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The distribution of Neogene and Paleogene diatoms from six sites located in the Argentine Basin, the Malvinas Outer Basin, and on the Falkland Plateau is presented. Biostratigraphic zonations based on diatoms are proposed for part of the late Paleocene from Site 327 and for the late Eocene and Oligocene from Site 328. Five new diatom taxa are described. INTRODUCTION Leg 36 started at Ushuaia, Argentina, on 4 April 1974 and ended at Rio de Janeiro, Brazil, on 22 May 1974. The original cruise plan called for an investigation of the evolution of the Scotia Sea and the development of the Circumpolar Current system. However, bad weather and other problems forced a reorganization of the cruise plan. Emphasis was shifted to problems of the evolution of the Falkland Plateau and the southernmost Atlantic. Six sites were occupied (Figure 1). Of these, four were successful (Sites 327, 328, 329, and 330); the other two (Sites 326 and 331) resulted in the recovery of only one and two near surface cores, respectively. Three of the successful sites (327, 329, and 330) are located on the Maurice Ewing Bank on the eastern end of the Falkland Plateau. The fourth site (328) is located in the Malvinas Outer Basin east of the Falkland Plateau. Diatoms ranging in age from late Paleocene to Recent were encountered at the Leg 36 sites. Extensive Neogene sections were penetrated at Sites 328 and 329. An upper Eocene to upper Oligocene sequence was penetrated at Site 328. The late Paleocene was encountered at Site 327. Table 1 summarizes coring operations on Leg 36. METHODS Samples were routinely examined from all core catchers as they were brought on deck during drilling operations. Samples from the top and bottom of core sections were examined as time permitted. Examination of these samples, during drilling operations, established the extent of diatomaceous sediment at each site. After completion of drilling operations cores were routinely sampled for future shore-based investigation. For this purpose, samples of 10 cc were taken from near the top and bottom of each core section as well as at approximately 30 to 50 cm intervals in between from all cores containing diatomaceous sediment. Samples were also taken at selected intervals, such as at lithologic boundaries, within the cores. Samples were prepared for shore-based investigation according to the method described by McCollum (1975). It was necessary to sieve (45 μm) certain samples in order to concentrate the diatoms. Unless noted otherwise, abundances derived from such samples are given as rare. Slides made from each preparation were mounted in Hyrax. Microscopic examination of prepared slides was carried out with the Zeiss Standard RA research microscope equipped with 100X, 40×, and 16× objectives and Nomarski differential interference contrast (DIC). All photomicrographs were taken on Panatomic-X film using a Nikon AFM 35-mm camera. Scanning electron micrographs were taken with a 35mm Nikon camera attached to the ISI Super Mini Scan electron microscope in the Geology Department of Florida State University. Selected specimens and type species were located on the microscope slides by means of a Leitz diamond stylus object marker adapted for use on the Zeiss microscope. All of the samples taken onboard ship were examined on shore with the exception of those from Site 329, which totaled 103. Of these, every fifth sample was examined, intervening samples being examined where necessary. Estimates of the relative frequency of taxa were made using the method suggested by Andrews (1972). A sample was defined as containing a trace amount of diatoms if one or two valves or fragments of valves were observed during 10 traverses of the slide at 400×. A sample was defined as being barren of diatoms if no valves or fragments of valves were observed during 10 traverses at 400 ×. Estimates of gross diatom abundance are given as rare, frequent, common, and abundant. Preservation is indicated as poor, moderate, or good (P, M, G), depending on the extent of valve destruction. Each strewn slide was systematically scanned at 160× and 400× until approximately 40% to 50% of the 18 mm × 18 mm cover slip was traversed. Specific identifications were made at 400× or lOOO× as necessary.

Paleogene and Neogene Diatoms from the Falkland Plateau and Malvinas Outer Basin: Leg 36, Deep Sea Drilling Project