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1.
In Tasmania shelly fossils are known from Middle and Upper Cambrian sediments of the Dundas Trough, Fossey Mountain Trough, Dial Range Trough, Beaconsfield Trough, Smithton Basin, Adamsfield Trough and from within sediments associated with the Mount Read Volcanics of Western Tasmania. In the Dundas Trough fossils range in age from early Middle Cambrian (Ptychagnostus gibbus Zone) to the middle Late Cambrian (pre‐Payntonian A or B). Late Middle Cambrian fossils occur in sediments associated with the Mount Read Volcanics in two places in Western Tasmania. Late Middle Cambrian fossils only are known from the Smithton Basin and the Beaconsfield Trough. Late Middle to early Late Cambrian faunas are known from the Dial Range Trough; the Adamsfield Trough contains middle Middle to middle Late Cambrian fossils. Tasmanian Cambrian faunas show affinities with those of Queensland, China, the northwest Siberian Platform and northern Victoria Land, Antarctica.  相似文献   

2.
In northwest Argentina, weakly metamorphic clastic and calcareous sedimentary rocks of latest Precambrian to Lower Cambrian age (Puncoviscana Formation and related units) contain an abundant ichnofauna of both chronostratigraphic and paleoenvironmental value. In the western and central Sierras Pampeanas, metasedimentary and metavolcanic rocks are considered to form part of the same geotectonic unit. This “Pampean orogenic cycle” includes geosynclinal sedimentation of latest Precambrian to Lower Cambrian age, as well as magmatism, metamorphism and deformation of Middle to Upper Cambrian age, documented by an angular unconformity below the Upper Cambrian to Devonian rocks of the “Famatinian orogenic cycle”. In some of the metamorphic rocks of the Pampean Cycle a pre-Ordovician folding is also distinguished from a later tectonic overprinting. Hence, the concept of a Pampean cycle differs from other concepts of late Precambrian orogenic cycles of South America which are only defined by radiometric ages. The Pampean orogenesis may be compared with the Ross orogenesis of the Transantarctic Mts., the Tyennan orogenesis of Australia and some of the deformation phases of the Damara orogen in Namibia.  相似文献   

3.
In western Tasmania Eocambrian and Cambrian rock sequences accumulated in narrow troughs between and within Precambrian regions which became geanticlines. The largest trough is meridional and is flanked by the Tyennan Geanticline to the east and the Rocky Cape Geanticline to the west. Within this trough ultramafic and mafic igneous masses, some of which are dismembered ophiolites, occur below a structurally conformable but erosional surface. This surface is at the base of an early-Middle Cambrian turbidite sequence, which grades upward into a probable correlate of the Owen Conglomerate that ranges into the Ordovician. Fault-bounded areas of Rocky Cape strata occur at the eastern boundary of the sedimentary trough deposits. A considerable pile of mineralized calcalkalic volcanic material, in which granite was emplaced, accumulated between the sedimentary trough deposits and the Tyennan Geanticline. Movements along Cambrian faults near and parallel to the margin of the Tyennan Geanticline caused angular unconformities. Above the unconformities occur volcaniclastic sequences that pass conformably upward into shallow marine and terrestrial Owen Conglomerate, derived from the Tyennan Geanticline.The transgressive Owen Conglomerate and its correlates are followed conformably by shallow marine limestone, of Early to Late Ordovician age. These limestone deposits covered much of western Tasmania and are succeeded conformably by Silurian to Early Devonian beds of shallow-marine quartz sandstone and mudstone.Pre-Middle Devonian rocks of western Tasmania extend to the Tamar Tertiary trough. In the northeast of Tasmania, immediately to the east of the Tamar trough, are sequences of interbedded mudstone and turbidite quartz-wacke of the Mathinna Beds, ranging in age from Early Ordovician to Early Devonian.The Cambrian to Early Devonian rocks of Tasmania are extensively deformed and show flattened parallel folds. In western Tasmania the folds are dated as late-Early to early-Middle Devonian because fragments of the deformed rocks occur in undisturbed Middle Devonian terrestrial cavern fillings. Folds of the northeastern Tasmania Mathinna Beds are probably of the same age. This widespread Devonian deformation is correlated with the Tabberabberan Orogeny of eastern Australia.In western Tasmania the geanticlines of Cambrian times behaved as relatively competent blocks during the Devonian folding, which is of two main phases. In the earlier phase the competent behaviour of the Tyennan Block determined the fold patterns. In the north the dominantly later folds resulted from movement from the northeast. During this later Devonian phase the Tyennan Block yielded in a northwesterly trending narrow zone of folding.In northeast Tasmania the Mathinna Beds exhibit folds which indicate a tectonic transportation opposite in direction to that which resulted in the folds of similar age in western Tasmania.Granitic rocks, dated 375-335 m.y., were emplaced within the folded rocks of Tasmania with usually sharp, discordant contacts. Foliations in the batholiths of northeast Tasmania suggest post-intrusion deformations involving east—west flattening. The late deformations may be related to lateral movements along a fracture zone which brought the Mathinna Beds of northeast Tasmania into juxtaposition with the rocks of contrasting stratigraphical and structural characteristics of western Tasmania.Flat-lying Late Carboniferous and younger deposits rest unconformably on the older rocks.  相似文献   

4.
In western Tasmania, Precambrian sedimentary sequences form the basement for narrow trough accumulations of Eocambrian and younger sequences. The main trough, the meridional Dundas Trough, is flanked to the west by the Rocky Cape region of Precambrian rocks within which major, apparently stratiform, exhalative magnetite-pyrite deposits are intercalated with metabasaltic volcanics and ultramafic bodies.The Eocambrian-Cambrian troughs apparently developed during extension of Precambrian continental crust. Early shallow-water deposition includes thick dolomite units in some troughs. Deepening of the troughs was accompanied by turbidite sedimentation, with minor limestone, and submarine basaltic volcanism with associated minor disseminated native copper. Ultramafic and related igneous rocks were tectonically emplaced in some troughs during a mild compressional phase. They contain only minor platinoids, copper-nickel sulphides and asbestos, but are source rocks for Tertiary secondary deposits of platinoids, chromite and lateritic nickel.In the Dundas Trough, Eocambrian-Early Cambrian rocks are separated by an inferred erosional surface from structurally conformable overlying Middle to Late Cambrian fossiliferous turbidite sequences. The structural conformity continues through overlying Ordovician to Early Devonian terrestrial and shallow-marine stable shelf deposits.A considerable pile of probable Middle Cambrian felsic volcanics accumulated between the sedimentary deposits of the Dundas Trough and the Tyennan region of Precambrian rocks to the east. A lava-dominated belt within the volcanics hosts major volcanogenic massive sulphide deposits, including those of the exhalative type, which in the south are enriched in copper, gold and silver, whereas in the north they are rich in zine, lead, copper, gold and silver. Cambrian movements along faults near the margin of the Tyennan region resulted in erosion of the mineralized volcanics, locally exposing sub-volcanic granitoids. Above the local unconformities occur unmineralized volcaniclastic sequences that pass conformably into Ordovician to Early Devonian shelf deposits. Ordovician limestone locally hosts stratabound disseminated and veined base metal sulphide deposits.Pre-Middle Devonian rocks of western Tasmania differ, for most part, from those in the northeast where deeper marine turbidite quartz-wacke sequences were deposited during the Ordovician and Early Devonian.The Eocambrian to Early Devonian rocks of Tasmania were extensively deformed in the mid-Devonian. The Precambrian regions of western Tasmania behaved as relatively competent blocks controlling early fold patterns. In northeastern Tasmania, folding is of similar age but resulted from movements inconsistent with those affecting rocks of equivalent age in western Tasmania.The final metallogenic event is associated with high-level granitoid masses emplaced throughout Tasmania during the Middle to Late Devonian. In northeastern Tasmania, extensive I-type granodiorite and S-type granite, with alkali-feldspar granites, are associated with mainly endogranitic stanniferous grelsens and wolframite ± cassiterite vein deposits. In contrast, scheelite-bearing skarns and cassiterite stannite pyrrhotite carbonate replacement deposits are dominant in western Tasmania, associated mainly with S-type granites. Several argentiferous lead-zinc vein deposits occur in haloes around tin-tungsten deposits. A number of gold deposits are apparently associated with I-type granodiorite, but some have uncertain genesis.The contrasting regions of western and northeastern Tasmania have probably been brought together by lateral movement along an inferred fracture. Flat-lying, Late Carboniferous and younger deposits rest on the older rocks, and the only known post-Devonian primary mineralization is gold associated with Creta ceous syenite.  相似文献   

5.
Detailed geological mapping and drilling has shown that the contact between the Cambrian volcano‐sedimentary sequence at Rosebery and the Mt Read Volcanics is formed by a major thrust fault dipping east at 40° and having a displacement of at least 1.5 km. The sedimentary sequence is part of the Dundas Group, a Middle to Late Cambrian forearc‐like sequence which unconformably overlaps the volcanics south of Rosebery. The Rosebery Thrust Fault marks the eastern boundary of a zone of folding, faulting and disruption which affects the Dundas Group and the tectonically interfingered and underlying basaltic greywacke‐mudstone sequence of the Crimson Creek Formation. At least some of this deformation occurred prior to deposition of the Ordovician Limestone, as evidenced by marked angular discordances. The complex area can be interpreted as a Cambrian accretionary prism‐forearc‐arc sequence developed above an east‐dipping subduction zone.

The Henty Fault System, which cuts obliquely through the Mt Read belt and encloses a misfit wedge of sediments, pillow lavas, gabbros and ultramafic rocks, is interpreted as a remnant of an inter‐arc basin. The fault system separates a dacitic‐andesitic arc segment to the northwest from a more rhyolitic segment to the southeast. The latter is overlain by a younger arc sequence, the Tyndall Group, which may have been the source for the Dundas Group volcanic detritus.  相似文献   

6.
Isotopic age determinations on granitic rocks from Tasmania   总被引：1，自引：1，他引：0  
Potassium‐argon and rubidium‐strontium isotopic age measurements show that emplacement of granitic rocks in Tasmania occurred during the Late Devonian and Early Carboniferous and in pre‐Devonian times, possibly in the Cambrian. In addition, a Precambrian granite, dated at about 750 m.y., has been recognized on the west coast of King Island.

The granitic bodies of pre‐Devonian age include the Murchison River Granite, the Dove River Granite and its correlatives, and the adamellite on the southwest coast of Tasmania at Elliott Bay. These rocks were deformed during the Devonian Tabberabberan Orogeny with the result that leakage of radiogenic daughter products has occurred from minerals. Hence the indicated ages are younger than the true ages. Possibly these granitic rocks were emplaced during the Jukesian Movement of the Tyennan Orogeny, in the Late Cambrian, although a Precambrian age cannot be excluded for some of the bodies.

As recognized by earlier workers the most important period of emplacement of granitic rocks in Tasmania was in the Middle Palaeozoic. The measured dates for this group of rocks range from 375 to 335 m.y., and indicate that intrusion occurred over an extended period from the Late Devonian to the Early or possibly Middle Carboniferous. There are distinct concentrations of measured ages at about 370 and 340 m.y. The granitic bodies of northeast Tasmania mainly yield the older age, whereas those of northwest Tasmania give the younger age. As the granites are post‐tectonic bodies the older age of about 375 m.y. provides a younger limit to the time of completion of the main folding in the Tabberabberan Orogeny, and this is consistent with the stratigraphic evidence.

The evidence suggests that generation of granitic magma was initiated during the main folding associated with the Tabberabberan Orogeny, but that emplacement of the granites into the upper crust continued over a long period subsequently to the main folding phase. Alternatively, the younger granitic bodies, dated at about 340 m.y., may indicate that these rocks are related to the Early Carboniferous Kanimblan Orogeny recognized in Victoria and New South Wales; however, there is no field evidence to support such a proposition.  相似文献   

7.
新疆塔县达布达尔地区二叠系神仙湾组位于塔阿西构造混杂岩带南侧,总体为一套深海复理石建造,主要以杂砂岩为主。源区岩石没有经过充分的搬运、分选,成熟度比较低。杂砂岩的稀土元素特征表现为轻稀土元素富集和Eu亏损明显的特征,与典型的后太古宙页岩和上地壳非常相似。微量元素含量也接近于大陆上地壳值,说明杂砂岩中的物源来自上地壳。沉积环境分析表明,杂砂岩母岩原岩为大量长英质火成物质和少量沉积物,其形成于深海厌氧环境。大地构造背景分析表明,杂砂岩物源区的构造背景以大陆岛弧为主,兼具活动大陆边缘的性质。结合区域地质构造背景,认为下-中二叠统神仙湾组为裂陷盆地沉积。  相似文献   

8.
A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole‐rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high‐level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low‐angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high‐level emplacement of ultramafic‐bearing allochthons and deep‐seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep‐seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions.  相似文献   

9.
江汉盆地海相探区中寒武统盐下层勘探潜力浅析   总被引：3，自引：0，他引：3  
江汉海相探区内中寒武统覃家庙组膏盐岩盐下层系中发育有两套良好的生储盖组合.对盐下层系生、储、盖特点和分布规律的分析表明,上震旦统陡山沱组及下寒武统水井沱组发育页岩烃源岩,上震旦统灯影组碳酸盐岩和下寒武统石龙洞组碳酸盐岩有良好的储集条件,而覃家庙组的膏盐岩和下寒武统石牌组-天河组泥质岩又为盐下的油气聚集提供了区域性盖层条...  相似文献   

10.
East Siberia comprises three petroleum provinces—Lena-Tunguska, Lena-Vilyuy, and Yenisey-Anabar—that occupy the area of the Siberian craton. Petroleum has been generated and has accumulated in Precambrian rifts beneath the sedimentary basins and, more importantly, within the section of the basin itself. The platformal deposits of the basins extend beneath overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian province on the west. Permafrost and gas hydrate deposits are present throughout most of East Siberia.

In the Lena-Tunguska province, rifts that developed during Riphean time are filled by thick sedimentary rocks, in which petroleum deposits have formed. In Early Cambrian time a barrier reef extended across the East Siberian craton from southeast to northwest. A lagoon to the west of this reef was the site of thick rhythmic salt deposits, which are the main seal for petroleum in the province. The sedimentary section of the platform cover ranges in age from Late Proterozoic to Permian. More than 25 oil and gas fields have been discovered in the province, all in Riphean through Lower Cambrian rocks.

The Lena-Vilyuy province includes the Vilyuy basin and the Cis-Verkhoyansk foredeep. During Middle Devonian time, a rift formed along the axis of what was to become the Vilyuy basin. This rift is filled by Upper Devonian and Lower Carboniferous basalt, elastics, carbonates, and evaporites. During this rift stage the region that was to become the Cis-Verkhoyansk foredeep was an open geosynclinal sea. The sedimentary cover consists of Permian, coal-bearing sedimentary rocks as well as elastics from the Lower Triassic, Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, the latter only in the Vilyuy basin. In the Lena-Vilyuy petroleum province as many as nine gas and gas-condensate fields have been discovered.

The Yenisey-Anabar province is largely an extension of the West Siberian petroleum province. Permian sedimentary rocks are present only in the east, where they consist of elastics and some salt. The Triassic, Jurassic, and Cretaceous each are represented by thick clastic deposits. Total thickness of the sedimentary cover is up to 15 km on the west and 8 km on the east. Twelve gas and gas-condensate fields have been discovered in the western part of the province.  相似文献   

11.
赋存于皖南—浙西的固体碳沥青分为古油藏裂解碳沥青和古油藏破坏次生充填碳沥青两种类型 ,阐明了两类碳沥青的不同成因机制。重新认定了浙西“康山沥青脉”为碳沥青而不是泥岩。论证了皖南、浙西碳沥青的烃源为下寒武统、中—上奥陶统至下志留统、中—上寒武统等。认为加里东运动—广西事件期间是下扬子盆地相区以下寒武统黑页岩为烃源的油藏形成和部分破坏的主要时期。针对南方的油气勘探 ,提出了只有在晚期成藏中作出贡献的源岩才是“有效烃源岩”的新概念。  相似文献   

12.
The biostratigraphy of the Cambrian of Kashmir based on trilobite assemblage zones and trace fossils has been attempted. Faunal gaps occur in lower part of Lower Cambrian, upper Lower Cambrian, lower Middle Cambrian and upper part of Upper Cambrian. In the Lower Cambrian Cruziana—Rusophycus and Redlichia Zones, in the Middle Cambrian Solenopleura—Tonkinella, Tonkinella—Anomocare, Anomocare—Bailiella and Bolaspidella Zones, and in the Upper Cambrian Chuangia and Dikelocephalites Zones are recognized. The position of intrasystem boundaries is also discussed. While the various taxa have lithological preferences and are not necessarily found in a continuous sequence, an attempt has been made to interpret the ranges of different genera. The affinities of the fauna with that of other Cambrian basins of the world are discussed. It is concluded that the bulk of the fauna is of a cosmopolitan nature.  相似文献   

13.

Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360–350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U–Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km2 and ≥500 km inboard of plate margin) and protracted, occurring over a period of ～15 million years. Zircon inheritance is commonplace in the Late Devonian — Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385–370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation. This contrasts with a lack of significant zircon inheritance in younger Permo‐Carboniferous igneous rocks intruded through, and emplaced on top of, the Devonian‐Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr–Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent.  相似文献   

14.
This paper is a synthesis of structural and geochronological data from eastern Mediterranean ophiolitic metamorphic rocks and surrounding units to interpret the intra‐oceanic subduction and ophiolite emplacement mechanism.

Metamorphic rocks occur as discontinuous tectonic slices at the base of the ophiolites, generally between the peridotite tectonites and volcanic‐sedimentary units, and locally in fault zones in the overlying peridotites. They consist essentially of amphibolite, and in lesser quantities, micaschist, quartzite, epidotite and marble.

Geological and geochronological data indicate that recrystallization of the metamorphic rocks occurred in the oceanic environment. The contact between the metamorphic rocks and the hanging‐wall is parallel to the foliation of the metamorphic rocks, and is interpreted as the fossil plane of intra‐oceanic subduction. Structural relationships suggest that intra‐oceanic subduction was situated between two lithospheric blocks separated by an oceanic fracture zone. Therefore the Neotethyan ophiolites with metamorphic soles represent the remnants of the overriding oceanic lithosphere's training slices of the metamorphic rocks at the base.

In the Anatolian region, radiometric dating of metamorphic rocks from the Taurus and Izmir‐Ankara‐Erzincan zone ophiolites yield nearly identical ages. Besides, palaeontological and structural data indicate coeval opening and similar oceanic ridge orientation. Consequently it is highly probable that Taurus and Izmir‐Ankara‐Erzincan zone ophiolites represent fragments of the same oceanic lithosphere derived from a single spreading zone. Palaeontological data from underlying volcanic and sedimentary units point out that the opening of the Neotethyan ocean occurred during Late Permian‐Middle Triassic time in the Iranian‐Oman region, during Middle Triassic in Dinaro‐Hellenic area, and finally during Late Triassic in the Anatolian region.

Radiometric dating of the metamorphic rocks exhibit that the intra‐oceanic thrusting occurred during late Lower‐early Late Jurassic for Dinaro‐Hellenic ophiolites, late Lower‐early Late Cretaceous for Anatolian, Iranian and Oman ophiolites well before their obduction on the Gondwanian continent. Neotethyan ophiolites were obducted onto various sections of the Gondwanian continent from late Upper Jurassic to Palaeocene time, Dinaro‐Hellenic ophiolites during late Upper Jurassic‐early Lower Cretaceous onto the Adriatic promontory, Anatolian, Iranian and Oman ophiolites from late Lower Cretaceous to Palaeocene onto the Aegean, Anatolian and Arabic promontories.  相似文献   

15.

Serpentinised peridotite and ultramafic breccia make up an approximately 5 km‐long, 1 km‐wide fault slice within turbidites in the Dolodrook River region of the central Lachlan Orogen. The serpentinite body is surrounded by juvenile, mafic‐ultramafic sedimentary rocks with Cambrian limestone olistoliths representative of locally derived debris flows, and Middle to Upper Ordovician black shale, chert, sandstone and mudstone. The antiformal geometry and nature of the ultramafic breccia and mafic‐ultramafic sedimentary rocks (Garvey Gully Formation) indicate that the serpentinite body may have been either a former oceanic transform fault zone, a Marianas‐style serpentine seamount or a combination of these. Observations of modern‐day forearc regions show that faulting processes have led to the exposure of serpentinised peridotite horst blocks and serpentine mud volcanoes that have intruded along fault conduits (e.g. Marianas and Izu‐Bonin forearcs). At Dolodrook, the structural and metamorphic relationships with the surrounding rocks, and the lithological associations, have much in common with these observations and indicate that Dolodrook may be an ancient, on‐land example of an accreted seamount or oceanic topographic high. Structural relationships, the very low metamorphic grade of all rocks at Dolodrook, and the presence of broken formation developed in not‐fully lithified Middle to Upper Ordovician sandstone and mudstone indicate that the serpentinite body was emplaced at shallow crustal levels within the turbidite wedge (Tabberabbera Zone), possibly as an offscraped topographic high during marginal basin closure. The Dolodrook serpentinite has previously been inferred as part of the Cambrian igneous sequence (‘greenstones’) exposed in the Governor, Mt Wellington and Heathcote Fault Zones, but structural and metamorphic relationships with surrounding rocks, and the Cambrian tectonic setting in which it formed, have remained speculative.  相似文献   

16.
从塔里木盆地看中国海相生油问题   总被引：175，自引：3，他引：172  
梁狄刚 《地学前缘》2000,7(4):534-547
塔里木盆地厚达 5～ 7km的海相寒武、奥陶系 ,可划分出下、中寒武统和中、上奥陶统两套工业性烃源岩。油源对比证实 :盆地目前保存下来的海相成因工业性油藏 ,主要来源于中上奥陶统泥灰岩。正是因为塔里木盆地比四川、鄂尔多斯盆地多了一套中等成熟的中上奥陶统油源岩 ,所以能够找到海相油田。笔者认为 :海相工业性烃源岩不必很厚 ,但w (TOC)应≥0 .5% ,碳酸盐岩要含泥质 ;海相源岩往往并不发育在凹陷中心 ,而发育在 4种有利沉积相带上 ;碳酸盐岩具有“双重母质”的特点 ,浮游藻类偏油 ,底栖藻类偏气。海相源岩的形成模式有“保存模式”和“生产力模式”两种 ,分别对应于塔里木寒武系和中上奥陶统烃源岩。塔里木古生代克拉通早期活动、晚期稳定、持续降温的演化史 ,有利于海相油气的多期成藏和晚期保存。  相似文献   

17.
黔中隆起及其周缘地区“下组合”油气地质特征   总被引：8，自引：1，他引：8  
黔中隆起及其周缘地区包括滇黔北部坳陷、黔中隆起、滇东隆起、黔西南坳陷、黔南坳陷和武陵坳陷等六个一级构造单元。“下组合”包括震旦系、寒武系、奥陶系和志留系,具有丰富的油气资源和较好的油气成藏条件。两套区域性海相烃源岩,包括下寒武统牛蹄塘组碳质页岩和上奥陶统五峰组—下志留统龙马溪组石灰岩和碳质页岩,Ro值普遍在2%以上,主体处于高成熟晚期—过成熟早期。上震旦统陡山沱组发育地区性黑色页岩和碳质灰岩等烃源岩。主力储层包括上震旦统灯影组、中—上寒武统、下奥陶统桐梓组—红花园组及下志留统石牛栏组。区域盖层发育于下寒武统下部和下志留统下部,皆以泥质岩为主。各区块海相“下组合”纵向生储盖组合发育情况有所差异,黔中隆起区和黔南坳陷有两套组合,滇黔北部坳陷则有四套组合。以下寒武统牛蹄塘组为烃源岩、上震旦统灯影组白云岩为储层、下寒武统泥岩为盖层的生储盖组合,是黔中隆起及其周缘地区“下组合”勘探的主要目的层系。  相似文献   

18.
The available paleomagnetic data on the Verkhnyaya Lena Group from different areas of the southern Siberian Platform are revised. The group rests unconformably upon the Lower Cambrian strata and is overlain by Lower Ordovician rocks, which determines conditionally the age of its red-colored deposits. Paleomagnetic correlation of composite sections through the region using defined zones of normal and reversed magnetic polarity serves as a basis for development of the magnetostratigraphic scale for the Verkhnyaya Lena Group. The scale includes nine magnetic zones, which play the role of markers; seven of them are traceable in all the examined sections of the southern Siberian Platform. By the distribution of zones with normal (N) and reversed (R) polarity, the magnetostratigraphic scale is subdivided into three parts. Its lower part is represented by reversed polarity, which is characteristic of the second half of the Lower Cambrian. The middle part is characterized by frequently alternating zones with normal and reversed polarity corresponding to the Middle Cambrian. The upper part of the scale corresponds to the interval of reversed polarity characteristic of the Upper Cambrian and Lower Ordovician. The Middle–Upper Cambrian boundary is located near the last N–R reversal of the geomagnetic field in the Cambrian. The magnetostratigraphic scale includes nine orthozones united into three superzones, which are attributed to two hyperzones of magnetic polarity.  相似文献   

19.
Aeromagnetic and field data suggest that meta‐igneous rocks exposed on the south coast of central Victoria at Waratah Bay, Phillip Island, Barrabool Hills and inland near Licola, are continuous—beneath Bass Strait—with Proterozoic/Cambrian igneous rocks in King Island and Tasmania. This correlation is supported by a pre‐Early Ordovician unconformity above gabbro protomylonite at Waratah Bay, age equivalent to the Tasmanian Tyennan unconformity. Cambrian volcanics at Licola and unusual features of the Melbourne Zone sequence indicate that Tyennan continental crust extends north as basement to the central Victorian portion of the Lachlan Fold Belt. In contrast, adjacent parts of the Lachlan Fold Belt in Victoria contain conformable sea‐floor sequences that span the Early Cambrian to Late Ordovician, with no evidence of either Cambrian deformation or underlying continental basement. The block of Tyennan continental crust beneath central Victoria—the Selwyn Block—is fundamentally different, and has influenced temporal and spatial patterns of sedimentation, deformation, metamorphism and plutonism. Palaeogeographical reconstructions suggest that the block was a submarine plateau that lay outboard of the Australian craton, upon which a condensed Ordovician sequence was deposited. The sequence above the Selwyn Block unconformity at Waratah Bay is similar to widespread post‐Tyennan sediments in western Tasmania. During Late Ordovician and Early Silurian deformation, the Selwyn Block protected much of the overlying sedimentary sequence. Instead, shortening was focused into the Stawell and Bendigo Zones to the west. These zones were sandwiched between the Selwyn Block and the Australian craton in a ‘vice’ scenario reminiscent of some Appalachian orogenic events. The region above the Selwyn Block was downwarped adjacent to the overthrust Bendigo Zone as a foreland deep, into which a conformable clastic wedge of sediment was deposited in Late Ordovician to Devonian time, prior to final Middle Devonian deformation. The Selwyn Block includes the Cambrian calc‐alkaline Licola and Jamieson Volcanics that are correlated with the Tasmanian Mt Read Volcanics. In Victoria, these form a basement high controlling the unusual down‐cutting thrusts in the overlying Melbourne Zone and explaining the major structural vergence reversal between the Melbourne and Tabberabbera Zones. The Selwyn Block has exerted some control on the timing, chemistry and distribution of post‐orogenic granites, and on central Victorian gold mineralisation. Reactivated faults in the block influenced deposition, and continue to control the deformation of the portions of the Otway and Gippsland Basins that lie above it.  相似文献   

20.
A geochemical soil survey was made over outcropping Cambrian and Lower Devonian formations in the Belgian Ardennes. About 300 soil samples were collected in an area of 2.5 × 1.1 km2.Analysis of rock samples from scarce, but stratigraphically well-known outcrops show that the Cambrian rocks are richer in copper than those of the Lower and Upper Gedinnian (Lower Devonian). The Upper Gedinnian rocks are more nickeliferous than the other horizons.In the well-drained soils, copper and lead distributions permit precise location of the boundary between Cambrian and Lower Gedinnian formations. The nickel distribution seems to be a good stratigraphic indicator for distinguishing Upper from Lower Gedinnian. Zinc distribution seems unrelated to underlying bedrock geology.Regression analysis confirms that the content of Cu, Pb and Ni is essentially a function of lithostratigraphy. However, the distribution of these elements is more influenced by pedological factors in the poorly drained soils.  相似文献   

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