Facies stacking and extinctions across the Triassic–Jurassic boundary in a peritidal succession from western Sicily
Facies stacking and extinctions across the Triassic–Jurassic boundary in a peritidal succession from western Sicily
复制标题
西西里岛西部潮汐连续中跨越三叠纪-侏罗纪边界的相堆积和灭绝
作者：
S. Todaro;P. Di Stefano;G. Zarcone;V. Randazzo
描述了西西里西北部一个厚达430 m的三叠纪-侏罗系碳酸盐台地序列，旨在为研究滨潮环境下三叠纪-侏罗系界线的沉积学和生物学变化提供新的资料。研究的继承属于镶边碳酸盐陆棚，在晚三叠世沿着爱奥尼亚特提斯的边缘发展。潮缘沉积物由潮下相、潮间相和潮上相所形成的米级向上变浅旋回组成。根据潮下带相记录的变化，沿着剖面划分出三个主要的非正式单元。根据有孔虫Triasina hantkeni的共同存在，下部和中部的单位被认为是Rhaetian，与几种底栖有孔虫，如Aulotortus sinuosus和Auloconus permodiscoides有关。巨齿龙在下单元特别丰富和巨大，而它们在中单元变得罕见，并在上单元消失。T. hantkeni，沿着底栖有孔虫动物群的消失，以及石灰质的Thaumatoporella parvovesiculifera的繁盛被认为是雷蒂阶-赫坦阶界线的代表。恢复生物群在早侏罗世发生约20米以上的边界区，标志着底栖有孔虫的外观，如Siphovalvulina sp.观察到的生物地层学签名的研究部分是很容易比较类似的特提斯部分已经描述的意大利，希腊和土耳其;因此，据信动物群的更替并不反映局部相的变化，而是响应于台地可容纳空间的变化，而是在更广阔的特提斯洋区域发生了区域性变化。
An uppermost Triassic–lowermost Jurassic carbonate platform succession, which is 430 m thick, in northwestern Sicily is described with the aim to provide new data on the sedimentological and biological variations across the Triassic–Jurassic boundary in peritidal environments. The studied succession belonged to the rimmed carbonate shelf that developed during the Late Triassic along the margins of the Ionian Tethys. The peritidal sediments consist of meter-scale shallowing-upward cycles formed by subtidal, intertidal, and supratidal facies. Three main informal units are differentiated along the section on the basis of the variations recorded by the subtidal facies. The lower and middle units are attributed to the Rhaetian, on the basis of the common presence of the foraminifer Triasina hantkeni, associated with several benthic foraminifers, such as Aulotortus sinuosus and Auloconus permodiscoides. Megalodontids are particularly abundant and large in the lower unit, whereas they become rare in the middle unit and disappear in the upper unit. The last occurrence of T. hantkeni, along with the disappearance of the benthic foraminifer fauna, and the bloom of the calcareous alga Thaumatoporella parvovesiculifera is assumed as a proxy of the Rhaetian–Hettangian boundary. Recovery biota during the early Jurassic occurs about 20 m upward of the boundary zone, marked by the appearance of benthic foraminifers, such as Siphovalvulina sp. The observed biostratigraphic signature in the studied section is easily comparable to similar Tethyan sections already described from Italy, Greece, and Turkey; thus, it is believed that the faunistic turnover does not reflect local facies variations, in response to changes in the accommodation space of the platform, but regional changes in a more wide area of ocean Tethys.