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Site 262 in the Timor Trough penetrated 442 meters of Recent, Pleistocene, and Pliocene sediments below a water depth of 2298 meters. Core 1 (0-5 m) is Recent. The Pleistocene measures 332.5 meters (Cores 2-36). It is characterized by uniform sedimentation and rich calcareous and siliceous plankton. A gradual shallowing of the Timor Trough begins within the upper Pliocene (Core 40), reaching shallow-water conditions Core 45 (?middle-lower Pliocene boundary). The section was subdivided following the planktonic foraminiferal zonal scheme of Bolli and Premoli Silva (1973). Because of the great thickness of the upper Pliocene-Pleistocene, Site 262 proved suitable for the investigation of evolutionary trends in the Globorotalia crassaformis-tosaensis -truncatulinoides groups. Globorotalia tosaensis tenuitheca and G. tosaensis tosaensis derived in the lower to middle Pliocene from G. crassaformis crassaformis. Somewhat later the thick-walled G. cf. tosaensis also evolved. All these taxa range into the lower Pleistocene. Branching off from Globorotalia tosaensis tenuitheca, with transitional stages in Cores 39-37, Globorotalia truncatulinoides truncatulinoides becomes fully developed in Core 36. The Pliocene-Pleistocene boundary is marked by the appearance of typical Globorotalia truncatulinoides. The thickwalled Globorotalia truncatulinoides pachytheca evolved from G. truncatulinoides truncatulinoides. The Globorotalia crassaformis subspecies crassaformis, oceanica, and ronda are distinguished in the Pliocene. Globorotalia crassaformis hessi, G. crassaformis cf. viola, and G. aff. crotonensis split off from this group within the lower to middle Pleistocene. Notable are the synchronized coiling changes of all these subspecies of G. crassaformis; of special interest is the one from left to right in Core 7 in the upper Pleistocene. INTRODUCTION The great thickness of Pliocene-Pleistocene sediments at Site 262 in the Timor Trough combined with a wellpreserved rich planktonic foraminiferal fauna, makes the section ideally suited for evolutionary studies in the Globorotalia crassaformis-tosaensis-truncatulinoides groups. The significance of Globorotalia truncatulinoides truncatulinoides as a marker for the Pliocene-Pleistocene boundary is well known. This boundary was based by Ericson et al. (1964) in deep-sea cores of the Atlantic on the first appearance of this taxon, together with the extinction of Discoasteridae and some other changes in the planktonic foraminiferal association. Banner and Blow (1965, 1967) also characterized the base of the Pleistocene and the Zone N22, in correlation with the type area of the Calabrian, by the first appearance of G. truncatulinoides. The occurrence of G. truncatulinoides and its ancestor G. tosaensis in the type locality of the Calabrian Stage (the base of the Pleistocene) in Sta. Maria di Catanzaro, Southern Italy, has recently been investigated by various authors including Bayliss (1969), Lamb (1969), Bandy and Wilcoxson (1970), and Poag (1971). The evolution of G. truncatulinoides was studied in detail in a deep-sea core from the central North Atlantic by Phillips et al. (1968) and more recently in Pliocene-Pleistocene sections of New Zealand by Hornibrook (in press). In addition to the Globorotalia mentioned above, some other planktonic index species were investigated and their stratigraphic distribution recorded. The figured specimens are deposited at the Museum of Natural History, Basel, under the numbers C3004330140. LOCATION, SEDIMENTOLOGY, AND PALEOECOLOGY OF SITE 262 Leg 27 investigated the eastern part of the northern Indian Ocean. Site 262, the easternmost of this leg, is located at 10°52.19'S, 123°50.78'E in the Timor Sea. At a water depth of 2298 meters, the site penetrated 442 meters of sediments with a total recovery of 365.5 meters (82.69%). The geology, morphology, and sedimentology of this area have been described by van Andel and Veevers

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The Evolution of the Globorotalia truncatulinoides and Globorotalia crassaformis Group in the Pliocene and Pleistocene of the Timor Trough, DSDP Leg 27, Site 262