bluuebunny/crossref_metadata_2025_split huggingface dataset:
Euconodont diversity changes in a cooling and closing Iapetus Ocean
Authors: Armstrong H. A. , Owen A. W. 
Published: April 2008

Abstract
Constrained seriation of euconodont generic presence-absence matrices for four time slices between the late Llanvirn and late Llandovery provides a qualitative method for defining shelf and oceanic biofacies, recosntructing biofacies architecture and analysing biodiversity within a regional context.

We propose many North Atlantic Province taxa had a pelagic mode of life and ranged widely across the Iapetus Ocean. Oceanic biofacies are considered to reflect water mass structure. Changes in vertical distribution of one such biofacies (including
Amorphognathus
and
Spinodus
) suggest adaptation to cold, nutrient-rich, oxygen-poor upwelling water. Biofacies distributions suggest that upwelling occurred along the Avalonian margin throughout the Ashgill, but was only initiated along the Laurentian margin immediately prior to the Hirnantian glacial maximum.

Clade diversities and trajectories differ between biofacies and latitudes, reflecting different causal mechanisms. In Laurentia, diversity fell in the early Ashgill, coincident with the onset of ocean cooling. Diversity declined in Avalonia when the microcontinent drifted into tropical latitudes. The stability of euconodont biofacies architecture during the Late Ordovician indicates that global cooling and plate reorganization had a low palaeoecological impact despite decreases in alpha and beta diversity.
The role of pyroclastic volcanism in Ordovician diversification
Authors: Botting Joseph P. 
Published: April 2008

Abstract
Pyroclastic volcanism has been tentatively correlated with Ordovician faunal diversification, but it is unclear whether the volcanism itself or associated tectonic effects were more influential. Elevated nutrient flux from uplifted areas has been widely discussed, but the link between enhanced productivity and diversification is unclear. Ecosystem compartmentalization due to irregular topography was probably significant, but it is debatable whether this was sufficient to explain the entire diversification. This paper introduces a further volcanic process, which may have been more significant than these established hypotheses, although it is emphasized that all relevant factors acted in combination. Recent studies of the local ecological effects of ash-fall have revealed dramatic post-depositional plankton and benthic blooms associated with overturning of a stratified water mass. The data are consistent through all studied sections from the Builth Inlier, Central Wales, while deeper-water sediments showed plankton blooms only. Repeated bloom events over localized dysaerobic shelf areas may have produced temporary benthic ‘islands’, enhanced genetic heterogeneity within affected regions, and increased speciation rates. In order to maximize bloom intensity (and possible effects on evolution), this process requires widespread pyroclastic volcanism combined with extensive shelf areas with well-developed stratification. The hypothesis potentially allows explanation of the differential rates of evolution between different groups, particularly the decoupled planktic-benthic patterns. A preliminary test using Welsh Basin ostracodes is presented, with predictions for the global database results.
Opening of the Hispanic Corridor and Early Jurassic bivalve biodiversity
Authors: Aberhan Martin 
Published: April 2008

Abstract
The Hispanic Corridor is a postulated marine seaway linking the eastern Pacific and western Tethyan oceans as early as Early Jurassic times. Two existing hypotheses relate the Pliensbachian-Toarcian bivalve extinction and recovery to immigration of bivalve species through the Hispanic Corridor. The extinction hypothesis implies that, in South America, the Pliensbachian-Toarcian extinction can be partly explained by the immigration of bivalves through the Hispanic Corridor and subsequent competitive replacement. The recovery hypothesis states that, in NW Europe, the renewed rise in diversity in the late Toarcian/Aalenian was largely a consequence of immigration of taxa from Andean South America via the Hispanic Corridor.
To test these hypotheses, I calculated immigration and origination rates of bivalves per million years. In both regions, early Pliensbachian to Aalenian immigration rates remained at low levels, thus disproving both hypotheses. By comparison, the origination of new species generally played a much more important role than immigration in controlling overall diversity of both regions. Future research should investigate if this is a more general pattern in the recovery of post-extinction biotas.
The apparently global Pliensbachian-Toarcian diversity crisis may be best explained by a combination of physicochemical factors, invoking intense volcanism, sea-level highstand and widespread anoxia, as well as biological factors. Recovery from this mass extinction commenced when origination rates increased again, which, in the Andean basins, was in the Aalenian and in NW Europe, the late Toarcian.
Cenozoic palaeogeography and the rise of modern biodiversity patterns
Authors: Crame J. A. , Rosen B. R. 
Published: April 2008

Abstract

The steepest latitudinal and longitudinal gradients in taxonomic diversity at the present day are those associated with tropical high diversity foci. Although there has been a tendency in the past to regard these features as either evolutionary ‘cradles’ or ‘museums’ of considerable antiquity, this may not be the case. Within the marine realm, a uniform, pan-tropical fauna was progressively disrupted by a series of plate tectonic events, the most important of which were the Early Miocene (
c.
20 Ma) collisions of Africa/Arabia with Europe and Australia/New Guinea with Indonesia, and the Middle Miocene-latest Pliocene rise of the Central American Isthmus. This had the net effect of establishing two main tropical high diversity foci: the Indo-West Pacific and the Atlantic-Caribbean-East Pacific. Similar foci were also established at the same time in the terrestrial realm.

Together with the physical isolation of Antarctica, these same tectonic events contributed significantly to global cooling throughout the Cenozoic Era. This in turn led to the imposition of a series of thermally defined provinces, and thus a considerable degree of biotic differentiation on a regional scale. However, something else seems to have been involved in the creation of very steep tropical diversity peaks. This could in part be a coincidental radiation of a series of unrelated taxa, or some sort of evolutionary feedback mechanism between interacting clades. Alternatively, Late Cenozoic rates of origination may have been enhanced by an external forcing mechanism such as changes in Orbital Range Dynamics.
Palaeontological databases for palaeobiogeography, palaeoecology and biodiversity: a question of scale
Authors: Markwick Paul J. , Lupia Richard 
Published: April 2008

Abstract
Computerized databases provide an essential tool for investigating large-scale spatial and temporal palaeontological problems. Although advances in both software and hardware have made the logistics of building a database much easier, fundamental problems remain concerning the representation and qualification of the data. Data from the fossil record are highly heterogeneous. Databases must be designed to account for variations in scale (grain, resolution), inconsistency in the data, and potential errors (inaccuracy). These issues vary with the scope of the study (extent), the biological group, and the nature and scale-dependence of supplementary, non-biological datasets (e.g. climate and ocean parameters). With the application of desktop geographic information systems (GIS) to global Earth systems science, and the ability to efficiently integrate and query large, diverse datasets, the need to ensure robust qualification of data, especially scale, has become all the more essential. This chapter examines some of the issues involved, defines terminology and offers pragmatic solutions.
Neotectonics on the Arabian Sea coasts
Authors: Vita-Finzi Claudio 
Published: April 2008

Abstract
The Holocene record on the coasts of the Arabian Sea provides information on the nature and rate of deformation generated by the interaction between the Indian, Arabian and Eurasian Plates. Holocene marine terraces show that the southern Makran has been subject to the infrequent but vigorous coseismic uplift (≤2 m) that characterizes other subduction settings and they indicate landward rotation of the imbricate faults among which shortening is distributed. The lack of significant Holocene deformation on the SE coast of the Arabian peninsula is consistent with its position parallel to a transform, although there is evidence for large-scale buckling driven by convergence at the Strait of Hormuz in the NE. Geomorphological and tide-gauge evidence for localized uplift on the southwestern coast of India may represent compressional buckling here too in response to Himalayan collision. Bathymetric and geodetic data can help to bridge these sequences and thus enhance their value for quantifying plate rheology and dynamics, notably by linking variations in plate-margin displacement with major sea-floor strike-slip structures and by eventually confirming transitory as well as sustained compressive buckling on land.
Gas hydrates acting as cap rock to fluid discharge in the Makran accretionary prism?
Authors: Delisle G. , Berner U. 
Published: April 2008

Abstract

We present a numerical model of the geothermal field of the Makran accretionary prism and of the slab being subducted below it. Calculated heat flow density values for the sea floor of the abyssal plain and the shelf slope are compared with
in situ
measured and bottom simulating reflector (BSR)-derived heat flow density values. The result suggests a predominance of conductive heat transport within the accretionary complex. Little evidence is found to suggest that fluid flow or frictional heat modifies the observed geothermal field to any great extent. We also studied the geothermal field associated with the decay of the potential gas hydrate layers (indicated by the presence of BSRs), as gas hydrate layers are being tectonically uplifted out of the gas hydrate stability field into shallower and warmer sea water. Theoretical considerations suggest a complete disappearance of gas hydrates at a water depth of about 750 m. The observed presence of numerous gas seeps almost exclusively at water depths of less than 800 m suggests that gas hydrate layers in the Makran accretionary prism act as a very effective cap rock to upward-directed flow of fluids containing notable amounts of dissolved gas from within the prism to the sea floor.
The geometry of structures in the Zagros cover rocks and its neotectonic implications
Authors: Sattarzadeh Yosef , Cosgrove John W. , Vita-Finzi Claudio 
Published: April 2008

Abstract

The Zagros Mountains are situated along the NE margin of the Arabian plate and are the product of complex deformation which began in Late Cretaceous time as a result of the collision between the Arabian and Central Iranian plates. During Pliocene time, deformation increased when plate convergence was accelerated by the opening of the Red Sea. This stimulated the migration of a deformation front from the collision zone towards the SW into the undisturbed Zagros basin and led to the creation of the Zagros Mountain Belt. The type and distribution of the deformation in the Zagros are controlled mainly by plate velocity, which is linked to the anticlockwise rotation of the Arabian plate around a pole in Syria, and the regional stratigraphy. The sedimentary cover and the underlying metamorphic basement decouple along an important detachment horizon, the Hormuz Salt Formation, and the uneven thickness and distribution of this salt plays a key role in determining the geometry of the deformation belt. Analysis of the distribution and geometry of the folds provides evidence for the southwestwards migration of the deformation front into the Arabian plate. The analyses are consistent with field evidence for serial folding, which indicates that each fold takes
c.
600 ka to develop fully, and with the model of a southwestward advancing deformation front driven by the processes of serial folding and footwall collapse.
Calcareous cyst-producing dinoflagellates: ecology and aspects of cyst preservation in a highly productive oceanic region
Authors: Wendler Ines , Zonneveld Karin A. F. , Willems Helmut 
Published: April 2008

Abstract

Absolute and relative abundances of calcareous dinoflagellate cyst species in surface sediment samples from the Arabian Sea are compared with environmental parameters of the upper 100 m of the water column to gain information on their largely unknown autecology. Ten species or morphotypes were encountered of which four occurred only as accessories. On the basis of the distribution patterns of the six more abundant species or morphotypes, the studied area is subdivided into three provinces, demonstrating a clear relationship to monsoon-controlled upper-ocean conditions. The two dominant species,
Thoracosphaera heimii
and
Orthopithonella granifera
, show opposite trends in distribution of both their absolute and relative abundances. In the NE Arabian Sea, low absolute and relative abundances of
T. heimii
are mainly attributed to enhanced dissolution of the small tests in this region, whereas elevated concentrations of
O. granifera
seem to be related to higher water temperatures and the influence of the Indus River.
Sphaerodinella albatrosiana
and
Calciodinellum operosum
are most abundant in the open ocean, associated with lower nutrient levels, relatively high temperatures and low seasonality. Spiny cysts (mainly represented by
Scrippsiella trochoidea
), in contrast, exhibit a more shelf-ward distribution and are most abundant in regions that are influenced by coastal upwelling, characterized by eutrophic and rather unstable conditions with seasonally lower temperatures and a shallow thermocline. A generally negative correlation of calcareous dinoflagellate cysts with primary productivity or high nutrient concentrations, as proposed by other workers, cannot be confirmed. Cyst accumulation rates off Somalia show that strong turbulence and high current speeds are unfavourable for calcareous dinoflagellates, suggesting that these organisms are more successful under rather stratified conditions.
Periodical breakdown of the Arabian Sea oxygen minimum zone caused by deep convective mixing
Authors: Reichart Gert Jan , Nortier Juriaan , Versteegh Gerard , Zachariasse Willem Jan 
Published: April 2008

Abstract

The northern Arabian Sea is at present characterized by a pronounced oxygen minimum zone (OMZ) with oxygen concentrations reaching values as low as 2 µM between 150 and 1250 m. This intense mid-water OMZ results from high annual organic particle fluxes and a moderate rate of thermocline ventilation. Sediment studies have shown that the intensity of the northern Arabian Sea OMZ has fluctuated on Milankovitch and sub-Milankovitch time scales, in conjunction with changes in either surface water productivity or thermocline ventilation. Here we evaluate the role of convective mixing in the periodical breakdown of the OMZ by reconstructing the density gradient for periods showing a well-ventilated water column. For this reason we reconstructed sea surface temperatures and salinities for the last 70 ka based on alkenone thermometry and δ
18
O analyses on planktic and benthic foraminifers. For the studied time span thermocline ventilation by intermediate water formation in the northern Arabian Sea is a viable mechanism to explain observed fluctuations in the intensity of the OMZ. We postulate that the necessary decrease in the vertical density gradient during well-ventilated periods resulted from intensified winter monsoonal winds in combination with effects caused by glacio-eustacy.
On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon
Authors: Staubwasser Michael , Dulski Peter 
Published: April 2008

Abstract

The evolution of the oxygen minimum zone within the permanent thermocline of the Arabian Sea (AS) during early and mid-Holocene time was reconstructed from a laminated sediment core taken from the Pakistani continental margin (316 m water depth). A trace metal proxy for water column ventilation (authigenic U) was extracted by principal component analysis from a large dataset of inorganic and total organic carbon (TOC) measurements. This proxy is compared with preservation of lamination and paired benthic-planktonic
14
C data. The latter record the Δ
14
C depth gradient in the AS and may provide a sensitive indicator for ventilation by enhanced surface convection. Laminated sediments were preserved between 10 and 7.5 ka bp on the Pakistani continental margin and accumulated authigenic U independently from TOC accumulation. The inferred reducing conditions in the AS thermoline are in agreement with high palaeoproductivity in the western AS upwelling region. Century-scale variability in northern AS surface hydrography (recorded as δ
18
O in planktonic foraminifera) is reflected in the accumulation of authigenic U on the Pakistani margin. The agreement of AS surface conditions, which generally reflect the South Asian monsoon (SAM), with ventilation of the OMZ confirms a dominant influence of the SAM and summer monsoon upwelling in particular on AS thermocline ventilation during early Holocene time. However, the preservation of laminated sediments off Pakistan and palaeoproductivity in the western AS disagree before 10 ka cal. bp, and between 7.5 and 5.5 cal. ka bp. Here, the absence of lamination indicates better ventilation of the thermocline, whereas palaeoproductivity in the upwelling region was high. This suggests that other factors may also have contributed in variable proportions to AS thermocline ventilation. At present, these factors include lateral advection of oxygenated Central Indian Water and ventilation by winter surface convection in the northern AS.
Present and past influence of the Iceland Plume on sedimentation
Authors: Jones Stephen M. , White Nicky , Clarke Benjamin J. , Rowley Eleanor , Gallagher Kerry 
Published: April 2008

Abstract
The Cenozoic development of the North Atlantic province has been dramatically influenced by the behaviour of the Iceland Plume, whose striking dominance is manifest by long-wavelength free-air gravity anomalies and by oceanic bathymetric anomalies. Here, we use these anomalies to estimate the amplitude and wavelength of present-day dynamic uplift associated with this plume. Maximum dynamic support in the North Atlantic is 1.5–2 km at Iceland itself. Most of Greenland is currently experiencing dynamic support of 0.5–1 km, whereas the NW European shelf is generally supported by <0.5 km. The proto-Iceland Plume had an equally dramatic effect on the Early Cenozoic palaeogeography of the North Atlantic margins, as we illustrate with a study of plume-related uplift, denudation and sedimentation on the continental shelf encompassing Britain and Ireland. We infer that during Paleocene time a hot subvertical sheet of asthenosphere welled up beneath an axis running from the Faroes through the Irish Sea towards Lundy, generating a welt of magmatic underplating of the crust which is known to exist beneath this axis. Transient and permanent uplift associated with this magmatic injection caused regional denudation, and consequently large amounts of clastic sediment have been shed into surrounding basins during Cenozoic time. Mass balance calculations indicate agreement between the volume of denuded material and the volume of Cenozoic sediments deposited offshore in the northern North Sea Basin and the Rockall Trough. The volume of material denuded from Britain and Ireland is probably insufficient to account for the sediment in the Faroe-Shetland Basin and an excess of sediment has been supplied to the Porcupine Basin. We emphasize the value of combining observations from both oceanic and continental realms to elucidate the evolution of the Iceland Plume through space and time.
Timing and mechanisms of North Atlantic Cenozoic uplift: evidence for mantle upwelling
Authors: Rohrman Max , van der Beek Peter A. , Van Der Hilst Rob D. , Reemst Paul 
Published: April 2008

Abstract

Postrift domal uplift patterns are a distinct feature of northern North Atlantic margins. On the basis of apatite fission-track data, offshore seismic stratigraphy, geomorphology, gravity and seismic tomography, we argue that southern Norway is characterized by predominantly Neogene domal uplift. The uplift is tectonically driven and estimated at around 1.5 km. Low flexural rigidity (
c
. 10
22
N m) and corresponding equivalent elastic thickness
T
e
(
c
. 15 km) values for the southern Norwegian lithosphere indicate that the lithosphere is relatively weak. Additionally, high temperature estimates derived from low-velocity mantle P- and S-wave seismic tomography below the dome suggest a thermal anomaly at depth. Therefore, the observed topography is most plausibly explained by mantle upwelling. This would supercede other previously proposed primary mechanisms such as eustasy, isostatic readjustment to glacial erosion, magmatic underplating and intraplate compression. Currently available data suggest similar processes for other uplifted regions such as Spitsbergen, northern Norway, the British Isles and parts of East Greenland.
Cenozoic inversion and uplift of southern Britain
Authors: Blundell Derek J. 
Published: April 2008

Abstract
Whereas significant exhumation of northern Britain took place during Paleocene time, probably as a consequence of uplift caused by a mantle plume, Paleogene basin inversion and uplift in southern Britain appears to be a consequence of Alpine tectonism. Recent publications demonstrate that inversion of Mesozoic basins across southern Britain was accompanied by subsidence of flanking basins in areas that had previously remained stable. Structures observed on seismic sections across the Weald Basin in SE England reveal that inversion occurred locally by north-directed reverse movements on pre-existing normal faults that cut down at a low angle deep into the basement. The overall effect of inversion of the Weald Basin, however, is a bulk deformation that produced a domal uplift, flanked by subsidence of the London and Hampshire-Dieppe basins. A 2D finite element thermomechanical model of continental lithosphere containing a region of reduced strength in the crust simulates Jurassic-Early Cretaceous extension to form the Weald Basin, followed by compression during the Tertiary to produce its inversion and the flanking basins. The timing of tectonic events across southern Britain correlates with times when Alpine stresses were transmitted into the foreland to the north sufficiently well to link them. Through most of Tertiary time, the landscape of southern England was of relatively low elevation and low-energy surface processes. However, late Neogene uplift, generally greater in the west, appears to have been part of a larger-scale uplift of land areas with hard rock at surface, which has no obvious tectonic explanation.