bluuebunny/crossref_metadata_2025_split huggingface dataset:
Benthos communities in oxygen deficient shelf and upper slope areas of the Peruvian and Chilean Pacific coast, and changes caused by El Niño
Authors: Arntz Wolf E. , Tarazona Juan , Gallardo Victor A. , Flores Luis A. , Salzwedel Horst 
Published: April 2008

Abstract

Besides a well oxygenated shallow water area characterized by an extremely rich benthic life, most of the Peruvian and Chilean continental shelf and upper slope lies within an oxygen minimum zone (omz), the poor macrobenthic colonization of which is in striking contrast to the abundant pelagic life in the overlying waters. However, the eukaryotic benthos in this zone shares the seafloor with an important prokaryotic component of filamentous (‘sphagetti’) bacteria belonging mainly to the genus
Thioploca
. Under ‘normal’, non-Niño conditions, near-seafloor oxygen saturation values in this area rarely exceed 0.5 ml 1
−1
, and in some cases the bottoms are even anoxic. During strong El Niños, saturation periodically increases to >3.5 ml l
−1
, and higher oxygenation may persist for more than a year after the end of the event proper (which is characterized by increased water temperatures). In the shallow parts of the omz, the changes induced by El Niño cause drastic increases of macrobenthic density, biomass and diversity; immigration of benthos and fish species from (sub)tropical equatorial and oceanic areas; changes in trophic structure; and reduction of ‘spaghetti’ bacteria. In the case of the particularly strong 1982–83 El Niño, the communities of the shallower part of the omz had shifted back into their pre-Niño state about 13 months after the end of the warming event. In the deeper part of the omz, despite a similarly strong increase of oxygen saturation, a clearly positive development of macrobenthos during El Niño could not be observed. The reasons that may be responsible for this difference are discussed.
Late Permian anoxia in central East Greenland
Authors: Piasecki Stefan , Stemmerik Lars 
Published: April 2008

Abstract
The Upper Permian Foldvik Creek Group of the East Greenland Basin provides excellent possibilities for studying regional anoxia, because the basinal, anoxic facies of the Ravnefjeld Formation are well exposed throughout this 400 km long and more than 80 km wide basin.
The shales of the Ravnefjeld Formation are dominated by two units of laminated, organic-rich, calcareous mudshales. The absence of a burrowing or benthonic fauna, and the high content of organic matter and sulphur suggest these units were formed during a basin-wide anoxic episode. The character of the graded laminae indicates deposition from suspension. In contrast, thin bioturbated units appear to have been deposited during episodes of more oxygenated bottom waters. The TOC, HI and sulphur content are all lower in these bioturbated units.
The associated marine limestones of the Wegener Halvø Formation record a depositional history of transgressions and regressions that can be directly related to the laminated—bioturbated units of the Ravnefjeld Formation. The anoxic period can therefore be correlated with the maximum transgression of the basin, which induced rapid vertical growth of reefs. A stratified water column with anoxic bottom conditions and restricted circulation was apparently induced by the maximum flooding of the basin. The extensive vertical growth of carbonate platforms may have further restricted the circulation in the basin, producing a ‘silled basin’ effect.
Distribution, dynamics and palaeoecology of Kimmeridgian (Upper Jurassic) shelf anoxia in western Europe
Authors: Oschmann Wolfgang 
Published: April 2008

Abstract
Facies and related macrobenthic associations in the Kimmeridgian epeiric basin in Western Europe are arranged along an onshore-offshore gradient. It ranges from an intermediate-to-high-energy nearshore zone to a low-energy oxygen-controlled offshore environment.
Anoxia in the Kimmeridgian epeiric basin was not a permanent feature and cannot be described by the classical models which define aerobic, dysaerobic and anaerobic facies zones. These models have been proposed for deep (slope and basin) environments, in which the oxygen values at a certain depth remain in general constant. In contrast, anoxia in the Kimmeridgian is more dynamic and resembles modern anoxia occurring in eutrophic shelf and epeiric basins (e.g. the coastal areas of Mid-Atlantic Bight, North Sea and Baltic Sea) and exhibit remarkable annual oxygen fluctuations.

Therefore, in contrast to the classical models, a modified oxygen zonation for shelf environments is introduced, in order to explain the palaeoenvironment and dynamic alternation of Kimmeridgian anoxia. Both end members, the aerobic and the anaerobic environment, do occur as well. However, the short-term fluctuations prevent establishment of the dysaerobic zone. Instead, there is a seasonal anaerobic to anoxic environment, here defined as
poikiloaerobic zone
, which is colonized only by a few opportunists.
Integration of geological data into hydrodynamic analysis of hydrocarbon movement
Authors: Davis Richard W. 
Published: April 2008

Abstract
As a general rule, when hydrodynamic analysis is used in the course of exploration for petroleum, it is used as a means of testing individual geological structures or stratigraphical variations to see if they can serve as traps for hydrocarbons. Hydrodynamic analysis can be used to accomplish much more, especially in the search for subtle and unusual traps. It can be used to evaluate whole basins, not just restricted areas of one prospect. In addition, by utilizing all the geological information available, it is possible to use the analysis as a test of the consequences of the geological model upon petroleum migration as well as entrapment. It is possible to use the geological information to improve the accuracy of potentiometric surface data. It cannot be stressed too much that the value of the hydrodynamic evaluation is only as good as the accuracy and detail of the geological model.
Hydrocarbon generation, migration, alteration, entrapment and mixing in the Central and Northern North Sea
Authors: Barnard P. C. , Bastow M. A. 
Published: April 2008

Abstract
There is little doubt that sediments of Upper Jurassic to lowermost Lower Cretaceous age, particularly those of the Kimmeridge Clay Formation and its equivalents, are the source of the vast bulk of the oil in the Central and Northern North Sea. This is true both of oil in conventional Mesozoic plays and in Tertiary clastic reservoirs. The timing of oil generation and migration ranges from the Late Cretaceous through to the present.
The oil productivity of the Kimmeridge Clay Formation in the Central Graben, Moray Firth and South Viking, Graben areas of the North Sea is estimated to be in excess of 250 billion barrels, of which about 25% is accounted for in accumulations discovered to date. There is strong areal differentiation between oil trapped in Mesozoic reservoirs as opposed to Upper Cretaceous Chalk and Tertiary reservoirs.
This paper is particularly concerned with hydrocarbons in Tertiary reservoirs, which have a wide range of compositions and appear to have complex accumulation and degradation histories. Migration to Chalk and younger Tertiary reservoirs occurs often through thick shale sequences. The evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration, mixing and degradation is proposed.
Contrasting characteristics attributed to migration observed in petroleums reservoired in clastic and carbonate sequences in the Gulf of Mexico region
Authors: Thompson K. F. M. 
Published: April 2008

Abstract
Systematic differences among two subsets of petroleums selected geographically and by reservoir type were attributed to lithologically-characteristic migration phenomena. Most oils in offshore Louisiana Tertiary clastic reservoirs are deficient in light ends, evidently because of evaporative fractionation. Residual oils are enriched in cycloalkanes and aromatic hydrocarbons. Spuriously low evident maturities based upon concepts of paraffinicity are observed. Numerous oils are both fractionated and biodegraded. Mesozoic carbonate-sealed reservoirs at the margins of the basin generally contain pristine oils with intact light ends. However, many oils appear to be depleted in preferentially water soluble compounds: benzene, toluene, light cycloalkanes and phenanthrene, evidently due to aqueous fractionation during intraformational migration.
Petroleum seepage and post-accumulation migration
Authors: Clarke R. H. , Cleverly R. W. 
Published: April 2008

Abstract
The processes governing the loss of petroleum from traps and its migration to the surface are poorly understood. Leakage from traps does not necessarily result in surface seeps, nor are all occurrences of surface petroleum the result of present-day trap leakage. Three types of seep are recognized: unaltered gassy seeps, seeps affected by surface dispersal processes, and seeps altered by subsurface processes. Unaltered seeps form about 30% of the recorded population and are characterized by the presence of a free gas component. The buoyancy of the gas phase appears to drive most seeps to the surface. Non-associated oil seeps, often sharing their point of efflux with spring water, are altered by near-surface processes, especially the segregation of the oil and gas phases at the water table. Seeps altered by subsurface processes are frequently sour, containing free hydrogen sulphide, and are often associated with leakage pathway mineralisation. The geological context and characteristics of seepage deserve attention, leading to more realistic models for oilfield growth and decay, and to a better understanding of the environmental and mineralising effects of seepage.
A review of platform sedimentation in the Early and Late Permian of Oman, with particular reference to the Oman Mountains
Authors: Lee C. W. 
Published: April 2008

Abstract
The Permian of Oman consists of two distinct portions. An early Permian sequence of clastics and carbonates, that are conformable with the Carboniferous, and a late Permian sequence of carbonates that may rest with strong unconformity on the underlying sequence. Lower Permian clastic rocks crop out in S and E Central Oman and they also occur extensively in the subcrop of South and Central Oman. They show a glacial affinity and are correlated with the Dwyka glaciogenic deposits of Gondwanaland. Lower Permian marine carbonates are also found in the Haushi region of E Central Oman and from the Batain coast where they are known as the Lusaba Limestone and Qarari Limestone, respectively. The Upper Permian carbonates are found extensively throughout the Oman Mountains where they constitute the Bih, Hagil and Saiq Formations, the Khuff Formation in the subcrop and as blocks in the Batain Melange of NE Oman. Permian carbonates are also found as ‘exotics’ masses in the higher thrust slices (Haybi Complex) beneath the Semail Ophiolite. These carbonates were deposited on block faulted crust by a major transgression (enhanced by a post-glacial rise in sea level) caused by the onset of continental rifting. The rocks which characterize the autochthonous (parautochthonous) portion of Oman show affinities with Gondwanaland or the southern side of Tethys, while the faunas collected from the Batain coast area of NE Oman have affinities with Timor and possibly the northern side of Tethys in Early Permian times.
Chronostratigraphy of the Cretaceous carbonate shelf, southeastern Arabia
Authors: Scott R. W. 
Published: April 2008

Abstract
Carbonate deposits dominated the southeastern part of the Arabian Shelf from Berriasian to Santonian time, approximately 60 Ma. Deposition was terminated by the development of the Oman Foredeep in Coniacian-Santonian following the initial emplacement of the Hawasina and Semail nappes in the Turonian. The Lower and middle Cretaceous units in Arabia correlate with European reference sections and the current ages of the stage boundaries can be used to form a quantitative scale.
The Thamama-Kahmah Group to the Ilam-Halul Limestone consists of four major unconformity-bounded, shoaling-up depositional sequences that range in duration from 3 to 22 Ma. These sequences represent significant transgressive events on the shelf. The Rayda-Salil-Habshan sequence represents drowning and extensive incursion of the deep shelf landward; it lasted about 13 Ma. Small-scale, possibly climatic cycles comprise the Salil and Rayda formations. The contact with the overlying Lekhwair-Kharaib-Shuaiba sequence is normally sharp with no evidence of erosion. This sequence lasted about 18 Ma and consists of numerous shoaling-up cycles and local disconformities. The unconformity between the Shuaiba and Nahr Umr is a regional disconformity with evidence of local exposure. The hiatus spans most of the Late Aptian in the Oman Mountains, and in Abu Dhabi it spans the youngest part of the Late Aptian.
The Nahr Umr-Natih sequence in Oman spanned about 22 Ma and consists of four shoaling-up cycles. An important drowning event in the Oman Mountains occurred during the earliest Middle Cenomanian and is represented by the submarine hardground at the top of the ‘E’ member. The youngest sequence consists of the Laffan-Ilam formations in the Khatiyah Basin and lasted about 3 Ma. These depositional sequences correspond to transgressive events on other plates and represent eustatic sea level changes. The onlapping unconformities in the Oman Mountains represent times when the peripheral swell was active.
Restricted, intraplatform basins, in which organic-rich muds were deposited, developed four times. These units are best developed in the Bab-Khatiyah Basin and locally extended eastward into Oman. The Bab Member of the Shuaiba Formation is mainly Late Aptian. The Khatiyah Formation is coeval with the Early Cenomanian, lower ‘E’ member of the Natih in Oman. The ‘B’ member of the Natih is Late Cenomanian in age. The Laffan Formation is mainly Coniacian in age and represents the final restricted basin upon the southeastern Arabian Shelf.
Geochemical stratigraphy and porosity controls in Cretaceous carbonates near the Oman Mountains
Authors: Wagner P. D. 
Published: April 2008

Abstract

Geochemical stratigraphy is an investigative tool useful (a) for discerning the mode and spatial extent of diagenetic processes in carbonates, (b) for making diagenetic correlations between localities, and (c) for inferring palaeotopography. δ
13
C and δ
18
O stratigraphies of a five-well transect across central Oman indicate that most of the Cretaceous U. Kahmah-Natih interval stabilized under semiclosed, shallow burial, marine-water-like conditions. A ‘depositional’ δ
13
C isotopic signal is preserved. Local anoxic-suboxic events are also recognized, as well as depth-limited effects of early meteoric diagenesis. Isotopic stratigraphic relationships clearly indicate the presence of a local palaeotopographic high in central Oman during deposition of the Natih E member. Good diagenetic-stratigraphic correlations are shown between locations in central Oman and Sharjah, a distance of about 300 miles.

Porosity type and distribution within Cretaceous carbonates is related both to early diagenesis and to later structural events. Early cementation associated with marine hardgrounds and subaerial exposure surfaces occluded primary porosity in a limited depth-thickness sense. Later, all existing porosity types were regionally destroyed below the Hawasina thrust sheet in central Oman by thrusting-induced burial stylolitization and associated cementation. Foreland basin carbonates not involved in nappe emplacement retained excellent reservoir properties. Porosity in foreland basin wells consists of primary macro- and micro-porosity, and secondary selective-leach microporosity; selective leaching fluids moved along the subsurface ‘plumbing system’ of the primary porosity-permeability network. Small volumes of pore space were formed in low porosity subthrust carbonates by late aggressive (meteoric?) leaching along fractures and stylolites. Rock texture (facies) did not play a major role in defining the distribution of porosity in the immediate study area.
Mesozoic carbonate slope facies marking the Arabian platform margin in Oman: depositional history, morphology and palaeogeography
Authors: Watts K. F. 
Published: April 2008

Abstract
Carbonate slope sediments of the Sumeini Group mark the northeastern margin of the Arabian carbonate platform. Most slope sediments exposed in the Oman Mountains are of Jurassic or Cretaceous age. Older slope deposits at Jebel Sumeini indicate establishment of the Oman continental margin and subsidence accompanied by faulting in the Early Triassic (Dienerian), Middle Triassic (Ladinian) and possibly earlier (Permian).
Widespread Jurassic slope deposits indicate significant variations in declivity and facing direction of the continental margin slope in Oman. At Jebel Sumeini, a gullied bypass slope formed an apron along the NNW-trending slope, previously established as a Triassic block-faulted escarpment. In the Dibba Zone, a steep bypass slope formed along an inactive, NE-trending, transform lineament. Farther south near Wadi Qumayrah, a Middle to Late Jurassic base-of-slope apron containing megabreccias formed along a possible NNW-trending fault scarp. East of Wadi Qumayrah, an open-end embayment in the margin separated this area from coarse-grained slope apron deposits at Jebel Sham. Carbonate slope deposits at Saih Hatat indicate a complex history of subsidence culminating in Jurassic platform drowning and development of a long-lived submerged plateau bounded by gently inclined ramp slopes. This general geometry of the Oman passive continental margin was maintained through Jurassic and Early Cretaceous time.
Major changes in platform margin sedimentation occurred in the Late Cretaceous (Cenomanian to Coniacian), as recorded by the upper Mayhah Formation and overlying siliceous Qumayrah Formation. Thick Cenomanian(?) to Coniacian syn-orogenic megabreccias associated with pelagic sediments formed due to collapse of oversteepened slopes, possibly resulting from tectonic downbowing of the Oman margin toward a northward-dipping oceanic subduction zone. Later, the geometry of the passive continental margin may have had a significant effect on the emplacement of nappes and formation of the Sumeini culminations during the structural development of the Oman mountain belt.
Sedimentary evolution and palaeogeographical reconstruction of the Mesozoic continental rise in Oman: evidence from the Hamrat Duru Group
Authors: Cooper D. J. W. 
Published: April 2008

Abstract
The mainly Mesozoic Hamrat Duru Group represents deep-water, primarily continental rise Neo-Tethyan sediments derived from the Oman continental margin and later emplaced onto the Arabian carbonate platform during the Late Cretaceous obduction of the Semail ophiolite.
Sediment patterns reflect fluctuations in sea level relative to the platform, with carbonate input dominant during periods of platform stability. High and low sea-level stands, controlled by eustacy or tectonism, were accompanied by significant reductions of carbonate production and input into the basins. Raised calcite compensation depths associated with high sea levels resulted in the deposition of cherts whereas, during low stands, terrigenous clastics prograded across or by-passed the platform into the Hawasina basin.
The Hawasina basin was divided into two sedimentary basins separated by a submarine high. The shale-rich ‘Al Ayn sub-basin’ contained coarse-grained sediments that formed either small fans, or laterally coalescing sediment bodies that were fed by multi-source input of carbonate and terrigenous clastics. This is preserved as the Hamrat Duru Group of the northern and central Oman Mountains. The carbonate-rich ‘Duru sub-basin’ was fed exclusively from the south and large sediment bodies with sheet-like morphologies extended northwards parallel to the margin, outboard from the Al Ayn sub-basin, with thinning and fining trends to the NW and NE. Duru basin units are found in the central and southern Oman Mountains. Contrasting sedimentation patterns in the Al Ayn subbasin and the Duru sub-basin may reflect the influence of prevailing SE trade winds on the margin.
Permian to Cretaceous radiolarian biostratigraphic data from the Hawasina Complex, Oman Mountains
Authors: De Weaver P. , Bourdillon-de Grissac Ch. , Bechennec F. 
Published: April 2008

Abstract
The analysis of foraminifera and radiolaria in 3000 carbonate and 150 siliceous rock samples from the Oman Mountains results in revision of the existing stratigraphy and supports the definition of new units. In the Hawasina allochthonous unit the main results are as follows: (i) Permian bedded chert exists near the base of the sequence and is thus the first Permian bedded chert occurrence reported from the Tethyan region); (ii) an important volcanic event is dated as Triassic; (iii) bedded chert horizons are dated as Liassic; (iv) the thick turbiditic sequence has been divided into several units of Middle and Late Jurassic age. In the Samail ophiolite: (i) the ages of four tectonic episodes were established from the beginning of oceanic spreading (Albian—Early Cenomanian), to the obduction of the ophiolitic nappe (Campanian).
Subduction and obduction: two stages in the Eo-Alpine tectonometamorphic evolution of the Oman Mountains
Authors: Le Métour J. , Rabu D. , Tegyey M. , Béchennec F. , Beurrier M. , Villey M. 
Published: April 2008

Abstract
The platform unit of the Oman Mountains is composed of shelf sedimentary and volcanic rocks, ranging in age from late Proterozoic to late Turonian-Coniacian, that were deformed mainly during the polyphase Eo-Alpine tectogenesis.
In the late Turonian-Coniacian tangential shearing deformation with NE (oceanward) vergence occurred under HP/LT conditions of regional metamorphism. This tectonic phase was largely responsible for the structural and metamorphic zonation of the platform unit. A SW-NE gradient from external to internal zones has been recognized from the south flank of Jabal Akhdar, where fracture cleavage appears, to the eastern part of Saih Hatat, where schistose glaucophane ecologites are preserved. This tectonometamorphic event was related to partial subduction of the northeast corner of the Arabian platform beneath the neo-Tethyan oceanic lithosphere.
A later phase of higher-level shearing deformation with SW (continentward) vergence, during the Campanian, accompanied the thrusting of the Hawasina Nappes and the obduction of the Semail Ophiolite. These tectonic units were transported SSW respectively from the Permian-Cretaceous cover of the Arabian continental margin and from the oceanic floor of the Semail marginal basin that opened during the Albian-Cenomanian. Tectonic slicing and strike-slip faulting within the platform unit, on the northern margins of Jabal Akhdar and Saih Hatat, formed frontal and lateral ramps during the advance of the nappes onto the Arabian Platform.
During a third phase of deformation, probably during the Campanian-Maastrichtian, large-amplitude, long-wavelength, open, near-upright folding accompanied by poorly developed, subvertical, SSW-NNE fracture cleavage indicates moderate shortening during uplift perpendicular to the earlier structures.
The resulting Eo-Alpine foreland belt of the Oman Mountains was partly covered by marine carbonate deposits during the middle Maastrichtian to late Maastrichtian or early Palaeogene before being affected by Alpine tectonics during the Miocene.