Jurassic microfossils of DSDP Hole 79-547B@en

The first marine incursion of the incipient North Atlantic Ocean is recorded in the uppermost Triassic to Lower Jurassic sequence of DSDP Site 547 off central Morocco. A lithologic change from continental red beds below to slope breccias and hemipelagic carbonates above indicates that a carbonate ramp was probably established by Sinemurian time along the Moroccan continental margin and that subsidence in the adjacent basin was rapid in the early phases of continental rift. Foraminifers recovered from the Liassic (Sinemurian-Pliensbachian) basinal deposits are diverse and well preserved. The faunas are compositionally similar to contemporaneous neritic assemblages of Europe and the Grand Banks of Newfoundland. The Middle Jurassic in Hole 547B is characterized by regressive deposits that are poor in foraminifers. The major Late Jurassic \"Atlantic\" transgression is again represented by basinal deposits consisting of limestone breccias and pelagic carbonates. Foraminifers recovered from this interval are transitional between Late Jurassic assemblages reported from deep-sea deposits in the North Atlantic and typical Late Jurassic neritic assemblages of Europe. The Late Jurassic assemblages of Hole 547B are primarily dominated by nodosariids and spirillinids with moderate abundances of simple arenaceous forms. Nonreticulate epistominids occur very rarely in the Upper Jurassic of Hole 547B. It is tentatively suggested that these represent upper bathyal assemblages.摩洛哥中部近海的深海钻探计划（Deep Sea Drilling Project, DSDP）547站位的晚三叠世至早侏罗世地层序列中，记录了初始北大西洋的首次海侵事件。该序列的岩性由下部陆相红层向上转变为斜坡角砾岩（slope breccias）与半远洋碳酸盐岩（hemipelagic carbonates），这一变化表明，摩洛哥大陆边缘的碳酸盐缓坡（carbonate ramp）可能在锡内穆阶时期即已形成，且邻近盆地在大陆裂谷（continental rift）早期阶段沉降迅速。从里阿斯统（Liassic，锡内穆阶-普林斯巴赫阶（Sinemurian-Pliensbachian））盆地沉积中采集的有孔虫（Foraminifers）种类多样且保存完好；其动物群组成与欧洲及纽芬兰大浅滩的同期浅海生物组合相似。547B钻孔的中侏罗统地层以有孔虫贫乏的海退沉积为特征。晚侏罗世主要的“大西洋型”海侵事件，再次由以石灰岩角砾岩（limestone breccias）与远洋碳酸盐岩（pelagic carbonates）为主的盆地沉积所记录。该层位采集的有孔虫介于北大西洋深海沉积中已报道的晚侏罗世生物组合与欧洲典型晚侏罗世浅海生物组合之间，呈现过渡特征。547B钻孔的晚侏罗世生物组合以节房虫类（nodosariids）和螺旋虫类（spirillinids）占主导，同时伴生有丰度中等的简单砂质壳有孔虫；无网纹似网虫类（Nonreticulate epistominids）在该钻孔的上侏罗统（Upper Jurassic）地层中极为罕见。研究初步认为，这些生物组合代表了上半深海（upper bathyal）环境的生物群。