Early Diagenetic Transformation Research Articles

Contact metamorphic reactions and fluid–rock interactions related to magmatic sill intrusion in the Guaymas Basin

Abstract. Igneous basaltic intrusions into young organic-rich sedimentary basins have a major impact not only on the carbon cycle but also on major and trace element transfers between deep and superficial geological reservoirs. The actively rifting Guaymas Basin in the Gulf of California, which was drilled by the International Ocean Discovery Program during Expedition 385, represents the nascent stage of an ocean characterized by siliceous organic-rich sediments (diatom ooze) intruded by a very dense network of basaltic sills. This study focuses on Site U1546 where the relatively high geothermal gradient (over 200 ∘C km−1) induces early diagenetic transformations in both pore waters and sediments, involving sulfide, carbonate and silica. Geochemical and mineralogical characterizations of the sediment at sill contacts indicate that sulfides and silica polymorphs are the main phases impacted by contact metamorphism, being evident by a transition from opal-CT to quartz and pyrite to pyrrhotite, respectively. Mass balance calculations have been used to estimate mass transfers in metamorphic aureoles. In the top contact aureole, predominantly isochemical metamorphism is reflected by the presence of authigenic quartz and disseminated 20–50 µm sized pyrrhotite crystals, filling primary interstitial space, and partial dissolution of detrital feldspar grains. In the bottom contact aureole, quartz and euhedral pyrrhotite crystals occur, which are up to 4 times larger than those at the top contact. Significant metamorphism of sediments is observed in the lower contact aureole, where plagioclase recrystallizes around the detrital feldspars and locally euhedral pyroxenes are included in patches of carbonate cement; this suggests precipitation from carbon-rich fluids at temperatures (T) higher than 300 ∘C. The lower contact aureole also is more enriched in CaO, Na2O, Fe2O3 and trace elements (Cu, As, Zn, etc.) compared to the upper contact. Based on these petrological investigations, a conceptual model of magma–sediment–fluid interaction is proposed distinguishing top and bottom contact processes. Initial contact metamorphism due to sill emplacement is characterized by dehydration reactions in sediments and crystallization of new minerals. It was followed by carbonate precipitation from the released fluids. At a final stage, the temperature re-equilibrated with the geothermal gradient and the rocks were further altered by hydrothermal fluids.

Critical assessment of U, Ba and Ni as redox and productivity proxies in organic-rich sediments underneath dynamic, highly productive waters

Sediments of the continental shelf anoxic zones of the Benguela upwelling system (BUS) and the Peruvian upwelling system are present-day hotspots of trace element accumulation. However, contribution of the lithogenic trace element fraction and early diagenetic transformation processes are poorly constrained. The identification of source and accumulation mechanisms is necessary for the validation of trace elements as proxies for productivity and redox cycling, notably in highly dynamic upwelling systems such as the BUS. Here, we analyzed redox- and biosensitive elements (U, Ba, Ni), lithogenic tracers (Al, Ti, Zr), total organic carbon (TOC) and P in eleven short sediment cores from the Namibian shelf (ca. 22–25°S) as well as grain size fractionated hinterland samples from the Tsauchab Valley at Sossusvlei (∼25°S). These samples help to constrain the lithogenic trace element contributions, a prerequisite for a realistic interpretation of marine authigenic trace element data. Our findings corroborate previous findings that Zr is a sensitive tracer of the coarse fraction in marine sediment for dust input and/or sediment reworking. Hence, the combined analysis of the coarse fraction (Zr), organic matter, and P enrichments (TOC/P) differentiates between a calm, organic matter-rich central shelf environment and a more energetic phosphorite-rich southern shelf environment. A significant correlation of U with P in cores from the southern shelf corroborates previous findings of U incorporation into apatite, the initial formation of which requires oscillating oxic to sulfidic redox conditions. Non-apatite associated U dominates in the cores from the central shelf, where it is only enriched in the buried, anoxic parts of the sediment. This also supports oscillating oxic to sulfidic redox conditions in surface sediment, where U may be recycled. Hence, U accumulates either (i) in apatite under oscillating oxic to sulfidic conditions or (ii) in buried anoxic sediment sections. This strongly questions the use of U as indicator of suboxic conditions but rather anoxic conditions. While lithogenic fractions of U were negligible, the lithogenic fractions of Ba and Ni were found to be elevated. The calculation of authigenic Ba when accounting for lithogenic Ba from the Sossusvlei fine fractions gives more realistic authigenic Ba values. The high Ba enrichment in the BUS is interpreted as uptake of Ba by diatoms and/or nucleation of barite in P-rich diatom remains, as suggested previously. Given the shallow water depth of the cores, barite formation must already take place in subsurface waters (<50 m water depth) as opposed to previous suggesting greater water depths. The lithogenic background of Ni strongly varies from 23°S to 25°S based on Sossusvlei data and the literature. When authigenic Ni contents are calculated accordingly and plotted versus TOC, more systematic trends are seen (compared to total Ni versus TOC). Essentially all cores show an increase in the authigenic Ni/TOC ratio with sediment depth suggesting better preservation and retention of Ni as compared to TOC consistent with previous observations in sediments from the Peruvian upwelling system. This trend corroborates the use of Ni as a productivity indicator for upwelling sediments.

Early diagenetic transformation stages revealed by micro-analytical studies of shelly phosphorites, Rakvere region

Early diagenetic transformation stages revealed by micro-analytical studies of shelly phosphorites, Rakvere region

From biogenic silica and organic matter to authigenic clays and dolomite: Insights from Messinian (upper Miocene) sediments of the Northern Mediterranean

AbstractThe biogeochemical cycles of carbon and silicon are tightly coupled in modern marine environments due to the pivotal role of planktonic diatoms. Once diatoms are sedimented, the fate of organic matter and biogenic silica is initially governed by bottom water oxygen levels and bacterial communities involved in remineralization processes. The early diagenesis of biosiliceous sediments may result in drastic changes in composition, sometimes hampering palaeoenvironmental reconstruction. Sedimentary successions deposited in the Mediterranean region during the Messinian salinity crisis (5.97–5.33 Ma) allow to explore the early diagenetic transformation of organic matter and biogenic silica in a restricted basin experiencing a severe palaeoceanographic turnover. Sedimentological and petrographic observations coupled to elemental, mineralogical, inorganic and organic geochemical analyses were carried out on biosiliceous (diatomaceous shales and diatom‐bearing mudstones) and associated clay‐rich and dolomite‐rich sediments (dolomitic mudstones) interbedded with primary gypsum layers in the Piedmont Basin (north‐west Italy). The state of preservation of biogenic silica was governed by different pathways of organic matter remineralization, depending on bottom and pore water redox conditions, which were controlled by the structure of the water column. Aerobic respiration of organic matter in a mixed water column and an oxygenated seafloor promoted biogenic silica preservation. In contrast, bottom water anoxia induced by permanent stratification of the water column favoured the concomitant formation of dolomite and authigenic clays. In particular, organic matter degradation through bacterial sulphate reduction increased pore water alkalinity, promoting the precipitation of dolomite. At the same time, the rise in pH promoted the dissolution of biogenic silica which, reacting with pore water cations, ultimately caused the formation of authigenic clays. This study suggests that the apparent annihilation of Mediterranean marine biota during the Messinian salinity crisis partially reflects an early diagenetic bias produced by interactions of the carbon, silicon and sulphur biogeochemical cycles in a restricted basin.

The diagenetic continuum of hopanoid hydrocarbon transformation from early diagenesis into the oil window

Hopanoid molecules are ubiquitous in sedimentary rocks and make up a significant proportion of sedimentary organic matter, oils, and bitumen. Due to their relatively stable chemical structure, they are generally well preserved in the rock record, making them extremely useful as biomarkers or geomarkers. Despite extensive industry and scientific interest, the early phase of their eogenetic and early diagenetic transformation has not been fully demonstrated or examined in a geologic setting. Most previous studies have focused on the oil window range from about 0.5–1.0 %VRo, and neglected transformations that happen at maturity levels below this. Additionally, the geological transformation of hopanoids has been extensively applied as a geochemical indicator of thermal maturity, however the mechanisms that result in these transformations are not fully understood.A major stumbling block in the study of hopanoid diagenesis is the availability of well constrained samples along a single stratigraphic horizon from very low maturity and through the oil window. This study utilizes a natural thermal maturity transect along a single stratigraphic horizon which stretches from thermally immature rocks, up to the middle of the oil window. The purpose of this study is to document the progressive changes in abundance of hopanoid hydrocarbon compound classes and between individual isomers with increasing thermal transformation. Samples for this study were taken from cores of the Upper Cretaceous Second White Specks Formation, a major source rock within the Western Canadian Sedimentary Basin, that has been extensively mapped and studied. This sample set represents a unique opportunity to examine the changes in hopanoid class with increasing thermal maturity.69 samples from 8 wells were examined for biomarkers. Thermal maturity was determined using HAWK programmed pyrolysis analysis of 87 samples from 9 wells. These geochemical methods were combined with a well established stratigraphic framework to ensure that sampling methods were stratigraphically controlled. Neohopenes, hopenes, ββ-hopanes, βα-hopanes, αβ-hopanes, and rearranged hopanes were differentiated and drastic changes in the proportions of these compound classes were observed with increasing thermal maturity. Thermally immature rocks are dominated by hopenes, neohopenes, and ββ-hopanes, whereas the middle of the oil window is dominated by αβ-hopanes and rearranged hopanes. These results allow a detailed determination of the maturity ranges that correspond to the transformation or disappearance of specific hopanoid molecule classes, for example the loss of hopenes in the maturity range of 0.28–0.35 %VRE. Additionally, this study allows the stages of episodic or punctuated transformations of hopanoid classes to be better delineated and narrowed down to specific maturity ranges. This work represents a novel examination of a natural thermal maturity transect and helps to consolidate our understanding of the early diagenetic transformations of hopanoid compounds.

Biomarkers as indicators of sedimentary organic matter sources and early diagenetic transformation of pentacyclic triterpenoids in a tropical mangrove ecosystem

Mangrove vegetation covers extensive areas along Brazilian tropical coasts and accumulates large amounts of organic carbon in the intertidal sediments. We have investigated the molecular biomarker composition of mangrove sediments from the Potengi estuary North-East Brazil. To characterise sources and fate of sedimentary organic matter (OM), a direct analytical pyrolysis approach was used. The sediment pyrolysates yielded homologous series of aliphatic compounds (n-alkane/n-alkene doublets, n-alkanoic acid and n-alkan-2-ones), triterpenoids and lignin-derived methoxphenols, indicating that most of the sedimentary OM input originates from terrestrial vascular plants. High abundance of long-chain n-alk-1-ene series with an even carbon number predominance peaking at C28:1 ―most likely originated from local mangrove vegetation― is found co-eluted with the saturated odd carbon n-alkane series. The occurrence of lignin and n-alkan-2-one biomarkers in the sediments has provided parallel information about the input from vascular plants dominating the intertidal zone. This was further corroborated by the presence of the triterpenols (β-amyrin, and germanicol), that provided chemotaxonomic information on mangrove derived leaf wax in sedimentary OM. The unsaturated triterpenoid including teraxerol acetate, olean-12-ene, olean-18-ene, oleana-11, 13(18)-diene, a-neoursa-3(5), 12-diene and aneooleana-3(5), 12-diene, were also observed in sediment pyrolysates. The presence of these unsaturated pentacyclic triterpenoids revealed an early diagenetic alteration of terrestrial OM in the sediments. This study has demonstrated that routine application of analytical pyrolysis may provide important insight into the sources of sedimentary OM and its diagenetic fate in mangrove intertidal sediments.

Potential Fossilized Sulfide-Oxidizing Bacteria in the Upper Miocene Sulfur-Bearing Limestones From the Lorca Basin (SE Spain): Paleoenvironmental Implications.

The sulfur-bearing limestones interbedded in the upper Miocene diatomaceous sediments (Tripoli Formation) of the Lorca Basin (SE Spain) are typified, as other Mediterranean coeval carbonate and gypsum deposits, by filamentous, circular and rod-shaped microstructures of controversial origin. These features have been interpreted both as fecal pellets of brine shrimps and/or of copepods, remains of algae or cyanobacteria and fossilized sulfide-oxidizing bacteria. To shed light on their origin, a multidisciplinary study including optical, UV and scanning electron microscopy, Raman microspectroscopy, and geochemical (carbon and oxygen stable isotopes) analyses has been carried out on three carbonate beds exposed along the La Serrata ridge. The different composition of the filamentous and circular objects with respect to the rod-shaped microstructures suggest that the former represent remains of bacteria, while the latter fecal pellets of deposit- or suspension-feeder organisms. Size and shape of the filamentous and circular microfossils are consistent with their assignment to colorless sulfide-oxidizing bacteria like Beggiatoa (or Thioploca) and Thiomargarita, which is further supported by the presence, only within the microfossil body, of tiny pyrite grains. These grains possibly result from early diagenetic transformation of original sulfur globules stored by the bacteria, which are a diagnostic feature of this group of prokaryotes. The development of microbial communities dominated by putative sulfide-oxidizing bacteria at Lorca was favored by hydrogen sulfide flows generated through degradation of organic matter by sulfate-reducing bacteria thriving in underlying organic-rich sediments.

Early diagenetic sequestration of microbial mat lipid biomarkers through covalent binding into insoluble macromolecular organic matter (IMOM) as revealed by sequential chemolysis and catalytic hydropyrolysis

Analyses of lipids in modern microbial mat ecosystems provide valuable insights into the taxonomic affinities of the dominant biological producers and consumers as well as carbon flow within the mat community. Such microbial mat biomarker assemblages also provide a window into the ancient biomarker record, facilitating paleobiological and paleoenvironmental reconstructions of analogous ecosystems on early Earth. Our focus was to investigate the covalent binding of lipid biomarkers into insoluble macromolecular organic matter (IMOM) during diagenesis in the well-studied hypersaline microbial mat ecosystems and underlying sediments at Guerrero Negro, Baja California Sur, Mexico. Following exhaustive solvent extraction, three different chemical degradation reagents of varying reactivity (acid methanolysis, trichloroacetic acid extraction, and periodate oxidation) were applied to two shallow sedimentary layers prior to fragmentation of the recalcitrant insoluble residues using catalytic hydropyrolysis (HyPy). The hydrocarbons released by HyPy included a complex variety of linear, branched and polycyclic alkane structures, including hopanes, methylhopanes and steranes. Our findings indicate that a significant fraction of the bound biomarker pool was strongly linked by covalent binding through functional groups into IMOM but that a portion of this bound pool was not recoverable by chemolysis treatment. These results provide new insights about the mode and timing of chemical binding of steroids and hopanoids, and their early diagenetic transformation products, into IMOM. The formation of sedimentary IMOM from the earliest stages of organic matter diagenesis, commencing on a timescale of only years, aids the long-term preservation of biomarker lipids in the geological record.

Source rock potential and depositional environment of Upper Cretaceous sedimentary rocks, Abu Gharadig Basin, Western Desert, Egypt: An integrated palynological, organic and inorganic geochemical study

The Abu Gharadig Basin in the northern part of the Western Desert, Egypt is among the most important petroleum provinces in Egypt. Here, Cenomanian to Santonian rocks of Bahariya Formation and Abu Roash A-G members from the GPT-3 well were investigated for their depositional environment, kerogen quality, petroleum generation potential and thermal maturity by geochemical, petrological and palynological methods. The sediments of the Bahariya and Abu Roash formations excluding the Abu Roash “F” Member represent variable shallow marine environments with poor preservation of marine organic matter, whereas there is an excellent preservation in the Abu Roash “F” Member. The basal part of this member is characterized by anoxic, carbonate-rich depositional conditions, high TOC values up to 7%, high HI up to 700 mgHC/gTOC and liptinite-dominated organic matter. Depletion of iron leads to sulfur incorporation into organic matter which is reflected in high thiophene/benzene ratios. Above, sediments are enriched in “terrestrial elements” Fe, Ti, as well as K and Mn. This pattern and the occurrence of the fresh/brackish water algae Botryococcus suggests a regression phase during deposition. The upper part of the Abu Roash “F” Member is again characterized by fully marine, suboxic conditions and a lower thiophene/benzene ratio. The source rock section demonstrates lower thermal maturity compared to the above and below sections based on all microscopic, pyrolysis and biomarker data. This indicates thermal maturity retardation/suppression most likely due to a different organic facies and early diagenetic transformation of kerogen as indicated by the geochemical and palynological data. The source rock heterogeneity indicates a relatively shallow marine environment where the changes in bottom water conditions are very sensitive to sea level fluctuations. Residual oil characterization reveals two reservoir compartments, which are in the Abu Roash “D” and “C” members.The Abu Roash “F” source rocks are compared with time-equivalent sediments in the Tarfaya Basin in Morocco, which represent more distal settings. The more proximal group (A) is characterized by S/Fe ratios between 0.57 and 0.67 indicating suboxic conditions. It has TOC and HI values not exceeding 4% and 600 mgHC/gTOC, respectively, at variable CaCO3 contents. The more distal Tarfaya sediments (group B) have higher TOC and HI as well as high organic sulfur contents. Group A is higher in terrigenous element concentrations. The Tmax of immature source rocks ranges from 410 to 415°C in organic‑sulfur rich samples and from 420 to 430°C in organic‑sulfur poor samples revealing an important impact of organic facies on maturity parameters. Furthermore, there is an inverse relationship between S/Fe and Al2O3/TOC which might become an important tool in paleoenvironmental reconstructions as well as petroleum source rock studies.

Compositional aspects of herbaceous litter decomposition in the freshwater marshes of the Florida Everglades

Litter decomposition in wetlands is an important component of ecosystem function in these detrital systems. In oligotrophic wetlands, such as the Florida Everglades, litter decomposition processes are dependent on nutrient availability and litter quality. The aim of this study was to assess the differences and changes in chemical composition of above- and belowground plant tissues at different stages of decomposition, and to compare them to organic matter accumulating in wetland surface soils. To understand the chemical changes occurring during the early stages of litter decomposition in wetlands, short-term subaqueous decomposition patterns of above- and belowground tissues from Cladium jamaicense and Eleocharis cellulosa were investigated at two freshwater marsh sites in the Florida Everglades. The composition of litter at different stages of decomposition was compared to that of the two end-members, namely fresh plant tissues and soil organic matter (SOM), in an effort to assess both the gradual transformation of this organic matter (OM) and the incorporation of above- vs. belowground biomass to wetland soils. The chemical composition of the litter and of surface soils was assessed using solid-state 13C nuclear magnetic resonance spectroscopy. Decomposition indices (alkyl/O-alkyl ratio, Aromaticity index) of Cladium and Eleocharis leaves varied during incubation likely reflecting physical leaching processes followed by a shift to microbial decomposition. Overall, Eleocharis leaves were more labile compared to Cladium leaves. Relative to aboveground litter, the belowground biomass of both species was more resistant to degradation, and roots were more resistant than rhizomes. Compared to the observed early diagenetic transformations of the plant litter, the SOM is at a more advanced stage of degradation, suggesting that the decomposition of litter and belowground biomass prior to its incorporation into wetland soils requires longer degradation times than those applied in this study. Litter decomposition in Everglades’ freshwater marshes is driven by a combination of tissue quality and site characteristics such as hydroperiod and nutrient availability, ultimately leading to the accumulation of peat.

MICRO‐ AND NANOPORES IN TIGHT ZECHSTEIN 2 CARBONATE FACIES FROM THE SOUTHERN PERMIAN BASIN, NW EUROPE

The study evaluates pore systems in samples of tight Upper Permian Zechstein 2 Carbonate (Z2C) facies from widely dispersed locations in the eastern and western parts of the Southern Permian Basin, NW Europe. Samples of Z2C drill cores comprising platform to shallow‐basin deposits were examined by petrographic techniques, porosity measurement and SEM analysis, in order to acquire a better understanding of porosity development and pore microstructure. Four carbonate lithofacies were identified by core‐scale and thin‐section analyses: subtidal / intertidal planar stromatolites and thrombolites; slope facies (laminated dolo‐ and lime‐mudstones and grain‐dominated turbidites); toe‐of‐slope / lower slope facies (laminated lime mudstones with turbidite beds); and shallow‐basin (embayment) facies (laminated lime mudstones and hemipelagic deposits). Porosity ranges from 0.08% to 9.6% and is lowest in the subtidal / intertidal planar and columnar stromatolites. The highest porosities, in the slope and shallow‐basin (embayment) lithofacies, probably resulted from catagenetic processes and microbial activity. High porosity in subtidal thrombolites is related to the original pore network. SEM analyses showed that pores are present within organic matter, pyrite framboids and microfossils, and between crystals. Subtidal / intertidal planar and columnar stromatolites and thrombolites have a high proportion of nanopores, probably resulting from microbial activity. Although porosity development is a combined function of the presence of organic matter and mineral components, together with sediment fabric and fractures, it is mostly a result of the early diagenetic transformation of mineral phases, microbial activity, and evaporite and carbonate dissolution.

Are the large filamentous microfossils preserved in Messinian gypsum colorless sulfide-oxidizing bacteria?

Research Article| October 01, 2015 Are the large filamentous microfossils preserved in Messinian gypsum colorless sulfide-oxidizing bacteria? Francesco Dela Pierre; Francesco Dela Pierre * 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy *E-mail: francesco.delapierre@unito.it Search for other works by this author on: GSW Google Scholar Marcello Natalicchio; Marcello Natalicchio 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Simona Ferrando; Simona Ferrando 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Roberto Giustetto; Roberto Giustetto 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Daniel Birgel; Daniel Birgel 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria Search for other works by this author on: GSW Google Scholar Giorgio Carnevale; Giorgio Carnevale 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Susanne Gier; Susanne Gier 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria Search for other works by this author on: GSW Google Scholar Francesca Lozar; Francesca Lozar 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Domenica Marabello; Domenica Marabello 3Dipartimento di Chimica, Università di Torino, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Jörn Peckmann Jörn Peckmann 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria4Institut für Geologie, Universität Hamburg, 20146 Hamburg, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Francesco Dela Pierre * 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Marcello Natalicchio 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Simona Ferrando 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Roberto Giustetto 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Daniel Birgel 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria Giorgio Carnevale 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Susanne Gier 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria Francesca Lozar 1Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy Domenica Marabello 3Dipartimento di Chimica, Università di Torino, 10125 Torino, Italy Jörn Peckmann 2Department für Geodynamik und Sedimentologie, Universität Wien, A-1090 Wien, Austria4Institut für Geologie, Universität Hamburg, 20146 Hamburg, Germany *E-mail: francesco.delapierre@unito.it Publisher: Geological Society of America Received: 27 May 2015 Revision Received: 23 Jul 2015 Accepted: 28 Jul 2015 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (10): 855–858. https://doi.org/10.1130/G37018.1 Article history Received: 27 May 2015 Revision Received: 23 Jul 2015 Accepted: 28 Jul 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesco Dela Pierre, Marcello Natalicchio, Simona Ferrando, Roberto Giustetto, Daniel Birgel, Giorgio Carnevale, Susanne Gier, Francesca Lozar, Domenica Marabello, Jörn Peckmann; Are the large filamentous microfossils preserved in Messinian gypsum colorless sulfide-oxidizing bacteria?. Geology 2015;; 43 (10): 855–858. doi: https://doi.org/10.1130/G37018.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The thick gypsum deposits formed in the Mediterranean Basin during the Messinian salinity crisis incorporate dense mazes of filamentous fossils, which were interpreted as algae or cyanobacteria, thus pointing to a shallow-marine subtidal or intertidal environment. The data presented here reveal that these filaments represent remains of colorless, vacuolated sulfide-oxidizing bacteria. This interpretation is supported by the presence of small crystal aggregates of iron sulfide (pyrite) and associated polysulfide within the filamentous fossils. Pyrite and polysulfide are considered to result from early diagenetic transformation of original zero-valent sulfur globules stored within the cells, which is a clade-diagnostic feature of living and degraded sulfur bacteria. In addition to filamentous fossils, the studied gypsum crystals contain remains of euryhaline and stenohaline diatoms and clay-rich aggregates interpreted as alteration products of marine snow floccules. This peculiar fossil assemblage reflects conditions of increased productivity in the water column, triggered by high fluxes of nutrients into the basin during phases of enhanced riverine runoff and freshwater discharge. This study confirms that gypsum evaporites have great potential to preserve the early stages of the taphonomic alteration of bacterial cells, shedding light on the paleoecology of ancient hypersaline environments. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Nickel as indicator of fresh organic matter in upwelling sediments

Trace metals involved in biological cycling (e.g. Cd, Cu, Ni, Zn) typically accumulate in upwelling sediments due to a high productivity-related particle flux and an enhanced preservation at depth. However, poor constraint on the contribution of lithogenic metal fraction, early diagenetic transformation processes and anthropogenic metal inputs may complicate sediment metal signatures. The identification of source and accumulation mechanisms is essential to the validation of these metals as productivity proxies.Here we combine data from various short cores (upper 50cm) and two longer cores of organic-rich upwelling sediments (Peru, Namibia, Chile and Gulf of California), which suggest a highly significant, linear and uniform relationship between Ni and total organic carbon (TOC). The overall high Ni enrichment may be explained by the occurrence of diatoms, which dominate productivity in these systems. The Peru surface sediments (upper 2cm) show a less pronounced Ni–TOC relationship and support a transition between lower Ni/TOC ratio of East Pacific water column particles and the higher Ni/TOC ratio observed in deeper sediments. In Peru surface sediments, the process is confirmed as a stoichiometric relation between Ni and total chlorins (the immediate degradation products of chlorophyll pigments), which is not observed for Cu or Zn.Our data strongly support previous findings that Ni is a clear (if not the best) indicator of the organic sinking flux. This is also due to the fact that Ni signatures undergo less alteration associated with sulfur and manganese cycling and low contribution from anthropogenic sources. The apparently exclusive Ni–chlorin stoichiometry suggests that Ni may be associated with enzymes that are involved in photoautotrophic production, which underlines the previous finding from laboratory experiments and field work that diatoms have a dominant role in marine Ni cycling. The Ni/chlorin ratio increases with increasing sediment depth suggesting that chlorins are effected by on-going diagenesis. Therefore, Ni may serve as a reliable indicator of the original chlorophyll flux rather than chlorins. The very good correlation between Ni and TOC and the preferential preservation of Ni over TOC justify previous (paleo)productivity estimates based on Ni accumulation.

Characterization of environmental conditions during microbial Mg-carbonate precipitation and early diagenetic dolomite crust formation: Brejo do Espinho, Rio de Janeiro, Brazil

Abstract For many years, sedimentary dolomite rocks have been considered to be primarily a replacement product of the calcium carbonate components comprising the original limestone, a process known as secondary replacement dolomitization. Although numerous dolomite formations in the geological record are composed of fine-grained crystals of micritic dolomite, an alternative process, that is, direct precipitation, is often excluded because of the absence of visible or geochemical indicators supporting primary precipitation. In this research, we present a study of a modern coastal hypersaline lagoon, Brejo do Espinho, Rio de Janeiro State, Brazil, which is located in a special climatic regime where a well-defined seasonal cycle of wet and dry conditions occur. The direct precipitation of modern high-Mg calcite and Ca-dolomite mud from the lagoonal waters under low-temperature hypersaline conditions is associated with the activity of microbial organisms living in this restricted environment. The mud undergoes an early diagenetic transformation into a 100% dolomite crust on the margins of the lagoon. The biomineralization process, characterized by the variations of the physico-chemical conditions in this environment during the annual hydrological cycle, is integrated with isotopic analysis to define the early diagenetic processes responsible for the formation of both dolomitic mud and crust. The carbon isotope values indicate a contribution of respired organic carbon, which is greater for the crust (δ 13 C=−9.5‰ Vienna Pee Dee Belemnite (VPDB)) than mud (δ 13 C=−1.2‰ VPDB). The oxygen isotope values reflect a moderate degree of evaporation during mud formation (δ 18 O=1.1‰ VPDB), whereas it is greatly enhanced during early diagenetic crust formation (δ 18 O=4.2‰ VPDB). The clumped isotope formation temperature derived for the Brejo do Espinho mud is 34 °C, whereas it is 32 °C for the crust. These temperatures are consistent with the upper range of measured values during the dry season when the lagoon experiences the most hypersaline conditions.

The role of iron in the diagenesis of organic carbon and nitrogen in sediments: A long-term incubation experiment

The burial and preservation of organic matter (OM) in marine sediments is tightly coupled to the diagenetic cycles of iron and manganese. Recently, it has been shown that approximately 20% of the sedimentary organic carbon (OC) may be bound to reducible iron oxides (Lalonde et al., 2012). These strong iron–OC complexes, formed within the oxic layer of the sediment, are transferred to the deeper anoxic sediment layers through sedimentation, physical reworking and bioturbation and are metastable over geological timescales. Using long-term (250-day) incubations under various redox and amendment conditions (Fe(II) and dissolved OM (DOM) additions), we examined the effect of iron on the early diagenetic transformations of OM in marine sediments. The fate of fresh, algal-derived DOM was monitored by tracking its stable carbon isotopic signature (δ13C). We demonstrate the incorporation of the 13C-depleted tracer into the sediment through sorption (adsorption and co-precipitation). In the presence of iron oxides, we observed an increased transfer of the dissolved algal material to the solid phase, revealing the role of iron in shuttling DOM from sediment pore waters to sediment particles. Furthermore, we show that the presence of iron has a differential effect on OC and organic nitrogen (ON), with preferential preservation of OC and accelerated degradation of ON in the presence of reactive iron oxide surfaces. Hence, we propose that redox-sensitive metals may regulate the global redox balance through increased carbon preservation as well as exerting a control on the concentration of fixed nitrogen species in marine sediments.

Early diagenesis in meteoric versus brackish environments: Example of the Late Oligocene-Early Miocene, littoral, mixed sedimentary succession of Carry-Le-Rouet (southeastern France)

AbstractIn the Carry-Le-Rouet region (southeastern France), the well exposed Late Oligocene-Early Miocene succession allows studying the early diagenesis in meteoric and brackish environments. This area provides unique and continuous outcrops of a mixed sedimentary succession (carbonate-siliciclastic shallow facies) with five particular sedimentary discontinuities resulting from various processes such as subaerial exposure, submarine erosion or bioturbation.Results from the diagenetic characterization (petrography and isotope geochemistry) show that the succession may be divided into three parts. The base of the series is dominated by diagenetic processes associated with brackish water, reflecting a restricted lagoonal environment. Dissolution and mineral replacement occurred directly under the sediment-water interface and a subsequent reprecipitation of the dissolved calcium carbonate took place below this layer. The precipitated calcite is non-ferroan and dull luminescent, showing highly variable stable C- &amp; O-isotopic signatures (−6.31‰ to −0.08‰ for δ13CV-PDB and −5,78‰ to −1,36‰ for δ18OV-PDB), organized in a covariant trend, typical of mixed fluids. The middle part of the series, show a progressive evolution to open marine conditions and records two potential emersion events, associated with the development of meteoric vadose and phreatic conditions. The postulated vadose zones are dominated by mineral replacement rather than leaching and characterized by two cements: a non-ferroan and non-luminescent calcite, changing downward to zoned cement. Isotopic signatures of these calcites are ranging from −6.45‰ to −5.10‰ for δ13CV-PDB and −5,44‰ to −4,17‰ for δ18OV-PDB. Below this zone, a ferroan, non-luminescent calcite (−3.25‰ to −1.18‰ for δ13CV-PDB and −4,93‰ to −3,52‰ for δ18OV-PDB) is observed, suggesting precipitation under reducing conditions associated to a confined phreatic zone, isolated from the overlying zones and the recharge area by a marly interval. The third part of the series (at the top), partly eroded, may have undergone at least one emersion event, with the initial development of a dull cement followed by a non-ferroan, non-luminescent cement. This is linked to a gradual change from downdip slightly reducing to updip oxidizing conditions.The early timing of the diagenetic modifications, the differences of diagenetic patterns observed in each interval and the absence of common trends in the series tend to indicate multiple episodes of early diagenesis, associated to sedimentary discontinuities (more specifically exposure surfaces). These discontinuities act as major controls on the repartition of the diagenetic phases. The excellent preservation of the early diagenetic transformations is linked to the shallow total burial depth, and the lack of mesogenetic and telogenetic imprint. This study also highlighted the influence of the Nerthe massif that acted as a principal meteoric fluid recharge area located less than 1 km away from the sedimentary system.

Comment on “Ozonation of triterpenoids: Implications for early diagenesis of biomarkers in oxic environments” by Tay et al. (2013)

The article entitled “Ozonation of triterpenoids: Implications for early diagenesis of biomarkers in oxic environments” (Tay, K.S., Rahman, N.A., Abas, M.R.B, Simoneit, B.R.T., 2013. Organic Geochemistry 57, 34–40) deals with an investigation of the early diagenetic transformations undergone by higher plant triterpenoids under oxic conditions by means of laboratory experiments involving various triterpenes in the presence of ozone. Several aspects of the publication by Tay et al. (2013) are questionable, and are discussed in detail here. These comprise (i) the analytical procedure (based mainly on gas chromatography–mass spectrometry, GC–MS) used for the investigation of reaction mixtures likely to contain thermally labile (poly)oxygenated triterpenoids, (ii) the proposed mechanisms involving the hydroxyl radical as the key oxidizing species, (iii) the interpretation of mass spectra of the products and the structural assignments therefrom, and (iv) the geochemical relevance of the experiments with respect to non-biological oxidative alteration undergone by higher plant triterpenes in sediments.

Variations of common riverine contaminants in reservoir sediments

Organic molecules in reservoir sediments can be used as tracers of contaminant inputs into rivers. Vertical variations in the molecular records can be ascribed to pre-depositional alteration within the water column, or in situ post-depositional alteration. We report the molecular stratigraphy of four common riverine contaminant groups in sediment of the largest reservoir on the Danube River, the Iron Gate I Reservoir. Sediments were rapidly deposited, with little variation in texture and, as revealed by analytical pyrolysis, in the concentration and composition of natural sedimentary organic matter. However, a detailed molecular inspection did reveal differences in distribution and organic carbon (OC)-normalized concentrations of contaminants.The OC-normalized concentrations of nonylphenol increased by one order of magnitude with depth down the 70cm sediment core. There is a strong correlation between sediment depth and the ratio of nonylphenol to its precursor (nonylphenol monoethoxylate). This indicated that nonylphenol was produced in situ. While the relative proportions of C10–C14 linear alkylbenzenes remained constant with increasing depth, they exhibited variations in isomer distribution. These variations, which are due to different degrees of degradation, appear to have occurred within the water column prior to sedimentation of suspended solids.The distribution of 40 polycyclic aromatic hydrocarbons revealed origins from both pyrogenic and petrogenic sources. The differences in their compositions were not depth-related, but rather were associated with variations in the sorption capacities of texturally different sediments. Perylene showed slightly higher concentrations at greater depths, while the OC-normalized concentration of retene systematically increased with sediment depth. This is consistent with formation of retene and perylene via very early diagenetic transformation. The presence of petroleum biomarkers indicated minor contamination by fossil fuels.

Early diagenetic transformation of terpenoids from conifers in the aromatic hydrocarbon fraction: A long term, low temperature maturation experiment

An artificial maturation experiment at 80°C was conducted for >5years to investigate the early diagenetic transformations of organic matter (OM), mainly terpenoids, in conifers. The diagenetic products of aromatic hydrocarbons were determined in the earlier and later stages of maturation, namely, after >1year and after ∼5.5years. The OM in contemporary coniferous plants (Cedrus deodara and Platycladus orientalis) was also characterized for comparison. The results reveal that during the early diagenesis of OM from conifers, biological terpenoids were transformed into diagenetic aromatic terpenoids and common polycyclic aromatic hydrocarbons. Some polar terpenoids, such as dehydroabietate aldehydes and abietatetraenoic acid, were detected and identified. Information on these biological and evolutionary terpenoids may improve the understanding of their diagenetic pathways. The experimental data also show that the diagenesis of dehydrogenated and aromatic terpenoids and polycyclic aromatic hydrocarbons is affected by different experimental inorganic conditions. High salinity is favourable to diagenesis in aromatic fractions. Meanwhile, heavy metals such as lead and iron may delay and interrupt the transformation of terpenoids, respectively.

Early diagenesis of Botryococcus braunii race A as determined by high resolution magic angle spinning (HRMAS) NMR

An algal culture of Botryococcus braunii race A and its residue obtained after 201 days of oxic biodegradation are characterized using high resolution magic angle spinning (HRMAS) NMR spectroscopy, a hybrid technique which provides molecular details non-invasively. The high resolution of two dimensional NMR using HRMAS gives precise structural assignments of different classes of compounds contained in the initial algae and biodegraded algae. The data indicate that some intracellular lipids and proteinaceous materials are more environmentally labile while other long chain polymethylenic structures with ether functional groups, likely from algaenan, are observed to survive the degradation process. The identification of similar structural entities in both fresh and degraded material clearly points to selective preservation as the main process responsible for the early diagenetic transformation of this type of algae.