Formation and Evolution of a Paleosol across the Lower Silurian-Lower Permian Boundary in Zunyi District, Northern Guizhou, China and Its Paleoenvironment and Paleoclimate Implications

This paper presents a set of bulk geochemical and mineralogical data from a paleoweathering profile located in Zunyi District, Northern Guizhou, China. It was formed at the top of the Hanjiadian Formation of the Lower Silurian. A truncated, argillic, gleyed, kryptic paleospodosol is recognized in the paleoweathering profile. Ratios of immobile elements (Ti/Zr, Ti/Al) and their binary (e.g., Nb vs. Zr/TiO2 and Th/Sc vs. Zr/Sc), triangular diagrams (La-Th-Sc, Th-Sc-Zr/10, Zr-Cr-Ga) reflect that the Gaojiayan paleosol is the product of in-situ weathering of gray-green silty mudstone of the underlying Hanjiadian Formation. Mass balance calculations indicate K enrichment and Na enrichment in the upper and lower portions of paleosol, respectively. These findings both are the results of transgression, which brings substantial concentrations of such elements as K, Na, and Sr. In particular, K enrichment is achieved by the illitization of kaolinite. The biological processes of terrestrial vascular plants also enhance K concentration, especially at the top of the paleosol. Na enrichment is a consequence of albitization and/or adsorption by clay minerals through cation exchange. The mass distributions and relative mass changes of rare earth elements (REEs) in the studied profile display characteristics of vertical zonation. Three peaks in total REEs content are observed, indicating two paleoclimatic or paleoenvironmental changes. Mineralogical characteristics indicate that the paleoclimate changed first from warm and humid to cold and dry and later, to dry and lightly warmer. The corresponding soil environment varies from weakly acidic to strongly alkaline and later, to weakly acidic. Mass translocation characteristics of REEs and several transition metals suggest that the Gaojiayan paleosol may have undergone top erosion.     

鄂尔多斯盆地塔然高勒地区直罗组上、下段的岩性-岩相特征及对铀成矿的差异性控制作用

为查明鄂尔多斯盆地塔然高勒地区直罗组上段、下段的岩性-岩相特征以及参与蚀变作用的流体强度差异,开展了系统的岩心观察、剖面对比,并结合黏土矿物、碳氧同位素和U、Th元素等手段进行分析。结果表明,研究区南部直罗组上段主要由灰绿色、红色泥岩夹透镜状红色、黄色、灰绿色砂岩组成,北部主要由红色泥岩与灰绿色砂岩构成,南北部下段均由灰白色、灰绿色砂岩或砂砾岩夹薄层泥岩组成。直罗组红色砂岩为原生沉积,灰绿色砂岩为后生改造类型;上段受含氧含铀水和深部还原性流体作用强度较下段变弱,且由北向南作用程度降低,北部还原蚀变岩石与原生岩石共存,南部基本保留原生岩石;下段则受流体改造更为充分,主体为后生蚀变岩石。直罗组不同类型砂体的展布兼受沉积相和后期流体双重作用,但强弱差异性明显,限制了铀矿化产出在直罗组下段砂体中的定位,因此,上、下段应作为不同的成矿体系讨论。     

天草凹陷下白垩统烃源岩的地球化学特征与凹陷含油气远景分析

研究了下白垩统巴音戈壁组、苏红图组一段两套烃源岩的地质、地球化学特征以及烃源岩的热演化, 评价了天草凹陷的含油气远景。研究表明,巴音戈壁组烃源岩规模大,有机质丰度高,有机碳平均1.34%,以Ⅱ1型有机质为主,已经历成熟热演化阶段,其质量与二连等盆地相当。天草凹陷总生烃量为18.37×108t, 石油资源量为0.74×108t,发育断鼻、断块与岩性圈闭等构造。圈闭和烃源岩在时空上的匹配较好,表明石油地质条件较好,可作为同规模、低勘探程度的新区凹陷中的首选勘探对象。     

长江中下游转换构造结的特征、属性及其研究意义

"长江中下游转换构造结"是特提斯构造体制与太平洋构造体制交汇、衔接和转换的焦点部位,主要包括大别造山带、郯庐断裂带、长江中下游成矿带三大著名的构造单元,是中国东部中新生代大陆动力学深部过程与浅表响应的经典地区。将大陆造山带、大型断层、矿集区结合起来,瞄准板内变形、运动学和动力学,建立区内大陆动力学的系统研究框架,研究两大构造体制转换的精细过程,分析陆内构造演化和动力学的深部过程与浅部效应,将有助于大陆动力学理论的新突破,指导"第二成矿空间"的深部找矿。     

Granulite and pyroxenite xenoliths from the Deccan Trap: insight into the nature and composition of the lower lithosphere beneath cratonic India

Granulite and pyroxenite xenoliths in lamprophyre dykes intruded during the waning stage of Deccan Trap volcanism are derived from the lower crust beneath the Dharwar craton of Western India. The xenolith suite consists of plagioclase-poor mafic granulites (55% of the total volume of xenoliths), plagioclase-rich felsic granulites (25%), and ultramafic pyroxenites and websterites (20%) with subordinate wehrlites. Rare spinel peridotite xenoliths are also present, representing mantle lithosphere. The high Mg #, low SiO₂/Al₂O₃ and low Nb/La (<1) ratios suggest that the protoliths of the mafic granulites broadly represent cumulates of sub-alkaline magmas. All of the granulites are peraluminous and light rare-earth element-enriched. The felsic granulites may have resulted from anatexis of the mafic lower crustal rocks; thus, the mafic granulites are enriched in Sr whereas the felsic ones are depleted. Composite xenoliths consisting of mafic granulites traversed by veins of pyroxenite indicate intrusion of the granulitic lower crust by younger pyroxenites. Petrography and geochemistry of the latter (e.g. presence of phlogopite) indicate the metasomatised nature of the deep crust in this region.Thermobarometric estimates from phase equilibria indicate equilibration conditions between 650 and 1200 °C, 0.7-1.2 GPa suggestive of lower crustal environments. These estimates provide a spatial context for the sampled lithologies thereby placing constraints on the interpretation of geophysical data. Integration of xenolith-derived P-T results with Deep Seismic Soundings (DSS) data suggests that the pyroxenites and websterites are transitional between the lower crust and the upper mantle. A three-layer model for the crust in western India, derived from the xenoliths, is consistent with DSS data. The mafic nature of this hybrid lower crust contrasts with the felsic lower crustal composition of the south Indian granulite terrain.     

松辽盆地中央坳陷南部下白垩统泉头组四段沉积相

松辽盆地中央坳陷南部下白垩统泉头组四段沉积时期,松辽盆地地形平缓,基底沉降缓慢,在湖平面整体扩张及浅水背景下河流入湖成三角洲沉积。通过岩心观察、相标志与测井相研究,该区储层主要为岩屑长石砂岩和长石岩屑砂岩,识别出三角洲平原、三角洲前缘、前角洲3种亚相,以及分支河道、天然堤、决口扇、分支河道间湾、水下分支河道、水下决口扇、河口坝、远沙坝、水下分支河道间湾9种微相三角洲平原、三角洲前缘广泛发育,前三角洲不发育。三角洲平原分支河道通过填积和频繁的分叉改道,向湖盆中心方向长距离推进,在三角前缘的浅水区域发育了大量水下分支河道,分支河道与水下分支河道砂体相互切割、叠加,形成了平均宽度200~600 m、平均厚度3~8 m的道单砂体,（水下）分支河道砂体构成了油气富集的主要储集体。该区沉积相的精细研究,为进一步调整开发井网奠定了基础。     

镇江大力山中,下三叠统沉积特征及环境分析

镇江大力山中、下三叠统青龙组2段和3段发育的瘤体灰岩属盆地边缘斜坡环境,杂乱瘤体灰岩横向相变为盆地边缘斜坡滑塌重力流成因(深水)的泥晶砾屑灰岩;蠕粒灰岩则为台地前缘斜坡的浅水沉积环境,与浅水重力流的砾屑泥晶灰岩共生.     

Hydrothermal Dolomite in the Upper Sinian (Upper Proterozoic) Dengying Formation,East Sichuan Basin,China

Hydrothermal Dolomite （HTD） is present in the Upper Sinian （Upper Proterozoic） Dengying Formation, east Sichuan Basin, China. The strata are comprised by primary dolomite. The HTD has various textures, including zebra dolomite, subhorizontal sheet-like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures. Also co-occur MVT type lead-zinc ores in the study area. The δ13C and δ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks, while STSr/86Sr is higher. The apparent difference in carbon, oxygen and strontium isotopes, especially the large difference in S7Sr/S6Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids. Saddle dolomite was precipitated at temperatures of 270-320℃. The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are： （1） dolomite host rock →sphalerite-galena-barite-fluorite; （2） dolomite host rock →saddle dolomite →quartz; （3） dolomite host rock →saddle dolomite→bitumen; （4） dolomite host rock →saddle dolomite →barite. The mean chemical composition of the host dolomite matrix and HTD didn＇t change much during hydrothermal process. The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian, fluids from diagenetic compaction and hydrocarbon generation ＆ expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones, and hydrothermal fluids from the basement. The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata. The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores. Dissolution cavities are extensive at the top of Dengying Formation, up to about 46m below the unconformity between Sinian an     

Histological bone structure of Lower Cretaceous dinosaurs from southwest Istria (Croatia)

Recently discovered dinosaur bones in submerged near-shore deposits of southwest Istria include one vertebra, one femur, and two rib fragments. They all show well-developed vascularization. The large amounts of primary bone tissue in the vertebral and femoral compacta as well as in one rib fragment suggest that they belong to sub-adult animals which were growing rapidly. The structure of a second rib fragment differs in that it consists of secondary bone. The absence of lines of arrested growth is evident in all investigated bones. This suggests a sustained manner of bone deposition.     

海南岛西部大广坝地区晚奥陶世-早志留世笔石地层的发现及意义

笔者于海南岛西部大广坝地区一套浅变质岩系中首次发现晚奥陶世-早志留世笔石,经鉴定属双笔石类。有关此套地层的时代归属长期存在争议,先后划归为寒武纪、前泥盆纪、泥盆纪-石炭纪、石炭纪、二叠纪,笔石的发现为其时代归属提供了依据,并进一步证实了该区晚奥陶纪-早志留纪地层的存在,为海南岛中北部地区奥陶纪-志留纪深水相地层的划分与对比、时代归属、及海南岛含笔石地层的研究提供了新资料,对古生物地理分区、沉积相、沉积大地构造背景及大地构造格局的研究也具重要意义。