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Reflection Profiles (reflection + profile)
Kinds of Reflection Profiles Selected AbstractsSedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic OceanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010H. Ruth Jackson SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source] Rapid seismic reflection imaging at the Clovis period Gault site in central TexasARCHAEOLOGICAL PROSPECTION, Issue 4 2007John A. Hildebrand Abstract Using a modified seismic reflection imaging system with rapid translation of receivers, stratigraphic profiles were collected at the Gault site in central Texas. For rapid data collection, spikeless geophone receivers were placed in sand-filled bags at tight spacing, and these receivers were rapidly pulled along the ground surface between shots. Shots were produced by a small hammer strike to a vertical pipe at 20-cm intervals. High quality ultrashallow seismic reflection profiles were collected at a rate of 25,m,h,1, significantly faster than what is possible with conventional seismic reflection imaging using individually planted geophones. Ground-penetrating radar was attempted, but abandoned owing to the poor penetration of the radar signals in the clay soils present at the Gault site. Electromagnetic induction grids were collected surrounding each seismic reflection profile, and provided information on near-surface ground water. Seismic reflection images of Gault site stratigraphy provided greater depth penetration than accessible from backhoe trenching and coring, and helped to better outline the site geological context. Seismic images reveal coherent reflections at shallow depths (0,2.5,m), and extensive scattering at deeper levels (2.5,8,m), underlain by reflection-free zones. These data are interpreted as clay and gravel layers overlaying palaeostream channels carved into the limestone bedrock. Where comparative data were available, the geophysical findings were corroborated by observations of site stratigraphy in archaeological excavation units, backhoe trenches and cores. Seismic reflection studies at the Gault site revealed a palaeochannel filled with pre-Clovis age sediments. Pre-Clovis age sediments are not known to occur at other locations within the Gault site. They provide a unique opportunity to test for cultural remains of great antiquity. Copyright © 2007 John Wiley & Sons, Ltd. [source] Geological evolution and structural style of the Palaeozoic Tafilalt sub-basin, eastern Anti-Atlas (Morocco, North Africa)GEOLOGICAL JOURNAL, Issue 1 2008E. A. Toto Abstract The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of Morocco, all of which probably underwent a similar tectono-stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000,km of 2-D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi-phase deformation history for the Palaeozoic-aged Tafilalt sub-basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic-aged strata, producing a structural style characteristic of thin-skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault-propagation folding related to the thrust imbricates that ramp up-section from the décollement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic OceanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010H. Ruth Jackson SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source] Seismic constraints on the three-dimensional geometry of low-angle intracrustal reflectors in the Southern Iberia Abyssal PlainGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2008S. M. Dean SUMMARY Several lines of evidence suggest that simple shear rifting of the continental crust, in the form of low-angle detachment faulting, occurred during the final stages of continental breakup between West Iberia and the Grand Banks. The primary evidence for such faulting is the occurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean,continent transition zone. Here we present a series of intersecting, depth migrated seismic reflection profiles that image one such reflector, the H-reflector, located on the southern edge of Galicia Bank. ,H' lies beneath several boreholes drilled during ODP Legs 149 and 173, in a region where the oceanward extent of extended continental crust steps at least 150 km westward from its location in the southern Iberia Abyssal Plain to its location off the relatively shallow Galicia Bank. In our profiles ,H' appears to define a surface that extends over a region of at least 200 km2 and that dips down ,19° to the north, towards Galicia Bank. The profiles show that a close affinity exists between ,H' and the most seaward continental crust. Based on geophysical data and ODP drilling results, we infer that the basement above ,H' is composed of continental crust deformed by extensional faults into a series of wedge-shaped blocks and thin slivers. These basement wedges have a complex 3-D geometry. ,H' rises to the basement surface on a number of the seismic profiles and appears to define locally the oceanward extent of continental fault blocks. [source] Tracking reflections through cryogenic cooling with topographyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006Jeffrey J. Lovelace The mosaic structure of a single protein crystal was analyzed by reflection profiling and topography using highly parallel and monochromatic synchrotron radiation. Fine-,-sliced diffraction images (0.002° stills) were collected using a conventional large-area CCD detector in order to calculate reflection profiles. Fine-,-sliced topographic data (0.002°) stills were collected with a digital topography system for three reflections in a region where the Lorentz effect was minimized. At room temperature, several different mosaic domains were clearly visible within the crystal. Without altering the crystal orientation, the crystal was cryogenically frozen (cryocooled) and the experiment was repeated for the same three reflections. Topographs at cryogenic temperatures reveal a significantly increased mosaicity, while the original domain structure is maintained. A model for the observed changes during cryocooling is presented. [source] Seafloor glacial features reveal the extent and decay of the last British Ice Sheet, east of Scotland,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2009Alastair G. C. Graham Abstract Three-dimensional (3D) seismic datasets, 2D seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf, offshore eastern Scotland (58° N, 1,2° W). The relic features are related to the activity of the last British Ice Sheet (BIS) in the Outer Moray Firth. A landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor. The assemblage comprises: (i) large seabed banks (interpreted as end moraines), coeval with the Bosies Bank moraine; (ii) morainic ridges (hummocky, push and end moraine) formed beneath, and at the margins of the ice sheet; (iii) an incised valley (a subglacial meltwater channel), recording meltwater drainage beneath former ice sheets; and (iv) elongate ridges and grooves (subglacial bedforms) overprinted by transverse ridges (grounding line moraines). The bedforms suggest that fast-flowing grounded ice advanced eastward of the previously proposed terminus of the offshore Late Weichselian BIS, increasing the size and extent of the ice sheet beyond traditional limits. Complex moraine formation at the margins of less active ice characterised subsequent retreat, with periodic stillstands and readvances. Observations are consistent with interpretations of a dynamic and oscillating ice margin during BIS deglaciation, and with an extensive ice sheet in the North Sea basin at the Last Glacial Maximum. Final ice margin retreat was rapid, manifested in stagnant ice topography, which aided preservation of the landsystem record. Copyright © 2008 John Wiley & Sons, Ltd. [source] A new approach to calculating powder diffraction patterns based on the Debye scattering equationACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2010Noel William Thomas A new method is defined for the calculation of X-ray and neutron powder diffraction patterns from the Debye scattering equation (DSE). Pairwise atomic interactions are split into two contributions, the first from lattice-pair vectors and the second from cell-pair vectors. Since the frequencies of lattice-pair vectors can be directly related to crystallite size, application of the DSE is thereby extended to crystallites of lengths up to ~200,nm. The input data correspond to unit-cell parameters, atomic coordinates and displacement factors. The calculated diffraction patterns are characterized by full backgrounds as well as complete reflection profiles. Four illustrative systems are considered: sodium chloride (NaCl), ,-quartz, monoclinic lead zirconate titanate (PZT) and kaolinite. The effects of varying crystallite size on diffraction patterns are calculated for NaCl, quartz and kaolinite, and a method of modelling static structural disorder is defined for kaolinite. The idea of partial diffraction patterns is introduced and a treatment of atomic displacement parameters is included. Although the method uses pair distribution functions as an intermediate stage, it is anticipated that further progress in reducing computational times will be made by proceeding directly from crystal structure to diffraction pattern. [source] Rapid seismic reflection imaging at the Clovis period Gault site in central TexasARCHAEOLOGICAL PROSPECTION, Issue 4 2007John A. Hildebrand Abstract Using a modified seismic reflection imaging system with rapid translation of receivers, stratigraphic profiles were collected at the Gault site in central Texas. For rapid data collection, spikeless geophone receivers were placed in sand-filled bags at tight spacing, and these receivers were rapidly pulled along the ground surface between shots. Shots were produced by a small hammer strike to a vertical pipe at 20-cm intervals. High quality ultrashallow seismic reflection profiles were collected at a rate of 25,m,h,1, significantly faster than what is possible with conventional seismic reflection imaging using individually planted geophones. Ground-penetrating radar was attempted, but abandoned owing to the poor penetration of the radar signals in the clay soils present at the Gault site. Electromagnetic induction grids were collected surrounding each seismic reflection profile, and provided information on near-surface ground water. Seismic reflection images of Gault site stratigraphy provided greater depth penetration than accessible from backhoe trenching and coring, and helped to better outline the site geological context. Seismic images reveal coherent reflections at shallow depths (0,2.5,m), and extensive scattering at deeper levels (2.5,8,m), underlain by reflection-free zones. These data are interpreted as clay and gravel layers overlaying palaeostream channels carved into the limestone bedrock. Where comparative data were available, the geophysical findings were corroborated by observations of site stratigraphy in archaeological excavation units, backhoe trenches and cores. Seismic reflection studies at the Gault site revealed a palaeochannel filled with pre-Clovis age sediments. Pre-Clovis age sediments are not known to occur at other locations within the Gault site. They provide a unique opportunity to test for cultural remains of great antiquity. Copyright © 2007 John Wiley & Sons, Ltd. [source] Crystal quality and differential crystal-growth behaviour of three proteins crystallized in gel at high hydrostatic pressureACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2005A. Kadri Pressure is a non-invasive physical parameter that can be used to control and influence protein crystallization. It is also found that protein crystals of superior quality can be produced in gel. Here, a novel crystallization strategy combining hydrostatic pressure and agarose gel is described. Comparative experiments were conducted on hen and turkey egg-white lysozymes and the plant protein thaumatin. Crystals could be produced under up to 75,100,MPa (lysozymes) and 250,MPa (thaumatin). Several pressure-dependent parameters were determined, which included solubility and supersaturation of the proteins, number, size and morphology of the crystals, and the crystallization volume. Exploration of three-dimensional phase diagrams in which pH and pressure varied identified growth conditions where crystals had largest size and best morphology. As a general trend, nucleation and crystal-growth kinetics are altered and nucleation is always enhanced under pressure. Further, solubility of the lysozymes increases with pressure while that of thaumatin decreases. Likewise, changes in crystallization volumes at high and atmospheric pressure are opposite, being positive for the lysozymes and negative for thaumatin. Crystal quality was estimated by analysis of Bragg reflection profiles and X-ray topographs. While the quality of lysozyme crystals deteriorates as pressure increases, that of thaumatin crystals improves, with more homogeneous crystal morphology suggesting that pressure selectively dissociates ill-formed nuclei. Analysis of the thaumatin structure reveals a less hydrated solvent shell around the protein when pressure increases, with ,20% less ordered water molecules in crystals grown at 150,MPa when compared with those grown at atmospheric pressure (0.1,MPa). Noticeably, the altered water distribution is seen in depressurized crystals, indicating that pressure triggers a stable structural alteration on the protein surface while its polypeptide backbone remains essentially unaltered. [source] Cenozoic stratigraphy and subsidence history of the South China Sea margin in the Taiwan regionBASIN RESEARCH, Issue 4 2003A. T. Lin Seismic reflection profiles and well data are used to determine the Cenozoic stratigraphic and tectonic development of the northern margin of the South China Sea. In the Taiwan region, this margin evolved from a Palaeogene rift to a latest Miocene,Recent foreland basin. This evolution is related to the opening of the South China Sea and its subsequent partial closure by the Taiwan orogeny. Seismic data, together with the subsidence analysis of deep wells, show that during rifting (,58,37 Ma), lithospheric extension occurred simultaneously in discrete rift belts. These belts form a >200 km wide rift zone and are associated with a stretching factor, ,, in the range ,1.4,1.6. By ,37 Ma, the focus of rifting shifted to the present-day continent,ocean boundary off southern Taiwan, which led to continental rupture and initial seafloor spreading of the South China Sea at ,30 Ma. Intense rifting during the rift,drift transition (,37,30 Ma) may have induced a transient, small-scale mantle convection beneath the rift. The coeval crustal uplift (Oligocene uplift) of the previously rifted margin, which led to erosion and development of the breakup unconformity, was most likely caused by the induced convection. Oligocene uplift was followed by rapid, early post-breakup subsidence (,30,18 Ma) possibly as the inferred induced convection abated following initial seafloor spreading. Rapid subsidence of the inner margin is interpreted as thermally controlled subsidence, whereas rapid subsidence in the outer shelf of the outer margin was accompanied by fault activity during the interval ,30,21 Ma. This extension in the outer margin (,,1.5) is manifested in the Tainan Basin, which formed on top of the deeply eroded Mesozoic basement. During the interval ,21,12.5 Ma, the entire margin experienced broad thermal subsidence. It was not until ,12.5 Ma that rifting resumed, being especially active in the Tainan Basin (,,1.1). Rifting ceased at ,6.5 Ma due to the orogeny caused by the overthrusting of the Luzon volcanic arc. The Taiwan orogeny created a foreland basin by loading and flexing the underlying rifted margin. The foreland flexure inherited the mechanical and thermal properties of the underlying rifted margin, thereby dividing the basin into north and south segments. The north segment developed on a lithosphere where the major rift/thermal event occurred ,58,30 Ma, and this segment shows minor normal faulting related to lithospheric flexure. In contrast, the south segment developed on a lithosphere, which experienced two more recent rift/thermal events during ,30,21 and ,12.5,6.5 Ma. The basal foreland surface of the south segment is highly faulted, especially along the previous northern rifted flank, thereby creating a deeper foreland flexure that trends obliquely to the strike of the orogen. [source] Frontal accretion and thrust wedge evolution under very oblique plate convergence: Fiordland Basin, New ZealandBASIN RESEARCH, Issue 4 2002P. M. Barnes ABSTRACT A thrust wedge with unusual geometry has developed under very oblique (50,60°) convergence between the Pacific and Australian Plates, along the 240-km length of the Fiordland margin, New Zealand. The narrow (25 km-wide) wedge comprises three overlapping components, lying west of the offshore section of the Alpine Fault, and straddles a change of > 30° in the regional strike of the plate boundary. Swath bathymetry, marine seismic reflection profiles, and dated samples together reveal the stratigraphy, structure, and evolution of the wedge and the underthrusting, continental, Caswell High (Australian Plate). Lateral variations in the composition and structure of the accretionary wedge, and the depth of the décollement thrust, result partly from variations in crustal structure and basement relief of the underthrust plate, and from associated variations in the thickness of turbidites available for frontal accretion. In the southern Fiordland Basin the underthrust plate is undergoing flexural uplift and extension, and a thick turbidite section is available for accretion. Along-strike, a structurally elevated portion of the underthrust plate is very obliquely colliding with the central part of the accretionary wedge, the turbidite section available for accretion is condensed, and structural inversion occurs in the underthrust plate. ,Growth of the thrust wedge is inferred to have commenced in the Pliocene prior to 3 ± 1 Ma, but much of the wedge developed in the Quaternary. The spatial distribution of thrusting has varied through time, with most late Quaternary shortening occurring on structures within 10 km of the right-stepping deformation front. Estimates of the magnitude and rates of deformation indicate that the wedge accommodates a significant component of the oblique convergence between the Pacific and Australian Plates. Shortening of up to 7.3 ± 1.4 km and 9.1 ± 1.8 km within the southern and central parts of the wedge, respectively, represent about 5,15% of the total 70,140 km of shortening predicted across the plate boundary since 6.4 Ma, and about 10,30% since 3 Ma. Late Quaternary shortening rates of the order of 1,5 mm yr,1, estimated across both the northern and southern parts of the wedge, represent about 10,50 and 5,21% of the total NUVEL-1 A shortening across the plate boundary at these respective latitudes, implying that most shortening is occurring onshore. Furthermore, possible oblique-slip thrusting within the wedge may be accommodating boundary-parallel displacement of 0,6 mm yr,1, representing 0,17% of the total predicted within the plate boundary. [source] Structural Evolution of the Eastern Qiulitagh Fold and Thrust Belt, Northern Tarim Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Minghui YANG Abstract: The eastern Qiulitagh fold and thrust belt (EQFTB) is part of the active Kuqa fold and thrust belts of the northern Tarim Basin. Seismic reflection profiles have been integrated with surface geologic and drill data to examine the deformation and structure style of the EQFTB, particularly the deformational history of the Dina 2 gas field. Seismic interpretations suggest that Dongqiu 8 is overall a duplex structure developed beneath a passive roof thrust, which generated from a tipline in the Miocene Jidike Formation, and the sole thrust was initiated from the same Jidike Formation evaporite zone that extends westward beneath the Kuqatawu anticline. Dongqiu 5 is a pop-up structure at the western part of the EQFTB, also developed beneath the Jidike Formation evaporite. Very gentle basement dip and steep dipping topographic slope in the EQFTB suggest that the Jidike Formation salt provides effective decoupling. The strong deformation in the EQFTB appears to have developed further south, in an area where evaporite may be lacking. Since the Pliocene, the EQFTB has moved farther south over the evaporite and reached the Yaken area. Restoring a balanced cross-section suggests that the minimum shortening across the EQFTB is more than 7800 m. Assuming that this shortening occurred during the 5.3 Ma timespan, the shortening rate is approximately 1.47 mm/year. [source] | |||||||||||||