Marine Genesis Research Articles

Studies of the composition of hydrocarbon components of the Yuzhno-Sakhalinsk and Pugachevo mud volcanoes

This report considers the results of studies of the composition of hydrocarbon components of the Yuzhno-Sakhalinsk and Pugachevo mud volcanoes (Sakhalin Island). The similarity in the chemical composition of hydrocarbons of these volcanoes was revealed, as was the variation in the ratios of hydrocarbon components under seismic activation. Two maxima of hydrocarbon concentrations were shown, and basically the marine genesis of the initial organic matter was substantiated. A possible interpretation of the obtained dada is presented.

Isotope composition of organic and carbonate carbon of surface horizons of bottom sediments in the area of the Shtokmanovskoe deposit and “pockmarks field” in the Barents Sea

One of the methods applied in searching hydrocar� bon (HC) deposits is the geochemical one, which is based on study of stable isotopes of organic (Corg) and carbonate (Ccarb) carbon in bottom sediments. In the second half of the twentieth century, a global natural phenomenon was discovered: the formation of isoto� pically light Corg and Ccarb in bottom sediments during aerobic and anaerobic microbe oxidation of migrating hydrocarbons [1]. The results of investigation of deposits of the Norway Sea neighboring the Barents Sea in the area of the caldera of the transpolar mud volcano Haakon Mosbi and pockmarks on the Vest� nese Ridge may be considered as an example of appli� cation of the isotope data. The isotope composition of Corg in these sediments was depleted in heavy isotope 13 C by 8–10‰ in comparison with Corg of normal marine sediments. Carbon of carbonates was also depleted in the 13 C isotope at the expense of incorpo� ration of isotopically light carbon from methane formed by methane oxidation by microorganisms [1]. Thus, the discovery of Corg and Ccarb depleted in the 13 C isotope in comparison with the isotope composi� tion of Corg and C carb of marine genesis in sediments may provide evidence for the release of fluids contain� ing hydrocarbons at the bottom and their partial microbe oxidation with the formation of isotopically light carbonate compounds. In this study we wanted to solve the opposite prob� lem and to determine the participation of gas–water fluids in the formation of overlying sedimentary series in the area of a known HC deposit and in the field of assumed pockmarks using analysis of the stable iso� topes of organic and carbonate carbon.

Carbonate characteristics of waters of the Arctic Ocean continental slope

Carbonate characteristics of the water mass of the deepwater part of the Arctic Ocean (AO) in the continental slope area were determined, and the range and reasons of their variability during summer-fall season were revealed. The AO water area is a meaningful sink for atmospheric carbon dioxide. The warm intermediate Atlantic waters (AW) are also undersaturated with carbon dioxide relative to its content in the atmosphere. While these waters move along AO continental slope, the value pCO2 in the AW core decreases to 8–10 μatm (mainly, due to drop in the water temperature). The potential absorption capacity of the AO deepwater basin is estimated at approximately 48 Tg of carbon (without sea ice taken into account). Joint analysis of carbonate and hydrological parameters showed that near-bottom waters formed on the shallow shelf of the Laptev Sea, which is rich in inorganic and organic carbon of terrestrial and marine genesis, take part in formation of halocline waters of the AO. They are modified due to interaction with AW penetrating to the shelf and are transferred to the deepwater AO segment, where they occur in the halocline according to their density. Transformed near-bottom waters of the Laptev Sea shelf, similar to waters of the halocline of Pacific origin in the eastern sector of the AO, are traced above the continental slope in Amundsen Basin on the basis of higher CO2 concentrations.

Geochemistry and mineralogy of Paleocene-Eocene Oum El Khecheb phosphorites (Gafsa-Metlaoui Basin) Tunisia

Upper Paleocene to Lower Eocene phosphates of the Jebel Oum El Khecheb profile (Gafsa-Metlaoui Basin GMB, Tunisia) are mostly composed of brown phospharenites lithified or not, granular, with pellets, coproliths, bone clasts and fish teeth. The matrix in analyzed samples is reduced and constituted of various clay minerals (dominantly smectites, palygorskite, sepiolite and rare kaolinite), opal-CT and carbonates. Clinoptilolite is recognized along the series; very few amounts of quartz and feldspar grains are sparsely present. The phosphate mineral is a carbonate-fluorapatite (CFA) sulphated, sodic enriched in strontium and rare earth elements (REE). Statistical analyses of mineralogical and geochemical data highlight the associated elements in the main mineral lattice. In the CFA, the group is composed of CaO-P2O5-Na2O-SO3-F-Sr-Th-REE-U-Ba-Zr-Cr. In the silicates, the group contains SiO2-Al2O3-Fe2O3-MgO-K2O-Na2O-TiO2-Co-Cs-Rb-Sc-Ta-Sb-Mo-As and Cu. Sulphides are represented by Zn and Cd; iron oxides by mainly Fe and Ni. Dolomite and gypsum are present; SO3 is contained in the latter, but CFA may also have some of this radical in its structure. The Upper Continental Crust (UCC) normalized REE patterns present a variably negative Ce-anomaly, suggesting that the imprint of the marine genesis environment is very well-preserved in the main phosphatic units. Positive-Eu and negative-Sm anomalies were detected in some samples. The fractionation of light-REE to heavy-REE, represented by the La/Yb ratio of untreated values varies between 8.28 and 12.94, somewhat less than UCC value (13.64). Enrichment of HREE is due to phosphates. Both ratios reflect the marine genesis environment wherein the formation of the CFA took place in a confined and oxygen poor environment. Then the CFA removed the REE and the trace elements present from the interstitial waters, as was proposed for the various phosphatic basins of Tunisia.

Palaeoenvironmental implications of ferruginous deposits related to a Middle–Upper Jurassic discontinuity (Prebetic Zone, Betic Cordillera, Southern Spain)

The Middle–Upper Jurassic boundary in the westernmost Tethyan basins is marked by a discontinuity. A thin iron crust with ferruginous ooids and pisoids and an overlying ferruginous oolitic limestone lithofacies occur in a genetic relationship to this discontinuity with a reduced thickness (< 50 cm) and very local distribution in the Prebetic Zone (Betic Cordillera). The ferruginous coated grains are subdivided into two types. Type A ooids are characterised by thin, regular lamination in concentric layers enclosing a nucleus; they are dominant in the top of the iron crust (100% of the ferruginous ooids) and in the ferruginous oolitic limestone (82%). Type B ooids typically have thick, irregular lamination in a few discontinuous concentric layers enclosing a variable nucleus including bioclasts and foraminifera; they are exclusive to the ferruginous oolitic limestone (18% of the ferruginous ooids). The bulk chemical composition varies between 80% Fe 2O 3 by weight in the iron crust and 67% by weight in the coated grains. In the ferruginous ooids, the contents in SiO 2 (5.4%), Al 2O 3 (6.5%), P 2O 5 (3.6%), and CaO (4.7%) are higher than in the crust. Trace elements (V, Cr, Co, Ni, Zn, Y, Mo, and Pb) in both the crust and ooids show enriched values compared with the bulk composition of the upper continental crust. The mineral composition of the iron crust and ooids is primarily goethite, with small amounts of Al-hydroxide (bohemite) and apatite, whereas hematite is identified only in the iron crust. The Type A ooids are interpreted as having an origin related to the iron crust. Since there is no evidence to support a marine genesis for the iron crust, the possibility of a subaerial origin is presented here. The crust has characteristics (chemical and mineralogical composition) similar to those of ferruginous pisolitic plinthite (highly weathered redoximorphic soil), and goethite shows an Al-substitution range (5–10 mol%) that indicates pedogenic conditions. Soil processes under periodic hydrous conditions are suggested; groundwater soils with hydrous conditions are congruent with the formation of the Type A ferruginous ooids and pisoids. In this situation, a coastal plain with periodically flooded soils would be the likeliest scenario. Callovian shallow carbonate shelf was possibly emerged and weathered, followed by marine sedimentation during the Middle Oxfordian, associated with major flooding of the Prebetic shelf and the erosion of ferruginous pisolitic plinthite. The first marine deposit was ferruginous oolitic limestones. Fragments of iron crust and Type A ferruginous ooids were reworked and incorporated into the marine sediments. A second phase of ferruginous ooids (Type B) with clear marine features developed, benefiting from iron-rich microenvironments due to the redistribution from iron crust fragments and Type A ferruginous ooids.

PTB mass extinction and earliest Triassic recovery overlooked? New evidence for a marine origin of Lower Triassic mixed carbonate–siliciclastic sediments (Rogenstein Member), Germany

The Central European Permo-Triassic basin was land-locked with occasional connections to the North Pangaea shelf and Tethys. A thick sequence of siliciclastic fluvial and floodplain sediments separates the Late Permian marine carbonate–evaporite cycles of the Zechstein Basin from marine Middle Triassic marls and carbonates of the Germanic Basin. Within this Latest Permian–Middle Triassic siliciclastic interval, the location of the Permian–Triassic Boundary (PTB) is difficult to recognize. The first limestones after the PTB are Induan mixed carbonate–siliciclastic oolites and microbialites of the Bernburg and Calvörde Formations (Untere Buntsandstein Group). Consensus emerged after a long-lasting controversy that the carbonates of the so-called Rogensteine are the relics of an alkaline playa lake. The idea of the marine genesis was finally rejected, because of the obvious lack of calcified metazoans. The existing depositional playa lake-model will be tested using previously unconsidered data, such as currently discussed Early Triassic recovery scenarios of marine benthic communities after the Permian–Triassic mass extinction, global patterns of Early Triassic carbonate production, Permian–Triassic tectono-sedimentary evolution of northern Pangaea and stable oxygen and carbon isotope data. The Rogenstein is interpreted as marine carbonate, showing the characteristic features of marine carbonates of the Early Triassic recovery period: – Calcified invertebrates are rare in many marine settings during the aftermath of the Permian–Triassic mass extinction. Thin shells of the oolites resemble opportunistic bivalves flourishing in marine Early Triassic oceans. – The oolites and microbialites are the product of abiotic and biotically-induced carbonate precipitation following the Permian–Triassic mass extinction while biomineralisation is insignificant; Rogenstein microbialites look like marine Early Triassic microbial reefs. – The extraordinary size of the Rogenstein ooids resembles marine Neoproterozoic ooids. The term “anachronistic” has been used in the literature to describe the similarities in the fabric and composition of Early Triassic and Early Palaeozoic/Neoproterozoic marine carbonates. – Stable carbon isotopes of least altered Rogenstein ooids and stromatolites exhibit trends similar to the composition of Triassic seawater. – The presence of flat pebble conglomerates and sediment structures similar to herring-bone cross stratification confirm the marine genesis. I propose that cool seawater transgressed during a global rise of Late Permian–Early Triassic base-level from the Barents shelf southward along reactivated extensional graben structures and flooded the Central European Permo-Triassic basin. There, the extremely hot and arid climate of the megacontinent Pangaea caused increased evaporation of seawater and subsequent supersaturation with respect to calcium carbonate. Insignificant biomineralisation and high water energy in the shallow sea give rise to largely abiotic and biotically-induced carbonate precipitation which resembles lake sediments at first sight. Benthic tropical carbonate production started with the next transgression during the Röt Formation, leading to the sedimentation of marls and limestones during the Spathian (late Olenekian).

Prima segnalazione di un terrazzo costiero con deposito marino nella Liguria orientale (Italia)

Remnants of a loose coarse deposit were found on a rock terrace 28 m above the present day sea level, along the coast of Eastern Liguria. A general geomorphological analysis of the site was carried out. The deposit sedimentological characteristics were detailed and a morphometric analysis of the coarse fraction was carried out. This enabled us to infer the marine genesis of the deposit; it is the first time that a Quaternary marine deposit is found along the coast of Eastern Liguria. Details regarding the nature of the deep weathering processes (in particular oxidation and decarbonatation) that affected it were collected by means of thin section. The age of an old sea level can be inferred, due to the absence of absolute dating, only relating it to similar surfaces present throughout the coastline of the region and linking them to the sea level curves obtained from oxygen isotope records. On the basis of the collected data we propose the chronological attribution of the studied terrace to theδ18O stage 11, considering that the area might have been affected by tectonic uplift.

Development of the Mozambique and Ruvuma sedimentary basins, offshore Mozambique

Two major sedimentary basins have been identified on the continental margin of Mozambique—Mozambique Basin and Ruvuma Basin. The formation of the basins is related to the break-up of Gondwana and opening of the western part of the Indian Ocean. The basins are relatively young, having developed discordantly to the structural plan of Gondwana sedimentary basins. The history of the formation of the East African continental margin sedimentary basins within Mozambique has been studied on the basis of the present-day concept of Gondwana break-up and Madagascar's drift with respect to Africa. Two stages in the history of the East African basins can be recognized: late-Gondwana and post-Gondwana. The late-Gondwana stage (303-157 Ma) is typified by sedimentary and volcanogenic rocks of the Karoo Group. The post-Gondwana stage (157-0 Ma) corresponds to the period of active Gondwana break-up and the formation of Indian Ocean marginal basins. The Mozambique Basin occupies both central and southern parts of the coastal plain of Mozambique, extending onto the continental shelf and slope. The sedimentary fill is composed of Upper Jurassic, Cretaceous and Cenozoic rocks which discordantly overly the Karoo basalts. The Upper Jurassic occurs as continental red-beds, mostly distributed within buried grabens. Cretaceous rocks occur as terrigenous sediments of continental and marine genesis. Cenozoic deposits are of predominantly marine and deltaic origin. The Ruvuma Basin, situated in the north of Mozambique, is part of an extended East African marginal basin which includes parts of the coastal plains and continental margins of Tanzania and Kenya. The basement of the basin is composed of crystalline and metamorphic rocks of pre-Cambrian age. The sedimentary fill is represented by continental terrigenous Karoo sediments, marine and lagoonal Jurassic deposits, and marine and deltaic rocks of Cretaceous and Cenozoic age. The main difference between the sedimentary fill of the Mozambique and Ruvuma basins is related to the changing sedimentary environment in the period of Gondwana break-up, Jurassic and Early Cretaceous, when the drift of Madagascar and sea-floor spreading took place and the marine basin gradually extended southwards between the East African margin and Madagascar. From the Late Cretaceous on, the sedimentary environment within both basins was similar, the Mozambique and Ruvuma basins forming a single system on the East African continental margin. The main stages of the basins' development are illustrated by a series of palaeogeographic reconstruction maps.