Physical Sciences and Mathematics Commons^™

Core-Log-Seismic Integration As A Framework For Determining The Basin-Wide Significance Of Regional Reflectors In The Eastern Equatorial Pacific, Stephen F. Bloomer, Larry A. Mayer

Affiliate Scholarship

ODP Leg 138 in the eastern equatorial Pacific (EEP) provided a unique opportunity to understand the paleoceanographic significance of seismic reflectors in this climatically sensitive region. Carefully offset multiple cores were spliced into a complete stratigraphic section for the upper 250 m at each site and accurate, astronomically tuned time scales were generated from these composites. Well log data provided a means to correct composite depths to true depths as well as density and velocity data for the generation of synthetic seismograms. These synthetic seismograms were used to determine the paleoceanographic significance of regionally traceable reflectors by linking variations in …

Swath Mapping On The Continental Shelf And Slope: The Eel River Basin, Northern California, John A. Goff, Larry A. Mayer, John E. Hughes Clarke, Lincoln F. Pratson

Affiliate Scholarship

First Paragraph

The STRATAFORM program sponsored by the Office of Naval Research (Nittrouer and Kravitz, 1996, this issue) seeks to understand how sedimentary processes lead to the formation of the stratigraphic sequences on continental margins. A central challenge facing this effort is to understand the transport of sediments in shore-parallel as well as shore-perpendicular directions• Multidimensionality is necessary to describe, for example, the accumulation of sediments from river inputs, the distribution of gullies and canyons on the slope, the meandering of channels, and the structure of slumps and slides.

1995, Spatial And Temporal Variability Of Late Neogene Equatorial Pacific Carbonate, T. K. Hagelberg, Nicklas G. Pisias, Larry A. Mayer, N. J. Shackleton, Alan C. Mix

Affiliate Scholarship

High-resolution, continuous records of GRAPE wet bulk density (a carbonate proxy) from Ocean Drilling Program Leg 138 provide one the opportunity for a detailed study of eastern equatorial Pacific Ocean carbonate sedimentation during the last 6 m.y. The transect of sites drilled spans both latitude and longitude in the eastern equatorial Pacific from 90° to 110°W and from 5°S to 10°N. Two modes of variability are resolved through the use of Empirical Orthogonal Function (EOF) analysis. In the presence of large tectonic and climatic boundary condition changes over the last 6 m.y., the dominant mode of spatial variability in carbonate …

Paleoceanography Of The Eastern Equatorial Pacific During The Neogene: Synthesis Of Leg 138 Drilling Results, Nicklas G. Pisias, Larry A. Mayer, Alan C. Mix

Affiliate Scholarship

The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north-south transects were drilled (95° and 110°W) within the region of equatorial divergence-driven upwelling (and thus high accumulation rates and resolution) and spanning the major equatorial ocean current boundaries (and thus recording a high-amplitude signal of the response of the sediment to climatically and/or tectonically driven changes in ocean circulation). The Neogene is marked by a number of well-known climatic and tectonic events (the closing of the Isthmus of Panama, the onset of North Atlantic Deep Water …

Seismic Stratigraphy Of The Eastern Equatorial Pacific Ocean: Paleoceanographic Implications, Stephen F. Bloomer, Larry A. Mayer, Ted C. Moore Jr

Affiliate Scholarship

The collection of Leg 138 well-log and shipboard physical-property data, in conjunction with high-resolution seismic profiles, provides an opportunity to understand the paleoceanographic significance of seismic reflectors and to gain insight into the paleoceanographic evolution of the eastern equatorial Pacific Ocean. A series of eight reflectors or reflector packages were traced between two transects connecting five Leg 138 sites. By generating synthetic seismograms at each of these sites and comparing these to the field records, the origin of these seismic reflectors was determined in terms of physical-property variations and other core measurements. In particular, these reflectors were usually associated with …

Acoustic Properties Of Fine‐Grained Sediments From Emerald Basin: Toward An Inversion For Physical Properties Using The Biot–Stoll Model, Robert C. Courtney, Larry A. Mayer

Affiliate Scholarship

Acoustic data from two long cores, comprising marine clays and silts taken from Emerald Basin off Nova Scotia, are presented. High‐resolution measurements of compressional wavevelocity,attenuation, and power law exponent are made using ultrasonic frequencies between 100 to 1000 kHz. The observed values of the frequency dependence of attenuation suggest that a nonconstant Q mechanism is needed to explain these data, and Biot–Stoll theory is used to model the experimental results. An inversion scheme is used to constrain physical parameters in the Biot–Stoll dispersion relation. The inversion shows that there is a restricted range of permeability and grain size. By assigning …

Calculation Of Acoustic Parameters By A Filter-Correlation Method, Robert C. Courtney, Larry A. Mayer

Affiliate Scholarship

This paper presents the filter correlation method, a technique for extracting consistent and accurate estimates of attenuation parameters from acoustic waveform data. The method minimizes problems associated with short time windows and multipath secondary arrivals. The method comprises two stages: a causal passband filter stage followed by a cross-correlation step. The results of the filter-correlation estimator are compared to those of the spectral difference approach for short time series with and without a secondary multipath arrival. Preliminary analyses of acoustic data collected on cored marine silts and clays show the attenuation properties of these materials cannot be described by a …

Laboratory And Well-Log Velocity And Density Measurements From The Ontong Java Plateau: New In-Situ Corrections To Laboratory Data For Pelagic Carbonates, Jozsef Urmos, Roy H. Wilkens, Frank Bassinot, Mitchell Lyle, Janice C. Masters, Larry A. Mayer, David Mosher

Affiliate Scholarship

During Ocean Drilling Program Leg 130, sonic velocity and bulk density/porosity well logs were measured in five separate holes drilled through the sequence of pelagic carbonate oozes, chalks, and limestones that comprise the thick, continuous sedimentary cover on the Ontong Java Plateau. An internally consistent and continuous suite of shipboard laboratory velocity and sediment physical properties measurements were made from the top of each hole down through the entire logged interval. Because of the high quality of the data, extensive overlap of 500 m or more between the log and laboratory measurements at each hole, and the homogeneous nature of …

Evolution Of Pliocene Climate Cyclicity At Hole 806b (5-2 Ma); Oxygen Isotope Record, Eystein Jansen, Larry A. Mayer, Jan Backman, R. Mark Leckie, Toshiaki Takayama

Affiliate Scholarship

A detailed Pliocene oxygen isotope record from the Ontong Java Plateau, based on measurements of the surface-dwelling planktonic foraminifer Globigerinoides sacculifer, was produced for the period from 5 to 2 Ma. The record documents major long and short-term climate changes. The results show periods of enhanced ice volume at 4.6 to 4.3 Ma and after 2.85 Ma, a long-term warming trend from 4.1 to 3.7 Ma, and a distinct cooling trend that was initiated at 3.5 Ma and progressed through the initiation of large-scale Northern Hemisphere glaciation after 2.85 Ma (according to the time scale of Shackleton and others proposed …

Seismic Stratigraphy Of The Ontong Java Plateau, David Mosher, Larry A. Mayer, Tom H. Shipley, Edward L. Winterer, Rick A. Hagen, Janice C. Marsters, Frank Bassinot, Roy H. Wilkens, Mitchell Lyle

Affiliate Scholarship

The Ontong Java Plateau, a large, deep-water carbonate plateau in the western equatorial Pacific, is an ideal location for studying responses of carbonate sedimentation to the effects of changing paleoceanographic conditions. These carbonate responses are often reflected in the physical properties of the sediment, which in turn control the appearance of seismic reflection profiles. Seismic stratigraphy analyses, correlating eight reflector horizons to each drill site, have been conducted in an attempt to map stratigraphic data. Accurate correlation of seismic stratigraphic data to drilling results requires conversion of traveltime to depth in meters. Synthetic seismogram models, using shipboard physical properties data, …

Velocity Anisotropy In Calcareous Sediments From Leg 130, Ontong Java Plateau, Frank Bassinot, Janice C. Marsters, Larry A. Mayer, Roy H. Wilkens

Affiliate Scholarship

During Leg 130, an intensive program of P-wave velocity measurements was conducted on calcareous sediments of varying induration (ranging from ooze to limestone) that cover the Ontong Java Plateau (west equatorial Pacific). The high quantity and quality of shipboard acoustical property measurements seemed to be particularly appropriate for gaining a better understanding of acoustic anisotropy in calcareous sediments. Major results can be summarized as follows: 1. In calcareous oozes, acoustic anisotropy exists even at shallow depths of burial. Values are low, ranging from -0.5% to 3.5% and averaging 1.2%. Anisotropy profiles are affected by coring disturbances, but they still roughly …

Climatic Cyclicity At Site 806; The Grape Record, Larry A. Mayer, Eystein Jansen, Jan Backman, Toshiaki Takayama

Affiliate Scholarship

We used the continuous saturated bulk density records collected by the gamma-ray attenuation porosity evaluator (GRAPE) at Ocean Drilling Program Site 806 on the top of the Ontong Java Plateau to evaluate the continuity of the recovered cores and to splice together a complete section from the multiple holes drilled at the site (for the upper 165 m, this is equivalent to approximately 0-5 Ma). The lack of offset in core breaks (between the 9.5-m-long, successive cores) from hole to hole made splicing difficult, and the results are not unambiguous. The composite section was converted to a time series by …

Variations Of Porosity In Calcareous Sediments From The Ontong Java Plateau, Frank Bassinot, Janice C. Marsters, Larry A. Mayer, Roy H. Wilkens

Affiliate Scholarship

Based on index properties measurements made on board the JOIDES Resolution, we studied porosity changes with depth in the fairly homogeneous deep-sea calcareous sediments cored during Ocean Drilling Program Leg 130 on the Ontong Java Plateau. Using Leg 130 data, we present evidence that the rate of porosity decrease with burial in calcareous oozes and chalks is related to the depth of deposition and thus probably depends on the "conditioning" of calcareous sediments by winnowing or dissolution processes during the time of deposition. The ooze-to-chalk transition is not clearly reflected in porosity profiles. In the ooze-chalk sections studied (the upper …

Basement Structure Of The Northern Ontong Java Plateau, Rick A. Hagen, Larry A. Mayer, David Mosher, Loren W. Kroenke, Tom H. Shipley, Edward L. Winterer

Affiliate Scholarship

Site surveys conducted in conjunction with Leg 130 on the Ontong Java Plateau reveal a strong seismic reflector at 0.8 to 1.0 s below the seafloor that drilling at Sites 803 and 807 confirmed is Cretaceous basalt. This reflector is generally smooth, except for the northeastern margin of the plateau, where it forms a series of small, irregularly shaped depressions. Correlatable reflectors present at the bottom of the depressions are also present on the adjacent highs, suggesting that these depressions are original volcanic topography. A strong sub-basalt reflector occurs on many seismic profiles on the northeastern portion of the plateau. …

Detailed Stratigraphic Correlation Of The Neogene Sedimentary Sequences On The Ontong Java Plateau By Well Logging; Odp Sites 803, 805, 806, 807, And Dsdp Site 586, Mitchell Lyle, Roy H. Wilkens, Larry A. Mayer

Affiliate Scholarship

We used well logs, in some cases combined with shipboard physical properties measurements to make more complete profiles and to correlate between sites on the Ontong Java Plateau. By comparing sediment bulk density, velocity, and resistivity logs from adjacent holes at the same site, we showed that even subtle features of the well logs are reproducible and are caused by variations in sedimentation. With only minor amounts of biostratigraphic information, we could readily correlate these sedimentary features across the entire top of the Ontong Java Plateau, demonstrating that for most of the Neogene the top of the plateau is a …

Downhole Logging As A Paeoceanographic Tool On Ocean Drilling Program Leg 138: Interface Between High-Resolution Stratigraphy And Regional Syntheses, Mitchell Lyle, Larry A. Mayer, Nicklas G. Pisias, T. K. Hagelberg, Kathleen A. Dadey, Stephen F. Bloomer, Shipboard Scientific Party

Affiliate Scholarship

On Ocean Drilling Program (ODP) Leg 138, standard shipboard procedures were modified to allow for the real-time monitoring of several laboratory core-scanning systems that provide centimeter-scale measurements of saturated bulk density, magnetic susceptibility and digital color reflectance. These continuous, high-resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections. Typically, the spliced, continuous sediment sections were found to be about 10% longer than the section drilled, as measured by the length of the drill string. While the source of this elongation is not yet fully understood, it must be compensated …

Marine Sediment Classification Using The Chirp Sonar, Lester R. Leblanc, Larry A. Mayer, Manuel Rufino, Steven G. Schock, John King

Affiliate Scholarship

The chirpsonar is a calibrated wideband digital FMsonar that provides quantitative, high‐resolution, low‐noise subbottom data. In addition, it generates an acoustic pulse with special frequency domain weighting that provides nearly constant resolution with depth. The chirpsonar was developed with the objective of remote acoustic classification of seafloor sediments. In addition to producing high‐resolution images, the calibrated digitally recorded data are processed to estimate surficial reflection coefficients as well as a complete sediment acoustic impulse profile. In this paper, surficial sediments in Narragansett Bay, RI are used to provide ground truth for an acoustic model. Quantitative acoustic returns from the chirpsonar …

Seabeam And Seismic Reflection Surveys On The Ontong Java Plateau, Larry A. Mayer, Tom H. Shipley, Edward L. Winterer, David Mosher, Rick A. Hagen

Affiliate Scholarship

No abstract provided.

Grape Density Records And Density Cyclicity, Eystein Jansen, Larry A. Mayer, Shipboard Scientific Party

Affiliate Scholarship

No abstract provided.

High-Resolution, Whole-Core Magnetic Susceptibility Data From Leg 130, Ontong Java Plateau, John A. Tarduno, Larry A. Mayer, Robert Musgrave

Affiliate Scholarship

High-resolution, whole-core magnetic susceptibility data, recorded at 3-cm intervals, were obtained for advanced hydraulic piston (APC) cores at Sites 805, 806, and 807 of Leg 130 on the Ontong Java Plateau. In this initial report, we present a preliminary evaluation of these data for their use in core correlations and paleoclimatic studies. The data allow detailed intrasite correlations between the offset APC cores and provide a means for intersite correlations of Pleistocene sediments. Variations in magnetic susceptibility values probably mirror variations in terrestrial influx and may act as proxy indicators of climate. Highly coherent cyclicity, representing Milankovitch orbital frequencies, is …

Ontong Java Plateau, Leg 130: Synopsis Of Major Drilling Results, W. H. Berger, Loren W. Kroenke, Larry A. Mayer, Shipboard Scientific Party

Affiliate Scholarship

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'N, 3410 m; 804: 01°00.3'N, 3861 m; 805: 01°13.7'N, 3188 m; 806: 00°19.1'N, 2520 m; and 807: 03°36.4'N, 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 …

Chirp Subbottom Profiler For Quantitative Sediment Analysis, Steven G. Schock, Lester R. Leblanc, Larry A. Mayer

Affiliate Scholarship

A wide‐band, frequency‐modulated, subbottom profiling system (the chirp sonar) can remotely determine the acoustic attenuation of ocean sediments and produce artifact‐free sediment profiles in real time. The chirp sonar is controlled by a minicomputer which performs analog‐to‐digital and digital‐to‐analog conversion, correlation processing, and attenuation estimation in real time. The minicomputer generates an FM pulse that is phase‐ and amplitude‐compensated to correct for the sonar system response. Such precise waveform control helps suppress correlation noise and source ringing. The chirp sonar, which has an effective bandwidth of 5 kHz, can generate chirp (Klauder) wavelets with a tuning thickness (Rayleigh’s criterion for …

Pisces Iv Submersible Observations In The Epicentral Region Of The 1929 Grand Banks Earthquake, John E. Hughes Clarke, Larry A. Mayer, David J.W. Piper, Alexander N. Shor

Affiliate Scholarship

The PISCES IVsubmersible was used to investigate the upper continental slope around 44 ON, 56" W, near the epicentre of the 1929 Grand Banks earthquake. Four dives in water depths of 800-2000 m were undertaken to observe speci3c features identijied with the SeaMARC I sidescan system in 1983. Two dives were made in the head of Eastern Valley where pebbly mudstones ofprobable Pleistocene age were recognized outcropping on the seafloor. Constructional features of cobbles and boulders, derived by exhumation and reworking of the pebbly mudstone, were also observed. These include gravel/sand bedforms (transverse waves) on the valley floor. Slope failure …

Lithostratigraphy, Biostratigraphy, And Stable-Isotope Stratigraphy Of Cores From Odp Leg 105 Site Surveys, Labrador Sea And Baffin Bay, D. B. Scott, P. J. Mudie, A. De Vernal, C. Hillaire-Marcel, V. Baki, K. D. Mackinnon, F. S. Medioli, Larry A. Mayer

Affiliate Scholarship

Trigger weight (TWC) and piston (PC) cores obtained from surveys of the three sites drilled during Ocean Drilling Program (ODP) Leg 105 were studied in detail for benthic foraminiferal assemblages, total carbonate (all sites), planktonic foraminiferal abundances (Sites 645 and 647), and stable isotopes (Sites 646 and 647). These high-resolution data provide the link between modern environmental conditions represented by the sediment in the TWC and the uppermost cores of the ODP holes. This link provides essential control data for interpretating late Pleistocene paleoceanographic records from these core holes. At Site 645 in Baffin Bay, local correlation is difficult because …

The Influence Of Biogenic Silica On Seismic Lithostratigraphy At Odp Sites 642 And 643, Eastern Norwegian Sea, Peter Hempel, Larry A. Mayer, Elliot Taylor, Gerhard Bohrmann, Alan Pittenger

Affiliate Scholarship

Drilling at ODP Sites 642 and 643 revealed a 250 m-thick section of diatomaceous Pliocene to Miocene sediments on the outer Vdring Plateau, eastern Norwegian Sea. These biogenic silica-rich sediments have a significantly lower saturated bulk density than the surrounding sediments, causing a decrease in acoustic impedance, which is seismically expressed as a negative polarity reflection. Variations in sonic velocity, the other key parameter in seismic analysis, is only of secondary importance in creating impedance contrasts in our study. Synthetic seismograms were produced from shipboard physical property measurements corrected for in situ conditions. These synthetic seismograms are in good agreement …

Geologic And Tectonic Setting Of The Mark Area, R. S. Detrick, P. J. Fox, N. Schulz, R. Pockalny, L. Kong, Larry A. Mayer, W.B. F. Ryan

Affiliate Scholarship

No abstract provided.

Cenozoic Paleoceanography 1986: An Introduction, W. H. Berger, Larry A. Mayer

Affiliate Scholarship

New developments in Cenozoic paleoceanography include the application of climate models and atmospheric general circulation models to questions of climate reconstruction, the refinement of conceptual models for interpretation of the carbon isotope record in terms of carbon mass balance, paleocirculation, paleoproductivity, and the regional mapping of paleoceanographic events by acoustic stratigraphy. Sea level change emerges as a master variable to which changes in the ocean environment must be traced in many cases, and tests of the onlap-offlap paradigm therefore are of crucial importance.

The Equatorial Pacific High-Productivity Belt: Elements For A Synthesis Of Deep Sea Drilling Project Leg 85 Resultspaleoceanography, Fritz Theyer, Larry A. Mayer, John A. Barron, Ellen Thomas

Affiliate Scholarship

Leg 85 of the Deep Sea Drilling Project operated in the eastern central Pacific in the region of the equatorial highproductivity belt. We recovered uppermost Eocene to Quaternary reference sections amenable to fine-scale stratigraphic and paleoceanographic research, using primarily the hydraulic piston corer. Four sites (572 to 575) were drilled along an east-west (about 114 to 133°W) and north-south (about 0.5 to 6°N) transect across the equatorial belt. At Site 572 an apparently complete lower middle Miocene to Quaternary sequence was recovered: the sediment sections are dominantly siliceous-calcareous oozes and chalks, and sediment accumulation rates were high (30 to 60 …

Seismic Modelling And Paleoceanography At Dsdp Site 574, Larry A. Mayer, Tom H. Shipley, Fritz Theyer, Roy H. Wilkens, Edward L. Winterer

Affiliate Scholarship

The analysis of high-resolution watergun seismic profiles collected in support of DSDP Leg 85 drilling reveals sev eral major, regionally traceable reflectors that can be correlated over more than 360,000 km2 in the central equatorial Pacific. Synthetic seismograms generated from shipboard physical property measurements (carefully corrected to in situ values) for DSDP Site 574 show excellent agreement with the field records; the agreement suggests that the traveltime to-depth conversion is accurate and permits the precise (± 5 m) location of reflectors in the cored section. The reflectors can be dated (±0.5 Ma) as follows: Orange, 21.5 to 22.5 Ma; Yellow, …

Initial Reports Of The Deep Sea Drilling Project, Vol. 85, Larry A. Mayer, Fritz Theyer, John A. Barron, Dean A. Dunn, Tim Handyside, Scott Hills, Ian Jarvis, Catherine A. Nagrini, Nicklas G. Pisias, Annick Pujos, Tsunemasa Saito, Paul Stout, Ellen Thomas, Norbert Weinreich, Roy H. Wilkens

Affiliate Scholarship

Covering Leg 85 of the cruises of the Drilling Vessel Glomar Challenger Los Angeles, California, to Honolulu, Hawaii March-April 1982.

Includes six chapters:

1. INTRODUCTION: BACKGROUND AND EXPLANATORY NOTES, DEEP SEA DRILLING PROJECT LEG 85, CENTRAL EQUATORIAL PACIFIC

2. SITE 571

3. SITE 572

4. SITE 573

5. SITE 574

6. SITE 575