Phytoliths from the Southwest Pacific, Site 591

Abstract

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.

Cenozoic climatic change and the development of the arid vegetation in Australia

“…The Aquarius site suggests an increase in the herbaceous elements Asteraceae and Chenopodiaceae (Hekel, 1972). Phytoliths found in a deep sea site off on the Lord Howe Rise, off the east coast of Australia suggests that grasslands became prominent in the Pliocene (Locker and Martini, 1986;Martin, 1998b), at a similar time to that seen in the northwest.…”

The Origin of Grass-Dominated Ecosystems

“…Brassospora) is indicated in pollen records of the southeast (MacPhail, 1996). After this, a substantial increase in the relative percentages of Asteraceae and Poaceae pollen concomitant with high charcoal counts and a dramatic increase in grass phytoliths in marine cores indicate a change to open woodlands, savannas, and grasslands (Locker & Martini, 1986;Martin, 1981Martin, , 1990a. PALEOFAUNA The sporadic fossil mammal record of Australia, much of which is only loosely constrained temporally, is summarized in Archer et al (1994aArcher et al ( , b, 1995, Vickers-Rich et al (1991), andWoodburne et al (1994).…”

“…Symbols as in Figures 2 and 5. Sources: (1) Mar-tin (1994), (2) MacPhail (1994), (3) Archer et al (1995), (4) Kemp (1978), (5) Martin (1990a), (6) Locker & Martini (1986), (7) Archer et al (1994a), (8) Archer et al (1994b), (9) Archer et al (1995). dicative of tropical or closed forest (Kemp, 1978). The hallmark of Australian palynofloras from the late Eocene through the middle Miocene is the presence of Nothofagus pollen, most significantly, Nothofagus subg.…”

“…At the same time, the occurrence of charcoal in pollen samples begins to increase. Marine records document the first appearance of grass phytoliths at 14.4 Ma (Locker & Martini, 1986;Martin, 1990a). The changes in pollen and charcoal indicate tall, open, wet sclerophyll forest where eucalypts form the canopy and rainforest taxa grow in the understory (Martin, 1990a;Kershaw et al, 1994).…”

Predicted World Distribution of C3 and C4 Grass Phytoliths

“…Ehrenberg (1854) and Deflandre (1963) used a binomial taxonomic system with parataxa. Locker and Martini (1986) adopted this system in describing the phytoliths recovered from deep sea cores east of Australia that extend from the Middle Miocene to Early Pleistocene. Other classifications are largely morphological and have been used by most workers (Twiss, Suess & Smith 1969;Bertoldi de Pomar 1971;Sase & Kondo 1974;Brown 1984;Piperno 1988;Mulholland & Rapp 1989).…”