Calpionellids from the Upper Jurassic and Neocomian of Deep Sea Drilling Project Site 416, Moroccan Basin, Eastern North Atlantic

A "flysch" sequence of Tithonian-Neocomian distal turbidites was continuously cored at DSDP Sites 416 and 370, in the deep Moroccan Basin, near the foot of the continental slope, at a water depth of approximately 4200 meters (Figure 1). The sites were drilled about 2 km apart, during Legs 50 and 41 (Lancelot, Seibold, et al., 1978) respectively, and their stratigraphic sequences were combined (Figure 2). A detailed lithologic description of the 740-meter Jurassic-Neocomian section (885-1624 m below sea floor; Cores 370-35 through 370-51 and Cores 416A-9 through 416A-57) is given in the Site 416 report (this volume). This series includes lithologic units VI and VII, which consist of alternations of terrigenous and carbonate-rich, thinly bedded cycles (5-20 cm thick) and a minor amount of silt-mud laminites and sand layers with sharp bases and tops. The majority of these cyclic beds are turbidites, as evidenced by graded bedding, erosional bottom structures and easily identifiable, classical Bouma sequences. Unit VII (1430-1624 m; Cores 416A-37 through 416A-57) differs from unit VI by the common occurrence of hard micritic limestone in the upper part of the calciturbidite beds and of lithoclasts of calpionellid limestone in their coarse basalt parts. The calciturbidites of unit VII form a distinct population, with thicker beds than their quartzose equivalents. A typical calciturbidite consists from bottom to top of (1) quartz-bearing calcarenite whose main components are lithoclasts of micritic limestone (some with calpionellids), skeletal fragments, aptychi, ostracodes, benthic foraminifers, and calcisphaerulids; (2) parallel or crosslaminated, micritic calcisiltite to quartz siltstone, with skeletal debris, particularly thin shells, and calpionellids (generally hydrodynamically sorted in layers); (3) dark, laminated marlstone rich in dolomite(?) rhombs and rather well-preserved nannofossils; and (4) laminated, micritic limestone with some marlstone, often burrowed from the top. Figures 3 and 4 show examples of variations around this ideal sequence. A detailed discussion on vertical variations in indexes of proximity (average bed thicknesses and percentage of bed containing complete or incomplete Bouma sequence) is given in the Site 416 report (this volume; see also Price, this volume).