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首页> 外文期刊>Bulletin de la Societe Geologique de France >Faunal specificity, endemism and paleobiogeography: the post-glacial(Hirnantian-early Rhuddanian) graptolite fauna of the North-Africanborder of Gondwana: a case study
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Faunal specificity, endemism and paleobiogeography: the post-glacial(Hirnantian-early Rhuddanian) graptolite fauna of the North-Africanborder of Gondwana: a case study

机译：动物的特异性，地方特有性和古生物地理学：冈瓦纳北部非洲边界的冰河后（赫南德人至早期的罗德丹人）笔石动物区系：一个案例研究

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摘要

Several types of stratigraphic successions are found at the top of the glacial to periglacial "Complexe termi-nal" forming the uppermost Ordovician of the North-African border of Gondwana. Locally, there may be a progressivetransition from microconglomeratic clays (diamictites) with dropstones to more normal marine clays accompanied bythe almost immediate reappearance of graptolites. Study of the graptolites has revealed a distinctive composition at thespecific level, differing from contemporaneous faunal associations in adjacent regions, which consist of such classicalspecies as "Glyptograptus" persculptus, Akidograptus ascensus, Parakidograptus acuminatus, etc. The faunal composition has long posed a chronostratigraphic problem, which has now been largely resolved, thefauna being interpreted as Hirnantian to early Rhuddanian in age. On the other hand, the clear evidence of faunal speci-ficity poses a number of problems in the post-glacial context, namely: a)the disappearance of graptolites in the mid-Caradoc from these regions poses a problem as to the origin of thenew specific fauna. Three hypotheses are considered, none of which is satisfactory. Most available data point to an east-ern communication, although it is possible that the rejuvenation of the Mauritanides to the west "erased" all prior evi-dence, giving a wrong idea as to the communications which existed in the area under consideration; b)what mechanisms caused and maintained this isolation? The hypothesis of a wide, east-west trending depres-sion produced by the overloading of the frontal ice sheet and its progressive disappearance concomitant with the glacialrebound is being considered; c)what were the effects of isolation on the morphology of graptolites and their population? The virgella and thevirgula in several species are remarkably long and this could be attributed to a reduction in water density. The size ofmonospecific populations also attests to an adaptation to a restricted regime with sandy deposition; d)how can one explain why some species like N. pseudovenustus, N. inazzaouae, N. normalis brenansi and Ps.kiliani, occur also in other parts of the world? If these species occur where the classical species are absent, the oppositeis even more difficult to explain, leading one to postulate the presence of a selective "filter"; e)how did this faunal specificity disappear progressively? The extent of the sea with Nd. africanus and Nd.fezzanensis put an end to isolation, although it respected the east-west trend. However, there was an opening to the adja-cent regions corresponding to present-day Libya. To conclude, if pelagic faunas are considered to be poor paleogeographic tools, faunal specificity rather thanendemism should be regarded as the starting point for further reflection. However, all faunal specificity must be fullydocumented and the results integrated in a framework that includes all aspects of sedimentology, tectonics and climatology. Seven new species are briefly described: Normalograptus nseirati sp. nov., Normalograptus gelidus sp. nov.,Normalograptus arrikini sp. nov., Normalograptus pretilokensis sp. nov., Neodiplograptus inezzani sp. nov.,Neodiplograptus incommodus sp. nov. and "Glyptograptus" saharensis sp. nov.
机译：在冰川到冰缘的“ Complexe终端”的顶部发现了几种类型的地层演替，形成了冈瓦纳北非边界最上层的奥陶纪。从局部看，可能会有微团聚体粘土（透辉石）和滴石逐渐过渡到更普通的海相粘土，同时几乎立即出现了石墨石。对涂鸦石的研究表明，在特定水平上有独特的组成，与相邻地区的同时期动物群落不同，后者由“ Glyptograptus” persculptus，Akidograptus ascensus，Parakidograptus acuminatus等经典物种组成。动物组成长期以来一直引起年代地层学问题。 ，现在已经大体上解决了，该动物区系在年龄上被解释为Hirnantian到Ruddanian早期。另一方面，动物专一性的明确证据在冰期后的背景下带来了许多问题，即：a）在卡拉多克中部，这些地区的石墨石消失使新起源的形成成为问题。特定的动物区系。考虑了三个假设，但没有一个令人满意。尽管有可能使毛里塔尼德斯复兴到西部“擦除”了所有先前的证据，但对于正在考虑的地区中存在的通信却产生了错误的认识;尽管如此，大多数现有数据都指向东部的通信。 b）造成并保持这种隔离的机制是什么？人们正在考虑这样一个假说，即前冰盖超载及其伴随冰川回弹而逐渐消失而产生的东西向趋势性下降。 c）隔离对涂鸦石形态及其种群有什么影响？几种物种的小肠和小肠很长，这可能归因于水密度的降低。单特异性种群的数量也证明适应了沙质沉积的局限性。 d）怎样解释为什么其他物种也出现在世界其他地区呢？例如：伪维氏猪笼草，inazzaouae猪笼草，brenansi猪笼草和kiliani猪笼草？如果这些物种出现在经典物种所不存在的地方，那么对立面就更加难以解释，导致人们推测存在选择性的“过滤器”。 e）这种动物特异性如何逐渐消失？海域含钕。尽管非洲人和非斯山民望尊重东西方趋势，但它结束了孤立。但是，与今天的利比亚相对应的邻近地区却开放了。总之，如果认为远洋动物群是古地理学的不良工具，那么应该将动物群特异性而不是地方特有性作为进一步反思的起点。但是，必须充分记录所有动物区系特异性，并将结果整合到一个包括沉积学，构造学和气候学各个方面的框架中。简要描述了七个新物种：Normalograptus nseirati sp。 11月，Normalograptus gelidus sp.。十一月，Normalograptus arrikini sp.。十一月，Normalograptus pretilokensis sp.。十一月，Neodiplograptus inezzani sp.。十一月，Neodiplograptus incommodus sp。十一月和“ Glyptograptus” saharensis sp。十一月

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