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1.
Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献
2.
Authigenic carbonate precipitates from the NE Black Sea: a mineralogical,geochemical, and lipid biomarker study 总被引:1,自引:0,他引:1
A. Bahr T. Pape G. Bohrmann A. Mazzini M. Haeckel A. Reitz M. Ivanov 《International Journal of Earth Sciences》2009,98(3):677-695
Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea)
were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements
to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ13C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane
(AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely
laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal,
yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ18O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish
LMC rims have been growing in slightly 18O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with
respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated
AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial
origin, reflecting the hemipelagic nature of the primary sediment. 相似文献
3.
Shovan Lal Chattoraj Santanu Banerjee P. K. Saraswati 《Journal of the Geological Society of India》2009,73(4):567-574
Glauconitic minerals are considered as one of the valuable input parameters in sequence stratigraphic analysis of a basin.
In the present study glauconitic minerals are reported from subtidal green shale facies in the lower part of the Late Paleocene-Early
Eocene Naredi Formation of western Kutch. On the basis of the foraminiferal assemblage the glauconite bearing beds are interpreted
to have formed in a mid shelf depositional settings of an unstable marine conditions. XRD studies confirm the glauconite mineralogy
of the green pellets and provide an estimation of glauconite maturity. Textural attributes of the glauconites confirm their
derivation by different degrees of alteration of precursor feldspar grains. Because of the authigenic origin and autochthonous
nature, these glauconites hold promise for understanding sequence stratigraphy of the Palaeogene succession of the western
Kutch. 相似文献
4.
Authigenic albites in carbonate rocks typically grow in a high-grade diagenetic to low-grade metamorphic environment and often show Roc-Tourné-twinning sensu Füchtbauer. Based on an investigation of four Middle to South European occurrences, they show Mn2+- and Fe3+-activated cathodoluminescence (CL), as revealed by combined high resolution spectroscopy of cathodoluminescence emission (HRS-CL), electron paramagnetic resonance (EPR), and proton-induced X-ray emission (μPIXE). 相似文献
5.
Seepage of hydrocarbon-rich fluids out of the marine sedimentary column is characterized by temporal changes of flow intensity and resultant spatially variable redox conditions. Authigenic carbonates at marine hydrocarbon seeps provide excellent geological and geochemical archives that serve to explore seepage dynamics over time. In this study, we investigated the potential of Mössbuaer spectroscopy and Fe contents of seep-related authigenic carbonates from the Congo Fan, the Gulf of Mexico, and the Black Sea for reconstructing past redox conditions and fluid seepage activity at cold seeps. The Fe speciation observed by Mössbauer spectroscopy and Fe contents suggest that (1) the Congo Fan carbonates precipitated in a sulfidic environment, (2) the formation conditions of seep carbonates were variable at the Gulf of Mexico seep site, ranging from oxic to suboxic and anoxic and even spanning into the methanogenic zone, and (3) the stratified water column of the Black Sea or suboxic condition resulted in low Fe contents of Black Sea carbonates. The study reveals that Fe speciation can provide constraints on the wide range of redox conditions that imprinted seep carbonates during the life span of seepage. Similarly, Mössbauer spectroscopy – particularly when used in combination with the analysis of redox-sensitive elements – is a promising tool to trace variable redox conditions in marine paleoenvironments other than seeps. 相似文献
6.
ULRICH HEIMHOFER DANIEL ARIZTEGUI MARC LENNIGER STEPHEN P. HESSELBO DAVID M. MARTILL ARISTOTELES M. RIOS‐NETTO 《Sedimentology》2010,57(2):677-694
The laminated limestones of the Early Cretaceous Crato Formation of the Araripe Basin (North‐eastern Brazil) are world‐famous for their exceptionally well‐preserved and taxonomically diverse fossil fauna and flora. Whereas the fossil biota has received considerable attention, only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the Crato Fossil Lagerstätte. The Nova Olinda Member represents the lowermost and thickest unit (up to 10 m) of the Crato Formation and is characterized by a pronounced rhythmically bedded, pale to dark lamination. To obtain information on palaeoenvironmental conditions, sample slabs derived from three local stratigraphic sections within the Araripe Basin were studied using high‐resolution multiproxy techniques including detailed logging, petrography, μ‐XRF scanning and stable isotope geochemistry. Integration of lithological and petrographic evidence indicates that the bulk of the Nova Olinda limestone formed via authigenic precipitation of calcite from within the upper water column, most probably induced and/or mediated by phytoplankton and picoplankton activity. A significant contribution from a benthonic, carbonate‐secreting microbial mat community is not supported by these results. Deposition took place under anoxic and, at least during certain episodes, hypersaline bottom water conditions, as evidenced by the virtually undisturbed lamination pattern, the absence of a benthonic fauna and by the occurrence of halite pseudomorphs. Input of allochthonous, catchment‐derived siliciclastics to the basin during times of laminite formation was strongly reduced. The δ18O values of authigenic carbonate precipitates (between ?7·1 and ?5·1‰) point to a 18O‐poor meteoric water source and support a continental freshwater setting for the Nova Olinda Member. The δ13C values, which are comparatively rich in 13C (between ?0·1 and +1·9‰), are interpreted to reflect reduced throughflow of water in a restricted basin, promoting equilibration with atmospheric CO2, probably in concert with stagnant conditions and low input of soil‐derived carbon. Integration of lithological and isotopic evidence indicates a shift from closed to semi‐closed conditions towards a more open lake system during the onset of laminite deposition in the Crato Formation. 相似文献
7.
8.
Occurrence of baddeleyite (ZrO2) which is a rare mineral has been recorded in ferromanganese
nodules of Central Indian Ocean Basin (CIOB). The mineral occurs either as independent isolated
sub-rounded to elliptical grains or in clusters forming fine subhedral crystals (<3 mm) within ferromanganese
concretionary growth bands. The mode of occurrence, textural features and chemistry of the
mineral suggest detrital and possibly an authigenic origin for baddeleyite. For authigenic origin it is
proposed that zirconium might have got released either from the terrigenous sediments or the altered
seafloor rocks forming halogen complexes and subsequently it has re-precipitated in the form of baddeleyite
within manganese nodules under oxic to sub-oxic conditions. 相似文献
9.
边缘海沉积物是海洋重要的碳储库,其内部的碳循环主要是由有机质矿化分解过程来驱动的。有机碳进入边缘海沉积物后,矿化分解为溶解无机碳(DIC)进入沉积物孔隙水并扩散到上层水柱,参与海洋系统碳循环;同时还有部分DIC与钙镁等离子结合形成自生碳酸盐,保存于沉积物碳库。从生物地球化学角度探讨有机质埋藏机制和效率,在此基础上重点综述沉积物硫酸盐还原、产甲烷和甲烷厌氧氧化过程的耦合机制,以及有机质矿化对自生碳酸盐形成的影响等方面的研究进展,以期加深对陆架边缘海沉积物在全球碳循环收支平衡中的作用及其气候环境效应的认识。 相似文献
10.
Santanu Banerjee Shovan Lal ChattorajP.K. Saraswati Somnath DasguptaUrbashi Sarkar 《Marine and Petroleum Geology》2012,30(1):144-160
Formation and maturation of glauconites within the early Middle Eocene Harudi Formation, built up in a lagoon to shelf transition in western Kutch, India is addressed taking recourse to a combined sedimentological, micropalaeontological and mineralogical investigation. The glauconite is authigenic and its occurrence coincides with maximum flooding. The glauconite is more matured within the fecal pellets and is less matured within the intra-particle pores of bioclasts namely, foraminifera, ostracoda, gastropoda and bryozoa. SEM-EDS, XRD and geochemical studies clearly document that the infilling within the intra-particle pores of bioclasts belong to nascent to slightly evolved glauconite (<5 wt% K2O), while the pellet belongs to slightly evolved to evolved glauconite (5-7 wt% K2O). Based on chemical characteristics and SEM investigations the glauconitization process can be best explained by the ‘verdissement theory’. The glauconite possibly formed as initial authigenic glauconitic smectite precipitates; while the pellet matured subsequently by addition of K, the process was hindered in case of infillings. The maturation process also involved addition of Si and release of Al, with or without release of Mg. The glauconite maturation was facilitated in case of fecal pellets because of higher porosity, inter-granular nature of pores and availability of necessary elements in semi-confined micro-environments. In contrast, the maturation was aborted at an early stage in case of infillings because of the minute, closed nature of the pores and prevalent alkaline conditions not allowing dissolution of calcitic tests. A low negative cerium anomaly suggests glauconite formation in sub-oxic micro-environments, created by decay of organic matters within the fecal pellets and bioclasts. A clear case of substratum control on glauconitization becomes apparent. 相似文献