Revised composite depth scale, Fe content and orbital tuning of Middle Eocene Climate Optimum samples from ODP Site 207-1260

A high-resolution stratigraphy is essential toward deciphering climate variability in detail and understanding causality arguments of events in earth history. Because the highly dynamic middle to late Eocene provides a suitable testing ground for carbon cycle models for a waning warm world, an accurate time scale is needed to decode climate-driving mechanisms. Here we present new results from ODP Site 1260 (Leg 207) which covers a unique expanded middle Eocene section (magnetochrons C18r to C20r, late Lutetian to early Bartonian) of the tropical western Atlantic including the chron C19r transient hyperthermal event and the Middle Eocene Climate Optimum (MECO). To establish a detailed cyclostratigraphy we acquired a distinctive iron intensity records by XRF scanning Site 1260 cores. We revise the shipboard composite section, establish a cyclostratigraphy and use the exceptional eccentricity modulated precession cycles for orbital tuning. The new astrochronology revises the age of magnetic polarity chrons C19n to C20n, validates the position of very long eccentricity minima at 40.2 and 43.0 Ma in the orbital solutions, and extends the Astronomically Tuned Geological Time Scale back to 44 Ma. For the first time the new data provide clear evidence for an orbital pacing of the chron C19r event and a likely involvement of the very long eccentricity cycle contributing to the evolution of the MECO.

Composite depth scale, tie points and magnetic susceptibilities of ODP Site 178-1098 sediments

Multiple holes were cored at Ocean Drilling Program Leg 178 Sites 1098 and 1099 in two subbasins of the Palmer Deep in order to recover complete and continuous records of sedimentation. By correlating measured properties of cores from different holes at a site, we have established a common depth scale, referred to as the meters composite depth scale (mcd), for all cores from Site 1098. For Site 1098, distinct similarities in the magnetic susceptibility records obtained from three holes provide tight constraints on between-hole correlation. Additional constraints come from lithologic features. Specific intervals from other data sets, particularly gamma-ray attenuation bulk density, magnetic intensity, and color reflectance, contain distinctive anomalies that correlate well when placed into the preferred composite depth scale, confirming that the scale is accurate. Coring in two holes at Site 1099 provides only a few meters of overlap. None of the data sets within this limited overlap region provide convincing correlations. Thus, the preferred composite depth scale for Site 1099 is the existing depth scale in meters below seafloor (mbsf).

(Table 22-30) Revised composite depth scales of IODP Sites 320-U1331, U1332, U1333, U1334 and ODP Sites 199-1218, 199-1219, 199-1220

Integrated Ocean Drilling Program (IODP) Expedition 320 recovered high-quality paleomagnetic records with over 800 dated reversals and decimeter-scale cyclic sediments which provide an outstanding framework to inter-calibrate major fossil groups and refine magnetic polarity chrons for the early Miocene, the entire Oligocene and the late Eocene Epoch. In order to reconstruct the climate history of the Equatorial Pacific one of the major objectives of the Pacific Equatorial Age Transect (PEAT) is the compilation of a Cenozoic Megasplice which integrates all available bio-, chemo-, and magnetostratigraphic data including key records from Ocean Drilling Program (ODP) Leg 199. Here we present extended post-cruise refinements of the shipboard composite depth scales and composite records of IODP Expedition 320 Sites U1331, U1332, U1333, U1334 as well as ODP Leg 199 Sites 1218, 1219 and 1220. The revised composite records were used to perform a site-to-site correlation and integration of Leg 199 and Exp. 320 sites. Based on this decimeter scale correlation a high resolution integrated paleomagnetic and biostratigraphic framework for the Equatorial Pacific is established covering the time from 20 to 40 Ma. This unprecedented sedimentary compendium from the Equatorial Pacific will be the backbone for paleoceanographic reconstructions for the late Paleogene.

Revised composite depth scales for ODP sites 198-1209, 198-1210 and 198-1211, Shatsky Rise

We present new revised composite depth scales for Ocean Drilling Program Leg 198 Sites 1209, 1210, and 1211, drilled at Shatsky Rise in the western Pacific Ocean. Reinterpretation of high-resolution physical property data, with the main focus on magnetic susceptibility as the primary parameter for hole-to-hole correlation, revealed that the shipboard composite records had to be revised below 124.87 meters composite depth (mcd) for Site 1209, below 142.45 mcd for Site 1210, and below 88.64 mcd for Site 1211. The revised composite records comprise Paleogene and Cretaceous sediments at all three sites. As a result of the additional adjustments, the revised mcd records of Sites 1209 and 1210 are 13.48 and 2.69 m longer than the original spliced records, respectively. The original splice of Site 1211 has undergone minor adjustments only to match those of Sites 1209 and 1210. Moreover, detailed correlation of sections outside the new spliced records enable samples already taken to be placed into the new revised composite depth scale.

Composite depth scales and splice tie points of ODP Sites 178-1095 and 178-1096

During Leg 178, multiple advanced piston corer holes were drilled at four sites (1095, 1096, 1098, and 1099). Cores from the holes were correlated on board to produce composite depths and optimal spliced sections, but the time limitations aboard ship caused these to be preliminary. Recomputed composite depths for Sites 1098 and 1099 in Palmer Deep are reported elsewhere in this volume (doi:10.2973/odp.proc.sr.178.2002). This paper reports recomputed composite depths and spliced sections for Sites 1095 and 1096, located on a sediment drift on the continental rise of the Pacific margin of the Antarctic Peninsula. Limits on the validity of the spliced sections arise from limited multiple coverage and possibly from the effects of ocean swell.

Automated composite depth scale reconstruction of ODP Leg 138 and 154 sites

A composite section, which reconstructs a continuous stratigraphic record from cores of multiple nearby holes, and its associated composite depth scale are important tools for analyzing sediment recovered from a drilling site. However, the standard technique for creating composite depth scales on drilling cruises does not correct for depth distortion within each core. Additionally, the splicing technique used to create composite sections often results in a 10-15% offset between composite depths and measured drill depths. We present a new automated compositing technique that better aligns stratigraphy across holes, corrects depth offsets, and could be performed aboard ship. By analyzing 618 cores from seven Ocean Drilling Program (ODP) sites, we estimate that ?80% of the depth offset in traditional composite depth scales results from core extension during drilling and extraction. Average rates of extension are 12.4 ± 1.5% for calcareous and siliceous cores from ODP Leg 138 and 8.1 ± 1.1% for calcareous and clay-rich cores from ODP Leg 154. Also, average extension decreases as a function of depth in the sediment column, suggesting that elastic rebound is not the dominant extension mechanism.

Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Composite depth scales, ash layer correlations and splice tie points of ODP Site 186-1151

We present composite depth scales for the multiply cored intervals from Sites 1150 and 1151. These new depth scales place coeval strata recovered in cores from different holes at a single site into a common stratigraphic framework. At Site 1150, double coring between Holes 1150A and 1150B occurred over only a short interval between ~703 and 713 meters below seafloor (mbsf), but this is sufficient to tie the upper portion of the stratigraphic section cored in Hole 1150A to the lower portion cored in Hole 1150B. The upper ~100 m of the sedimentary section at Site 1151 was double cored with the advanced piston corer and partially cored with the rotary core barrel, resulting in the complete recovery of this interval. The composite depth scales were constructed using Splicer software to vertically adjust the relative depths of various cores from one hole to the depths from another hole so as to align distinct physical properties measured on cores. The magnetic susceptibility data was the physical property most easily correlated between holes, and therefore primarily used to create a composite depth scale and spliced stratigraphic section. The spliced section is a continuous stratigraphic section constructed from representative cored intervals from the holes at a site. Both the splice and the composite depth scale can be applied to other data sets from Site 1151 to provide a stratigraphically continuous and laterally consistent basis for interpreting lithologic features or data sets. The resulting composite scale showed a 30% improvement in correlation of the magnetic susceptibility data relative to the original mbsf depth scale, and comparable improvement when applied to the other data sets.