Distribution of Jurassic nannofossils at DSDP Leg 79 Holes@en

Sites 544, 545, and 547, drilled on DSDP Leg 79, recovered Jurassic calcareous nannofossils. Lower Jurassic (Sinemurian - lower Pliensbachian) nannofossils are found in Hole 547B; these are the oldest yet recovered by deep sea drilling. Three other Jurassic intervals are delineated by nannofossil biostratigraphy: the Lower-Middle Jurassic in Hole 547B; the Lower-Middle Jurassic in Hole 545; and the Upper Jurassic in Hole 547B. Low species diversity makes age determinations difficult for these portions of the Jurassic. Two new genera, Calcivascularis and Orthogonoides, have been described from these Lower Jurassic sediments.深海钻探计划（Deep Sea Drilling Project, DSDP）第79航次在544、545及547号钻探站位开展的钻探作业，采获了侏罗纪钙质超微化石（calcareous nannofossils）。547B孔中发现的下侏罗统（西涅缪尔期—早普林斯巴期）钙质超微化石，是深海钻探迄今获取的最古老的同类化石。另有三处侏罗纪地层单元通过钙质超微化石生物地层学（nannofossil biostratigraphy）得以厘定：分别为547B孔的下—中侏罗统、545孔的下—中侏罗统，以及547B孔的上侏罗统。上述侏罗纪地层段物种多样性较低，导致年代判定存在较大难度。从这套下侏罗统沉积物中，已描述出两个新属：Calcivascularis与Orthogonoides。