Site U1334

Integrated Ocean Drilling Program (IODP) Site U1334 (7°59.998?N, 131°58.408?W; 4799 meters below sea level [mbsl]) (Fig. F1; Table T1) is located ~380 km southeast of previously drilled Ocean Drilling Program (ODP) Site 1218 (~42 Ma crust) in the central area drilled during the Pacific Equatorial Age Transect (PEAT) program (IODP Expedition 320/321). Site U1334 (~38 Ma crust) is situated ~100 km north of the Clipperton Fracture Zone on abyssal hill topography draped with ~280 m sediment (Fig. F2). The fabric of the abyssal hills within the sites is oriented either due north or slightly east of due north.Water depth in the vicinity of Site U1334 ranges between 5.0 and 5.1 km for the depressions between the abyssal hills. The abyssal hills range between 4.70 and 4.85 km water depth and generally show a thicker and more consistent sediment cover than the basins. In fact, a significant amount of the bathymetric difference between hills and basins is controlled by the amount of sediment cover. The comparison of sediment thickness and clarity of seismic sections led us to select a location on the middle elevation of one of the abyssal plateaus.Site U1334 sediments were estimated to have been deposited on top of late middle Eocene crust with an age of ~38 Ma and target the events bracketing the Eocene–Oligocene transition with the specific aim of recovering carbonate-bearing sediments of latest Eocene age prior to a large deepening of the calcium carbonate compensation depth (CCD) that occurred during this greenhouse to icehouse transition (Kennett and Shackleton, 1976; Miller et al., 1991; Zachos et al., 1996; Coxall et al., 2005). The Eocene–Oligocene transition experienced the most dramatic deepening of the Pacific CCD during the Paleogene (van Andel, 1975), which has now been shown by Coxall et al. (2005) to coincide with a rapid stepwise increase in benthic oxygen stable isotope ratios, interpreted to reflect a combination of growth of the Antarctic ice sheet and decrease in deepwater temperatures (DeConto et al., 2008; Liu et al., 2009).<br/

Pacific Equatorial Age Transect : expeditions 320 and 321 of the riserless drilling platform from and to Honolulu, Hawaii (USA), Sites U1331–U1336, 5 March–4 May 2009 and Honolulu, Hawaii (USA), to San Diego, California (USA), Sites U1337–U1338, 4 May–22 June 2009

Integrated Ocean Drilling Program Expedition 320/321, "Pacific Equatorial Age Transect" (Sites U1331–U1338), was designed to recover a continuous Cenozoic record of the equatorial Pacific by coring above the paleoposition of the Equator at successive crustal ages on the Pacific plate. These sediments record the evolution of the equatorial climate system throughout the Cenozoic. As we gained more information about the past movement of plates and when in Earth's history "critical" climate events took place, it became possible to drill an age transect ("flow-line") along the position of the paleoequator in the Pacific, targeting important time slices where the sedimentary archive allows us to reconstruct past climatic and tectonic conditions. The Pacific Equatorial Age Transect (PEAT) program cored eight sites from the sediment surface to basement, with basalt aged between 53 and 18 Ma, covering the time period following maximum Cenozoic warmth, through initial major glaciations, to today. The PEAT program allows the reconstruction of extreme changes of the calcium carbonate compensation depth (CCD) across major geological boundaries during the last 53 m.y. A very shallow CCD during most of the Paleogene makes it difficult to obtain well-preserved carbonate sediments during these stratigraphic intervals, but Expedition 320 recovered a unique sedimentary biogenic sediment archive for time periods just after the Paleocene/Eocene boundary event, the Eocene cooling, the Eocene–Oligocene transition, the "one cold pole" Oligocene, the Oligocene–Miocene transition, and the middle Miocene cooling. Expedition 321, the second part of the PEAT program, recovered sediments from the time period roughly from 25 Ma forward, including sediments crossing the Oligocene/Miocene boundary and two major Neogene equatorial Pacific sediment sections. Together with older Deep Sea Drilling Project and Ocean Drilling Program drilling in the equatorial Pacific, we can delineate the position of the paleoequator and variations in sediment thickness from ~150°W to 110°W longitude

Site U1338

In principle, the age-transect strategy of this expedition would not be complete without data from the Pliocene and Pleistocene. However, in addition to the logistical reasons of cruise length, near-equatorial records have already been recovered during Ocean Drilling Program (ODP) Legs 138 (Pisias, Mayer, Janecek, et al., 1995) and 202 (Mix, Tiedemann, Blum, et al., 2003). This earlier drilling provides information about the development of Northern Hemisphere glaciation. Our last site focuses instead on the interesting events during and just after a mid-Miocene maximum in sediment deposition (van Andel et al., 1975) and temperature (Zachos et al., 2001).Integrated Ocean Drilling Program (IODP) Site U1338 (2°30.469?N, 117°58.178?W; 4200 m water depth; PEAT-8 site survey) (Fig. F1; Table T1) was sited to collect a 3–18 Ma segment of the Pacific Equatorial Age Transect (PEAT) equatorial megasplice. Site U1338 is on ~18 Ma crust just north of the Galapagos Fracture Zone, 324 nmi (600 km) southeast of Site U1337 (Fig. F1), in abyssal hill topography that strikes 350° (Fig. F1). The topography slopes down to the north-northwest from a regional high in the south. A seamount (3.7 km water depth) with a surrounding moat is found ~25 km north-northwest of Site U1338, at the downslope end of the survey area. Originally a site (proposed Site PEAT-8C) was chosen ~10 km from the seamount. However, alternate proposed Site PEAT-8D was selected and drilled uphill and further away from the seamount to avoid possible turbidites, as were found near seamounts at Sites U1331 and U1335.Site U1338 is on a minor ridge along Line 1 of the PEAT-8 survey (Fig. F2) under 4200 m of water. In the survey area, sediment thickness ranges from ~400 ms two-way traveltime (TWT; ~320 m) at the top of the abyssal hills to a maximum of a little more than 550 ms TWT (~450 m) within basins. Estimated sediment thickness from the seismic reflection profile using an ODP Site 849 velocity-depth age model is 402 m at the Site U1338 location. The sediment pattern is typical "pelagic drape" and lies conformably on basement. Ridges at the seafloor reflect basement highs even though the sediment layer is about twice as thick as the original relief. Basement topography has been subdued somewhat by preferential infilling of the abyssal valleys. Pits often occur along the edge of the ridge lines away from the location of Site U1338 (Moore et al., 2007). Good examples of pits lie just west of Line 5 at 2°30?N in Figure F1. Moore et al. (2007) attributed these features to a variety of processes that fracture the sediments and establish conduits for warm fluid flow from the basement, and Moore et al. (2007) hypothesized that sediments are partly dissolved by the fluid flow.Based on stage-pole reconstructions of Pacific plate motion, observations of basement age from previous drilling, and magnetic maps (Cande et al., 1989) we determined Site U1338 to be located on ~18 Ma basement. During the AMAT-03 site survey we collected magnetic anomaly data that can be correlated to additional collated observations (Barckhausen et al., 2005; Engels et al., 2007) and can confirm the anomaly location

Expedition 320/321 summary

Integrated Ocean Drilling Program Expedition 320/321, "Pacific Equatorial Age Transect" (Sites U1331–U1338), was designed to recover a continuous Cenozoic record of the equatorial Pacific by coring above the paleoposition of the Equator at successive crustal ages on the Pacific plate. These sediments record the evolution of the equatorial climate system throughout the Cenozoic. As we gained more information about the past movement of plates and when in Earth's history "critical" climate events took place, it became possible to drill an age transect ("flow-line") along the position of the paleoequator in the Pacific, targeting important time slices where the sedimentary archive allows us to reconstruct past climatic and tectonic conditions. The Pacific Equatorial Age Transect (PEAT) program cored eight sites from the sediment surface to basement, with basalt aged between 53 and 18 Ma, covering the time period following maximum Cenozoic warmth, through initial major glaciations, to today. The PEAT program allows the reconstruction of extreme changes of the calcium carbonate compensation depth (CCD) across major geological boundaries during the last 53 m.y. A very shallow CCD during most of the Paleogene makes it difficult to obtain well-preserved carbonate sediments during these stratigraphic intervals, but Expedition 320 recovered a unique sedimentary biogenic sediment archive for time periods just after the Paleocene/Eocene boundary event, the Eocene cooling, the Eocene–Oligocene transition, the "one cold pole" Oligocene, the Oligocene–Miocene transition, and the middle Miocene cooling. Expedition 321, the second part of the PEAT program, recovered sediments from the time period roughly from 25 Ma forward, including sediments crossing the Oligocene/Miocene boundary and two major Neogene equatorial Pacific sediment sections. Together with older Deep Sea Drilling Project and Ocean Drilling Program drilling in the equatorial Pacific, we can delineate the position of the paleoequator and variations in sediment thickness from ~150°W to 110°W longitude

Site U1336

Integrated Ocean Drilling Program Site U1336 (site survey PEAT-5C; 7°42.067?N, 128°15.253?W; 4286 meters below sea level [mbsl]) (Fig. F1; Table T1) is in the central area drilled during the Pacific Equatorial Age Transect (PEAT) program (Expedition 320/321). Site U1336 (~32 Ma crust) is between Site U1334 ~410 km to the west and Site U1335 ~330 km to the southeast and ~100 km to the west of Deep Sea Drilling Project (DSDP) Site 78. Site U1336 is also ~30 km north of the center of the Clipperton Fracture Zone. The site survey data (Lyle et al., 2006; Pälike et al., 2008) show that Site U1336 is on abyssal hill topography draped with thick sediment (Fig. F2). The fabric of the abyssal hills is oriented slightly west of due north.Water depth in the vicinity of Site U1336 is relatively shallow for the age of the crust, between 4200 and 4400 m. Surprisingly, the crust south of the Clipperton Fracture Zone is only 100 m deeper than the crust north of the zone, despite a water depth of nearly 5 km in the middle of the fracture zone trace. A few oblique ridges and depressed topography occur in the south of the survey area, showing some interaction between the fracture zone and the Site U1336 region. The site is thickly covered with sediment (300–400 ms two-way traveltime [TWT]) (Fig. F2) and has a very thin layer of recent to middle Miocene sediment, with frequent sediment erosion on flanks of abyssal hills. Based on correlation to the Neogene central equatorial Pacific seismic stratigraphy of Mayer et al. (1985) and the Paleogene equatorial Pacific stratigraphy of Lyle et al. (2002), we estimated ~120 m of Oligocene sediment for an average Oligocene sedimentation rate of 13 m/m.y., assuming a crustal age of 32 Ma. The total sediment thickness, using the velocity-depth conversion for DSDP Site 574 (Mayer et al., 1985) was estimated as 253 m prior to drilling.Based on stage-pole reconstructions of Pacific plate motion, observations of basement age from previous drilling sites, and magnetic anomaly maps (Cande et al., 1989), we estimated that Site U1336 is on 32 Ma crust. The best control on age is information from Site 78, ~100 km east of Site U1336. The base of Site 78 reaches the lower Oligocene

Site U1331

The Pacific Equatorial Age Transect (PEAT) program, which includes Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321, was the first scientific program following the complete refit of the R/V JOIDES Resolution. During this process, scientific facilities on the ship were replaced with a completely new structure and all major drilling and ship systems were completely refurbished. All laboratory equipment used on these first two expeditions was new, refurbished, upgraded, or replaced. This was also the first scientific use of the new software controlling the instruments and new database system.Information assembled in this chapter will help the reader understand the basis for our shipboard observations and preliminary conclusions. It will also enable the interested investigator to identify data and select samples for further analysis. Information presented here concerns only shipboard operations and analyses described in the site chapters. Methods used by various investigators for shore-based analyses of Expedition 320/321 data will be described in individual publications in various professional journals and the "Expedition research results" of this Proceedings volume. This introductory section provides an overview of operations, curatorial conventions, and general core handling and analysis

Site U1333

Integrated Ocean Drilling Program (IODP) Site U1332 (11°54.722?N, 141°02.743?W; 4924 meters below sea level [mbsl]) (Fig. F1; Table T1) is located ~120 km east and slightly south of IODP Site U1331, near the northwesternmost area drilled during the Pacific Equatorial Age Transect (PEAT) program (IODP Expedition 320/321). This site is situated on 50 Ma crust ~750 km north of the Clipperton Fracture Zone, ~380 km south of the Clarion Fracture Zone, and ~270 km northeast of the nearest previously drilled Ocean Drilling Program (ODP) Site 1220 (56 Ma crust)

Site U1335

Integrated Ocean Drilling Program (IODP) Site U1335 (5°18.735?N, 126°17.002?W; 4327.5 meters below sea level [mbsl]) (Fig. F1; Table T1) is located in the central area drilled during the Pacific Equatorial Age Transect (PEAT) program (IODP Expedition 320/321). Site U1335 (~26 Ma crust) is situated halfway between IODP Site U1336 ~340 km to the northwest and IODP Site U1337 ~390 km to the southeast, ~250 km south of the Clipperton Fracture Zone. Site U1335 is located on a broad plateau within north-northeast–trending abyssal hill topography. Thick sediment deposits cover the abyssal hills, with a thinning sediment cover on the hills. Site U1335 is draped with ~420 m of sediment cover (Fig. F2), estimated to be ~360 m prior to drilling. Water depth in the vicinity of Site U1335 is between 4300 and 4400 m, apart from the topography around seamounts that are 15–20 km away from the drill site (Fig. F1B).Based on stage-pole reconstructions of Pacific plate motion and observations of basement age from previous drilling sites, along with magnetic anomaly maps (Cande et al., 1989), we estimated prior to drilling that Site U1335 is located on 26 Ma crust. The best control on age is information from Deep Sea Drilling Project (DSDP) Site 79, located ~600 km and 4.5° east and 3° south of Site U1335, apparently on the same fracture zone segment, with the Clipperton Fracture Zone to the north. The base of Site 79 reaches the Miocene/Oligocene boundary, or ~23 Ma on the most recent astronomically calibrated timescales.Site U1335 was proposed for drilling to focus on the paleoceanographic events in the late Oligocene and into the early and middle Miocene, including the climatically significant Oligocene–Miocene transition and recovery from the Mi-1 glaciation event. In conjunction with Sites U1336 and U1337, it was also designed to provide a latitudinal transect for early Miocene age slices

Methods

The Pacific Equatorial Age Transect (PEAT) program, which includes Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321, was the first scientific program following the complete refit of the R/V JOIDES Resolution. During this process, scientific facilities on the ship were replaced with a completely new structure and all major drilling and ship systems were completely refurbished. All laboratory equipment used on these first two expeditions was new, refurbished, upgraded, or replaced. This was also the first scientific use of the new software controlling the instruments and new database system.Information assembled in this chapter will help the reader understand the basis for our shipboard observations and preliminary conclusions. It will also enable the interested investigator to identify data and select samples for further analysis. Information presented here concerns only shipboard operations and analyses described in the site chapters. Methods used by various investigators for shore-based analyses of Expedition 320/321 data will be described in individual publications in various professional journals and the "Expedition research results" of this Proceedings volume. This introductory section provides an overview of operations, curatorial conventions, and general core handling and analysis