bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cambrian Antarctic archaeocyaths
Authors: Debrenne Françoise , Kruse Peter D. 
Published: April 2008

Abstract
Most Antarctic archaeocyaths have been collected as allochthonous blocks, but in situ collections from the Shackleton Limestone in the vicinity of Nimrod and Byrd Glaciers (Transantarctic Mountains) provide stratigraphic control. Collections from King George Island, the Weddell Sea, Whichaway Nunataks, Argentina Range, Beardmore Glacier, Nimrod Glacier and Byrd Glacier (Cracking Cwm) are all of Botomian age according to the Siberian stage scale for the Early Cambrian. One collection from the Byrd Glacier (Mt Egerton) may be of slightly younger, Toyonian age. A unique species from the Minaret Formation in the Heritage Range has a Late Cambrian (Idamean) age, and is the youngest archaeocyath known. All existing collections are taxonomically revised here. Strong faunal affinities are evident at the species level with in situ Early Cambrian faunas in South Australia and allochthonous faunas in the Permo-Carboniferous Dwyka Tillite of South Africa. This allows the recognition of an Early Cambrian Gondwana province and confirms the existence of a Gondwana supercontinent throughout the Palaeozoic. Archaeocyatha are the most abundant and characteristic early Palaeozoic macrofossils of the Antarctic continent (Fig. 1). Most Antarctic collections have been recovered as allochthonous blocks in moraine or in dredgings at sea, but some in situ faunas are now known. To date, the only in situ collections studied in detail are from the Shackleton Limestone in the environs of the Nimrod and Byrd Glaciers, Transantarctic Mountains (Debrenne & Kruse 1986). On the basis of this latter work, we here make critical comparisons (and synonymies where necessary) of the faunal lists of previous authors to tentatively establish the composition of the Antarctic archaeocyathan fauna (Figs 2–4).
The phenomenon of forest growth in Antarctica: a review
Authors: Chaloner W. G. , Creber G. T. 
Published: April 2008

Abstract
The existence of a temperate Antarctic flora in the Permian, Mesozoic and early Tertiary poses a number of problems that are not soluble by reference to any environmental situation obtaining at the present day (i.e. in which plants live in a regime where a warm summer is followed by a winter without sunlight).

Certain characteristics of the polar climate during a number of geological periods can be deduced from the remains of forests which grew at very high latitudes where tree growth cannot take place at the present day. The demands of tree growth of the order of 3 to 4 mm increase in trunk radius each year are such that an input of light energy of at least 3000 MJ m
−2
a
−1
would be necessary.

Light energy inputs of this magnitude have been measured at very high latitudes in both North and South polar regions and it would appear that polar forest growth would be possible today if the ambient temperatures were sufficiently raised above their present levels. It is also significant that the forest productivity of about 10 t ha
−1
as estimated for the Lower Cretaceous forest on Alexander Island (Palaeolat. 70°S), is a terrestrial productivity that is only matched at the present day in a variety of temperate and subtropical regions of the world.

The evolution of photoperiodic ecotypes in tree species must have facilitated the colonization of polar regions by tree varieties adapted to make all of their annual growth during the long summer light period. There is evidence also that these photoperiodic ecotypes have a high rate of cambial activity concentrating the more rapid growth of wood into the polar summer.
Early Cretaceous biota from the northern side of the Australo-Antarctic rift valley
Authors: Rich T. H. , Rich P. V. , Wagstaff B. , McEwen-Mason J. , Douthitt C. B. , Gregory R. T. 
Published: April 2008

Abstract
A diverse biota including vertebrates, invertebrates, and plants is known from the Early Cretaceous of southeastern Australia. It is preserved in sediments that accumulated in the rift valley formed as Australia began to separate from Antarctica. As there was no significant terrestrial barrier between the two continents at the time, it is likely that the Early Cretaceous biota of the nearest region of East Antarctica may have been quite similar to that of southeastern Australia.

Dominant among the vertebrates are turtles and at least four hypsilophodontid dinosaur species. Three species of theropods, including
Allosaurus
sp., are the only other dinosaurs represented. Other tetrapods include a few scant traces of plesiosaurs, pterosaurs, a lizard, and a labyrinthodont amphibian.

Southeastern Australia was located well inside the Antarctic Circle of the day. Oxygen isotope studies suggest mean annual temperatures for the area between −5 and 8°C. These low temperatures are concordant with the character of both the flora and invertebrate fauna. The presence of juvenile hypsilophodontids implies that these animals were breeding in the area. The large eyes and optic lobes of the brain of these dinosaurs relative to other ornithopods suggests they may have been adapted for active behaviour under low light conditions.
Terrestrial tetrapods in Cretaceous Antarctica
Authors: Molnar R. E. 
Published: April 2008

Abstract
The fossil record of continental vertebrates from Antarctica is practically nonexistent, hence the composition of the supposed Mesozoic terrestrial vertebrate fauna must be inferred indirectly. This may be done using the reconstructed positions of the continents during the Mesozoic. These positions suggest the presence in Antarctica of primitive sauropods, large theropods, hypsilophodontian and iguanodontid ornithopods, ankylosaurs, pterosaurs, crocodilians, lungfish and possibly birds. In the absence of evidence to the contrary, monotremes are considered endemic Australian forms during the Cretaceous. The discovery of hypsilophodontian material in New Zealand corroborates the inference of Antarctic hypsilophodontians from their occurrence in Australia. The existence in the Australian Early Cretaceous of relict taxa and taxa that seem unusual compared to their overseas relatives suggests that the south polar tetrapod fauna was characterized by singular forms.
The nature and timing of biotic links between New Zealand and Antarctica in Mesozoic and early Cenozoic times
Authors: Stevens G. R. 
Published: April 2008

Abstract
Until the Early Cretaceous, when the first phases of rifting that preceded the eventual breakup of the Australasian sector of Gondwana occurred, New Zealand and Antarctica had a close geographic relationship on the eastern margin of Gondwana.

After having been influenced by proximity to the Permian ice sheet, during which New Zealand and Antarctica shared elements of the
Glossopteris
flora, the eastern margin of Gondwana entered into a phase of predominantly cool-temperate climates that lasted throughout the Triassic.

In the Jurassic, rotation of Gondwana had moved New Zealand and Antarctica into mid-latitudes and they experienced warm-temperate climates. These climatic conditions facilitated the dispersion of Tethyan marine faunas into the SW Pacific sector of eastern Gondwana. New Zealand and Antarctica shared many elements of the Tethyan marine faunas.
Starting in Middle Jurassic times, earth movements of the Rangitata Orogeny began to create considerable areas of land in the New Zealand region. Eventually, by Late Jurassic and Early Cretaceous times, a large landmass had been developed, extending northwards towards New Caledonia, eastwards to the Chatham Islands, westwards to the Lord Howe Rise and southwards to the edge of the Campbell Plateau. Creation of this landmass, and its associated land and marine links, together with the equable warm-temperate conditions then apparent over large areas of Gondwana, provided favourable conditions for the dispersal of Gondwana elements into New Zealand. Ancestral stocks of at least some of New Zealand’s archaic endemic terrestrial biota may have dispersed from eastern Gondwana into New Zealand at this time.
In the Early Cretaceous, land connections to eastern Gondwana became weakened by the onset of rifting along the future sites of the Tasman Sea and Southern Ocean. The eastern edge of Gondwana was rotated into high latitudes, and cool-temperate climates returned to New Zealand and Antarctica. Cool-temperate Austral marine faunas developed and were shared between New Zealand, Antarctica and southern South America. Land links between New Zealand and West Antarctica provided access for early angiosperms. However, all land links between New Zealand and Australia/Antarctica were broken after 85 Ma. From this time onwards the ancestral Tasman Sea and Southern Ocean became effective barriers to overland dispersal between eastern Gondwana and New Zealand. Subsequently, all terrestrial colonists had to arrive by either flying, swimming or floating. Many birds did so, but no terrestrial snakes and no mammals, except bats.
Although land connections had been broken in the Late Cretaceous, shallow-water marine links continued to exist between New Zealand and West Antarctica until the late Paleocene (the Weddellian Province). However, as New Zealand moved progressively northwards and the Southern Ocean widened, such southern links gave way in latest Paleocene and early Eocene times to northern (Australian and Malayo-Pacific) links.
Origins and evolution of Antarctic marine mammals
Authors: Fordyce R. Ewan 
Published: April 2008

Abstract
Austral marine mammals evolved in a Southern Ocean influenced by changing post-Gondwana geography and consequent new water-masses, progressive cooling, increased thermal gradients and physical and biological seasonality. The biology of extant species and temperate-to high-latitude fossils suggests, but does not confirm, that such factors have governed evolution, and that details of marine mammal evolution therefore differed from those of the north. Cladistic analyses may eventually allow better interpretation of the record.
Cetacea were present in high southern latitudes by the late Eocene. Mysticetes appeared in the south, where they may have originated, about the early Oligocene. They were diverse by the late Oligocene. Early records of Odontoceti are more ambiguous, but they were diverse by the latest Oligocene, when some taxa had circum-Antarctic distributions. The Neogene records of Austral Odontoceti and Mysticeti broadly complement the taxonomic and ecological diversification seen in the north. Amongst largely southern seals, lobodontine Phocidae radiated in the south about the late Miocene, and perhaps ecologically excluded the later arctocephaline Otariidae from high-latitude pagophilic lifestyles. There are no reports of the important northern groups Odobenidae, Sirenia or Desmostylia. Overall, southern marine mammal faunas were ecologically and/or taxonomically similar to extant faunas by the later Miocene to Pliocene.
Sedimentary structures of clastic rocks identified from electrical borehole images
Authors: Luthi Stefan M. 
Published: April 2008

Abstract

High-resolution electrical borehole images are obtained from the Formation Micro Scanner
*
(FMS) by scanning the borehole wall with arrays of small electrodes pressed against the borehole surface. The images provide detailed sedimentary structural information from clastic rocks which is of great value for geological and reservoir modelling as illustrated by two case studies. Analysis of electrical borehole images through a Pennsylvanian deltaic cycle from Texas shows different types of bedding surfaces, including channel base scours, cross-bedding, slump folds and growth-faulting. The ensemble of the data constrains the subsurface geometry of the reservoir and helps to establish a depositional model. Thresholding may produce a segmentation of sand/shale images. In the aeolian Rotliegendes of the North Sea, electrical borehole images provide a vertical succession of facies, dip and azimuth measurements of interdune layers, bounding surfaces and foresets, as well as thickness measurements of the cross-bedded sets. Statistical modelling using the data indicates scale-invariant crescentic bedforms, and describes sizes, shapes and layering of the cross-bedded sandstones. Computer-aided design tools are used for forward-modelling of structures observed on borehole images in order to test possible interpretation hypotheses. The use of graphic workstations greatly facilitates the interpretation process.
Methodology of Formation MicroScanner image interpretation in Claymore and Scapa Fields (North Sea)
Authors: Harker S. D. , McGann G. J. , Bourke L. T. , Adams J. T. 
Published: April 2008

Abstract

The Formation MicroScanner (FMS)
*
tool is an advanced dipmeter tool capable of producing high-resolution resistivity images of a borehole wall. When integrated with core and open hole logs, FMS images are of great utility in evaluating the thin bedded reservoir sequences of the Claymore and Scapa North Sea oil fields. Sedimentary features as small as 0.5 inches (1.2 cm) can be resolved on FMS images. Such detail is employed in the distinction of massive, parallel laminated, ripple cross-laminated, bioturbated and conglomeratic bedding types. The application of the FMS tool to reservoir description is not limited to bedding type identification. Bed boundaries, as well as small and large scale structural features, can be distinguished, including erosional contacts, slumps, fractures and faults. In the hydrocarbon-bearing zone permeability distribution outwith cored intervals can inferred. This can be confirmed by relating resistivity changes to core measured permeability values. The proposed approach to FMS interpretation involves the integration of all available open hole logs with detailed local geological knowledge and core data. Aspect and image quality of the FMS log are important considerations. By imaging the borehole wall, the aspect of the FMS tool provides a direct method of relating features detected using open hole logs to those observed in cores. Image quality is largely dependent on resistivity contrast in the formation and correlation with cores is imperative to establish confidence limits for extrapolation into uncored intervals.
The language of rocks: an example of the use of syntactic analysis in the interpretation of sedimentary environments from wireline logs
Authors: Griffiths C. M. 
Published: April 2008

Abstract
The sedimentary sequence as recorded in vertical section, i.e. by boreholes and logged sections, is a very uneven representation of the passage of time. Thick sand sequences may be deposited instantaneously with respect to geological time, whereas thin shales may represent either millions or hundreds of years, depending on their environment of deposition. This uncertainty concerning the relative time values of sedimentary units and the breaks between them adds a certain spice to attempts to correlate rather than match well sequences. Consideration of Gressly’s original facies concept, and the formal application of ‘Walthers Law’ suggests the basis of a sequence analysis tool that can be used to correlate adjacent wells. The syntactic pattern recognition technique demonstrated here is based on the development of a grammar of unit associations, and the parsing of logderived lithology units. The development of stratigraphic syntax is shown for both wireline log and grain-size data, with example taken from the North Sea.
Geophysical logging of water exploration boreholes in the Deccan Traps, Central India
Authors: Buckley D. K. , Oliver D. 
Published: April 2008

AbstractDrilling and geophysical logging of Deccan basalt during groundwater exploration in Central India demonstrated that the Deccan lavas comprise a series of simple lava flows, 15–20 m thick, having a porous upper cooling surface with thin clay development and a layered structure. Geophysical logging has proved capable of resolving the layering and produced consistent log responses. Gamma-ray logs were especially useful to identify the weathered flow surfaces but further revealed certain lavas have distinctly higher radioactivity. The higher radioactivity flows were found to be of regional significance. The resolution of the layering and positive identification of flows by geophysical logging permitted individual lavas to be recognized and traced over distances of at least 100 km with no apparent displacement. The logs provided a framework for a detailed stratigraphic sub-division of the lava sequence, and also a key to investigate lateral and vertical variation in aquifer properties.
Geochemical well logs: calibration and lithostratigraphy in basaltic, granitic and metamorphic rocks
Authors: Anderson R. N. , Dove R. E. , Pratson E. 
Published: April 2008

Abstract

Elemental analyses of rock compositions have been measured
in situ
with a geochemical logging tool (GLT) in drillholes through igneous and metamorphic terrains. Comparisons of dry weight percent oxide analyses from laboratory measurements on core samples and the log-derived results demonstrate that accuracies are fair in Ocean Drilling Program Hole 504B basalts, good in Cajon Pass, California granites, and very good in Moodus, Connecticut metamorphic rocks and Palisades, New York diabases. Improved accuracies of GLT measurements are attainable through the use of a boron sleeve to isolate the borehole fluid from wellbore effects, and in smaller diameter, land-based boreholes. Precisions within each well are very good in all cases. That is, only a linear calibration shift was required to bring core and laboratory analyses into general agreement in all cases. Variations in mineralogy, derived from inversion models of the log-derived elemental abundances at each well, produce a lithostratigraphic interpretation that is useful for determining the structure of the oceanic crust (Hole 504B), the fractionation sequence of basaltic intrusions in a new rift basin (Palisades Sill), the deformation history near the San Andreas Fault (Cajon Pass), and the variations in degree of metamorphism across a shallow decollement surface caused by collision tectonics (Moodus).
Preliminary geochemical results from DSDP/ODP Hole 504B: a comparison of core and log data
Authors: Brewer T. S. , Lovell M. A. , Harvey P. K. , Pelling R. , Atkin B. P. , Adamson A. 
Published: April 2008

Abstract
DSDP/ODP Hole 504B, located in the Eastern Equatorial Pacific in 5.9 Ma old crust, penetrates both basaltic pillows and dykes down to a depth of 1562.1 m below the sea floor. Core recovery is poor, averaging 230ut falling to a 12% average in the deepest sections. Geochemical logs give a continuous measure of elemental (Si, Ca, Fe, S, Ti, Gd, H, Cl, K, Th, U) abundances. Correlation between laboratory (XRF) geochemical data and log data is difficult because of the lack of accurate depth information for the cores. Pattern recognition techniques are of little help for locating sample depths in the uniform basaltic lithologies. Non-hierarchical clustering techniques prove the existence of relationships between core descriptions and gross geochemical variations; major lithostratigraphic zones are readily identified from the log-derived data.
Fracture detection from logs of North Sea chalk
Authors: Lehne Karl Audun 
Published: April 2008

Abstract
Depending on the rock type, logs are variously affected by fractures. Only field experience permits us to define logging methods which give the best results locally. This article presents the results of different fracture detection methods based on logs from two wells in the Tommeliten Gamma Field in the North Sea. Cores, dipmeter, formation microscanner, circumferential acoustic, digital sonic (amplitude, spike and criss cross analysis and Stoneley reflection) and echolog (Stoneley reflection) have been used, which allows a comparison of almost all the tools that are available on the market for fracture detection. The Borehole Televiewer was not used because of the high mud weight. The two wells are both deviated, which affects some of the fracture logs. Conventional logs (caliper, resistivity, density-neutron etc.) were of no significant value in fracture detection. Well tests and production logs will be run later to improve this fracture evaluation.
A correlation of hydraulic conductivity from pulse tests with sonic log amplitudes
Authors: Goldberg D. , Speed D. , Wilkinson C. , Scholz E. 
Published: April 2008

Abstract

A 100 m water resource well penetrating shaly dolostone in East Fishkill, NY was tested to identify fracturing and to relate in situ hydraulic conductivity to acoustic properties derived from sonic waveform logs. The vertical fracture distribution was determined by borehole televiewer imaging. Sonic full waveforms were also recorded in the well and were analysed for compressional and Stoneley amplitudes, and differential energy logs were calculated. Hydraulic pulse tests were conducted in 1.5 m intervals isolated using a re-inflatable borehole packer system, and the measured conductivity in unfractured zones ranged from 10
−9
to 10
−5
cm s
−1
. Our preliminary comparison of results show that hydraulic conductivity is not related to Stoneley amplitude and weakly related to compressional amplitude and Stoneley differential energy. However, hydraulic conductivity may be reduced by partially closed or clay-filled fractures and volumetric differences in the packed interval which simultaneously increase attenuation. Further analysis by hydraulic flow tests in highly permeable zones are expected to improve the correlation. In principle, independent estimation of hydraulic conductivity from sonic attenuation measurements alone could be extended to untested intervals in nearby wells.
Investigating stress regimes in sedimentary basins using information from oil industry wireline logs and drilling records
Authors: Bell J. S. 
Published: April 2008

Abstract
Estimates of the in situ stress tensor in sedimentary basins can be inferred from information gathered during the drilling and logging of hydrocarbon exploration wells. Principal stress magnitudes can be obtained from information provided by density logs, drilling histories, leak-off test results and pore pressure measurements. Horizontal principal stress orientations are indicated by borehole breakouts recorded on four-arm dipmeter logs. The stress magnitude estimates are comparable with values obtained from hydraulic fracturing and the orientation data provide a level of detail hitherto unobtainable. The information obtained assists in designing hydraulic fractures, in secondary recovery programmes and in obtaining optimum drill bit performance. It also contributes to understanding lithospheric plate movements, crustal subsidence and tectonic deformation.