BouDagher-Fadel Marcelle, Price Geoffrey David
Office of the Vice-Provost (Research), University College London, 2 Taviton Street, London WC1H 0BT, UK.
UCL Open Environ. 2019 Aug 2;1:e001. doi: 10.14324/111.444/ucloe.000001. eCollection 2019.
Members of the Larger Benthic Foraminiferal (LBF) family Orbitolinidae occurred from the Cretaceous to the Paleogene, however, they were most diverse during the mid-Cretaceous, and dominated the agglutinated LBF assemblages described from limestones of that period. Various orbitolinid species have been used to zone and date lithologies formed in the shallow, warm waters of the Aptian to the early Cenomanian, and many, sometimes inaccurate, generic and sub-generic nomenclatures have been proposed to differentiate the often-subtle morphological changes that orbitolinids exhibit over time. Also, until now, it has not been possible to develop an effective global overview of their evolution and environmental development because descriptions of specimens from Asia have been relatively rare. Following our recent study of over 1800 orbitolinid-rich thin sections of material from 13 outcrops of Langshan limestone, from the Southern Tibetan Plateau, and from the Barito Basin, South Kalimantan, Indonesia, it has been possible to compare the stratigraphic ranges of these orbitolinids with previously described Tethyan and American forms, based on the use of a planktonic zonal (PZ) scheme, itself tied to the most recent chronostratigraphic scale. This has allowed the reconstruction of the phylogenetic and paleogeographic evolution of the orbitolinids from their Valanginian origin in the Tethys. Although the Tethys remained the paleogeographic centre for the orbitolinids, it is inferred here for the first time that a bi-directional paleogeographic migration of some orbitolinid genera occurred from the Tethys to the Americas and also to the Western Pacific region. Our observations and dating suggest that global marine regressions in the Aptian were coincident with, and may well have facilitated, these orbitolinid transoceanic migrations. Migration stopped however after rising sea level in the early Albian appears to have again isolated these provinces from each other. Tectonic forces associated with the subduction of the Farallon Plate and further sea level raises led to the opening of the Western Interior Seaway in North America, which correlates with, and may have been the cause of, the middle Albian (top of PZ Albian 2) extinction of the American orbitolinids. The extinction of the orbitolinids revealed that the Western Pacific province was split into two sub-provinces, with extinction occurring at the end of the early Albian (top of PZ Albian 1) in the Northwest Pacific sub-province, and at the end of the Albian (top of PZ Albian 4) in the subprovince that is today South East Asia (on the margins and west of the Wallace Line). The final near extinction of the orbitolinids occurred at the end of the Cenomanian in the Tethyan province, which coincides with, and may have been caused by, global anoxic oceanic events that correlate with a near-peak Mesozoic eustatic sea level high-stand that led to the overall global collapse of the paleotropical reef ecosystem at that time.
大型底栖有孔虫（LBF）科的圆笠虫科成员生存于白垩纪至古近纪，然而，它们在白垩纪中期最为多样，并在该时期石灰岩中描述的胶结大型底栖有孔虫组合中占主导地位。各种圆笠虫物种已被用于对阿普特阶至早森诺曼阶浅暖水域形成的岩性进行分层和定年，并且已经提出了许多（有时不准确的）属和亚属命名法，以区分圆笠虫随时间表现出的往往很细微的形态变化。此外，直到现在，还无法对它们的演化和环境发展进行有效的全球概述，因为来自亚洲的标本描述相对较少。在我们最近对来自青藏高原南部郎山石灰岩、印度尼西亚南加里曼丹巴里托盆地的13个露头的1800多个富含圆笠虫的薄片材料进行研究之后，基于使用与最新年代地层表相关的浮游生物带（PZ）方案，有可能将这些圆笠虫的地层范围与先前描述的特提斯和美洲类型进行比较。这使得能够重建圆笠虫从其在特提斯的凡兰吟阶起源的系统发育和古地理演化。尽管特提斯仍然是圆笠虫的古地理中心，但在此首次推断，一些圆笠虫属从特提斯向美洲以及西太平洋地区发生了双向古地理迁移。我们的观察和定年表明，阿普特阶的全球海退与这些圆笠虫的跨洋迁移同时发生，并且很可能促进了这些迁移。然而，在早阿尔比阶海平面上升似乎再次使这些区域相互隔离之后，迁移停止了。与法拉隆板块俯冲相关的构造力和进一步的海平面上升导致了北美西部内陆海道的开启，这与美洲圆笠虫在中阿尔比阶（PZ阿尔比阶2顶部）的灭绝相关，并且可能是其原因。圆笠虫的灭绝表明西太平洋区域被分裂为两个亚区域，在西北太平洋亚区域，灭绝发生在早阿尔比阶末期（PZ阿尔比阶1顶部），而在现今东南亚的亚区域（在华莱士线边缘和西侧），灭绝发生在阿尔比阶末期（PZ阿尔比阶4顶部）。圆笠虫的最终近乎灭绝发生在特提斯区域的森诺曼阶末期，这与全球缺氧海洋事件同时发生，并且可能是由该事件导致的，这些事件与中生代海平面上升接近峰值相关，进而导致了当时古热带珊瑚礁生态系统的整体全球崩溃。
