SEMINAR - R. Mark Leckie

Closure of the Indonesian Seaway during the Miocene: Early History of the Western Pacific Warm Pool

R. Mark Leckie
Department of Geosciences
University of Massachusetts, Amherst

Wednesday, May 7th, 2008

We document the waxing and waning of a ‘proto-Western Pacific Warm Pool’ and Equatorial Undercurrent (EUC) based on a study of multi-species planktic foraminiferal isotope ratios and census data spanning the 13.2-5.8 Ma interval at ODP Site 806 in the western equatorial Pacific (WEP). We hypothesize that the presence or absence of a proto-warm pool in the WEP, caused by the progressive tectonic constriction of the Indonesian Seaway and modulated by sea level fluctuations, created El Niño/La Niña-like alternations of hydrographic conditions across the equatorial Pacific during the late Miocene. This hypothesis is supported by the general antithetical relationship observed between carbonate productivity and preservation in the western and eastern equatorial Pacific, a phenomenon caused by these alternating ocean-climate states in the modern ocean. The two-step development and intensification of a proto-warm pool 11.6-9.6 Ma coincides with ice sheet expansion associated with Miocene isotope events Mi5 and Mi6, resulting in a cumulative sea level fall of 50 m and production of Northern Component Water. It also marks the initiation of a more modern equatorial current system as La Niña-like conditions became established across the tropical Pacific. This situation sustained carbonate and silica productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening after 10 Ma may have contributed to the nadir of a similar ‘carbonate crash’ in the EEP. Decay of the proto-warm pool and resultant El Niño-like conditions brought higher productivity to the WEP, particularly 9.0-8.8 Ma coincident with a major perturbation in tropical nannofossil assemblages. This interval of increased productivity records the initial phase of the widespread ‘biogenic bloom’. Resurgence of a later proto-warm pool in the WEP 6.5-6.1 Ma may have spurred renewed La Niña-like conditions, which contributed to a strong late phase of the ‘biogenic bloom’ in the EEP.

SEMINAR - Daniel Brothers

Imaging the fault structure and earthquake history beneath the Salton Sea

Daniel S. Brothers
Scripps Institution of Oceanography
Institute of Geophysics and Planetary Physics
University of California, San Diego

April 30th, 2008

The Salton Sea, California, covers an important section of the plate boundary where the Gulf of California ridge-transform system to the south transitions into the San Andreas strike-slip system to the north. However, this transition zone is poorly understood due to an absence of detailed geological and geophysical data beneath the Sea. To constrain deformation models and seismic hazards in this region we need to define the location, kinematics and rupture history of faults beneath the Sea and determine how these structures affect stress conditions along major faults in the region, such as the San Andreas and San Jacinto.

High-resolution seismic reflection data collected in 2006 and 2007 provide the first regional-scale imagery of faulting and stratigraphy beneath the Salton Sea. Seismic profiles reveal structural features that were previously unknown, including the continuation of the Extra Fault Zone (EFZ) between the San Felipe Hills and Durmid Hill, as well as several faults and seafloor scarps in the Brawley Seismic Zone. By correlating acoustic marker beds in the seismic data with stratigraphy documented in paleoseismic trenches onshore, we are able to constrain both the depositional history and the timing of past earthquakes beneath the Sea.

Thesis Defense - Spring 2008 - Adam Cosentino

Detrital zircon U-Pb geochronology of Paleozoic prebatholithic rocks in the northeastern Peninsular Ranges of Southern and Baja California

Adam Cosentino
M.S. Candidate
Department of Geological Sciences
San Diego State University

Friday, April 25th

ABSTRACT
In the northern Peninsular Ranges of southern and Baja California carbonate - quartzite dominated prebatholithic assemblages display lithologic similarities to in-situ cratonic North American miogeoclinal sequences. Correlation of the Peninsular Ranges rocks to the miogeocline and offshore equivalents however has proven difficult due to pervasive metamorphism and structural disruption associated with Cretaceous batholith emplacement. This study utilizes detrital zircon laser ablation ICPMS U-Pb ages to constrain the provenance and age of the Peninsular Ranges assemblages and make regional stratigraphic correlations in insitu North American rocks.
This study is focused on two main stratigraphic packages that represent the thickest and most complete prebatholithic assemblages within this ~350 km-long carbonate - quartzite belt: the Desert Divide Group (DDG) in the north and the Playa San Felipe Group (PSFG) in the south. The DDG at the northern end of the belt is divided into the structurally lower Bull Canyon Formation, comprised of schist, carbonate, and quartzite, and the structurally higher Ken Quartzite, an ~ 700 m thick package of relatively pure quartzite. Upper amphibolite metamorphism has obliterated fossils and sedimentary structures and the relationship between the Bull Canyon Fm and Ken Quartzite has remained uncertain. Detrital zircon U-Pb ages from closely spaced samples within an ~250 m thick section across the Bull Canyon-Ken Quartzite contact record a shift in provenance that matches closely a major Middle Ordovician regional detrital zircon provenance shift associated with the onset of “Peace River Arch” detritus. This shift is documented widely throughout the Cordilleran miogeocline (associated with the Eureka Quartzite) and the timing of the shift is so far best documented from the Vinini Formation where it occurs in the mid to late Middle Ordovician.
Detrital zircon U-Pb age spectra from PSFG Unit G quartzite (~430 m thick) yield a post shift, Peace River Arch signature which verifies previous detrital zircon studies on this unit. The close match of Unit G and the Ken Quartzite zircon spectra suggests these are correlative units. It also raises the possibility that the detrital zircon shift from the Bull Canyon to the Ken Quartzite in the DGG may be present in the PSFG.
Results from PSFG Unit A quartzite yield a maximum depositional age of Late Devonian based on 3 concordant grains at ~376 Ma. This result suggests that there are much younger Paleozoic stratigraphic elements in the PSFG than has been previously recognized as well as unrecognized structural complications in the area. The Unit A rocks may have correlatives in late Paleozoic sequences documented from the Sierra Las Pintas area ~85 km to the north.
Detrital zircon ages were also determined from an olistolith quartzite block deposited into early Mesozoic prebatholithic flysch near Rancho San Marcos in northern Baja California. The quartzite here is associated with carbonates that have yielded late Early Ordovician conodonts; this sample yields a “pre-shift” detrital zircon spectra consistent with the fossil age call.

SEMINAR - Wesley Danskin

Real-time Ground-water Management in San Diego




Wesley R. Danskin
Research Hydrologist
U.S. Geological Survey




April 23rd, 2008

• Advances in real-time monitoring of ground-water systems have improved the ability of local water managers to make timely decisions regarding recharge and pumpage. The goal is to avoid expensive problems, improve knowledge of the local aquifer, and to provide managers with real-time ground-water levels. Data are collected from each transducer every 15 minutes, and are transmitted via the satellite to the database every four hours. This easy access to real-time data from wells located three-dimensionally throughout the aquifer help enable water managers to make informed decisions regarding how much water to import from northern California, where to discharge imported water for artificial recharge, and how much and where to pump ground water for municipal supply.

Professional Expertise:

• Optimal water management
• Ground-water simulation, constrained optimization
• Hydrogeologic analysis of regional systems
• Integrated surface-water/ground-water interpretations
• Conflict resolution, technical mediation of water issues
• USGS offices: Alaska (1978-79), Menlo Park (1979-84), San Diego (1985-present).
• Project Chief: all projects, listed below, involve optimal water-management, regional systems, surface-water/ground-water interaction, and conflict resolution.
• Advising: Optimal management of regional ground-water systems: Texas, New Mexico, Nebraska, Hashemite Kingdom of Jordan
• Teaching: Optimal ground-water management training courses (1994, 1997, 2005-07)
  

Research Interests:

• Real-world application of constrained optimization techniques
• Real-time water management
• Conflict resolution of water issues
• Integrated management of biologic/hydrologic resources
• Land deformation caused by ground-water recharge/extraction
  

Projects:

• San Bernardino Optimal Basin Management - http://ca.water.usgs.gov/sanbern
• San Diego Hydrogeology - http://ca.water.usgs.gov/sandiego
• Owens Valley - http://ca.water.usgs.gov/owens
• Temecula - http://ca.water.usgs.gov/temecula
• Enhancing Ground-water Management in Jordan - http://international.usgs.gov/projects/jd-groundwater.htm

SEMINAR - John Warme

Interpretation and Significance of Cretaceous and Eocene Coastal Outcrops, San Diego County

John E. Warme
Professor Emeritus, Colorado School of Mines, Golden, Colorado

April 16th, 2008

The Upper Cretaceous and Eocene formations that crop out along seacliffs and landward in San Diego County have been studied and reinterpreted several times over the last century. By the 1970's they were regarded as prime examples of lateral facies relationships from continental to deep marine, then reinterpreted as pioneering examples of sedimentary intervals separated by significant surfaces that formed discrete unconformity-bounded intervals, or sequences, of the evolving concept of Sequence Stratigraphy.

Cretaceous examples include the Point Loma thin bedded turbidites and mudstones and overlying Cabrillo Formation conglomerates that are still validly argued as genetically-related lateral facies, or conversely, completely separate sequences; these units require more analyses.

In contrast, the uppermost lower Eocene to upper Eocene series exhibit superb examples where unconformity surfaces that separate genetically unrelated intervals define stratigraphic "Sequences". However, such surfaces do not in every case follow the prior definitions of formation boundaries. One of several examples is the unconformity the cuts across the shallow-water to intertidal beds of the Delmar Formation and Torrey Sandstone and is overlain by a sandy and conglomeratic facies of the Ardath "Shale", which is interpreted as the floor of a fossil submarine canyon. Because petrographically similar sandstones occur above and below this surface, the beach-cliff outcrop was everywhere mapped as Torrey. Attention to bedding thicknesses and physical and biogenic sedimentary structures reveals that the sandstones below and above the newly recognized sequence boundary have very different character.

Of special interest is the variegated-fill channel system contained within the boundaries of this "Eocene Torrey Submarine Canyon"; the system is proposed as a submarine canyon facies model. Moreover, the unconformity that defines the boundaries of the canyon is the same age as bounding surfaces that contain canyons on several other continents, implying that they all formed during the same eustatic fall in sea level at about 49.5 million years ago, and all were the conduits that delivered coarse-grained sediments to coeval deep-basin submarine fans.

SEMINAR - Jennifer Lewis

Wide-azimuth seismic at the subsalt Jack asset: Is it worth the early investment?

Jennifer L. Lewis
Chevron Energy Technology Company, Houston, USA

April 9th, 2008

For decades, hydrocarbon accumulations beneath the Gulf of Mexico allochthonous salt canopy were largely considered implausible. The paradigm shift that success could be achieved in deepwater subsalt settings began in 1990 with the subsalt Mica discovery. Today, besides an expanding exploration portfolio, industry has the fortunate task of facing the many and variedfocusing on challenges of subsalt appraisal and development. With this transition comes the need for robust and accurate subsurface characterization. Beneath a salt canopy often many thousands of feet thick, this is a challenge from many viewpoints, from drilling and reservoir management to seismic imaging.

Answers to new and increasingly detailed questions are sought in an effort to minimize risk and optimize project value at a Chevron-operated Deepwater Gulf of Mexico field called Jack. The seismic data quality covering the field is typical of many subsalt images. Data at the reservoir level are low frequency (~10 Hz dominant) and contaminated with remnant multiple noise, making characterization of key reservoir uncertainties, e.g., faulting, an onerous undertaking at best. Recently, industry has recognized a step-change improvement in subsurface imaging in deepwater subsalt settings with wide-azimuth (WAz) towed streamer acquisition and processing. IntegratePresented with the opportunity for a similar improvement in the data quality over the Jack field, an integratedd modeling effort was undertakens, which includedincluding simple 1D synthetics, 3D ray tracing, and 2.5D finite difference models. While these analyses , facilitate the understanding comprehension of the advantages as well as the limitations of proposed WAz survey designs, they are not able to directly aid in the determination of the value that the improved data quality may have to the project. To help address the value of information, a parallel reservoir modeling project was conducted to, while simulated reservoir production models address the implications of acquiring a WAz survey prior to development decisions. Together, Tthese models provide an integrated analysis that can be used to means of effectively communicateing the impact and value of a WAz investment early in the appraisal phase of a project.

Pat Abbott Receives the Pacific Section SEPM Lifetime Achievement Award

Pat Abbott was presented with the A. Eugene Fritsche Lifetime Achievement Award from the Pacific Section SEPM at the AAPG Pacific Section meeting in Bakersfield. Presenter was Dr. Mario Caputo, Pacific Section SEPM's Secretary, Newsletter Editor, and Publication Sales Manager. Abbott is 3rd recipient of this prestigious award in recognition of his untiring devotion and service to the Pacific Section SEPM society. Pat served as President in 1989 and authored/edited serveral publications over his career here at SDSU.