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1.
Ahad N. Chowdhury 《Sedimentary Geology》1982,32(4):247-263
Petrographic and geochemical evidence shows convincingly that the diagenetic environment changes from marine phreatic through freshwater phreatic to vadose during lithification of the oolites and the overlying Coral Rag of the Osmington Oolite Formation in the Oxford—Berkshire area. This change is thought to be a consequence of tectonic uplift following deposition of the Coral Rag. Extensive neomorphic replacement of the corals took place in a freshwater phreatic environment created by tectonic uplift. Retention of Sr in the Coral Rag is related to differing diagenesis: pore-fluids remained for protracted periods within the Coral Rag as the downward flow was greatly retarded because of obliteration of porosity in the oolites by marine phreatic cementation before deposition of the Coral Rag. 相似文献
2.
Simon Wills Emma Louise Bernard Philippa Brewer Charlie J. Underwood David J. Ward 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(2):170-186
Woodeaton Quarry in Oxfordshire has previously yielded a number of large sauropod vertebrae and other (unpublished) dinosaur remains from a horizon in the Rutland Formation. No review of the wider terrestrial fauna from Woodeaton has been published to date. Here we present an overview of new material recovered from a microvertebrate site at the top of the White Limestone Formation (Middle Jurassic, Bathonian, Great Oolite Group, Retrocostatum Zone) and review the stratigraphy to provide a comprehensive local stratigraphic framework and place the quarry in the correct regional context. The terrestrial fauna is similar to that found from other UK Bathonian microvertebrate sites and includes probable dromaeosaurid theropods, ornithischians, tritylodontids and mammaliaforms such as amphitheriids, docodonts, ‘eutriconodonts’, ‘haramyids’ and multituberculates. Placement of the White Limestone Formation boundaries are clarified with respect to the Rutland and Forest Marble Formations. This indicates that the microvertebrate bed from Woodeaton is slightly older than that of the well-known mammal bed from nearby Kirtlington Quarry. 相似文献
3.
Robert B. Chandler 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(3-4):307-325
Two new species of stephanoceratid ammonites are erected: Stephanoceras (Riccardiceras) eoeteosum sp. nov. and Stephanoceras (Skirroceras) englandi sp. nov. from the Inferior Oolite Formation of Dorset, UK. They represent the first and last members of a chronocline of serpenticonic morphospecies. The stratigraphical position of Rhytostephanus rhytus Buckman is reviewed, necessitating a change in the faunal horizon scheme. The term mesoconch is proposed for use in describing microsomic macroconchs, the function of which is considered. Names applied to morphospecies and their uses are reviewed. The role of conservation is discussed in respect of preserving Dorset Inferior Oolite exposures. 相似文献
4.
N.J. Hogancamp V.P. Wright 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):93-101
A revised age provided by conodonts from the Gilwern Oolite of the Clydach area of South Wales allows a clearer understanding of the palaeohydrology, palaeoclimatic history and diagenesis of previously correlated oolitic units. Earlier uncertainty over the apparent sub-regional differences in climate during the early Visean (Chadian—Arundian) lowstand is resolved. Previously a humid interval evidenced by prominent palaeo-epikarst capping the Gilwern Oolite along the northern outcrops of the South Wales synclinorium, was not recognized in what were regarded as correlative outcrops in the Chadian Gully Oolite in the southern part of the synclinorium. Conodont dating now shows that the Gilwern Oolite is much older (Courceyan) than the Chadian Gully Oolite, and during the prolonged exposure of the former there was an interval of weathering under a humid climate. This also explains the contrast between the diagenesis seen between the Gilwern and Gully oolites, which are no longer seen as correlatives. 相似文献
5.
《Proceedings of the Geologists' Association. Geologists' Association》2023,134(2):216-245
Ammonites of the family Lytoceratidae from the Middle Jurassic Inferior Oolite Formation, Aalenian to lowermost Bathonian, of Dorset are rarely described, perhaps because the macroconchs are often very large and difficult to collect intact and the microconchs are very small and easily overlooked. Detailed stratigraphical collecting over several years has shown them to be a minor part of the ammonite fauna but more common at certain horizons. Four genera, Lytoceras, Megalytoceras Nannolytoceras and Pleurolytoceras have been shown to have different stratigraphical ranges and abundances in the Aalenian and Bajocian but they have not been found in the Lower Bathonian of Dorset. The taxonomic basis of several of the well-known species is poorly described in the literature and is remedied here. 相似文献
6.
GEOLOGICAL SIGNIFICANT OF SPOROPOLLEN ASSEMBLAGE IN THE XUESHAN FORMATION 相似文献
7.
运用露头层序地层学原理与方法，将中扬子台地早奥陶世含礁地层划分为4个Ⅱ型层序，并阐述了各层序的体系域特征和形成的沉积动力学机制以及海平面变化对沉积、生物迁移、生物礁及环境的控制作用。认为在含礁层序形成过程中，存在着4个海平面变化旋回，第一旋回为两河口期早至中期，第二旋回为两河口期晚期至道保湾期早期，第三旋回为道保湾期早至晚期，第四旋回为大湾期早至中期，其中两河口期存在着3个次一级的旋回，第一旋回发生于分乡组二段(鲡粒段)；第二旋回发生于分乡组三段(互层段)；第三旋回发生于分乡组四段(夹层段)；识别出3个平衡型碳酸盐体系和一个滞后型碳酸盐岩沉积体系。研究结果表明，分乡组与红花园组生物礁均形成于高海平面时期。由于海平面变化过程中存在多个次一级的旋回，致使本区生物礁具有厚度和规模小、数量多和分布广等特点。 相似文献
8.
Robert B. Chandler 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(3):316-323
Rare ammonite species are reported from the Inferior Oolite Formation of Dorset. In the Aalenian the ammonite Shahrudites is described from the Scissum Zone for the first time and Malladaites is recorded from the Murchisonae Zone. Tmetoceras regleyi occurs in the Scissum and Murchisonae zones and Tmetoceras henriquesae is described from the Concavum Zone. In the Lower Bajocian, specimens of Zurcheria are presented from the Discites Zone. A revised zonal scheme is used for the Aalenian Stage and two new biohorizons are introduced. The Leioceras subglabrum biohorizon is erected in the Opalinum Subzone and Leioceras evolutum in the Bifidatum Subzone. 相似文献
9.
A carbonate island barrier from the Great Oolite (Middle Jurassic) of central England 总被引：1，自引：0，他引：1
Over part of south-central England the widespread shallow-water carbonate sedimentation represented by the White Limestone Formation (Great Oolite Group: Middle Jurassic), culminated locally with the formation of a sun-cracked, stromatolitic micrite indicating a supratidal environment. The emergent area can be mapped as a broad strip running at an angle to, and offshore from, the coast-line of the ancient Anglo-Belgian landmass. As a result of the emergence of this carbonate area a polarization of environments occurred. To the north-east a series of clay-rich sediments containing lignite and a brackish and fresh-water fauna were laid down: a lagoonal environment is indicated. To the south-west fully marine shelf carbonates continued to be deposited. We suggest that isolation of the northerly area of reduced salinity from the open sea was due directly to emergence of this carbonate area, which can thus be specifically interpreted as an island barrier or spit. 相似文献
10.
11.
This paper describes 11 microfacies types in late Bathonian–Early Callovian carbonates of the Kuldhar Member of the Jaisalmer Formation (Rajasthan) and the Keera Golden Oolite Member of the Chari Formation (Kachchh Mainland) western India. The different microfacies associations reported in this study reflect an ideal shallowing upward sequence, representing a system of bioclastic bars developed on the lower ramp, evolving into an oolitic bar-to-bank system separating restricted lagoonal—from lower ramp environment. Four main types of cements, i.e. bladed, fibrous, syntaxial overgrowth and blocky cement (characterized in a few cases by ferroan calcite and anhydrite II) occur in these carbonates. The study also reveals that chemical compaction followed the two phases of early mechanical compaction that largely governed porosity of these limestones. However, micritization and neomorphism also contributed significantly in this respect. Diagenetic signatures in these carbonates suggest that marine phreatic and fresh water phreatic environments dominated, but deep burial diagenesis also played its role in shaping these rocks. The early and late diagenetic changes have been controlled by the depositional facies evolving in a basin riddled with rifting in an extensional tectonic regime forcing regional-scale sea level fluctuations. 相似文献
12.
The sedimentary succession of a Late Jurassic (Oxfordian to basal Kimmeridgian) carbonate ramp is described and interpreted.
The study area is located in the central part of the Lower Saxony Basin in NW Germany, which forms part of the Central European
Basin. Eight well-exposed and undeformed sections of the study area (Süntel area, Wesergebirge and eastern part of the Wiehengebirge)
provide detailed information about lithofacies and lateral thickness variations. Biostratigraphically, the age of these sediments
is poorly constrained. Twenty microfacies types are recognized that can be grouped into seven facies associations: (a) strongly
bioturbated marlstones deposited near storm wave base (SWB), (b) foraminifera-rich wackestones, (c) wackestones and floatstones
with biostromes and (d) bioclastic limestones deposited between SWB and fair-weather wave base (FWWB), (e) oolitic and iron-oolitic
limestones and (f) siliciclastic sediments deposited above FWWB, and (g) lagoonal deposits. These facies associations characterize
a storm dominated shallow mixed carbonate-siliciclastic ramp. Based on facies changes, quartz content, and gamma ray logs,
the Korallenoolith Formation can be subdivided into a lower carbonate-dominated and an upper siliciclastic-dominated part,
build up by different scales of small- to large-scale deepening- and shallowing-upward cycles. A preliminary correlation of
measured outcrops of this formation is presented. 相似文献
13.
The carbon isotope measurements, carried out on subsurface carbonate samples from Oxfordian Jaisalmer Formation, western India, yield positive d13C values up to +3.17%. The most positive Oxfordian C-isotope value corresponds to the carbon isotope excursion measured in samples from from other late Jurassic basins of world. The latest Oxfordian C-isotope values of Jaisalmer Basin fluctuate around 2% while the C-isotope values of 1.50% mark the base of Kimmeridgian. The Oxfordian C-isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level. 相似文献
14.
Ricardo M. Palma Diego A. Kietzmann Susana Adamonis Jos Lpez Gmez 《Sedimentary Geology》2009,221(1-4):127-140
The Neuquén back-arc basin is located on the west margin of the South American platform between latitudes 36° and 40° S. The basin is famous for its continuous sedimentary record from the Late Triassic to Cenozoic comprising continental and marine clastic, carbonate, and evaporitic deposits up to 2.600 m in thickness.The stratigraphical and paleontological studies of the outcrops of the La Manga Formation, Argentina, located near the Bardas Blancas region, Mendoza province (35° S and 69° O) allow the reconstruction of the sedimentary environments of an Oxfordian carbonate ramp, where outer ramp, middle ramp, inner ramp (oolitic shoal), inner ramp margin (patch reef) lagoon and paleokarst were differentiated. The reefs consist of back reef facies and in situ framework of coral boundstones that was formed at the top of shallowing-upward succession.Coral reefs were analyzed by defining coral colonies shapes, paleontological content, coral diversity and taphonomy studies. In some studied sections abundant fragments of gryphaeids, encrusting bryozoans, and isolated sponges provided a suitable substrate for coral colonization; however, other sections show an increase in the proportions of ooids, peloidal and coral intraclasts.The core reef facies is composed of white-grey unstratified and low diversity scleractinian coral limestone dominated by robust and thinly branching corals with cerioid–phocoid growths and massive coral colonies with meandroid–thamnasteroid growth forms.The assemblage is characterized by Actinastraea sp., Australoseris sp., Thamnasteria sp. and Garateastrea sp. Internal facies organization and different types of coral colonies allow to recognize the development of varying framework as well as intercolony areas. A superstratal growth fabric characterizes the coral assemblage. On the basis of coral growth fabric (branche and domal types), the reef of La Manga Formation is considered a typical mixstones. The intercolony areas consist of biomicrites and biomicrorudites containing abundant coral fragments, parautochthonous gryphaeids and another bivalves (Ctenostreon sp.), gastropods (Harpagodes sp., Natica sp.), echinoderms test and spines (Plegiocidaris sp.), miliolids, Cayeuxia sp., Acicularia sp., Salpingoporella sp., intraclasts, ooids, peloids and coated grains.The domal growth forms are probably more protected against biological and physical destruction, meanwhile delicate branching growth forms with very open and fragile framework were more affected and fragmented due to wave action and bioerosion.The reef fabric shows different intervals of truncation as consequence of erosion resulting from coral destruction by storm waves or currents. The maximum flooding surface separates oolitic shoal facies below from the aggradational and progradational coralline limestones facies above. Subsequent sea-level fall and karstification (148 Ma) affected reef and oolitic facies. 相似文献
15.
A reexamination of large caenagnathid material from the Upper Cretaceous (Campanian) Dinosaur Park Formation of Alberta, Canada, reveals undescribed material referable to Caenagnathus collinsi. A femur, two astragalocalcanei, two metatarsals, two unguals, and a caudal vertebra provide anatomical information on Caenagnathus collinsi. Estimates of femoral length based on the proportions of other oviraptorids suggest that the non-femoral material represents a taxon intermediate in size between Chirostenotes pergracilis from the Dinosaur Park Formation and Anzu wyliei from the Maastrichtian Hell Creek Formation. The femur is within the range of predictions, and confirms the body size estimates based on the other material. The large size of the material and a number of morphological characters distinguish the material from Chirostenotes pergracilis and suggest that it is referable to Caenagnathus collinsi. The relative diversity of caenagnathids in the Dinosaur Park Formation is likely underestimated. 相似文献
16.
Udo Zimmermann Daniel G. Poir�� Luc��a G��mez Peral 《International Journal of Earth Sciences》2011,100(2-3):489-510
The Cryogenian to Uppermost Ediacaran successions of the Tandilia System (Sierras Bayas Group and Cerro Negro Formation) in central-eastern Argentina is exceptional because of its unmetamorphosed and nearly undeformed character, its sediment provenance trend and the absence of any identified glacial deposit and the deposition of warm water carbonates. We decipher a dramatic change in the basin evolution from small-scale depositional areas during the Neoproterozoic to a larger basin related to an active continental margin throughout the Uppermost Ediacaran. The base of the succession is represented by immature detritus of alkaline composition (Villa Mónica Formation), but towards the top of this formation, the material is sorted and reworked, nonetheless still reflecting in its detritus the local rocks. The clastic deposition is interrupted by diagenetic overprinted dolomites. The unconformable overlying quartz-arenitic Ediacaran Cerro Largo Formation reworked the Cryogenian Villa Mónica Formation and contains mainly felsic granitic and metamorphic basement material of slightly wider variety, while the dominant alkaline geochemical signature in rocks of the Villa Mónica Formation disappears. Based on diagenetic, petrographic and sedimentological data, we can interpret the unconformity representing a longer time of erosion. The Cerro Largo Formation shows a transition to mudstones and the heterolithic facies of the Olavarría Formation. The top of the Sierras Bayas Group is represented by limestones (Loma Negra Formation), which are discordantly overlain by the Uppermost Ediacaran Cerro Negro Formation. The latter displays detrital material derived from a continental arc, mafic and felsic sources. Several arc-related geochemical proxies (Th/Sc?<?0.8; Zr/Sc?<?10; La/Sc?<?2; Ti/Zr?>?20) are recorded in the sediment detritus, as are syn-depositional pyroclastites. The absence of volcanic material in the underlying rocks allows proposing that the Cerro Negro Formation is related to an active continental margin fringing Gondwana (??Terra Australis Orogen??) as a retro-arc or retro-arc foreland basin. 相似文献
17.
西藏措勤盆地下白垩统多巴组沉积环境分析 总被引：9，自引：3，他引：6
西藏措勤前陆盆地下白垩统多巴组是一套分布面积广大,比较特征的碳酸盐、陆源碎屑混合沉积的地层,本文通过对几条较完整的主干剖面的详细沉积相分析,揭示了多巴组的主要沉积环境包括潮坪、低能潮下带、近岸碳酸盐台地缓坡、台缘介壳滩及碳酸盐台地等几种主要类型,建立了多巴组的沉积相模式,并指出多巴组的沉积演化主要受控于盆地构造运动和全球海平面变化,这将有助于该地区的构造沉积演化研究。 相似文献
18.
Contrasting diagenesis of two Carboniferous Oolites from South Wales: a tale of climatic influence 总被引：2，自引：0，他引：2
Two oolites in the Dinantian (Mississippian/Lower Carboniferous) of Glamorgan, SW Britain, were deposited in similar depositional environments but have contrasting diagenetic histories. The Brofiscin and Gully Oolites occur in the upper parts of shallowing-upward sequences, formed through strandplain progradation and sand shoal and barrier growth upon a southward-dipping carbonate ramp. The Brofiscin Oolite is characterized by a first-generation cement of equant calcite spar, preferentially located at grain-contacts and forming non-isopachous fringes around grains, interpreted as meteoric vadose and phreatic in origin. Isopachous fibrous calcite fringes of marine origin are rather rare and occur only at a few horizons. Burial compaction was not important and porosity was occluded by poikilotopic calcite spar. Fitted grain-grain contacts locally occur and could be the result of near-surface vadose dissolution-compaction. Syntaxial overgrowths on echinoderm debris are common. Pre-compaction overgrowths are cloudy (inclusion-rich) and probably of meteoric origin, and post-compaction overgrowths are inclusion-free. By contrast, the Gully Oolite has little first-generation cement. However, marine fibrous calcite is common in oolitic intraclasts, as isopachous fringes of acicular calcite crystals closely associated with peloidal internal sediment; and early equant, drusy calcite spar occurs in the uppermost part of the Gully, beneath a prominent palaeokarst where pedogenic cements also occur. The major feature of Gully diagenesis is burial compaction, resulting in extensive grain-grain dissolution and microstylolitic grain contacts, and post-compaction poikilotopic spar occluded remaining porosity. The Brofiscin Oolite is pervasively dolomitized up-dip but the Gully Oolite for the most part only contains scattered pre-compaction dolomite rhombs and late veins of baroque dolomite, with less pervasive dolomitization. The difference in diagenetic style of the two Dinantian oolites is attributed to prevailing climate. The paucity of early meteoric cements in the Gully is a result of an arid climate, and this is supported by the nature of the capping palaeokarst. The abundant meteoric cements in the Brofiscin reflect a more humid climate, and effective meteoric recharge also resulted in up-dip pervasive mixing-zone dolomitization. The style of early diagenesis in these two oolites exerted a major control on the later burial diagenesis: in the Brofiscin, the early cements inhibited grain-grain dissolution and pressure solution, while these processes operated extensively in the Gully Oolite. Thus, prevailing climate can influence a limestone's diagenetic history from near-surface through into deep burial. 相似文献
19.
秦岭岩群为北秦岭微陆块的主要组成部分,其时代的准确厘定对秦岭造山带构造演化研究具有重要的地质意义。本次工作对五里川—寨根一带秦岭岩群雁岭沟岩组钠长二云片岩和郭庄岩组矽线二云二长片麻岩进行碎屑锆石LA-ICP-MS U-Pb同位素年代学研究。钠长二云片岩具有岩浆成因特征的碎屑锆石核部年龄主要存在545~551 Ma、754~778 Ma、900~1000 Ma、1340~1830 Ma和2300~2500 Ma 5个年龄段,并以900~1000 Ma段碎屑锆石的峰最明显;部分数据点在锆石U-Pb谐和图上拟合成一条上交点年龄为(2478±25)Ma的不一致线。矽线二云二长片麻岩年龄主要集中于1400~1800 Ma,另有4颗锆石年龄为1134~1243 Ma,其中最年轻的1颗碎屑岩浆锆石年龄为(1134±17)Ma。根据分析结果,推断本地区雁岭沟岩组的形成时代应晚于900 Ma,早于438 Ma的五垛山岩体。郭庄岩组的主体形成于中元古代晚期,时代应该晚于1122 Ma,老于962 Ma的新元古代花岗岩类。雁岭沟岩组最主要的物质来源为新元古代花岗岩,其次为新太古代—古元古代陆壳,少部分来源于郭庄岩组;郭庄岩组物质来源主要为的古元古代晚期至中元古代早期的花岗岩陆壳。雁岭沟岩组与郭庄岩组形成时代不同,二者之间存在沉积间断,主要物源区也不相同,雁岭沟岩组中甚至有少量郭庄岩组剥蚀后再沉积的物质。因此,二者是不同的构造岩片,本地区雁岭沟岩组应从秦岭岩群中解体出来。 相似文献
20.
R. M. Gilaev A. V. Stupakova A. N. Stafeev A. A. Suslova E. S. Shelkov 《Moscow University Geology Bulletin》2018,73(4):361-365
A new variant of the structural-facies zonation of the Bazhenov horizon (Tithonian–Lower Berriasian) in the northeastern part of West Siberia was considered using lithofacies and structural analysis. The low content of terrigenous sedimentary material in the high-carbon facies of the Bazhenov Formation is explained by the capturing of the material by the relatively deep Pur–Taz Paleobasin, where the fan of the Yenisei–Khatanga strait was formed. The Pur–Taz Paleobasin was filled by the sediments of the Yanovstanov Formation. In the northeast the basin borders the vast and relatively shallow Ob Paleobasin, where the black shales of the oil-source Bazhenov Formation were accumulated. 相似文献