bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of gas hydrate accumulations on the continental slope of the Crimea from geophysical studies
Authors: Bouriak S. V. , Akhmetjanov A. M. 
Published: September 2007

Abstract

The Sorokin Trough on the south-eastern Crimean margin (northern part of the Black Sea) is known for mud diapirism. Gas hydrates in the sea-bed sediments have previously been recovered from this area in 1988. During the TTR-6 cruise of the R/V
Gelendzhik
in 1996 gas hydrates were observed in five cores containing mud breccia. A comprehensive geophysical survey was carried out, which allowed more insight to be gained into the local distribution of gas hydrates and the linkage of hydrate accumulations to fluid vents. It is therefore suggested that gas hydrates in the study area have most probably been formed from allochthonous gas. Preliminary results from a lithological study of the gas hydrate bearing cores suggested a complex mechanism for the mud volcanoes from which the gas hydrates were sampled, and a complicated history of the gas which was a source for the hydrates.
Detection of gas-charged sediments and gas hydrate horizons along the western continental margin of India
Authors: Veerayya M. , Karisiddaiah S. M. , Vora K. H. , Wagle B. G. , Almeida F. 
Published: September 2007

Abstract
High-resolution seismic reflection and sub-bottom profiling on the continental margin off western India has revealed the presence of characteristic acoustic maskings in the form of wipe-outs, reflector terminations and seep-associated features in the inner shelf. These maskings suggest the presence of gas-charged sediments. Further seaward on the outer shelf-middle slope, pockmarks and prominent plumes in the overlying water column indicate a significant seepage of gas from the slope sediments, and it is the seepage which may demonstrate the existence of source rocks. Seismic profiles also revealed the presence of bottom simulating reflectors (BSRs) in the mid-lower slope-rise regions, presumably suggesting the presence of gas hydrates. The BSRs occur at roughly 300–600 ms (TWTT) beneath the sea floor at water depths between 525 and 2200 m; they occasionally show discontinuities. Distinct blanking zones as well as acoustic voids have also been observed above the BSR. In contrast, chaotic and/or scattered hyperbolic reflectors occur in places below the BSR, which may suggest the presence of gas-charged sediments. Folds, diapiric features and faults present in the slope-rise areas may probably serve as traps and conduits for upward migration of fluids and methane gas from the deep.
Reflection characteristics, depth and geographical distribution of bottom simulating reflectors within the accretionary wedge of Sulawesi
Authors: Neben S. , Hinz K. , Beiersdorf H. 
Published: September 2007

Abstract
Several reflection seismic profiles across the subduction zone north of Sulawesi show strong bottom simulating reflectors (BSRs) below the lower and upper slopes of the accretionary wedge. The geographical distribution, depth and the reflection characteristics of the BSRs have been described in detail. Along one reflection seismic profile the depth of BSR was correlated with heat flow data. These correlations indicate that at locations, where the heat flow is high and the BSR interrupted, active venting of methane may occur at the sea floor. The occurrence of BSRs is limited to the central part of the North Sulawesi subduction zone (between 121°30′E and 123°30′E). In the westernmost part of the surveyed area only short BSR segments are found, which may be a result of slope instability and slumping of sediments. On the easternmost profile, no bottom simulating reflectors are found at all.
The geothermal field of the North Sulawesi accretionary wedge and a model on BSR migration in unstable depositional environments
Authors: Delisle G. , Beiersdorf H. , Neben S. , Steinmann D. 
Published: September 2007

Abstract

The distribution of heat flow in the North Sulawesi accretionary wedge was derived from the depths of a bottom simulating reflector (BSR) and nine
in situ
heat flow measurements. The values obtained by both types of measurements agree reasonably well and suggest high heat flow of the order of 70–100 mW m
−2
near the deformation front and a systematic decrease to 30 mW m
−2
landwards. In addition, we have tested on the basis of one numerical model the likelihood of the BSR being in a position of complete thermal equilibrium with the surrounding rocks. The model describes the rate by which a BSR layer re-equilibrates after a thermal disturbance at the sea floor (sediment slumping). The result suggests that the BSR does not regain complete thermal equilibrium after slumping in the course of several 10
5
years.
Cometary capture and the nature of the impactors
Authors: Bailey M. E. , Emel’yanenko V. V. 
Published: September 2007

Abstract

The inclination-averaged capture probability from nearly parabolic orbits to Halley-type orbits with periods
P
< 200 years and
q
< 1.5 AU is 0.0128 for an isotropic long-period source flux with perihelion distances
q
< 4 AU. The observed near-parabolic flux brighter than visual absolute magnitude
H
10
= 7 is approximately 0.2 comets AU
−1
a
−1
, and the dynamical lifetime of the captured Halley-type comets is on the order of 0.3 Ma. The predicted steady-state number of such comets is thus about 3000, many times more than the number of observed Halley-type comets. Provided that long-period comets do not totally disintegrate during the capture process (e.g. into streams of small bodies such as cometary meteoroids and dust), this indicates that there should be a large population of undiscovered Halley-type ‘asteroids’ in the inner Solar System. The predicted number of dark Halley-type objects is sufficient to produce a terrestrial cratering rate comparable with that from observed near-Earth asteroids, and hence could explain the reported Galactic signal seen in the geological and biological records. The assessment of the terrestrial impact hazard should consider the possibility that a significant number of dark Halley-type objects may exist.
The mass distribution of crater-producing bodies
Authors: Hughes David W. 
Published: September 2007

Abstract

The physical phenomena governing planetary cratering can be represented by three equations. The first, the cratering rate equation, originates from the observation of areas of the Earth’s land-mass that have been exposed to an extraterrestrial flux for a known time, and the detection, counting and measurement of the resultant craters. The second, the energy-diameter equation, is much more uncertain. It relates the kinetic energy of an impacting body to the diameter of the crater that it produces. The third, the mass distribution equation, is also somewhat uncertain. This describes the way in which the flux of incident bodies varies as a function of their masses. This paper investigates the interrelationship between these three equations and comments on the comet/asteroid ratio among the extraterrestrial bodies responsible for producing the 19 <
D
< 45 km craters on Earth.
Calculating flux from meteorite decay rates: a discussion of problems encountered in deciphering a 10
5
–10
6
year integrated meteorite flux at Allan Hills and a new approach to pairing
Authors: Bland P. A. , Conway A. , Smith T. B. , Berry F. J. , Swabey S. E. J. , Pillinger C. T. 
Published: September 2007

Abstract

Meteorite accumulation sites offer the prospect of observing changes in flux over time; however, two main problems must be overcome: calculating a decay constant for samples in an area, and providing accurate pairing data, such that the number of true meteorites (not fragments) can be ascertained. We have used a comparison of meteorite terrestrial age and weathering data to constrain decay constants for hot desert meteorite populations. Meteorites resident in these sites typically have terrestrial ages <50 ka. Our estimates of the flux of meteorites to the Earth are within a factor of 2–3 of independent estimates made by the Meteorite Observation and Recovery Project network, and suggest no change in the flux over the last 50 ka. A similar approach applied to meteorites from Allan Hills, Antarctica, finds much lower levels of weathering, although terrestrial ages for these samples are much longer. We also observe a correlation between terrestrial age and degree of weathering in the Allan Hills meteorites, suggesting a weathering rate 2–3 orders of magnitude slower than values typical of hot desert sites. Given that blue ice regions are subject to some horizontal flow, we propose a model in which the observed oxidation-terrestrial age distribution is largely a result of ice movement, rather than weathering. Comparing oxidation and terrestrial age data in the Antarctic and hot desert accumulations, we estimate a lifetime for the Allan Hills population of 200–300 ka. Given the distance to the nearest ice divide (200 km), this suggests an average horizontal flow rate of 1 m a
−1
. This approach may allow an estimate of the catchment area for these samples to be made. In addition, we suggest an alternative method for pairing samples which makes use of automated image processing and data analysis of reflected light photomicrographs to acquire a ‘textural fingerprint’ of a sample, and a genetic algorithm to compare the numerous data variables.
14
C terrestrial ages of meteorites from Victoria Land, Antarctica, and the infall rates of meteorites
Authors: Jull A. J. T. , Cloudt S. , Cielaszyk E. 
Published: September 2007

Abstract

The results of
14
C measurements of 95 meteorites from the Allan Hills region in Antarctica are reported, and terrestrial residence ages calculated. This includes meteorites from the different icefields at Allan Hills and the adjacent Elephant Moraine meteorite stranding area. We determined that terrestrial ages of these Antarctic meteorites can range from recent falls to >40 ka, which is the practical limit for these
14
C measurements. The terrestrial age determinations on meteorites from these sites can vary dramatically; the differences between the ages observed from these sites and some of the factors influencing them are discussed. Weathering products found on these meteorites show
14
C ages younger than the terrestrial age of the meteorites studied. Calculation of infall rates based on meteorites recovered and their age distributions suggests a minimum infall rate of 40–60 meteorites (>10 g) per 10
6
km
2
per year, in reasonable agreement with the infall rates estimated by Halliday’s group based on meteoroid fluxes.
The flux of meteorites to Antarctica
Authors: Zolensky Michael 
Published: September 2007

Abstract
It is premature to report firm conclusions regarding the past meteorite flux rate from the Antarctic record, as variables related to ice flow, meteorite catchment area, weathering and removal rate are not well constrained. The relative population of meteorite types appears to be broadly compatible with the modern fall population, although there are minor differences. In particular, there are populations of small unusual irons, carbonaceous chondrites and lunar samples not found among the modern falls. In addition, slight compositional differences between modern and old (Antarctic) H chondrites may signal a time-dependent change in the flux to Earth of more common meteorites.
Identification of meteoritic components in impactites
Authors: Koeberl Christian 
Published: September 2007

Abstract
The verification of an extraterrestrial component in impact-derived melt rocks or breccias can be of diagnostic value to provide confirming evidence for an impact origin of a geological structure. Geochemical methods are used to determine the presence of the minor traces of such a component. This is because even under ideal conditions, meteoritic fragments are preserved only at very young and small craters, but are destroyed in larger and older structures as a result of erosion and/or vaporization. The absence of meteorite fragments can, therefore, not be used as evidence against an impact origin of a crater structure. The determination of such an extraterrestrial component can be done by studying the concentrations and interlement ratios of siderophile elements, especially the platinum group elements, which are several orders of magnitude more abundant in meteorites than in terrestrial upper-crustal rocks. More recently, the Re-Os isotopic system has been used for identifying the presence of a meteoritic component in a number of impact melt rocks and breccias. This method avoids the ambiguities that may affect the usage of elemental abundances and ratios; for example, if the target rocks have high abundances of siderophile elements, or if the siderophile element concentrations in the impactites are very low. The presence of a meteoritic component has been established for about 41 impact structures (out of about 150 known on Earth), which reflects also the detail in which these structures were studied. In some of the smaller of these craters, fragments of the meteorite (the ‘projectile’) are preserved, but in most others, only a minor extraterrestrial component (mostly <1 wt %) is mixed in with impact melt rocks or breccias. The identification of the projectile type (i.e. meteorite type) is not straightforward, as vapour fractionation during the impact, as well as post-impact fractionation in the melt or hydrothermal mobilization, may lead to changes in the interlement ratios.
Preliminary results from a passive seismic array over the Chicxulub impact structure in Mexico
Authors: Maguire P. K. H. , Mackenzie G. D. , Denton P. , Trejo A. , Kind R. ,   Members
Published: September 2007

Abstract

A passive, 20-element, short-period (1 Hz) and broadband seismic array was deployed over the Chicxulub impact structure for
c.
100 days in early 1996. The principal objective was to study the shear-wave anisotropy associated with the structure; in particular, to determine the presence (or absence) of radial symmetry which will allow comment on the time variance of that anisotropy. A total of 15 teleseismic, 75 regional, and 100 local events were recorded. Preliminary results from studies of the surface-wave dispersion of the local events, and a receiver function analysis of a single teleseismic event are reported here. Thirty local events have been located, a number of which originated from quarries within the array. Analysis of seismo grams from three of these events demonstrates a bimodal distribution; those whose ray-paths cross the outer part of the impact structure show a strong inverse dispersion, whereas those with ray-paths crossing the centre do not. The pattern may be produced by the sedimentary depositional environment, with deeper water sedimentation in the outer part of the post-impact crater basin and shallower water sedimentation over the upraised peak-ring block at the centre. Receiver functions derived for an event originating in Peru are dominated by an efficient mode conversion, simply modelled as a P-S multiple from the base Tertiary boundary. This shows a strong correlation with distance from the centre of the impact structure and implies it has an S-wave radial symmetry. The multiple also has a variable delay probably related to the depth of the conversion boundary. Unfortunately, the Moho conversion occurs at almost exactly the same time as this surface layer sediment multiple, restricting any modelling of Moho topography and its influence on the receiver functions.
Charles Lyell and the Geological Society
Authors: Thackray John C. 
Published: September 2007

Abstract

Charles Lyell was a loyal and committed Fellow of the Geological Society from 1819 until 1875, serving as Secretary, Foreign Secretary and President. He was principally a theorist, his uniformitarian outlook strongly influenced by the work of James Hutton. The Society on the other hand was devoted to the collection and dissemination of facts; on the whole, theorizing was unwelcome. In line with this tradition the papers Lyell read to the Society are largely factual, and do not add a great deal to the ideas put forward in the
Principles of Geology
. However, his theories were not ignored by the Society, being noticed in the annual presidential address and, more importantly, in the unscripted and largely spontaneous discussions that took place after many of the papers read at the Society’s evening meetings.
Charles Lyell in New York State
Authors: Friedman Gerald M. 
Published: September 2007

Abstract
In 1842 Amos Eaton (1776–1842), founder of the Rensselaer School in Troy, New York (later Rensselaer Polytechnic Institute), had become the most influential American geologist. The period between 1818 and 1836 is known as the ‘Eatonian era’. In 1841, Lyell visited Eaton at Rensselaer. He states ‘at Troy I visited Professor Eaton … The mind of this pioneer in American geology was still in full activity, and his zeal unabated; but a few months after my visit he died.’ In company with Eaton’s former student James Hall (1811–1898), Lyell journeyed to Niagara Falls. After describing sediments and geological features near Niagara Falls, Lyell returned to his uniformitarian concepts and used the Niagara Falls as a point of departure to reiterate his message of the enormity of geological time but continuity of geological processes. Lyell was most impressed with the Helderberg Mountains. The ‘Helderberg war’, however, distracted him. According to a history, ‘Sir Charles Lyell, … geologizing on the Helderbergs that day, found the farmers “in a ferment.” Sir Charles took time from his study of fossils embedded in the rocks of the Helderbergs to criticize (New York) Governor Seward.’ In Troy Lyell reported on landslides in which people were killed. Much of Lyell’s account relates to non-geological descriptions.
Charles Lyell and the evidences of the antiquity of man
Authors: Cohen Claudine 
Published: September 2007

Abstract

This paper examines the importance of Lyell’s book,
The Geological Evidences of the Antiquity of Man
(1863), in Lyell’s work and career, as well as its contribution to the founding of two scientific disciplines, Prehistoric Archaeology and Palaeoanthropology. It first focuses on Lyell’s two ‘conversions’ (to the idea of the antiquity of man and to Darwin’s theory of transmutation of species) both of which he acknowledged in his book; it turns then to a study of the nature of the ‘evidences’ that Lyell advances. These evidences were of several kinds — archaeological, palaeontological, anthropological, and, most importantly, geological; at the time, the best way to prove the existence of fossil Man was to demonstrate geologically the contemporaneity of man-made objects and extinct animals.

This paper insists in particular on Lyell’s relationship to French science of the time, and examines the circumstances and modalities of a collaboration which was essential to the international acceptance of the antiquity of man. The fact that Lyell was a major scientific authority, whose expertise could validate the authenticity of evidence, allowed him to play a central role in the founding of a new field of knowledge.
Lyell’s
Principles of Geology
: foundations of sedimentology
Authors: Leeder M. R. 
Published: September 2007

Abstract

This chapter examines the extensive arguments Lyell brought to bear on the interpretation of sedimentary rocks through the operation of ‘present causes’ in the first Edition of
Principles of Geology
(1830–1833). A case is made
inter alia
for Lyell, rather than Sorby, being the true originator of sedimentology and basin analysis, amongst much else of course. Lyell had a special interest in Earth surface processes, and the effects of tectonics and climate on them, because he saw that the evidence is firmly written in the sedimentary products of observable events. His own explanations for the sedimentary and geomorphic processes of erosion and deposition were acutely sensible: he analysed (in today’s parlance) river avulsions, controls on delta morphology, oceanic brine pools, cross stratification, confluence bars, boundary layers, hydraulic geometry, debris flows, sediment budgets, alluvial basin architecture, and clinoforms. Much of Sorby’s work in some of these areas must have been inspired by his reading of the
Principles
. Lyell was occasionally too much guided by theory, as in the famous sophistry of his 1830 analysis (in the first edition) of the sedimentary and geomorphological evidence for Holocene Fenno-Scandinavian uplift. His willingness in subsequent editions of
Principles
to abandon such firmly held views in the light of empirical and personally collected field evidence to the contrary presages his momentous decision to throw his weight behind Darwin’s natural selection theories some 30 years later. Lyell was not so rigidly an anti-catastrophist and inductionist as is commonly made out. His writings make very clear his ability to state bold theories. For example, his discussions of climatic change and his concept of the ‘great year’ were outstandingly incisive, holistic and original. They include the role of land-sea interactions, ocean currents and precessional orbital cycles. He even considered the probability that continents and oceans changed position, albeit by vertical movements. The motive for all this came from observations he and others had made on the distribution of Cenozoic molluscs and the need for some general global cooling to explain these. He included in his actualism all manner of extreme (but not ‘catastrophic’) events, for example earthquakes and volcanic eruptions. He was also willing to consider (but then rejected) the possibility of catastrophes, most obviously in his discussion in the seventh edition of
Principles
(1846) of the possible ‘lake-burst’ of Lake Superior into the headwaters of the Mississippi. One feels he would have welcomed probability theory and the development of magnitude/frequency analysis, and that he would have laughed at any modern description of himself as the ‘father of uniformitarianism’.
The Cenozoic Era: Lyellian (chrono)stratigraphy and nomenclatural reform at the millennium
Authors: Berggren William A. 
Published: September 2007

Abstract
The historical and intellectual framework and contemporary influences and sources leading to, and associated with, Charles Lyell’s studies of Tertiary stratigraphy are reviewed. The nomenclatural hierarchy into which some of Lyell’s stratigraphic terms have been subsequently grouped is then analysed.
Lyell’s terms ‘Eocene’, ‘Miocene’, ‘Pliocene’ (1833) and ‘Pleistocene’ (1839) were essentially biostratigraphic/biochronologic in nature. Together with the subsequently defined ‘Oligocene’ (1854) and ‘Paleocene’ (1874), they have gradually aquired a chronostratigraphic connotation over the past 100 years. The term ‘Neogene’ (Hörnes 1853, 1856, 1864), when transferred from its original biostratigraphic/biochronologic (Lyellian) to a chronostratigraphic connotation, includes the stratigraphic record of the Miocene, Pliocene, Pleistocene and Recent (subsequently termed Holocene) epochs (equivalent to the ‘periods’ of Lyell). Thus a Neogene/Quaternary boundary is wholly inappropriate as a standard chronostratigraphic boundary. The ‘Palaeogene’ (Naumann 1866) now comfortably accomodates the stratigraphic record of the Paleocene, Eocene and Oligocene epochs
The terms ‘Palaeogene’ and ‘Neogene’ should be used as period/system subdivisions of the Cenozoic Era. ‘Tertiary’ and ‘Quaternary’ should be abandoned, relicts of a now outmoded, and inappropriate, pre-Lyellian stratigraphy. Retention of the term ‘Quaternary’ for geopolitical purposes (institutional affiliation or scientific/professional identification), as opposed to its retention as part of the standard stratigraphic hagiography, is recommended and would reduce, if not eventually eliminate, continuing but unnecessary, and unscientific, rancorous debate over standard Cenozoic chronostratigraphic terminology.