共查询到20条相似文献，搜索用时 663 毫秒
1.
根据鲁家坪组的岩性、岩相和变质程度的变化以及区域分布特征,原定义所包含的岩石内容过于庞大,混淆了岩石地层单位和年代地层单位。通过对鲁家坪组的命名地点和标准剖面所在地——北大巴山南部的陕西紫阳县鲁家坪村的鲁家坪剖面及其他剖面的详细研究,原鲁家坪组按岩性可分为三段,下段以白云岩为主;中段以厚层硅质岩为主,中段下部的硅质岩中夹磷质白云岩和灰岩,其中产小壳化石Archaeooidessp.、Protohertinasp.、Chan-celloriasp.和Hyolithids,中段上部的硅质岩中夹多层毒重石或重晶石矿层以及砂炭(石煤)和火山岩层,即以硅质岩类为主;上段以黑灰色(风化后为浅灰色)含硅炭板岩和泥灰质含炭板岩为主。根据原鲁家坪组各段岩层的岩性、岩相、岩层层序、厚度和分布范围等,原鲁家坪组的下部的厚层状灰质白云岩和硅质白云岩等与原鲁家坪组中部的厚层硅质岩及硅质板岩,以及上部的板岩和千枚岩和页岩的岩性和岩相差别较大,应从原鲁家坪组划出,暂仍称为灯影组,与三峡地区的灯影组可对比;原鲁家坪组的中上部为鲁家坪组的主体,仍称鲁家坪组。厘定后的鲁家坪组与扬子地台的下寒武统的筇竹寺组(云南)、牛蹄塘组(贵州)和宽川铺组(陕南宁强)可以对比,而与后者的主要区别在于后者的下部以黑色页岩为主、硅质岩岩层薄,而鲁家坪组下部的硅质岩特别发育,厚度大,常常夹有毒重石矿层、砂炭和火山岩等。 相似文献
2.
内蒙古西部的温都尔庙群下部为含铁石英岩、变质火山岩与绢云石英片岩,上部由各类绢云石英片岩、石英岩组成,局部夹碳酸盐沉积。利用SHRIMP和ICP-MS定年方法,获得该群下部的变质火山岩时代为(460±4) Ma,上部绢云石英片岩中最年轻的峰值年龄为417 Ma和444 Ma。结合已有的锆石年龄分析结果,本文认为温都尔庙群的发育时代可能为500~415 Ma。根据温都尔庙群的物质组成,推测其形成于松辽-浑善达克地块周围的大陆边缘海域并命名为温都尔庙洋,代表我国境内早古生代时期的古亚洲洋。根据碰撞造山带理论探讨了温都尔庙群的构造位置,提出在早-中古生代时期,以温都尔庙群为代表的古亚洲洋发生了向南部华北地块和向北部兴安-艾力格庙地块的双向俯冲,其主体部分形成南、北两个加积楔,而其边缘部分卷入南、北混杂岩带成为基质,因此温都尔庙群的褶皱及变质历史记录了中亚造山带东段的演化过程。对碎屑锆石年龄分布的研究表明,温都尔庙群的前寒武纪物源特征与蒙古国下古生界的相似,而与华北陆块显著不同,表明温都尔庙群的物源很可能来自华北陆块之外的前寒武纪古陆。 相似文献
3.
ZHANG Xianqiu Lü Junchang BIAN Geguo QIU Licheng HUANG Dong YUAN Weiqiang China New Star 《《地质学报》英文版》2005,79(5):598-604
The red beds of the northern Heyuan Basin （Guangdong Province, China） are more than 4,000 m thick. Based on the lithological characters, in ascending order these beds are divided into the Dafeng Formation, Zhutian Formation, and Zhenshui Formation of the Nanxiong Group, Shanghu Formation and Danxia Formation. The Nanxiong Group with relatively mature coarse clastic rocks attains about 2940 m in thickness. The Dafeng Formation is 837 m thick, consisting of conglomerates and sandy conglomerates; the Zhutian Formation, which is 1.200 m thick, consists of purplish red sandstone with gravels, poorly sorted sandstone, feldspathic quartzose sandstone banded granular conglomerate, siltstone, and sandy mudstone. The Zhutian Formation is rich in calcareous concretions. Heyuannia （Oviraptoridae） and turtle fossils were found in this formation. The Zhenshui Formation deposited to a thickness of 900 m consists of coarse sediments, including granular conglomerate, and gravelly sandstone with well developed cross-beddings; the Shanghu Formation, which is 820 m thick, consists of purplish red granular conglomerate coarse sandstone intercalated with fine si~tstone; the Danxia Formation characterized by the Danxia ~andform is composed of coarse c~astic gravels and sandy gravels. The lower part of the Nanxiong Group whence dinosaur eggs and derived oviraptorosaurs come, belongs to the Late Cretaceous. No fossils are found in the Shanghu Formation or the Danxia Formation, but their stratigraphic order of superposition on the Nanxiong Group clearly shows their younger age. 相似文献
4.
Bruce W. Fouke Aubrey L. Zerkle Walter Alvarez† Kevin O. Pope‡ Adriana C. OcampO§ Richard J. Wachtman Jose Manuel Grajales Nishimura¶ Phillipe Claeys & Alfred G. Fischer†† 《Sedimentology》2002,49(1):117-138
The depositional and diagenetic history of Cretaceous–Tertiary (KT) impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize, has been investigated using integrated cathodoluminescence and isotopic analyses. A quarry exposes 26 m of Upper Cretaceous Barton Creek Formation dolomitized marine limestone overlain by 16 m of dolomitized Albion Formation impact ejecta. The Albion Formation consists of a lower fine‐grained ≈1‐m‐thick spheroid bed and an upper 15‐m‐thick coarse conglomeratic diamictite bed. A 14‐event paragenetic sequence has been documented and used as a temporal framework to interpret chemostratigraphic trends in bulk rock δ18O, δ13C and 87Sr/86Sr. The uppermost surface of the Barton Creek Formation was subaerially exposed before the KT impact, as indicated by a brecciated palaeosol that caps upsection decreases in δ13C and δ18O. Small 1‐cm‐diameter spheroids in the spheroid bed exhibit vermicular crystalline textures but lack the concentric zonations common to accretionary lapilli. These spheroids are hypothesized originally to have been impact glass or reactive Ca and Mg oxide dusts that adhered to water vapour particles condensing from the cooling impact vapour cloud. The spheroids were dolomitized soon after deposition. The earliest dolomitization in the matrix sediments of the Albion Formation was also post‐depositional, replacing clays formed by devitrification of impact glass. Dolomite and clay 87Sr/86Sr exhibit a distinct symmetrical distribution in the spheroid bed ranging from 0·707745 to 0·707872. Although unproven, this may represent primary changes in the chemical composition of the impact glass. The limestone clasts in the diamictite bed were dolomitized before the KT impact and exhibit upsection decreases in bulk rock 87Sr/86Sr. This suggests that the clasts were excavated from strata equivalent in age or older than the Barton Creek Formation at locations closer to, or in, the Chicxulub crater. 相似文献
5.
6.
RICHARD J. BEHL 《Sedimentology》2011,58(2):325-351
Chert spheroids are distinctive, early‐diagenetic features that occur in bedded siliceous deposits spanning the Phanerozoic. These features are distinct in structure and genesis from similar, concentrically banded ‘wood‐grain’ or ‘onion‐skin’ chert nodules from carbonate successions. In the Miocene Monterey Formation of California (USA), chert spheroids are irregular, concentrically banded nodules, which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite. During shortening, there is brittle fracture of diatomite around, and horizontally away from, the convex surface of strain‐resistant chert nodules. Unlike most older siliceous deposits, the Monterey Formation still preserves all stages of silica diagenesis, thus retaining textural, mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures. Chert spheroids found in opal‐A diatomite form individual nodules composed of alternating bands of impure opal‐CT chert and pure opal‐CT or chalcedony. With increased burial diagenesis, surrounding diatomite transforms to bedded porcelanite or chert, and spheroids no longer form discrete nodules, yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony. Petrographic observations show that the purer silica bands are composed of void‐filling cement that precipitated in curved dilational fractures, and do not reflect geochemical growth‐banding in the manner of Liesegang phenomena invoked to explain concentrically banded chert nodules in limestone. Chertification of bedded siliceous sediment can occur more shallowly (< 100 m) and rapidly (< 1 Myr) than the bulk silica phase transitions forming porcelanite or siliceous shale in the Monterey Formation and other hemipelagic/pelagic siliceous deposits. Early diagenesis is indicated by physical properties, deformational style and oxygen‐isotopic composition of chert spheroids. Early‐formed cherts formed by pore‐filling impregnation of the purest primary diatomaceous beds, along permeable fractures and in calcareous–siliceous strata. 相似文献
7.
《Journal of South American Earth Sciences》1999,12(5):435-451
This paper is a contribution to the knowledge of the sedimentation of Neoproterozoic sequences, known as the Jequitaı́ Formation and Macaúbas Group. These sequences are present along the transitional zone between the São Francisco Craton and the Brasiliano (≌600 Ma) Araçuaı́ fold belt in Minas Gerais, Brazil. A sedimentological study of these Neoproterozoic sequences enables us to distinguish between true continental and marine glacial facies and glacial material reworked by various subaqueous gravitational processes. The cratonic Jequitaı́ Formation consists of massive and stratified diamictites up to 100 m thick. This diamictite association is tentatively interpreted as glaciomarine in origin. It continues eastward, in the Araçuaı́ fold belt, as the metasedimentary Macaúbas Group, which is composed of metadiamictites, quartzites and schists from 5–12(?)km thick. The Macaúbas Group consists of resedimented glacial material deposited by subaqueous debris flows and turbidity currents. A depositional model is proposed for the Jequitaı́–Macaúbas glacial/gravitational sequence. From west to east, a glaciomarine sequence, possibly deposited from an ice-sheet and slightly reworked by gravitational processes, was reworked along the São Francisco cratonic border and generated a slope apron system made up of diamictites associated with turbidites and rhythmites. 相似文献
8.
Patrick G. Quilty 《Australian Journal of Earth Sciences》2013,60(3):301-318
This paper is a summary of the present knowledge of the Tertiary stratigraphy of Western Australia. Also included is new information on the Cainozoic of the Carnarvon Basin, a result of petroleum exploration in the area. Tertiary rocks formed during more than one cycle of deposition in three basins (Eucla, Perth, and Carnarvon), and also as thin units deposited in a single transgression along the south coast. The Tertiary stratigraphy of the Bonaparte Gulf Basin is not well known. Drilling in the Eucla Basin has encountered up to 400 m of Tertiary in the south central part, with uniform thinning towards the margins. The section begins with a middle‐upper Eocene carbonate unit which represents the dominant event in the Tertiary sedimentation in this basin. More carbonates were deposited in the late Oligocene‐early Miocene and middle Miocene. Along the south coast, the so‐called Bremer Basin, the Plantagenet Group (up to 100 m) of siltstone, sandstone, spongolite, and minor limestone, was deposited during the late Eocene. The Perth Basin contains up to 700 m of Tertiary sediment, formed during at least two phases of sedimentation. The upper Paleocene‐lower Eocene Kings Park Formation consists of marine shale, sandstone, and minor limestone, with a thickness of up to 450 m. The Stark Bay Formation (200 m) includes limestone, dolomite, and chert formed during the early and middle Miocene. Events after deposition of the Stark Bay Formation are not well known. The northern Carnarvon Basin and Northwest Shelf contain by far the most voluminous Tertiary sediment known from Western Australia: 3500 m is known from BOCAL's Scott Reef No. 1. A more usual maximum thickness is 2500 m. Most sediments were laid down in four episodes, separated by unconformities: late Paleocene‐early Eocene; middle‐late Eocene; late Oligocene‐middle Miocene; and late Miocene to Recent. The Paleocene‐early Eocene cycle consists of about 100–200 m (up to 450 m in the north) of carbonate, shale, and marl of the Cardabia Group containing rich faunas of planktonic foraminifera. The middle‐late Eocene sediments include diverse rock types. Marine and nonmarine sandstone formed in the Merlinleigh Trough. At the same time, the Giralia Calcarenite (fauna dominated by the large foraminifer Discocyclina) and unnamed, deeper water shale, marl, and carbonate (with rich planktonic foraminiferal faunas) formed in the ocean outside the embayment. Thickness is usually of the order of 100–200 m. The main cycle of sedimentation is the late Oligocene‐middle Miocene, during which time the Cape Range Group of carbonates formed. This contains dominantly large foraminiferal faunas, of a wide variety of shallow‐water microfacies, but recent oil exploration farther offshore has recovered outer continental shelf facies with abundant planktonic foraminifera. A minor disconformity representing N7 and perhaps parts of N6 and N8 is now thought to be widespread within the Cape Range Group. The last part of this cycle resulted in sedimentation mainly of coarse calcareous marine sandstone (unnamed), and, in the Cape Range area, of the sandstone and calcareous conglomerate of the Pilgramunna Formation. Maximum thickness encountered in WAPET wells is 900 m. After an unconformity representing almost all the late Miocene, sedimentation began again, forming an upper Miocene‐Recent carbonate unit which includes some excellent planktonic faunas. Thickness is up to 1100 m. Thin marine sediments of the White Mountain Formation outcrop in the Bonaparte Gulf Basin. They contain some foraminifera and a Miocene age has been suggested. 相似文献
9.
10.
南岭东段龙头寨群南迳组的建立及其地质时代厘定 总被引：1，自引：0，他引：1
南岭带东段晚奥陶世广泛发育一套浅变质岩系,称为龙头寨群。以南迳乔子山剖面和中寨剖面为层型剖面建立南迳组,并置于龙头寨群顶部。用SHRIMP法测得南迳盆地南迳组安山岩样品14个锆石U-Pb年龄数据,其~(206)Pb/~(238)U年龄变化范围为460~425Ma,年龄加权平均值为442.1±3.9Ma(MSWD=0.75);英安岩15个锆石~(206)Pb/~(238)U年龄变化范围为450~420Ma,年龄加权平均值为439.9±3.7Ma(MSWD=0.50)。结合司前河口破火山口碎斑熔岩的SHRIMP锆石U-Pb年龄(443.6±5.4Ma(MSWD=1.3)),可将南迳组的地质时代归于晚奥陶世末期—早志留世初期。龙头寨群南迳组的建立和地质时代的厘定,不仅为龙头寨群的地质时代归入晚奥陶世—早志留世初期提供了可靠的依据,而且为南岭带东段晚奥陶世—早志留世浅变质岩系属含有火山岩的优地槽型沉积提供了证据。 相似文献
11.
柴达木盆地北缘早古生代碰撞造山系统 总被引：18，自引：6，他引：18
柴达木盆地北缘在早古生代形成了一条碰撞造山带，该造山带结构保存较完整，可分辨出深俯冲板片、火山岛弧带、蛇绿杂岩带、岛弧深成岩带等组成单元。其中，俯冲板块主要由中元古代鱼卡河岩群和中新元古代花岗片麻岩构成，在寒武纪末-奥陶纪可能全部或部分俯冲到岩石圈深部，发生了高压-超高压变质作用。火山岛弧主要由中基性火山岩、细碎屑岩等组成，成岩时代为晚寒武世-奥陶纪。蛇绿杂岩带由超镁铁质岩、辉长岩、玄武岩和少量硅质岩组成，形成于弧后扩张脊构造背景，成岩时代为寒武纪-奥陶纪。岛弧深成岩成分变化较大，由闪长岩变化到花岗岩，成岩时代为奥陶纪。而造山带北侧的欧龙布鲁克微陆块则具有双层结构，由德令哈杂岩和达肯大坂岩群构成基底，盖层为全吉群。 相似文献
12.
The Reid's Mistake Formation represents the stratigraphic interval that separates the Lower and Upper Pilot Coals within the Boolaroo Sub‐Group of the Newcastle Coal Measures. At Swansea Head it consists mainly of intercalated cherts and claystones with minor amounts of sandstone. The cherts, which frequently have a vitroclastic texture, are composed of chalcedony and analcime with or without feldspars and clay whereas the claystones consist of chalcedony and mixtures of mixed‐layer clay minerals. The intergradation between these rock types indicates that the entire sequence was derived from a common source, either acid volcanics of the New England fold belt or, more likely, contemporaneous ash showers. The detritus apparently accumulated in a flood basin environment where the climate was arid giving rise to saline conditions and the breakdown of the volcanic materials to clay minerals and chalcedony. During protracted periods of desiccation however, sodium ions were concentrated and the pH rose accordingly, sufficient to promote conversion of the clay minerals in the uppermost layers to analcime. 相似文献
13.
下扬子区早二叠世孤峰期泥化火山岩 总被引：8，自引：0，他引：8
下扬子区早二叠世弧峰组是以层状硅岩为主的海相层系，厚度为２０－８０ｍ。在硅岩层间产出火山岩，火山岩夹层的厚度小但层数众多，并几乎已全部泥化。但仍保留着残留的流动构造；长石、磷灰石、黑云母、角闪石等矿物或其晶屑以及各种形态的玻屑。在大量蒙脱石、伊利石、绿泥石等因泥化而形成的火山岩中特征性矿物。根据宏观及显微镜下特征、岩石化学成分的不同特征进行判断，火山岩包含有基性熔岩、酸性凝灰岩，还有大量含火山碎屑 相似文献
14.
Akindele O. Oyinloye 《Journal of African Earth Sciences》1998,26(4):633-641
The basement complex in the Ilesha area consists of two distinct units — the gneisses and the schists. The Ilesha Schist Belt is a back-arc basin where there has been a subduction of an ocean slab into the mantle. This was followed by partial melting of mantle and ocean sediments to generate a wet basaltic magma, as revealed by spidergrams and REE fractionation patterns for the rocks in this belt. In this environment, differentiation of the wet basaltic magma led to the emplacement of a set of rocks, which formed a proto-continent. These rocks were then eroded to generate a sedimentary sequence which was metamorphosed into banded gneiss from which the granite gneisses were derived. The banded gneiss, characterised by alternation of felsic and mafic bands, is composed of medium to very coarse plagioclase, hornblende, quartz and biotite. The granite gneiss, composed of biotite, K--feldspars, quartz and minor garnet, occurs in close association with the banded gneiss.Chemical evidence revealed that elements that are depleted in the banded gneiss are concentrated in the granite gneiss and vice-versa; suggesting a petrogenetic link between these rocks.The schists were deposited as sediments composed of quartz, muscovite, biotite and Fe oxides. These sediments were metamorphosed to form quartzite schists which were folded into the gneisses. After the emplacement of these rocks, there was transpressive tectonic activity in this schist belt, causing deformation of these rocks, and emplacement of the northeast-southwest Ifewara-Zungeru Fault System, which separates the Ilesha Schist Belt into two halves. 相似文献
15.
辽河群大石桥组形成时代——来自酸性火山岩LA-ICP-MS锆石U-Pb测年的制约 总被引：2，自引：0，他引：2
大石桥组是辽河群中一个重要的含矿层位,其岩性主要由白云石大理岩、方解石大理岩、云母片岩组成.在本次研究中,在辽阳南部八会镇辽河群大石桥组地层大理岩中首次发现有一层酸性火山岩夹层,岩性为流纹质角砾凝灰岩.根据野外产状判断,酸性火山岩与大理岩为同时沉积.清晰的振荡环带及比较高的Th/U比值,显示流纹质角砾凝灰岩的锆石为岩浆锆石,对其进行LA-ICP-MS U-Pb测年,结果显示其成岩年龄为2171±11 Ma,首次精确地厘定了大石桥组的形成时代.此年龄也进限定了置于大石桥组之下的浪子山组、里尔峪组、高家峪组等3个地层的沉积时限为2171 Ma之前. 相似文献
16.
The Karoo Supergroup in Madagascar is subdivided into three lithostratigraphical units: the Late Carboniferous-Early Permian Sakoa Group; the Late Permian-Middle Triassic Sakamena Group; and the Triassic-Early Jurassic Isalo Group. The Sakamena Group is fairly well exposed in the southern Morondava Basin, where it is approximately 4000 m thick. The Sakamena Group is separated from the Sakoa Group by an angular unconformity. The Lower Sakamena Formation is characterised by two major facies associations: (1) interbedded muddy conglomerates and coarse sandstones; and (2) interbedded sandstones and mudstones, which were deposited in a rejuvenated rift setting by coarse-grained fluvial systems and debris flows on the rift margins. In the Vatambe area, facies represent fandelta deposition in a saline lake or tongue of the ocean. The Middle Sakamena Formation comprises three major facies: (1) laminated mudstones and sandstones; (2) sandstones; and (3) mudstones. The Middle Sakamena facies were deposited by low gradient meandering streams and in shallow lakes. The Upper Sakamena Formation was deposited in similar environments, except that it is comprised predominantly of red beds. The Isalo Group consists predominantly of coarse-grained sandstones (up to 6000 m thick). These sandstones were deposited by braided streams with the coarse detritus derived from a structural uplift in the east. 相似文献
17.
福建政和东际金-银矿床的热液蚀变特征及其勘探指示意义 总被引：2，自引：0，他引：2
福建东际金-银矿床产于中生代东坑火山岩盆地西缘的流纹质凝灰岩中,矿区及周边火山-沉积岩系遭受了广泛且强度不等的热液蚀变。本文工作采用红外反射光谱技术在东际矿区三个勘探剖面上对钻孔岩心进行系统性高密度采样分析,结果显示蚀变矿物组合及分带的大框架样式主要受原岩成分控制,具体表现为绢云母化趋向于发育于流纹质火山岩中,而绿泥石化则富集在安山质和英安质火山岩中。在更小的矿区局部空间范围内或单一岩性中,热液作用的物化条件作为次级控制因素决定着特定蚀变矿物的成分变化和蚀变类型的强度差异。从层状硅酸盐组合考虑,东际矿区热液蚀变以绢云母化和绿泥石化为最主要类型,而缺失发育良好的蒙脱石带,金-银矿化赋存在以伊利石为主的绢云母化带中,表明成矿环境属于低硫到中硫之间的浅成热液系统。含矿火山岩的热液蚀变组合和强度变化,以及金-银矿化的似层状特点,均指示成矿时流体是沿着南园组凝灰岩层内侧向流动,而蚀变分带细节显示在凝灰岩层中存在着二至三条流体主通道,金-银矿化则赋存在主通道中。流体主通道的热液蚀变标志是富铝绢云母,其与主通道之外的相对贫铝绢云母在红外光谱特征上反差明显。因此,采用红外光谱技术圈定整体热液蚀变系统的空间构型、解译成矿环境的物化条件及变化、并确定绢云母的铝含量变化用以判断成矿流体主通道位置,可以有效地缩小勘探目标和提高找矿工作的预测性。 相似文献
18.
The Middle Marker is a thin (3–6 m) sedimentary unit at the base of the Hooggenoeg Formation in the 3.4 Ga old Onverwacht Group, Barberton Mountain Land, South Africa. The original sediments consisted largely of current-deposited volcaniclastic detritus now represented by green to buff-colored silicified volcaniclastic rock and fine-grained gray chert. Black chert, possibly formed by the silicification of a non-volcaniclastic precursor, makes up a significant part of the unit. The Middle Marker is underlain and overlain by mafic and commonly pillowed volcanic flowrock. Although the original sediment has been replaced by and/or recrystallized to a microquartz, chlorite, sericite, carbonate and iron oxide mosaic under lower greenschist-grade metamorphism, sedimentary textures and structures are remarkably well preserved. Textural pseudomorphs indicate the primary volcaniclastic sediment consisted of a mixture of crystal, vitric and lithic debris. Middle Marker sediments were deposited as a prograding, cone-flanking volcaniclastic sedimentary platform in a relatively-shallow and locally current/wave-influenced subaqueous sedimentary environment. Available paleocurrent data indicate a largely bimodal, orthogonal distribution pattern which is quite similar to both ancient and modern shallow marine/shelf systems. Diagnostic evidence for tidal activity is lacking. As felsic volcanic activity waned, an extensive airfall blanket of fine-grained volcanic ash and dust was deposited in a low-energy subaqueous environment. The sedimentary cycle was terminated with a renewal of submarine mafic volcanism. Middle Marker volcaniclastic sediments accumulated in an anorogenic basin removed or isolated from the influence of continental igneous and metamorphic terranes. Although compositionally dominated by a volcanic source, Middle Marker sediments owe their final texture and sedimentary structures to subaqueous sedimentary rather than volcanogenic processes. 相似文献
19.
The Late Proterozoic Conception Group, exposed on the Avalon Peninsula in Newfoundland, Canada, is a 4 km thick turbidite succession containing a conformable 300 m thick sequence of diamictites (the Gaskiers Formation) near the base. Massive and crudely-stratified diamictites form beds up to 25 m thick which have a tabular geometry with slightly erosive basal contacts and are interbedded with mudstones and fine-grained, thin-bedded turbidites. These diamictites are interpreted as submarine debris flow deposits. Disrupted diamictites form strongly deformed units that contain large, complexly folded rafts of mudstone and turbidite facies. These diamictite units are interpreted as submarine slumps. Diamictites contain glacially-striated and faceted clasts; clasts and matrix are predominantly of volcanic provenance. One outcrop shows interbedded volcanic agglomerate and diamictite, and volcanic bombs can also be identified. The interbedding of diamictites with turbidites and the stratigraphic context provided by the thick sequences of turbidites below (Mall Bay Formation) and above (Drook Formation) indicate a deep marine slope setting of diamictite deposition. Diamictite facies record remobilization and downslope transfer of large volumes of unstable volcanic and glacial debris initially deposited in a shallower water marginal marine zone. The regional tectonic framework suggests the Conception Group accumulated in a deep, southward-opening ensialic rift basin with active but waning volcanic centres to the north. The Gaskiers Formation may be representative of other Late Precambrian glacially-influenced diamictite sequences that were deposited around the North Atlantic region and in Europe. These deep marine diamictite sequences characterized by debris flows, turbidites, and slump deposits, can be contrasted with more extensive shallow marine shelf diamictite sequences found in association with dolomites and tidally influenced shallow water facies in other basinal settings. 相似文献
20.
《Journal of Asian Earth Sciences》2010,39(6):233-254
The Bone Mountains, located in Southwest Sulawesi along the SE margin of Sundaland, are composed of Oligocene to possibly lower Miocene marginal basin successions (Bone Group) that are juxtaposed against continental margin assemblages of Eocene–Miocene age (Salokalupang Group). Three distinct units make up the latter: (i) Middle–Upper Eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part (Matajang Formation), reflecting a period of arc volcanism and carbonate development along the Sundaland margin; (ii) a well-bedded series of Oligocene calc-arenites (Karopa Formation), deposited in a passive margin environment following cessation of volcanic activity, and (iii) a series of Lower–Middle Miocene sedimentary rocks, in part turbiditic, which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity (Baco Formation), formed in an extensional regime without subduction.The Bone Group consists of MORB-like volcanics, showing weak to moderate subduction signatures (Kalamiseng Formation), and a series of interbedded hemipelagic mudstones and volcanics (Deko Formation). The Deko volcanics are in part subduction-related and in part formed from melting of a basaltic precursor in the overriding crust. We postulate that the Bone Group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west (Sundaland) and by a newly initiated westerly-dipping subduction zone on its eastern side.Around 14–13 Ma an extensional tectonic event began in SW Sulawesi, characterized by widespread block-faulting and the onset of potassic volcanism. It reached its peak about 1 Ma year later with the juxtaposition of the Bone Group against the Salokalupang Group along a major strike-slip fault (Walanae Fault Zone). The latter group was sliced up in variously-sized fragments, tilted and locally folded. Potassic volcanism continued up to the end of the Pliocene, and locally into the Quaternary. 相似文献