安徽肥西中生代碎屑岩地球化学特征及其对物源制约

位于合肥盆地南部安徽肥西地区的中生代地层，包括防虎山组、园筒山组和周公山组，主要由砂岩组成。虽然初步研究表明物源主要来自大别造山带，但是，进一步限制物源区类型、建立和大别山造山带构造单元之间的对应关系、查清大别山造山带和华北陆块作为物源在研究区的影响范围，具有重要地质意义。本文根据砂岩主元素、REE和微量元素研究表明，研究区砂岩主要是杂砂岩、岩屑砂岩和长石砂岩，主元素含量比较接近晚元古代造山带砂岩。砂岩非常一致的REE模型，基本显示了同一的物源和相同的构造背景。REE和微量元素特征显示肥西地区中生代砂岩物源主要为佛子岭群和卢镇关群，大别杂岩的影响比较局限，更没有来自华北克拉通的物质。同时，在中生代，大别山造山带的物源没有影响到华北陆块南部沉积。Th-Co-Zr／10和Th-Sc-Zr／10判别图以及微量元素比值都支持碎屑岩的物源形成于大陆岛弧构造背景，这不仅验证了已有的结论，同时也揭示了在造山带周缘盆地中碎屑岩地球化学特征具有构造背景的继承性。     

南堡凹陷新近系馆陶组砂岩地球化学、构造背景和物源探讨

对南堡凹陷馆陶组(粉)砂岩的主量、微量及稀土元素的地球化学特征研究表明：多数主量元素含量中等,SiO₂、Al₂O₃等主元素含量及其相关比值反映大多数砂岩属于岩屑砂岩和长石砂岩,个别为杂砂岩;镁铁族元素(Co,Cr,Ni,Sc,V)和大离子亲石元素(Rb,Cs,Ba,Sr)含量类似于上地壳。砂岩十分相似的REE分布模式显示了相似的物源和构造背景。SiO₂-K₂O/Na₂O图解、主元素双变量判别图解及Th-Sc-Zr/10和Th-Co-Zr/10等构造背景判别图解均表明,馆陶组物源区属于活动大陆边缘构造背景。根据主元素物源判别方程图、La/Sc-Co/Th和Th-Hf-Co图投影及(Gd/Yb)_N值,表明馆陶组物源主要来自由长英质岩石组成的后太古宙上陆壳。通过与燕山地区不同时代(期)中酸性火山岩和花岗岩REE的对比,表明母岩主要来自燕山褶皱带地区于燕山期发育的中酸性火山岩和/或花岗岩体。     

大别山东南麓中新生代碎屑岩地球化学特征及其对物源的制约

位于大别山东南麓的安庆-潜山地区中新生代碎屑岩比较发育,主元素分析表明,砂岩主要为杂砂岩,其次是岩屑砂岩和长石砂岩。根据主元素、微量元素和稀土元素特征值分析结果,中、上三叠统和下、中侏罗统的源岩来源广泛,属于大陆岛弧、活动大陆边缘和被动大陆边缘构造背景,可能反映了前陆盆地物源的二元特征。古近系源岩主要为活动大陆边缘和大陆岛弧构造环境,说明物源仅来自大别山造山带。稀土元素比值及相关系数分析揭示,中晚三叠世黄马青群的源岩主要为宿松群的长英质片岩、浅粒岩以及大别杂岩,侏罗纪磨山组大致类似于大别群的花岗片麻岩,罗岭组与大别群比较类似。显示大别山造山带在中晚三叠世已经隆升并遭受剥露。     

Modal analysis and geochemistry of two sandstones of the Bhander Group (Late Neoproterozoic) in parts of the Central Indian Vindhyan basin and their bearing on the provenance and tectonics

The Neoproterozoic Bhander Group in the Son Valley, central India conformably overlying the Rewa Group, is the uppermost subdivision of the Vindhyan Supergroup dominantly composed of arenites, carbonates and shales. In Maihar-Nagod area, a thick pile of unmetamorphosed clastic sedimentary rocks of Bhander Group is exposed, which provides a unique opportunity to study Neoproterozoic basin development through provenance and tectonic interpretations. The provenance discrimination and tectonic setting interpretations are based on modal analysis and whole rock geochemistry. The average framework composition of the detrital sediments composed of quartz and sedimentary lithic fragments are classified as quartz arenite to sublitharenite. The sandstone geochemically reflects high SiO₂, moderate Al₂O₃ and low CaO and Na₂O type arenite. The high concentration of HFSE such as Zr, Hf, and Th/Sc, Th/U ratios in these sandstones indicate a mixed provenance. The chondrite normalized REE pattern shows moderate to strong negative Eu anomaly which suggests that major part of the sediments were derived from the granitic source area. The sandstone tectonic discrimination diagrams and various geochemical plots suggest that the provenance of the lower and upper Bhander sandstone formations was continental interior to recycled orogen.     

大兴安岭南段兴-蒙草原区二叠纪砂岩物源分析

对大兴安岭南部兴-蒙草原区二叠纪砂岩的统计研究表明,本区二叠纪砂岩主要为长石岩屑砂岩,大量非成熟组分为该区二叠纪砂岩的形成提供了物源。主量、微量和稀土元素特征指示,二叠纪砂岩物源区的构造背景主要为大陆岛弧环境,砂岩碎屑来自上地壳长英质源区。二叠纪砂岩的时代由老到新表现出由再旋回造山带向切割岩浆弧源区过渡的特征。结合沉积学特征,反映中、晚二叠世构造背景由活动陆缘逐渐趋于稳定,该时期记录了中亚造山带东段最终闭合的过程。     

东营凹陷南坡沙河街组四段砂岩地球化学特征

基于东营凹陷南坡沙河街组四段砂岩的某些常量元素和微量元素(包括稀土元素)含量的变化规律,研究了该地区砂岩的地球化学特征。本地区沙河街组四段砂岩类型以岩屑长石砂岩和长石岩屑砂岩为主,部分砂岩为岩屑砂岩和长石砂岩。A-CN-K三角图解反映了砂岩的母岩中斜长石含量要高于钾长石含量,主要在花岗闪长岩和花岗岩(含相应的片麻岩)之间变化。砂岩在风化过程中受到了钾的交代作用。化学风化作用指标(CIW)和化学蚀变作用指标(CIA)反映了该地区砂岩受到了强烈的风化作用,尤以纯梁地区为强。化学组份变化指标(ICV)反映了有些砂岩中含有第一次旋回沉积物。微量元素比值(La/Yb)_N、(La/Lu)_N等也反映了该地区砂岩来源于花岗闪长岩和花岗岩的混合物。     

西秦岭造山带徽成盆地早白垩世地层物源综合分析

徽成盆地是西秦岭造山带内一个具有代表性的盆地,保留较完整的地层记录.早白垩世田家坝组、周家湾组和鸡山组为一套砂砾岩沉积组合序列.本文通过对早白垩世砂岩的古水流恢复、砾石成分与含量、重矿物和地球化学分析,对沉积岩物源区特征和原型盆地进行探讨.古水流恢复和砾石成分统计表明,沉积物主要是近源堆积,主要来自于盆地南缘和北部.重矿物研究结果表明,早白垩世砂岩母岩以岩浆岩为主,并有少量变质岩/沉积岩.地球化学分析表明,早白垩世砂岩为成熟度较低的硬砂岩和长石/岩屑砂屑岩.稀土元素标准化配分曲线呈现轻稀土富集、重稀土平坦和弱Eu负异常特征.砂岩物源区组成判别图研究表明,早白垩世砂岩的物源区主要出露长英质火山岩.砂岩源区构造环境判别图解及特征指数分析表明,早白垩世砂岩源区主要形成于大陆岛弧和活动大陆边缘.结合区域资料和前人研究,表明早白垩世徽成地区发育走滑拉分盆地.     

Classification and Diagenetic Characteristics of the Cretaceous Sandstones in the Southern Bredasdorp Basin,Offshore South Africa

A systematic petrographic and geochemical studies of 92 representative sandstone samples from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 in the southern part of the Bredasdorp Basin was undertaken to classify the sandstones as well as unravel the main diagenetic processes and their time relations. Petrographic study shows that the sandstones are largely subarkosic arenite and arkosic litharenite, which have underwent series of diagenetic processes as a result burial, rifting and subsequent uplift. The main diagenetic processes that have affected the reservoir properties of the sandstones are cementation by authigenic clay, carbonate and silica, growth of authigenic glauconite, dissolution of minerals and load compaction. The major diagenetic processes reducing the porosity are calcite cementation in the subarkosic arenite, and compaction and quartz cementation in arkosic litharenite. On the other hand, the formation of secondary porosity due to the partial to complete dissolution of early calcite cement, feldspars and minor grain fracturing has improved the reservoir property of the sandstone to some extent. The clay minerals in the sandstones commonly acts as pore choking cement, which reduces porosity. In general, there is no particular diagenetic process that exclusively controls the type or form of porosity evolution in the sandstones.     

山东省牛庄洼陷古近系沙河街组沙三中亚段储集层成岩作用研究

山东省牛庄洼陷古近系沙河街组沙三中亚段储集层岩石类型以长石岩屑砂岩和岩屑长石砂岩为主,岩石结构成熟度和成分成熟度均较低。砂岩成岩作用包括压实作用、胶结作用、交代作用、溶解作用等。压实作用主要有刚性颗粒发生脆性破裂、颗粒之间呈线接触和凹凸接触、岩石碎屑颗粒呈明显的定向排列、塑性颗粒挤压变形或刚性颗粒嵌入变形颗粒中、粘土质碎屑被挤压变形发生假杂基化等五种表现形式。胶结物主要有泥质胶结物、碳酸盐胶结物、自生粘土矿物和自生石英、长石。交代作用主要有石英交代长石颗粒、碳酸盐胶结物交代石英、长石及岩屑颗粒、碳酸盐胶结物之间的相互交代。发生溶解作用的主要是石英、长石和岩屑颗粒,胶结物中主要是碳酸盐矿物。目前研究区沙三中亚段储集层成岩演化处于晚成岩A期。影响成岩作用的主要因素为岩石成分、沉积环境、孔隙流体性质等。成岩作用对储集物性的影响主要表现在孔隙度和渗透率的变化,其中压实作用和胶结作用使储层原生孔隙迅速减少、渗透率降低,使得储集物性变差;而溶解作用是次生孔隙发育的主要因素,从而改善砂岩的储集性能。     

五宝场沙溪庙组裂缝成因分析

五宝场沙溪庙组裂缝主要是构造缝,包括充填缝、部分充填的张开缝、溶蚀缝,局部裂缝发育处溶洞,洞密度局部0.111个/m～26.67个/m。裂缝成因主要为构造成因。五宝场盆地受来自喜山期起主导作用的来自南东方向的挤压力和其在工区南西方向派生的指向北东的应力、来自北东的挤压力及其派生的应力控制;五宝场沙溪庙组储集岩主要为灰、灰白色长石石英砂岩、长石砂岩、浅灰色长石岩屑砂岩、岩屑长石砂岩及岩屑砂岩等类型,总体上储层砂岩为脆性岩层,具有低胶结物含量,低成份成熟度,高结构成熟度的岩石学特征[8]。     

松辽盆地南部钱家店铀矿床姚家组砂岩地球化学特征及地质意义

沉积物的地球化学成分在沉积岩物源分析及构造背景的研究中具有重要的作用.对研究区4口钻孔中的姚家组砂岩进行了详细的岩石学和地球化学研究,结果显示,砂岩碎屑颗粒石英含量最高,长石次之,岩屑含量最低,平均值分别为42%、37%和21%,具有锆石+钛磁铁矿+石榴子石的重矿物组合,反映源岩以酸性岩浆岩或变质岩为主,Dickinson判别图解表明物源主要来自于大陆物源区;姚家组砂岩的稀土元素以轻稀土富集、重稀土平坦、中度铕负异常为特征.砂岩CIA值为52.02~60.16,平均值为56.69,反映了干燥气候背景下弱的化学风化作用.源岩属性判别图解表明源岩为再旋回的古老沉积物及长英质火山岩.主量、微量和稀土元素的构造背景判别图解综合表明姚家组砂岩物源区为被动大陆边缘构造环境,结合区域构造演化,认为姚家组砂岩的物源为华北克拉通北缘燕山陆内造山带发育的火山-沉积岩系.      

Geochemistry of the Paleocene Clastic Rocks in Lishui Sag, East China Sea Shelf Basin: Implications for Tectonic Background and Provenance

The Lishui Sag, in the East China Sea Shelf Basin, is rich in hydrocarbons, with the major hydrocarbon-bearing layers being the Paleocene Mingyuefeng clastic rocks. Analysis of the implicit geologic background information of these Paleocene clastic rocks using petrological and geochemical methods has significant practical importance. These Paleocene sandstones are mainly lithic arenite, lithic arkose and greywacke, composed of K-feldspar, plagioclase, authigenic clays, silica and carbonates. As continental deposits, Yueguifeng clastic rocks have high aluminosilicate and mafic detritus contents, while the Lingfeng and Mingyuefeng Formations are rich in silica due to an oscillating coastal marine depositional environment. The major element contents of these Paleocene sandstones are low and have a concentrated distribution, indicating that the geochemical composition is non-epigenetic, transformed by sedimentary processes and diagenesis. The Yueguifeng detritus comprises recycled sediments, controlled by moderate weathering and erosion, while the Lingfeng and Mingyuefeng detritus is interpreted as primarily first-cycle materials due to low chemical weathering. In the Late Cretaceous to Early Paleocene, the Pacific Plate began subducting under the Eurasian Plate, causing an orogeny by plate collision and magma eruption due to the melting of subducted oceanic crust. This resulted in the dual tectonic settings of “active margin” and “continental island arc” in the East China Sea Shelf Basin. During the Late Paleocene, the Pacific Plate margin migrated eastward along with development of the Philippine Ocean Plate, and the tectonic setting of the Lishui Sag gradually turned into a passive continental margin. Detrital sources included both orogenic continental blocks and continental island arcs, and the parent rocks are primarily felsic volcanic rocks and granites.     

Integrated petrographic,mineralogical, and geochemical study of the upper Kaimur Group of rocks,Son Valley,India: Implications for provenance,source area weathering and tectonic setting

The upper Kaimur Group (UKG) of the Vindhyan Supergroup in central India, primarily consists of three rock types-Dhandraul sandstone, Scarp sandstone and Bijaigarh shale. The present study aims to reconstruct the parent rock assemblages, their tectonic provenance, mineralogy, weathering intensity, hydraulic sorting and depositional tectonic setting. Samples from the UKG rocks representing the Dhandraul sandstone, Scarp sandstone and Bijaigarh shale were studied using a combination of petrographic, mineralogical, and geochemical techniques. Texturally, medium to coarse grained UKG sandstones are mature and moderate to well sorted. Deficiency of feldspars in these sandstones indicates that the rocks are extensively recycled from distant sources. Their average modal composition for Scarp (avg. Qt₉₉ F₀.₂L_0.8) and Dhandraul (avg. Qt₉₉ F_0.1L_0.8) sandstones, classifies them as quartz arenite to sub-litharenite types, which is consistent with geochemical study. Major element concentrations revealed that sandstones have high SiO₂, K₂O < Na₂O, and low Fe₂O₃, which are supported by the modal data. On the other hand, sandstone samples are enriched in most trace elements such as Ce, Sr, V, Sc and Zr and depleted in U and Th. The CIA values (43.17–76.48) of the UKG rocks indicate low to moderate weathering, either of the original source or during transport before deposition, which may have related to low-relief and humid climatic conditions in the source area. Further, petrographic and geochemical interpretations indicate that they are derived from craton interior to quartzose recycled sedimentary rocks and deposited in a passive continental margin. Therefore, granitic and low grade metamorphic rocks of Mahakoshal Group and Chotanagpur granite-gneiss, situated on the southern and south-eastern side of the Vindhyan basin are suggested as possible provenance for the UKG rocks.     

新疆库鲁克塔格南华系砂岩碎屑组成对其物源及盆地演化的指示

库鲁克塔格南华系记录了塔里木北缘同期的火山-沉积事件和蚀源区物质组成及演化的信息。该区不同剖面内南华系各组砂岩碎屑组分的统计分析显示,贝义西组砂岩在不同剖面内组成差异显著:西山口剖面以岩屑砂岩为主,且岩屑为火山岩岩屑与沉积岩岩屑,物源为再旋回地层,而依格孜塔格剖面以长石砂岩和岩屑长石砂岩为主,岩屑主要为变质岩岩屑,物源为下伏古元古代高级变质岩。砂岩碎屑组成在剖面上垂向的变化表明贝义西组沉积期与照壁山组沉积期间（725 Ma±）存在一个沉积转型事件,导致贝义西组之上的照壁山组、阿勒通沟组及特瑞艾肯组砂岩组成在不同区域趋于一致,转变为代表基底隆起-过渡大陆区物源的典型“长石砂岩”。南华系砂岩碎屑组成与大陆裂谷盆地沉积砂岩相似,且物源区存在由前裂谷地层-过渡裂谷肩部-切割裂谷肩部-克拉通内部的连续演化过程,是库满凹陷早期裂解的岩相学记录。     

Petrography and geochemistry of Jurassic sandstones from the Jhuran Formation of Jara dome,Kachchh basin,India: Implications for provenance and tectonic setting

Sandstones of Jhuran Formation from Jara dome, western Kachchh, Gujarat, India were studied for major, trace and rare earth element (REE) geochemistry to deduce their paleo-weathering, tectonic setting, source rock characteristics and provenance. Petrographic analysis shows that sandstones are having quartz grains with minor amount of K-feldspar and lithic fragments in the modal ratio of Q ₈₉:F ₇:L ₄. On the basis of geochemical results, sandstones are classified into arkose, sub-litharenite, wacke and quartz arenite. The corrected CIA values indicate that the weathering at source region was moderate to intense. The distribution of major and REE elements in the samples normalized to upper continental crust (UCC) and chondrite values indicate similar pattern of UCC. The tectonic discrimination diagram based on the elemental concentrations and elemental ratios of Fe₂O₃ + MgOvs. TiO₂, SiO₂ vs. log(K₂O/Na₂O), Sc/Cr vs. La/Y, Th–Sc–Zr/10, La–Th–Sc plots Jhuran Formation samples in continental rift and collision settings. The plots of Ni against TiO₂, La/Sc vs. Th/Co and V–Ni–Th ?10 reveals that the sediments of Jhuran Formation were derived from felsic rock sources. Additionally, the diagram of (Gd/Yb) _N against Eu/Eu ^? suggest the post-Archean provenance as source possibly Nagar Parkar complex for the studied samples.     

Petrographical and geochemical signatures of Jurassic rocks of Chari Formation,Western India: implications for provenance and tectonic setting

The sandstones of the Ridge and Athleta members of Chari Formation (Callovian-Oxfordian) exposed at Jara have been analyzed for their petrographical and geochemical studies. Texturally, these sandstones are medium to coarse grained, poorly to well sorted, sub-angular to sub-rounded, and show low to medium sphericity. These sandstones were derived from a mixed provenance including granites, granite-gneisses, low and high-grade metamorphic, and some basic rocks of Aravalli range and Nagarparkar massif. The petrofacies analysis reveals that these sandstones belong to the continental block and recycled orogen tectonic regime. The studied sandstones are modified by paleoclimate, distance of transport, and diagenesis. Mineralogically and geochemically, sandstones are classified as quartzarenite, subarkose, arkose, sublithic arenite, and wacke, respectively. The A-CN-K ternary plot and CIA, CIW, PIA, and ICV values suggest that the similar source rocks suffered moderate to high chemical weathering under a hot-humid climate in an acidic environment with higher \({\text{P}}_{{{\text{CO}}_{ 2} }}\). Generally good to strong correlations between Al₂O₃ and other oxides in these sediments indicate clay mineral control. The K₂O/Na₂O versus SiO₂ diagram indicates that the studied samples occupy passive margin fields but the SiO₂/Al₂O₃ versus K₂O/Na₂O plot suggests that the Athleta Sandstone and Ridge Sandstone fall within the passive margin field, while Ridge Shale falls within the active continental margin field.     

Petrography and provenance of subsurface Neogene sandstones of Bengal Basin, Bangladesh

This study deals with petrography and provenance of the Neogene reservoir sandstones encountered in the Kailas Tila, Titas, Bakhrabad and Shahbazpur Gas Fields of Bengal Basin. Framework grains are sand-sized to silt-sized particles of mainly detrital origin. The most common detrital grains are quartz, feldspars, and rock fragments. Mica occurred as minor and non-opaque heavy minerals found as minor accessories. Among the main detrital framework grains, quartz constitutes 51–60%, feldspar 3–15%, lithic fragments 8–22%. Sandstones encountered in the studied wells have been classified as sublithic arenite, feldspathic arenite and lithic arenite in order of abundance. Different triangular plots reveal that the Neogene sandstones of the studied wells exhibit a quartzolithic composition, low feldspar, very low volcanic grains and abundant sedimentary and low grade metamorphic lithic clasts indicating that the sands were derived from quartzose recycled orogen province, such as a fold thrust province or a collision suture zone. This study suggests that either the eastern Himalayas or Indo-Burman Ranges might act as the source of the sandstones of the studied wells of the Bengal Basin.     

Diagenetic differences in tight sandstone reservoirs in two delta fronts: an example from the Chang 4 and 5 members of the Yanchang Formation in the Longdong area,Ordos Basin,China

With the intensification of oil and gas exploration, tight sandstone reservoirs have received an increasing amount of attention, particularly with regard to the genesis of tight reservoir rock. The Upper Triassic Yanchang Formation in the Longdong area of the Ordos Basin has developed a typical tight, oil-bearing, clastic reservoir (lithic arkose and feldspathic litharenite, grain size is mainly 0.1~0.3 mm in diameter). During the depositional period of the Chang 4 and 5 members, the two provenance systems of the southwest and northeast developed in the study area. In the southwest, sandstones in the lower part of distributary channels are coarser with fewer quartz overgrowth and ankerite and better reservoir quality (porosity about 12%, permeability about 1 mD). In the northeast, chlorite coating is thicker (>?4 vol%) in the underwater channel sandstones (porosity is about 14%, permeability is about 2 mD) than in the mouth bar sandstones. Sandstones in the upper part of distributary channels are finer with lower permeability (about 0.1 mD). Authigenic ankerite mainly appears around detrital dolomite as an overgrowth. The SiO₂ in the quartz overgrowth most likely came from the transformation of smectite to illite and the dissolution of feldspar. In the northeast, only 2 vol% of chlorite rims significantly inhibited quartz overgrowth, but they probably blocked and delayed the dissolution of feldspars by acids. We present results here that show the diagenetic differences in sand bodies in delta fronts are influenced by sediment size, maturity, and the composition of framework grain; the materials that compose authigenic minerals mainly come from the alteration of sandstones. As a whole, the formation of tight reservoir rocks in the study area is closely related to sedimentary facies, composition of framework grain, cement type and content, and development of dissolution.     

Depositional environment and tectono-provenance of Upper Kaimur Group sandstones,Son Valley,Central India

The Mesoproterozoic Upper Kaimur Group consists of Bijaigarh Shale, Scarp Sandstone, and Dhandraul Sandstone. Based on the lithofacies data set, two major facies associations were identified, namely—tidal sand flat/sand bar facies association (TSFA) and tidally influenced fluvial channel facies/tidal channel facies association (TIFCFA). The Dhandraul Sandstone has been interpreted as a product of TIFCFA and the underlying Scarp Sandstone in TSFA which endorses a tidal dominated estuarine setting. Detrital modes of the Dhandraul and Scarp Sandstones fall in the quartz arenite to sub-litharenite types. Petrographical data suggest that the deposition of the Upper Kaimur Group sandstones took place in humid climate and was derived from mixed provenances. The sandstone composition suggests detritus from igneous rocks, metamorphic rocks, and recycled sedimentary rocks. The sandstone tectonic discrimination diagrams suggest that the provenances of the Upper Kaimur Group sandstones were continental block, recycled orogen, rifted continental margin to quartzose recycled tectonic regimes. It is envisaged that the Paleo- and Mesoproterozoic granite, granodiorite, gneiss, and metasedimentary rocks of Mahakoshal Group and Chotanagpur granite–gneiss present in the western and northwestern direction are the possible source rocks for the Upper Kaimur Group in the Son Valley.