bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endemism and heterochroneity in the Late Cretaceous (Campanian) to Paleocene palynofloras of Seymour Island, Antarctica: implications for origins, dispersal and palaeoclimates of southern floras
Authors: Askin Rosemary A. 
Published: April 2008

Abstract
Late Cretaceous (Campanian) to Paleocene nearshore marine-coastal/deltaic sediments (López de Bertodano and Sobral Formations) from Seymour Island, Antarctica, contain abundant marine and terrestrial palynomorphs. Marine dinoflagellate cysts, and spores and pollen of land plants from 510 samples exhibit varying levels of provincialism: (1) Seymour Island-James Ross Island basin endemic species; (2) Antarctic endemic species; (3) Weddellian Province (southern South America-Western Antarctica-New Zealand-southeastern Australia) species; (4) Austral species; and (5) Cosmopolitan species.
A significant proportion of the Antarctic Cretaceous-Tertiary terrestrial vegetation evolved in southern polar latitudes. Almost half of the late Maastrichtian angiosperm pollen flora is apparently endemic to the Seymour Island-James Ross Island basin or Antarctica. The late Campanian-Maastrichtian dinoflagellate cyst assemblages also include a significant Antarctic or Weddellian provincial component. Climatic conditions in the Late Cretaceous were moist and equable. Many species that evolved in these polar latitudes became isolated due to various geographical, climatic or biological barriers. Other species dispersed northward, presumably following routes of similar climate. Some Seymour Island latest Cretaceous angiosperm species which subsequently appeared in the Paleocene or Eocene in New Zealand and southeastern Australia, have modern relatives living in mid- to low latitudes.
New plesiosaurs from the Upper Cretaceous of Antarctica
Authors: Chatterjee Sankar , Small Bryan J. 
Published: April 2008

Abstract
New plesiosaur remains from the Upper Cretaceous Lopez de Bertodano Formation (late Campanian-Maastrichtian) of Seymour Island, Antarctic Peninsula include Cryptoclididae and Elasmosauridae. The occurrence of Cryptoclididae is reported from the Antarctic region for the first time. The taxon represents a new genus and species, based on a skull and associated cervical vertebrae. The long, slender and delicate teeth may have formed a ‘trapping’ device that enabled cryptoclidids to feed on small fish and crustaceans that abound in the same deposits. The cryptoclidids had a restricted distribution, being known so far from the Middle and Late Jurassic of England, and the Late Cretaceous of Chile, Argentina, and Antarctica.

Other specimens, represented by several postcranial skeletons, are taxonomically indeterminate, but they share some features with other contemporary elasmosaurid genera such as
Hydrotherosaurus, Morenosaurus, Thalassomedon
, and
Mauisaurus
. Unlike the cryptoclidids, the elasmosaurids had a cosmopolitan distribution during the Jurassic and Cretaceous periods.

Trophic diversity within guilds of marine predators is examined in the Lopez de Bertodano palaeocommunities. Three predator guilds are recognized on the basis of tooth morphology and prey preference. The mosasaurs composed the ‘Cut guild’, and were the principal predators. The elasmosaurids constituted the ‘Pierce guild’, and the cryptoclidids formed the ‘Trap guild’. These marine reptiles exploited the various pelagic resources such as sharks, bony fish, soft cephalopods and crustaceans, and survived until the end of the Cretaceous. The plesiosaurs were excellent swimmers, and used their hyperphalangic paddles for subaqueous flight in the manner of modern sea lions.
Late Cretaceous-early Tertiary floras of King George Island, West Antarctica: their stratigraphic distribution and palaeoclimatic significance
Authors: Birkenmajer K. , Zastawniak E. 
Published: April 2008

Abstract
Stratigraphic positions of Late Cretaceous and Tertiary floras have been established on King George Island, West Antarctica, based on K-Ar dating of associated volcanics. The oldest dated floras, of Late Cretaceous and Paleocene ages, provide evidence for a warm climate phase preceding the early Eocene glacial event termed the Kraków Glaciation. Late Eocene through early Oligocene floras indicate another warm period termed the Arctowski Interglacial, which post-dates the Kraków Glaciation. The youngest floras, of Oligocene-Miocene boundary age, indicate a temperate (or cool-temperate) climate, corresponding to the Wawel Interglacial which separated late Oligocene glacial and interglacial epochs (Polonez Glaciation, Wesele Interglacial and Legru Glaciation) from early Miocene glaciation (Melville Glaciation).
Evolution of the Antarctic fish fauna with emphasis on the Recent notothenioids
Authors: Eastman J. T. , Grande L. 
Published: April 2008

Abstract

The composition of the Antarctic fish fauna has undergone remarkable changes through time. Fossil fishes are known from Devonian, Jurassic, Cretaceous and early Tertiary deposits of the region. The Recent fauna does not appear to be derived from any part of any of the known fossil faunas. The Devonian fish fauna includes agnathans, placoderms, acanthodians, chondrichthyans and osteichthyans all belonging to families now extinct. The Jurassic fauna is known by only one species, a neopterygian of the now extinct family Archaeomaenidae. Both the Palaeozoic and early Mesozoic fish faunas known from Antarctica indicate Australian biogeographic affinities based on other (
i.e.
, non-Antarctic) known Palaeozoic and Mesozoic fish faunas. Late Cretaceous and early Tertiary species from the Antarctic region (Seymour Island) belong largely to families of fishes that today live in other regions of the world, but are extinct in the Antarctic region. The Recent (extant) fish fauna is drastically different from any of the fossil faunas and is dominated by perciforms of the suborder Notothenioidei. To date the fossil record has provided no fossils identifiable as notothenioids, or even species closely related to the group. It is unlikely that low water temperatures were directly respnsible for the local extinction of the Tertiary Seymour Island ichthyofauna or for the lack of diversity in the Recent fauna. The decline of suitable substrate and trophic factors may have been more important in changing the composition of the fish fauna. There is considerable morphological, physiological and ecological diversification within the Notothenioidei. Although the emergence of this group was probably not a direct response to cooling, the subsequent radiation of notothenioids was associated with a variety of specializations related to low water temperature.
The origin of the Southern Ocean marine fauna
Authors: Clarke Andrew , Crame J. Alistair 
Published: April 2008

Abstract

Current knowledge of the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present. Although direct fossil evidence is sparse after the Eocene, geophysical evidence suggests that shallow waters have been present since the late Mesozoic, and possibly much longer. The break-up of Gondwana was accompanied by a more or less steady lowering of both surface and bottom temperatures in the Southern Ocean from about 15°C in the Late Cretaceous to the present range of roughly +2 to −1.8°C. Microfossils in deep-sea drilling cores indicate that temperature drops were particularly sharp in the early Oligocene (
c.
38 Ma), mid-Miocene (10–14 Ma) and Pliocene (
c.
4 Ma BP). Geological evidence suggests that the Drake Passage opened, and the present oceanographic regime established, about 25–30 Ma BP. This is now known to be about the time of full-scale development of the East Antarctic ice cap. Subsequently ice sheets extended across, and deeply eroded, the continental shelves but the effects of these glacial maxima on the marine biota are not fully understood. Late Cretaceous/early Tertiary marine fossils from the James Ross Island group indicate a diverse shallow water marine fauna, including two groups notably lacking in diversity in the living fauna: decapods and teleost fish. In several genera occurrences in this fauna predate first occurrences in lower latitudes by as much as 40 Ma, suggesting the possibility that a number of groups originated at high southern latitudes.

The living fauna exhibits a high biomass in many areas, and within-site diversity can be as high as anywhere in the world. Some individual taxonomic groups, however, (notably bivalves and gastropods) have a lower diversity than in the tropics, supporting the concept of a latitudinal cline in diversity. Studies of physiological adaptation to temperature suggest that the decline in seawater temperature during the Cenozoic has not presented a particularly severe evolutionary problem. The reasons for the absence of large decapods and the low diversity of fish in the present fauna are unclear. Most of the biological features of the modern fauna are more likely a response to the seasonality of the ecosystem rather than low temperature
per se
. Overall the evidence suggests that the present Southern Ocean shallow water marine fauna largely evolved in situ, having been present since at least the Late Cretaceous, and possibly much longer. Some groups have invaded, for example along the Scotia arc, but the isolation of the Southern Ocean by the present oceanographic regime and the limited dispersal ability of many forms means that exchange with lower latitudes is very slow.
Incorporating geological data in well log interpretation
Authors: King D. E. 
Published: April 2008

Abstract
A multi-step technique is presented that permits a variety of quantitative and qualitative geological data to be incorporated in the log interpretation process to derive a detailed lithological analysis. The geological data are used to develop and refine explicit tool response and interpretation models. The models include synthetic wireline log data generated from input mineralogical and fluid data. These models are used in an interpretation system together with wireline data to provide a geologically reasonable lithological solution appropriate to the stratigraphic framework of a basin. An application of this technique is presented for a lithologically complex reservoir. A full suite of conventional logs was used together with core-derived data to provide an accurate level-by-level lithological analysis. The results contribute to the refined geological interpretation of the well.
New techniques in lithofacies determination and permeability prediction in carbonates using well logs
Authors: Dorfman M. H. , Newey J.-J. , Coates G. R. 
Published: April 2008

Abstract
Carbonate reservoirs pose many challenges to geologists and engineers. Lithofacies variations are often the key to the determination of commercial value and efficient reservoir exploitation. Thus, techniques which permit the identification of the involved lithofacies would be useful. This paper illustrates a successful application of multidimension techniques in two-dimensional space, by using cross plots of a variety of well logs that have a principle component sensitivity to the lithofacies. This paper also examines the appropriateness of techniques which relate log data to core-derived permeability. These approaches have previously been associated with the intergranular shaly sand rocks and not carbonates. The technique shown approaches this from a Kozeny-core correlation which is used to predict the surface area parameter. This is then followed by development of a link to log-derived bulk water values. The log derived variables can be made to work providing irreducible conditions are present or can be established.
Sediment cyclicity from well logs
Authors: Worthington P. F. 
Published: April 2008

Abstract
The application of wireline well logs to the recognition and interwell correlation of sediment cyclicity is governed by the resolving powers of the different logging tools relative to measured sedimentation rates and cyclic periodicities. These variables, which are not always well defined, give rise to diverse capabilities of well logs in recording and correlating cyclic events. It is therefore important that criteria be established for the successful application of wireline logs in cyclostratigraphy, especially when a succession reflects several lithoperiodicities due to climate forcing. Quantification of these criteria leads to the introduction of a log association parameter (LAP) to compare the effective cyclic resolutions of different logging tools in diverse geological environments. This parameter relates sedimentation rates and tool vertical resolutions to the targeted time-periods of cyclicity. It is tool- and site-specific but is independent of formation lithology and chemistry. High LAP values, above the critical level of unity, suggest a strong cyclic resolution. Similar supracritical LAP values for (different) logs in different boreholes imply a high degree of potential interwell correlation. The benefits of a LAP-based approach are evident from illustrative examples, even at this preliminary stage. Field application ideally requires the conjunctive use of log and core information, a strategy which reflects the current trend in earth science towards a more meaningful integration of data measured at different scales.
Interwell matching using a combination of petrophysically derived numerical lithologies and gene-typing techniques
Authors: Griffiths C. M. , Bakke S. 
Published: April 2008

Abstract
The use of gene-typing techniques in stratigraphic matching problems has been steadily developing since Smith & Waterman published an example in 1980. The regular use of these techniques to assist in stratigraphic correlations using wireline log data has, however, been hindered by the lack of suitable precisely defined lithological units. In an oil-field production or exploration environment, the porosity logs and a natural gamma log can be used to derive various types of numerical lithologies. These lithologies provide a convenient starting point for the use of gene-typing algorithms since they comprise a relatively small set of precisely defined reproducible units. The advantage of using a gene-typing technique is that it enables multiple matching hypotheses to be produced from sequences which contain gaps, stretched zones, and duplicated sections. These matches can assist the production of stratigraphic correlations. Examples of matching are presented from reservoir sections in the Statfjord and Murchison fields.
Feasibility of in situ elemental analysis in mudrock evaluation
Authors: Primmer T. J. , Kerr S. A. , Myers K. J. 
Published: April 2008

Abstract
Geochemical logging now offers the possibility of performing quantitative in situ elemental analysis. Laboratory measurements of element abundances on selected sections of mudrocks were made to simulate the potential use of data available from geochemical logging. The analyses centre on mudrocks from the Magnus Field (North Sea) and Dorset Kimmeridge Clay Formation sequences (Southern England). Subsequent multivariate statistical processing of these analyses showed that pre-defined units within the sections studied can be distinguished geochemically without recourse to mineralogical description. This is demonstrated firstly by cross plotting elemental abundances to pick out significant sympathetic trends and thereafter by clustering and factor analysis techniques which utilize a more extensive dataset. This study shows that the direct application of statistical tests to raw element abundances determined downhole is an appropriate methodology by which conventionally impractical topics, such as the subsurface discrimination of mudrock facies, may be tackled. This conclusion will, no doubt, be tested further as geochemical logging develops over the next few years.
An investigation into nuclear log responses of North Sea Jurassic sandstones using mineralogical analysis
Authors: Humphreys B. , Lott G. K. 
Published: April 2008

Abstract

The results of laboratory mineralogical analyses have been compared with downhole log responses to determine the possibility of detecting individual minerals using the gamma-ray, natural gamma-ray spectroscopy, formation density and litho-density logs. Cored sequences from the Murchison, Thistle, Kittiwake, Gannet and Tartan Fields, North Sea, are used as case examples. K-feldspars, micas, detrital clays (illite, and possibly kaolinite) and phosphatic cements are shown to produce a measurable response on the gamma-ray and natural gamma-ray logs. Authigenic kaolinite did not impart radioactivity to the sandstones in the examples studied. The photoelectric absorption index (
Pe
) was found to be particularly sensitive to Fe-bearing minerals and baryte. A number of problems constrain full characterization of the mineralogy of a sandstone: specific detection of quartz and plagioclase feldspars is not possible by nuclear logs, distinction between minerals is problematical when a log responds to several minerals simultaneously, and calibration for minerals with a variable composition such as ferroan dolomite and mixed-layer illite-smectites is difficult.
Identification of source rocks from wireline logs
Authors: Stocks A. E. , Lawrence S. R. 
Published: April 2008

Abstract
This paper reviews the properties of organic-rich rocks which constitute petroleum source rocks and investigates petrophysical methods which can be used for their assessment. A review is made of the common log data and their response to an appreciable organic content in shale formations. Associations and effects which might lead to an erroneous assessment are also discussed. Previous researchers have highlighted relationships between organic content and various log parameters or values. These rely on geochemical control and tend to be stratigraphically and regionally specific. In this paper we show how standard petrophysical processing can be applied for qualitative and semi-quantitative evaluation of organic content and therefore source rock potential. Recommendations are made for a reform in geochemical sampling which will enable better quantitation methods for more widespread application.
In situ crustal stress in the United Kingdom from borehole breakouts
Authors: Evans C. J. , Brereton N. R. 
Published: April 2008

Abstract
Until recently very little in situ stress data have been available from the UK crust. Literature reviews list only a limited number of measurements which include information on the direction of maximum horizontal compression. Unequal horizontal crustal stresses imposed on vertical boreholes will often cause localized rock spalling along the direction of least compressive stress. The resultant elongations of the borehole cross section, called breakouts, can be identified from four arm caliper records collected routinely with conventional geophysical dipmetre logs. Eighty-one boreholes in the United Kingdom have been analysed for breakouts using criteria for identification of breakouts unique to this paper. The majority of borehole breakouts in southern Britain are aligned NE-SW, indicating a maximum horizontal stress in a NW-SE direction. There are insufficient data to confidently assess a dominant borehole breakout direction in Northern Britain, although the four boreholes analysed indicate possible variations in the crustal stress field.
Electrical properties of basalts from DSDP Hole 504B: a key to the evaluation of pore space morphology
Authors: Lovell M. A. , Pezard P. A. 
Published: April 2008

Abstract
Archie’s Law is a well known empirical relationship between electrical formation factor and porosity:

FF =
a
φ

−
m

.

As such it is widely applied in the analysis and interpretation of downhole measurements. Despite its frequent application, however, the mechanics underlying the relationship that it embodies remain largely a mystery. A brief review of some previously published, but often neglected, data is used here to describe recent results for laboratory and downhole electrical measurements in basaltic ocean crust. The results disagree with many previously published studies of crystalline rocks in that
a
≠ 1.0 and
m
is not always close to 2.0. Instead
a
increases with increasing fracturing, while
m
remains low and constant, though it increases slightly in the altered rock, possibly implying increased ‘tortuosity’. The value of
a
allows discrimination between fractured pillows and massive flows and may be inversely related to the degree of crack connectivity. Cation exchange capacity measurements on core samples show there is potential for surface conduction to occur, but probably only at higher temperatures. The precise nature of this temperature dependence is unclear, as is the interplay of the surface conduction mechanism with that of electrolytic (pore fluid) conduction.
An assessment of the use of Christensen’s equation for the prediction of shear wave velocity and engineering parameters
Authors: Entwisle D. C. , McCann D. M. 
Published: April 2008

Abstract
The full wave train sonic log is widely used in civil engineering for the determination of formation dynamic elastic moduli. In some instances, the shear wave amplitude is too small to time its arrival accurately. In these situations Christensen’s equation can be used to predict the shear wave velocity from the compressional wave velocity and the formation density. In this paper the origins of Christensen’s equation are investigated in relation to both field and laboratory studies on a wide range of natural materials. It is suggested that differences between the measured and predicted shear wave velocities are lithologically based. The equation is not valid for uncemented sediments. The dynamic elastic moduli reflect these differences. Bulk modulus is least affected by large differences in shear wave velocity. There is no relationship between the predicted and the measured values for Poisson’s ratio. The use of Christensen’s equation will be improved if corrections are made locally for lithology.
Geological integration and evaluation of Northern Monagas, Eastern Venezuelan Basin
Authors: Aymard R. , Pimentel L. , Eitz P. , Lopez P. , Chaouch A. , Navarro J. , Mijares J. , Pereira J. G. 
Published: April 2008

Abstract
Over the last 60 years, the Eastern Venezuelan Basin has been heavily explored with giant oil accumulations being developed in such areas as Oficina, Anaco, Quiriquire and the Orinoco Oil Belt in the states of Anzoategui and Monagas. Since 1986, interdisciplinary studies and seismic interpretations have led to discovery of a trend of deep structures on the northern flank of the basin, some of them beneath old early Tertiary producing fields. The first exploratory well, FUL-1, tested 12 000 BOPD of 28° API crude. The new reservoirs consist of massive sandstones of the Eocene Caratas Formation and Oligocene Naricual and Los Jabillos Formations between depths of 13 000 and 17 000 feet. The main structures placed in a thrust fold belt as a series of anticlines, extending over 100 km across Northern Monagas; currently four wells are being drilled and six more exploratory wells are planned to be drilled in the new future. To date over 1900 MMBBLS of reserves have been discovered, and possible reserves for the area are close to 8.6 billion BBLS.