Age of the Silurian Wuxiahe Formation in Langao,Northwest China: New conodont data

A recent study of conodonts from the Wuxiahe Formation (lower to middle part) in the Ziyang-Langao region suggested its age of middle Telychian (Llandovery) to lower Sheinwoodian (Wenlock), contradicted by subsequent graptolite studies indicating an age of late Telychian for the same interval. New samples from the Qiaoxi section for conodonts to re-access the age of the Wuxiahe Formation collected in this study show that the lower to middle part of the formation belongs to the Pterospathodus amorphognathoides amorphognathoides Biozone, suggesting the age of late Telychian; thus, the Llandovery–Wenlock boundary in the section is most probably higher than previously estimated, but its precise position is not determined since the identification of the Wenlock graptolite Cyrtograptus cf. lundgreni in the section is to be further confirmed. Based on the conodont faunas recognized in the Qiaoxi and Tianwancun sections, the base of the Wuxiahe Formation in the Ziyang-Langao region is diachronous, i.e., not higher than the upper Telychian Pterospathodus amorphognathoides amorphognathoides Biozone at Qiaoxi, but not lower than the lower Sheinwoodian Kockelella ranuliformis Biozone at the Tianwancun setion.     

黔东北石阡志留系雷家屯组的生物-岩相分异

黔东北石阡志留系兰多维列统埃隆阶上部的雷家屯组属灰岩和碎屑岩混合相,其分布限于滇黔桂古陆以北离岸几十千米范围内的浅海区。出露于枫香铺子沟、雷家屯、白沙龙口—筷子山、白沙均田和本庄岩门的5个剖面存在生物-沉积相的差异性。铺沟村粉砂岩—泥岩含量高于灰岩,达到4∶1,壳相化石丰度最低且无生物礁滩灰岩沉积;其它4个剖面的碎屑岩—灰岩比例约1∶1,雷家屯壳相化石最丰富,上部出现米级厚度的珊瑚-层孔虫点礁;筷子山剖面的雷家屯组下部开始出现雏形礁,之上的礁核灰岩现已被剥蚀掉,但从礁基的菲利普构造和礁翼塌积岩推测,点礁的正向隆起规模是很明显的;均田剖面仅出露雷家屯组上部约7m的地层,多为粉砂岩和生屑灰岩薄层;岩门剖面多为薄层细颗粒生屑滩相灰岩,近顶部出现钙质微生物形成的叠层石。偏西剖面的雷家屯组顶部展现侵蚀面、泥裂等现象,是桐梓上升期海底暴露的证据,唯有最靠东的铺沟村雷家屯组顶部未见暴露标志,与之上马脚冲组呈整合接触。     

The Palaeobiogeography Of Silurian Ramphoprionid Polychaete Annelids

Silurian palaeobiogeography of the Ramphoprionidae (Annelida; Polychaeta) is outlined. Members of the family are reported from northern Europe (Estonia, Sweden and England), the Russian Arctic (Severnaya Zemlya), and the Canadian Arctic (Baillie–Hamilton Island). These areas were located fairly close to the palaeoequator during the Silurian and a faunal exchange is indicated by the broad, intercontinental distribution of the family. A few taxa may, however, have been endemic. Ramphoprionids had long stratigraphical ranges and were generally fairly rare during the Silurian, infrequently exceeding ten per cent of the jawed polychaete faunas.     

A Silurian porpitoid hydrozoan from Cumbria, England, and a note on porpitoid relationships

A porpitoid hydrozoan, Pseudodiscophyllum windermerensis gen. et sp. nov., from Cumbria, represented by a well-preserved internal float (pneumatophore), is only the fourth porpitoid reported from Silurian rocks world-wide and the first to be found in any geological formation in England. Its circular pneumatophore is more than 110 mm in diameter. Because of the paucity of hard parts, these animals are not common as fossils but may have been important elements of the Palaeozoic oceanic plankton. Although the new species is superficially similar to the Ordovician Discophyllum , there are what appear to be fundamental differences. Similarities to species of Paropsonema , from the Devonian and Silurian, are also probably superficial. The wider relationships of these animals have long been misinterpreted in the palaeontological literature. They are not siphonophores. Correct understanding involves a complete re-interpretation of various homologies and of the evolutionary history of the group.     

Identification of the late Homerian Mulde Excursion at the base of the Salina Group (Michigan Basin,USA)

Constraining the age of strata is a fundamental source of uncertainty in the study of sedimentary rocks, particularly in restricted basins that generally lack index fossils. An illustrative example of this is the evaporite‐bearing Salina Group in the Michigan Basin. Our integrated study of facies, paleontology, and stable isotope geochemistry from the base of the Salina Group in Wisconsin addresses long‐standing chronostratigraphic uncertainty surrounding these units. Conodont samples from the basal boundary interval (Racine‐Waubakee formation contact) produced non‐diagnostic ‘disaster’ and ‘recovery’ faunas typical of both the Mulde (Homerian) and Lau (Ludfordian) events. Strontium isotope analysis (⁸⁷Sr/⁸⁶Sr) of these conodonts from five horizons just below the boundary yield values between 0.70844 and 0.70850 confirming a Homerian age. Multiple carbon isotope profiles through this interval confirm the presence of a 2.5–3‰ positive excursion. Cumulatively these data constrain the base of the Salina Group in Wisconsin to the Mulde Excursion interval (late Homerian). This integrated study provides a sound initial step towards a deeper understanding of the processes of Silurian evaporite formation in the Michigan Basin.     

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.     

鄂西志留纪早期三叶虫Latiproetus Lu,1962的新材料

本文描述湖北宜昌、兴山志留纪兰多维列世艾隆期蚜头虫类三叶虫Latiproetus latilimbatus(Grabau,1925)和Latiproetus tenuis Chang,1974的新材料.Latiproetus Lu,1962的有效性长期多有争论,通过新材料研究确认,该属和Prantlia P(r)ibyl,1946的区别在于其较短的鞍前区,向前收缩较少的头鞍,较微弱的尾肋沟和间肋沟,并不具鞍前区横脊.该属和Astroproetus Begg,1939的区别在于其较深的S1,清晰的S2,较小的活动颊刺,及宽而清晰的尾边缘.因此,笔者认为Latiproetus应为有效属.     

Fragmentary non-vascular plant microfossils from the late Silurian of Wales

A wide variety of cuticles and tubular elements is described from a late Silurian (Ludlow Series) locality in Wales which has already yielded a macroflora containing Cooksonia Lang, Steganotheca Edwards and vascularized axes. These microfossils are compared with Lang's Downtonian .Nematothallus complex and Silurian assemblages of similar composition from north America. It is concluded that the majority of these microfossils derive from non-vascular plants of uncertain affinity which lived on land.     

Late Ordovician-Early Silurian fluctuations in sea level from eastern Anticosti Island, Quebec

Over 1,000 m of Upper Ordovician to Lower Silurian mixed carbonate and clastic strata on Anticosti Island are nearly tectonically undisturbed, despite their proximity to the Northern Appalachians fronting Quebec's Gulf of St. Lawrence. Natural cliffs exposed along the coast and rivers in the eastern part of the island make a relatively conformable sequence belonging to the Ashgill and Llandovery Series. Fossil communities interpreted as depth-associated in life are especially repetitious in the Becscie, Gun River, Jupiter, and Chicotte Formations (Llandovery Series), and to a lesser degree in the Upper Vaureal and Ellis Bay Formations (Ashgill Series). Preliminary study of the pattern of changeovers in Eocoelia, Pentamerus and Stricklandia communities suggests that Anticosti seas deepened and shallowed three and a half times during the Early Silurian. High water peaks were reached during B₁-B₂, C₁-C₂ and C₄-C₅ times, with a final deepening trend beginning in late C₅ time. Age determinations of these events are based on the occurrence of graptolites (with some new records from Anticosti) keyed to the standard graptolite zones, and species of the Eocoelia lineage are also useful for correlation. The profile of the Anticosti sea-level curve compares well with other curves reconstructed from the Lower Silurian of New York, Michigan, and Iowa. Widespread synchronism in sea-level changes on the North American platform is thus corroborated.     

THE GEOLOGICAL SIGNIFICANCE OF SINACANTHUS FROM TARIM, CHINA

TheSinacanthusfossiIlocalitieswererestrictedtotheYangtzeregionbeforethediscoveryoftheTarimfossils.TheyusedtobereferredtoasDevonianorEarlyDevonianinage,butlaterdiscoverieshavedemostratedthattheageofSinacanthus-bearingbedsshou1dbeSilurian(Li,198O).In1988,fiveSinacanthusfossill,edswerefoundintheTataertagPormationofKalping,NWTarimandtheageoftheTataertagFormationwasconsideredMiddle-LateSilurian(Table2).Inthesummerofl992,WangJunqing,ZhuMinandtheauthorofthispaperfoundalotoffossilfinspinesi…