef-builders, in the older sediments. Alterations of pristane/phytane ratios, gammacerane indices, Chlorobi biomarkers, δDkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic/euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column. Simultaneous excursions in δ13C profiles of carbonates, organic matter (OM) and hydrocarbons in the older sediments reflect the stratification-induced enhancement of OM-recycling by sulfate reducing bacteria. Alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans (MTTCs) and perylene indicate an increased terrigenous nutrient input via riverine influx, which would have promoted stratification, phytoplankton blooms and the development of lower water column anoxia.The detected palaeoenvironmental conditions around the G–F boundary may reflect a local or global extinction event. Our data furthermore suggest a contribution of the higher plant-expansion and photic zone euxinia to the Late Devonian extinctions, consistent with previous hypotheses. Furthermore, this work might contribute to the understanding of variations in Devonian reef margin and platform-top architecture, relevant for petroleum exploration and development in the global Devonian hydrocarbon resources