Geology topics

H. Chezar

Publications and source records attributed to H. Chezar.

5 recordsLinked to original sources

USGS2007

A rapid method to characterize seabed habitats and associated macro-organisms

This study presents a method for rapidly collecting, processing, and interrogating real-time abiotic and biotic seabed data to determine seabed habitat classifications. This is done from data collected over a large area of an acoustically derived seabed map, along multidirectional transects, using a towed small camera-sled. The seabed, within the newly designated Point Harris Marine Reserve on the northern coast of San Miguel Island, California, was acoustically imaged using sidescan sonar then ground-truthed using a towed small camera-sled. Seabed characterizations were made from video observations, and were logged to a laptop computer (PC) in real time. To ground-truth the acoustic mosaic, and to characterize abiotic and biotic aspects of the seabed, a three-tiered characterization scheme was employed that described the substratum type, physical structure (i.e., bedform or vertical relief), and the occurrence of benthic macrofauna and flora. A crucial advantage of the method described here, is that preliminary seabed characterizations can be interrogated and mapped over the sidescan mosaic and other seabed information within hours of data collection. This ability to rapidly process seabed data is invaluable to scientists and managers, particularly in modifying concurrent or planning subsequent surveys.

Special Paper - Geological Association of Canada↗

USGS2003

Headless submarine canyons and fluid flow on the toe of the Cascadia accretionary complex

Headless submarine canyons with steep headwalls and shallowly sloping floors occur on both the second and third landward vergent anticlines on the toe of the Cascadia accretionary complex off central Oregon (45 °N, 125° 30′W). In September 1993, we carried out a series of nine deep tow camera sled runs and nine ALVIN dives to examine the relationship between fluid venting, structure and canyon formation. We studied four canyons on the second and third landward vergent anticlines, as well as the apparently unfailed intercanyon regions along strike. All evidence of fluid expulsion is associated with the canyons; we found no evidence of fluid flow between canyons. Even though all fluid seeps are related to canyons, we did not find seeps in all canyons, and the location of the seeps within the canyons differed. On the landward facing limb of the second landward vergent anticline a robust cold seep community occurs at the canyon’s inflection point. This seep is characterized by chemosynthetic vent clams, tube worms and extensive authigenic carbonate. Fluids for this seep may utilize high-permeability flow paths either parallel to bedding within the second thrust ridge or along the underlying thrust fault before leaking into the overriding section. Two seaward facing canyons on the third anticlinal ridge have vent clam communities near the canyon mouths at approximately the intersection between the anticlinal ridge and the adjacent forearc basin. No seeps were found along strike at the intersection of the slope basin and anticlinal ridge. We infer that the lack of seepage along strike and the presence of seeps in canyons may be related to fluid flow below the forearc basin/slope unconformity (overpressured by the impinging thrust fault to the west?) directed toward canyons at the surface.

Basin Research↗

USGS1999

Tidally generated sea-floor lineations in Bristol Bay, Alaska, USA

Highly reflective linear features occur in water depths of 20-30 m in northern Bristol Bay (Alaska, USA) and are, in places, over 600 m in length. Their length-to-width ratio is over 100:1. The lineations are usually characterized by large transverse ripples with wavelengths of 1-2 m. The lineations trend about N60??E, and are spaced between 20 and 350 m. Main tidal directions near the lineations are N60??E (flood) and S45??W (ebb), which are parallel to subparallel to the lineations. They suggest that the lineations may be tidally generated. The lineations may be bright sonar reflections from a winnowed lag concentrate of coarse sand.

Geo-Marine Letters↗

USGS1985

A new look at deep-sea video

A deep-towed photographic system with completely self-contained recording instrumentation and power can obtain color-video and still-photographic transects along rough terrane without need for a long electrically conducting cable. Both the video- and still-camera systems utilize relatively inexpensive and proven off-the-shelf hardware adapted for deep-water environments. The small instrument frame makes the towed sled an ideal photographic tool for use on ship or small-boat operations. The system includes a temperature probe and altimeter that relay data acoustically from the sled to the surface ship. This relay enables the operator to monitor simultaneously water temperature and the precise height off the bottom.

Deep Sea Research Part A, Oceanographic Research P↗

USGS1984

Observations on Cretaceous abyssal hills in the northeast Pacific

An abyssal hills area of 50 × 60 km in the northeast Pacific was studied using bottom transponder navigation, closely spaced survey lines, and long-traverse oblique photography. The block-faulted north—south hills are bounded by scarps, commonly with 40° slopes. On these steep scarps sedimentation is inhibited and pillow basalts often crop out. An ash layer of high acoustic reflectivity at about 7 m subbottom depth blankets the area. This ash occurs in multiple beds altered to phillipsite and is highly consolidated. A 24 m.y. age for the ash is based on ichthyolith dates from samples in the overlying sediments. Acoustically transparent Neogene sediments above the ash are thickest in trough bottoms and are absent or thin on steep slopes. These Neogene sediments are composed of pale-brown pelagic clays of illite, quartz, smectite, chlorite and kaolinite. Dark-brown pelagic clays, rich in smectite and amorphous iron oxides, underlie the Neogene surficial sediments. Manganese nodules cover the bottom in varying percentages. The nodules are most abundant near basement outcrops and where the subbottom ash layer is absent.

Marine Geology↗