bluuebunny/crossref_metadata_2025 huggingface dataset:
Archaean ecology: a review of evidence for the early development of bacterial biomes, and speculations on the development of a global-scale biosphere
Authors: Nisbet E. G.
Published: April 2008

The antiquity of the carbon cycle, which began prior to 3.5 Ga ago, implies that a complex and diverse biosphere has existed for most of the Earth’s history. The earliest living community may have consisted of a variety of chemotrophic bacteria, including both archaea and eubacteria, that existed around hydrothermal systems. It is possible that photosynthesis began in thermophilic bacteria that originally developed infra-red thermotaxis for detecting hot vents, maximizing the chance of survival in the close vicinity of hydrothermal systems. The post-photosynthetic biosphere may have inhabited a set of distinct habitats, including marine littoral, open ocean, terrestrial and hydrothermal biomes. Sequestration of oxidation power, by partitioning into zones of oxidation and reduction, may have allowed an inflationary biosphere to develop, limited ultimately by the availability of crucial nutrients such as phosphorus. Biomes develop and collapse, and, in consequence, selective pressures over time would have created a cooperative, Gaian biosphere.
Zircon geochronology of Archaean felsic sequences in the Zimbabwe craton: a revision of greenstone stratigraphy and a model for crustal growth
Authors: Wilson James F. , Nesbitt Robert W. , Fanning C. Mark
Published: April 2008

U-Pb ion-microprobe (SHRIMP) work on zircon populations from 13 Zimbabwean Archaean felsic rocks are presented and interpreted. Samples were extracted from felsic volcanic sequences from most of the major greenstone belts and represent the first zircon geochronological data from within the greenstone belts themselves. The data demonstrate a Late Archaean volcanicity spanning 250 Ma which began at least 2900 Ma ago and ended at 2650 Ma. The intrusion of extensive granitoid sills of the Chilimanzi suite at
c.
2.6 Ga marks the widespread stabilization of the craton. Based on the new zircon data and a re-evaluation of published mapping, a new stratigraphic subdivision is presented for the Late (<2.9 Ga) Archaean of Zimbabwe. A feature of the stratigraphic model is the cyclicity of magmatism which begins with ultramafic-mafic rocks, progresses through felsic volcanism and ends with a granitoid event. These cycles are repeated at least three or four times in the 250 Ma time span. An important characteristic of the felsic volcanic rocks is that the bulk of the material examined contains inherited, xenocrystic zircons whose ages range from 1000 Ma to 20 Ma older than the host rocks. The oldest xenocrystic zircons (
c.
3.6 Ga) are restricted to volcanic rocks which erupted through the Tokwe segment; itself the only known > 3.3 Ga fragment of Archaean crust in Zimbabwe. These data suggest that the Early Archaean crust is restricted to the Tokwe segment in the south of the country. Since even the oldest of the felsic volcanics (2.90 Ga, Lower Belingwean) have zircons which are 50 Ma older, it is suggested that remnants of earlier cyclic greenstone-granitoid events must underlie the present craton and that all of the currently exposed greenstone belts of Zimbabwe were developed on sialic crust.
Palaeoproterozoic Laurentia-Baltica relationships: a view from the Lewisian
Authors: Park R. G.
Published: April 2008

Using a modified Patchett
et al.
(1978) pre-Grenville fit of Laurentia and Baltica, tectonic information from the Lewisian complex of Britain and from neighbouring Palaeoproterozoic belts of Laurentia and Baltica is reviewed. It is shown that a remarkable consistency in convergence directions existed across the whole region in the period 1.9–1.8 Ga suggesting that the reconstruction used may be correct, and that a common movement pattern can be inferred for the Palaeoproterozoic period within the North Atlantic region.

A speculative plate tectonic history for the region between
c.
2.6 and
c.
1.5 Ga is discussed in four stages. (1) 2.6–2.4 Ga: development of conjugate shear-zone systems in the North Atlantic craton. (2) 2.4–2.0 Ga: rifting and dyke emplacement in older cratons; creation of oceanic and intracontinental basins. (3) 2.0–1.8 Ga: subduction at active margins of older cratons with creation of magmatic arcs; collision of cratons accompanied by closure of intra-cratonic basins and accretion of arc terranes. (4) 1.8–1.5 Ga: development of new active margin discordant to the previous ones, with significant changes in convergence direction within the amalgamated continental assembly.
Deformation in the mid to lower continental crust: analogues from Proterozoic shear zones in NW Scotland
Authors: Wynn Timothy James
Published: April 2008

A suite of 1.8–1.7 Ga (Laxfordian), E-W striking, amphibolite-facies shears in the Lewisian of NW Scotland have been mapped across a pre-existing rheological boundary in the Laxford-Scourie area. The rheological contrast is provided by the southern boundary of the NW striking Laxford shear zone (LSZ), which displays complex Proterozoic folding and shearing of relict Archaean granulites. The more competent Archaean gneisses lie to the SW of the LSZ which has been a focus of shearing, amphibolitization and metasomatism from 2.6 to 1.4 Ga. The shears of interest display a second-order, extensional shear band relationship to the LSZ and formed during a phase of sinistral transtensional shearing and granite intrusion at 1.8–1.7 Ga. The second-order shears show displacement variations consistent with their propagation from the strongly foliated, less competent gneisses in the LSZ into the Archaean granulites to the SW.

A map of the Laxford-Scourie area can be regarded as a section through the mid to lower crust as observed on some deep seismic lines such as the BIRPS DRUM line from the north of Scotland. In the Laxford area, the change in geometry of the second order shears from SW to NE, as they curve into the LSZ, is comparable to the curvature of extensional shears in the mid to lower continental crust. Displacement variations indicate that the shear zones may nucleate at the base of the upper/mid crust and propagate up and down dip. Alternatively the shears may nucleate in the mid/lower crust and propagate up dip, becoming steeper as they do so.
Development of the Witwatersrand Basin, South Africa
Authors: Coward Mike P. , Spencer Richard M. , Spencer Camille E.
Published: April 2008

The Witwatersrand basin is a large hinterland basin of Archaean age developed on already consolidated continental crust south of the Limpopo plate margin. It is a flexural basin formed southeast of a major thick-skinned thrust system, modified by a second thrust system to the southeast. Studies of several thousand kilometres of seismic data, together with geophysical modelling and new field data, have allowed the thrusts and their associated hanging-wall uplifts to be mapped and dated, relative to sediments of Central Rand age. The basin subsequently underwent extension on large detachment faults. Associated half-grabens are infilled with growth sequences of Platberg sediments and intermediate volcanics. These grabens were inverted during post-Platberg and post-Transvaal times. Studies of the Witwatersrand Basin allow tectonic models to be developed for the Archaean which can be used to help interpret Cenozoic mountain belts.
Asian analogues for Precambrian tectonics?
Authors: Graham R. H.
Published: April 2008

A non-specialist view is that the Archaean crust comprises either tonalite/greenstone belt associations or gneissic terrains in granulite facies. Archaean crustal remnants lie as undeformed pods between ramifying Proterozoic mobile belts. The cratons themselves may have unconformable remnants of undeformed Proterozoic ‘platform’ sediments.

Coward, Windley and others have already drawn attention to similarities between the accretionary collage which makes Central Asia and the tectonic patterns of the Precambrian. These similarities are developed and amplified in this paper. Central Asian basins such as Tarim, Junggar and their satellites have developed on stretched continental fragments now accreted within the Asian collage. This stretched lithosphere, having been equilibrated and strengthened, now forms resistant kernels around which the surrounding ramifying accretionary deformation belts have been moulded.

Enclosed foreland basins have developed on the continental fragments in response to loading of the adjacent mountain belts, and great thicknesses of mostly Tertiary sediments have accumulated in them. The ‘mobile belts’ which surround the basins have been reactivated by later, distant, collision events with corresponding loading and sedimentation events in the basin.

The Black Sea and South Caspian basins are back-arc small ocean basins incorporated within the collage. They also form resistant kernels around which the mountain chains are moulded.

Deep erosion levels through these systems might provide broad analogues for Precambrian tectonic patterns, i.e. the Black Sea for the tonalite/greenstone belt terrains, the deep levels of Tarim for ‘reworked’ granulite terrains like John Sutton’s homeground of the NW Highland foreland. Sutton and Watson’s two orogenies are manifested as a ductile shear fabric associated with back-arc stretching (Scourian) reworked in zones after a substantial time interval (Laxfordian). Dykes like the Scourie dykes might be associated with stretching and incipient continental separation, and therefore be close in time with the ductile stretching as, arguably, the Scourie dykes are with the late Scourian (Inverian) deformation in Scotland.
The formation of the Strait of Dover
Authors: Gibbard P. L.
Published: April 2008

The Strait of Dover (Pas-de-Calais) is a narrow sea passage that links the North Sea and the English Channel between Britain and France. Much evidence suggests that the Dover Strait did not exist throughout most of the Pleistocene. Instead, a Chalk barrier was present, formed by the Weald-Artois anticline. Advance of the continental ice-sheet across the North Sea in the Middle Pleistocene Elsterian/Anglian Stage apparently dammed the southern part of the basin and water discharging into it was prevented from reaching the Atlantic to the north. The resulting lake apparently drained by spilling over the barrier and initiated the gap. This scenario is supported by sediments at Wissant, France. This theory contrasts with one, proposed by French geologists, that favours a structural origin.

Overflow from the lake has been interpreted as having been catastrophic. This was invoked to explain the origin of the complex anastomosing system of valleys or channels that occurs on the floor of the Channel cut into bedrock, predominantly of Mesozoic age. These valleys are interlinked to form a drowned drainage system and can also be linked to present rivers that enter the Channel on both the British and French sides. However, it is highly probable that the drowned valley system is multigenetic, resulting from repeated fluvial and marine erosion and deposition rather than representing a single, short-lived event. The valley system probably originated in the late Early to early Middle Pleistocene as a consequence of uplift of the Weald-Artois region.

Once the Dover Strait was formed, the rivers Thames and Scheldt were deflected through the gap and into the Channel River system during periods of low relative sea-level. Subsequently these rivers were probably joined by the Maas and Rhine, diverted by glaciation in the Drenthe Sub-stage (Saalian/Wolstonian Stage). The narrows seem to have been progressively enlarged by marine tidal scour and coastal erosion during high sea-level events.
Raised beaches and sea-levels in the English Channel in the Middle and Late Pleistocene: problems of interpretation and implications for the isolation of the British Isles
Authors: Keen D. H.
Published: April 2008

This paper discusses the problems of the interpretation of the evidence for pre-Holocene high sea-level events and their age in the Strait of Dover and adjacent areas. This review suggests that there is evidence for the isolation of Britain from the continent in Oxygen Isotope Stages 7 and 5. The evidence for isolation in Stage 9 is less certain, and in Stage 11 is rather poor. In Stage 5, at least, isolation may have lasted for as long as 60 000 years.
Insularity and the Quaternary tree and shrub flora of the British Isles
Authors: Bennett K. D.
Published: April 2008

The distribution of trees and shrubs within the British Isles and elsewhere in northern Europe is considered in the light of palaeoecological evidence for Holocene distributions. A small number of species appear to be capable of spreading across any seachannel in the region, and the overwhelming majority are capable of spreading across channel of 10–100 km extent. Thus, there is little evidence that insularity would have been a significant factor in controlling the tree and shrub flora in the present or previous interglacials, and hence the presence or absence of any species cannot be used as evidence or otherwise for isolation. However, there have been significant losses of tree and shrub species from islands during the late Holocene as a consequence of anthropogenic activities. These may be among the more dramatic prehistoric extinctions yet described.
Structuring soil and rock descriptions for storage in geotechnical databases
Authors: Toll D. G. , Oliver A. J.
Published: April 2008

The paper describes the development of a database for geotechnical information. The database is part of a knowledge-based (expert) system for the interpretation of geotechnical information. It has been implemented using the INGRES relational database management system. A particular feature, unique to the database structure developed, is the ability to store layer descriptions in a structured form. In other database systems these are simply stored as single text fields. A complex structure has been derived which can accommodate the full range of layer descriptions; for example, interbedded soils/rocks within a layer, the variation in description from top to bottom of a layer, and the existence of multiple soil or rock types within a description. The paper presents details of the database tables with examples of how the structured representation is used.
Transfer and SERPLO: powerful data quality control tools developed by the British Oceanographic Data Centre
Authors: Lowry Roy K. , Loch Stephen G.
Published: April 2008

Quality control is a vital component of data management. However, in the current data volume explosion, practising quality control with finite resources presents a very real problem. During 18 years of operation, the British Oceanographic Data Centre has developed a cost-effective quality control strategy.

In this paper we describe the quality control procedures developed with emphasis on two vital components, the transfer system and SERPLO. The transfer system provides the initial interface between external data and the BODC system, combining reformatting with extensive data checking. SERPLO is a powerful, interactive, non-destructive graphical editor. It is shown how the internal development of these systems has dramatically increased the efficiency of the data management operation.
Data management in the National Geological Records Centre
Authors: Bowie R. C.
Published: April 2008

The National Geological Records Centre (NGRC) has collated large collections of borehole records (600 000) manuscript geological maps (50 000) and site investigation reports (19 000) with other collections of original and archive material. The majority of these data are now digitally indexed and searches can be carried out interactively on computer or via a GIS as part of a comprehensive enquiry service.
Magnetic mineral assemblages and magnetic contrasts in diagenetic environments — with implications for studies of palaeomagnetism, hydrocarbon migration and exploration
Authors: Machel Hans G.
Published: April 2008

Magnetic mineral assemblages in diagenetic environments are governed by microbial and inorganic/chemical processes. Empirical evidence and thermodynamic modelling of diagenetic environments ranging from near-surface settings to depths of about 6–7 km suggests that microbial processes are very important in surface and near-surface diagenetic settings, whereas inorganic diagenetic processes dominate in most deeper subsurface diagenetic settings. In all diagenetic environments, molecular oxygen and hydrocarbons are important because they control which types of bacteria can thrive and because they drive various redox reactions via changes in the redox potential.

Iron oxides, such as hematite and goethite, are stable under relatively oxidizing/aerobic conditions. With decreasing redox potential, i.e. under relatively reducing/anaerobic conditions, magnetite and pyrrhotite are the most important stable magnetic minerals, whereas hematite is unstable. Other magnetic minerals, such as greigite, may be important in some instances. Pyrite and siderite are also important because they may form at the expense of magnetic minerals. A significant decrease in the redox potential in diagnetic settings, via the invasion of hydrocarbons during migration or seepage from traps, for example, almost invariability results in diagenetic remagnetization. As a result ‘positive’, ‘absent’ or ‘negative’ magnetic contrasts are generated relative to the total magnetization (or remanence, or susceptibility) before such a decrease, depending on the relative amounts of magnetic to non-magnetic minerals formed and destroyed. Thermodynamic modelling further suggests that magnetic contrasts are more probable and tend to become more ‘positive’ with depth and with proximity to hydrocarbon pools.

Any significant change in the redox potential is likely to cause magnetic contrasts via the formation or destruction of magnetic minerals, thus generating secondary (chemical) magnetization and resetting original detrital or bacterial magnetization. The predicted magnetic contrasts are also likely to form as a result of hydrocarbon migration, and it appears possible to delineate migration timing and pathways by geomagnetic methods. Hence the predicted magnetic mineral assemblages can aid in the interpretation of palaeomagnetic studies, particularly via the recognition and proper interpretation of remagnetization. Magnetic contrasts, measured from the air, at the surface or on drill core, can be used for hydrocarbon exploration in association with other exploration methods.
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

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

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

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

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

Progenitor 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

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

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

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

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

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

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

A 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

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.
Latest Cretaceous mollusc species ‘fabric’ of the US Atlantic and Gulf Coastal Plain: a baseline for measuring biotic recovery
Authors: Koch Carl F.
Published: April 2008

Studies of biosphere changes with time risk serious misinterpretation if they are based on a single section or closely spaced sections because lateral geographical changes in a fauna’s distribution can be interpreted erroneously as profound temporal change. This problem can be ameliorated if the variation in fauna geographical distribution is well documented because such information would provide a reference to which temporal changes may be compared. That is, if temporal changes are greater than documented lateral changes, extinction or origination may have occurred. If temporal changes are within the observed lateral changes, then no compelling need to suggest evolutionary change exists.

Data for the
Haustator bilira
Assemblage Zone in the Atlantic and Gulf Coastal Plain are given in terms of nine areas distributed along a 2100 mile outcrop belt. The data result from examination of over 110 000 larger invertebrate fossil specimens, most of which are mollusc. Each mollusc species encountered was classified by feeding types, habitat and size. Because the
Haustator bilira
Assemblage Zone represents the youngest Cretaceous sediments of the Coastal Plain, the data assembled provide a reference plane just prior to the K/T boundary. It is hoped that these data will be used to evaluate the significance of biosphere changes in the vicinity of the K/T boundary.
Scaling of fault displacements and implications for the estimation of sub-seismic strain
Authors: Pickering G. , Bull J. M. , Sanderson D. J.
Published: April 2008

Fault displacement populations have been shown to follow a power-law scaling relationship characterized by an exponent D. This relationship can be used to make predictions of the sub-seismic fault population from data derived from seismic surveys. Although fault populations exist in three dimensions the use of section data is recommended.
D
-values derived from sections can be applied directly to several problems, and are also related to the
D
-value for the fault set in higher dimensions. Accurate determination of
D
requires proper consideration of the scale range and sample size limitations of available data. The most common technique of using a cumulative frequency graph often leads to an upwards bias. An iterative correction procedure is proposed. Discrete frequency methods avoid this bias, but as a standard linear interval graph has other associated problems, a log-interval graph method is preferred. Simulations of these methods, applied to random computer generated samples from power-law distributions, have been made to examine the accuracy of D-values derived from typical data. Equations to estimate the confidence intervals for these D-values have been derived from a synthesis of the results. The application of the techniques is shown using fault data measured on seismic sections from the Southern North Sea and the Inner Moray Firth. Where local differences in D are shown to be significant, there is usually a marked change in structural style. Fault data are used to make improved estimates of crustal extension (β) by extrapolating the derived power-law relationship. A value of β = 1.20 is calculated for the Inner Moray Firth. Applications predicting the intersection of horizontal wells with ‘large’ sub-seismic faults and quality control of fault interpretation on seismic sections are also described.
Ductile strain effects in the analysis of seismic interpretations of normal fault systems
Authors: Walsh J. J. , Watterson J. , Childs C. , Nicol A.
Published: April 2008

The limited vertical resolution of reflection seismic data results in sub-resolution structures accommodating appreciable ductile strains which should be taken into account in structural restoration and balancing and in analysis of fault displacements. Non-ductile strains are expressed as discontinuities, such as fault offsets. A fault map of an intensively mined coal-seam is used to demonstrate the role of structures which would not be detected by a typical offshore seismic survey. Four examples are given of interpretations of seismic datasets in which significant ductile strain can be demonstrated; (i) an array of normal faults in which significant extension is accommodated by sub-seismic faults, (ii) a relay zone in which ductile shear strain accommodates significant displacement and change of bed-lengths, (iii) an intersection zone between conjugate normal faults which is effectively a zone of ductile pure shear strain with horizontal extension, and (iv) a hanging-wall fold which accommodates appreciable ductile displacement and ductile bed extension. In all these cases the ductile strains and displacements can be estimated from the seismic interpretation. Unless ductile strains are incorporated in restorations bed lengths will not balance. Balancing nevertheless remains the prime method for detection of grossly invalid sections.
The application of cross-section construction and validation within exploration and production: a discussion
Authors: Buchanan James G.
Published: April 2008

Numerous published studies have shown that cross-section balancing and validation techniques are a powerful method of structural analysis. This paper outlines reasons why cross-section validation also is a valuable methodology within the oil/gas industry.

Cross-section validation is a vehicle of getting analytical rigour into seismic and non-seismic interpretation by testing the section against the rules of structural geology (in particular geometry).

In addition to the analysis of structural traps, cross-section validation can be used in oil or gas sourcing studies, especially in the relative timing of hydrocarbon migration and trap formation/destruction. It is therefore a valuable methodology in both 3D basin analysis and prospect risking/ranking.

Cross-section validation should be an integral part of the petroleum geologist’s tool kit to aid further understanding of the 3D evolution of a basin and basin fluids through time. This technique, when used with other methodologies, such as sequence stratigraphy and basin modelling, allows the interpreter to use all the available data sets to constrain geological models on hydrocarbon prospectivity.