29. SEDIMENTARY AND VOLCANIC HISTORY: EAST MARIANA BASIN AND NAURU BASIN1 Seymour O. Schlanger, Department of Geological Sciences, Northwestern University and Ralph Moberly, Hawaii Institute of Geophysics2 ABSTRACT The sedimentary section recovered during Leg 89 at Deep Sea Drilling Project Site 525 provided a record of volcan- ism, plate motion, and other events of the Cretaceous and Cenozoic history of the East Mariana Basin. This part of the Pacific lithosphere had formed in the Jurassic; by late Aptian time it was at about 22°S and had subsided to a depth of about 5000 m. In the Aptian and Albian, eruptions built major volcanic edifices nearby that were the sources of mas- sive volcaniclastic debris flows and turbidites found at Site 525. The now deeply altered sediment originally was of quartz-normative tholeiitic basalt composition, with some later alkalic basalt contributions. Reefal debris, ooids, and displaced benthic foraminifers within the hyaloclastic and other volcanogenic components show that some of the volca- noes reached shallow water. They are now the seamounts and guyots north and south of the eastern end of the East Mariana Basin. Recovered cores show evidence of the Cenomanian-Turonian oceanic anoxic event in debris rich in or- ganic carbon redeposited in turbidites, of passage under the equator in Campanian-Maestrichtian time from core Pa- leomagnetism, and of the Oligocene (P21-P22) fall of sea level that exposed seamounts and thereby caused renewed tur- bidite activity. The Nauru Basin igneous complex discovered during Leg 61 yielded cores of 12 additional volcanic units as a result of the deepening of Hole 462A during Leg 89. The mineralogical and geochemical homogeneity within these (and over- lying) sheet flows, as well as their little-altered nature and small amount of interlayered sediment, indicate that the great volume of midplate magma was generated and erupted rapidly. The lowest flows drilled during Leg 89 probably are 130 Ma (Valanginian). They lie on M26-aged ridge-crest crust (about 145 Ma, Oxfordian), and underlie volcanogenic sediment and sills representing at least two other episodes of midplate igneous activity, namely in the Aptian and Albian (about 100 Ma) and in the Campanian (about 75 Ma). INTRODUCTION flow complex found there. A third objective was to oc- cupy Site 289, drilled on Leg 30, and by use of the rela- The major drilling target for Leg 89 was the section tively new hydraulic piston core obtain undisturbed sam- of Cretaceous and Late Jurassic pelagic sediments pre- ples of the pure carbonate pelagic sequence there to sumed to overlie the Jurassic-age lithospheric basalt plate depths of approximately 300 m. This drilling effort was in the western Pacific. The JOIDES Ocean Paleoenvi- assigned to Leg 89 in order to shorten the transit time ronment Panel had as one of its concerns during the for Leg 90 whose primary objective was to drill a north- decade of the 1970s recovery of cores of Mesozoic pe- south transect from the Ontong-Java Plateau (Site 289) lagic sediments in order to decipher the paleoceanogra- to the latitude of New Zealand as part of the JOIDES phy of the old Pacific superocean. Previous drilling in planning for Neogene paleoceanographic objectives. Re- the area had revealed the presence of widespread and in- sults of this drilling are reported in both this volume and tensive Cretaceous volcanism; products of this volcanic in the Leg 90 volume. activity in the form of widespread basalt flows, hyalo- To these ends Glomar Challenger left Yokohama, Ja- clastite sheets, and large edifices had either covered or pan, shortly after midnight on 11 October 1982 and ar- destroyed the Early Cretaceous and Late Jurassic open- rived at Noumea, New Caledonia, on the evening of 29 ocean pelagic record over wide areas of the western Pa- November. cific. Following the discovery, on Leg 61, of thick basalt Despite the fact that the Jurassic sedimentary objec- flows of Early Cretaceous age in the Nauru Basin that tives were not reached, Leg 89 did add to our knowledge thwarted efforts to penetrate the pelagic sediments thought of the timing and areal extent of the mid-Cretaceous vol- to overlie the deeply buried lithospheric plate, new site canic events that have left their imprint over much of surveys were commissioned to explore for drill sites in the western Pacific. the Mariana Basin. Thus the basic plan for Leg 89 was This chapter summarizes the sedimentary and volcanic to drill a multiple reentry hole in the East Mariana Ba- history revealed by drilling in the East Mariana Basin at sin to Jurassic sediments and, it was hoped, into the Site 585 (MZP-6 of the Leg prospectus); new data from ~ 145-Ma plate. A secondary objective was to deepen the reoccupation of Site 462 (MZP-2 of the Leg prospec- Site 462 drilled on Leg 61 in the hope of penetrating the tus) is included as it is relevant to that history. For addi- tional details on results from the drilling on the Ontong- Java Plateau at Site 586 (SWP-9 of the Leg prospectus), 1 Moberly, R., Schlanger, S. O., et al., Init. Repts. DSDP, 89: Washington (U.S. Govt. Printing Office). readers are referred to the Leg 90 Initial Reports (Ken- ^ Addresses: (Schlanger) Dept, of Geological Sciences, Locy Hall, Northwestern Univer- nett, von der Borch et al., in press). Sites occupied on sity, Evanston, Illinois 60201; (Moberly) Hawaii Institute of Geophysics, University of Hawaii at Manoa, 2525 Correa Rd., Honolulu, HI. Leg 89 are shown in Figure 1. 653 S. O. SCHLANGER, R. MOBERLY 40c 30c 20c Site MZP-6 Guam * 10c Site MZP-2 (DSDP 462) 10c 140° 150° 160° 170° 180° Figure 1. Magnetic lineations in the western Pacific in relation to proposed Leg 89 drilling Sites MZP-6 (Site 585), MZP-2 (a reentry at DSDP Site 462, Leg 61), and SWP-9 (a reoccupation and HPC drilling at DSDP Site 289, Leg 30). EAST MARIANA BASIN 199 and 200, 201, and 202 were drilled (Fig. 2); 200 and 201 are in close proximity to 202. At Site 199 566 m Site 585 (MZP-6) is located near the eastern end of of section was penetrated and spot-cored to a depth of the Mariana Basin, an elongate deep, surrounded in the 457 m. The upper 209 m consisted of early Pliocene to east by submarine volcanic edifices of Cretaceous age middle Miocene turbidites made up of nannofossil ooze, (Fig. 2). The water depth in the Basin of -6100 m is in brown silty zeolitic clay, and radiolarian ooze; this sec- accord with the presumed plate age of Jurassic accord- tion was interpreted (Heezen, MacGregor, et al., 1973) ing to accepted subsidence curves for cooling lithosphere. as indicating that the Caroline Abyssal Plain existed as The penetration of a thick sequence of Early Cretaceous early as the middle Miocene. Below this section, to a volcanic flows in the Nauru Basin at Site 462 on Leg 89 depth of 447 m, late Paleocene to early Maestrichtian appeared to confirm the argument that the anomalously nannofossil chalk, chert, and siliceous limestone were shallow depth of the Nauru Basin could be ascribed to a encountered; in the early Maestrichtian strata tuffs were Cretaceous thermal regeneration and uplift of the Nau- common. The deepest core, at 447 to 457 m, consisted ru Basin that resulted in a resetting of the subsidence of brown zeolitic tuff made up almost exclusively of glass path (Larson and Schlanger, 1981). It was thought that shards. Heezen, MacGregor, et al. (1973) interpreted this because the Mariana Basin was at its predicted depth tuff as a record of the final eruption of the volcanoes the influence of Cretaceous thermal resetting would be that formed the guyots that now lie along the eastern lacking there. margin of the Caroline Abyssal Plain. Since the drilling Previous drilling in the Mariana Basin took place on of Leg 20, this Late Cretaceous volcanism has been re- Leg 20 (see Heezen, MacGregor, et al., 1973) when Sites corded over large areas of the western Pacific (Schlanger 654 SEDIMENTARY AND VOLCANIC HISTORY 16C 15C 14C 13C 12C 11' 10° 154° 155° 156° 157° 158° 159° 160° Figure 2. Bathymetric chart of the East Mariana Basin and surrounding seamounts showing the location of MZP-6 (Site 585, Leg 89). Drilling on Leg 20 (Heezen, MacGregor, et al., 1973) revealed Late Creta- ceous pelagic sediments at Site 199 and shallow-water carbonate sediments atop Ita Maitai Guyot at Site 282, which was presumed to be a Cretaceous volcanic edifice (bathymetry in fathoms after Chase et al., 1970). and Premoli Silva, 1981). Sites 200, 201, and 202 of Leg (Larson and Schlanger, 1981) and Late Cretaceous vol- 20 were drilled atop Ita Maitai Guyot (Fig. 4). At Sites canism was recorded in the East Mariana Basin on Leg 200 and 201 the drilling penetrated the acoustically de- 20 (Heezen, MacGregor, et al., 1973), the depth of the termined pelagic cap of early Eocene to Quaternary Glo- Mariana Basin suggested that intensive Early Cretaceous bigerina ooze; a few basalt fragments were found in the volcanism had not occurred there. Therefore the East ooze. At Site 202, however, tan oolitic limestone was en- Mariana Basin was chosen for a site survey as shown in countered at 100 m sub-bottom depth. Below the oolitic Figure 3 (see Shipley et al., 1983; Petersen et al., this limestone were lime muds containing bryozoans and gas- volume). tropods. The oolitic limestones and lime mud were in- Mapped magnetic lineations of the Mesozoic M-series terpreted as pre-early Eocene shallow-water materials de- (Fig.