Navy Fan, California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes. Margin setting represents fan and/or source area     

Mississippi Fan: Internal structure and depositional processes

The Mississippi Fan is a Quarternary accumulation composed of more than seven elongated fan lobes. Isopach and structure maps show frequent shifting of these lobes. The Mississippi Canyon, formed by retrogressive slumping, connects to the youngest fan lobe. The upper fan-lobe is characterized by a large, incised, partially infilled, leveed channel. The middle fan-lobe is aggradational, convex in cross section, with a channel-levee complex on its apex. The lower fan-lobe contains a recently active small channel and several abandoned ones. Depositional patterns can be explained by several processes: “fluvial,” debris flows, and turbidity currents. Margin setting represents fan and/or source area     

Mississippi Fan: Internal structure and depositional processes

The Mississippi Fan is a Quarternary accumulation composed of more than seven elongated fan lobes. Isopach and structure maps show frequent shifting of these lobes. The Mississippi Canyon, formed by retrogressive slumping, connects to the youngest fan lobe. The upper fan-lobe is characterized by a large, incised, partially infilled, leveed channel. The middle fan-lobe is aggradational, convex in cross section, with a channel-levee complex on its apex. The lower fan-lobe contains a recently active small channel and several abandoned ones. Depositional patterns can be explained by several processes: “fluvial,” debris flows, and turbidity currents.     

Morphology,sedimentation processes,and growth pattern of the Amazon Deep-Sea Fan

The Amazon Deep-Sea Fan began to form in the Early Miocene and is characterized by a highly meandering distributary channel system. On the middle fan, these leveed channels coalesce to form two broad levee complexes. Older, now buried levee complexes are also observed within the fan. These levee complexes grow through channel migration, branching, and avulsion. Probably only one or two channels are active at any given time. Sediments reach the fan only during glacio-eustatic low stands of sea level. Coarse sediments largely by-pass the upper and middle fan via the channels and are deposited on the lower fan.     

Morphology, sedimentation processes, and growth pattern of the Amazon Deep-Sea Fan

The Amazon Deep-Sea Fan began to form in the Early Miocene and is characterized by a highly meandering distributary channel system. On the middle fan, these leveed channels coalesce to form two broad levee complexes. Older, now buried levee complexes are also observed within the fan. These levee complexes grow through channel migration, branching, and avulsion. Probably only one or two channels are active at any given time. Sediments reach the fan only during glacio-eustatic low stands of sea level. Coarse sediments largely by-pass the upper and middle fan via the channels and are deposited on the lower fan. Margin setting represents fan and/or source area     

Late Quaternary changes in depositional processes along the western margin of the Indus Fan

Detailed sedimentological, geochemical and isotopic analyses were carried out on sediment samples from ODP Site 720A on the Indus Fan, Arabian Sea. High values of calcium carbonate associated with low values of Al and Ti from 0 to 375 ka, and low values of calcium carbonate along with high values of Al and Ti from 375 to 525 ka represent two distinct sedimentary sequences. The sediments deposited from 525 to 375 ka correspond to a turbidite sequence, characterized by a high terrigenous input of coarse-grained sediments composed mostly of sand and silt. The sediments deposited from 375 ka to the present day comprise a pelagic sequence, consisting of pelagic material and clay. The major turbidity flow between 375 and 525 ka resulted in the greatest development of the Indus Fan during the late Quaternary. Most of the active channels were buried by 375 ka, followed by deposition of mainly pelagic sequences since then. Enrichment of an Indus-derived Himalayan clay mineral assemblage (illite and chlorite) in both the turbiditic and pelagic sequences reveals that the source and supply of clay minerals to the Indus Fan were the same during pre- and post-turbidite deposition. At ODP Site 720A, Al, Ti and terrigenous material do not show any systematic changes with respect to glacial and interglacial periods, suggesting that sea-level changes are not directly responsible for the terrigenous material supply to this site. Rather, a major switch in distributary channels away from the western margin of the Indus Fan is suggested.     

Deformation and patterns of sedimentation,South San Clemente Basin,California Borderland

Seismic reflection profiling in the South San Clemente Basin and the southern portion of the San Diego Trough has revealed at least six sedimentary units exhibiting varying stages of deformation. Four of the units are interpreted to be marine turbidites supplied by adjacent submarine canyons. Sediments comprising the Descanso Plain and correlative material within the South San Clemente Basin are attributed to a southerly source (Banda Canyon), while the more recent Quaternary turbidites from Coronado Canyon filled the southern San Diego Trough and then spilled over into South San Clemente Basin. The relatively high but intermittent rates of sedimentation, together with shifting sources and areas of deposition, have resulted in sedimentary units that were emplaced in comparatively short episodes but which were subjected to relatively continuous tectonic activity. Consequently, the sedimentary layers of each unit appear uniformly affected by deformation which increases in successively older units.     

Monterey Fan: Growth pattern control by basin morphology and changing sea levels

Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. Margin setting represents fan and/or source area     

Monterey Fan: Growth pattern control by basin morphology and changing sea levels

Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition.     

Geotechnical aspects of fine-grained mass flow deposits: California Continental Borderland

Seismic reflection profiling demonstrates the importance of mass movement in the north-central California Borderland. Bulk properties of surficial hemipelagic sediments in the Santa Barbara, Santa Cruz, and San Nicolas basins show that different types of mass-transported sediments have different properties, although their general sedimentologic characteristics are very similar. Slump deposits have moderate water contents (48% wet weight basis), high plasticity indices (46%), and moderate activities (1.6). For debris flows these values are low: 28%, 5%, and 0.3, respectively, and for other types (liquefied flow, mudflows, and turbidities) the values are high: 54 to 63%, 49 to 58%, and 1.2 to 1.5, respectively.     

The Bengal Fan: morphology, geometry, stratigraphy, history and processes

The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from several other large rivers in Bangladesh and India.The sedimentary section of the fan is subdivided by seismic stratigraphy by two unconformities which have been tentatively dated as upper Miocene and lower Eocene by long correlations from DSDP Leg 22 and ODP Legs 116 and 121. The upper Miocene unconformity is the time of onset of the diffuse plate edge or intraplate deformation in the southern or lower fan. The lower Eocene unconformity, a hiatus which increases in duration down the fan, is postulated to be the time of first deposition of the fan, starting at the base of the Bangladesh slope shortly after the initial India–Asia collision.The Quaternary of the upper fan comprises a section of enormous channel-levee complexes which were built on top of the preexisting fan surface during lowered sea level by very large turbidity currents. The Quaternary section of the upper fan can be subdivided by seismic stratigraphy into four subfans, which show lateral shifting as a function of the location of the submarine canyon supplying the turbidity currents and sediments. There was probably more than one active canyon at times during the Quaternary, but each one had only one active fan valley system and subfan at any given time. The fan currently has one submarine canyon source and one active fan valley system which extends the length of the active subfan. Since the Holocene rise in sea level, however, the head of the submarine canyon lies in a mid-shelf location, and the supply of sediment to the canyon and fan valley is greatly reduced from the huge supply which had existed during Pleistocene lowered sea level. Holocene turbidity currents are small and infrequent, and the active channel is partially filled in about the middle of the fan by deposition from these small turbidity currents.Channel migration within the fan valley system occurs by avulsion only in the upper fan and in the upper middle fan in the area of highest rates of deposition. Abandoned fan valleys are filled rapidly in the upper fan, but many open abandoned fan valleys are found on the lower fan. A sequence of time of activity of the important open channels is proposed, culminating with formation of the one currently active channel at about 12,000 years BP.     

Origin of mass flow sedimentary structures in hemipelagic basin deposits: Santa Barbara Basin,California Borderland

Holocene mass flow processes produce distinctive sedimentary structures in this silled, anoxic basin characterized by high sedimentation rates of fine-grained fill. Mud flow deposits possess a 0899 1444 V 3 diagnostic vertical sequence of structures on the lower slope. Basin floor turbidites possess a variety of bed set combinations of: 1) finely laminated layers, 2) graded silt and clay layers, and 3) ungraded, massive silts and clays with floating sand grains. Massive, ungraded flood-derived suspensate deposits can be distinguished from turbidites. Turbidites and suspensate deposits constitute 30% of the sampled sediment column. Varve counting of the remaining 70% provides frequencies of turbidite and flood suspensate layer deposition.     

Miocene Blanca Fan, Northern Channel Islands, California: Small fans reflecting tectonism and volcanism

Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively. Margin setting represents fan and/or source area     

Ferrelo Fan,California: Depositional system influenced by Eustatic sea level changes

Remnants of an Eocene fan system are preserved onshore at San Diego and in the central part of the southern California borderland. Even though faults and erosion have truncated its margins, geophysical data and exploratory wells indicate that remaining parts of the fan extend beneath an offshore area nearly 400-km long and 40- to 100-km wide. Environments representing fluvial, fan-delta, shelf-channel, overlapping inner- to outer-fan, and basin-plain facies are recognized or inferred. Three progradational cycles onshore and two distinct pulses of sand accumulation offshore are attributable to eustatic low sea-level stands rather than to tectonic uplift or shifts in depositional patterns.     

Miocene Blanca Fan,Northern Channel Islands,California: Small fans reflecting tectonism and volcanism

Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively.     

Weddell Fan and associated abyssal plain,Antarctica: Morphology,sediment processes,and factors influencing sediment supply

The newly discovered Weddell Fan, Antarctica, covers 0.75 million km². The adjacent continental shelf is characterized by deep, rugged topography; the inner shelf is covered by a grounded polar ice sheet. The upper fan has numerous deep, V-shaped canyons that intersect a slope-base, leveed fan valley. Piston cores from the valley contain disorganized gravel grading upward into graded gravel and sand. Levee cores contain interbedded hemipelagic sediments and fine-grained turbidites. The lower fan is sand-rich. Sediment supply to the fan apparently occurred before development of glacial shelf topography and during a more temperate glacial setting.     

The Central Submarine Canyon in the Qiongdongnan Basin, northwestern South China Sea: Architecture, sequence stratigraphy, and depositional processes

Submarine canyons have been the subject of intense studies in recent years because of their close link to deepwater systems. The Central Canyon is a large unusual submarine canyon in the northwestern margin of the South China Sea, has a total length of about 425 km and is oriented sub-parallel to the continental slope. Using integrated 2D/3D seismic, well log, core, and biostratigraphy data, the current study documents the stratigraphic framework, internal architecture, depositional processes, and controlling factors of the segment of the Central Canyon located in the Qiongdongnan Basin.The integrated analysis shows that the canyon fill consists of four 3^rd-order sequences, SQ4, SQ3, SQ2, and SQ1. Each of them is bounded by regionally important erosional surfaces (3^rd-order sequence boundaries). Within each 3^rd-order sequence there is maximum regressive surface separating a regressive systems tract in the lower part and a transgressive systems tract in the upper part. Nine facies are identified and are further grouped into five depositional units, DU1 through DU5.The canyon evolved through four cut-and-fill stages, with a change from predominantly axial cut-and-fill to primarily side cut-and-fill. Axial cut-and-fill dominated during the first stage, and the slope-subparallel paleo Xisha Trough was intensely eroded by large-scale axial gravity flows. During the second cut-and-fill stage, the Central Canyon experienced both axial and side cut-and-fill. The third stage was dominated by side cut-and-fill. The canyon was eroded and fed by slope channels that transported sandy sediments from the shelf to the north during regression, and was covered by side-derived muddy MTCs during transgression. The last stage was also dominated by side cut-and-fill. The canyon, however, was filled predominantly by side-derived muddy MTCs.Evolution and depositional processes in the Central Canyon were likely controlled by slope-subparallel negative-relief induced by paleo-seafloor morphology, structural inversion of the Red River Fault and the slope-subparallel basement faults. Additionally, Coriolis force, sea-level fluctuations, high sedimentation rate, and rapid progradation of the slope also controlled and influenced the depositional processes, and internal architectures of the canyon.     

Patterns and processes in the California Current System

The California Current System (CCS) is forced by the distribution of atmospheric pressure and associated winds in relation to the west coast of North America. In this paper, we begin with a simplified case of winds and a linear coast, then consider variability characteristic of the CCS, and conclude by considering future change. The CCS extends from the North Pacific Current (～50°N) to off Baja California, Mexico (～15–25°N) with a major discontinuity at Point Conception (34.5°N). Variation in atmospheric pressure affects winds and thus upwelling. Coastal, wind-driven upwelling results in nutrification and biological production and a southward coastal jet. Offshore, curl-driven upwelling results in a spatially large, productive habitat. The California Current flows equatorward and derives from the North Pacific Current and the coastal jet. Dominant modes of spatial and temporal variability in physical processes and biological responses are discussed. High surface production results in deep and bottom waters depleted in oxygen and enriched in carbon dioxide. Fishing has depleted demersal stocks more than pelagic stocks, and marine mammals, including whales, are recovering. Krill, squid, and micronekton are poorly known and merit study. Future climate change will differ from past change and thus prediction of the CCS requires an understanding of its dynamics. Of particular concern are changes in winds, stratification, and ocean chemistry.     

Modern sedimentary processes in the Santa Monica,California continental margin: sediment accumulation,mixing and budget

Sediment input to SMB appears to be associated with at least two point sources on the shelf, with Malibu Creek and the Hyperion sewage outfall being the most significant. Sediment contributions are sufficient to support apparent mass accumulation rates near these sources up to approximately 1.8 g/cm(2) year, which with distance decrease to approximately 0.5 g/cm(2) year near the shelf break (approximately 80-100 m water depth). Sequestering of material on the shelf and decreasing sediment supply to the slope is evident as rates decrease between 100 and 200 m water depths to less than 0.2 g/cm(2) year. Below 100-200 m water depth, rates are relatively slow throughout a broad region of the slope (0.07-0.14 g/cm(2) year). These slower rates are in general agreement with rates determined on the flanks of the California Borderland basins. Sediment texture fines from approximately 3.5 phi to approximately 7 phi with distance offshore. Texture does not exhibit significant changes from surficial values with depth in the seabed at any given site or between sites on the slope. This similarity in rates and downcore texture over such a broad extent suggests that hemiplegic sedimentation is the dominant mechanism of sediment delivery in water depths >200 m. Seabed distributions of radionuclides suggest that apparent accumulation rates in SMB may be twice the actual accumulation rates. A sediment budget documents that over the past century at least, SMB has served as a sink for 50-100% of the natural and anthropogenic inputs to the coastal ocean.     

Sedimentation styles and depositional processes in a Middle to Late Jurassic slope environment, Bowser Basin, northwestern British Columbia, Canada

The Middle to Upper Jurassic Todagin assemblage in northwestern British Columbia, Canada, was deposited in the Bowser Basin above arc-related rocks of the Stikine terrane. Sedimentary structures indicate that a variety of gravity flow processes were involved in transport and deposition in deep-water slope environments. At Mount Dilworth, laterally continuous and channelized turbidites are interbedded with and overlain by mass-transport deposits in which sedimentary clasts are supported in a mudstone matrix. More than 50% of the succession consists of mass-transport deposits, indicating significant slope instability. A 300 m thick mass-transport complex exposed near the top of the succession is interpreted to result from tectonic activity, which triggered a major change in sediment supply from a local source area. At Todagin Mountain, a channel complex displays three successive channel-fills with associated overbank sedimentation units. Mass-transport deposits are rare, and confined to channel axes. Channels 1 and 2 are characterized by 40-50 m thick, ungraded pebble clast-supported conglomerate while the uppermost Channel 3 contains graded beds and occasional traction structures. The gradual change from erosive and amalgamated channel deposits at the base, to more aggradational channels at the top, is related to elevation of the equilibrium profile. Creation of accommodation favored aggradation on the mud-dominated slope succession and construction of well-developed channel-levee systems. The vertical succession exposed at Todagin Mountain is consistent with normal progradation of the slope under high sedimentation rates. In the Mount Dilworth area, extensional faulting associated with development of the restricted Eskay rift in the early Middle Jurassic produced a dissected basement above which the Todagin assemblage was deposited. These structures were inverted during collision of the Stikine and Cache Creek terranes, and likely played a major role in the stratigraphic evolution of the deep-water architectures.