Km Of Multichannel Seismic Data Research Articles

Stacked debris flows offshore Sakarya Canyon, western Black Sea: morphology, seismic characterization and formation processes

Analysis of ca. 1400 km of multichannel seismic data indicate that the distal part of the Sakarya Canyon within the continental rise is an unstable region with sediment erosion. Fourteen buried debris flows (DB1-DB14), in the stacked form within Plio-Quaternary sediments between 1400 and 1950 m water depth, were observed in the surveyed area. Their run-out distances range from 3.8 to 24.4 km. The largest debris flow DB10 affects ca. 225 km2 surficial area transporting ca. 15 km3 of sediment in S to N direction. The debris flows in the area are considered as gravity flows of unconsolidated sediments mobilized due to the excess pore pressures occurred in the unconsolidated shallow sediments arising from the high sedimentation rate. We also suggest that extensive seismic activity of North Anatolian Fault (NAF) located ca. 140 km south of the of the study area along with the possible local fault activity is also a significant triggering factor for the flows. The stacked form of the debrites indicates that the excess pore pressure conditions are formed periodically over the time in the continental rise, which makes the region a potentially unstable area for the installation of offshore engineering structures.

New insights on the Adria plate geodynamics from the northern Adriatic perspective

Abstract The interpretation of approximately 1300 km of multichannel seismic data, acquired in the northern Adriatic Sea, revealed that the Apennine foredeep in the northern Adriatic does not show any evidence of tilting since Early Pliocene, suggesting that slab retreat cannot be the geodynamic driving force for the northern Adriatic subsidence and for the northern Apennine kinematic since that time. Moreover, the presence of two fault systems that developed since the Pliocene indicates that the northern Adriatic underwent intraplate deformation during the Plio-Pleistocene. These considerations suggest that, since Early Pliocene, subduction below the northern Apennine ceased, and that the Adria Plate movements were mainly driven by the kinematics of the adjacent plates, particularly by the Nubia-Europe convergence. At present, on the basis of the foredeep setting, four distinct sectors can be recognized in the Adriatic foreland: Po Plain, northern, central and southern Adriatic, separated by major tectonic lineaments. The northern Adriatic differs from the two adjoining sectors because its foredeep deposits are still well preserved. In the Po Plain in fact, the Adriatic foredeep is almost totally incorporated into the Alpine and Apennine chains while in the central Adriatic, it is affected by a considerable intraplate deformation (e.g. the Mid Adriatic Ridge). In this framework, the northern Adriatic region may be regarded as a triangular shaped sector indented below the Southern Alps to the north and the northern Dinarides to the north-east and bounded to the west by the Schio-Vicenza fault system and to the south-east by the Kvarner fault.

The Offshore New Harbour Project: deciphering the Middle Miocene through Late Eocene seismic stratigraphy of Offshore New Harbour, western Ross Sea, Antarctica

Abstract In the Austral spring of 2008, over 48 km of multi-channel seismic data were collected offshore of New Harbour, which is located in the western most Ross Sea, Antarctica. This project is part of the ANDRILL (Antarctic Geological Drilling) Programme's Offshore New Harbour Project, with its aim to investigate the stratigraphic and tectonic history of the inner shelf of southern McMurdo Sound. Correlating the seismic data to CIROS-1 and ANDRILL AND-2A drillholes provided age dates ranging from Late Miocene to at least Late Eocene for the reflectors and lithological descriptions for the seismic units. This permitted development of a glacial history of this area, resulting in dividing the seismic data into three units: an Upper Eocene–Lower Oligocene unit; an Upper Oligocene–Lower Miocene unit; and a Middle Miocene and younger unit. The seismic section below 700 mbsf has two possible interpretations: (1) substantial Eocene strata are present downdip of CIROS-1, which would represent a potential future-drilling objective for the ANDRILL Programme; or (2) these reflectors may be equivalent to Devonian strata recovered at the Cape Roberts 3 as the two-way traveltime of Eocene and Devonian strata are nearly identical, making it difficult to discriminate between them in seismic data.

Frozen magma lenses below the oceanic crust

The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies.

Improved Seismic Stratigraphy of the Mesozoic Weddell Sea

We present a compilation of more than 45,000 km of multichannel seismic data acquired in the last three decades in the Weddell Sea. In accordance with recent tectonic models and available drillhole information, a consistent stratigraphic model for depositional units W1–W5 is set up. In conjunction with existing aeromagnetic data, a chronostratigraphic timetable is compiled and units W1.5, W2 and W3 are tentatively dated to have ages of between 136 Ma and 114 Ma. The age of W3 is not well constrained, but might be younger than 114 Ma. The data indicate that the thickest sediments are present in the western and southern Weddell Sea. These areas formed the earliest basins in the Weddell Sea and so the distribution of Mesozoic sediments is in accordance with the tectonic development of the ocean basin. In terms of Cenozoic glacial sediments, the largest depocenters are situated in front of the Filchner–Ronne Shelf, i.e. at the Crary Fan, with a thickness of up to 3 km.

Multibranch Antarctic Seismic Data Library facilitates research

In 1991, investigators from 11 nations involved in Antarctic multichannel seismic (MCS) reflection research sought a way to keep the Antarctic Treaty's promise of open access to data, and in the process to encourage Earth‐science research using seismic data. The Antarctic Seismic Data Library System for Cooperative Research (SDLS) was the solution, and is now a recommendation of the Antarctic Treaty Consultative Parties (ATCP). Today—at 12 branches spanning the world—researchers can access over 68,000 km of marine MCS data to use for cooperative research.More than 150,000 km of MCS data have been accumulated since 1976 by 13 countries on nearly 70 cruises. The majority of data now in the library cover the Ross Sea, Wilkes Land, and Prydz Bay sectors of the Antarctic margin, with smaller amounts from the Weddell Sea and the Antarctic Peninsula.

Shortening within underplated oceanic crust beneath the Central California Margin

Structures within a tectonically underplated layer of early Miocene age oceanic crust indicate that the lower crust of offshore central California has been deformed under compression prior to the inception of the San Andreas transform system along the continental margin. Shortening in the lower crust is inferred from the geometry of two structures, the Santa Lucia monocline and the Santa Maria antiform, delineated by an integrated interpretation of multichannel and wide‐angle seismic reflection data in conjunction with regional gravity data and teleseismic receiver functions. The 700 km of multichannel seismic data and 300 km of wide‐angle seismic data from the 1986 Pacific Gas and Electric/EDGE seismic experiment form the primary data base used to establish the northwesterly trend and extent of the monocline and the WNW trend of the antiform. In cross‐sectional view, the Santa Lucia monocline is a 30° kink in the oceanic crust, while the Santa Maria antiform is characterized by local thickening of the oceanic crust. These structures are probably the result of convergence between the Monterey and Arguello microplates that took place as subduction along the margin waned. The multichannel seismic reflection data image two Miocene age shelf basins, the Santa Lucia and offshore Santa Maria basins that formed within a transtensional stress regime. The offshore Santa Maria basin directly overlies the Santa Maria antiform, suggesting that either the upper and lower crustal stress regimes were completely decoupled in Miocene time or that the two features formed in different places. Differential slip between the upper crust and lower crust may have been accommodated along a detachment zone located above oceanic crust. Convergence within the oceanic crust and apparent differential motion between upper and lower crust are indicative of the processes that can affect the transition from subduction to an oceanic‐continental transform zone.

Project SYD VEST SEIS - 3285 km of multichannel seismic data acquired on the southern West Greenland shelf

During the three years since 1988, there has been renewed activity within the Geological Survey of Greenland (GGU) to reassess the geology and petroleum prospectivity of the southern West Greenland offshore area (Chalmers, 1989; Chalmers, 1990; Chalmers & Pulvertaft, in press; Ottesen, 1991). Pulvertaft (1991) gives a summary of the present state of the re-evaluation. This work has shown that the geology of the northern Labrador Sea and offshore southern West Greenland is poorly understood. A number of questions about the area's petroleum prospectivity remain unanswered despite re-interpretation and in some cases reprocessing of the existing seismic data. These problems derive from limitations in both the quality and extent of the existing seismic coverage.

Plate Tectonics and Petroleum Potential of the Laptev Sea Region

About 1,600 km of multichannel seismic data with simultaneous gravity and magnetic measurements were collected in the Laptev Sea during 1989. Additionally, a 100 km onshore seismic reflection profile transected the northern termination of the Verrkoyansky Mountains. Data interpretation showed the following. The tectonic patterns of the Laptev Sea region was formed as a result of two major tectonic phases. The first phase was associated with collisions between the Paleozoic passive margin of Siberia and a number of allochthonous terrains which were previously parts of the North American Paleo-Pacific plate. These tectonic events accompanied the opening of the Canadian basin and ended in the second half of the Early Cretaceous. The second phase was a result of the opening of the Makarov and the Europeo-Asiatic basins, which caused the rifting processes within the Laptev Sea Shelf. Seismic onshore data show that the orogenic sequence consists of allochthonous plates which were thrust onto the thick sedimentary cover the Siberia platform. An underthrusting sedimentary sequence is situated at depths from 3 to 5 km, which present a good possibility to reach by the drill. The geological analogy with Appalachian Mountains United States, permits one to propose a high petroleum potential for thismore » area. A system of offshore Laptev Sea grabens consisting of a series of alternating tilted and thrusted blocks, along with intrablock pre-drift sediments, are promising as potential hydrocarbon traps. This is akin to structural setting within North Sea oil and gas province.« less

Re-evaluation of the geology of the southern West Greenland shelf - Project VEST SOKKEL

From 1970 to 1977 approximately 40000 km of multichannel seismic data were acquired between latitudes 63°N and 68°N on the continental shelf of southern West Greenland. In 1976 and 1977 five wells were drilled to explore for hydrocarbons, but all of them were dry. All exploration licences were relinquished by 1979.

Distribution, crustal properties and significance of seawards-dipping sub-basement reflectors off E Greenland

Summary We report in this paper the existence of seawards-dipping sub-basement reflectors along the entire E Greenland margin. The study is based on 8000 km of multichannel seismic data and a sonobuoy refraction seismic study providing information on the geographical and stratigraphical extension, internal geometry and crustal structure of the E Greenland dipping reflector sequence. A basaltic, subaerial seafloor-spreading origin of the reflector sequence is concluded from seismic stratigraphic analysis, including well information from the Rockall Plateau and the Vøring Plateau. Formation of the basaltic dipping reflector sequence off E Greenland took place within a period of a few million years along the axis of opening within the NE Atlantic. Duration of spreading above sea-level was relatively short (2 My) in areas of present-day deep basement, as opposed to 5–8 My in areas of present-day more shallow basement. On the highly elevated Iceland-Greenland Ridge, subaerial seafloor spreading continued into the Neogene and most likely into present-day subaerial spreading in Iceland. Following the mid-Tertiary westward shift of spreading towards Greenland, N of Iceland, spreading again took place above sea-level along this part of the Greenland margin until late Miocene, but this development only caused an erratic and shallow development of seawards-dipping reflectors. Application of the kinematic model for crustal formation in Iceland (Pálmason 1980) onto the E Greenland dipping reflector sequence demonstrates a striking similarity between the two structures. However, volcanic productivity rate within the oldest part of the E Greenland dipping reflector sequence may be as much as three times the volcanic productivity rate recorded in Iceland with an original rift width equal to, or somewhat less than, that in Iceland. The high volcanic productivity rate caused the development of a thick extrusive upper crust (> 5–6 km) dominated by seawards-dipping reflections arising from lava flows or groups of flows which acquired their dip through postdepositional differential subsidence towards the rift zone. Refraction seismology defines a fairly flat-lying velocity zonation of the igneous crust with an anomalously thick layer 2 (3–5.5 km) in areas of well-developed dipping reflectors. The layer 2/3 boundary is seen to cut strongly across the dipping reflectors suggesting a metamorphic origin of this boundary. Initiation of seafloor spreading above sea-level is seen as a result of early upwelling of anomalously hot asthenospheric material that was able to ascend through a relatively mechanically unstretched crust and lithosphere and create a thick extrusive upper crust. Formation of a thick extrusive upper crust above sea-level only continued beyond the early spreading phase in the area of the Icelandic hot-spot (Iceland-Greenland Ridge).

STRUCTURE AND STRATIGRAPHY OF THE CEDUNA TERRACE REGION, GREAT AUSTRALIAN BIGHT BASIN

The Ceduna Terrace is a bathymetric feature covering some 70,000 sq km, in the continental slope of South Australia. Its most gently sloping part lies between the 500 and 2500m isobaths, and is underlain by the main depocentre of the Great Australian Bight Basin.A systematic interpretation of the region has been made, based on 17,000 km of multi-channel seismic data from Shell surveys, 8000 km of single-channel seismic, gravity and magnetic data from the BMR Continental Margins Survey, and 6000 km of gravity and magnetic data from surveys by Lamont-Doherty Geological Observatory. Seismic ties were made to the wells Potoroo-1 and Platypus-1.Mapping of the key seismic horizons confirms the picture of the basin as a sedimentary wedge, more than 10 km thick, extending from the edge of the shelf to the continental rise. Three important unconformities can be mapped over a wide area and tied to Potoroo-1 well-a basement reflector separating Lower Proterozoic crystalline rocks of the Gawler Craton from an overlying, block-faulted sequence of mainly Lower to mid-Cretaceaus sediments; an unconformity at the base of an Upper Cretaceous sequence which includes a major prograded unit in the west; and a break-up unconformity at the base of a Tertiary marine transgressive sequence, that, in turn, is overlain by marine carbonate deposits. Widespread shallow marine sediments are believed to exist in the west of the basin, in both the Lower and Upper Cretaceous sequences.Structure is dominated by normal, west to NW trending, down-to-the-south faults, many of which are synsedimentary. Fault displacements are greatest beneath the shelf-break, where basement has been downthrown 5 to 6 km. Farther south, synsedimentary faulting has resulted in a marked thickening of both Upper and Lower Cretaceous sequences.The basin has been barely explored for hydrocarbons. Regional seismic coverage is good, but drilling in the main part of the basin is limited to one well on the northern margin. The petroleum potential of the western half of the basin is rated as good, in view of the interpreted existence of abundant marine source beds and the recognition of situations favourable for generation, migration and entrapment of hydrocarbons.