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171.
J. Paul F. Blume S. Jade V. Kumar P. S. Swathi M. B. Ananda V. K. Gaur Roland Burgmann Roger Bilham B. Namboodri Dave Mencin 《Journal of Earth System Science》1995,104(1):131-146
We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related
to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of
India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using
GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey
to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional
dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In
addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994)
in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate
motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern
Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya
of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian
plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin,
which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent
deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region
of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence
intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation
of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates
that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable
scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of
the 19th century GTS survey. 相似文献
172.
Salt tectonics in an intracontinental transform setting: Cumberland and Sackville basins,southern New Brunswick,Canada
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Salt tectonics have markedly influenced the rapid evolution of the Upper Palaeozoic Cumberland Basin of Atlantic Canada, including the ca. 5 km‐thick Mississippian – Pennsylvanian stratigraphic succession exposed along the UNESCO World Heritage coastline at Joggins, Nova Scotia. A diapiric salt wall is exposed in the Minudie Anticline to the north of the Joggins section on the Maringouin Peninsula of New Brunswick, which corresponds to the fault‐bounded northern margin of the Cumberland Basin. The salt wall is of Visean evaporites of the Windsor Gp that originally were buried by red‐beds of the Mabou Gp in the Serpukhovian, and later by fluvial and floodplain strata (Boss Point Fm, Cumberland Gp) in the Yeadonian (mid‐Bashkirian, Early Pennsylvanian). Folds and faults in the Boss Point and overlying basal Little River formations are truncated by an angular unconformity at the base of overlying red‐beds of the Grande Anse Fm. Re‐evaluation of the palynological data delimits the Grande Anse Fm as Langsettian, providing a tight constraint of less than 2 myr on the timing of deformation. Diversion of palaeoflows by the rising salt structure, noted in previous work on the upper Boss Point Fm, occurs to the north of the diapiric anticline. This is interpreted to signify the development of a mini‐basin on commencement of diapirism once a ~1.5 km‐thick succession of clastic strata had buried the salt. Faults and folds in the succession below the unconformity indicate an initial phase of dextral transpressive strike‐slip motion, which may have promoted halokinesis. Reverse faults indicate shortening associated with northward development and overturn of the Minudie Anticline during transpression; subsequent normal faulting was associated with collapse of the sediment pile and underlying salt structure. 相似文献
173.
174.
D. Reide Corbett Dave Vance Erin Letrick David Mallinson Stephen Culver 《Estuarine, Coastal and Shelf Science》2007,71(3-4):717-729
During the summer of 2001, several short cores (<50 cm) were collected in the Albemarle Estuarine System (AES). Down-core measurements for radiochemical tracers (210Pb, 137Cs) and organic matter signatures (δ13C, δ15N, C:N ratio, and LOI) have been used to elucidate potential temporal changes in fluxes and cycles of organic matter in the AES. Pb-210 geochronology indicates temporal and spatial variations in sediment deposition rates (0.08–0.57 cm y−1) with highest rates near the AES western limit relative to the rest of the estuary. Low accumulation rates, deficient excess 210Pb inventories, and near linear 137Cs profiles throughout the AES suggest that sediments are resuspended by wind-generated waves and currents and flushed from the system by river discharge and wind-tides, probably to Pamlico Sound to the south. Sediments in the AES are accumulating at rates less than the current rate of relative sea-level rise for this region except in protected portions of the estuary. Thus sediment accumulation in the AES is controlled in the short term by storm wave-base and in the long term by the creation of accommodation space by basin subsidence and sea-level rise. The geochemical and sedimentological data characterize the evolution of the Albemarle Sound and associated tributaries over the past 200–300 years. The majority of cores collected throughout the system show a significant decrease in 13C and increase in 15N isotopic signatures up-core. Thus, the estuarine system of eastern North Carolina has changed from a marine-influenced, high brackish environment to the modern-day system, which is a highly variable, terrestrially influenced, low brackish environment. 相似文献
175.
Circulation and mixing at the New England shelfbreak front: Results of purposeful tracer experiments 总被引:1,自引:0,他引:1
We present the results of six dye tracer experiments that measured the mixing and circulation at the shelfbreak front on the New England Shelf. The last three were conducted during the New England Shelfbreak Productivity Experiment (NESPEX) with concurrent isopycnal float deployments. The results are consistent with the Chapman and Lentz [Chapman, D.C., and Lentz, S.J. (1994). Trapping of a coastal density front by the bottom boundary layer. Journal of Physical Oceanography, 24, 1465–1479.] model prediction of the separation and upwelling along the shelfbreak front of bottom boundary layer (BBL) water forced by an Ekman buoyancy flux, but show considerable variability. Cross-shelf velocities at the detachment point are 2–3 × 10−2 m/s. But seaward, over the slope region, dye tagged water was sheared from the main patch into small filaments that upwelled along the front with cross-shelf speeds up to 0.1 m/s. Cross-shelf diffusion was of order 10 m2/s in the mixed bottom layer and 1 m2/s in the interior along the front. Within the stratified front, the mean vertical diffusivity was Kz 4 × 10−6 m2/s. The dispersion of shelfwater in the slope region is effected by turbulent flow with advective speeds exceeding the small scale diffusive mixing. The mean flux of the detached BBL water is sufficient to account for the net loss of shelf water during its transit from Cape Cod to Cape Hatteras. 相似文献
176.
Sarah McMullan Denis Vida Hadrien A. R. Devillepoix Jim Rowe Luke Daly Ashley J. King Martin Cupák Robert M. Howie Eleanor K. Sansom Patrick Shober Martin C. Towner Seamus Anderson Luke McFadden Jana Horák Andrew R. D. Smedley Katherine H. Joy Alan Shuttleworth Francois Colas Brigitte Zanda Áine C. O'Brien Ian McMullan Clive Shaw Adam Suttle Martin D. Suttle John S. Young Peter Campbell-Burns Richard Kacerek Richard Bassom Steve Bosley Richard Fleet Dave Jones Mark McIntyre Nick James Derek Robson Paul Dickinson Philip A. Bland Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947
On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures. 相似文献
177.
178.
The aim of the Geospatial Assessment of Marine Ecosystems (GAME) project is to develop an inventory of habitat-related data within the Gulf of Mexico and East coast of Florida. This will serve as a foundation to develop a spatial framework for ecosystem-based management associated with regulatory and planning programs and areas of governmental coordination. 相似文献
179.
Reactive transport modelling of reflux dolomitization in the Arab‐D reservoir,Ghawar field,Saudi Arabia
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It has long been recognized that the Arab‐D reservoir in Ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir. Previous studies indicated that dolomite occurs with either a stratigraphic or non‐stratigraphic distribution; when mapped, dolomite tends to form several parallel linear trends across the field. Although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits, non‐stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below. This study focuses primarily on these non‐stratigraphic dolomites, and proposes that: (i) these dolomites initially formed via seepage reflux, but were reinforced by late stage hydrothermal dolomitization; and (ii) reflux is also responsible for the formation of parallel, linear trends of dolomite. The reflux model hypothesizes that an evaporative lagoon (which is the source of dolomitizing fluids) formed during the falling stage systems tract of a depositional sequence, and that with continuing sea‐level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the Ghawar field, leaving behind lines of dolomite bodies along a series of temporary coastlines. Two‐dimensional reactive transport models have been built to test this hypothesis, and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non‐stratigraphic dolomite, as well as the mapped lateral distribution of the dolomite trends. In addition, the major ion compositions of Late Jurassic seawater are calculated based on fluid inclusion data in the literature. Using Jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over‐dolomitization than using modern seawater. 相似文献
180.
The importance of geochronology in the study of mineral deposits in general, and of unconformity-type uranium deposits in
particular, resides in the possibility to situate the critical ore-related processes in the context of the evolution of the
physical and chemical conditions in the studied area. The present paper gives the results of laser step heating 40Ar/39Ar dating of metamorphic host-rock minerals, pre-ore and syn-ore alteration clay minerals, and laser ablation inductively
coupled plasma mass spectrometer (LA-ICP-MS) U/Pb dating of uraninite from a number of basement- and sediment-hosted unconformity-related
deposits in the Athabasca Basin, Canada. Post-peak metamorphic cooling during the Trans-Hudson Orogen of rocks from the basement
occurred at ca 1,750 Ma and gives a maximum age for the formation of the overlying Athabasca Basin. Pre-ore alteration occurred
simultaneously in both basement- and sandstone-hosted mineralizations at ca 1,675 Ma, as indicated by the 40Ar/39Ar dating of pre-ore alteration illite and chlorite. The uranium mineralization age is ca 1,590 Ma, given by LA-ICP-MS U/Pb
dating of uraninite and 40Ar/39Ar dating of syn-ore illite, and is the same throughout the basin and in both basement- and sandstone-hosted deposits. The
mineralization event, older than previously proposed, as well as several fluid circulation events that subsequently affected
all minerals studied probably correspond to far-field, continent-wide tectonic events such as the metamorphic events in Wyoming
and the Mazatzal Orogeny (ca 1.6 to 1.5 Ga), the Berthoud Orogeny (ca 1.4 Ga), the emplacement of the McKenzie mafic dyke
swarms (ca 1.27 Ga), the Grenville Orogeny (ca 1.15 to 1 Ga), and the assemblage and break-up of Rodinia (ca 1 to 0.85 Ga).
The results of the present work underline the importance of basin evolution between ca 1.75 Ga (basin formation) and ca 1.59 Ga
(ore deposition) for understanding the conditions necessary for the formation of unconformity-type uranium deposits.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献