Comparison of Michigan Basin crude oils

Michigan Basin oils from the Ordovician Trenton, Silurian Niagaran, and Devonian Dundee formations have been geochemically compared by GC, GC-MS, and carbon isotope mass spectrometry. One oil from each formation was selected for detailed analysis which included measurement of individual n-alkane δ¹³C values. The Ordovician and Devonian oils are strikingly similar to one another, yet clearly different from the Silurian oil. This pattern is unexpected because Ordovician and Devonian reservoirs are physically separated by the Silurian strata. From time-temperature considerations, the Devonian oil probably was formed in older strata and has migrated to its present location. Our analyses suggest a common source for the Devonian and Ordovician oils.     

Late Silurian (Ludlow–Přídolí) microfossils and sedimentation in the Welsh Basin near Clun,Shropshire

The base of the Clun Forest Formation at Clun, Shropshire, has previously been taken to correlate with the base of the Downton Castle Sandstone Formation (Přídolí Series, upper Silurian) on the basis of brachiopod, bivalve, gastropod and ostracod faunas. The detailed distribution of microfossils (acritarchs, chitinozoans, conodonts and ostracods) is documented at Nantyrhynau Quarry, Clun, Shropshire, to test this correlation. Three new species of chitinozoans, Eisenackitina clunensis, Eisenackitina kerria and Angochitina paucispinosa, are described from the quarry. Macrofossil and ostracod distributions suggest that the correlation is correct. However, a typical Ludlow acritarch flora is present throughout the section and suggests that the basal part of the Clun Forest Formation is Ludlow in age. The mixture of characteristic Ludlow and Přídolí microfossils at Nantyrhynau Quarry may be the result of differing environmental conditions between the Ludlow (shelf) and Clun (basinal) areas at this time. Alternatively, the strata exposed at Nantyrhynau Quarry may represent a period towards the end of the Ludlow Series when there are no strata represented in corresponding shelf sections due to non-deposition or erosion. © 1997 John Wiley & Sons, Ltd.     

Pre‐Tabberabberan deformation in eastern Tasmania: A southern extension of the Benambran Orogeny

Recumbent folding in eastern Tasmania affected turbidites containing Lower to Middle Ordovician (Bendigonian Be1 to Darriwilian Da3) fossils, but not stratigraphically overlying turbidites containing Silurian (Ludlow) graptolites, and is of a timing consistent with Ordovician to Silurian Benambran orogenesis on the Australian mainland. Two subsequent phases of upright folding post‐date deposition of turbidites containing Devonian plant fossils but pre‐date intrusion of Middle Devonian granitoids, and are of Tabberabberan age. A closely spaced disjunctive cleavage (S₂), associated with the first phase of Tabberabberan folding, everywhere cuts a slaty cleavage (S₁) associated with the earlier formed recumbent folds. However, refolding associated with development of S₂ is not always clear in outcrop and it is proposed that coincident tectonic vergence between the two events has resulted in reactivation of recumbent D₁ structures during the D₂ event. The transition to rocks not affected by recumbent folding coincides with a marked change in sedimentology from shale‐ to sand‐dominated successions. This contact does not outcrop but, from seismic data, appears to dip moderately to the east, and can only be explained as an unconformity. The current grouping of all pre‐Middle Devonian turbidites in eastern Tasmania into the one Mathinna Group is misleading in that the turbidite sequence can be subdivided into two distinct sedimentary packages separated by an orogenic event. It is proposed that the Mathinna Group be given supergroup status and existing formations placed into two new groups: an older Early to Middle Ordovician Tippogoree Group and a younger Silurian to Devonian Panama Group.     

四川盐边稗子田志留系与泥盆系的界线划分及地质意义

四川省盐边县北部稗子田地区的志留系发育良好,牙形刺化石极为丰富,与上覆泥盆系连续沉积,并呈整合接触。该剖面为我国扬子区较为理想的志留纪地层剖面,其代表和反映了扬子区西部一种新的断陷盆地碳酸盐岩沉积类型,丰富了区内志留系的研究内容。
笔者详细记述了稗子田志留系至下泥盆统下部剖面的岩性特征和生物化石的垂直分布状况,在此基础上建立和完善区内新的地层系统,提出地层划分的对比依据和建议。新方案除对志留系底的黑色硅质碳质页岩沿用龙马溪组这一岩石地层单位名称外,其上的碳酸盐岩均重新划分和建立了新的岩石地层单位,并确定其涵义和时限标准。
新的地层划分和对比方案,下志留统自下而上包括龙马溪组、国胜组和乡涧组;中志留统下部为下稗子田组,中志留统上部至上志留统下部为上稗子田组;上志留统上部为沟口组;顶志留统为岩口组;下泥盆统自下而上为榕树组和小梁子组。     

Silurian to mid-Devonian basin development of the Melbourne Zone, Lachlan Fold Belt, southeastern Australia

The Melbourne Zone comprises Early Ordovician to Early Devonian marine turbidites, which pass conformably upward into a mid-Devonian fluviatile succession. There are four pulses of Silurian to mid-Devonian deep-marine sandstone-dominated sedimentation: Early Silurian (late Llandovery), Late Silurian (Ludlow), earliest Devonian (Lochkovian) and late Early Devonian (Emsian). Two dispersal patterns have been defined using more than 1100 palaeocurrent measurements, mainly from sole marks and cross-laminations in graded beds, together with sandstone compositions. The older pattern, of Silurian to earliest Devonian age, contains the lowest three sandstone pulses. Palaeocurrents and provenance define a wedge of southwesterly derived sediment, of largely cratonic provenance, thinning eastward. This older dispersal pattern is part of an Early Ordovician to earliest Devonian east-facing passive continental margin succession. Palaeocurrents and provenance in the Emsian sandstone pulse comprise three patterns: (1) west- to southwesterly directed palaeocurrents associated with fine- to coarse-grained, locally conglomeratic, lithic sandstones containing a high proportion of volcanic detritus; (2) east- to northeasterly directed palaeocurrents associated with fine- to medium-grained quartz-lithic sandstones; (3) north- to northwesterly and south- to southeasterly directed palaeocurrents associated with fine- to medium-grained sandstones of variable lithic composition. The palaeocurrent and provenance pattern defines a NNW-elongate basin with a tectonically active eastern margin, and is similar to the coeval Mathinna basin of northeastern Tasmania. Both basins are part of the same system of wrench basins, which developed along the western side of the Wagga–Omeo Metamorphic Belt during the earliest Devonian to Middle Devonian. The change in tectonic setting in the earliest Devonian appears to have occurred during an interval of significant dextral translation of the eastern Lachlan Fold Belt towards the SSE along the Governor and associated fault zones.     

中国西藏南部珠穆朗玛峰地区的地层

珠穆朗玛峰(以下简称珠峰)地区系指亚东以西,吉隆以东,雅鲁藏布江以南的我国境内广大地区。于1966年～1968年我国无产阶级文化大革命期间,由中国科学院主持,对这一地区进行了大规模的科学考察。在地层古生物方面,也同其它学科一样,获得了非常丰富的资料。在这个地区首次发现了奥陶系、志留系和泥盆系,并对中生代和新生代地层作了较详细的分层工作,从而初步建立了珠峰地区比较完整的地层系统。由奥陶系至老第三系厚达一万米的海相地层,大多是连续沉积的。     

北祁连造山带晚奥陶世-泥盆纪构造演化: 碎屑锆石年代学证据

北祁连造山带晚奥陶世-泥盆纪处于同造山的构造背景.上奥陶统-泥盆系沿造山带不对称分布.上奥陶统-泥盆系碎屑锆石年代学特征显示, 造山带东段武威一带上奥陶统底部沉积物主要来自北祁连岛弧, 南部中祁连地块和北部华北板块的沉积物在上奥陶统上部才出现, 根据同沉积锆石年龄将中祁连地块和华北板块在东段初始碰撞的时间限定在470~450 Ma之间; 中祁连地块和华北板块的物质在造山带西段肃南一带被保存在下志留统, 地层中也有大量来自早古生代北祁连岛弧和同碰撞花岗岩的物质, 暗示造山带西段的碰撞时间在早志留世.而造山带东段下志留统中却仅有来自中祁连地块和华北板块的物质, 缺乏代表北祁连岛弧的早古生代碎屑锆石年龄, 对比上奥陶统-下志留统岩相分布和碎屑锆石年代学特征, 北祁连造山带的碰撞具有"东早西晚"的"斜向碰撞、不规则边缘碰撞"的特征, 而这种碰撞方式导致中祁连地块在造山带东段仰冲到北祁连岛弧之上, 阻止北祁连岛弧为盆地提供沉积物; 泥盆纪早期, 北祁连岛弧年龄在东段下、中泥盆统中重新出现, 结合志留系和泥盆系在造山带东、西两段的分布和变形特征推断, 泥盆纪早期北祁连造山带具有"东强西弱"的不均一隆升特征, 这种差异隆升特征是由"东早西晚"的"斜向碰撞、不规则边缘碰撞"引起的, 它导致了北祁连岛弧在造山带东段被重新剥露出地表, 同时来自早期中、上志留统以及同碰撞花岗岩的物质也被汇入盆地.河西走廊盆地性质经历了弧后盆地-弧后残留洋盆-前陆盆地的转换过程.      

西藏北部拉竹龙地区泥盆纪岩石地层单位划分与时代讨论

在详细描述西藏北部拉竹龙地区泥盆纪地层剖面的基础上,根据在前人所划的奥陶系兽形湖组中采集到的大量属于泥盆纪的腕足类化石,修订了兽形湖组的定义,从而将区内泥盆纪地层划分为兽形湖组、拉竹龙组,并根据生物化石资料讨论了各组的时代。     

阿尔及利亚438 区块古生代构造演化及油气成藏特征

阿尔及利亚438 区块位于阿尔及利亚Oued Mya 盆地北部。利用石油地质理论和测试、测井解释资料,解析阿尔及利亚438 区块古生代地层和油藏特征。分析表明,438 区块所属的Oued Mya 盆地古生代属于克拉通盆地,沉积了奥陶系、志留系和泥盆系多套海相地层,发育有志留系泥页岩和奥陶系页岩两套烃源岩,具备良好的生储盖条件。根据NGS-P1 井的实探资料,裂缝在奥陶系的Hamra 石英砂岩的成藏中起主导作用,应为裂缝型圈闭; 构造和岩性在Dale de M'Kratta 砂岩和泥盆系砂岩的成藏中起主导作用,应为构造--岩性圈闭,推断本区古生代油气成藏模式为断层输导型。     

下扬子区加里东期构造古地理问题

一般将江绍断裂作为扬子地块和华夏地块在下扬子区的分界,但江绍断裂是晋宁期缝合带,二者在加里东期的关系需要解决。赣东北和皖南元古界变质岩构成复背斜核部,两翼的寒武-奥陶系由里向外由盆地-斜坡相转为台地相,相界线标志出扬子台缘位置在皖南石台-泾县一线,华夏台缘位置在浙西江山-开化-临安一线,中央的变质岩区应为当时江南海盆的一部分。奥陶纪末沉积格局有重大变化,显示这里的江南海盆转化为陆屑来源的楔形”江南隆起”。复背斜两翼寒武-奥陶系的构造变形则由外向里增强,直至同斜倒转的褶皱形态,表明江南隆起属加里东褶皱带。隆起两侧及东北方有很厚的志留系碎屑岩,沉积序列自下而上由浅海相转为滨海相和三角洲相以至陆相沉积。空间上往东北方江苏境内海相沉积更为发育,志留纪晚期仍有海相记录,与泥盆系之间为平行不整合接触,到印支期才发生构造变形。在下扬子区,扬子和华夏地块之间,加里东褶皱带和印支褶皱带并存。     

Geochemistry of Early–Middle Palaeozoic basalts in the Hodgkinson Province: a key to tectono-magmatic evolution of the Tasman Fold Belt System in northeastern Queensland, Australia

The Palaeozoic Hodgkinson Province in northeastern Queensland, Australia, is host to Late Ordovician to Devonian rock assemblages that contain tholeiitic to calc-alkaline basalts. These basalts occur as massive fault-bounded units interspersed with marine sedimentary rocks and limestones that are metamorphosed to lower greenschist facies in the Ordovician Mulgrave, Silurian Chillagoe and Devonian Hodgkinson formations, respectively. The petrogenetic and Sm–Nd isotope characteristics of these mafic volcanic rocks were investigated to constrain the tectonic setting in which they erupted. Major, trace and rare earth element analyses were carried out on samples from these formations and intrusive dolerites. The mafic rocks can be classified as basalts and basaltic andesites with distinct MORB characteristics. Furthermore, the basalts are characterized by a slight to moderate enrichment in Th and concomitant depletion in Nb, both of which become less pronounced with basalt evolution through time. These features are consistent with decreasing volcanic arc affinity of Silurian and Devonian MORB-type basalts in the Hodgkinson Province. Sm–Nd isotope characteristics of these basalts indicate a change in source region from dominantly sub-continental lithospheric mantle in the Silurian to asthenospheric input in the Devonian. Collectively, the geochemical and isotopic characteristics of the Hodgkinson Province basalts are interpreted to reflect deposition in an evolving back-arc basin setting. The onset of basin extension was initiated in the Silurian. Accelerated basin subsidence occurred throughout the Devonian and was halted by basin inversion in the Late Devonian. Basin evolution was controlled by an eastward stepping subduction zone outboard of the Australian Craton.     

湖南张家界地区志留纪晚期地层新见兼论小溪组的时代

就华南板块而言,志留纪晚期(Ludlow世—Pridoli世)近岸浅海、非笔石相地层多分布在边缘海湾处,是否在扬子地台内部发育,以往尚无确凿记载。依据来自湘西北张家界—桑植地区新近发现的微体化石(主要指植物碎片),确认志留纪晚期地层在扬子地台内部确实存在。对原小溪组(又称小溪峪组)进行厘定,将它"一分为二":上部仍称小溪组,命名地在桑植瑞塔铺,发育最好的是张家界温塘剖面,岩性为黄绿色碎屑岩,富含大型虫管遗迹化石,时代为Ludlow晚期—Pridoli早期;下部称迴星哨组,归于Llandovery统Telychian阶上部。小溪组与迴星哨组之间为假整合接触,缺失Telychian末期、Wenlock世和Ludlow世早期地层。由此得出结论:在"扬子上升"后,扬子地台内部曾被志留纪晚期的海水侵漫;对其他地区迴星哨组与上覆地层的研究需要细化。     

Regional tectonic and megadepositional cycles of the Paleozoic of northwestern and central Saudi Arabia

The Paleozoic succession of the Greater Arabian basin is severely affected by series of major tectonic and climatic events which have caused major stratigraphic breaks and pronounce facies change. The major tectonic movements have resulted in dividing the succession into pronounced megatectonic and depositional cycles. In more tectonically active areas, the succession is less preserved and boundaries between the cycles are more complicated due to longer periods of erosion by later movements and/or nondeposition. Minor stratigraphic breaks within the megacycles subdivide the cycles into smaller subcycles. Following the stabilization of the Arabian–Nubian shield, the Gondwana shelf went through a gentle uplift and tilt probably related to the Assyniyc tectonic movements and thick siliciclastics of the Saq and Qasim Formations were deposited. During Late Caradocian and following the deposition of the Qasim Formation, the area went through a gentle uplift and tilt probably related to the Taconic tectonic movements. Thick succession of the Qasim and Saq Formations were eroded and deep paleovalleys incised in the two formations and underlying basement. The movements were followed by drop of sea level due to glaciation events. Glacial and periglacial deposits of the Zarqa and/or Sarah Formations filled paleovalleys and rest on older units from Ordovician to Precambrian. The third main event occurred during Late Silurian where the preexisting successions, mainly on paleohighs, were affected by tectonic movements synchronous with the Acadian tectonic phase of the Caledonian tectonic movements. The Early Devonian Tawil Formation unconformably rests on eroded Silurian and Late Ordovician deposits of the Sharawra, Qusayba (Qusaiba), and Sarah Formations in the Qusayba Depression in central Arabia. The forth main event is a regional movement contemporaneous with the Hercynian tectonic movement which has reached its maximum phase in the Late Carboniferous. Earlier successions from Carboniferous to Precambrian were affected and the Permo-Carboniferous Shajra Formation unconformably rests on all underlying Paleozoic rock units toward the central Arabia arch and other paleohighs. The Shajra rests on the Devonian Jawbah (Jubah), Jawf (Jauf) and Tawil formations, the Silurian Sharawra, Qusayba, and Uqlah formations, the Ordovician Zarqa/Sarah, and Qasim formations, the Cambro-Ordovician Saq Formation, and finally rests on Precambrian Basement complex in Central Arabia. The tectonic movements played important role in shaping the structural framework of Arabia. The Paleozoic succession included source, reservoir, and seal rocks. Oil and gas have been discovered in sandstone and limestone reservoirs in these rocks in several oilfields in the basin.     

从弧后盆地到前陆盆地——北祁连造山带奥陶纪—泥盆纪的沉积盆地与构造演化

北祁连加里东期造山带是在新元古代Rodinia联合大陆(Pangea-850)基础上裂解,经由寒武纪裂谷盆地、奥陶纪初期成熟洋盆、奥陶纪中晚期北祁连活动大陆边缘、志留纪—早、中泥盆世碰撞造山而形成的。奥陶纪中、晚期,北祁连、走廊地区中、上奥陶统发育洋壳-岛弧-弧后火山岩,形成典型的沟-弧-盆体系的沉积。志留纪—早、中泥盆世是北祁连-走廊沉积盆地的转换时期。除天祝、古浪、景泰及肃南等局部地区发育下志留统钙碱性系列火山岩以外,全区志留系均以碎屑岩沉积为主。志留系底部多见一套砾岩层。下—中志留统为典型复理石相的浊流沉积。上志留统变为滨浅海相磨拉石沉积。早、中泥盆世雪山群为典型的陆相粗碎屑磨拉石沉积。从空间分布上看,志留系—泥盆系在走廊—北祁连地区也有自北向南厚度加大、粒度变粗的特征,古流以由南向北、来自造山带的古流为特征。北祁连-河西走廊奥陶纪弧后盆地火山岩—志留系复理石-海相磨拉石—中、下泥盆统陆相磨拉石的充填序列以及空间分布特点,反映为典型的弧后盆地向前陆盆地转化的沉积序列。     

吉中呼兰镇地区呼兰群的划分及时代

吉中呼兰镇一带分布的轻变质岩系称呼兰群，曾划分为黄莺屯组、小三个顶子组和北岔屯组，对其划分和时代一直分岐较大。本文重新厘定了黄莺屯组，其主要为片麻岩、变粒岩、片岩等夹大理岩和石英岩，小三个顶子组由大理岩夹片岩和变粒岩组成；北岔屯组由大理岩、钙质砂岩和板岩组成，时代为晚志留世。北岔屯组在变质程度、岩性组合和时代上与另两组都有很大差别。因此，呼兰群仅包括黄莺屯组和小三个顶子组，时代为寒武－奥陶纪。     

滇东曲靖地区志留纪四射珊瑚的动物群特征及地层时代讨论

本文着重从四射珊瑚动物群的角度讨论了滇东曲靖地区志留系的地层划分及对比问题。并提出曲靖地区的中、晚志留世具有4个珊瑚化石组合。对部分四射珊瑚属种（其中包括9个新种,4个相似种和一个未定属种）进行了描述。     

滇西保山熊洞村栗柴坝组牙形石的发现及其地质意义

针对保山地层区熊洞剖面原属栗柴坝组的灰岩进行了牙形石样品分析,总计建立了5个牙形石带,分别为Pterospathodus pennatus procerus带、Kockelella walliseri带、Ancoradella ploeckensis带、Polygnathoides siluricus带和Polygnathus nothoperbonus带。该剖面第8层原属栗柴坝组,Polygnathus nothoperbonus分子的出现证实其为下泥盆统埃姆斯阶的地层,应归为向阳寺组。剖面总体对应志留系温洛克统底部到下泥盆统埃姆斯阶中部,中间缺失志留系罗德洛统卢德福特阶—下泥盆统埃姆斯阶之间的8～10个标准牙形石带,说明该地区后期可能受构造作用影响,志留系和泥盆系界线为断层接触。该剖面牙形石序列的建立一定程度上完善了滇西保山地层区志留系生物地层的研究程度,为下一步该区生物地层格架的建立奠定了基础。     

北祁连造山带东段上奥陶统一下、中泥盆统砂岩碎屑组分与物源分析

北祁连造山带东部武威斜豪-古浪石城子-靖远水泉-带上奥陶统一下、中泥盆统砂岩碎屑组分源区大地构造背景的判别结果表明,上奥陶统砂岩中的沉积物主要来自弧造山带内的过渡岛弧源区,并且早期可能含有较多的来自未分割岛弧源区的物质,下志留统砂岩中的沉积物主要来自碰撞造山带,而下、中泥盆统砂岩中的沉积物主要来自卷入碰撞造山带内的分割...     

塔中地良奥陶系地层格架与沉积演化

塔里木中部地区奥陶系大致以Ⅰ号断裂为界分东北和西南两个地层分区,自下而上分白云岩段、灰岩段、泥质灰岩段、泥岩夹灰岩段、泥岩夹砂岩段、砂砾岩段、泥岩夹砂岩段、泥岩灰岩互层段和砂岩段等9个岩性段。早奥陶世,塔中地区以碳酸盐岩台地相为主,自西向东为局限台地相、开阔台地相、台地边缘相和深水斜坡相。中——晚奥陶世,塔中地区西部以混积陆架相为主,东部以深水斜坡相为主。中—晚奥陶世,塔中东部及塔东地区在构造上具弧后前陆盆地性质。中—上奥陶统地层完整地记录了该盆地从形成发展到消亡的过程,即早期为深水斜坡相复理石活动沉积,晚期演化为浅海陆架相稳定沉积。     

Geology of the Severnaya Zemlya Archipelago and the North Kara Terrane in the Russian high Arctic

The Severnaya Zemlya Archipelago is located at 80°N near the continental shelf break, between the Kara and Laptev seas. Sedimentary successions of Neoproterozoic and Palaeozoic age dominate the bedrock geology. Together with Northern Tajmyr, Severnaya Zemlya constitutes the main land areas of the North Kara Terrane (NKT), which is inferred here to have been a part of the Timanide margin of Baltica, i.e. an integral part of Baltica at least since the Vendian. Vendian turbidites derived from the Timanide Orogen are inferred to have been deposited on Neoproterozoic greenschist facies, granite-intruded basement. Shallow-water siliclastic deposition in the Early to Mid-Cambrian was followed by highly organic-rich shales in the Late Cambrian and influx of more turbidites. An episode of folding, the Kan’on River deformation, separates these formations from the overlying Tremadocian conglomerates and sandstones. In the Early Ordovician, rift-related magmatic rocks accompanied the deposition of variegated marls, sandstones, carbonates and evaporites. Dark shales and gypsiferous limestones characterise the Mid-Ordovician. Late Ordovician quartz-sandstones mark a hiatus, followed by carbonate rocks that extend up into and through most of the Silurian. The latter give way upwards into Old Red Sandstones, which are inferred to have been deposited in a Caledonian foreland basin. Deformation, reaching the area in the latest Devonian or earliest Carboniferous and referred to as the Severnaya Zemlya episode, is thought to be Caledonian-related. The dominating E-vergent structure was controlled by décollement zones in Ordovician evaporite-bearing strata; detachment folds and thrusts developed in the west and were apparently impeded by a barrier of Ordovician igneous rocks in the east. Below the décollement zones, the Neoproterozoic to Early Ordovician succession was deformed into open to close folds. The exposed strata in the lower structural level have been juxtaposed with those in the upper structural level along the major N-trending Fiordovoe Lake Fault Zone, which involved several kilometres of dextral strike-slip movement and downthrow to the west. A major Early Carboniferous unconformity separates the folded Mid-Palaeozoic and older rocks from overlying Carboniferous formations, as on Franz Joseph Land and Svalbard. Subsequent latest Palaeozoic to Early Mesozoic orogeny, as on Taimyr, apparently had little influence on the Severnaya Zemlya successions.