Conodonts across the Permian-Triassic boundary in the Southern Alps
Conodonts across the Permian-Triassic boundary in the Southern Alps
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发表时间：
2003
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通讯作者：
Maria Cristina Pfrri;E. Farabegoli
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作者：
Maria Cristina Pfrri;E. Farabegoli
目前被认为是特提斯西部三叠纪（P-T）界线的特塞罗和胡拉剖面（Dolomites，意大利）的“关键重要性”，其特征是中到高速率的页岩碎屑-海洋沉积（5-）（）cm k.y.- ').二叠纪Bellerophon Fmn（此处命名为“Bulla Mem Meber”）的最上层碳酸盐相薄，在区域上以不整合面为界。上部不整合面与Werfen组的基底一致，历史上Werfen组与P-T边界一致。在泡状化石中，它稍微早于牙形刺（特别是冷杉）定义的P-T边界（1.3 m）！小Hindeodus parvus。Bulla Mbr产生了Hi。typicalis和Hi.从Werfen组下部开始的牙形刺组合主要由hindcodids和isarcicclids组成，其形态逐渐向上变化。牙形刺基腔的厚度和牙形刺附着区的膨胀度（使牙形刺呈肿胀状）对划分牙形刺的分类具有重要的经济意义。描述了四种新记录种：皮赛伊芬德欧齿象Ifindeodus pisai。大叶鸢尾是. m（lala）和Is.特别的共划分出7个牙形石生物带，其中3个为首次定义：Lower和Upper praeparvlIs。小家伙们。loba！a. slaesehei、isareica和aeqllabi/is区。并提出了Hindeodus属和（mreicclla）属之间的一个可能的分系。JJi preeparvus被认为是Hi的祖先。parvus，南阿尔卑斯山最后一个代表性的离林古龙。伊利praeparvII也是Isarcicella prisea的祖先，随后的Isarcifla谱系进化，即Is。普里斯卡是。图尔吉达群岛洛巴塔岛是的！aeschei和Is.伊萨西亚。P-T界线附近的碳酸盐-陆源沉积以薄（dm-m厚）的沉积旋回出现，记录了高频率的叠加，第四（100 k.y.期间）和第五-（\ 0-25 k.y.）短期海平面波动驱动的有序克莱斯主要的生物大灭绝事件发生在贝尔费罗丰和韦尔芬断裂带的接触处，海平面迅速下降，随后海平面上升。低水位剥蚀了Bellerophon Fmn浅水碳酸盐岩的顶部，导致了基岩的中度风化和侵蚀。在基底Werfen组中发现了许多残留的二叠纪化石。下泰塞罗河牙形石多样性高与气候变化后快速的适应性辐射相一致。在此基础上，我们提出，布拉剖面--
The Tesero and Hulla sections (Dolomites, Italy) currently considered 01' pivotal importance l'or thc l'er mian-Triassic (P-T) boundary in the western Tethys were characterised hy a medium to high rate of shal low-marine sedimentation (5-)() cm k.y.-'). The thin, uppermost carbonate facies ofthe Permian Bellerophon Fmn (here named the "Bulla Mem ber") is bounded regionally by unconformable surfaces. The upper unconforrnity coincides with the base of the Werfen Fmn historically identificd with the P-T boundary. In the Bulla scction, it slightIy antedates (by 1.3 m) the P-T boundary-defined hy conodonts, specifically the firs! appearance of Hindeodus parvus. The Bulla Mbr yielded Hi. typicalis and Hi. praeparvus, extending their ranges above the P-T boundary into the Wcrfcn Fmn The conodont associations l'rom the lower part ofthe Werfen Fmn consist mainly ofhindcodids and isarciccllids showing graduai morphological change up-scction. The thickness and swcll1l1g ofthe basai cavity anu of th.e attachment area of the denticlcs-giving the conodont a swollen appearance-has been considercd laxonomically significant for uefining rorms to be grouped in Isareiee/la. Four ncw specics are describcd: Ifindeodus pisai. Isareicella lobala. Is. m(lala and Is. peculiaris. Seven conodont biozoncs have been discriminated, three are defined for the first time: Lower and Upper praeparvlIs. parvlIs. loba!a. slaesehei, isareica and aeqllabi/is zones. A possible lincagc between the genera Hindeodus and (mreicclla is suggested. JJi. praeparvus has been considered the anccstor of Hi. parvus, the last represcntativc offlindc odus in the Southern Alps. Ili. praeparvIIs is also ancestral to Isarcicella prisea tI'om which the subsequent Isarcicefla lineage evolved, namely Is. prisca to Is. turgida, Is. lobata, lI'. s!aeschei and Is. isarciea. The carbonate-terrigenous deposits around the P-T boundary oceur in thin (dm-m thick) depositional cycles, recording superimposed high frequency, fourth- (l 00 k.y. period) and fifth- (\ 0-25 k.y.) order cy cles driven by short-terrn sea-Ievel fluctuations. The main mass-extinction event occurred dunng the rapid sea-Ievel fall followed by sea-Ievel rise at the contact of the Belferophon and Werfen Fmns. The lowstand exhumed the top of the Bellerophon Fmn shallow-watcr carbonates resulting in moderate weathering and erosion ofbcdrock. Many remanie Perrnian fossils occur in the basai Werfen Fmn transgrcssive trae!. The high conodont diversity in the lower Tesero \llbr accords with rapid adaptative radiation following c1imatic change. On the basis ofour resu\ts, we propose thallhe Bulla section---(;haracterised by relatively abundant conodonts prccisely located in readily discriminahle high- depositional cycles-is the mosl rcliahle paras tratotype scction for the P-T boundary in the western Palaeotethys.