5. Site 1073

Site 1073 constitutes one of four second-priority sites approved for drilling that were to be undertaken in the event that either time allowed or that operations had to be curtailed at both primary shelf sites. With 5 days remaining on Leg 174A, the decision was made to move to the slope, because it seemed unlikely that at Sites 1071 and 1072 it would be possible to reach objectives deeper than surface m1(s) without unreasonable risk of equipment loss because of unstable hole conditions. Site 1073 was designed to drill as deeply as time would allow into “Icehouse” sediments (Oligocene and younger) at a location where the physical stratigraphy could be related to sequence boundaries traced seaward from the shelf. The objective at Site 1073 is to provide the age and deep-water facies control for surfaces that in shallow water can yield paleobathymetry and facies characterization relevant to determining the history and geologic impact of glacial-eustatic change

3. Site 1071

Site 1071 is one of two sites approved for JOIDES Resolution drilling on the New Jersey continental shelf; these sites form part of a transect of holes from the slope (ODP Leg 150) to coastal outcrops (150X and 174AX) that constitute the Mid-Atlantic Sea-level Transect. The primary goals of the transect are (1) to date sequence boundaries of Oligocene to Holocene age and compare this stratigraphic record with the timing of glacial-eustatic changes inferred from deep-sea d18O variations; (2) to place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; (3) to assess the relationships between depositional facies and sequence architecture; and (4) to provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive margins. Site 1071 provides information primarily about late middle Miocene and younger sequences at locations landward of their respective rollovers/breakpoints, the positions at which each sequence boundary steepens seaward into a clinoform

4. Site 1072

Site 1072 is the second of two sites approved for JOIDES Resolution drilling on the New Jersey continental shelf; together with Site 1071, it forms part of a transect of holes from the slope (Ocean Drilling Program [ODP] Leg 150) to coastal outcrops (Legs 150X and 174AX) that constitute the Mid-Atlantic Sea-level Transect. The primary goals of the transect are to: (1) date sequence boundaries of Oligocene to Holocene age and compare this stratigraphic record with the timing of glacial eustatic changes inferred from deep-sea d18O variations; (2) place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; (3) assess the relationships between depositional facies and sequence architecture; and (4) provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive margins. Site 1072 is ~3.5 km seaward of Site 1071 and coincides with the rollover or breakpoint in sequence boundary m0.5(s). This site provides information primarily about upper Miocene and younger strata and permits a comparison, in the direction of progradation, with the succession at Site 1071

The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone

The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and fi eld studies in accretionary wedges. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. The total thickness encompassing all simultaneously active strands increases to ~100–350 m at ~1–2 km below seafl oor, and this thickness is maintained down to a depth of ~15 km. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-ofmeters- thick fault strands. Although fl attening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. These observations suggest that models should treat the subduction thrust plate boundary fault as <1–20 cm thick during earthquakes, with a concentration of postseismic and interseismic creep in single to several strands 5–35 m thick, with lesser distributed interseismic deformation in stratally disrupted rocks surrounding the fault strands

Ontong Java Plateau, Leg 130: Synopsis of major drilling results

Sixteen holes were drilled at five sites on the northeastern flank of Ontong Java Plateau during Leg 130 (Sites 803 through 807). All of these sites are near the equator, but are at different depths (803: 02°26.0\u27N, 3410 m; 804: 01°00.3\u27N, 3861 m; 805: 01°13.7\u27N, 3188 m; 806: 00°19.1\u27N, 2520 m; and 807: 03°36.4\u27N, 2805 m). One of our goals was to obtain a depth transect of Neogene carbonate deposition for reconstructing the history of ocean climate, chemistry, and productivity, and for understanding the origin of acoustic reflectors. Another goal was to achieve considerable penetration into basement for elucidating the origin of the plateau. All sites yielded multiple Neogene sequences, which were cored using the advanced hydraulic piston corer (APC) to the ooze-chalk transition (10-14 Ma) and with the extended core barrel (XCB) below that. Sites 803 and 807 were drilled to basement and yielded incomplete Paleogene and Cretaceous sections. Penetration into basement was 25 m at Site 803 and 149 m at Site 807; 98 m of basalt was recovered. In all, we cored 5889 m, taking 639 cores. Of the record 4822 m recovered, 55% was taken with the APC, 39% with the XCB, and 6% with the rotary core barrel (RCB). All sites except Site 804 were logged. Neogene sedimentation rates were found to vary by more than a factor of 2, with a striking maximum in the latest Miocene to early Pliocene and a strong minimum in the Pleistocene. Fluctuations in carbonate content on the millionyear scale are highly coherent among depths over the last 12 m.y., perhaps less so before that. Many acoustic reflectors appear synchronous with carbonate reduction events (CREs) and other paleoceanographic events. Other reflectors are tied to diagenesis (e.g., the ooze-chalk transformation, which is diachronous). Recovery of the Cretaceous/Tertiary (K/T) boundary at Sites 803 and 807 demonstrates the presence of a deep carbonate-compensation depth (CCD) across the transition: one sequence is calcareous, the other is not. Because the K/T sections occur below and above major hiatuses, we postulate that special conditions for preservation existed during the transition. In addition, there is evidence of volcanic activity at that time. The basalts cored at Sites 803 and 807 are predominantly olivine-bearing and were erupted during the mid-Cretaceous. At Site 807, pillow lavas buried sediments. One thick flow (at about 28 m) was penetrated here, apparently a flood basalt. Magnetic paleolatitudes suggest that the Ontong Java Plateau has moved coherently with the Pacific Plate since the Early Cretaceous