Quantitative textural analysis of packings of elongate crystals     

John F. Rudge  Marian B. Holness  Graham C. Smith 《Contributions to Mineralogy and Petrology》2008,156(4):413-429

The spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush, and in turn is controlled by the rate of crystal growth and accumulation. A predominant non-spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution. Furthermore, variations of crystal clustering/ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours. Using random close packings of spherocylinders, we demonstrate the importance of aspect ratio for the aggregation index (usually known as R) and show that packings of spherical particles have more structure than packings of rods. The spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the Holyoke basalt are clustered on a length scale of 0.5 mm. Understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well-understood environments.  相似文献   

新疆准噶尔盆地西北缘吐谷鲁群沉积体系分析   总被引：2，自引：0，他引：2  

姜勇彪  刘帅  巫建华  饶明辉  鲁克改  朱成刚 《铀矿地质》2008,24(1):17-23

根据在新疆准噶尔盆地西北缘乌尔禾-夏子街地区的野外地层露头观察、追索及钻孔资料分析研究,笔者认为,该区下白垩统吐谷鲁群是一套以灰绿色砂岩和红色、棕红色泥岩组成的干燥气候条件下形成的内陆湖相碎屑沉积,发育浅水三角洲体系,主要由三角洲平原和三角洲前缘相组成.吐谷鲁群碎屑岩的碎屑粒度由下而上可分为两个大的韵律旋回,即粗-细-粗-细,反映了水体扩展到萎缩再扩展的过程.有利铀成矿的砂岩层主要集中在两个韵律旋回的底部,形成于三角洲平原分流河道、决口扇、三角洲前缘水下分流河道和水下堤环境.  相似文献   

High-resolution sediment echosounding off Peru: Late Quaternary depositional sequences and sedimentary structures of a current-dominated shelf     

Reinhardt  L.  Kudrass  H.-R.  Lückge  A.  Wiedicke  M.  Wunderlich  J.  Wendt  G. 《Marine Geophysical Researches》2002,23(4):335-351

About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure.  相似文献   

珊瑚礁岩心声速垂向跃变及其指相意义     

李赶先  卢博 《台湾海峡》2001,20(3):308-313

本文在南沙群岛永署礁南永1井珊瑚礁岩心声速测量的基础上，研究了珊瑚礁岩心声速的垂向跃变特征和相应地层沉积相变及地层侵蚀间断面的关系，分析了珊瑚礁岩心相变造成其声速跃变的原因，阐明了海平面升降形式珊瑚礁地层侵蚀间断面和产生相变的具体过程, 明了珊瑚礁岩心声速垂向跃变与相应地层古气候和海平面变化的关系，该项研究在岛礁工程建设和礁灰岩区石油勘探声学测井以及西太平洋边缘海古海洋学研究学方面具有重要的实用价值和理论意义。  相似文献   

Post-Miocene stratigraphy and depositional environments of valley-fill sequences at the mouth of Tampa Bay, Florida     

Thomas W. Ferguson  Richard A. Davis  Jr.   《Marine Geology》2003,200(1-4):157-170

Post-Miocene sea-level low stands allowed rivers and karst processes to incise the exposed carbonate platform along the Gulf Coast of Florida. Few Miocene to mid-Pleistocene deposits survived erosion along the present coast except within incised valleys. Since their formation, these valleys have been filled and incised multiple times in response to sea-level changes. The thick sedimentary sequences underlying the mouth of Tampa Bay have been recorded as a range of depositional environments and multiple sea-level incursions and excursions during pre-Holocene time and subsequent to the accumulation of the Miocene carbonate sequences. Sediment analysis of cores collected from a north–south transect across the mouth of Tampa Bay has enabled the identification of lithofacies, ranging from well-sorted, quartz sand to dense, fossiliferous, phosphatic grainstone. These facies were deposited in freshwater, estuarine, and shallow, open marine environments. As a result of channel development and migration within the paleovalley, and cut-and-fill associated with individual transgressions and regressions, correlation of the lithofacies does not extend across the entire transect. Fining-upward sequences truncated by tidal ravinement surfaces that extend throughout the paleovalley can, however, be identified. Age determinations based on 14-C analysis, amino-acid racemization, and strontium isotope analysis dating of numerous samples yield ages of Miocene, Pliocene, early Pleistocene, and late Pleistocene, as well as Holocene for sequences that accumulated and were preserved in this valley-fill complex. Numerous inconsistencies in the stratigraphic organization of the age determinations indicate that there are bad dates, considerable reworking of shells that were dated, or both. For this reason as well as the lack of detailed correlation among the three relatively complete cores, it is not possible to place these strata in a sequence stratigraphic framework.  相似文献   

南海北缘东部盆地油气资源研究   总被引：5，自引：0，他引：5  

杜德莉  王树民  陈弘  陈泓君  万玲 《海洋地质与第四纪地质》2001,21(3):67-74

南海北缘东部的珠江口盆地及台西南盆地蕴藏着十分丰富的油气资源，根据区域构造背景、盆地发育分布的特点及中、新生代的油气地质条件，结合含油气构造、油气田、油气井的分布规律，利用油气资源评价的理论、方法，对区内的油气资源进行了综合研究，并按照油气资源状况划分出油气富集区、油气潜力区、油气远景区，在此基础上，再进一步划分出4条油气富集带、11条油气潜力带、8条油气远景带，充分显示了该区石油、天然气的分布规律和油气地质特点，为商业性的勘探开发和理论研究奠定了基础。  相似文献   

Vertical Sound Velocity Transition in the Coral Reef Core and Its Significance of Indicating Facies     

李赶先  卢博 《海洋通报(英文版)》2002,4(1):19-26

On the basis of the sound velocity measurements of the coral reef core from Nanyong No.1 well of Yongshu Reef in the Nansha Islands,the paper studies the relations between the vertical sound velocity transition features in the coral reef core and the corresponding stratigraphic depositional facies change as well as stratigraphic gap of erosion,analyses the cause of the sound velocity transition,expounds the concrete process of the sea level change resulting in the stratigraphic gap of erosion and facies change in the coral reef and explains the relations between the vertical sound velocity transition in the coral reef core and the corresponding stratigraphic paleoclimate and the sea level change.This study is of important practical value and theoretical significance to the island and reef engineering construction and the acoustic logging for oil exploration in the reef limestone area as well as the paleoceanographic study of the marginal sea in the westerm Pacific Ocean.  相似文献   

浊积砂体沉积微相及储层非均质性研究——以东营胜坨油田T74地区古近系沙河街组三段中亚段浊积砂体为例   总被引：1，自引：0，他引：1  

蔡传强  严科  杨少春  任怀强  陈宁宁 《高校地质学报》2008,14(3)

利用岩心观察、测井相分析、测井资料处理与评价、图像分析等方法,系统研究了胜坨油田T74地区古近系沙河街组三段中亚段浊积砂体的沉积微相及储层非均质性.研究表明,T74地区沙河街组三段中亚段储层由三期浊积砂体叠加形成,可划分为中心微相和边缘微相两种沉积微相带;各期浊积砂体储层非均质性较强,层内非均质性以韵律性不明显、渗透率差异大为主要特征,层间及平面非均质性主要受沉积微相控制,中心微相储层的物性要好于边缘微相;不同沉积相带储层微观孔隙结构存在差异,中心微相主要发育中孔中喉和细孔中喉型孔隙结构,边缘微相主要发育细孔细喉以及微孔型孔隙结构.  相似文献   

黄骅坳陷北大港构造带沙河街组沉积体系定量研究   总被引：2，自引：0，他引：2       下载免费PDF全文

吴林钢  朱筱敏  范乐元  钟大康 《古地理学报》2008,10(3):241-250

针对陆相湖盆沉积特征,以T A Cross高分辨率层序地层学理论为指导,在大量岩心、测井和地震资料研究的基础上,定量研究了黄骅坳陷北大港构造带沙河街组沉积体系和沉积物源特征,确定了沙河街组沉积时期总体发育近岸水下扇、滩坝、深水重力流水道、扇三角洲前缘和滑塌浊积扇等主要沉积相类型。中期基准面旋回A-D层序沉积时期发育近岸水下扇和扇三角洲前缘—前扇三角洲—滑塌浊积扇沉积体系;中期基准面旋回E-F层序沉积期间发育有利于油气储集的近岸水下扇和滩坝砂体;中期基准面旋回G层序沉积时期主要发育重力流主水道—重力流水道侧缘以及近岸水下扇沉积砂体;中期基准面旋回H层序沉积时期主要发育重力流主水道—重力流水道侧缘沉积体系。最后,预测了有利岩性圈闭发育的沉积相带和地区。  相似文献   

鄂尔多斯盆地西南部上三叠统延长组长8、长6油层组 的沉积体系与物源方向   总被引：14，自引：0，他引：14  

罗静兰  李忠兴  史成恩  李建  韩永林  王海宏  李进步  王成玉 《地质通报》2008,27(1):101-111

野外露头剖面的岩石学与岩相组合,沉积特征与相标志,古流向测定,室内砂岩的骨架矿物、重矿物组合及其平面分布规律的研究结果表明：鄂尔多斯盆地西南部上三叠统延长组长8油层组是以线状或点状物源为特征的一套近源快速堆积的冲积扇与扇三角洲沉积体系,形成于盆地由快速拗陷转入逆冲负荷沉降期间。长8沉积期盆地西南部的古水流与物源主要来自盆地西南方向,其次为西北和东南方向。长6油层组沉积期,盆地内部底床下沉作用减缓,湖盆开始收缩,湖盆西岸除北部有少量扇三角洲沉积外,主要为辫状河三角洲沉积：而盆地东北部与东部的沉积作用大大加强,致使在盆地东部形成一系列大型曲流河三角洲沉积体系,至盆地西南部相变为半深湖-深湖相与浊流相沉积。长6沉积期古水流除来自西南、西北和东南方向外．还有来自北东和正东方向的次要物源,它们在盆地西南部悦乐-玄马-板桥-固城-合水-带汇合,使该地带成为混合物源区。  相似文献