Sedimentary 12-n-Propylcholestanes, Molecular Fossils Diagnostic of Marine Algae

Organic geochemistry of the middle Paleozoic Ora Formation in Iraq: Implications for source rock assessment and hydrocarbon potentiality

The Ora Formation (late Devonian-early Carboniferous) is thought to be a potential source rocks for the Paleozoic petroleum system of Iraq. The source potential from the Ora Formation is evaluated for the first time ever in this study from western and northern Iraq which integrates data from organic geochemistry including Total Organic Carbon (TOC) analysis, HAWK pyrolysis, gas chromatography (GC), and gas chromatography mass spectrometry (GC-MS) and mineralogical X-ray diffraction and scanning electron microscopy. The shale and muddy carbonate succession within the Ora Formation from surface section in northernmost Iraq and subsurface section from two wells (Akkas-1 and Akkas -3) from western Iraq have been employed to assess the source rock potentiality, thermal maturity, kerogen type, organic content, and depositional environment. In addition to organic geochemical analyses, mineralogical XRD and SEM-EDS were used to support the paleoenvironmental interpretation of the Ora Formation. The results from TOC and HAWK analyses reveal that the Ora Formation ranges from poor to good as a source rock. However, the HAWK data suggests that the surface samples from northernmost Iraq are highly mature, highly weathered, or both. Kerogen analysis revealed that the Ora Formation contains immature type III and mixed II-III kerogens. Low TOC values were attributed to factors such as significant clastic input, weathering effects, and the prevailing oxic environment during deposition. The presence of detrital influx of quartz and feldspars, along with the occurrence of illite and kaolinite clay minerals, suggest a detrital input with weathering influence under hot arid and warm humid conditions. Biomarker analysis of the light hydrocarbons using GC and GC-MS revealed that these light hydrocarbons were generated from marine planktonic algae sources, possibly with some contributions from terrestrial and/or microbially reworked organic matter. These high mature light hydrocarbons in subsurface section were originated from anoxic marine shale source rocks. They were most likely from the Cambro-Ordovician Khabour Formation and were contaminated from another source.

The characterisation and provenance of crude oils stranded on the South Australian coastline. Part II: Potential parent petroleum systems

In 2014-2016 more than 600 specimens of semi-solid crude oil were recovered from 30 ocean beaches along the coastline of South Australia, as part of the recently completed Great Australian Bight Research Program. All are believed to be products of submarine oil seepage. Their source-specific biomarker signatures provide the basis for their assignment to sixteen oil families, some previously unrecognised. Two of these families (asphaltite and asphaltic tar) likely originated from Cretaceous marine source rocks in the offshore Bight Basin. The others comprise waxy oils of lacustrine, fluvio-deltaic and marine source affinity. Their biomarker characteristics do not match those of any Australian crude oil. However, they are strikingly similar to those of oils found in Cenozoic and Mesozoic basins throughout the Indonesian Archipelago and elsewhere in Southeast Asia.

Biomarker stratigraphy in the Athel Trough of the South Oman Salt Basin at the Ediacaran-Cambrian Boundary

The South Oman Salt Basin (SOSB) has been studied extensively for knowledge concerning the habitat of the enigmatic Ediacaran-Cambrian oils that are produced from that region. Geological, geochemical, geophysical, and geochronological investigations have all contributed to improved understanding of the range of late Neoproterozoic depositional environments recorded there. Of particular interest has been the deep Athel depocenter within the SOSB that features a silica-rich interval known as the Al Shomou Member or Athel Silicilyte and the co-eval A4 carbonate-evaporite sequence that straddles the Ediacaran-Cambrian boundary. The deep basin has been suggested to be anoxic and euxinic based on studies of sulfur isotopes, trace metal distributions and other proxies. Organic geochemistry has provided some clues concerning aspects of the depositional environments and microbial communities prevailing during this interval. However, ambiguities remain including a paucity of convincing molecular evidence for euxinia in the photic zone of the basin. Here, we present a comprehensive study of biomarker hydrocarbons, including steroids, triterpenoids, and carotenoids. Among the compounds detected is a distinctive array of aromatic carotenoids. Relatively low abundances of monoaromatic carotenoids, such as chlorobactane, okenane, and β-isorenieratane, suggest the possibility of transient photic zone euxinia with a shallow chemocline or, perhaps, exogenous inputs from microbial mats. However, it is the dominance of renieratane and renierapurpurane over isorenieratane in diaromatic carotenoids and their association with abundant C₃₈ and C₃₉ carotenoids that identifies cyanobacteria as major contributors to the inventory of carotenoids. Our results, based on multiple lines of molecular evidence and statistical analysis, also suggest that the Athel Silicilyte was biogeochemically distinct from the other units of the Ara Group. Overall, our study has important implications for understanding other late Neoproterozoic depositional environments.

A stable and productive marine microbial community was sustained through the end-Devonian Hangenberg Crisis within the Cleveland Shale of the Appalachian Basin, United States

The end-Devonian Hangenberg Crisis constituted one of the greatest ecological and environmental perturbations of the Paleozoic Era. To date, however, it has been difficult to precisely constrain the occurrence of the Hangenberg Crisis in the Appalachian Basin of the United States and thus to directly assess the effects of this crisis on marine microbial communities and paleoenvironmental conditions. Here, we integrate organic and inorganic chemostratigraphic records compiled from two discrete outcrop locations to characterize the onset and paleoenvironmental transitions associated with the Hangenberg Crisis within the Cleveland Shale member of the Ohio Shale. The upper Cleveland Shale records both positive carbon (δ¹³ C_org ) and nitrogen (δ¹⁵ N_total ) isotopic excursions, and replenished trace metal inventories with links to eustatic rise. These dual but apparently temporally offset isotope excursions may be useful for stratigraphic correlation with other productive end-Devonian epeiric marine locations. Deposition of the black shale succession occurred locally beneath a redox-stratified water column with euxinic zones, with signs of strengthening denitrification during the Hangenberg Crisis interval, but with an otherwise stable and algal-rich marine microbial community structure sustained in the surface mixed layer as ascertained by lipid biomarker assemblages. Discernible trace fossil signals in some horizons suggest, however, that bioturbation and seafloor oxygenation occurred episodically throughout this succession and highlight that geochemical proxies often fail to capture these rapid and sporadic redox fluctuations in ancient black shales. The paleoenvironmental conditions, source biota, and accumulations of black shale are consistent with expressions of the Hangenberg Crisis globally, suggesting this event is likely captured within the uppermost strata of the Cleveland Shale in North America.

Collagens of Poriferan Origin

The biosynthesis, structural diversity, and functionality of collagens of sponge origin are still paradigms and causes of scientific controversy. This review has the ambitious goal of providing thorough and comprehensive coverage of poriferan collagens as a multifaceted topic with intriguing hypotheses and numerous challenging open questions. The structural diversity, chemistry, and biochemistry of collagens in sponges are analyzed and discussed here. Special attention is paid to spongins, collagen IV-related proteins, fibrillar collagens from demosponges, and collagens from glass sponge skeletal structures. The review also focuses on prospects and trends in applications of sponge collagens for technology, materials science and biomedicine.

Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran-Cambrian boundary, Sultanate of Oman

The Athel silicilyte is an enigmatic, hundreds of meters thick, finely laminated quartz deposit, in which silica precipitated in deep water (>~100-200 m) at the Ediacaran-Cambrian boundary in the South Oman Salt Basin. In contrast, Meso-Neoproterozoic sinks for marine silica were dominantly restricted to peritidal settings. The silicilyte is known to contain sterane biomarkers for demosponges, which today are benthic, obligately aerobic organisms. However, the basin has previously been described as permanently sulfidic and time-equivalent shallow-water carbonate platform and evaporitic facies lack silica. The Athel silicilyte thus represents a unique and poorly understood depositional system with implications for late Ediacaran marine chemistry and paleoecology. To address these issues, we made petrographic observations, analyzed biomarkers in the solvent-extractable bitumen, and measured whole-rock iron speciation and oxygen and silicon isotopes. These data indicate that the silicilyte is a distinct rock type both in its sedimentology and geochemistry and in the original biology present as compared to other facies from the same time period in Oman. The depositional environment of the silicilyte, as compared to the bounding shales, appears to have been more reducing at depth in sediments and possibly bottom waters with a significantly different biological community contributing to the preserved biomarkers. We propose a conceptual model for this system in which deeper, nutrient-rich waters mixed with surface seawater via episodic mixing, which stimulated primary production. The silica nucleated on this organic matter and then sank to the seafloor, forming the silicilyte in a sediment-starved system. We propose that the silicilyte may represent a type of environment that existed elsewhere during the Neoproterozoic. These environments may have represented an important locus for silica removal from the oceans.

Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth

The period 800-717 million years (Ma) ago, in the lead-up to the Sturtian Snowball glaciation, saw an increase in the diversity of eukaryotic microfossils. To afford an independent and complementary view of this evolutionary period, this study presents the distribution of eukaryotic biomarkers from three pre-Sturtian successions across the supercontinent Rodinia: the ca. 780 Ma Kanpa Formation of the Western Australian Officer Basin, the ca. 800-740 Ma Visingsö Group of Sweden, and the 740 Ma Chuar Group in Arizona, USA. The distribution of eukaryotic steranes is remarkably similar in the three successions but distinct from all other known younger and older sterane assemblages. Cholestane was the only conventional structure, while indigenous steranes alkylated in position C-24, such as ergostane, stigmastane, dinosterane and isopropylcholestane, and n-propylcholestane, were not observed. This sterane distribution appears to be age diagnostic for the pre-Sturtian Neoproterozoic. It attests to the distinct evolutionary state of pre-Snowball eukaryotes, pointing to a taxonomic disparity that was still lower than in the Ediacaran (635-541 Ma). All three basins also show the presence of a new C28 sterane that was tentatively identified as 26-methylcholestane, here named cryostane. The only known extant organisms that can methylate sterols in the 26-position are demosponges. This assignment is plausible as molecular clocks place the appearance of the earliest animals into the pre-Sturtian Neoproterozoic. The unusual 26-methylsterol may have protected sponges, but also other eukaryotes, against their own membranolytic toxins. Some protists release lytic toxins to deter predators and kill eukaryotic prey. As conventional membrane sterols can be the site of attack for these toxins, sterols with unusual side-chain modification protect the cell. This interpretation of cryostane supports fossil evidence of predation in the Chuar Group and promotes hypotheses about the proliferation of eukaryophagy in the lead-up to the Cryogenian.

Sterol and genomic analyses validate the sponge biomarker hypothesis

Molecular fossils (or biomarkers) are key to unraveling the deep history of eukaryotes, especially in the absence of traditional fossils. In this regard, the sterane 24-isopropylcholestane has been proposed as a molecular fossil for sponges, and could represent the oldest evidence for animal life. The sterane is found in rocks ∼650-540 million y old, and its sterol precursor (24-isopropylcholesterol, or 24-ipc) is synthesized today by certain sea sponges. However, 24-ipc is also produced in trace amounts by distantly related pelagophyte algae, whereas only a few close relatives of sponges have been assayed for sterols. In this study, we analyzed the sterol and gene repertoires of four taxa (Salpingoeca rosetta, Capsaspora owczarzaki, Sphaeroforma arctica, and Creolimax fragrantissima), which collectively represent the major living animal outgroups. We discovered that all four taxa lack C30 sterols, including 24-ipc. By building phylogenetic trees for key enzymes in 24-ipc biosynthesis, we identified a candidate gene (carbon-24/28 sterol methyltransferase, or SMT) responsible for 24-ipc production. Our results suggest that pelagophytes and sponges independently evolved C30 sterol biosynthesis through clade-specific SMT duplications. Using a molecular clock approach, we demonstrate that the relevant sponge SMT duplication event overlapped with the appearance of 24-isopropylcholestanes in the Neoproterozoic, but that the algal SMT duplication event occurred later in the Phanerozoic. Subsequently, pelagophyte algae and their relatives are an unlikely alternative to sponges as a source of Neoproterozoic 24-isopropylcholestanes, consistent with growing evidence that sponges evolved long before the Cambrian explosion ∼542 million y ago.

Seawater Incursion Events in a Cretaceous Paleo-lake Revealed by Specific Marine Biological Markers

Many large paleo-lakes in North China were formed after the Triassic Era. Seawater incursion events (SWIEs) in these lakes have been extensively discussed in the literature, yet lack reliable methodology and solid evidence, which are essential for reconstructing and confirming SWIEs. The present study employs specific marine biological markers (24-n-propyl and 24-isopropyl cholestanes) to trace SWIEs in a dated core taken from the Songliao Basin (SLB). Two SWIEs were identified. The first SWIE from 91.37 to 89.00 Ma, was continuous and variable but not strong, while the second SWIE from 84.72 to 83.72 Ma was episodic and strong. SWIEs caused high total organic carbon (TOC) and negative δ¹³C_org values in the sediments, which were interpreted as an indication of high productivity in the lake, due to the enhancement of nutrient supplies as well as high levels of aqueous CO₂, due to the mixing of alkaline seawater and acidic lake water. The SWIEs in SLB were controlled by regional tectonic activity and eustatic variation. Movement direction changes of the Izanagi/Kula Plate in 90 Ma and 84 Ma created faults and triggered SWIEs. A high sea level, from 90 to 84 Ma, also facilitated the occurrence of SWIEs in SLB.

Genetic biomarkers of the sterol-biosynthetic pathway in microalgae

Sterols are cyclic isoprenoid lipids present in all eukaryotes. These compounds have been used to determine the composition of algal communities in marine and lake environments, and because of their preservation potential have been used to reconstruct the evolution of eukaryotes. In the last years, there have been major advances in understanding the sterol biosynthetic pathways and the enzymes involved. Here, we have explored the diversity and phylogenetic distribution of the gene coding the cycloartenol synthase (CS), a key enzyme of the phytosterol biosynthetic pathway. We propose a gene-based approach that can be used to assess the sterol-forming potential of algal groups. CS coding gene was annotated in genomes of microalgae using protein homology with previously annotated CS sequences. Primers for the detection of CS gene sequences of diatoms, one of the most dominant groups of microalgae, were designed and evaluated in cultures and environmental samples. A comparison of the phylogeny of the recovered CS sequences in combination with sequence data of the gene rbcL coding for the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) demonstrates the potential of the CS gene as phylogenetic marker, as well as an indicator for the identity of sterol-producing organisms in the environment.

The Namibian and Brazilian southern South Atlantic petroleum systems: are they comparable analogues?

Tectonic reconstructions made across the southern South Atlantic Ocean indicate a diversity of rift and drift basin characteristics on the conjugate margins that define them as different stratigraphic and structural entities. In terms of petroleum systems, the basins are not as unlike as some characteristics suggest. Given the lack of significant hydrocarbon discoveries to date south of the Walvis Ridge, doubts have been cast on the presence in this area of the prolific Lower Cretaceous lacustrine and marine source rock systems, which are well known in the Greater Campos Basin and offshore Angola. Oils and condensates from the basins south and north of the Walvis Ridge exhibit geochemical similarities suggesting that comparable source rock systems are present in both areas. The condensate geochemical analysis results from the Kudu Field in Namibia are compared with oils from marine and lacustrine sources in Brazil, indicating that the Kudu condensates are derived from at least two different source rocks. These results suggest that the underexplored basins offshore Namibia contain thermally mature Lower Cretaceous lacustrine and marine source rocks, offering a new frontier for petroleum exploration in Africa's southern South Atlantic.

Sandblasted-acid-etched titanium surface influences in vitro the biological behavior of SaOS-2 human osteoblast-like cells

Osseointegrated dental implants have been successfully used over the past several years, allowing functional replacement of missing teeth. Surface properties of titanium dental implants influence bone cell response. Implant topography appears to modulate cell growth and differentiation of osteoblasts thus affecting the bone healing process. Optimal roughness and superficial morphology are still controversial and need to be clearly defined. In the present study we evaluated in vitro the biological behavior of SaOS-2 cells, a human osteoblast-like cell line, cultured on two different titanium surfaces, smooth and sandblasted-acid-etched, by investigating cell morphology, adhesion, proliferation, expression of some bone differentiation markers and extracellular matrix components. Results showed that the surface topography may influence in vitro the phenotypical expression of human osteoblast-like cells. In particular the tested sandblasted-acid-etched titanium surface induced a significantly increased Co I deposition and α2-β1 receptor expression as compared to the relatively smooth surface, promoting a probable tendency of SaOS-2 cells to shift toward a mature osteoblastic phenotype. It is therefore likely that specific surface properties of sandblasted-acid-etched titanium implants may modulate the biological behavior of osteoblasts during bone tissue healing.

Unravelling ancient microbial history with community proteogenomics and lipid geochemistry

Our window into the Earth's ancient microbial past is narrow and obscured by missing data. However, we can glean information about ancient microbial ecosystems using fossil lipids (biomarkers) that are extracted from billion-year-old sedimentary rocks. In this Opinion article, we describe how environmental genomics and related methodologies will give molecular fossil research a boost, by increasing our knowledge about how evolutionary innovations in microorganisms have changed the surface of planet Earth.

Fossil steroids record the appearance of Demospongiae during the Cryogenian period

The Neoproterozoic era (1,000-542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C(30) sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation ( approximately 635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, approximately 713 Myr ago in Oman).

Sterols in red and green algae: quantification, phylogeny, and relevance for the interpretation of geologic steranes

Steroids, a class of triterpenoid lipids with high preservation potential, are widely distributed in sedimentary rocks. All eukaryotes have a physiological requirement for these molecules, making steroids important biomarkers for aiding our understanding of eukaryote molecular evolution and geologic history. C(26)-C(30) sterols are the molecules most commonly incorporated or synthesized by eukaryotes, and correspond to C(26)-C(30) steranes ubiquitously and abundantly preserved in petroleums and sedimentary bitumens. Because these sterols occur in evolutionarily diverse taxa, it can be difficult to associate any particular compound with a single group of organisms. Nevertheless, geochemists have still been able to draw parallels between the empirical patterns in geologic sterane abundances and the age of petroleum source rocks. Paleobiologists have also used sterane data, in particular the patterns in C(29) and C(28) steranes, to support fossil evidence of an early radiation of green algae in latest Proterozoic and Paleozoic and the succession of the major modern phytoplankton groups in the Mesozoic. Although C(29) sterols are found in many eukaryotes, organisms that produce them in proportional abundances comparable to those preserved in Proterozoic and Paleozoic rocks are limited. Based on a large, phylogenetically based survey of sterol profiles from the kingdom Plantae, we conclude that modern ulvophyte and early diverging prasinophyte green algae produce high abundances of C(29) relative to C(27) and C(28) sterols most consistent with the sterane profiles observed in Paleozoic rocks. Our analysis also suggests that ancestral stem groups among the Plantae, including the glaucocystophytes and early divergent red algae are also plausible candidates.

A molecular and isotopic study of the organic matter from the Paris Basin, France

Thirteen Liassic sedimentary rocks of increasing depth and three petroleums from the Paris Basin were studied for 13C/12C isotopic compositions and biological markers, including steranes, sterenes, methylphenanthrenes, methylanthracenes, and triaromatic steroids. The isotopic compositions of n-alkanes from mature sedimentary rocks and petroleums fall in a narrow range (2%), except for the deepest Hettangian rock and the Trias petroleum, for which the short-chain n-alkanes are enriched and depleted in 13C, respectively. Most of the molecular parameters increase over the 2000-2500 m depth range, reflecting the transformation of the organic matter at the onset of petroleum generation. In this zone, carbonate content and carbon isotopic composition of carbonates, as well as molecular parameters, are distinct for the Toarcian and Hettangian source rocks and suggest a migration of organic matter from these two formations. Two novel molecular parameters were defined for this task: one using methyltriaromatic steroids from organic extracts; the other using 1-methylphenanthrene and 2-methylanthracene from kerogen pyrolysates. The anomalous high maturity of the Dogger petroleum relative to the maturity-depth trend of the source rocks is used to estimate the minimal vertical distance of migration of the organic matter from the source rock to the reservoir.