Calcareous nannofossil biostratigraphy of the marine Oligocene and Miocene succession in some wells in Northern Egypt

Twelve calcareous nannofossil biozones of Late Oligocene-Late Miocene in Northern Egypt were defined and correlated with their corresponding biozones in Egypt and other parts of the world. These are arranged from the top to base as Zone NN12, Zone NN11, Zone NN10, Zone NN8, Zone NN7, Zone NN6 Zone NN5, NN4, Zone NN3, Zone NN2 Zone NP25 and Zone NP24. In the present study (Boughaz-1 Well), the Late Miocene unconformably overlies the Middle Miocene. This unconformity surface is recognized by the missing of calcareous nannofossil zones NN7 to NN9. While, in North Sinai (Malha-1 Well), the Early/Middle Miocene boundary cannot be recognized, where the Middle Miocene unconformably overlies the topmost Oligocene, and it is defined by the missing calcareous nannofossil zones NN1 to NN4.     

南海北部深水区LS33a钻井微体古生物年代地层格架

南海北部琼东南盆地深水区接收了渐新世以来数千米厚的海相沉积地层,蕴藏着丰富的微体古生物化石。对深水区LS33a钻井岩芯的取样和化石鉴定,识别出21个浮游有孔虫化石带（N22带～P19带）和12个钙质超微化石带（NN19带～NP24带）。通过与大洋钻探（ODP）在南海实施的184航次的钻探结果和“国际年代地层表（2012）”等的对比分析,探讨了化石事件的地质年代意义,构建了LS33a钻井生物年代地层格架。在此基础上,讨论了更新统与上新统、上上新统与下上新统、上新统与中新统、上中新统与中中新统、中中新统与下中新统、中新统与渐新统、上渐新统与下渐新统之间地层界线位置以及崖城组、陵水组、三亚组、梅山组、黄流组、莺歌海组和乐东组地层的时代归属,建立了适用于南海北部深水区的高分辨率综合年代地层格架。     

Tertiary Calcareous Nannofossil Biostratigraphy in the North Part of the South China Sea

The marine Tertiary sequence in the north part of the South China Sea may be divided into 18 LateOligocene to Pliocene calcareous nannofossil zones and one unnamed Eocene assemblage based on an analysisof calcareous nannofossils from 40 offshore boreholes. The unnamed Eocene assemblage has been found onlyon the northeast margin of the Zhujiangkou basin. The 18 cakareous nannofossil zones of the Late Oligoceneto Pliocene were deposited in succession, but their development degrees are different. Among the 18 calcareousnannofossil zones, those corresponding to Martini's (1971) NN4- NN5 zones, NN11 zone and NN13-NN15zones are well developed, relatively persistent laterally and also widely distributed. They are the importantmarkers for the stratigraphical subdivision and correlation of the Upper Tertiary between the various basins inthe north part of the South China Sea. Based on the calcareous nannofossils and the sedimentsry features coup-led with the foraminifer zonation in certain basins, the present paper discusses the sedimentary characteristicsof the marine Tertiary and as well as the distribution and development of the sedimentary hiatus in the region.The calcareous nannofossil markers for the Upper / Lower Tertiary and the Quaternary / Tertiary boundaries,and the characteristics and geological significance of the reworked calcareous nannofossils are also discussed inthe paper.     

Middle and Late Tertiary Palaeogeography and Palaeoenvironment on the Northern Continental Margin of the South China Sea

Based essentially on research results of calcareous nannofossils, combined with some other microfossil da-ta and several secondary depositional breaks, this paper discusses the criteria of division and comparison of themiddle and late Tertiary marine sediments, palaeogeographical and palaeoenvironmental evolution andpalaeoclimates on the northern continental margin of the South China Sea, comprising the Tainan basin, PearlRiver Mouth basin. Southeast Hainan basin and Beibu Gulf basin. Study shows that the upper Oligocene toPliocene strata in the whole area consist essentially of marine sediments except in the Beibu Gulf basin. Theyinclude littoral. neritic and deltaic sediments as well as carbonate rock-bioherm limestone. The sea advancedfrom southeast to northwest. During the transgression there appeared three culminations coinciding to thestages of deposition of nannofossil zones NN4-5, NN11 and 13-15.     

中太平洋海山区富钴结壳的钙质超微化石地层学研究

对“大洋一号”调查船在中太平洋采集的N1-15和N5E-06 2个富钴结壳样品进行了钙质超微化石及其生物地层学的研究与分析.这2个结壳从结构上分为3层: 致密型上层、疏松型中层和致密型下层.在研究中对各结构层和各层中有颜色或细微结构变化的层位都进行了详细的取样和分析.在识别了12个新生代钙质超微化石事件的基础上, 确定了2个结壳致密型上层结壳都为晚更新世以来的沉积, 它们的疏松型中层结壳为上新世到中更新世的沉积.对N5E-06富钴结壳来说, 其致密型下层结壳下部形成于中晚古新世到早渐新世的59.7~ 32.8 Ma期间.N1-15富钴结壳致密型下层的形成时代目前暂时定为中新世.研究注意到在2个结壳中都没有发现可信的晚渐新世到中新世的化石记录, 在个别层位之间存在着沉积间断.      

Late Oligocene Sedimentary Hiatus in Deep Sea Area of South China Sea, Result of Calcareous Nannofossils from ODP Site 1148

In order to determine the age of the sedimentary hiatus and its geological significance, a study of the calcareous nannofossil biostratigraphy was carried out. Detailed strutigraphical data of the Late Oligocene-Eariy Miocene diagnostic species thus obtained. The nannofossil zonation of this interval was subdivided and the Oligocene-Miocene boundary was further determined. Several last Late Oligocene events were recognized, indicating a long-term sedimentary hiatus in the uppermost Upper Oligocene.The time span of the hiatus was estimated for about 2.2 Ma, at least from 23. 9 to 26. 1 Ma. The lithological and geophysical data from Site 1148 indicate some abrupt sedimentary changes that occurred below and above the hiatus. This hiatus at Site 1148 was probably related to the tectonic change, a major ridg ejmnp during the seafloor spreading in the Late Oligocene South China Sea.     

太平洋海山富钴结壳钙质超微化石生物地层学及生长过程

正确判断富钴结壳生长年代及过程有助于研究结壳形成地质历史和重建古海洋环境.利用生物地层学方法(生物遗留印痕)对太平洋不同海山结壳样品进行生长时代和阶段研究,发现麦哲伦海山CM3D06结壳和中太平洋海山CB14结壳最初形成年代和富集特征差异显著: 前者为白垩纪(或更古老)、晚古新世-早始新世、中-晚始新世、中-晚中新世、上新世-更新世等5个阶段;后者为晚古新世-早始新世、中-晚始新世、中中新世、上新世-更新世等4个阶段.两座海山结壳层内部超微化石组合具有极强的区域性特征,反映了大洋环境对生物的影响以及生物对环境的适应.结壳层间的不整合和结构构造的变化指示在渐新世其生长存在间断期,与成矿作用的间断有关.      

东海白垩纪-第三纪古地理

作者据海区和周边岛屿的地质、地球物理和钻井资料描述了东海的白垩纪-第三纪古地理。并绘制了该时期的系列古地理图，从而有可能归纳出东海在某些时期具有“南海北陆”，古地貌上犹如今日渤海-黄海陆缘海盆及其周边陆地环抱等特点。同时简略地讨论了海水进退和古气候，分析了东海东部活动大陆边缘构造背景出现的时间。     

Calcareous nannofossil biostratigraphy of the Paleocene at the Misheiti section,East Central Sinai,Egypt

Integration of calcareous nannofossil data, δ¹³C and δ¹⁸O values, and carbonate contents of the lower Paleocene–upper Paleocene sequence that crops out at the Misheiti section, East Central Sinai, Egypt, were used to denote the Danian/Selandian (D/S) and Selandian/Thanetian (S/T) stage boundaries. The study interval belongs to the Dakhla and Tarawan formations. Four calcareous nannofossil zones (NP4, NP5, NP6, and NP7/8) were recognized. The base of the Selandian Stage is tentatively placed at the lowest occurrences (LOs) of taxa ascribable to the second radiation of fasciculiths (i.e., Lithoptychius janii). This level is marked by a sudden drop of δ¹³C and δ¹⁸O values and carbonate content. No distinctive lithological changes were observed across the D/S boundary at the study section. A hiatus at the NP5/NP6 zonal boundary is indicated by the condensation of zones NP5 and NP6.The base of the Thanetian is placed at the base of Zone NP7/8 at the lithological change observed in correspondence to the boundary between the Dakhla and Tarawan formations. The δ¹³C and δ¹⁸O values abruptly decrease slightly above the base of Zone NP7/8. No consistent variations in the carbonate contents were recorded within Zone NP6 or across the NP6/NP7/8 zonal boundary.     

从东海油气勘探谈台湾海峡油气地质

上海海洋地质调查局从1974年开始对东海进行了包括反射地震、重力、磁法、测深、浅地层剖面等多种疗法的综合调查,基本上建立了东海的新生代地层层序、构造分区及其构造演化历史。台湾海峡在地理上位于东海陆架的西南延伸部位,但其地质演化既具东海陆架盆地早第三纪构造演化的特点,又深受渐新世至中新世南海深海盆扩张的影响。根据地震资料和钻井资料之对比,台西盆地至少经历了古新世、始新世和中新世三次海侵,从而使其既区别于南海之珠江盆地,又有别于东海陆架盆地。     

The Monte Orfano Conglomerate revisited: stratigraphic constraints on Cenozoic tectonic uplift of the Southern Alps (Lombardy, northern Italy)

The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (“molassa”). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.     

Paleogene-Neogene calcareous nannofossil biostratigraphy and paleoecological inferences from northern Campos Basin,Brazil (well Campos-01)

Quantitative analyses of calcareous nannofossils were performed on 50 ditch-cuttings samples from a well drilled in the northern Campos Basin, Brazil. Nine zones and two subzones were recognised in the Paleogene-Neogene section. The absence of zones NN9-NN7 (earliest late-latest middle Miocene), NP25-NP21 (Oligocene) and NP18-NP1 (earliest late Eocene-Paleocene) implies the occurrence of three stratigraphic breaks/unconformities within the studied interval. Nannofossil assemblages present suggest an open-ocean depositional environment under oligotrophic-surface water conditions for the Miocene section of the well. Hughesius spp. and Umbilicosphaera spp., here named the “small dark” group, were recognised as an index of high nutrient concentration. We suggest that small coccolith/nannolith size is a better indicator of eutrophic condition than taxonomic affinity. Morphometric analysis of specimens of Sphenolithus belemnos and Sphenolithus disbelemnos showed that size tends to decrease within the highstand system tract. The influx of nutrients associated with the highstand could explain this size reduction and may also support our hypothesis that small specimens are indicative of high nutrient concentrations in the surface water.     

阿尔金山脉新生代剥露历史——前陆盆地沉积记录

新疆且末县江尕勒萨依盆地位于阿尔金山脉的北西山前,其内连续沉积了中生代一新生代地层。盆地内古新统一始新统为河流相沉积;渐新统至中新统为山麓河流相灰色砾岩和棕色砂岩;上新统为山麓洪积相砾岩夹泥岩;下更新统全为砾岩层。岩性组合特征及其砂岩碎屑、砾石组分变化规律,反映出阿尔金山脉的新生代剥蚀历史：古近纪早、中期,阿尔金山脉的地形高差小,古生界双峰式火山岩首先被剥蚀;至渐新世末一中新世早期,山脉高差加大,基底元古宇开始出露地表被剥蚀;中新世末期,山脉高差进一步加大,剥蚀速率加快;至第四纪早期西域砾岩开始沉积时,地形高差加剧,中、古元古界开始暴露被剥蚀。区域资料分析表明,阿尔金山脉在新生代具有多期次阶段性隆升的特征,存在3期次快速隆升事件：渐新世末一中新世早期、中新世晚期(大约8Ma)和第四纪早期。     

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.     

Sedimentary filling characteristics of the South China Sea oceanic basin,with links to tectonic activity during and after seafloor spreading

ABSTRACT

Based on approximately 11,000 km of seismic reflection data collected across the South China Sea oceanic basin, we describe the sedimentary filling characteristics of the basin since its Oligocene opening, as well as connections between this history and contemporaneous regional tectonic events. The seismic lines are spaced ~50 km apart, and the data are tied to International Ocean Discovery Program (IODP) Expedition 349 drilling data. Basin filling occurred in three phases, with basin-wide mean sedimentation rates increasing through time. During the Oligocene to middle Miocene, sediments accumulated primarily in the northern East and Northwest Sub-basins, with a mean basin-wide sedimentation rate of 8 m/m.y. The presence of these deposits over deep basement floor indicates that seafloor spreading initiated in these northern regions. During the late Miocene, deposition occurred primarily in the Northwest Sub-basin and partly in the southern East Sub-basin, with a mean basin-wide sedimentation rate of 30 m/m.y. Basin filling during this time seems to have been linked to slip reversal of the Red River Fault and collision of the North Palawan Block with the Luzon Arc. During the Pliocene and Pleistocene, sediments accumulated rapidly in the northeastern and southern East Sub-basin and the Southwest Sub-basin. The mean basin-wide sedimentation rate was 70 m/m.y. Basin filling during this phase seems to have been associated with the Taiwan and North Palawan collisions, SCS subduction along the Manila Trench, and Tibetan Plateau uplift. Gravity flow deposits predominate throughout the basin fill.     

Late Oligocene sedimentary environments and provenance abrupt change event in the northern South China Sea

A significant change in composition was recorded in late Oligocene sediments from the northern South China Sea. This abrupt event coincided with the seafloor spreading axis jump across the Oligocene/Miocene boundary, leading to sedimentation breaks and slumps as well as obvious changes in sediment geochemical composition, and representing the greatest tectonic activity in the South China Sea region since the Oligocene. Through this tectonic event, the sedimentary environment in the Baiyun sag area transformed from a continental shelf in the late Oligocene to a continental slope since the early Miocene, the provenance of the sediments changed from neighboring areas to the hinterland of the South China block, and the sea level rose since the early Miocene in the area. Therefore, this abrupt change event has a profound influence on the evolution of petroleum offshore in the northern South China Sea. __________ Translated from Geology in China, 2007, 34(6): 1022–1031 [译自: 中国地质]     

塔里木北部库车前陆盆地晚白垩世和古新世的钙质超微化石组合

库车前陆盆地是中国大型油气基地之一,盆地中的白垩系及古近系为盆地油气的主要储层。对本区白垩系的时代划分和沉积环境的精确确定直接关系到对油气田的规模、储量和分布范围的正确评价。本研究在前人划分为陆相下白垩统巴什基奇克组的顶部首次发现了由10属15种组成的晚白垩世海相钙质超微化石组合Arkangelskiellacymbiformis—Quadrumgartneri。此外,在由前人定为古新统—始新统的塔拉克组下段也发现了晚白垩世Arkangel skiellacymbiformis—Quadrumgartneri组合,在该组上段发现了古新世化石Biantholithussparsus。该成果既为准确确定这两个岩组的地质时代提供了可靠的古生物证据,又为本区存在晚白垩世地层和海相沉积提供了佐证,表明巴什基奇克组顶部存在晚白垩世的海相沉积,塔拉克组下段属于上白垩统,上段属于古新统。     

平湖油气田油气成藏新模式

通过对区域构造演化、沉积背景、盖层特性以及油气生成和运聚条件等的分析,结合前人研究成果,重新建立了平湖油气田的成藏模式.平湖油气田含上部渐新统花港组和下部始新统平湖组两套储层,呈上油下气的油气分布特征.古新世-始新世的断块阶段在区域上初步形成了大断裂控制下的断背料构造,在平湖组形成圈闭.中新世中期(平湖组沉积后期)发生...     

南海北部渐新世末沉积环境及物源突变事件

南海北部沉积物成分在渐新世末(23.8Ma)发生剧烈改变,出现地球化学成分上的突变,并在深海沉积中发生沉积间断及滑塌堆积。这些沉积事件在时间上与南海扩张轴由东西方向转为北东—南西方向发生跳跃的时间十分吻合,是渐新世以来南海构造演化史上最为重大的构造事件。经过这次构造事件,白云凹陷由渐新世晚期的浅水陆架环境转为中新世以后的深水陆坡环境,南海北部地区沉积物源由渐新世近源为主转变为中新世远源为主的供给特点;并使南海北部地区自中新世以来总体呈现海侵的特征。这次沉积环境与物源突变事件对南海北部地区油气藏的形成影响深远。     

Significance of indigenous Eocene larger foraminifera Discocyclina dispansa in Western Foothills,Central Taiwan: A Paleogene marine rift basin in Chinese continental margin

The Western Foothills of Taiwan was known to be composed of Late Oligocene to Pleistocene shallow marine strata continuously deposited on the stable passive Chinese continental margin without significant stratigraphic break. Here we present multiple micropaleontological evidences, including occurrence of larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannoplanktons, to show that there are Middle Eocene marine strata (first named as the Chungliao Formation) exposed in the Tsukeng anticline of the Western Foothills, central Taiwan. Occurrences of intact tests with thin delicate outer rims and well-preserved embryonic chambers suggest that the Discocyclina dispansa ex. interc. sella-dispansa (Lutetian to Bartonian in the Tethys region) are buried indigenously on shallow inner shelf during an episodic transgression in the Early Middle Eocene. The conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons (Zones NP14–15) in the shale/sandstone alternations overlying the Discocyclina-bearing bed of the Chungliao Formation and calcareous nannofossils of Zone NP16 integrated with an age dating of 38.8 ± 1 Ma (Late Middle Eocene) on zircon grains of the overlying Pinglin Tuff. The Middle Eocene syn-rift sequences (Chungliao Formation and Pinglin Tuff) exposed along the Tsukeng anticline are unconformably covered by the latest Oligocene–Miocene post-rift sequence, a scenario similar to what have been drilled in the East China Sea-Taiwan Strait-South China Sea. This rift basin (named as the Nantou Basin) is sitting on the Peikang Basement High margin which further extends southwestward to the Central Uplift of the Pearl River Mouth Basin in the northern slope of the South China Sea. The present work documents a hitherto unknown occurrence of the exposed early Tertiary marine rift basin sequence in the Western Foothills of Taiwan. The study extends our knowledge of the Western Foothills geohistory from the Late Oligocene downward to the Early Middle Eocene. The occurrence of the Paleogene Nantou rift basin in the Western Foothills may also suggest that there could have similar Paleogene rift sequences exposed in other parts of the Taiwan mountain belt like the Hsüehshan Range and the Central Range east of the Western Foothills.