bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial heterogeneity in an intertidal sedimentary environment and its macrobenthic community
Authors: Meadows Azra , Meadows Peter S. , McLaughlin Pat 
Published: April 2008

Abstract

The intertidal sedimentary environment is an extremely varied one in which marked differences in habitats and animal communities occur over very short distances. This study reports small scale heterogeneity of an intertidal macrobenthic community and its sedimentary environment in large sand waves in a bay in the Clyde Estuary, Scotland. Three 50 m transects ran across sand waves along a peak (P), along a trough (T) and across a peak and trough (P/T). Five sediment parameters [redox potential (Eh), organic carbon, particle size, shear strength and water table] and abundance of 14 macrobenthic species were measured in contiguous 1 m
2
quadrats along each transect. There were more positive and negative significant correlations along the P/T transect than the P and T transects. Thirteen correlations were common between pairs of transects. Multivariate cluster and principal component analyses were conducted on the data. The results of the two techniques were broadly in agreement. Distinct clusters of macrobenthic species and sediment parameters were identified. Some species clustered with sediment parameters. Others clustered only with species. These analyses may imply important causal relationships some of which are physically controlled and some of which are biologically controlled. Some clusters contained solely species that were deposit feeders. Clusters of quadrats along the P/T transect grouped quadrats on the peaks, in the troughs and on the slopes of the sand waves. These show that the peaks, troughs and slopes are significantly different sedimentary microenvironments. Clusters of quadrats along the P and along the T transect grouped quadrats that were spatially adjacent. These clusters indicate significant small scale spatial variability along the peaks and along the troughs of the sand waves.
The role of vegetation in determining patterns of the accretion of salt marsh sediment
Authors: Boorman L. A. , Garbutt A. , Barratt D. 
Published: April 2008

Abstract

Vegetation contributes to the stability of the salt marsh surface both through the soil reinforcement provided by the root mass and by the ability of the aerial component of plant growth to increase the rates of sediment deposition. Salt marsh vegetation is variable in height, thickness and also in stiffness. These characteristics can all modify the role of the vegetation in trapping sediment. As the height of the vegetation increases so also does Manning’s ‘
n
’, coefficient of roughness, but the taller vegetation is more easily flattened by moving water. It is not necessarily, therefore, more effective in slowing water flow and increasing sediment deposition. Shorter vegetation (mean height = 50 mm) has been shown to be quite effective, particularly if it is stiff enough to resist being flattened by the water at the rates of flow experienced.

The interplay of rates of sediment deposition is discussed with reference to data relating vegetation structure and pattern to local variations in accretion rates in salt marshes at Stiffkey, Norfolk, and Tollesbury, Essex, over a period of three years. At Tollesbury the mean annual rate of accretion was estimated to be 4.27 mm a
−1
but there was no correlation between the vegetation height (mean height = 148 mm) and changes in surface level. At Stiffkey however the annual rate of accretion was estimated to be 3.08 mm a
−1
, but there was a significant positive correlation between vegetation height (mean height = 75 mm) and accretion.

There is evidence that the relationship between effective vegetation height and the process of sediment accumulation is complex. Factors that can affect the relationship include the nature of the sediment, the height and composition of the vegetation and the microtopography and elevation of the marsh itself.
Basin modelling: how well have we done?
Authors: Waples D. W. 
Published: April 2008

Abstract
Model developers have been highly successful in building usable, useful, and reliable one-dimensional models, and in convincing explorationists to use them. Development of convenient, universal software played an instrumental role in the acceptance of 1-D modelling. The remaining weaknesses in technology and training, while serious, can be resolved through a few years of intensive work in certain specific areas. 2-D and 3-D fluid-flow modelling, in contrast, finds itself today largely in the position occupied by 1-D modelling more than a decade ago. The concept of fluid-flow modelling has not yet been adequately sold to explorationists, mainly because existing software is often inadequate to meet the real needs of exploration personnel. Development of appropriate software will probably have to precede widespread popularization of fluid-flow modelling. To improve existing software, two major areas must be addressed: (1) making models more comprehensive by including all relevant geologic phenomena, and (2) making software easier to use.
Geochemical modelling in an organic-rich source rock: the Bazhenov Formation
Authors: Hegre J. A. , Pittion J. L. , Herbin J. P. , Lopatin N. V. 
Published: April 2008

Abstract

Three wells located in the West Siberian basin have a high density of geochemical information (closely spaced samples) from the Upper Jurassic Bazhenov Formation. The nature of the organic matter is homogeneous and is classified as a marine type II (Hydrogen Indices up to 700 mg of HC g
−1
of TOC). The organic content is very high with TOC values up to 20 %. The source rock potential is also very good (S2 up to 100 kg HC tonne
−1
of rock). The maturity level in the wells varies from immature (T
max
around 435 °C) to near the end of the oil window (T
max
around 455 °C). This situation is somewhat puzzling since the source rock is at the same depth in the three wells (between 2800–2900 m). The IFP 1-D software GENEX, which is a maturity model that integrates subsidence, thermal reconstruction, hydrocarbon generation and expulsion, was used in order to:

(a)
test a geological hypothesis, which could reasonably explain this situation;

(b)
investigate the accuracy of the model’s ability to calibrate with geochemical data;

(c)
test the applicability of calibrating the expulsion saturation threshold from S1 and PI data. The very high S1 values with respect to the immaturity are also discussed. Model results indicate that different expulsion saturation thresholds are required in order to calibrate S1 and PI data. This is probably related to an inadequate definition of the formation’s porosity.
The proto-Andean margin of Gondwana: an introduction
Authors: Pankhurst R. J. , Rapela C. W. 
Published: April 2008

Abstract
A basic background is presented for the discussion of the Early Palaeozoic geology of western Argentina covered by this book. This includes the definition and terminology of orogenic cycles on this part of the Gondwana margin, represented by the Eastern Sierras Pampeanas. The Pampean orogeny (Early Cambrian) relates to an intense but short-lived period of terrane collision predating the rifting of the Precordillera terrane from Laurentia. The Famatinian cycle is predominantly represented by intense subductionrelated magmatism of Early-Middle Ordovician age, developed on the continental margin of Gondwana during the rifting and drifting of the Precordillera terrane. The Grenvillian basement of the latter is further exemplified by a new Rb-Sr whole-rock isochron age of 1021 ± 12 Ma for orthogneisses from the Western Sierras Pampeanas. A mid-Ordovician granite in this area (dated at 481 ± 6 Ma by U-Pb ion microprobe data) may be related to rifting while the Precordillera terrane was still attached to Laurentia. A divergence of opinion is pointed out between some authors in this book who favour mid-Ordovician collision of the Precordillera with Gondwana, and others who place it much latter, in Silurian or Devonian times.
Stratigraphical evidence supporting the rifting, drifting and collision of the Laurentian Precordillera terrane of western Argentina
Authors: Astini Ricardo A. 
Published: April 2008

AbstractMajor stratigraphical evidence points toward initial rifting of the Precordillera terrane of western Argentina during the Early Cambrian from the Ouachita embayment in southeastern Laurentia. A first fully developed rifting episode is suggested from subsidence analysis and the sedimentary record. Restricted graben-fill red-beds and evaporites in the eastern tectofacies, together with coarse arkose and quartz conglomerate preserved as blocks in the western tectofacies, are interpreted as deposits of the initial rift-related brittle extension. Stratigraphical similarities with localities surrounding the Ouachita embayment leads to a model in which the Precordillera was the southern part of the pre-Appalachian Laurentia margin and the conjugate margin of the Texas promontory, separated along the Alabama-Oklahoma transform and the Ouachita rift, respectively. Overstepping of syn-rift facies by a thick succession of Lower Cambrian to Lower Ordovician carbonates indicates completion of rift-to-drift transition and initiation of thermo-tectonic subsidence characteristic of continental terrace passive-margin development. Slope facies, marginal faunal belts and recently dated mafic rocks indicate the development of an ocean basin separating the Precordillera from Laurentia by the Mid-Cambrian. A 20–30 Ma period of drifting and isolation is indicated from faunal and sedimentological evidence. Subsidence-induced incipient drowning and abundant K-bentonites suggest the influence of subduction and the progressive approach of the terrane to western Gondwana. Continuous Mid- and Late Ordovician post-collisional extension brackets the collision, although no clear evidence of shortening has been detected in the preserved former sedimentary bank. Post-collisional extension is separated by >70 Ma from the initial rifting.
The stratigraphical record of the Argentine Precordillera and its plate-tectonic background
Authors: Keller Martin , Buggisch Werner , Lehnert Oliver 
Published: April 2008

Abstract
The stratigraphical record of the Argentine Precordillera from Early Cambrian to Late Devonian times reveals its plate-tectonic history from incipient rifting and the evolution of a marginal platform to the separation from Laurentia, its drift in higher latitudes and amalgamation with Gondwana. This pre-Carboniferous succession can be subdivided into four supersequences bounded by major unconformities and their main features are discussed with respect to plate-tectonic implications. The basal two supersequences which include the carbonate platform deposits are subdivided into 13 third-order sequences, each with a duration of 2–10 Ma. Supersequence A reflects intracratonic rifting, creating a graben system and forming a marginal plateau. In its in higher part a progradational carbonate complex covered the entire platform. Supersequence B shows the development of an aggradiational carbonate succession and the evolution of reef ecosystems comparable to those that developed around the margins of the Ouachita embayment. It also shows the demise of the carbonate platform by drowning. Deposits of Supersequence C reflect crustal extension and rifting, which led to the final separation of the Precordillera from mainland Laurentia. Supersequence D reveals the approach, and probably the accretion, of the Argentine Precordillera to Gondwana.
The geochemistry and provenance of Ordovician turbidites in the Argentine Puna
Authors: Bahlburg Heinrich 
Published: April 2008

AbstractPetrographical and major, trace and rare earth element data are combined in a provenance study of Early and Mid-Ordovician volcaniclastic turbidites in the Puna of NW Argentina. The tectonic setting of the depositional basin béhind a west-facing volcanic arc is well established from the literature, so that the new data may be used to test published geochemical discrimination schemes of tectonic setting of sedimentary rocks. However, there is a controversy whether volcanism took place in an island arc or a mature continentalmargin arc. The data show that the arc had a sediment source of average upper crustal composition dominated by silicic and intermediate magmatic rocks. Major elements document that subaerial weathering significantly influenced the detritus composition, whereas the HFS elements in particular retained the original source signal. The HFS and REE characteristics, as well as other parameters, compare favourably with those of Recent deep sea sands derived from continental arcs.
Laurentia-Gondwana collision: the origin of the Famatinian-Appalachian Orogenic Belt (a review)
Authors: Dalla Salda Luis H. , López de Luchi Mónica G. , Cingolani Carlos A. , Varela Ricardo 
Published: April 2008

AbstractEvidence from Cambrian to Devonian palaeogeography, the Laurentian provenance of Precordillera, and comparison of Lower Palaeozoic tectonic, metamorphic, and magmatic events, suggests a common collisional origin for the Taconian Appalachians and the Famatinian (Puna, Sierras Pampeanas, North Patagonian Massif) orogenic belt. Detached from Eastern Laurentia following collision, the Occidentalia terrane (west of the Famatinian orogenic belt) is partly covered by the Precordillera carbonate bank, which contains syn-collisional 460 Ma K-bentonites, related to the Puna and Famatinian arcs. In both the Appalachian and the Famatinian belts, a mostly Cambrian pre-collisional subduction regime developed at the western margin of Gondwana, following the opening of Iapetus. Laurentia-Gondwana collision produced deep thrusting and crustal melting. As in the Blue Ridge of the Appalachian Mountains, oceanic and mantle rocks, and slices of Grenvillian basement were emplaced along the western side of the Famatinian belt. This hypothesis gives continuity to a paired Taconian-Famatinian tectonic setting: a western Lower Palaeozoic platform overlying Grenvillian basement, and an eastern complex of a Lower-Middle Palaeozoic igneous-metamorphic belt with Proterozoic inliers.
Structural evolution of the Sierra de San Luis (Eastern Sierras Pampeanas, Argentina): implications for the Proto-Andean Margin of Gondwana
Authors: Von Gosen W. , Prozzi C. 
Published: April 2008

Abstract

The Western Basement Complex of the Sierra de San Luis underwent a complex deformational and metamorphic history of presumed Proterozoic age. The Phyllite Group and equivalents consist of a thick clastic sequence, whose time of deposition is compared with that of the Late Precambrian-Early Cambrian Puncoviscana Formation. This is intruded by early Famatinian magmatic arc tonalites to granodiorites, whereas an eastern basement unit was affected by early Famatinian mafic/ultramafic intrusions, metamorphism, and deformation. This Early Ordovician plutonism is related to east-directed subduction beneath the western margin of the Pampean terrane. Subsequent compression, plutonism, and variable-grade metamorphism are considered to be Mid- to Late Ordovician in age. Post-Famatinian
c.
WNW-ESE contraction under greenschist facies conditions led to folding of the cover sediments and uplift of different metamorphic units along mylonite zones which record an oblique sinistral component in the western part of the sierra. Based on a few radiometric data, this stage is interpreted as Devonian in age. It is possible that the compressive event was the result of the collision with the Precordillera (Cuyania) terrane in the west: oblique kinematic displacements, together with some evidence from outside the Sierra de San Luis, can be interpreted as the effect of the indenting terrane.
Age and duration of the Mississippi Valley-type mineralizing fluid flow event in the Viburnum Trend, southeast Missouri, USA, determined from palaeomagnetism
Authors: Symons D. T. A. , Lewchuk M. T. , Leach D. L. 
Published: April 2008

Abstract

The Viburnum Trend is a world-class Mississippi Valley-type (MVT) lead-zinc ore deposit in platform carbonates of the Upper Cambrian Bonneterre Dolomite in the midcontinent of the USA. Palaeomagnetic methods have been used to analyse 233 specimens from early octahedral (nine sites) and late-stage cubic (13 sites) galena ore from four mines along the
c.
70 km north-south length of the Trend. The characteristic remanence is carried by single to pseudo-single domain pyrrhotite and magnetite. This is the first MVT deposit in which pyrrhotite is shown to be a remanence carrier and present in galena crystals. The remanence directions define an Early Permian mean age of 273 ± 10 Ma for the ore-stage mineralization, a maximum duration for the mineralization event of 12 Ma, and a time difference of 5 Ma between the early octahedral and late cubic galena ore stages. The Early Permian age for the ore is consistent with models of ore genesis that invoke fluid flow from the Ouachita orogen during Ouachitan orogenesis.
Dating and duration of hot fluid flow events determined using AFTA® and vitrinite reflectance-based thermal history reconstruction
Authors: Duddy Ian R. , Green Paul F. , Hegarty Kerry A. , Bray Richard J. , O’Brien Geoffrey W. 
Published: April 2008

Abstract

Heating due to lateral introduction of hot fluids is becoming an increasingly recognized feature of the thermal histories of sedimentary basins. In some basins, heating by fluids may have an important effect on hydrocarbon source rock maturation history, so that quantification of the magnitude and timing of heating become essential elements in hydrocarbon prospectivity. In other cases, determining the time of fluid heating in a reservoir may provide a key constraint on hydrocarbon migration history. Examples are presented using AFTA apatite fission track analysis and vitrinite reflectance (VR) data to identify and quantify fluid heating in well sequences from several regions. In the West of Shetland region, in the vicinity of the Rona Ridge, non-linear palaeotemperature profiles defined by AFTA and VR results provide evidence of local heating shallow in the section. AFTA timing constraints suggest introduction of heated fluids produced by nearby Tertiary intrusive activity, although the time constraints are broad because of the low maximum palaeotemperatures involved (
R
0
max < 0.6%). In a well from Asia, transient maximum palaeotemperatures > 120°C resulted in
R
0
max > 0.6% in an Eocene section, with AFTA constraining the fluid flow event responsible for the early to mid Miocene (25 to 10 Ma). On the North West Shelf of Australia transient fluid flow associated with hydrocarbon leakage, and possibly charge, has been previously identified by a combination of AFTA, VR and fluid inclusion homogenization temperature (
T
h
) results. In the East Swan-2 well, a fracture inclusion in quartz from shallow Eocene sandstones gives a minimum
T
h
value of 88°C,
c.
40°C higher than the present temperature. AFTA and VR data show no direct evidence of
sustained
heating at such a temperature, and can only be reconciled if the duration of heating was
c.
20 000 years. The results are consistent with this event being associated with passage of a hot brine and hydrocarbon fluid (O’Brien and Woods, 1995). These case studies demonstrate that a combination of thermal history tools can be used to identify and quantify the thermal effect of fluid flow, potentially allowing much tighter constraints on hydrocarbon generation and migration histories.
Geology and timing of palaeohydrogeological events in the MacKenzie Mountains, Northwest Territories, Canada
Authors: Morris George A. , Nesbitt Bruce E. 
Published: April 2008

Abstract
Six distinct fluid events, which span a time frame from syndeposition (Cambrian-Devonian) to the last stages of the Laramide Orogeny (early Tertiary), have been identified in the MacKenzie Mountain range of the northern Canadian Rocky Mountains. The earliest event was a sedimentary exhalative event associated with the expulsion of brines onto the seafloor along extensional faults associated with a Silurian sedimentary basin. This was followed by a widespread diagenetic dolomitization event that affected the majority of carbonates from the early Devonian and older. The third event produced the stratigraphically restricted but regionally extensive Manetoe Facies dolomites, host to Mississippi Valley-type mineralization and reserves of natural gas. The formation of the Manetoe Facies dolomites is interpreted to have resulted from late diagenetic fluid flow in the late Devonian to early Carboniferous, possibly driven by the Antler Orogeny. The fourth fluid event, the vug-fill event, is constrained by low δD values to being early Cretaceous, or later in age. Features produced by this event are in turn cut by veins associated with the Laramide Orogeny (early Cretaceous to early Tertiary). The final recorded fluid event in this region is the calcite-barite event, interpreted to have been deposited by inflowing meteoric water. This study represents one of the most complete records of the fluid history of an area that has seen many palaeohydrogeological events. The combination of field and geochemical observations allows us to estimate the age, as well as the origin, of each event described.
Secondary oil migration: oil-rock contact volumes, flow behaviour and rates
Authors: Carruthers Dan , Ringrose Philip 
Published: April 2008

Abstract
Determining oil-rock contact volumes associated with secondary migration is a major challenge due to the heterogeneous nature of the sedimentary structures and petrophysical properties of carrier systems at multiple length scales. In this paper, we argue that migration occurs at, or near, the percolation threshold of the carrier system and show that the oil-rock contact volumes are a function of the heterogeneity of the threshold pressure field of the medium, as well as the orientation of the sedimentary fabric relative to the orientation of the net migration vector. The flow properties are intimately tied to the flow mechanism, which for secondary oil migration is likely to occur via capillary creep. An understanding of the distribution of threshold pressures within a sample volume will enable us to estimate the oil-rock contact volume during secondary oil migration, whether the volume considered is a core plug in size or an entire carrier sequence.
Dating Quaternary groundwater flow events: a review of available methods and their application
Authors: Metcalfe R. , Hooker P. J. , Darling W. G. , Milodowski A. E. 
Published: April 2008

Abstract
During the Quaternary (the last 1.6 Ma), episodic groundwater flow occurred to depths of several hundred metres. In many regions, climatic fluctuations induced episodes of rapid and slow groundwater flow. The former, termed here ‘groundwater flow events’, were characterized by extensive fresh-water recharge, and flushing of pre-existing water. It is important to identify and characterize such events to: (i) calibrate predictive models for future flow, thereby underpinning Performance Assessments for underground waste repositories; (ii) establish what proportion of global fresh-water resources was recharged during early Holocene or Pleistocene flow; and (iii) help interpret the timing and nature of Pleistocene climatic changes. To date, hydrogeochemical, mineralogical and petrological data have been interpreted in terms of post-glacial Holocene groundwater flow, or pre-Quaternary palaeofluid flow. Typically, Pleistocene recharge before the last glacial maximum has been unresolved. The effect of any given Quaternary climate change on the flow of pre-existing groundwaters is rarely identified. This paper considers the methods available to date these flow events, and finds that mineralogical evidence has been under-used to interpret Quaternary groundwater flow. Used together with hydrogeochemical data, mineralogical observations offer the best prospect of improving our understanding of Quaternary groundwater flow events.