北黄海盆地东部坳陷下白垩统砂岩成岩作用及其储层意义     

宫辰  程日辉  沈艳杰  高丹 《世界地质》2018,37(1):171-184

通过对取芯井砂岩镜下特征及孔隙度渗透率变化的分析,研究了北黄海盆地东部坳陷下白垩统砂岩的成岩作用及其储层意义。结果显示,储层砂岩类型以长石砂岩、长石石英砂岩和岩屑石英砂岩为主,处于中成岩作用阶段的A亚期末期至B亚期早期。主要的成岩作用类型有压实作用、压溶作用、胶结作用、交代作用、蚀变作用、溶蚀作用和重结晶作用,主要孔隙类型有粒间孔隙、粒内孔隙、填隙物内孔隙和次生裂缝。长石砂岩是主要储层。压实作用、压溶作用、胶结作用和重结晶作用使砂岩孔隙度减小,降低了储层物性,起到破坏性作用;交代作用、蚀变作用和溶蚀作用使砂岩孔隙度增大,改善了储层物性,起到建设性作用。孔隙度和渗透率整体上由浅变深而呈现由大到小趋势,在深度为3 000~3 020 m和3 140~3 250 m时出现异常高值,孔隙度与渗透率的异常高值带是次生孔隙发育带。  相似文献   

内蒙古索伦地区中二叠统哲斯组碎屑岩成岩作用及其对储层物性的影响     

李嘉慧  朱占平  李广存  齐洪亮  楚江涛  李伟 《世界地质》2018,37(2):548-558

利用薄片确定砂岩类型、扫描电镜观察碎屑岩微观特征并划分成岩阶段以及对岩石储层进行物性测试分析等方法,系统地探究了内蒙古索伦地区中二叠统哲斯组碎屑岩成岩作用及其对储层物性的影响。研究表明该地区砂岩胶结物有钙质胶结物、硅质胶结物、黏土矿物胶结物和凝灰质胶结物,其中钙质胶结物多为方解石,硅质胶结主要表现为石英次生加大,黏土胶结物以伊利石为主,凝灰质胶结物在该地区出现较少。地化数据显示哲斯组泥岩有机质镜质体反射率值(Ro)在2%~4%之间、最高热解温度(T_(max))490℃、伊利石/蒙皂石(I/S)的蒙皂石层15%;薄片镜下观察发现碎屑颗粒间以线接触为主,扫描电镜观察石英次生加大级别为Ⅲ—Ⅳ级。综合分析确定内蒙古索伦地区哲斯组碎屑岩处于晚成岩阶段B期—C期。压实和胶结作用一定程度上降低砂岩的孔隙度和渗透率;而溶蚀溶解作用提高砂岩的孔隙度和渗透率。  相似文献   

Stable carbon‐isotope record of shallow‐marine evaporative epicratonic basin carbonates,Ordovician Williston Basin,North America          下载免费PDF全文

Antun Husinec  Stig M. Bergström 《Sedimentology》2015,62(1):314-349

Secular variations in stable carbon‐isotope values of marine carbonates are used widely to correlate successions that lack high‐resolution index fossils. Various environmental processes, however, commonly may affect and alter the primary marine carbon‐isotope signal in shallow epicratonic basins. This study focuses on the marine carbon‐isotope record from the carbonate–evaporite succession of the upper Katian (Upper Ordovician) Red River Formation of the shallow epicratonic Williston Basin, USA. It documents the carbon‐isotope signal between the two major Ordovician positive shifts in δ¹³C, the early Katian Guttenberg and the Hirnantian excursions. Eight δ¹³C stages are identified based on positive excursions, shifts from positive to negative values and relatively uniform δ¹³C_carb values. A correlation between carbon‐isotope trends and the relative sea‐level changes based on gross facies stacking patterns shows no clear relation. Based on the available biostratigraphy and δ¹³C trends, the studied Williston Basin curves are tied to the isotope curves from the North American Midcontinent, Québec (Anticosti Island) and Estonia, which confirm the Late Katian age (Aphelognathus divergens Conodont Zone) of the upper Red River Formation. The differences in the δ¹³C overall trend and absolute values, coupled with the petrographic and cathodoluminescence evidence, suggest that the carbon‐isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated Williston Basin, and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids.  相似文献   

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments     

《Organic Geochemistry》2015

Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are ³⁴S-enriched relative to coexisting sulfide, and experiments have produced ³⁴S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography – inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6 m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in ³⁴S relative to coexisting kerogen and porewater sulfide. We hypothesize that this ³⁴S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon–sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary porewater. The ³⁴S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.  相似文献   

Constitutive modelling of Otaniemi soft clay in both natural and reconstituted states     

《Computers and Geotechnics》2015

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早期成岩作用过程中硫酸盐还原反应研究进展   总被引：3，自引：0，他引：3  

施春华  颜佳新  韩欣 《南方国土资源》2001,14(1):21-26

文章概述近年来早期成岩作用中硫酸盐还原反应研究的某些新资料和新成果 ,综合分析了各种沉积环境下的早期成岩作用中的硫酸盐还原反应。重点论述贫氧缺氧条件下的反应机制。并讨论了判别沉积环境的Fe -C -S的关系及黄铁矿的形成和碳酸盐的溶解、沉淀与氧化还原带的对应关系。简要讨论了早期成岩作用中硫酸盐还原反应的研究意义。  相似文献   

Microbiological processes in banded iron formation deposition     

Nicole R. Posth  Kurt O. Konhauser  Andreas Kappler 《Sedimentology》2013,60(7):1733-1754

Banded iron formations have been studied for decades, particularly regarding their potential as archives of the Precambrian environment. In spite of this effort, the mechanism of their deposition and, specifically, the role that microbes played in the precipitation of banded iron formation minerals, remains unresolved. Evidence of an anoxic Earth with only localized oxic areas until the Great Oxidation Event ca 2·45 to 2·32 Ga makes the investigation of O₂‐independent mechanisms for banded iron formation deposition relevant. Recent studies have explored the long‐standing proposition that Archean banded iron formations may have been formed, and diagenetically modified, by anaerobic microbial metabolisms. These efforts encompass a wide array of approaches including isotope, ecophysiological and phylogeny studies, molecular and mineral marker analysis, and sedimentological reconstructions. Herein, the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post‐depositional alteration are described. The main findings of recent years are summarized and compared here, and suggestions are made regarding cross‐disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition.  相似文献   

Percolation of diagenetic fluids in the Archaean basement of the Franceville basin     

《Comptes Rendus Geoscience》2014,346(1-2):13-19

The Palaeoproterozoic Franceville basin, Gabon, is mainly known for its high-grade uranium deposits, which are the only ones known to act as natural nuclear fission reactors. Previous work in the Kiéné region investigated the nature of the fluids responsible for these natural nuclear reactors. The present work focuses on the top of the Archaean granitic basement, specifically, to identify and date the successive alteration events that affected this basement just below the unconformity separating it from the Palaeoproterozoic basin. Core from four drill holes crosscutting the basin–basement unconformity have been studied. Dating is based on U–Pb isotopic analyses performed on monazite. The origin of fluids is discussed from the study of fluid inclusion planes (FIP) in quartz from basement granitoids. From the deepest part of the drill holes to the unconformable boundary with the basin, propylitic alteration assemblages are progressively replaced by illite and locally by a phengite + Fe chlorite ± Fe oxide assemblage. Illitic alteration is particularly strong along the sediment–granitoid contact and is associated with quartz dissolution. It was followed by calcite and anhydrite precipitation as fracture fillings. U–Pb isotopic dating outlines three successive events: a 3.0–2.9-Ga primary magmatic event, a 2.6-Ga propylitic alteration and a late 1.9-Ga diagenetic event. Fluid inclusion microthermometry suggests the circulation of three types of fluids: (1) a Na–Ca-rich diagenetic brine, (2) a moderately saline (diagenetic + meteoric) fluid, and (3) a low-salinity fluid of probable meteoric origin. These fluids are similar to those previously identified within the overlying sedimentary rocks of the Franceville basin. Overall, the data collected in this study show that the Proterozoic–Archaean unconformity has operated as a major flow corridor for fluids circulation, around 1.9 Ga.  相似文献   

风成红黏土序列磁化率各向异性特征对区域应力变化的响应     

高新勃  强小科  赵辉  陈艇 《地球科学进展》2014,29(3):369-380

对六盘山以西132 m水洛红黏土剖面磁化率各向异性特征的研究表明,水洛红黏土剖面记录的14.8~8.7 Ma沉积序列受到了同沉积时期不同程度的应力作用,磁化率各向异性变化特征对应于应力作用强度较弱的初期和应力作用强度有所加强的中期。进一步分析发现,14.8~11.0 Ma之间显示出3次应力增强和后续应力减弱交替变化的特点,这一应力作用事件可能与青藏高原东北缘在此阶段强烈构造活动的区域应力传递相关,而11.0~8.7 Ma期间存在一个相对较强的应力作用事件,可能是对局部地区应力增强事件的响应。  相似文献   

Exploring aberrant bivalve shell ultrastructure and geochemistry as proxies for past sea water acidification     

Sabine Hahn  Erika Griesshaber  Wolfgang W. Schmahl  Rolf D. Neuser  Ann‐Christine Ritter  Rene Hoffmann  Dieter Buhl  Andrea Niedermayr  Anna Geske  Adrian Immenhauser 《Sedimentology》2014,61(6):1625-1658

Throughout much of Earth's history, marine carbonates have represented one of the most important geological archives of environmental change. Several pivotal events during the Phanerozoic, such as mass extinctions or hyperthermal events have recently been associated with ocean acidification. Nevertheless, well‐defined geological proxies for past ocean acidification events are, at best, scarce. Here, experimental work explores the response of bivalve shell ultrastructure and isotope geochemistry (δ¹³C, δ¹⁸O and δ²⁶Mg) to stressful environments, in particular to sea water acidification. In this study, the common blue mussel, Mytilus edulis, was cultured (from early juvenile stages to one year of age) at four pH regimes (pH_NBS 7·2 to pH 8·0). Shell growth rate and ultrastructure of mainly the calcitic portion of the shells were compared between experimental treatments. Specimens exposed to low‐pH environments show patches of disordered calcitic fibre orientation in otherwise well‐structured shells. Furthermore, the electron backscattered diffraction analyses reveal that, under acidified conditions, the c‐axis of the calcite prisms exhibits a bimodal or multi‐modal distribution pattern. Similar shell disorder patterns have been reported from mytilids kept under naturally acidified sea water conditions. In contrast, this study found no evidence that different pH regimes affect shell carbon, oxygen or magnesium isotope ratios. Based on these observations, it is proposed that: (i) stressful environments, in this case low sea water pH, predictably affect bivalve biomineralization patterns; and (ii) these findings bear potential as a novel (petrographic) proxy for ancient sea water acidification. An assessment of the applicability of these data to well‐preserved fossil shell material from selected time intervals requires additional work.  相似文献