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1.
《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):696-700
Well-preserved specimens, such as complete individuals, crowns and cups, are the common focus for crinoid systematic research. Yet the majority of specimens are disarticulated ossicles which are essentially ignored. The incompleteness of the fossil record is even more so when we ignore potential sources of data. A new species of crinoid comes from a monospecific assemblage from the Pennsylvanian (Upper Carboniferous) of western Ireland. All specimens are from a float block of the Clare Shale Formation (Bashkirian stage) at Fisherstreet Bay, Doolin, County Clare, western Ireland. Heloambocolumnus (col.) harperi gen. et sp. nov. has a pentagonocyclic, heteromorphic column; the small, central lumen is in a shallow, circular claustrum; the articulation is radial symplectial; the crenulae are slightly swollen and peg-like close to the circumference; nodals have rounded, unsculptured epifacets; nodal articular facets are sunken and in which narrow internodals are situated; and circlets of tubercles on epifacet surround priminternodals. These columnals are associated with robust, uniserial brachial ossicles. This crinoid is most likely a cladid. 相似文献
2.
Robbert Folmer Stephen K. Donovan 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):102-109
Salthill Quarry, Clitheroe, Lancashire (Mississippian, Visean) is a Site of Special Scientific Interest (SSSI), in part based on its diverse fauna of invertebrates, particularly echinoderms. A small collection of crinoid pluricolumnals are described herein, collected from muddy horizons in the Hodder Mudstone Formation to typify the diversity and frequency of their encrusting and boring fauna. These specimens are infested by a range of episkeletozoans, namely a single occurrence of Sutherlandia parasitica (Phillips), four occurrences of Cladochonus sp. and eight of Oichnus paraboloides Bromley. Two variants of the pit (boring or embedment or both) O. paraboloides are recognised: those in which a living crinoid showed a growth reaction to pit formation; and those that did not and which were presumably dead at the time of infestation. The epizoozoan tabulate coral Cladochonus sp. is also common, including specimens intergrown between and within the columnals. Sutherlandia parasitica is relatively uncommon; the only specimen likely infested a dead pluricolumnal on the sea floor. A comparative collection of pluricolumnals infested by Cladochonus beecheri Grabau from the Mississippian Borden Group of the Midwest, USA, showed superior preservation to the Clitheroe Cladochonus sp. Cladochonus beecheri in the Borden Group infested platycrinitid crinoid stems, an association not noted from Salthill Quarry. Similar suites of borings-episkeletozoans, from two other sites – the Visean of Feltrim, Co. Dublin, Ireland, and the Permian of Timor – suggest that these were persistent associations for much of the Late Palaeozoic. 相似文献
3.
S.J. Gallagher C.V. MacDermot I.D. Somerville M. Pracht A.G. Sleeman 《Geological Journal》2006,41(1):61-91
The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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5.
The most complete Hungarian Valanginian perisphinctid ammonite fauna of the Mecsek Mountains (South Hungary) consists of 14 species is reported. Thurmanniceras sp. aff. otopeta, Fuhriella michaelis, F. cf. hoheneggeri, Sarasinella cf. ambigua, Neocomites (Neocomites) subtenuis, Neocomites (Eristavites) platycostatus are reported for the first time from Hungary. The fauna comprises 23 ammonite species and is reported from Valanginian tuffaceous marl, alternating marl–limestone beds and loose limestone blocks. Two studied sections represent the Lower Valanginian Thurmanniceras pertransiens and partly the Busnardoites campylotoxus Zones while ammonites from loose blocks indicate the latter and possibly the Upper Valanginian Saynoceras verrucosum Zone. Variations in the faunal composition of the marl beds and the limestone blocks respectively, refer to the contrast between the ammonite ecological demands. Phylloceratid and lytoceratid ammonites prevail the marl beds, while olcostephanid and neocomitid ammonites prevail the shallower platform-like limestones. Sediment accumulation rate in that palaeo volcano related environment was high and bottom currents frequently washed together ammonite shells or filled their body chambers with smaller ammonite shell fragments. Due to the fast sedimentation the sections represent only partially the recognized ammonite zones therefore long-term or even infra-regional correlation was not possible. Palaeobiogeographically, the ammonite fauna has Mediterranean character and it shows close relationships to the Valanginian faunas of the Bakony Mts. (Hungary), Western Carpathians (Slovakia), Northern Calcareous Alps (Austria), and SE Spain. The presence of Fuhriella species is remarkable and enlarges our knowledge on the distribution of this enigmatic ammonite taxon adding new data to its Valanginian stratigraphic position and geographic distribution. 相似文献
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7.
E. V. Bugdaeva V. S. Markevich E. B. Volynets 《Stratigraphy and Geological Correlation》2014,22(3):256-268
The plant remains and palynological assemblages are studied in detail in the section of the coal-bearing upper part of the Aptian Starosuchan Formation near the village of Molchanovka (Partizansk Basin, South Primorye region). On the basis of the light and electron microscopic study of the disperse cuticles, it was established that the coals are mostly composed of remains of taxodialean Elatides asiatica (Yok.) Krassil., subordinate Miroviaceae, rare ginkgoalean Pseudotorellia sp., and bennettite Nilssoniopteris rithidorachis (Krysht.) Krassil. The spores Gleicheniidites and pollen Taxodiaceaepollenites are dominant in the palynospectrum of the coal interlayer. It was found that dominant taxodialeans and gleicheniaceous ferns with less abundant Miroviaceae, ginkgoaleans, and rare bennettites occurred in the Aptian swamp communities of the Partizansk basin. Shoots and leaves of Elatides asiatica, fronds of Birisia onychioides (Vassil. et K.-M.) Samyl., are dominant in the burials of plants from the clastic rocks. The fragments of leaves of Nilssoniopteris, scale-leaved conifers, and Ginkgo ex gr. adiantoides are rare. The disperse cuticle of these layers mostly includes Pseudotorellia sp.; however, its remains in burials were not found. The spores Laevigatosporites are dominant in the palynospectra from the clastic interlayers. Ginkgocycadophytus and taxa close to Pinaceae are plentiful among the pollen of gymnosperms. 相似文献
8.
Christopher R. C. Paul Stephen K. Donovan Lucy A. Muir Joseph P. Botting Jih‐Pai Lin Yuandong Zhang 《Geological Journal》2016,51(1):143-156
Pelmatozoans diversified primarily during the Middle and Late Ordovician Period, with Early Ordovician records being much more limited, resulting in many gaps in our knowledge of the early stages of their diversification. Dissociated pelmatozoan ossicles have been found abundantly in one section in the Tonggao Formation (Tetragraptus approximatus Biozone, Floian, Early Ordovician). Most of the ossicles are thecal plates and stem ossicles from hemicosmitoid and glyptocystitoid cystoids. Thecal plates of ‘Cheirocrinus’ sp., Polycosmites sp., and other plates of uncertain affinity are described. A different ossicle type, Pentagonopentagonalis (col.), may represent crinoid remains; this would be one of the earliest occurrences of the class. The thecal ossicles and columnals are all considered, as both sets of data are desirable to determine the most complete estimate of generic diversity. The echinoderm ossicles may have been transported in from shallower water palaeoenvironments and clusters of ossicles may represent coprolites or regurgitates. Estimates of Early Ordovician palaeogeography that place this site at 30°S or near the palaeoequator are supported by the physiological requirements of the primitive echinoderms described herein. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
J.J. Bhatt 《Sedimentary Geology》1973,10(3):225-231
The highly dolomitized Main Limestones of approximately Mississippian age, which crop out in South Wales, are classified according to their ratio values. The results based upon the ratio determination of these rocks permitted their classification into six major categories, namely: (1) limestone; (2) slightly dolomitized limestone; (3) dolomitic limestone; (4) calcitic dolostone; (5) dolostone proper; and (6) magnesian dolostone.It is concluded that dolostone proper and calcitic dolostone tend to dominate in the Main Limestone rocks of South Wales. 相似文献
10.
Jian-Wei Shen Hai-Jun Yang Hairuo Qing Li-Juan Zhang Hong-Qiang Yang 《International Journal of Earth Sciences》2012,101(1):109-127
Carbonates of Mississippian age (Viséan) in the Midale Beds, Charles Formation of southeastern Saskatchewan, Canada, produce
significant amounts of hydrocarbons. The Midale Beds represent deposition in a shallow-water, periodically restricted, epeiric
setting. The sedimentation is characterized by a variety of shallow-water carbonate lithologies ranging from wackestone, packstone,
grainstone, to microbial boundstone. Algae, calcimicrobes, and related microbial fabrics are common features in these limestones.
Cores and thin sections through the Midale Beds in the Glen Ewen and Midale pools of southeastern Saskatchewan were examined
in order to study the contribution of calcimicrobes and microbial fabrics to the sedimentation of Mississippian carbonate
rocks in southeastern Saskatchewan. Calcimicrobes and microbial fabrics are the important components in the grainstones and
microbial boundstone. The calcimicrobes are commonly found as porostromate forms, including Garwoodia sp. and Ortonella sp., and other forms such as Archaeolithoporella-like, Girvanella-like, Wetheredella-like, and problematic microbes also occur but are not common. Microbial fabrics are characterized by microstromatolites,
microbial laminations, thrombolite, clotted peloids, and fenestrate forms. Calcimicrobes stabilized grains and modified and
created sediments, and the related syndepositional microbial fabrics affected the development of porosity/permeability of
Midale carbonates. Calcimicrobes and microbial fabrics in Midale Beds highlighted a significant account of microbial facies
associated with the Mississippian carbonates worldwide. 相似文献
11.
The Jahrum Formation (Upper Paleocene to Middle Eocene) is composed of carbonate and dolomitic carbonate rocks in the Zagros Basin. The Zagros is located at the boundary between the Arabian and Eurasian lithosphere plates and represent the orogenic response to a collision between Eurasia and advancing Arabia during the Cenozoic. The study area is located in the northern part of Kuh-E-Tudej, ~175 km southeast of Shiraz in the Folded Zagros Zone. The Jahrum Formation at Kuh-E-Tudej, with a thickness of 190 m, consists of medium to massive bedded limestone. The following foraminiferal index species are identified in the studied section: Fallotella alavensis, Kathina sp., Miscellanea sp., Lockhartia sp.,Orbitolites shirazeinsis, Nummulites sp., Opertorbitolites sp., Dictyoconus cf. egyptiensis, Orbitolites cf. complanatus, Dictyoconus sp., Coskinolina sp., Somalina stefaninii, Discocyclina sp., Praerhapydionina sp., Coskinolina cf. liburnica, Nummulites cf. globulus, Nummulites cf. aturicus, and Alveolina sp. The age of the studied sediments ranges from Upper Paleocene to Middle Eocene. The microbiostratigraphic studies revealed four biozones based on the foraminifers identified in the studied section. 相似文献
12.
Yu. D. Zakharov S. P. Pletnev M. E. Mel’nikov O. P. Smyshlyaeva V. D. Khudik G. A. Evseev T. A. Punina P. P. Safronov A. M. Popov 《Russian Journal of Pacific Geology》2007,1(1):29-41
The occurrence of belemnites in Mesozoic sediments of the Pacific guyots is established for the first time (rostra Dimitobelidae gen. et sp. indet. from the late Campanian-Maastrichtian detrital limestone of the DVGI Guyot, Belemnitella? sp. from oolitic limestone of the Gelendzhik Guyot, which are presumably of the Santonian-Maastrichtian age, and Belemnitidae? gen. et sp. indet. from the Maastrichtian oolitic limestone of the Butakov Guyot, the Magellan Rise). In recent years, fossil cephalopods important in stratigraphic and paleobiogeographic aspects have been found at five guyots of that rise. New data on fossil invertebrates from the study region suggest breaks in the sedimentation here at the terminal Maastrichtian, Paleogene, and initial Neogene time. Possible limits of vertical migration in the tropical Pacific are estimated for the Late Cretaceous belemnites based on preliminary results of the oxygen isotope analysis. 相似文献
13.
Late Barremian ammonite fauna from the epipelagic marlstone and marly limestone interbeds of Boljetin Hill (Boljetinsko Brdo) of Danubic Unit (eastern Serbia) is described. The ammonite fauna includes representatives of three suborders (Phylloceratina, Lytoceratina and Ancyloceratina), specifically Hypophylloceras danubiense n. sp., Lepeniceras lepense Rabrenović, Holcophylloceras avrami n. sp., Phyllopachyceras baborense (Coquand), Phyllopachyceras petkovici n. sp., Phyllopachyceras eichwaldi eichwaldi (Karakash), Phyllopachyceras ectocostatum Drushchits, Protetragonites crebrisulcatus (Uhlig), Macroscaphites perforatus Avram, Acantholytoceras cf. subcirculare (Avram), Dissimilites cf. trinodosus (d'Orbigny) and Argvethites? sp. The taxonomic composition and percent abundance of the identified ammonites indicate that their taxa are predominantly confined to the Tethyan realm. Ammonites with smooth and slightly sculptured shells predominate among the studied fauna. The ammonite-bearing succession from Boljetin represents the lower part of the Upper Barremian, ranging in ammonite zonation from the Toxancyloceras vandenheckei Zone to the lower part of the Imerites giraudi Zone. The associated organic-walled dinoflagellate cysts confirm the Late Barremian age of the ammonite-bearing levels. 相似文献
14.
Permo-Carboniferous Radiolarians from the Wupata＇erkan Group, Western South Tianshan, Xinjiang, China 总被引：1，自引：0，他引：1
The Wupata‘erkan Group, also called Wupata‘erkan Formation, distributed in the South Tianshan, Xinjiang,China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively.However, radiolarian fossils obtained from 24 chert specimens of the Wupata‘erkan Group, mainly include Albaillella sp.cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp.indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata‘erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite mrlange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan. 相似文献
15.
Krystian Konieczyński Andrzej Pisera Maria Aleksandra Bitner Andras Galácz 《Swiss Journal of Geoscience》2013,106(1):109-118
The Bathonian crinoid fauna that occurs in red nodular limestone and argillaceous limestones from the Hidas Valley, Mecsek Mts (southern Hungary) consists of three isocrinid and six cyrtocrinid species. Isocrinids are represented by Balanocrinus inornatus (d’Orbigny), B. berchteni Hess and Pugin and Balanocrinus sp. Cyrtocrinids are represented by Phyllocrinus stellaris Zar?czny, P. birkenmajeri G?uchowski, P. malbosianus d’Orbigny, Apsidocrinus sp., Lonchocrinus sp., and the new species Psalidocrinus hidasinus sp. nov. This last species is the earliest occurrence of the genus Psalidocrinus previously known from the Early Tithonian to Valanginian. This is the first crinoid fauna described from the Middle Jurassic (Bathonian) of Hungary. The co-occurrence of isocrinids and cyrtocrinids indicates an environment subject to weak currents. The stratigraphical and geographical distribution of the identified cyrtocrinid genera and species suggests a Tethyan origin and subsequent migration to the northern Tethyan shelf. 相似文献
16.
B. C. Richards S. V. Nikolaeva E. I. Kulagina A. S. Alekseev E. N. Gorozhanina V. M. Gorozhanin V. A. Konovalova N. V. Goreva M. M. Joachimski Y. A. Gatovsky 《Stratigraphy and Geological Correlation》2017,25(7):697-758
The Verkhnyaya Kardailovka section is one of the best candidates for the GSSP (Global Stratotype Section and Point) at the base of the Stage (Mississippian). For boundary definition, the first appearance of the conodont Lochriea ziegleri Nemirovskaya, Perret et Meischner, 1994 in the lineage Lochriea nodosa (Bischoff, 1957)?L. ziegleri is used. L. ziegleri appears in the Venevian Substage somewhat below the base of the Serpukhovian in the Moscow Basin. The position of the FAD of L. ziegleri within the Hypergoniatites?Ferganoceras Genozone is confirmed and lies between 19.53 and 19.63 m above the section’s base. Before 2010, deep-water stylonodular limestone containing the boundary in unnamed formation C at Kardailovka was well exposed but only 3 m of Viséan strata cropped out immediately below. Recent trenching exposed another 10 m of underlying Viséan carbonates in formation C and older Viséan siliciclastics and volcanics in unnamed formation B. The contact between formation B and underlying crinoidal limestones in unnamed formation A representing the middle Viséan Zhukovian (Tulian) regional Substage was excavated. The boundary succession, situated in the Magnitogorsk tectonic zone above the Devonian Magnitogorsk arc and Mississippian magmatic and sedimentary rift succession, was deposited west of the Kazakhstanian continent during closure of the Ural Ocean. In the lower part of the section, Viséan tuffaceous siliciclastics and volcanics of formation B record rapid deepening after deposition of neritic middle Viséan crinoid lime grainstone of formation A and subsequent subaerial exposure. The overlying condensed upper Viséan to Serpukhovian succession in formation C comprises deep-water limestone deposited in a sediment-starved basin recording minor turbidite influx and carbonate-mound development. The δ13Ccarb plot shows a positive shift of 1‰ V-PDB (from +2 to +3‰) between 17.0 and 17.75 m (3.05 and 1.97 m below FAD L. ziegleri). The δ18Oapatite graph displays a prominent upward shift from 19.9 to 21.1‰ V-SMOW (at 19.15 to 19.51 m) in the nodosa Zone below FAD of Lochriea ziegleri. 相似文献
17.
Stephen K. Donovan Mart J.M. Deckers John W.M. Jagt A.J. de Winter 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):66-69
In the Netherlands, Late Palaeozoic pelmatozoans – that is, stalked echinoderms – are known from building stones and cobbles in rivers, but there are no in-situ carbonate rocks from which they might be collected. Unsurprisingly, most recognisable specimens are columnals and pluricolumnals. Two small thecae, collected in the mid-1970s from silexite cobbles in the bedload of the River Maas in the Venlo-Tegelen area (province of Limburg, south-east Netherlands) are exceptional finds. One specimen, the diplobathrid camerate crinoid Rhodocrinites sp., has an unsculptured theca and some minor differences of form, yet otherwise satisfies the diagnosis of this genus. The other, the pentremitid blastoid Doryblastus? sp. is rather poorly preserved, yet is the first blastoid to be recorded from the Netherlands. Either or both of these specimens may be juveniles, particularly the blastoid. They are unlikely to be coeval, coming from separate cobbles and being of slightly different preservation. Their provenance from silexite cobbles suggest they originated from Lower Carboniferous (Tournaisian-Visean = Mississippian) carbonates in the southern Ardennes (south-central Belgium). 相似文献
18.
Stephen K. Donovan William I. Ausich Mark A. Wilson Mark E. Peter 《Proceedings of the Geologists' Association. Geologists' Association》2014
Reworked fossils may be exotic, but more typically are locally derived. Echinoderms have only rarely been identified from beach clasts; most commonly, these are Upper Cretaceous echinoids from the Chalk. A pebble collected from a beach in Estonia has yielded a moderately well preserved specimen of the crinoid stem, Baltocrinus (col.) antiquus (Eichwald). This species is typical of the Baltic region, only being known from the Middle Ordovician (Darriwilian) of Estonia, but is exotic because the local outcrop is Upper Ordovician to Silurian. 相似文献
19.
南天山西端的乌帕塔尔坎群为一套灰色、深灰色细碎屑岩,夹火山岩、硅岩和碳酸盐岩,其中分布有一些超基性岩(块)。以往曾据灰岩夹层中的化石将其划归志留系-中泥盆统或前泥盆系。我们对乌帕塔尔坎群中所采集的24块硅岩样品进行室内分离和鉴定,发现的放射虫化石主要有Albaillella sp. cf A. undulata Deflandre,Albaillella sp. cf A. paradoxa Deflandre,Albaillella cf. A. deflandrei Gourmelon,Albaillella sp. cf. A. indensis Won,Albaillella sp. cf. Albaillella excelsa Ishiga, Kitoand Imoto,Albaillella sp.和Latentifistulidae gen. et. sp. indet.。其中可划分出两个放射虫化石组合,一个是以Albaillella sp. cf A. undulata Deflandre,Albaillella sp.cf A. paradoxa Deflandre,Albaillella cf. A. deflandrei Gourmelon和Albaillella sp. cf. A. indensis Won为代表的早石炭世早期的化石组合;另一个是以Albaillella sp. cf. Albaillella excelsa Ishiga, Kito and Imoto为代表的晚二叠世化石组合。说明乌帕塔尔坎群至少可能包含有志留系到二叠系不同时代的岩石,可能是蛇绿混杂岩。这是该群首次发现放射虫化石,特别是再次发现晚二叠世放射虫化石,进一步证实了南天山西段晚二叠世(残余)古洋盆存在的可能性。 相似文献
20.
Stephen K. Donovan Anthony Butcher 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(2):170-173
Complete fossils must be preferred to fragments for most palaeontological studies, but disarticulated specimens are nonetheless potential sources of noteworthy data. Two crinoid pluricolumnals are recorded from the lower Palaeozoic; informed discussion shows each is a basis for palaeobiological interpretation. Both are gracile and are probably belong to disparids. Floricrinus (col.) sp. is from the Silurian of Wenlock Edge, Shropshire, either from the Much Wenlock Limestone Formation (Wenlock) or, more likely, the Lower Elton Formation (Ludlow). This is the first crinoid from the Silurian of the British Isles with a pentapetaloid arrangement of the areola, a geometry common in the Middle-Upper Ordovician and higher in the geologic column. Pluricolumnal gen. et sp. indet. is from the Lower Llanvirn of Powys. One end of the otherwise straight specimen is tightly coiled. This is likely the proxistele, the most flexible region of the column, and the coiling occurred after the crown was lost by autotomy in response to an environmental disturbance. 相似文献