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Geology topics

J.V. Gardner

Publications and source records attributed to J.V. Gardner.

At least 19 recordsLinked to original sources
USGS2017

Revised Ages for Laminated Sediment and a Holocene-Marker Diatom from the Northern California Continental Slope

Conventional and accelerator mass spectrometry 14C ages indicate that laminated sediment in three cores from the northern California continental slope near 38??N and 39??N were deposited between 42,000 and 25,000 yr B.P. This revises and refines our previous estimates that laminated sediment accumulated during the late Pleistocene to early Holocene (J. V. Gardner and E. Hemphill-Haley, 1986, Geology 14, 691-694). Preservation of laminated sediment on the upper slope in this area suggests a period of intense coastal upwelling, high primary productivity, and resultant depletion of oxygen in bottomwaters preceding the onset of global glacial conditions. The transition from Pleistocene to Holocene conditions, and the establishment of a modern climatic regime driven by the California Current, included the incursion of the subtropical diatom, Pseudoeunotia doliola. P. doliola is common in sediment younger than about 10,000 yr and thus is a reliable marker species for identifying Holocene deposits off northern California.

Quaternary Research↗
USGS2017

A climate-related oxidizing event in deep-sea sediment from the Bering Sea

Many cores from the deep basins of the Bering Sea have a thin oxidized zone within otherwise reduced sediment. This oxidized zone began to form about 6000 yr ago and represents an interval of about 3200 yr. Mineralogically, the oxidized and reduced sediments are similar, but chemically they differ. Concentrations of Fe and C are lower, and concentrations of Mn, Ba, Co, Mo, and Ni are higher in the oxidized than in the reduced sediment. Mn is enriched about 10-fold in the oxidized zone relative to its concentration in the reduced sediment, Mo about threefold, and Ba, Co, and Ni about twofold. These data suggest that the oxidized zone developed diagenetically as the result of the balance between the flux of organic matter and the available dissolved oxygen in bottom and interstitial waters. We propose that the Bering Sea was substantially ice covered when global glacial conditions prevailed. during the transition to global interglacial conditions, seasonal meltwater from thawing sea ice formed a lens of fresh water that decreased organic productivity. During the winter seasons, however, sea ice reformed and caused downwelling of dense, oxygen-rich waters to recharge bottom waters. The combination of lower organic productivity and more oxygen-rich bottom water allowed oxidized sediment to accumulate. Once full interglacial conditions were established, the volume of sea ice produced was insufficient to affect either productivity or the supply of dissolved oxygen and so bottom conditions again became reducing. Similar events probably occurred during the onset of global glacial conditions, and similar oxidized layers probably formed at these times. Such oxidized zones are highly unstable, however, in a reducing environment and, once buried beyond the influence of bacterial and infaunal activities, are depleted of their available oxygen and converted to reduced sediment.

Quaternary Research↗
USGS2017

Persistent late Pleistocene-Holocene seasonal upwelling and varves off the coast of California

Seasonal production of siliceous phytoplankton and a seasonal flux of terrigenous clastic material produced varved sediments along the continental slope off California during the late Pleistocene to mid-Holocene. Light-colored sediment within laminations and in sediment-trap samples was deposited during summer upwelling and contains an abundance of the diatoms Skeletonema costatum and Chaetoceros spp. resting spores. Dark-colored sediment deposited in the fall and winter contains abundant Thalassiosira pacifica, and has more terrigenous material. Distribution of diatoms in varves shows that seasonal upwelling has persisted along the California coast and has remained strongly seasonal since the late Pleistocene. ?? 1987.

Quaternary Research↗
USGS2017

The role of deep-water sedimentary processes in shaping a continental margin: The Northwest Atlantic

The tectonic history of a margin dictates its general shape; however, its geomorphology is generally transformed by deep-sea sedimentary processes. The objective of this study is to show the influences of turbidity currents, contour currents and sediment mass failures on the geomorphology of the deep-water northwestern Atlantic margin (NWAM) between Blake Ridge and Hudson Trough, spanning about 32° of latitude and the shelf edge to the abyssal plain. This assessment is based on new multibeam echosounder data, global bathymetric models and sub-surface geophysical information. The deep-water NWAM is divided into four broad geomorphologic classifications based on their bathymetric shape: graded, above-grade, stepped and out-of-grade. These shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope-accommodation. This descriptive method of classifying continental margins, while being non-interpretative, is more informative than the conventional continental shelf, slope and rise classification, and better facilitates interpretation concerning dominant sedimentary processes. Areas of the margin dominated by turbidity currents and slope by-pass developed graded slopes. If sediments did not by-pass the slope due to accommodation then an above grade or stepped slope resulted. Geostrophic currents created sedimentary bodies of a variety of forms and positions along the NWAM. Detached drifts form linear, above-grade slopes along their crests from the shelf edge to the deep basin. Plastered drifts formed stepped slope profiles. Sediment mass failure has had a variety of consequences on the margin morphology; large mass-failures created out-of-grade profiles, whereas smaller mass failures tended to remain on the slope and formed above-grade profiles at trough-mouth fans, or nearly graded profiles, such as offshore Cape Fear.

Marine Geology↗
USGS2012

Morphology and growth history of Delgada Fan: Implications for the Neogene evolution of Point Arena Basin and the Mendocino Triple Junction

Long-range side scan (GLORIA) sonographs and seismic reflection data acquired during a survey of the western U.S. Exclusive Economic Zone in 1984, coupled with information from Deep Sea Drilling Project sites, provide new insights into the growth and evolution of the Delgada Fan. Construction of the fan commenced in the latest Miocene (∼6 Ma) following the filling of the Neogene Point Arena Basin. The fan presently covers more than 50×10 3 km 2 of the Pacific plate and contains approximately 15×10 3 km 3 of predominantly terrigenous detritus. The large size of the fan is incompatible with the small present-day supply of sediment to the canyon system. The GLORIA data show the Delgada Fan to be a hybrid-type fan, exhibiting characteristics of both elongate and radial fans. The morphology and volume of the fan, along with evidence for a decline in accumulation rates on the lower fan during the Quaternary period, suggest that the fan experienced an early growth phase (latest Miocene and Pliocene) characterized by relatively rapid progradation of elongate fan lobes followed by a period (Quaternary) of slower growth that has featured a shift of depocenters to sites closer to the canyons and a transition to distributary channels bordered by less prominent levees and overbank deposits. We examine the growth of Delgada Fan in relation to the Neogene evolution of the North American-Pacific plate boundary using a series of paleogeographic reconstructions based on recently published time displacement histories of the Mendocino triple junction (MTJ), the San Andreas fault (SAF), and the Pacific plate, upon which the fan rests. The time displacement curves for the SAF and the MTJ suggest that the MTJ and Mendocino Fracture Zone overtook and passed Point Arena Basin at about 10 Ma when the basin lay immediately southwest of the present San Francisco Bay area. We suggest that the MTJ joined the SAF at approximately that time and location, thus making the SAF the master fault in the transform system. This interpretation is compatible with evidence from seismic reflection profiles over the fan, which demonstrate that the fan and the canyon system and therefore Point Arena Basin have moved as a unit since the inception of fan growth (∼6–7 Ma). Point Arena Basin lay southwest of the San Francisco area at 10–12 Ma, and the passage of the MTJ caused the disruption of the forearc shelf and slope and the development of local uplifted and subsiding blocks. In particular, uplift of the “bay block” immediately east of the SAF may have provided the source area for the late Miocene sediments that filled Point Arena Basin and set the stage for the growth of Delgada Canyon and Fan system. The growth rate of the fan has decreased, and the style of deposition has changed as the system was tectonically transported to its present location adjacent to the small youthful drainages of the King Range.

Journal of Geophysical Research Solid Earth↗
USGS2010

Biogenic sedimentation beneath the California Current system for the past 30 kyr and its paleoceanographic significance

A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33° to 42°N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO 3 , C org , and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model. Biogenic sedimentation shows responses that are sometimes time-transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decrease in CaCO 3 , C org , and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the North Pacific and western North America and the establishment of a strong seasonality in the central California region. A carbonate preservation event occurred at 10 ka that appears to reflect the uptake of CO 2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relatively strong coastal upwelling along the central California margin, relatively weak upwelling along the northern California margin, and the northward migration of the divergence zone of the West Wind Drift.

Paleoceanography and Paleoclimatology↗
USGS2005

Shelf-edge deltas and drowned barrier-island complexes on the northwest Florida outer continental shelf

A high-resolution multibeam survey of the northwest Florida shelf mapped six relict shelf-edge deltas, each with a drowned barrier-island system developed on its south and southwestern rims. The deltas appear to have formed during periods of sea-level stasis that occurred between 58,000 and 28,000 years ago. The barrier islands formed on the deltas during periods of slow regression during this same time interval. Large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas. The asymmetry and orientation of the dunes suggest that a northward-flowing current was sheared by the presence of the delta topography, and as a result, the upper layer of the flow continued to the north, whereas the lower layer was steered by the topography. The topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes. The flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north. The age of the dune formation is unknown, and no northward-flowing geostrophic flow has been reported in the literature from this area. ?? 2004 Elsevier B.V. All rights reserved.

Geomorphology↗
USGS2004

Holocene to Pliocene tectonic evolution of the region offshore of the Los Angeles urban corridor, southern California

Quaternary tectonism in the coastal belt of the Los Angeles urban corridor is diverse. In this paper we report the results of studies of multibeam bathymetry and a network of seismic reflection profiles that have been aimed at deciphering the diverse tectonism and at evaluating the relevance of published explanations of the region's tectonic history. Rapid uplift, subsidence in basins, folds and thrusts, extensional faulting, and strike-slip faulting have all been active at one place or another throughout the Quaternary Period. The tectonic strain is reflected in the modern physiography at all scales. Los Angeles (LA) Basin has filled from a deep submarine basin to its present condition with sediment impounded behind a large sill formed behind uplifts near the present shoreline. Newport trough to the south-southeast of LA Basin also accumulated a large volume of sediment, but remained at midbathyal depths throughout the Period. There is little or no evidence of Quaternary extensional tectonism in either basin although as much as 6 km of subsidence, which mainly occurred by sagging, has been recorded in places since the middle Miocene. The uplifts include folded and thrust faulted terranes in the Palos Verdes Hills and the shelves of Santa Monica and San Pedro Bays. The uplifted areas have been shortened in a southwest-northeast direction by 10% or slightly more, and some folds are reflected in the bathymetry. Two large adjacent midbathyal basins, Santa Monica and San Pedro, show strong evidence of subsidence and slight west-northwest extension (10%) during the same time folding was taking place in the uplifts. The tectonic boundaries between uplifts and basins are folded, normal faulted, reverse-faulted, and strike-slip faulted depending on location. The rapid Quaternary uplift and subsidence, along with the filling of LA Basin, have produced a reversal in the regional physiography. In the early Pliocene, LA Basin was a submarine deep, Palos Verdes and the shelves comprised a northeast basin slope, and the present offshore basins and Catalina Island formed an emergent or shallowly submerged shelf. Since extensional, compressional, and lateral strains are all locally in evidence, simple notions that this part of southern California underwent a change from Miocene transtension to Quaternary transpression fail to explain our observations.

Tectonics↗
USGS2004

Sedimentary processes of the lower Monterey Fan channel and channel-mouth lobe

The distribution of deposits, sediment transport pathways and processes on the lower Monterey Fan channel and channel-mouth lobe (CML) are studied through the integration of GLORIA and TOBI sidescan sonar data with 7-kHz subbottom profiler records and sediment cores for ground-truthing. The lower Monterey channel is characterised by an up to 30-m-deep channel with poorly developed levees and alternating muddy and silty muddy overbank deposits. The channel is discontinuous, disappearing where gradients are less than about 1:350. Ground-truthing of the large CML shows that the entire CML is characterised by widespread deposits of generally fine sand, with coarser sand at the base of turbidites. Sand is particularly concentrated in finger-like areas of low-backscatter intensity and is interpreted as the result of non-turbulent sediment-gravity flows depositing metres thick massive, fine sand. TOBI sidescan sonar data reveal recent erosional features in the form of scours, secondary channels, large flow slides, and trains of blocks at the distal end of the CML. Erosion is probably related to increasing gradient as the CML approaches Murray Fracture zone and to differential loading of sandy submarine fan deposits onto pelagic clays. Reworking of older flow slides by sediment transport processes on the lobe produces trains of blocks that are several metres in diameter and aligned parallel to the flow direction. ?? 2004 Elsevier B.V. All rights reserved.

Marine Geology↗
USGS2004

Submarine landslides of San Pedro Escarpment, southwest of Long Beach, California

The coastal infrastructure of the southern greater Los Angeles metropolitan area would be profoundly affected by a large tsunami. Submarine slope failures and active faults, either of which could have generated a tsunami, are known on the shelf and slope near Long Beach. Large slope failures are present on the San Pedro Escarpment and on the basin slope adjacent to the San Pedro shelf. The southeastern part of the escarpment has had a long history of slope failure. The most recent failure, the Palos Verdes slide, is over 4.5 km long, has been dated as 7500 years old, and involved over 0.34 km 3 of material, which now litters the adjacent basin floor. Other, smaller, deposits from nearby failures are also present, as are buried wedges of debris that indicate slope failures have occurred locally throughout the Holocene and much of the late Pleistocene. Slope failures have occurred in response to continual Quaternary uplift of the Palos Verdes anticlinorium. The Palos Verdes slide could potentially have generated a failure-related tsunami with an amplitude in the range of 8-12 m because it apparently failed catastrophically, started in shallow water, evolved on low-drag bedding planes, had a long slide path, and involved high-strength lithified material. ?? 2003 Elsevier B.V. All rights reserved.

Conference Paper↗
USGS2002

The significance of pockmarks to understanding fluid flow processes and geohazards

Underwater gas and liquid escape from the seafloor has long been treated as a mere curiosity. It was only after the advent of the side-scan sonar and the subsequent discovery of pockmarks that the scale of fluid escape and the moonlike terrain on parts of the ocean floor became generally known. Today, pockmarks ranging in size from the 'unit pockmark' (1-10 m wide, <0.6 m deep) to the normal pockmark (10-700 m wide, up to 45 m deep) are known to occur in most seas, oceans, lakes and in many diverse geological settings. In addition to indicating areas of the seabed that are 'hydraulically active', pockmarks are known to occur on continental slopes with gas hydrates and in association with slides and slumps. However, possibly their potentially greatest significance is as an indicator of deep fluid pressure build-up prior to earthquakes. Whereas only a few locations containing active (bubbling) pockmarks are known, those that become active a few days prior to major earthquakes may be important precursors that have been overlooked. Pockmark fields and individual pockmarks need to be instrumented with temperature and pressure sensors, and monitoring should continue over years. The scale of such research calls for a multinational project in several pockmark fields in various geological settings.

Geofluids↗
USGS2002

Morphology, volcanism, and mass wasting in Crater Lake, Oregon

Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-plattform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was ~80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhydacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to ~280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at ~1845 m elevation. Thereafter, a gradual, climatically modulated rise in lake level to the present 1883 m produced a series of beaches culminating in a modern wave-cut platform, commonly ~40 m wide, where suitable material is present. The new survey reveals landforms that result from intermediate-composition volcanism in rising water, delineates mass wasting and sediment transport into a restricted basin, and yields a more accurate postcaldera history leading to improved assessment of volcanic hazards.

Oregon↗
USGS2001

Physiography and late Quaternary-Holocene processes of Northeastern Gulf of Mexico outer continental shelf off Mississippi and Alabama

High-resolution multibeam mapping of the mid- and outer continental shelf and upper slope off Mississippi and Alabama reveals a complex bathymetry that reflects conditions during the last eustatic rise and the present high stand of sea level. The most prominent bathymetric features are pinnacles and hardgrounds that are scattered throughout the area. These features generally stand <10 m above the surrounding seafloor, cover large areas, and display a variety of morphologies. Almost all the reef pinnacles and hardgrounds have zones of high acoustic backscatter on their summits and on the seafloor immediately adjacent to their southwest walls. In addition, they also have erosional moats on the seafloor to the southwest. Large fields of bedforms are scattered throughout the mapped area. The asymmetries and orientations of the bedforms suggest that they were formed by excursions of the northeast-flowing Loop Current. In contrast, the pervasive ponding of sediment on the northeast sides of bathymetric highs indicates that one of the predominant directions of sediment transport has been to the south and southwest. The shelf break is a zone of numerous landslides of various sizes and complexities. The morphology of several landslide scars indicates that some of the failures occurred recently. One large reef-capped salt dome was mapped in the area, surrounded by a large field of pock-marks. Fields of pockmarks are also scattered on the shelf. The growth and demise of the reefs are related to the fluctuating transgression of eustatic sea level during the last deglaciation. Two episodes of reef drowning are correlated with the increased rates of sea-level rise during documented melt-water pulses; the first occurred from 14.8 to 14.2 ka and the second from 11.8 to 11.2 ka. Rates of sea-level rise exceeded the maximum growth rate of hermatypic corals only during these two intervals since the last glacial maximum and thus drowned the coral communities.

Alabama, Mississippi↗
USGS1999

Geometry and significance of stacked gullies on the northern California slope

Recent geophysical surveys off northern California reveal patterns of gullies on the sea floor and preserved within continental-slope deposits that represent both erosional and aggradational processes. These surveys, conducted as part of the STRATAFORM project, combined multibeam bathymetry and backscatter with high-resolution seismic profiles. These data provide a new basis for evaluating gully morphology, distribution, and their significance to slope sedimentation and evolution. The continental margin off northern California exhibits an upper slope that has undergone both progradation and aggradation. The slope surface, which dips at <2??to 4.0??, contains a set of straight, evenly spaced, and parallel to sub-parallel gullies that begin at the 380-m isobath and extend onto the Eel and Klamath plateaus and into Trinity Canyon. The surface gullies are typically 100-m wide or more and only 1-2 m deep. The gullied slope is underlain by a sedimentary sequence that contains abundant buried gullies to subsurface depths of over 150 m. Although some of the buried gullies are distinctly erosional, most are part of the aggradational pattern responsible for the overall growth of the slope. The latest phase of gully erosion is marked by a gullied surface lying <20 m below the present-day sea floor. These erosional gullies locally truncate individual reflectors, have small depositional levees, and exhibit greater relief than do overlying gullies exposed on the sea floor. The older subsurface gullies document a period of widespread, but minor, erosion and downslope transport, presumably from a large, proximal sediment source. The cycles of downcutting and gully excavation are a minor part of the stratigraphic section, and are likely related to the combined influence of lower sea levels and higher sediment yields. During aggradation of the slope depositional sequences, sediment was draped over the gully features, producing sediment layers that mimic the underlying gully form. Consequently, gully morphology and geometries were preserved and migrated upwards with time. The processes that produce aggraded gully drape also resulted in laterally continuous strata and were most likely related to a period when the sediment source was dispersed from a more distal (10s of km) source, such as during present conditions. The draped sequences also contain a few new gullies, which indicates that gullies can be initiated at all or most stages of slope growth.

Marine Geology↗
USGS1999

Humboldt slide - A large shear-dominated retrogressive slope failure

Humboldt Slide is a large, complex slide zone located on the northern California continental margin. Its three-dimensional architecture has been imaged by a combination of multibeam bathymetry, Huntec Deep-Tow seismic profiling, and sidescan sonar. The slide is interpreted to be Late Pleistocene to early Holocene in age and was caused by a combination of factors. The area of the slide is a local depocenter with high accumulation rates of organic-rich sediment; there has been local steepening of slopes by tectonic uplifts; and the entire area is one of high seismicity. Overall, the failure occurred by retrogressive, shear-dominated, minimum movement apparently as a sequence of events. Failure initially occurred by subsidence extension at the middle of the feature, followed by upslope retrogressive failure and downslope compression, and finally by translational sliding at the top of the slide. Degassing, as evidenced by abundant pockmarks, may have inhibited downslope translation. The slide may still be active, as suggested by offsets in Holocene hemipelagic sediment draped over some of the shear surfaces. Crown cracks occur above the present head of the failure and may represent the next generation of failure.

Marine Geology↗