珠江口盆地东沙隆起生物礁地质及地震特征

东沙隆起珠江组生物礁是珠江口盆地重要的储层类型,礁灰岩主要为珊瑚藻灰岩,分为骨架岩、粘结岩及障积岩。研究区生物礁发育于开阔台地、台地边缘及台地前缘斜坡3类沉积相中,生物礁类型可分为台内点礁、台地边缘堡礁及台缘斜坡塔礁,以台地边缘堡礁为主。珠江组沉积早期,东沙隆起发育滨岸砂质沉积;中期海水逐渐淹没东沙隆起,形成镶边浅水碳酸盐台地,发育生物礁;晚期海侵台地逐渐淹没消亡,被浅海陆棚泥质沉积代替。流花台地厚度最大,最厚达563m,台地顶面地震强反射使外形轮廓清晰,台地内部中-弱振幅至空白反射,连续性降低;惠州台地厚度较流花台地薄,厚度多大于100m,顶界面强反射轮廓清晰,内部层状反射能量强-中振幅、高-中连续、中-低频,局部空白反射;陆丰台地厚约30m,只有一个高连续的强振幅。生物礁地震响应以丘形、箱型、低丘-透镜状为特征,礁顶常为强振幅,内部为波状、有时见前积结构,翼部可见上超和披覆现象等。     

Geochronology,geochemistry and Hf isotope of Late Triassic magmatic rocks of Qingchengzi district in Liaodong peninsula,Northeast China

The initiation timing and mechanism of lithospheric thinning of the North China Craton (NCC) was still controversial. Late Triassic igneous rocks especially mantle derived mafic rocks would provide constrains on Early Mesozoic lithospheric mantle geodynamics and initiation of lithospheric thinning. This paper reports Late Triassic magmatic rocks, including lamprophyre, diorite dykes and biotite monzogranite cropped out in Qingchengzi district of Liaodong peninsula, northeastern NCC. LA–ICPMS zircon U–Pb dating yield ages of 210–227 Ma and 224 Ma for lamprophyres and biotite monzogranite respectively. Lamprophyre is ultrapotassic, strongly enriched in REE and LILEs, depleted in HFSEs, and negative Hf isotopes, which are discriminating signatures of crustal source, but distinguishingly high compatible element contents indicate the primary magma originated from mantle source—a fertile one. Lamprophyre derived from partial melting of an enriched lithospheric mantle, which was modified by slab-derived hydrous fluids/melts associated with deep subduction between the Yangtze Craton and the NCC. The diorite displays distinct features with relatively enriched Nb, Ta, HREE and depleted Th, U, which suggest it derived from a relatively depleted source. The depletion was caused by break-off of the Yangtze slab during deep subduction introducing asthenospheric mantle into the source. The biotite monzogranite shows adakitic affinity, and originated from partial melting of the thickened lower crust with addition of small proportion of mantle material. The recognition of Late Triassic magmatism implies extensional tectonic settings in Liaodong peninsula and suggests initiation of lithospheric thinning of North China Craton in eastern segment might begin early in Late Triassic.     

Restudy of conodont biostratigraphy of the Permian–Triassic boundary section in Zhongzhai,southwestern Guizhou Province,South China

New conodont samples have been systematically collected at high stratigraphic resolution from the upper part of the Longtan Formation through to the lower part of the Yelang Formation at the Zhongzhai section, southwestern Guizhou Province, South China, in an effort to verify the first local occurrence of Hindeodus parvus in relation to the Permian–Triassic boundary at this section. The resampled conodont fauna from the Permian–Triassic boundary interval comprises five identified species and two undetermined species in Hindeodus and Clarkina. Most importantly, the first local occurrence of Hindeodus parvus is found for the first time from the bottom of Bed 28a, 18 cm lower than the previously reported first local occurrence of this species at this section. Considering the previously accepted PTB at the Zhongzhai section, well calibrated by conodont biostratigraphy, geochronology and carbon isotope chemostratigraphy, this lower (earlier) occurrence of H. parvus suggests that this critical species could occur below the Permian–Triassic boundary. As such, this paper provides evidence that (1) the first local occurrences of H. parvus are diachronous in different sections with respect to the PTB defined by the First Appearance Datum (FAD) of this species at its GSSP section in Meishan, China and that (2) the lower stratigraphic range of H. parvus should now be extended to latest Permian.     

长江三峡地区成冰纪-埃迪卡拉纪转换时期微量元素和稀土元素地球化学特征

通过微量元素和稀土元素地球化学分析,对长江三峡地区陡山沱组层型剖面--田家园子剖面成冰系南沱组顶部和埃迪卡拉系陡山沱组下部102个岩石样品进行了地球化学研究。重点分析了氧化还原敏感元素(Zn,Co,U,Mo,Ni,V)的富集特征,并探讨其可能成因机制以及三峡地区成冰纪-埃迪卡拉纪转换时期的水体特征。结果表明:在南沱组顶部仅Zn和Co富集;在盖帽白云岩下部,氧化还原敏感元素均富集,而在盖帽白云岩上部,除Zn和V外,其他氧化还原敏感元素均亏损;在陡山沱组Ⅱ段下部,氧化还原敏感元素由最初的亏损,逐渐变为较稳定的富集。在陡山沱组下部,出现2次明显的富集峰值,分别出现在剖面的0.4m处(盖帽白云岩中间)和6.5m处(陡山沱组Ⅱ段下部)。整个剖面大部分样品具有Eu的轻微正异常(Eu/Eu^*＜1.6), 而在剖面0.4m和6.5m处,Eu具有明显的正异常,结合稀土配分类型、Y/Ho值、La异常、Ce异常等指标,推测这2次异常均可能受到深海热液流的影响,而缺氧海水的上涌造成水体缺氧,导致这些元素出现富集峰值。U/Th、V/(V+Ni)以及稀土元素指标综合指示,三峡地区南沱组顶部冰碛岩应为氧化环境下的沉积物;随着冰川消融,冰融淡水注入古海洋,陡山沱组盖帽碳酸盐的沉积受冰融淡水的影响,深部缺氧海水的上涌使沉积水体经历氧化-缺氧-氧化的转变,海水的分层性较强;而陡山沱组Ⅱ段下部沉积环境以分层性较弱的弱氧化环境为主。     

四川盆地震旦系灯影组葡萄状白云岩成因

四川盆地震旦系灯影组发育巨厚的白云岩,其中灯影组二段和四段发育大量具有各种形态的葡萄状白云岩,其直径最长可达75cm,有的平行于层面,有的穿层。剖面资料表明,葡萄状白云岩发育多期等厚环边胶结物,中部残留大量未充填的不规则洞穴,这成为与岩溶喀斯特作用相关的地下溶蚀作用的证据。围岩泥晶白云石为早期海水中原生结晶的产物,后来的胶结物可划分为4期: (1)自泥晶化白云石(部分样品中可见)作为最早的一期胶结物,由于各种生物化学作用和生物作用的影响而紧贴着围岩发育;(2)第2期胶结物纤维状白云石可能为海水中直接沉淀的产物,经历后期成岩作用后,具有完全有序的结构,晶胞参数接近理想值;(3)细—中晶白云石为第3期胶结物,包含纤维状白云石溶蚀残余,形成于构造抬升之后的近地表大气淡水环境;(4)第4期胶结物中—粗晶白云石为埋藏环境下直接结晶的产物,充填了孔洞中心,残留部分未充填孔洞。灯影组受到了岩溶喀斯特作用、胶结作用以及白云石化作用等成岩作用的影响,其中与葡萄状白云岩有关的岩溶喀斯特作用对于灯影组储集层的发育至关重要。对灯影组葡萄状白云岩的研究,不仅有助于深入探讨灯影组储集层成因和演化及灯影组白云岩的成因,而且有助于指导四川盆地前寒武系油气勘探。     

黔北务川—正安—道真地区下二叠统大竹园组和梁山组孢粉学研究

文中材料采自黔北务川—正安—道真地区下二叠统大竹园组和梁山组。大竹园组孢粉化石类型单调,保存较差;而梁山组孢粉化石丰富,保存良好。孢粉组合特征为:(1)大竹园组包含丰富的Calamospora和Florinites及少量Torispora verrucosa,Gulisporites,Alisporites,Hamiapollenites和Striatopodocarpites,这一孢粉组合主要出现在上石炭统至下二叠统。按照大竹园组层位和孢粉化石特征,其地质时代应为早二叠世Asselian期—Artinskian期(相当于紫松期—隆林期)。(2)梁山组中可建立孢粉组合Laevigatosporites vulgaris-Gulisporites-Florinites ovalis,共计发现孢粉化石34属49种,其中蕨类植物孢子含量为51.6％～56.1％,裸子植物花粉含量为43.9％～48.4％。与大竹园组沉积时期相比,这一时期植被极为繁盛。根据孢粉组合特征,梁山组地质时代可能为早二叠世隆林期,即Kungurian期。     

藏北龙木错—双湖—澜沧江板块缝合带发现晚石炭世—早二叠世洋岛型岩石组合

天泉群岛出露于龙木错—双湖—澜沧江板块缝合带的中西段,也是目前该缝合带上所发现的第一套洋岛型岩石组合。通过野外踏勘、剖面测制等对天泉群岛进行了较为详细的研究,结果显示,天泉群岛由9个孤立、岩石组合不同的洋岛组成,其中独泉沟洋岛、屏风岭洋岛的洋岛组分齐全,见玄武岩、灰岩、砾岩、硅质岩等,其他洋岛的洋岛组分不全。天泉群岛与展金组复理石沉积为整合接触,表明其形成时代为晚石炭世—早二叠世。天泉群岛的厘定,说明龙木错—双湖—澜沧江大洋在晚石炭世—早二叠世仍具有成熟的洋壳。该项研究进一步丰富了龙木错—双湖—澜沧江板块缝合带的演化内容,为反演区域地质演化历史提供了依据。     

广西南部凭祥中三叠世沉积盆地构造环境——来自岩相学和碎屑岩地球化学的证据

岩相学特征表明,广西凭祥盆地砾岩可分为颗粒支撑和基质支撑2种,砾石成分主要为生物碎屑灰岩,其次为砂岩和泥岩。盆地砂岩主要由成分成熟度和结构成熟度较低的亚岩屑(杂)砂岩和岩屑(杂)砂岩组成,物源区为碰撞造山带或再旋回造山带。碎屑岩地球化学特征表明,凭祥中三叠世盆地中的砂岩和泥岩样品SiO2含量为61.71%~74.85%,接近于上地壳的平均值。具有高的K2O/Na2O值(6.50~0.51)和高的TFe2O3+MgO含量(7.29%~10.31%),TFe2O3/K2O值为2.05%~5.54%,矿物稳定性较差。稀土元素标准化配分曲线呈现出轻稀土元素富集、重稀土元素平坦和明显的Eu、Ce负异常特征,类似于上地壳和典型的太古宙页岩,具有海相沉积的特征。砂岩风化蚀变指数CIA高(71~88),Th/U值为3.68~9.53,表明砂岩和泥岩经历了较强的风化作用。砂岩物源区判别图表明,凭祥盆地物源与酸性岛弧具明显的亲缘性,增生楔和活动陆缘是主要的物源区。这些特征综合表明,凭祥盆地是一个伴随古特提斯分支洋盆闭合、经强烈构造改造的残余弧前盆地。     

川南地区龙马溪组页岩有机质特征及其对页岩含气量的影响

四川盆地南部地区广泛发育下古生界寒武系、志留系等多套海相页岩层,其中龙马溪组是该区页岩气勘探开发的重点目标层。根据钻井岩心资料,通过有机碳、热解、碳同位素、等温吸附等地球化学实验分析,对川南地区下志留统龙马溪组页岩的有机质特征及其对页岩含气量的影响进行了研究。结果表明,川南地区龙马溪组页岩有机碳含量较高(平均1.53%),有机质类型较好(Ⅰ型和Ⅱ1型),热演化程度高(Ro为1.94%~2.42%),且页岩含气量较高(平均1.85m3/t)。页岩有机质特征是影响页岩含气量的主要因素,有机质丰度、有机质类型和热演化程度三者共同决定了川南地区龙马溪组页岩的含气量。     

湘中及湘东南地区上泥盆统佘田桥组页岩气勘探前景

湘中及湘东南地区泥盆纪佘田桥组具有良好的页岩气成藏条件,为页岩气勘探远景区。选取地质条件优越、页岩气特征明显的泥盆纪佘田桥组含气页岩作为主要研究对象,对页岩气储气特征和勘探开发潜力进行了分析。研究表明：含气页岩层分布面积广、有机碳含量高（TOC均值0.61%）、热演化程度高（Ro均值2.71%）,低孔低渗（孔隙度为0.7%,渗透率小于0.04×10^-3μm2）,且吸附能力强。含气页岩层厚度展布在凹陷盆地形成独特的“中心薄边缘厚”格局,结合其成藏特征和物化指数,划分出页岩气潜力较大的四个有利区。