bluuebunny/crossref_metadata_2025_split huggingface dataset:
Palaeomagnetic and rock magnetic properties of hydrocarbon reservoir rocks from the Permian Basin, southeastern New Mexico, USA
Authors: Hall Stuart A. , Evans Ian 
Published: April 2008

Abstract
To evaluate the influence of fluid hydrocarbons on the magnetic properties of sedimentary rocks, two cores (V1 and V2) have been examined from a producing oil field reservoir (Vacuum Field) in the Permian Basin of southeastern New Mexico. The cores sample back-reef dolomitic mudstones-packstones of the Guadalupian San Andres Formation that were deposited on the northern shelf margin of the Delaware Basin. Rock magnetic and palaeomagnetic analyses show that low natural remanance magnetization (NRM) intensities and negative susceptibility values are better correlated with petrophysical properties (i.e. relatively high porosity and permeability) than with lithological patterns (core V1). These petrophysical properties are well correlated with zones of oil production (flow zones) identified in core V1. Samples from zones of lower porosity and permeability, non-productive horizons (no-flow zones), are characterized by more variable magnetic properties, but almost uniformly exhibit higher values of NRM and susceptibility.
The palaeomagnetic results indicate that these rocks were subjected to at least two identifiable magnetization events. The weakness of the magnetic signal in many samples allowed this observation to be made in only some instances. A high blocking temperature (300–500°C), low inclination (0–10°) component is believed to record a magnetization event early in the history of the unit (Late Permian). A low blocking temperature (<300°C), moderately steep (30–40°) inclination component may have been acquired in the medial Jurassic, marking a diagenetic event possibly associated with the migration of hydrocarbons or formation waters that preceded the introduction of hydrocarbons into the reservoir.
Application of a palaeomagnetic reversal stratigraphy to constrain well correlation and sequence stratigraphic interpretation of the Eocene C1 Sands, Maui Field, New Zealand
Authors: Turner Gillian M. , Bryant Ian D. 
Published: April 2008

Abstract

The giant, offshore Maui gas condensate field covers an area of 160 km
2
that straddled NE-SW oriented shorelines during the deposition of the main reservoir interval (C1 Sands) in the mid-late Eocene. These sands were deposited as highstand shoreline deposits and lowstand channel-fills that are vertically partitioned by thin, tight transgressive deposits. Correlation of shelf mudstones basinward of the shoreline with equivalent, tight coastal sands is important to define the distribution of barriers to vertical permeability within this approximately 100 m thick interval, but is ambiguous using a lithostratigraphic approach alone.

A palaeomagnetic study of 273 samples of shales, siltstones and sandstones was undertaken from three cored wells, Maui-6, -7 and -A1, to place further constraints on well correlation. A variety of magnetic behaviour was observed: from strong, stable primary remanent magnetization, to weak magnetization carrying secondary overprints which sometimes could not be removed completely. Primary polarities were retrieved from about 950f samples.
Maui-6, the most basinward well, contains a significant proportion of marine shales and is considered to provide the most complete record. The upper and lowermost parts of the magnetostratigraphic records from the other two wells correlate well with that from Maui-6. Incision of a channel system in the area of Maui-A1 is interpreted to have removed significant parts of the record from the middle C1 interval of this well. The palaeomagnetic data support the correlation of the high permeability, tidally influenced fill of this valley with time-equivalent, tight transgressive sands in interfluve areas.
The composite magnetostratigraphic record shows a high frequency of reversals: it is of predominantly normal polarity and contains 10 intervals of reversed polarity. Five of these reversed intervals are apparently less than about 30 000 years in duration. On the basis of biostratigraphic evidence that the interval studied is Bortonian (Mid-Eocene) in age, the magnetostratigraphic record is correlated with Chrons 17 and 18 of the global polarity time-scale.
Magnetic field of a core barrel
Authors: Shi H. , Tarling D. H. 
Published: April 2008

Abstract
The magnetic field associated with a core barrel is almost entirely restricted to a small volume near to its tip and is insignificant within the barrel, except immediately adjacent to the wall. At the tip of the barrel the field is lowest along its axis and directed almost entirely parallel to it. As the volume occupied by the field is small, the processes operating to produce any drilling imposed remanent magnetization can only be effective while this volume of borecore is passing through the field in this restricted location. This means that the borecore is only subjected to this field as it passes through about 2 cm length and consequently can only be affected by it for a few minutes during normal drilling operations. Consequently, viscous remanences are likely to be minimal and the processes by which the drilling imposed remanence are acquired (thermal, chemical or vibrational) appear to be associated with the actual cutting process. It should thus be possible to minimize the magnitude of these remanences by inserting a short (a few centimetres long), non-magnetic barrel immediately behind the drill bit, on to which the later barrels then screw. This would effectively result in the field being displaced away from the volume of rock near the crown where the processes producing the remanence occur, enabling more successful orientation and palaeomagnetic analyses to be undertaken of the natural remanence.
Comparative evolutionary palaeoecology: assessing the changing ecology of the past
Authors: Bottjer David J. , Schubert Jennifer K. , Droser Mary L. 
Published: April 2008

Abstract
Various palaeoecological trends have been identified in the Phanerozoic, each focusing on different aspects of the fossil record. Patterns that have been described include histories of tiering, palaeocommunity species richness, and guild occupation in evolutionary faunas, as well as onshore-offshore trends in origination, expansion and retreat. Patterns of change through time have also been documented from biosedimentological features (ichnofabrics, microbial structures, shell beds). Such trends can be compared and contrasted to yield unique insights into understanding the changing ecology of the past, and in particular may be helpful in evaluating the relative degree of ecological degradation caused by a mass extinction. This comparative approach can also shed light on a variety of fundamental palaeobiological problems, for example, why no new body plans (phyla) have evolved since the early Phanerozoic. Causes of this phenomenon are thought to be either: (1) ecospace was not sufficiently open after the early Phanerozoic for survival of new body plans; or (2) accumulating developmental constraints after the early Phanerozoic have prevented the evolution of new body plans. Because the Permian-Triassic mass extinction was the most devastating biotic crisis of the Phanerozoic, one might expect new body plans to appear if ecospace were the primary limiting factor and opened sufficiently by this mass extinction. Although previous studies have shown that ecospace availability in the Cambrian and Early Triassic was indeed different, this comparative approach indicates that ecological conditions in the Early Triassic were most like those of the Late Cambrian/Early Ordovician. Thus, if ecospace availability has constrained the survival of new body plans, then ecospace has always been sufficiently filled after the Cambrian explosion to inhibit their evolution.
The importance of crisis progenitors in recovery from mass extinction
Authors: Kauffman Erle G. , Harries Peter J. 
Published: April 2008

AbstractProgenitor taxa are defined as species or lineages which arise, commonly through punctuated or macroevolutionary processes, during the main phases of a mass extinction interval, and which then survive to seed the evolution of dominant groups during ensuing radiation and ecosystem recovery. Their success in surviving the severe environmental perturbations commonly associated with mass extinctions and their immediate aftermath lies in the fact that they are initially adapted in their evolution to these dynamically changing environments. This differentiates them from other surviving clades of ecological generalists, opportunists, disaster taxa, taxa with specialized survival mechanisms, etc., all of which may have a long pre-extinction evolutionary history. Progenitor taxa characterize those ecosystems which are most severely affected by mass extinction processes (perturbations and feedback loops), e.g. those of tropical to warm temperate climate zones. Progenitor taxa are rarer in those ecosystems with relatively minor response to environmental perturbations of mass extinction intervals (deep sea and more poleward areas), where many established pre-extinction lineages survive the extinction event(s) with little change. In several published records of ‘explosive radiation’ among new lineages following mass extinctions, high-resolution stratigraphic sampling has shown that many of these ‘new’ recovery taxa actually had their origins as small, relatively rare progenitor taxa during the preceding mass extinction intervals. Examples from Cretaceous mass extinction intervals are presented (Cenomanian-Turonian, Cretaceous-Tertiary).
Models for biotic survival following mass extinction
Authors: Harries Peter J. , Kauffman Erle G. , Hansen Thor A. 
Published: April 2008

Abstract

Mass extinction intervals are characterized by three dynamic processes: extinction, survival, and recovery. It has been assumed that the taxa surviving a mass extinction are composed predominantly of eurytopic groups and opportunistic/disaster species. However, high-resolution stratigraphic and palaeontological analyses of several mass extinction intervals show that the repopulation of the global ecosystem takes place among ecologically and genetically diverse and complex taxa and occurs far too rapidly to be solely attributed to rapid radiation from a few ecological generalists. We suggest a number of potential survival mechanisms or strategies (
sensu
Fryxell 1983) which have evolved in diverse taxa and which could have allowed them to survive mass extinction intervals. These mechanisms consist of: rapid evolution, preadaptation, neoteny/progenesis, protected and/or unperturbed habitat, refugia species, disaster species, opportunism, broad adaptive ranges, persistent trophic resources, widespread and rapid dispersion, dormancy, bacterial-chemosymbioses, skeletonization requirements, reproductive mechanisms, larval characteristics and chance. Because of the wide variety of potential survival mechanisms, the range of survivors may be far higher than previously hypothesized. This would account, in part, for the diversity and evolutionary state of Lazarus taxa and for the rapid re-establishment of some complex ecosystems following many mass extinction intervals, without calling on “explosive” radiation from generalist/opportunist stocks following a mass extinction interval.
Insect origination and extinction in the Phanerozoic
Authors: Jarzembowski E. A. , Ross A. J. 
Published: April 2008

Abstract
Insects (Superclass Hexapoda) are the most successful group of living terrestrial arthropods and the richness of their fossil record is only just beginning to be realized with the recent publication of two extensive databases. Hexapods first appeared in the Early Devonian, post-dating the Cambrian ‘explosion’ of marine arthropods by some 140 Ma. The earliest Hexapoda belong to primitively wingless taxa; however, these ‘Apterygota’ comprise less than 1% of all hexapod species. The appearance of winged insects (Pterygota) in the mid-Carboniferous was accompanied by a major adaptive radiation of non-holometabolous hexapods at ordinal level This was supplemented in the Permian by the radiation of insects with complete metamorphosis (Holometabola). The number of insect orders present in this period was similar to that at the present day. The family data suggest four major periods of origination in the Phanerozoic, with peaks in the Permo-Carboniferous, Early Jurassic, Early Cretaceous and Eocene. Unlike the Tertiary, the Palaeozoic and Cretaceous peaks are accompanied by considerable turnover of families; they are followed by reduced palaeodiversity in the Early Triassic and Late Cretaceous and Palaeocene. The former decline may be linked with the general extinction at the Permian/Triassic boundary and the latter with the rise of the angiospermous flowering plants. Insect generic data for the Phanerozoic reflect the pattern shown by families but not orders. In general, insect diversity may be explained by an overall trend towards low extinction and steady origination at a subordinal level since the Palaeozoic.
Reef ecosytem recovery after the Early Cambrian extinction
Authors: Zhuravlev Andrey Yu. 
Published: April 2008

Abstract

Revised and new stratigraphic data indicate a complex extinction event in the late Early Cambrian which consisted of two, temporally separate, but related phases. The earliest phase (mid-Botomian, Sinsk Event) may be related to widespread anoxia due to eutrophication and phytoplankton blooms. The later event (early Toyonian, Hawke Bay Event), is connected to a world wide regression. This double extinction event severely injured the reefal biota which has undergone a further rejuvenation during the remainder of the Cambrian. As a result of the lowering of grazing pressure and unhealthy metazoan-calcimicrobial interactions, the remaining metazoan reef-builders were eliminated by the end of the Early Cambrian. Consequent reduction of space heterogenity led to the decline of calcified microbes (
Renalcis
, etc.) in both diversity and abundance which gave way to the thrombolite-stromatolite community. The recovery of the reefal biota occurred during the very end of the Late Cambrian-Early Ordovician and may be attributed to Elvis-taxa, with the exception of the spicular demosponges. This recovering biota intruded into the thrombolite-stromatolite community and created a space for the more successful encrusting reef dwellers of Middle-Late Ordovician time.
Biotic recovery after mass extinction: the role of climate and ocean-state in the post-glacial (Late Ordovician-Early Silurian) recovery of the conodonts
Authors: Armstrong H. A. 
Published: April 2008

Abstract

The pattern of recovery in conodonts following the Late Ordovician mass extinction does not conform to the classical adaptive radiation model of transgression, shelf area expansion and cladogenesis. An alternative hypothesis is proposed in which progenitor ‘survivor’ species evolved in the bathyal ecozone during Ashgill global cooling. Their appearance in low latitude shallow water environments occurred as the result of two phases of migration from the bathyal ecozone. The first, during the
extraordinarius
Biozone sea-level fall, included species attributed to the
Ozarkodina
and
Oulodus
? assemblages. This migration is considered to have been a response to the upward movement of the permanent thermocline, as high latitude climate and ocean conditions developed at low latitudes. The second phase of emergence occurred during the
persculptus
Biozone transgression when species of the
Dapsilodus-Distomodus
assemblage, appeared ahead of advancing anoxia.

Mean rates of per taxon origination and extinction, measured from an Upper Ordovician to Lower Silurian (low latitude) graphical composite reference section, were unequal at 0.09 and 0.19 taxa per standard time unit. The mean value for net rate of change in diversity was −0.66. Species originations and extinctions were non-random, a feature consistent with the dramatic changes in environment at this time.
Recovery of post—Late Ordovician extinction graptolites: a western North American perspective
Authors: Berry William B. N. 
Published: April 2008

Abstract

Late Ordovician to Early Silurian graptolite-bearing sequences have been recognized in three primary western North American areas: southeastern Alaska, northern Canadian Cordillera and the Great Basin (Nevada-Idaho). A spectrum of marine environments is represented in strata in these sequences, ranging from those of volcanic islands and deep oceans to those of shelves and shelf margins. During the time of glacial maximum, the time of the
extraordinarius
zone, sea-level lowered and oxic conditions prevailed on the ocean floor. The prominent Late Ordovician near-extinction among graptolites denotes the
pacificus—extraordinarius
zone boundary. Normalograptids appear to be the only taxa in the
extraordinarius
zone. They are the prominent taxa in the superjacent
persculptus
and
acuminatus
zones. Normalograptids are joined by a few diplograptids in the
persculptus
zone, and by a few more diplograptids as well as
Parakidograptus
and
Cystograptus
in the
acuminatus
zone. The first monograptids appear in the
atavus
zone in western North America. The
atavus
zone fauna is primarily diplograptids. Significant sea-level rise and transgression across the shelf following after deglaciation did not occur in western North America until the
acinaces
zone. At that time, new monograptids, including
Lagarograptus, Pristiograptus
and
Pribylograptus
, appeared as did many new diplograptid taxa. Stratigraphic occurrence data indicate that the major post near-extinction reradiation took place in western North America as shelf seas expanded and shelf sea habitats became increasingly available. That pattern of new taxa appearing during transgression continued into the
gregarius
zone.
Juvenile goniatite survival strategies following Devonian extinction events
Authors: House Michael R. 
Published: April 2008

Abstract
During the Devonian there is a correlation between certain periods of sedimentary perturbations, often associated with hypoxia, and extinction events in the evolution of the goniatite and clymeniid ammonoids. A review is given of the survival and diversification strategies associated with these events. Survivors generally show novelty recognizable even in early stages. Characters involved include protoconch size and form, ornament and whorl form and degree of enrolling of the first whorl or so which completes the ammonitella. In post-ammonitella stages to the adult, changes include the nature of coiling, which is often polyphase, ornament and whorl form. Principally the character of new groups is defined by sutural changes following the proseptum, and new features of sutural ontogeny are usually recognizable in the first few millimetres of growth. Far from being a character merely indicating the plasticity of early stages, as is often claimed, it is suggested that larval strategy is crucial for both survival and subsequent radiation. Since, after an extinction event, radiation is only possible for survivors, the available biotic parameters for evolution are the stress-controlled factors at extinction events.
Climate change, plant extinctions and vegetational recovery during the Middle-Late Pennsylvanian Transition: the Case of tropical peat-forming environments in North America
Authors: DiMichele William A. , Phillips Tom L. 
Published: April 2008

AbstractA major extinction of terrestrial plants occurred at the end of the Westphalian (Middle Pennsylvanian) in the lowland tropics of North America. Approximately 67% of the species in peat-forming mires, and at least half the species in clastic wetlands were eliminated by changing climatic conditions, probably protracted moisture deficits or exaggeration of seasonal dryness. Independent studies suggest that the end of the Westphalian was marked by deglaciation in Gondwana and increase in global temperature.In peat-forming habitats major floristic changes followed the extinction. Earliest Stephanian (Late Pennsylvanian) dominance-diversity patterns were highly variable temporally; several different plant groups that were of minor importance in Westphalian mires became major framework dominants, with high coal to coal variability. Ultimately opportunistic tree ferns, previously subdominant, became the dominant elements. Westphalian tree ferns were mostly small, cheaply constructed colonists with massive reproductive outputs and broad ecological amplitudes. Stephanian tree ferns were much larger and appear to have occupied sites for extended periods; they retained the cheap construction of earlier forms but added massive root mantles, which permitted greater height and girth. The ‘marsh’-forming lycopsidChaloneriaalso became common in Stephanian mires. These elements formed mire landscapes that had few analogues in the older Westphalian mire forests, dominated by tree lycopsids. Generic dominance patterns in the Stephanian became fairly consistent after the initial period of irregularity; however, the species composition of Stephanian mires was highly variable within generic themes.Ecological assemblages were persistent during most of the Westphalian and Stephanian. Patterns at the end-Westphalian suggest that high levels of species extinction disrupt self-regulatory properties of groups of species and create intervals of lóttery-like ecological dynamics. Opportunists may have an advantage during these periods, but ultimately they must give rise to species capable of site occupation. Thus the size of the extinction, and the proximity of existing species that can recolonize vacated resource space, will dictate whether speciation or colonization will rebuild the new landscapes.
Benthonic foraminiferal mass extinction and survival assemblages from the Cenomanian-Turonian Boundary Event in the Menoyo Section, northern Spain
Authors: Peryt Danuta , Lamolda Marcos 
Published: April 2008

Abstract

Foraminiferal response to the Cenomanian-Turonian Boundary Event was studied from a 50 m thick section in Menoyo, northern Spain, representing the uppermost
Rotalipora cushmani
and
Whiteinella archaeocretacea
Zones. Taxonomic and stratigraphic studies on benthonic foraminiferal assemblages indicate that the studied section represents mass extinction and survival intervals, with the mass extinction boundary in the lowermost part of the
Whiteinella archaeocretacea
Zone.

Stepped extinction within benthonic foraminifers was observed in the uppermost
Rotalipora cushmani
Zone. In the late phase of mass extinction several species became extinct (e.g.
Gavelinella intermedia-cenomanica-baltica
group,
Tritaxia pyramidata
(Reuss)), some others temporarily disappeared; Lazarus taxa (e.g.
Tritaxia tricarinata
(Reuss), nodosariids) and progenitor (e.g.
Globoratalites
sp. 1) taxa appeared. Disaster (e.g.
Praebulimina elata
) species along with opportunistic taxa (e.g.
Gyroidinoides praestans
(Magniez-Jannin),
Ammobaculites parvispira
Ten Dam) colonized vacated ecospace in the middle part of the survival interval, i.e. in the topmost part of the
Rotalipora cushmani
Zone. Opportunistic taxa dominated assemblages in the
Whiteinella archaeocretacea
Zone, i.e. in the higher part of the survival interval.

The recorded changes in benthonic foraminiferal assemblages most likely reflect the decline in oxygenation level of the bottom waters at the end of the
Rotalipora cushmani
Zone and the persistence of these unfavourable conditions in the
Whiteinella archaeocretacea
Zone.