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1.
Paul D. Taylor Consuelo Sendino 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(3):492-500
When first described in 1922, Dinocochlea ingens, an Early Cretaceous (Valanginian) fossil from the Wadhurst Clay Formation (Wealden) of Hastings in Sussex, England, was regarded as the steinkern of a huge gastropod over 2 m in length and claimed to be the largest gastropod ever to have lived. Most subsequent researchers have doubted the identity of D. ingens as a gastropod, usually believing it to be a pseudofossil, but no convincing explanation has been proposed for its origin. Restudy of the type material leads to the new hypothesis that Dinocochlea originated as a horizontal, corkscrew-shaped burrow resembling Helicodromites that acted as a nucleus for concretion growth. Sectioned specimens of Dinocochlea are filled with concentrically banded sediment interpreted to be growth rings of a concretion. Modification of a computer simulation designed to illustrate gastropod shell growth shows how the development of a concretion around a corkscrew-shaped burrow could lead to the morphology seen in Dinocochlea. The most likely tracemaker for Dinocochlea was a capitellid polychaete (‘threadworm’) with a body just a few mm in diameter. 相似文献
2.
The characteristics of seismicity prior to the series of eight very strong earthquakes (M
w
= 7.0–9.0) in Northeast Japan are discussed. Ring seismicity structures that appeared prior to all eight events in two depth
ranges of 0–33 and 34–70 km are identified. The epicenters of the main shocks were located near areas of crossing or touching
of shallow and deep rings. It was shown that the sizes of shallow rings and threshold magnitudes corresponding to seismicity
rings grow with the energy of the main shocks. It was noted that the prognosis with respect to the place and magnitude of
the catastrophic earthquake on March 11, 2011, had been made before it based on the data obtained prior to July 1, 2009. Use
of the new data obtained prior to March 10, 2011, enabled us to specify this prognosis significantly. We obtained correlation
dependences of threshold magnitudes on the energy of the main shocks (with a high correlation coefficients). It was shown
that the duration of the period for seismicity rings to emerge in the considered region nearly did not depend on magnitude.
The nature of annular structures and the possibility of application of their parameters for prognosis of strong earthquakes
were discussed. 相似文献
3.
A new Late Pennsylvanian species of gymnospermous fossil wood, Zalesskioxylon xiaheyanense sp. nov. is described from the Lower Taiyuan Formation (Stephanian B-C) near the village of Xiaheyan, Ningxia Hui Autonomous Region, northwestern China. The specimen consists only of silicified secondary xylem. The tracheids are pycnoxylic with 2–3 seriate bordered pits, arranged in subcircular or hexagonal alternate (araucaroid) pattern. The pores of the pits are small, linear, and regularly tilted. Xylem rays are homogeneous, uniseriate, 1–25 cells high. Cross-fields are filled with numerous mixed simple pits of various sizes. Growth rings, axial parenchymatous elements and resin canals are absent. The geographic distribution of Zalesskioxylon woods is reviewed. Zalesskioxylon xiaheyanense sp. nov. grew at low latitudes, and because of the lack of growth rings, probably lived under relatively uniform climatic conditions. Our new species supplements the poorly known distribution of Carboniferous wood in China. 相似文献
4.
Snehasis Tripathy Ramakrishna Bag Hywel Rhys Thomas 《Geotechnical and Geological Engineering》2014,32(4):749-763
The effects of post-compaction residual lateral stress and salt concentration in the hydrating fluid on swelling pressures of compacted MX80 bentonite is brought out in this paper. In order to release the residual lateral stresses, following the static compaction process during preparation of specimens, compacted bentonite specimens were extruded from the specimen rings and then inserted back prior to testing them for swelling pressures in isochoric condition. The swelling pressure tests were carried out at several dry densities of the bentonite with distilled water and solutions of NaCl (0.1 and 1.0 M) as the hydrating fluids. With water, the test results showed that specimens that underwent extrusion and insertion processes exhibited about 10–15 % greater swelling pressures as compared to the specimens those that were compacted and tested. The influence of saline solutions was found to reduce the swelling pressure of the bentonite, but their impact was less significant at high compaction dry densities. 相似文献
5.
Quantitative analysis of the tree-ring width record features essential for paleoclimatic reconstructions 总被引：2，自引：0，他引：2
Datsenko N. M. Ivashchenko N. N. Sonechkin D. M. Yang B. 《Doklady Earth Sciences》2010,434(2):1410-1413
Tree-ring width records provide a primary data source for millennial paleoclimatic reconstructions. However, a problem exists
connected with taking into consideration the complex age-dependence within these records. Analyzing a set of very long-lived
trees of Sabina przewalskii Kom. from the Dulan area of the northeastern Tibetan Plateau, we found for the first time that the annual basal-radius increment
is larger for the outermost rings in comparison with the inner rings, especially for very long-living trees. Neglecting this
circumstance when the so-called regional curve standardization is used can distort paleoclimatic reconstructions. 相似文献
6.
7.
The Carys Mills Formation of NE Maine represents the SW extension of the Matapedia Group and the White Head Formation of southern Gaspé, Quebec. This formation has yielded two main collections, one hitherto considered of Middle Ordovician age (zone 13 of Berry's 1960 Marathon, Texas, zonation) with 7 species referred to 4 genera, and one of the Early Silurian age. A revision of the supposed Middle Ordovician collections reveals that the graptolites are basal Silurian and consist of only one species, Glyptograptus? persculptus. Several hundred specimens, preserved both flattened and in three dimensions, the latter in iron pyrites, allow an analysis of both the rhabdosome changes wrought by diagenetic flattening and those caused by severe tectonic deformation. It is shown that those specimens lying parallel to the bedding plane lineation caused by a high-angle main cleavage have a silhouette appearance close to Glyptograptus tamariscus (Nicholson), whilst those at right angles to this direction superficially resemble robust Amplexograptus spp., or Diplograptus s.s., or Diplograptus s.l. spp., thus explaining the stratigraphic assignment of earlier workers. An analogue video reshaper confirms the above conclusions. This determination assigns the whole Carys Mills Formation to the Lower Silurian, but the possibility that part of the formation is of Late Ordovician age cannot be excluded. This much is suggested by the Matapedia Group and the White Head Formation which are of Late Ordovician to Early Silurian age, and the Honorat Group, which has yielded graptolites of late Middle Ordovician age. 相似文献
8.
Raman spectra and lattice dynamics calculations are presented for the silicate mineral gillespite, BaFeSi4O10, which contains sheets of linked four-membered silicate rings. The results are analyzed in relation to earlier work done
on the isolated four-membered ring silicate BaCuSi2O6 and to published claims that vibrational modes of four-membered rings are responsible for the sharp D
1“defect line” observed in the Raman spectra of SiO2 glass. The crystal structure of gillespite (space group P4/ncc or D
) consists of puckered Si4O12 rings, where each SiO4 tetrahedron is linked to two neighboring tetrahedra within a ring and to a third tetrahedron within a different ring. The
rings are linked to each other in a staggered configuration to form sheets, which are also bonded together by Ba2+ and Fe2+. The calculation adjusts the bond bending and bond stretching force constants so that calculated fundamental mode frequencies
best fit observed fundamental frequencies in the Raman spectra; eigenmodes associated with each calculated fundamental mode
are then generated. Some eigenmodes calculated are unique to the gillespite structure, but many of the more localized four-membered
ring modes are similar to those calculated for the four-membered rings in BaCuSi2O6 and for the three- and six-membered rings in the cyclosilicates studied earlier. The results for gillespite indicate that
the Raman-active A
1g
mode at 450 cm−1 is a four-membered ring bridging oxygen breathing mode that is mixed with other minor ring deformation displacements; because
of this mixing, the calculated frequency of this mode is 45 to 61 cm−1 lower than that calculated for bridging oxygen binding breathing modes of puckered four-membered rings in BaCuSi2O6 and in simulated glass structures.
Received: 9 April 1997 / Revised, accepted: 19 August 1997 相似文献
9.
<正>A new species of gymnospermous fossil wood,Protophyllocladoxylon jingyuanense sp.nov., is described from the lower part of the Tsingyuan Formation(Serpukhovian/Late Mississippian),near the coal mine of Ciyao,Gansu,northwestern China.The specimen is preserved only in silicified secondary xylem,while growth rings are absent.Pits in radial tracheidal walls are araucaroid in type, uniseriate,occasionally biseriate.Xylem rays are homogeneous,uniseriate,occasionally biseriate. Cross-field pits are simple,large,one to two in number.Axial parenchyma is absent.The anatomical characters and geographic distribution of Protophyllocladoxylon woods through geological ages are documented.Those species with axial parenchyma and without growth rings live in warm climate, whereas the species without axial parenchyma and with growth rings are present either in warm or cool climate.The ideal living climate for Protophyllocladoxylon woods is warm and wet.Our new species,as a fossil wood of Early Carboniferous,is likely the earliest known species of Protophyllocladoxylon. 相似文献
10.
Recent excavations in the Middle Triassic Prosanto Formation (Ladinian, Ct. Grisons, Switzerland) have produced new material
of the genus Besania Brough 1939. These specimens show many previously unrecorded details. Some features differ from those of the type species
Besania micrognathus, and we therefore erect a new species, Besania schaufelbergeri sp. nov. This new material has prompted a re-evaluation of the phylogenetic interrelationships of the genus. The taxon seems
to be closely related to basal Halecostomi.
An erratum to this article is available at . 相似文献
11.
Investigating the Effect of Cyclic Loading on the Indirect Tensile Strength of Rocks 总被引：1，自引：1，他引：0
This paper presents the results of laboratory experiments during the investigation of the stress–strain characteristics of
Brisbane tuff disc specimens under diametral compressive cyclic loading. Two different cyclic loading methods were used: namely,
sinusoidal cyclic loading and cyclic loading with increasing mean level. The first method applied the S–N curve approach to the indirect tensile strength (ITS) of rock specimens for the first time in the literature, and the second
method investigated the effect of increasing cyclic loading on the ITS of rock specimens. The ITS of Brisbane tuff disc specimens
was measured using the Brazilian tensile strength test. The reduction in ITS was found to be 33% with sinusoidal loading tests,
whereas increasing cyclic loading caused a maximum reduction of 37%. It is believed that the fracturing under cyclic loading
starts at contact points between strong grains and weak matrices, and that contact points at grain boundaries are the regions
of stress concentration (i.e., indenters). Transgranular cracks emanate from these regions and intergranular cracks sometimes
pass through the contact points. Once cracking begins, there is a steady progression of damage and a general ‘loosening’ of
the rock, which is a precursor to the formation of intergranular cracks. 相似文献
12.
Size and strain rate are two key factors that dramatically influence the estimation of rock mechanical behaviors. To better understand the effects of size and strain rate on measured rocks, rock specimens with six different sizes were tested at six different strain rates under uniaxial compression using the MTS 815 Rock Mechanics Test System. Having determined that the size and strain rate significantly affect the peak strain, peak stress, elastic modulus, acoustic emission (AE), and failure pattern of the rock specimens, the relation was established between the strength and the size and strain rate of red sandstone. And the variation was revealed among the size and strain rate, the AE, and the failure pattern. It turned out that the peak stress was negatively correlated with the rock size and was positively correlated with the strain rate. When the length to diameter ratio (L/D) of the rock specimen was less than 2.0, the AE appeared mildly. The AE quantities gradually increased before the peak stress, and then sharply decreased after the peak stress. The failure pattern of the rock specimen was relatively complicated, with a fracture plane appearing along the axial direction. Conical failure type was also presented. When the L/D ratio of the specimen was greater than 2.0, the AE characteristics of red sandstone showed the radical model. There were relatively few AE rings before the peak stress. But the AE rings increased suddenly and dramatically during the peak stress. The rock specimens primarily failed with a single shear plane. Moreover, with an increase in the strain rate, the AE activities were enhanced and the AE quantities increased. When the strain rate of the rock specimen was less than 5.0?×?10?4/s, the rock specimen failed with a shear or tensile-shear pattern. And when the strain rate was greater than 5.0?×?10?4/s, the rock specimen tended to fail in a conical pattern. 相似文献
13.
Estelle Arbellay Markus Stoffel Armelle Decaulne 《Boreas: An International Journal of Quaternary Research》2013,42(3):568-574
Dendrogeomorphic research has long relied on scarred trees to reconstruct the frequency of mass‐movement processes. Injuries have mostly been dated macroscopically by counting the tree rings formed after wounding. Tree‐ring anatomical anomalies induced by cambial injury, in contrast, have only recently been recognized as proxy records of past events. We investigated 12 sub‐arctic downy birch (Betula pubescens Ehrh.) trees scarred by snow avalanches in Norway and Iceland. Earlywood vessel lumina were measured for each tree in the xylem tissue bordering the scars. Seven successive rings were examined, namely two control rings laid down prior to wounding and five rings in the wound xylem. We provide evidence that snow‐avalanche‐induced wounding resulted in atypically narrow earlywood vessels over at least two years. Our data demonstrate that wound‐associated vessel anomalies represent tangible markers of mass‐movement processes, and as such make a viable tool for reconstructing past events. Similar dendrogeomorphic studies based on tree‐ring anatomy can be readily conducted with other mass‐movement processes, as well as with other broad‐leaved tree species. Ultimately, this new approach will foster increment coring over more invasive sampling techniques. 相似文献
14.
We reconstructed the long‐term spruce budworm (SBW) (Choristoneura fumiferana Clem.) outbreak dynamics in the boreal forest of Quebec (Canada) using a dendrochronological approach with subfossil trees. Although the majority of the excavated wood belonging to the genus Picea could potentially reveal the past activity of spruce budworms in the tree rings, very few were cross‐dated due to a lack of marker rings. All cross‐dated trees were found within a particular zone of the peat bogs and the floating chronology was radiocarbon dated to ca. 5.1 cal ka BP. The results presented in this study suggest that the dynamics of SBW outbreaks in the studied area fluctuated during the last millennia and that severe outbreaks as observed during the 20th century seldom occurred in that part of the boreal forest since the end of the last glaciation. These results are in agreement with observations from other parts of eastern North America. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
A New Ichnogenus Kailidiscus Produced by Attachment from the Middle Cambrian Kaili Formation in Taijiang, Guizhou Province, China 总被引：1，自引：0，他引：1
WANG Yue 《《地质学报》英文版》2006,80(1):27-37
Over 190 specimens of an attachment ichnofossil Kailidiscus （n. ichnogen.） have been found in the Kaili Bitoa, a Burgess Shale-type biota, from the middle Kaili Formation （early Middle Cambrian） in Taijiang County, Guizhou Province, southern China. Kailidiscus is an epichnia with a circular to oval attachment platform, on which there is a carbonaceous film probably formed by the body of the living organism. Structures such as a marginal furrow, an inner and outer marginal ride, many convex fold-ridges, and a large caved peripheral furrow on the attachment platform may be the result of basal tissues of a sessile organism that wrinkled to increase the attachment＇s surface area. The Kailidiscus organism may have been a sessile cnidarian attached to the muddy seafioor. Kailidiscus organisms lived in relatively quiet water, and were buried by a sudden influx of sediment. 相似文献
16.
17.
N. Al-Shayea 《Rock Mechanics and Rock Engineering》2002,35(4):271-297
Summary
A fracture toughness study was conducted on a limestone rock formation from a petroleum reservoir in Saudi Arabia, and results
were compared with those for outcrop specimens from the same geological formation. The objective was to investigate the possibility
of using outcrop specimens to estimate the fracture toughness behavior of reservoir rock at in-situ conditions of temperature and confining pressure. The study was made on reservoir specimens from a depth of about 3.5 km,
at both ambient and reservoir conditions. Mixed mode I–II fracture toughness at reservoir conditions of high temperature and
confining pressure was studied using straight notched Brazilian disk (SNBD) specimens under diametrical compression. Tests
were conducted at ambient conditions, at an effective confining pressure (σ3) of 28 MPa (4000 psi), and at a temperature of 116°C. The results showed a substantial increase in fracture toughness under confining pressure. Under σ3=28 MPa, the pure mode-I fracture toughness (K
IC), increased by a factor of about 3.2, and the pure mode-II fracture toughness (K
IIC) increased by a factor of 4.4, compared to those under ambient conditions. On the other hand, K
IC at 116°C was only 25% more than that at ambient conditions. These results were compared with recent results for outcrop specimens
from the same geological formation. The results reveal that outcrop specimens can be successfully used to predict the fracture
behavior of reservoir specimens at in-situ conditions, in spite of some differences at ambient conditions. Additionally, fracture toughness envelopes were obtained
for reservoir specimens at ambient and high pressure conditions, in both positive and negative regions.
Received September 14, 2000; accepted February 22, 2002 Published online September 2, 2002 相似文献
18.
Amin Jamshidi Mashalah Khamehchiyan Reza Zarei Sahamieh 《Geomechanics and Geoengineering》2016,11(1):13-19
Estimation of uniaxial compressive strength (UCS) by P-wave velocity (VP) is of great interest to geotechnical engineers in various design projects. The specimen diameter size is one of the main factors that influence rock parameters such as UCS and VP. In this study, the diameter size of specimens that effect UCS and VP is investigated. Moreover, the correlation between UCS and VP are examined via empirical analysis. For this purpose, 15 travertine samples were collected and core specimens with a diameters size of 38, 44, 54, 64 and 74 mm were prepared. Then, uniaxial compressive strength and P-wave velocity tests were conducted according to the procedure suggested by ISRM (1981). It is concluded that the diameter size of the specimen has a significant effect on UCS and VP. Moreover, it was found that the best correlation between relevant parameters obtained for the specimen diameter of 38 mm. 相似文献
19.
本文研究的双切尾虫Ditomopyge是一个新种,定名为四川双切尾虫Ditomopyge sichuanensis (sp.nov),标本产自四川南部古宋下二叠统铜矿溪组。该组过去很少发现三叶虫化石,故四川双切尾虫的发现,不仅对铜矿溪组的划分、对比提供了可靠的三叶虫化石依据,而且对研究双切尾虫的地质地理分布,提供了新的化石资料。 相似文献
20.
The paper presents a comparison between the behavior of slurry-consolidated Kaolin specimens tested under axisymmetric Conventional
Triaxial Compression (CTC) and Plane Strain (PS) loading conditions. The PS experiments were conducted on an instrumented
apparatus capable of capturing the onset of shear bands. The specimens were consolidated and then sheared under undrained
condition. The PS specimens failed via a well-defined shear band that began to develop during the hardening stress regime
whereas CTC specimens failed through a diffuse bulging mode. The undrained shear strength (S
u) of CTC experiments is smaller than the S
u of PS experiments. However, the normalized S
u of CTC experiments is very close to PS1, which was consolidated under similar K
o condition. 相似文献