Geological Society Special Publication
0305-8719
Anh Quốc
Cơ quản chủ quản: Geological Society of London
Lĩnh vực:
Ocean EngineeringGeologyWater Science and Technology
Phân tích ảnh hưởng
Thông tin về tạp chí
Special Publications are renowned throughout the global geoscience community for their high quality of science and production. They represent a state-of-the-art treatment of their subject matter. Although they do not have to be comprehensive (they are not text books), we expect the editors to provide a balanced coverage of the subject matter. The Society has high standards of quality control for book proposals, and the volume editors are required to undertake full peer review of all papers to the standards expected for our journals. The Geological Society is actively commissioning new volumes for the series, and will consider all branches of the Earth sciences except engineering geology for this series. Most, but not all, result from conferences. However, they are not conference proceedings. We will consider proposals from independent meetings and those of other organisations.
Các bài báo tiêu biểu
Deformation processes in unconsolidated sands Summary
Deformation in unconsolidated sands requires the action of a deformation mechanism to reduce sediment strength and a driving force to induce deformation. Deformation mechanisms include liquefaction and fluidization and are reflected in the style of deformation and grain orientation fabrics. They are initiated by a trigger, including groundwater movements, wave action and seismic shaking. Driving forces include gravitational body force, unevenly distributed loads, unstable density gradients and shear forces, and are reflected in the geometry of deformation. These components are combined to produce a genetic classification of soft-sediment deformation processes and structures.
Tập 29 Số 1 - Trang 11-24 - 1987
Rootless cones on Mars: a consequence of lava-ground ice interaction Abstract
Fields of small cratered cones on Mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow. Melting and vaporization of the ice, and subsequent explosive expansion of the vapour, act to excavate the lava and construct a rootless cone around the explosion site. Similar features are found in Iceland, where flowing lavas encountered water-saturated substrates. The martian cones have basal diameters of
c
. 30–1000 m and are located predominantly in the northern volcanic plains. High-resolution Mars Orbiter Camera images offer significant improvements over Viking data for interpretation of cone origins. A new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features. This is consistent with the likely low availability of water ice in the martian regolith. The scarcity of impact craters on many of the host lava flows indicates very young ages, suggesting that ground ice was present as recently as <10–100 Ma, and may persist today. Rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on Mars, which is of key significance in understanding the evolution of the martian climate. The location of water in liquid or solid form is of great importance to future robotic and human exploration strategies, and to the search for extraterrestrial life.
Tập 202 Số 1 - Trang 295-317 - 2002
The liquification and remobilization of sandy sediments Abstract
A number of large, unusually shaped sandbodies have been interpreted from three-dimensional seismic data of hydrocarbon-bearing Tertiary submarine fan deposits of the North Sea. The unusual sandbody shape is considered to have resulted from post-depositional liquification of turbidite deposits. An understanding of liquification processes may therefore be important in delineating reservoir body geometry. The unusual shapes take the form of sheet-like intrusions, either along faults or as dyke and sill complexes, and domes with oversteepened sides. Three processes can cause liquification: (1) fluidization, which results from pore fluid movement; (2) liquefaction, caused by the agitation of grains during cyclic shear stress; and (3) shear liquification which results from the movement of grains during the application of a shear stress across the sandbody. In laboratory experiments each liquification process produces its own style of deformation. Fluid escape and dish structures are produced during fluidization, load structures form during liquefaction, and mass flow structures result from shear liquification. The three liquification processes can interact to create an even greater diversity in deformation style. The active liquification process, or combination of processes, can change in both space and time. In the natural environment it is unlikely that one liquification process will occur independently and therefore most natural liquification must be considered in terms of two or more interactive processes. The large-scale deformation of sandbodies and hence their geometry may vary according to which liquification process or processes are active. In natural systems the sandbody will not deform in isolation from the surrounding material. The rheology of the surrounding material and the nature of the stress field active at the time of deformation will play an important part in controlling the behaviour of the sandbody during remobilization.
Tập 94 Số 1 - Trang 63-76 - 1995
A primer on the geological occurrence of gas hydrate Abstract
Natural gas hydrates occur world-wide in polar regions, usually associated with onshore and offshore permafrost, and in sediment of outer continental and insular margins. The total amount of methane in gas hydrates probably exceeds 10
19
g of methane carbon. Three aspects of gas hydrates are important: their fossil fuel resource potential; their role as a submarine geohazard; and their effects on global climate change. Because gas hydrates represent a large amount of methane within 2000 m of the Earth’s surface, they are considered to be an unconventional, unproven source of fossil fuel. Because gas hydrates are metastable, changes of pressure and temperature affect their stability. Destabilized gas hydrates beneath the sea floor lead to geological hazards such as submarine slumps and slides, examples of which are found world-wide. Destabilized gas hydrates may also affect climate through the release of methane, a ‘greenhouse’ gas, which may enhance global warming and be a factor in global climate change.
Tập 137 Số 1 - Trang 9-30 - 1998
The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology Abstract
The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology divides Triassic time into eight land-vertebrate faunachrons (LVFs) with boundaries defined by the first appearance datums (FADs) of tetrapod genera or, in two cases, the FADs of a tetrapod species. Definition and characterization of these LVFs is updated here as follows: the beginning of the Lootsbergian LVF=FAD of
Lystrosaurus
; the beginning of the Nonesian=FAD
Cynognathus
; the beginning of the Perovkan LVF=FAD
Eocyclotosaurus
; the beginning of the Berdyankian LVF=FAD
Mastodonsaurus giganteus
; the beginning of the Otischalkian LVF=FAD
Parasuchus
; the beginning of the Adamanian LVF=FAD
Rutiodon
; the beginning of the Revueltian LVF=FAD
Typothorax coccinarum
; and the beginning of the Apachean LVF=FAD
Redondasaurus
. The end of the Apachean (= beginning of the Wasonian LVF, near the beginning of the Jurassic) is the FAD of the crocodylomorph
Protosuchus
. The Early Triassic tetrapod LVFs, Lootsbergian and Nonesian, have characteristic tetrapod assemblages in the Karoo basin of South Africa, the
Lystrosaurus
assemblage zone and the lower two-thirds of the
Cynognathus
assemblage zone, respectively. The Middle Triassic LVFs, Perovkan and Berdyankian, have characteristic assemblages from the Russian Ural foreland basin, the tetrapod assemblages of the Donguz and the Bukobay svitas, respectively. The Late Triassic LVFs, Otischalkian, Adamanian, Revueltian and Apachean, have characteristic assemblages in the Chinle basin of the western USA, the tetrapod assemblages of the Colorado City Formation of Texas, Blue Mesa Member of the Petrified Forest Formation in Arizona, and Bull Canyon and Redonda formations in New Mexico. Since the Triassic LVFs were introduced, several subdivisions have been proposed: Lootsbergian can be divided into three sub-LVFs, Nonesian into two, Adamanian into two and Revueltian into three. However, successful inter-regional correlation of most of these sub-LVFs remains to be demonstrated. Occasional records of nonmarine Triassic tetrapods in marine strata, palynostratigraphy, conchostracan biostratigraphy, magnetostratigraphy and radioisotopic ages provide some basis for correlation of the LVFs to the standard global chronostratigraphic scale. These data indicate that Lootsbergian=uppermost Changshingian, Induan and possibly earliest Olenekian; Nonesian=much of the Olenekian; Perovkan=most of the Anisian; Berdyankian=latest Anisian? and Ladinian; Otischalkian=early to late Carnian; Adamanian=most of the late Carnian; Revueltian=early–middle Norian; and Apachean=late Norian–Rhaetian. The Triassic timescale based on tetrapod biostratigraphy and biochronology remains a robust tool for the correlation of nonmarine Triassic tetrapod assemblages independent of the marine timescale.
Tập 334 Số 1 - Trang 447-500 - 2010
Crustal structure of the Mid Black Sea High from wide-angle seismic data Abstract
The Mid Black Sea High comprises two en echelon basement ridges, the Archangelsky and Andrusov ridges, that separate the western and eastern Black Sea basins. The sediment cover above these ridges has been characterized by extensive seismic reflection data, but the crustal structure beneath is poorly known. We present results from a densely sampled wide-angle seismic profile, coincident with a pre-existing seismic reflection profile, which elucidates the crustal structure. We show that the basement ridges are covered by approximately 1–2 km of pre-rift sedimentary rocks. The Archangelsky Ridge has higher pre-rift sedimentary velocities and higher velocities at the top of basement (
c.
6 km s
−1
). The Andrusov Ridge has lower pre-rift sedimentary velocities and velocities less than 5 km s
−1
at the top of the basement. Both ridges are underlain by approximately 20-km-thick crust with velocities reaching around 7.2 km s
−1
at their base, interpreted as thinned continental crust. These high velocities are consistent with the geology of the Pontides, which is formed of accreted island arcs, oceanic plateaux and accretionary complexes. The crustal thickness implies crustal thinning factors of approximately 1.5–2. The differences between the ridges reflect different sedimentary and tectonic histories.
Tập 464 Số 1 - Trang 19-32 - 2018
Local tomography model of the northeastern Black Sea: intra-plate crustal underthrusting Abstract
The Greater Caucasus and southern Crimean Mountains form part of a fold–thrust belt located on the northern margin of the Black Sea, south of the Precambrian craton of eastern Europe. Its southern limit is approximated by the Main Caucasus Thrust, which runs to the west from onshore Russia and Georgia along the whole of the northern margin of the Black Sea. The Main Caucasus Thrust is related to a zone of present-day seismicity along the southern Crimea–Caucasus coast of the Black Sea called the Crimea–Caucasus Seismic Zone. Thick continental crust north of the Main Caucasus Thrust lies adjacent to the thin ‘suboceanic' or transitional crust of the Black Sea Basin. A local seismic tomography study of this area in the vicinity of the Kerch and Taman peninsulas, which lie between the Azov Sea and the Black Sea, has been carried out based on 195 weak (m
b
≤3) earthquakes occurring from 1975 to 2010 and recorded at four permanent and three temporary seismological stations on the Kerch and Taman peninsulas. The results, for a volume of about 200×100 km (east–west and north–south, respectively) and a depth of about 40 km, provide evidence for significant heterogeneity in the P-wave and S-wave velocities. Velocities inferred in the northern part of the model suggest that the continental crust underlying the Crimea–Azov region north of the Main Caucasus Thrust is of different tectonic affinity (cratonic) than that underlying the northeastern part of the Black Sea, south of the Main Caucasus Thrust (Neoproterozoic–Palaeozoic accretionary domain). In the southern part of the model, at depths of 25–40 km, the uppermost mantle below the thin quasi-oceanic crust of the Black Sea has anomalous low P-wave velocities with high P- to S-wave velocity ratios. This is tentatively interpreted as representing serpentinized upper mantle of continental lithosphere exhumed during Cretaceous rifting and lithospheric hyperextension of the eastern Black Sea. The transition between the continental domains and the crust underlain by anomalous upper mantle is closely related to the Crimea–Caucasus Seismic Zone, where earthquake foci deepen northwards, suggesting that the latter is being thrust under the former in this intra-plate setting.
Tập 428 Số 1 - Trang 221-239 - 2017
Interactive inverse methodology applied to stratigraphic forward modelling Abstract
An effective inverse scheme that can be applied to complex 3-D hydrodynamic forward models has so far proved elusive. In this paper we investigate an interactive inverse methodology that may offer a possible way forward. The scheme builds on previous work in linking expert review of alternate output to rapid modification of input variables. This was tested using the SEDSIM 3-D stratigraphic forward-modelling program, varying nine input variables in a synthetic example. Ten SEDSIM simulations were generated, with subtle differences in input, and five dip sections (fences) were displayed for each simulation. A geoscientist ranked the lithological distribution in order of similarity to the true sections (the true input values were not disclosed during the experiment). The two or three highest ranked simulations then acted as seed for the next round of ten simulations, which were compared in turn. After 90 simulations a satisfactory match between the target and the model was found and the experiment was terminated. Subsequent analysis showed that the estimated input values were ‘close’ to the true values.
Tập 239 Số 1 - Trang 147-156 - 2004
The metamorphism of the Tibetan Series from the Manang area, Marsyandi Valley, Central Nepal Abstract
In the Manang area a distinctive metamorphic zonation with grade increasing downward to deeper structural levels of the Tibetan Series can be observed. The first appearance of prograde biotite/phlogopite introducing the metamorphic zonation can be located in the Devonian Tilicho Pass Formation. The Silurian Dark Band Formation contains prograde titanite. Tremolite is not observed to the west of the Mutsog region (Nilgiri Limestone). In the lower parts of the Nilgiri Limestone, tremolite appears together with K-feldspar. Diopside only occurs in the lowest parts of the Nilgiri Limestone. Maximum temperatures for the prograde metamorphism, derived from carbonate solvus thermometry, are in the range of 510–530°C for the middle Nilgiri Limestone and 370–390°C for the Lower Carboniferous. The fluid composition during the prograde metamorphism at the base of the Tibetan Series was CO
2
rich (
X
CO
2
between 0.4 and 0.7). A strong retrogressive phase with a fluid composition rich in H
2
O is documented by secondary growth of sphene, clinozoisite and amphibole. This retrograde phase is rare in formations above the Nilgiri Limestone and might be contemporaneous with detachment at the base of the Tibetan Series. The prograde mineral phases are related to a first deformation phase. A second deformation phase, most probably related to detachment movements between the Tibetan Series and the High Himalayan Crystalline, resulted in a partly developed crenulation cleavage unrelated to any metamorphic change. The formation of the dominating E-W-orientated syncline took place in a third deformation phase.
Tập 74 Số 1 - Trang 357-374 - 1993
On the mechanics of the collision between India and Asia Summary
Field studies of active faulting in S Tibet indicate that Quaternary extension has been taking place at a rate of ≃1 cm yr
−1
in a direction of ≃ 100°. This implies that underthrusting in the Himalayas now absorbs less than half of the total convergence between rigid India and Asia, the rest being taken up primarily by strike-slip faulting N of the collision belt.
En échelon
right-lateral, strike-slip faults in S Tibet now allow this corresponding eastward displacement of the plateau with respect to India. The reproducible pattern of faulting obtained from plane-strain indentation experiments on unilaterally confined blocks of plasticine suggests that this extrusion process has occurred during most of the collision history. The Tertiary geological record in SE Asia corroborates a polyphase extrusion model, with displacements in excess of 1000–1500 km, in which India has successively pushed Sundaland, then Tibet and S China towards the ESE. Most of the Middle Tertiary movements may have occurred along the then left-lateral Red River-Ailao Shan Fault Zone, together with the opening of most of the eastern S China Sea. Regional geology, stratigraphy and deformation observed in Yunnan are consistent with this inference, as well as the timing, geometry and rates of sea-floor spreading in the S China Sea. Fast spreading (5 cm yr
−1
) in that sea implies that the Tibetan highlands formed mostly after 17 Ma BP. Sideways movements can also account for the existence of large, conjugate but asymmetric, Tertiary strike-slip faults within Sundaland and the formation of Middle Tertiary pull-apart and rift basins on the Sunda Shelf. Changing directions of opening are predicted in the Mergui and Andaman Basins and the lowlands of Burma, as well as large right-lateral displacements along the Shan Scarp. Most of Sundaland probably lay initially in a frontal position with respect to impinging India and the Shan Plateau may have been a Middle Tertiary analogue of the present Tibetan Plateau. In contrast with dominant overthrusting in the Himalayas, Tertiary strike-slip faulting, with more subordinate folding and thrusting, appears to have been important along and N of the Zangbo Suture. This difference must be accounted for in all models of formation of the Tibet Plateau. The surface of the indentation mark, left by the impaction of India onto the presumably simpler Early Tertiary margin of Asia (> 6 million km
2
), implies that mountain building and strike-slip faulting have absorbed, perhaps alternately, roughly equal amounts of collisional shortening. Since analogous interplays of extrusion and thickening probably govern the evolution of most collision zones, the Tertiary tectonics of Asia may be the best guide to unravel the interactions between Palaeozoic and Precambrian plates, for which sea-floor spreading constraints are unattainable.
Tập 19 Số 1 - Trang 113-157 - 1986