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Geology topics

Paul R. Carlson

Publications and source records attributed to Paul R. Carlson.

At least 19 recordsLinked to original sources
USGS2004

Shifting shoals and shattered rocks: How man has transformed the floor of west-central San Francisco Bay

San Francisco Bay, one of the world's finest natural harbors and a major center for maritime trade, is referred to as the 'Gateway to the Pacific Rim.' The bay is an urbanized estuary that is considered by many to be the major estuary in the United States most modified by man's activities. The population around the estuary has grown rapidly since the 1850's and now exceeds 7 million people. The San Francisco Bay area's economy ranks as one of the largest in the world, larger even than that of many countries. More than 10 million tourists are estimated to visit the bay region each year. The bay area's population and associated development have increasingly changed the estuary and its environment. San Francisco Bay and the contiguous Sacramento-San Joaquin Delta encompass roughly 1,600 square miles (4,100 km2) and are the outlet of a major watershed that drains more than 40 percent of the land area of the State of California. This watershed provides drinking water for 20 million people (two thirds of the State's population) and irrigates 4.5 million acres of farmland and ranchland. During the past several decades, much has been done to clean up the environment and waters of San Francisco Bay. Conservationist groups have even bought many areas on the margins of the bay with the intention of restoring them to a condition more like the natural marshes they once were. However, many of the major manmade changes to the bay's environment occurred so long ago that the nature of them has been forgotten. In addition, many changes continue to occur today, such as the introduction of exotic species and the loss of commercial and sport fisheries because of declining fish populations. The economy and population of the nine counties that surround the bay continue to grow and put increasing pressure on the bay, both direct and indirect. Therefore, there are mixed signals for the future health and welfare of San Francisco Bay. The San Francisco Bay estuary consists of three subembayments--north bay (San Pablo and Suisun Bays), central bay, and south bay--each characterized by a central area of open water surrounded by intertidal mudflats and marshes. Central bay includes Alcatraz and Angel Islands and also a number of submerged bedrock knobs that protrude through the sediment of the bay floor and rise to within about 40 feet (12 m) of the water surface. The most prominent of these are Harding, Shag, Arch, and Blossom Rocks. These rocks have been lowered by blasting several times in the past, but they remain a potential hazard to shipping because newer cargo vessels are designed with increasingly deeper drafts. Central bay's location adjacent to two major population and commerce centers, San Francisco and Oakland, subjects it to greater human influences than less developed parts of the estuary. The western part of central San Francisco Bay is adjacent to the Golden Gate, the estuary's outlet to the Pacific Ocean. The changing submarine topography of the west-central bay, as well as its geology, form the main focus of this book.

California↗
USGS2004

Seafloor habitat mapping and classification in Glacier Bay, Alaska: Phase 1 & 2 1996-2004

Glacier Bay is a diverse fjord ecosystem with multiple sills, numerous tidewater glaciers and a highly complex oceanographic system. The Bay was completely glaciated prior to the 1700’s and subsequently experienced the fastest glacial retreat recorded in historical times. Currently, some of the highest sedimentation rates ever observed occur in the Bay, along with rapid uplift (up to 2.5 cm/year) due to a combination of plate tectonics and isostatic rebound. Glacier Bay is the second deepest fjord in Alaska, with depths over 500 meters. This variety of physical processes and bathymetry creates many diverse habitats within a relatively small area (1,255 km 2 ). Habitat can be defined as the locality, including resources and environmental conditions, occupied by a species or population of organisms (Morrison et al 1992). Mapping and characterization of benthic habitat is crucial to an understanding of marine species and can serve a variety of purposes including: understanding species distributions and improving stock assessments, designing special management areas and marine protected areas, monitoring and protecting important habitats, and assessing habitat change due to natural or human impacts. In 1996, Congress recognized the importance of understanding benthic habitat for fisheries management by reauthorizing the Magnuson-Stevens Fishery Conservation and Management Act and amending it with the Sustainable Fisheries Act (SFA). This amendment emphasizes the importance of habitat protection to healthy fisheries and requires identification of essential fish habitat in management decisions. Recently, the National Park Service’s Ocean Stewardship Strategy identified the creation of benthic habitat maps and sediment maps as crucial components to complete basic ocean park resource inventories (Davis 2003). Glacier Bay National Park managers currently have very limited knowledge about the bathymetry, sediment types, and various marine habitats of ecological importance in the Park. Ocean floor bathymetry and sediment type are the building blocks of marine communities. Bottom type and shape affects the kinds of benthic communities that develop in a particular environment as well as the oceanographic conditions that communities are subject to. Accurate mapping of the ocean floor is essential for park manager’s understanding of existing marine communities and will be important in assessing human induced changes (e.g., vessel traffic and commercial fishing), biological change (e.g., rapid sea otter recolonization), and geological processes of change (e.g., deglaciation). Information on animal-habitat relationships, particularly within a marine reserve framework, will be valuable to agencies making decisions about critical habitats, marine reserve design, as well as fishery management. Identification and mapping of benthic habitat provides National Park Service mangers with tools to increase the effectiveness of resource management. The primary objective of this project is to investigate the geological characteristics of the biological habitats of halibut, Dungeness crab, king crab, and Tanner crab within Glacier Bay National Park. Additionally, habitat classification of shallow water regions of Glacier Bay will provide crucial information on the relationship between benthic habitat features and the abundance of benthic prey items for a variety of marine predators, including sea ducks, the rapidly increasing population of sea otters, and other marine mammals.

Alaska↗
USGS2003

Giant submarine canyons: Is size any clue to their importance in the rock record?

Submarine canyons are the most important conduits for funneling sediment from continents to oceans. Submarine canyons, however, are zones of sediment bypassing, and little sediment accumulates in the canyon until it ceases to be an active conduit. To understand the potential importance in the rock record of any given submarine canyon, it is necessary to understand sediment-transport processes in, as well as knowledge of, deep-sea turbidite and related deposits that moved through the canyons. There is no straightforward correlation between the final volume of the sedimentary deposits and size of the associated submarine canyons. Comparison of selected modern submarine canyons together with their deposits emphasizes the wide range of scale differences between canyons and their impact on the rock record. Three of the largest submarine canyons in the world are incised into the Beringian (North American) margin of the Bering Sea. Zhemchug Canyon has the largest cross-section at the shelf break and greatest volume of incision of slope and shelf. The Bering Canyon, which is farther south in the Bering Sea, is first in length and total area. In contrast, the largest submarine fans-e.g., Bengal, Indus, and Amazon-have substantially smaller, delta-front submarine canyons that feed them; their submarine drainage areas are one-third to less than one-tenth the area of Bering Canyon. some very large deep-sea channels and tubidite deposits are not even associated with a significant submarine canyon; examples include Horizon Channel in the northeast Pacific and Laurentian Fan Valley in the North Atlantic. Available data suggest that the size of turbidity currents (as determined by volume of sediment transported to the basins) is also not a reliable indicator of submarine canyon size.

GSA Special Papers↗
USGS2002

Multibeam bathymetry and selected perspective views of main part of Glacier Bay, Alaska

Glacier Bay is a diverse fjord ecosystem with multiple tidewater glaciers and complex biological, geological, and oceanographic patterns that vary greatly along its length. The bay was completely glaciated prior to the 1700's, and subsequently experienced the fastest glacial retreat recorded in historical times. As a result, some of the highest rates of glacial sedimentation and uplift are observed here. Glacier Bay is the deepest silled fjord in Alaska, with depths of over 450 meters. The variety of physical processes and depths creates many diverse habitats within a relatively small area. Mapping benthic (seafloor) habitats is thus crucial to understanding and managing Glacier Bay's complex marine ecosystem and the marine species therein. High-resolution multibeam mapping of the bay, funded jointly by USGS and the National Park System, provides an unprecedented new baseline for resource and habitat assessment. Full integration of the new data set will require additional ground-truthing data (sampling) and analysis. The USGS goal is to develop integrated geological and oceanographic habitat models for the marine benthos in Glacier Bay, as a step toward determining the habitat relationships of critical species and resources within the Park.

Alaska↗
USGS2000

Map of Distribution of Bottom Sediments on the Continental Shelf, Gulf of Alaska

Introduction The U.S. Geological Survey has a long history of exploring marine geology in the Gulf of Alaska. As part of a cooperative program with other federal and state agencies, the USGS is investigating the relations between ocean-floor geology and benthic marine biohabitats. This bottom sediment map, compiled from published literature will help marine biologists develop an understanding of sea-floor geology in relation to various biological habitats. The pattern of sea-floor sedimentation and bottom morphology in the Gulf of Alaska reflects a complex interplay of regional tectonism, glacial advances and retreats, oceanic and tidal currents, waves, storms, eustatic change, and gravity-driven processes. This map, based on numerous cruises during the period of 1970-1996, shows distribution of bottom sediments in areas of study on the continental shelf. The samples were collected with piston, box, and gravity corers, and grab samplers. The interpretations of sediment distribution are the products of sediment size analyses combined with interpretations of high-resolution seismic reflection profiles. The sea floor was separated into several areas as follows: Cook Inlet -- Hazards studies in this embayment emphasized sediment distribution, sediment dynamics, bedforms, shallow faults, and seafloor stability. Migrating mega-sandwaves, driven by strong tidal currents, influence seabed habitats and stability of the seafloor, especially near pipelines and drilling platforms. The coarseness of the bottom sediment reinforces the influence of the strong tidal currents on the seafloor habitats. Kodiak Shelf -- Tectonic framework studies demonstrate the development of an accretionary wedge as the Pacific Plate underthrusts the Alaskan landmass. Seismic data across the accretionary wedge reveal anomalies indicative of fluid/gas vent sites in this segment of the continental margin. Geologic hazards research shows that movement along numerous shallow faults poses a risk to sea floor structures. Sea-floor sediment on shallow banks is eroded by seasonal wave-generated currents. The winnowing action of the large storm waves results in concentrations of gravel over broad segments of the Kodiak shelf. Northeastern Gulf of Alaska -- Tectonic framework studies demonstrate that rocks of distant origin (Yakutat terrane) are currently attached to and moving with the Pacific Plate, as it collides with and is subducted beneath southern Alaska. This collision process has led to pronounced structural deformation of the continental margin and adjacent southern Alaska. Consequences include rapidly rising mountains and high fluvial and glacial sedimentation rates on the adjacent margin and ocean floor. The northeastern Gulf of Alaska shelf also has concentrations of winnowed (lag) gravel on Tarr Bank and on the outer shelf southeast of Yakutat Bay. Between Kayak Island and Yakutat Bay the outer shelf consists of pebbly mud (diamict). This diamict is a product of glacial marine sedimentation during the Pleistocene and is present today as a relict sediment. A prograding wedge of Holocene sediment consisting of nearshore sand grading seaward into clayey silt and silty clay covers the relict pebbly mud to mid-shelf and beyond. Shelf and slope channel systems transport glacially derived sediment across the continental margin into Surveyor Channel, an abyssal fan and channel system that reaches over 1,000 km to the Aleutian Trench.

Miscellaneous Field Studies Map↗
USGS1998

Multibeam data and socio-economic issues in west-central San Francisco Bay

San Francisco Bay is the largest estuary on the conterminous U.S. Pacific Coast and is one of the world's largest natural harbors. It is a biologically productive and diverse environment. San Francisco Bay has a maritime economy that annually generates over $7.5 billion, handles 50 million tons of cargo, and involves thousands of jobs. Recent investigations by the USGS in this estuary help address both socio-economic and scientific issues: *Trimming pinnacles may prevent a calamitous oil spill. *Can San Francisco Bay accept more dredge spoil? *Bay floor biological habitats are quite varied. *How thick and how variable is the sediment fill in central San Francisco Bay?

California↗
USGS1998

Physical characteristics of dungeness crab and halibut habitats in Glacier Bay

In Glacier Bay National Park, Alaska there are ongoing studies of Dungeness Crab (Cancer magister) and Pacific Halibut (Hippoglosus stenolepis). Scientists of the United States Geological Survey (USGS) are attempting to ascertain life history, distribution, and abundance, and to determine the effects of commercial fishing in the park (Carlson et al., 1998). Statistical sampling studies suggest that seafloor characteristics and bathymetry affect the distribution, abundance and behavior of benthic species. Examples include the distribution of Dungeness crab which varies from 78 to 2012 crabs/ha in nearshore areas to depths of 18 m (O'Clair et al., 1995), and changes in halibut foraging behavior according to bottom type (Chilton et al., 1995). This report discusses geophysical data collected in six areas within the park in 1998. The geophysical surveying done in this and previous studies will be combined with existing population and sonic-tracking data sets as well as future sediment sampling, scuba, submersible, and bottom video camera observations to better understand Dungeness crab and Pacific halibut habitat relationships.

Alaska↗
USGS1992

Submarine sedimentary features on a fjord delta front, Queen Inlet, Glacier Bay, Alaska

Side-scan sonar images provide a view of an actively changing delta front in a marine outwash fjord in Glacier Bay, Alaska. Numerous interconnected gullies and chute-like small channels form paths for the transport of sand and coarse silt from the braided glacial outwash streams on the delta plain to the sinuous turbidity-current channels incised into the fjord floor. These turbidity-current channels carry coarse sediment through the fjord and into the adjoining glacial trunk valley. Several sedimentary processes affect the development of this delta front: overflow plumes deposit fine sediment; sediment gravity flows result from episodic delivery of large loads of coarse sediment; and mass movement may be triggered by earthquakes and, more regularly, by spring-tidal drawdown or hydraulic loading.

Canadian Journal of Earth Sciences↗
USGS1990

Development of slope valleys in the glacimarine environment of a complex subduction zone, Northern Gulf of Alaska

Morphological, seismic-reflection, and sedimentological evidence indicates that glacial ice tongues cut large sea valleys into the Gulf of Alaska continental shelf during the Pleistocene. During the Holocene, glacially-derived sediments from the Copper River and other meltwater streams have been prograding seaward across the shelf, covering the glacial and glacimarine upper Yakataga diamicts that blanketed the shelf and accumulated on the upper slope seaward of the sea valleys during the Pleistocene. GLORIA imagery near Middleton Island provides a new perspective on the glacimarine depositional environment on the continental slope in a collision zone between the Pacific and North American plates. Southwest of Middleton Island, along the subduction margin, sinuous valleys funnel sediment around shelf-edge-parallel, subduction-created, anticlinal ridges that have deflected and locally trapped glacimarine sediment. The slope south and southeast of Middleton Island where oblique convergence occurs, is incised by dendritic, erosional gulley systems, contains no compressional ridges, and thus, the apparently active sediment pathways to the trench are unrestricted. However, below the sea valley mouths, apparently both glacial and glacimarine sediments blanket the upper slope, covering any dendritic gulley systems that may have formed during or since the Pleistocene low stands of sea level.

Alaska↗
USGS1988

The Mount Mazama climactic eruption (6900 BP) and resulting convulsive sedimentation on the continent, ocean basin, and Crater Lake caldera floor

The climactic eruption of Mount Mazama and the resulting sedimentation may have been the most significant convulsive sedimentary event in North America during Holocene time. A collapse caldera 1,200 m deep and 10 km in diameter was formed in Mount Mazama, and its floor was covered by hundreds of meters of wall-collapse debris. Wind-blown pyroclastic ash extended 2,000 km northeast from Mount Mazama and covered more than 1,000,000 km 2 of the continent. On the Pacific Ocean floor, Mazama ash was transported westward 600 to 700 km along deep-sea channels by turbidity currents. The initial single-vent phase of the climactic eruption, a Plinian column, emptied over half of the magma erupted. Debris from this phase accumulated as a pumice deposit 10 m thick at the rim to 50 cm thick as much as 100 km from the vent. This deposit created a mid-Holocene stratigraphic marker over the continent and the continental margin of western North America. A ring-vent phase followed as a second part of the climactic eruption and produced highly mobile pyroclastic flows. These flows covered the mountain for at least 14 km from the vent, continued down the valleys nearly 60 km, and deposited as much as 100 m of pumiceous ignimbrite. After the caldera collapsed as a result of the eruption of more than 50 km 3 of magma, heat of the climactic eruption apparently created phreatic explosion craters along the ring fracture zone of the caldera floor. Initially, explosion debris and sheetwash of pyroclastics off highlands seems mainly to have filled the local craters with bedded volcaniclastics. This basal, generally flat-lying unit, was quickly covered by wedges of chaotically bedded debris flow and avalanche-type deposits that thin inward from the caldera walls. These deposits may have formed in response to seismic activity associated with postcaldera volcanism that apparently began soon after the caldera collapsed. The lower two units of non-lacustrine beds (50 to 60 m) make up the majority of the postcaldera sedimentary deposits and seem to have deposited rapidly after the climactic eruption. Twenty to 25 m of lacustrine sediment has been accumulating more slowly over the subaerial debris during the past 6,900 yr. Some Mazama ash probably was transported by rivers to the sea immediately after the climactic eruption because significant amounts of this ash appear in mid-Holocene turbidites of Cascadia Basin. The presence of Mazama ash mixed with Columbia River sand in texturally and compositionally graded turbidites shows that Mazama ash periodically was moved by sediment-gravity flows down the canyons and through channels to deposition sites in the Astoria Fan and the Cascadia Channel. The coarsest and thickest tuffaceous turbidites were deposited on channel floors, and the ash-rich suspension flows that overtopped the levees were deposited as thin-bedded turbidites in interchannel areas. Study of the Mount Mazama climactic eruption shows that such an event in the Cascade Mountains has the potential to: (a) cause major destruction within 100 km of the vent, (b) severely affect biota as far as 2,000 km downwind, and (c) disrupt commercial river and marine transportation or natural sedimentation as far as several hundred kilometers in the opposite direction from wind-blown debris. Present geologic characteristics on the Crater Lake caldera floor suggest that geologic hazards from a significant volcanic event appear to be minimal for the next few thousand years.

Mount Mazama↗
USGS1985

Seismic and geochemical evidence for shallow gas in sediment on Navarin continental margin, Bering Sea

Marine seismic studies coupled with geochemical investigations demonstrate that hydrocarbon gases are ubiquitous in the near-surface (<= 250 m or 820 ft depth) sediment of the Navarin continental margin in the northern Bering Sea. Three types of acoustic anomalies appear to be related to the presence of gas in the sediment. These anomalies are most prevalent in the northern half of the Navarin basin. Acoustic anomalies attributed to gas hydrates and to diagenetic boundaries are present on seismic records of the lower slope between Navarinsky and Zhemchug Canyons. Hydrocarbon gases, methane through butanes, are common in the surface (<= 5 m or 17 ft depth) sediment of the Navarin continental margin. Methane, the most abundant hydrocarbon gas, is present in amounts ranging from 84,000 to 1 µL/L of wet sediment. These concentrations are two to three orders of magnitude greater than the other hydrocarbon gases. The highest concentrations of methane (greater than 1,000 µL/L) were measured in sediment of Navarinsky Canyon and over the central part of the Navarin basin. The source of methane is mainly biogenic, but the hydrocarbon gas compositions in 17 of 141 cores suggest the presence of thermogenic gas. Most of these 17 cores are from the continental slope at water depths greater than 150 m (490 ft). No direct correlation could be found between acoustic anomalies and gas concentrations in the sediment. This lack of correlation is probably due to the limited penetration of the gravity corer and the spotty distribution of hydrocarbon concentrations.

Alaska↗
USGS1984

Discovery of two new large submarine canyons in the Bering Sea

The Beringian continental margin is incised by some of the world's largest submarine canyons. Two newly discovered canyons, St. Matthew and Middle, are hereby added to the roster of Bering Sea canyons. Although these canyons are smaller and not cut back into the Bering shelf like the five very large canyons, they are nonetheless comparable in size to most of the canyons that have been cut into the U.S. eastern continental margin and much larger than the well-known southern California canyons. Both igneous and sedimentary rocks of Eocene to Pliocene age have been dredged from the walls of St. Matthew and Middle Canyons as well as from the walls of several of the other Beringian margin canyons, thus suggesting a late Tertiary to Quaternary genesis of the canyons. We speculate that the ancestral Yukon and possibly Anadyr Rivers were instrumental in initiating the canyon-cutting processes, but that, due to restrictions imposed by island and subsea bedrock barriers, cutting of the two newly discovered canyons may have begun later and been slower than for the other five canyons.

Bering Sea↗
USGS1982

Geologic hazards in Navarin Basin Province, Northern Bering Sea

Navarin Basin, scheduled for leasing in 1984 (OCS sale 83), may contain vast accumulations of oil and gas. Several geologic and oceanographic processes that may be active in and around Navarin Basin province could be hazardous to commercial development. These potential hazards include submarine slides; sea-floor instability resulting from disturbance of gas-charged sediment; sediment transport and erosion caused by storm waves, tsunamis, internal waves, or bottom currents; pack ice; and active faults and ground motion.

Bering Sea, Navarin Basin↗
USGS1982

Submarine valleys in the northeastern Gulf of Alaska: Characteristics and probable origin

The continental shelf of the northeastern Gulf of Alaska Between Prince William Sound and Cross Sound is cut by at least eight major valleys. From west to east, these are Hinchinbrook Seavalley, Egg Island Trough, Kayak Trough, Bering Trough, Pamplona Troughs, Yakutat Valley, Alsek Valley and Yakobi Valley. Evidence common to most of these troughs or valleys indicating that the present morphology is due to glacial processes includes: (1) a pre-Holocene subbottom erosional surface incised into the underlying lithified strata of the shelf; (2) U-shaped cross sections, both at the sea floor and at the pre-Holocene erosional surface; (3) concave longitudinal sections, commonly shoaling at the seaward end; (4) till-like sediments collected from the walls or outer shelf adjacent to the troughs; and (5) seismic stratigraphy that can be correlated with bottom samples indicative of glacially derived strata. Depressions with tens of meters of relief are present on the pre-Holocene subbottom erosional surface beneath most of these valleys. These depressions have been partially filled by a seaward-thinning wedge of Holocene glacial flour (clayey silt) that is filling the valleys and blanketing the inner shelf at rates as high as 15 mm/yr (based on 210 Pb measurements). Although glaciation played a dominant role in the modern morphology of these sea valleys, structural features, including structurally controlled topographic highs on the shelf (e.g. Tarr Bank, Kayak Island, Pamplona Spur and Fairweather Ground) influenced the flow directions of the glacial lobes.

Alaska↗