Phytoliths are described from deep sea sediments at Site 591 in the southwestern Pacific. Their regional distribution is related to the arid and semiarid regions of Australia, from where they were blown by westerly winds into the Tasman Sea area. The stratigraphic record ranges from the middle Miocene, at about 14.4 m.y., until the early Pleistocene. A distinct increase in frequencies observed during the Pliocene and a maximum at about 2.5 m.y. coincide with important trends in paleogeography and paleoclimatology: the development of the Antarctic ice cap, the northward drift of the Australian Plate, and the generation of arid conditions on the Australian continent.
INTRODUCTIONDuring Leg 90 phytoliths were found in fair numbers in Holes 591, 591 A, and 591B, and very sporadically also in Hole 594A. They were investigated in detail only in the first three holes. Site 591 is situated on the eastern flank of the Lord Howe Rise (31°35.06'S; 164°26.92'E) in a present water depth of 2131 m (Fig. 1). Sediments recovered at this site consist mainly of foraminifer-bearing or foraminifer-rich nannofossil ooze. Biosiliceous components are present in low numbers compared with calcareous components, and include diatoms, silicoflagellates, radiolarians, and phytoliths. The investigated sections cover the middle Miocene to early Pleistocene interval.
PHYTOLITHS IN MARINE SEDIMENTSPhytoliths are siliceous casts of various shapes that occur mainly in epidermal cells of grasses. They generally indicate that a certain fraction of a sediment sample is derived from a terrestial source.Phytoliths have been described from terrestial localities (Ehrenberg, 1854;Baker, 1960a;Deflandre, 1963;Hajós, 1968) as well as from marine sections (see Table 1). In marine sediments they commonly occur in areas which are close to continents and where permanent eolian transport of dust in particular directions is possible (Folger et al., 1967;Folger, 1970). The main areas of phytolith distribution are in the Atlantic Ocean off the coast of northwest Africa and in the eastern equatorial Pacific. In both areas easterly winds, that is, winds blowing in a westerly direction, cause phytoliths to occur in Recent and ancient sediments. To these occurrences we can now add the southwest Pacific, where phytoliths were found in fair numbers during Leg 90 of the Deep Sea Drilling Project, distributed from Australia by westerly winds.Kennett, J. P., von der Borch, C. C, et al., Init. Repts. DSDP, 90: Washington (U.S.