首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 453 毫秒
1.
The microbiota of the upper Viséan (Asbian–Brigantian) rocks in the Lough Allen Basin in northwest Ireland is analysed. The Middle Mississippian sequence studied extends from the upper part of the Dartry Limestone/Bricklieve Limestone formations of the Tyrone Group to the Carraun Shale Formation of the Leitrim Group. The rocks have been traditionally dated by ammonoid faunas representing the B2a to P2c subzones. The Meenymore Formation (base of the Leitrim Group) also contains conodont faunas of the informal partial‐range Mestognathus bipluti zone. The upper Brigantian Lochriea nodosa Conodont Zone was recognized by previous authors in the middle of the Carraun Shale Formation (Ardvarney Limestone Member), where it coincides with upper Brigantian ammonoids of the Lusitanoceras granosus Subzone (P2a). Foraminifera and algae in the top of the Dartry Limestone Formation are assigned to the upper Cf6γ Foraminifera Subzone (highest Asbian), whereas those in the Meenymore Formation belong to the lower Cf6δ Foraminifera Subzone (lower Brigantian). The Dartry Limestone Formation–Meenymore Formation boundary is thus correlated with the Asbian–Brigantian boundary in northwest Ireland. For the first time, based on new data, a correlation between the ammonoid, miospore, foraminiferan and conodont zonal schemes is demonstrated. The foraminiferans and algae, conodonts and ammonoids are compared with those from other basins in Ireland, northern England, and the German Rhenish Massif. Historically, the Asbian–Brigantian boundary has been correlated with several levels within the P1a Ammonoid Subzone. However, the new integrated biostratigraphical data indicate that the Asbian–Brigantian boundary in northwest Ireland is probably located within the B2a Ammonoid Subzone and the NM Miospore Zone, but the scarcity of ammonoids in the Tyrone Group precludes an accurate placement of that boundary within this subzone. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

2.
The Triassic–Jurassic systemic boundary was recently reported in the middle part of the Antimonio Formation, northwestern Sonora, where five informal sedimentary packages were delineated and characteristic ammonoid faunas were used to establish age control within the succession. The boundary was suggested to lie within the middle part of the 24 m-thick package 4, in relatively unfossiliferous and organic-rich, laminated clay-silt mudstone. Despite the absence of diagnostic Hettangian fossils above the postulated boundary interval, its existence was predicted on characteristic uppermost Triassic Crickmayi Zone Choristoceras ammonoids occurring below in package 3 and upper Hettangian to lower Sinemurian (Badouxia Zone) ammonoids found above in package 5. Recent field investigations yielded new ammonoids of the uppermost Triassic Crickmayi Zone, which are described herein. They are assigned to Choristoceras cf. C. nobile Mojsisovics and Rhabdoceras cf. R. suessi Hauer. These characteristic ammonoids occur within the middle and top of package 4. Their discovery along with other stratigraphic evidence necessitates a revision of the boundary and recognition of a previously unrealized unconformity at the Triassic–Jurassic boundary in Sonora. A revised sea-level curve is necessary to account for these new stratigraphic and paleontological findings.  相似文献   

3.
纵瑞文  龚一鸣 《中国地质》2019,46(6):1259-1269
西准噶尔地区广泛分布的和布克河组已被证明是洪古勒楞组的晚出异名,本文在西准噶尔克拉赛勒克山原划为下石炭统"和布克河组"的碎屑岩地层中发现了丰富的动、植物化石,包括:三叶虫Phacops sp.,菊石Manticoceras sp.,腕足类Tylothyris sp.,Aulacella sp.,"Mucrospirifer"sp.,Cyrtospirifer sp.,植物Leptophloeum rhombicum,Syringodendron sp.,Knorria sp.,其时代显示为晚泥盆世。根据岩性组合特征将其厘定为上泥盆统铁列克提组,而非"和布克河组"的替代名称洪古勒楞组。通过区域地质调查工作,证明了西准噶尔玛依力山地层小区内没有洪古勒楞组的分布,其晚泥盆世地层仅由铁列克提组组成,洪古勒楞组只分布在沙尔布尔提山地层小区,两个地层小区的界线为孟布拉克北侧至谢米斯台山南坡的深大断裂。晚泥盆世两个地层小区沉积分异明显,直到早石炭世早期才进入统一的盆地演化阶段,地层小区的分区性也随之消失。  相似文献   

4.
Goniatites     
Most people are familiar with ammonites (see Fossils Explained 62, this issue), with their beautiful, logarithmically spiralled shells, but not everyone has heard of goniatites. They too were fascinating dwellers of past oceans. Goniatites are extinct cephalopods ranging from the middle of the Devonian to the end of the Permian. Although, in the strictest definition, goniatites are those ammonoids that belong to the order Goniatitida, the term goniatite is commonly used as a synonym for all Palaeozoic ammonoids. In the course of this article, the looser definition will apply.  相似文献   

5.
The Late Cretaceous (Cenomanian to Coniacian) marine sediments of central India prevalently known as ‘Bagh Beds,’ have been deposited in the E-W extending Narmada Basin. The stratigraphy of these Cenomanian — Coniacian sediments has been reviewed and summarized. The Bagh Beds have been found to consist of three formations: Nimar Sandstone, Nodular Limestone and Corallian Limestone in ascending order. Main emphasis has been given to Nodular Limestone Formation (Turonian), which is the most fossiliferous horizon of the Bagh Beds. Nodular Limestone Formation has more or less alternating bands of varying thickness of nodular limestone and marl. It yielded numerous ammonoid specimens, which have been found to belong to a morphologically highly variable ammoniod taxon Placenticeras mintoi Vredenburg.  相似文献   

6.
The advent of chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) has revolutionised U–Pb dating of zircon, and the enhanced precision of eruption ages determined on volcanic layers within basin successions permits an improved calibration of biostratigraphic schemes to the numerical time-scale. The Guadalupian and Lopingian (Permian) successions in the Sydney, Gunnedah, Bowen and Canning basins are mostly non-marine and include numerous airfall tuff units, many of which contain zircon. The eastern Australian palynostratigraphic scheme provides the basis for much of the local correlation, but the present calibration of this scheme against the numerical time-scale depends on a correlation to Western Australia, using rare ammonoids and conodonts in that succession to link to the standard global marine biostratigraphic scheme. High-precision U–Pb zircon dating of tuff layers via CA-IDTIMS allows this tenuous correlation to be circumvented—the resulting direct calibration of the palynostratigraphy to the numerical time-scale highlights significant inaccuracies in the previous indirect correlation. The new data show: the top of the Praecolpatites sinuosus Zone (APP3.2) lies in the early Roadian, not the middle Kungurian; the top of the Microbaculispora villosa Zone (APP3.3) lies in the middle Roadian, not the early Roadian; the top of the Dulhuntyispora granulata Zone (APP4.1) lies in the Wordian, not in the latest Roadian; the top of the Didecitriletes ericianus Zone (APP4.2) lies in the first half of the Wuchiapingian, not the latest Wordian; the Dulhuntyispora dulhuntyi Zone (APP4.3) is exceptionally short and lies within the Wuchiapingian, not the early Capitanian; and the top of the Dulhuntyispora parvithola Zone (APP5) lies at or near the Permo-Triassic boundary, not in the latest Wuchiapingian.  相似文献   

7.
The upper Bathonian Ammonites Cadoceras perrarum Voron. and Kepplerites ex gr. rosenkrantzi Spath are reported for the first time from the western coast of Anabar Bay, loosely collected. Both ammonoids represent index species of two biostratigraphic units: the Cadoceras barnstoni Beds and Cadoceras variabile Zone. The occurrence of genus Kepplerites (Kosmoceratidae) in North Siberia is evidence in favor of the migration of that family into the seas of the Arctic region.  相似文献   

8.
Northern pipefish,Syngnathus fuscus, and dusky pipefish,Syngnathus floridae, are among the most abundant ichthyofauna components of the Chesapeake Bay, USA, eelgrass beds,Zostera marina, but population structure and many life history traits remain uncharacterized. We conducted monthly collections from May through September 2003–2005 in Chincoteague Bay, Virginia, to investigate seasonal migration and spawning, sex ratios, size at maturity, sexual dimorphism in length, and growth rates. BothS. fuscus andS. floridae spawned from May through September. Water temperature was significantly correlated withS. fuscus catches, whereasS. floridae abundance peaked after maximum water temperatures. Sex ratio data indicatedS. floridae populations are balanced, whileS. fuscus populations are strongly female-biased. Both species can quickly reach reproductive maturity, potentially within one season, becauseS. fuscus andS. floridae population growth rates average 1.0 mm d−1 and minimum standard length at maturity measures 125 and 103 mm, respectively, for females and 99 and 91 mm, respectively, for males. ForS. fuscus, females were significantly longer than conspecific males during time periods when juveniles were not rapidly maturing. Size sexual dimorphism in this species coincides with reports of extensive paternal care and supports the hypothesis that the strength of sexual selection differs in these species.  相似文献   

9.
Section D at Meishan, Changxing County in the Zhejiang Province, China, has been extensively studied in various aspects of the stratigraphy during the past 20 years. It was ratified by the International Union of Geological Sciences (IUGS) as the Global Standard Stratotype Section and Point (GSSP) for the Permian–Triassic boundary in 2000, and is also a potential stratotype for the Wuchiapingian–Changhsingian boundary. However, the contact relationship between the Longtan (Wuchiapingian) and Changxing (Chainghsingian) formations has been a controversial subject for years. Recent studies on Section C, about 300 m west of Section D, at Meishan confirm a complete depositional succession around the boundary and suggest that the proposed boundary level, the FAD of Clarkina wangi within the lineage from C. longicuspidata to C. wangi, is consistent with the first appearance of the index Changhsingian fusulinid Palaeofusulina sinensis and tapashanitid ammonoids.  相似文献   

10.
Species of the ammonite genus Metoicoceras are not generally strongly differentiated with respect to coiling and ornament. The present study addresses the problem of how well purely visual (subjective) identification succeeds in identifying taxonomically and hence evolutionarily relevant differences between forms. Multivariate statistical analysis, based on coiling, standard dimensions of the conch and ornamental properties, indicates that quantitative procedures reproduce traditional methods to a conspicuous degree, with the added advantage of objective repeatability. Additionally, uncertain phylogenetic relationships could be resolved by appropriate methods of multivariate statistical analysis and possible new information on dimorphism in the conch was obtained.  相似文献   

11.
《International Geology Review》2012,54(12):2235-2245
Bogoslovskiy describes the first known occurrence of Early Devonian ammonoids in the Soviet Union. These indicate that the sediments in which they occur are Coblentzian in age and not Givetian as previously thought. The author reviews the higher taxonomic categories used for early ammonoids, and places his materials in the genera: Erbenoceras Bogoslovskiy, Mimosphinctes Eichenberg, Teicherticeras (Teicherticeras) Erben, and Teicherticeras (Convoluticeras) Erben. — John Pojeta, Jr.  相似文献   

12.
The stratigraphic distribution of ammonoids was analyzed in the Daxatina canadensis Subzone of the Trachyceras Zone distinguished in the Dolomites of Italy. It was established that ammonoids of the Daxatina and Trachyceras genera are confined to the lower and upper parts of the canadensis Subzone in the Stuores-Wiesen section, which was suggested as a global stratigraphic section of the lower boundary of the Carnian Stage. Owing to discreteness of the ammonoid complex and absence of the Trachyceras genus, the lower part of the canadensis Subzone was excluded from the Trachyceras generic zone and is considered as the independent Daxatina canadensis Zone, which overlies the Frankites regoledanus Zone. On the basis of the principle of priority and similar ammonoids of the canadensis and regoledanus zones, the lower boundary of the Carnian Stage was accepted in the basement of the Alpine Trachyceras aon Zone and coincides with appearance of the Trachyceras genus. The main problems of the Boreal-Tethyan correlation of the Lower Carnian and adjacent stratigraphic levels are reviewed. The composition and distribution of the Lower Carnian ammonoids of northeastern Asia are specified taking into account the results of the revision of the Early Carnian trachyceratids of this region. Being the traditional biomarkers of the basal beds of the Carnian Stage in the Tethys, the ammonoids of the Trachyceras genus, which were unknown before in the Boreal Realm, were identified for the first time in the Lower Carnian of northeastern Asia. The Lower Carnian rocks of northeastern Asia, British Columbia, and the Alps were zonally correlated and the Lower Carnian boundaries were substantiated in the Boreal Realm. The Boreotrachyceras omkutchanicum Zone correlates with the Alpine Trachyceras aon Zone by the presence of the Trachyceras genus and stratigraphic position over the Stolleyites tenuis Zone and its analogs in British Columbia. The ammonoid complex of the Neosirennites armiger Zone includes Sirenites s.s., in particular, Sirenites ovinus Tozer species, known in the upper zone of the Lower Carnian of British Columbia (Sirenites nanseni), which allows comparison of the armiger and nanseni zones and, through it, with the upper part of the Alpine Austrotrachyceras austriacum Zone.  相似文献   

13.
Plug-shaped ichnofossils Conichnus conicus, Conostichus broadheadi and C. stouti are found in the intercalated micritic sandstone and sandy allochemic limestone shale sequence of Bagh Group, Narmada district, Gujarat. These ichnospecies occur at two stratigraphic levels and shows distinct morphological features interpreted as resting/dwelling structures of sea anemone. The occurrence of these ichnospecies along with oyster fossils genera like Bosostrea and Indostrea indicate shallow marine environment.  相似文献   

14.
The Bathonian ammonite assemblages have been previously poorly recorded in Kutch. The present study has unearthed a rich array of ammonite taxa ranging from the Middle to Upper Bathonian. While Oxycerites Rollier (1909) is a new record from Kutch, the oldest occurrence of Choffatia Siemiradzki (1898) has been found from the Middle Bathonian horizon. Oxycerites cf. orbis (Giebel) is a zonal index of the Late Bathonian in other areas and thus facilitates interprovincial correlation. Besides, palaeobiogeographic and stratigraphic distribution of many species have been modified based on new information. For example, macrocephalitin species, i.e., Kamptokephalites cf. etheridgei Spath (1928), Macrocephalites bifurcatus transient intermedius Spath (1928), M. cf. mantataranus Boehm (1912) were previously known from West Pacific, Indonesia have been now found in Kutch. Gracilisphinctes Buckman (1920) has been previously known to occur during the Middle Bathonian time, the present work extends its stratigraphic distribution up to the definite Upper Bathonian horizon. Procerites hians (Waagen) an endemic species in Kutch previously known from the Upper Bathonian beds, its stratigraphic range has been extended down to the Middle Bathonian.Detail taxonomy of the newly obtained taxa has been done and in many cases sexual dimorphism has been recognized.  相似文献   

15.
We report the first record of Bathonian–Callovian calcareous nannofossils from a marine sedimentary sequence of the eastern Karakoram block, in northern India. The calcareous mudstones and packstones, occasionally bearing red chert nodules, yielded calcareous nanofossils and Middle Jurassic Choffatia furcula ammonoids. Middle to Upper Jurassic nannofossil assemblage is dominated by representatives of the genus Watznaueria. The occurrence of Ansulasphaera helvetica whose range is Upper Bathonian–Upper Callovian, indicates a correlation with nannofossil zones NJ12–13. The occurrence of Cyclagelosphaera wiedmannii further infer an Upper Bathonian–Callovian age. These specimens show affinities with those found in a similar sedimentary formation exposed in north Karakoram. This suggests the existence of a narrow and elongated sedimentary basin, oriented in a NW–SE direction, at a latitude of c. 25°–30°N. At that time, the Karakoram block was situated near the already welded Qiangtang block of Asia. The northern and eastern Karakoram blocks were connected during Middle Jurassic. The activity and dextral offset of the Karakoram fault separated the Jurassic sedimentary formations of the northern and eastern Karakoram blocks by c. 150 km.  相似文献   

16.
An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Böse, Agathiceras? sp., and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand. The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clastic-dominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoid fauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Böse, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting.  相似文献   

17.
Reproductive pentoxylalean material from the Albian Triton Point Formation, Fossil Bluff Group of Alexander Island, Antarctica is the youngest record of this group globally. Leaves are referred to Taeniopteris daintreei McCoy, ovulate reproductive organs to Carnoconites cranwelli Harris, and stem material to Pentoxylon sp. Occurring in leaf litter layers on palaeosol surfaces the sedimentology suggests that pentoxylalean plants grew upon areas of the floodplain distal to the river channel, where they covered the forest floor in a similar habit to modern brambles. The forest floor was shared with Equisetales and liverworts, an abundance of ferns [Cladophlebis Brongniart, Gleichenites Goeppert, Phyllopteroides Medwell, Sphenopteris (Brongniart) Sternberg], as well as angiosperms. Bennettitales, Ginkgoites Seward and Nilssonia Brongniart were rare within these communities, as were coniferous trees.  相似文献   

18.
This paper considers Swiss experiences of in situ agrobiodiversity conservation. The Swiss recognise the multifunctionality of agriculture, particularly within the marginal, mountainous areas of the country and are spending public and private funds to maintain crop landraces, agroecosystems, landscapes, agricultural practices, and rural communities. State programs in marginal agricultural regions tie economic assistance to biodiversity conservation practices, through the use of direct payment systems. With the removal of many import restrictions and state-led marketing, alternative innovative programs linked to local values of diversity provide opportunities for conservation. In situ agrobiodiversity conservation ideas being pursued include awareness-raising schemes, scientific initiatives, the establishment of diversity gardens and community-based programs. Any extension of the in situ conservation programs could have substantial implications for regional development. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

19.
We report here the first Dichotomoceras of the Indian subcontinent at Kantkote (Wagad) in the proximal most exposed part of the Kachchh Basin. This is further addition to the significant enlargement of the Oxfordian ammonoid record made earlier (Krishna et al. 1994, 1995, 1998, 2000). Near continuous presence of ammonoids has been recorded in ca 55 m thick succession, almost immediately above the Schilli Subzone, that was considered ammonoid devoid earlier. The ammonoid density, diversity and frequency in this just discovered ca 55 m thick column are much scarcer in comparison to the underlying 10 m thick ammonoid abundant Schilli Subzone. Examples of Dichotomoceras are determined almost throughout the said interval which in our preliminary taxonomic evaluation appear identical or close to D. rotoides (Ronch.), D. stenocycloides (Siem.), D. bifurcatus (Quenst.) and D. crassus Enay. It thus suggests the characterization of the Rotoides Subzone of the Transversarium Zone and the superjacent Bifurcatus Zone of the column at least up to the early Late Oxfordian.  相似文献   

20.
Power-law relationship between tidal prism (P) and the cross-sectional area of the entrance channel (A) is applicable to assess the equilibrium conditions of a tidal inlet system. The classic method of determining P-A relationships proposed by O’Brien depends on datasets from multi-tidal inlet systems, which has shown some limitations and is unable to assess equilibrium of a single tidal inlet. This paper focuses on establishing a new P-A relationship for a single tidal inlet. Our experimental result shows that in order to maintain the status, power n should be > 1, implying that the inlet width will narrow and current speed within the entrance will increase as tidal prism becomes smaller. A possible explanation for power n <,1.0, as many researchers argued before, is that the influence of tidal prism has been exaggerated. Meanwhile, the magnitude of coefficient C is dependent on many factors such as longshore drift, freshwater discharge, etc, resulting in a wide range of variation of C. It should be pointed out that P-A relationship given by the sediment dynamical approach is still a representative of average status for tidal inlets in equilibrium. As tide, wave, freshwater discharge and tidal inlet morphology change with time, actual P-A relationships will fluctuate also. The problems that need to be solved when applying sediment dynamic methods to P-A relationships include the cross-sectional distribution pattern of tidal current speeds in the entrance channel, the relationship between the tidal current and the tidal water level at the entrance, and the calculation of the ratio of width to depth. This paper will establish a sediment dynamical approach of P-A relationship for a single tidal inlet. The results are tested for P-A relationships of Yuehu Inlet, a small inlet-lagoon system located in Shandong Peninsula, China. __________ Translated from Oceanologia Et Limnologia Sinica, 2005, 36(3): 269–276 [译自: 海洋与湖沼]  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号