bluuebunny/crossref_metadata_2025_split huggingface dataset:
River flow, phytoplankton production and oxygen depletion in Chesapeake Bay
Authors: Malone Thomas C. 
Published: April 2008

Abstract
Oxygen depletion leading to a summer anoxia in subpycnocline waters of the mesohaline reach of Chesapeake Bay has been an annual event for at least five decades. It is generally assumed that the spatial and temporal extent of bottom water anoxia has increased in response to higher phytoplankton productivity due to anthropogenic nutrient loading. However, synoptic observations of environmental conditions (river flow, temperature, salinity, dissolved oxygen, and nutrients) and phytoplankton from 1984 to 1988 indicate that oxygen depletion is not related to phytoplankton productivity on seasonal to interannual scales. Rather, nutrient loading is linked to oxygen depletion and summer anoxia via the spring accumulation of phytoplankton biomass which is more than sufficient to fuel oxygen depletion. Thus, interannual variability in the magnitude of summer anoxia is primarily driven by climatic factors which govern vertical density stratification (mixing).
Hypoxic conditions in the northern Adriatic Sea: historical development and ecological significance
Authors: Justić Dubravko 
Published: April 2008

Abstract
In the northern Adriatic Sea the occurrence of anoxic events and related benthic mortalities has considerably increased in frequency during the past 15 years. This paper summarizes recent findings and presents new evidence on the causes and consequences of this phenomenon. Trends in the oxygen content 1911–1984, trends in the Secchi disk depth 1911–1982 and long-term changes in the communities of benthos and meroplankton are described. The relative importance of a set of factors which create favourable conditions for the development of hypoxia is discussed.
The role of sedimentary biogeochemistry in the formation of hypoxia in shallow coastal waters (Gulf of Trieste, northern Adriatic)
Authors: Faganeli Jadran , Pezdič Jož , Ogorelec Bojan , Herndl Gerhard J. , Dolenec Tadej 
Published: April 2008

Abstract

Pore water measurements of dissolved organic matter (DOM) and inorganic nutrients in the surficial sediment of the Gulf of Trieste showed the highest concentrations to be in late summer due to the higher microbial activity and restricted upward fluxes to the overlying water because of density stratification in the water column. The benthic fluxes of DOM, in terms of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP), and the inorganic nutrients NH
+
4
and PO
3−
4
, measured in parallel with sediment oxygen consumption (SOC) and production, showed in general a net influx indicating benthic consumption. Only strong DOC fluxes out of the sediment prevail in late summer. The bulk of DOC in pore water was found to be refractory, with a significant proportion consisting of a high molecular weight fraction. DON and DOP were more reactive in aerobic and anaerobic pathways of decomposition and not directly temperature dependent, probably because of a randomly fluctuating supply of degradable sedimentary organic matter and oxidants. In constructing the mass balance of C, N, and P it emerged that the sediment is primarily anoxic because the SOC is higher than benthic oxygen production. Oxygen must be therefore introducted to the sediment-water interface by physical factors and water column photosynthesis to prevent bottom layer hypoxia and anoxia in the period of strong density stratification in the water column. The role of particulate organic matter (POM) sedimentation is not of primary importance to SOC, and a fraction of summer POM is probably refractory and of allochtonous origin.
The Lower Oxford Clay: production and preservation of organic matter in the Callovian (Jurassic) of central England
Authors: Hudson J. D. , Martill David M. 
Published: April 2008

Abstract
The Lower Oxford Clay of the English Midlands is a thermally immature, organic-rich mudrock with a rich and well preserved invertebrate and vertebrate fauna. Biological productivity in the water column was high, as inferred from abundant cephalopods and the presence of large predatory marine reptiles and giant plankton-feeding fish. The sea floor was never anoxic but remained mostly dysoxic, resulting in a dysaerobic benthic biofacies. The ‘soupy’ substrate was inhabited by deposit-feeding bivalves, as well as gastropods and arthropods. The skeletons of large vertebrates at times provided ‘islands’ for the attachment of sessile benthos. Aragonite is well preserved, allowing isotopic palaeotemperature estimates of around 15°C for the bottom waters. Abundant pyrite formed within and beneath a shallow zone of bioturbation. At certain horizons early diagenetic concretions formed, preserving the original, pelletal, sediment texture, and three-dimensional fossils. Net sediment accumulation rates were extremely slow, around 1 to 15 mm of compacted sediment per 1000 years; sedimentation must have been episodic. Some diastems are represented by shell-beds, but others are cryptic. Nutrient supply is thought to be mainly from a well vegetated, swampy hinterland. Variations in bottom water oxygenation, sedimentation rate and substrate consistency can be inferred from the subtle facies variations within the Lower Oxford Clay, and controlled the accumulation of organic matter.
Estimating the petroleum expulsion behaviour of source rocks: a novel quantitative approach
Authors: Pepper Andrew S. 
Published: April 2008

Abstract
Estimates of potential volume, composition and phase of petroleum charges to traps are an integral part of petroleum prospect evaluation. Such estimates are directly sensitive to the timing and efficiency of petroleum expulsion from the source rock.
To date, geochemists have adopted two approaches to prediction of expulsion behaviour. The first is an heuristic approach based on a limited number of case studies. The second, a theoretical approach based on extrapolation of permeability concepts used in reservoir engineering, has popular appeal but may be of limited application to the pores of fine-grained petroleum source rocks, where the behaviour of interstitial water is rather different. Consequently the processes controlling expulsion are still a subject for debate.
It remains possible to challenge established relative permeability models, and to argue that the concepts of petroleum saturation and discrete-phase flow are either unimportant in the expulsion process, or else involve such low concentrations of petroleum within the pore volume that they can be considered negligible. Instead, kerogen itself may exert the prime control on expulsion behaviour by retaining (adsorbing) generated petroleum. If so, a simple quantitative model can be devised to predict expulsion efficiency of both oil and gas as a function of the initial kerogen composition (proportions of petroleum-generative versus petroleum-retentive kerogen).
Expulsion behaviour modelled in this way compares favourably with previously observed behaviour of a wide variety of source rocks. In particular, a case history presented demonstrates the capability of the model in predicting the differences in the expulsion behaviour of different coals, and the consequences in terms of composition of the expelled products.
Modelling 1D compaction-driven flow in sedimentary basins: a comparison of the Scotian Shelf, North Sea and Gulf Coast
Authors: Mudford B. S. , Gradstein F. M. , Katsube T. J. , Best M. E. 
Published: April 2008

Abstract

A one-dimensional model of fluid pressure evolution in a compacting sedimentary sequence has been developed and used to investigate some of the physical processes which occur during sediment deposition and burial. It is well known that the permeability assigned to low permeability lithologies, such as shales, has a large effect upon the fluid pressures predicted by basin models. Shales are common in many sedimentary basins, however, the behaviour of their permeability as a function of pressure is poorly constrained. This leads to considerable uncertainty in the predictions of many basin models. Recent measurements of the permeability of overpressured Jurassic shales from the Scotian Basin, off Nova Scotia have yielded values around 10
−21
m
2
(approximately 1 nanodarcy) for a range of effective pressures between 10 and 60 MPa. We have used these results in a number of single phase simulations of one dimensional, compaction-driven, fluid pressure evolution in the Scotian Basin, the North Sea, and the United States Gulf Coast. In all these areas chronostratigraphic data can be used to determine Neogene sedimentation rates, which strongly affect the present-day levels of overpressure. In the Scotian Basin predicted present-day pressures fall below those observed. This is in contrast to the North Sea and Gulf Coast where rapid Neogene sedimentation, together with Cenozoic sediments containing a high percentage of shale, causes predicted levels of compaction-driven overpressuring similar to those observed. The poor agreement between predicted and observed pressures in the Scotian Basin indicates that mechanisms other than compaction disequilibrium, for instance lateral fluid migration, mineral diagenesis, or ice loading, should be considered as causes of overpressuring.
Hydrocarbon maturation, migration and tectonic loading in the Western Alpine foreland thrust belt
Authors: Butler Robert W. H. 
Published: April 2008

Abstract

The Western Alpine foreland fold and thrust belt developed in late Miocene times through the Neogene foredeep basin, superimposed on an early Mesozoic and local Palaeogene shelf-basin system. The relative timing between subsidence, tectonic burial and thermal maturation is examined along a section line through the Annecy district of the French Alps. Available stratigraphic data are used to define burial-time paths, using suitable decompaction parameters. The tectonic burial history is determined from regional structural sections. These burial histories are used with a simple thermal model (geothermal gradients: 28°C km
−1
before thrusting, 30°C km
−1
for the post-orogenic period) to establish hypothetical time-temperature histories. Both the Lopatin method and peak temperature model of source rock maturation suggest that the Jura anticlines are undermature while the Subalpine chains are overmature. However, Subalpine maturation occurred during foredeep subsidence with overmaturation during thrust sheet loading. Large-scale lateral migration of hydrocarbons is required to explain the distribution of bitumen accumulations in the foreland basin offering the possibility of a series of structural and stratigraphic traps in the palaeo-foreland which are not associated with the thrust belt. A complex secondary and remigration history would be needed if liquid hydrocarbons are to have accumulated in traps associated with compressional structures in this part of the thrust belt.
Evolution of the Triassic Hawasina Basin, Central Oman Mountains
Authors: Bernoulli D. , Weissert H. , Blome C. D. 
Published: April 2008

Abstract

Sediments of Late Triassic age preserved in the upper Hawasina nappes of the Central Oman Mountains document the early sedimentary and oceanographic evolution of a segment of the Triassic seaway bordering the northern Gondwanian continental margin. Within the Zulla Formation of Glennie
et al.
four members can be distinguished.

4.
Halobia limestones (Lower to ?Upper Norian)

3.
Radiolarian cherts (Ladinian to Lower Norian)

2.
Sandstone-shale member

1.
Calcarenite-shale member

Changes in composition and abundance of turbiditic sediments in the Zulla Formation reflect environmental changes in the source areas, probably linked to sea-level fluctuations, whereas changes in the pelagic facies reflect basin-wide oceanographic fluctuations. Episodic low-oxygen conditions are indicated by laminated dolomites in the calcarenite-shale member. An increase in radiolarian abundance may record an increase in surface-water productivity possibly related to a sea-level rise and corresponding changes in the circulation pattern. A deepening of the CCD during the Early Norian is documented by the Halobia limestones. Similar facies types are encountered along the South-Tethyan seaway (Lagonegro-Pindos-Antalya-Pichakun). However, diachroneity of facies changes from radiolarite to limestone point to differences in the bathymetric and/or oceanographic evolution of the basins.
Triassic ammonoids from Jabal Safra and Wadi Alwa, Oman, and their significance
Authors: Tozer E. T. , Calon T. J. 
Published: April 2008

Abstract
Triassic ammonoids are recorded from Jabal Safra and Wadi Alwa, Oman. Most or all are from olistoliths. The ammonoids from Jabal Safra are of Early Triassic (Smithian and Spathian) age and are from metre-sized blocks in the Jurassic Guwayza Formation. Those from Wadi Alwa are from blocks ranging from metre- to more than decimetre-size and are Early Triassic (Smithian and Spathian), Middle Triassic (Anisian) and Late Triassic (Norian).
The Early and Middle Triassic ammonoids from both localities are in dense, highly fossiliferous, commonly red limestone where they occur to the exclusion of all other macrofossils. The facies is that of the Hallstatt Limestone which is known from many localities, all in the Tethys. The Late Triassic ammonoids are in a red argillaceous limestone like the Ammonitico Rosso, another characteristic facies in Tethys.
The occurrences at Jabal Safra are in the Hawasina allochthon. The olistoliths evidently came from the east, not from the platform to the west. Seamounts east of the main Hawasina depocentre seem the most likely source for all the Triassic blocks.
The Hawasina Nappes: stratigraphy, palaeogeography and structural evolution of a fragment of the south-Tethyan passive continental margin
Authors: Bechennec F. , Le Metour J. , Rabu D. , Bourdillon-de-Grissac Ch. , de Wever P. , Beurrier M. , Villey M. 
Published: April 2008

Abstract
Lithostratigraphic and biostratigraphic revision of the Hawasina Nappes in the eastern and central Oman Mountains, including the redefinition of the Hamrat Duru Group and the definition of the three new groups, the Al Aridh, Kawr and Umar Groups, has led to a new interpretation of the palaeogeographic and structural evolution of the south-Tethyan continental margin. Margin history began in the Late Permian with a phase of extension and rifting, accompanied by considerable magmatic activity, and led to the development of the Hamrat Duru Basin separating the Arabian Platform to the south from the Baid Platform to the north. In the Middle to Late Triassic renewed extension led to rifting, again accompanied by important magmatic activity, with the break-up of the Baid Platform, and the development of the Al Aridh Trough, the Misfah Horst and the Umar Basin. These Permian and Triassic tectonic units together constituted the Hawasina Basin. A third phase of extension during the Late Tithonian—Berriasian caused a general foundering of the continental margin. The development of the Hawasina Basin terminated in the Santonian, when compression initiated the first stage of obduction that closed the basin. Ongoing obduction, during the Campanian, led to thrusting of the Hawasina and the Samail ophiolite nappes onto the Arabian Platform by gravitational mechanisms.
Evolution of the Arabian continental margin in the Dibba Zone, Northern Oman Mountains
Authors: Robertson A. H. F. , Blome C. D. , Cooper D. W. J. , Kemp A. E. S. , Searle P. 
Published: April 2008

Abstract

The Dibba Zone, Northern Oman Mountains, documents the history of an oblique-rifted (transtensional) segment of the Arabian passive margin. Unmetamorphosed Palaeozoic, pre-rift (Ordovician to ?Devonian) successions, exposed in rifted continental slivers (Oman Exotics), record stable siliciclastic and carbonate platform deposition. Early Permian rifting of the Neo-Tethys initiated a carbonate platform in the Musandam Peninsula, while shallow marine bioclastic carbonate and quartzose sediments accumulated in the subsiding axial zones (Asfar Fm., Jebel Qamar Exotics). During final continental break-up, in the Late Triassic-Early Jurassic, a carbonate platform in the Musandam Peninsula was bordered by an escarpment-bypass margin with a turbiditic apron to the southeast (Zulla Fm.). Rifted continental slivers underwent mass-wasting, giving rise to detached blocks, or olistoliths that slid into organic-rich muds and turbiditic sands (Kub Melange). During the Jurassic, the subsiding Musandam carbonate platform was bordered by a steep slope (Sumeini Gp.) and redeposited carbonates accumulated on the continental rise (Guweyza Limestone Fm.). A switch to mainly siliceous accumulation, from Late Jurassic to Early Cretaceous (Tithonian-Berriasian Sid’r Fm.) ensued, mainly in response to tensional faulting, combined with eustatic sea level rise. Following re-establishment of the platform, carbonate sediment was again shed into the basin in the Early Cretaceous (Nayid Fm.). During Cenomanian time, tholeiitic and alkaline basalt extrusions formed seamounts that locally built-up into shallow water (99–92 Ma). Platform deposition halted in the Turonian (
c.
90 Ma), with flexural upwarp and erosion, followed by subsidence and slumping of shelf edge and upper slope sediments into a syntectonic foredeep, accumulating siliceous sediments and redeposited lithoclastic carbonates (Riyamah unit, Muti Fm.). Associated with emplacement of the Semail ophiolite, the passive margin successions were then imbricated by foreland-progagating thrusts (76–65 Ma), modified by the effects of possible oblique convergence, sidewall ramping and late-stage (dorsal) culmination collapse. Following erosion in the Campanian-Maastrichtian (Juweiza Fm.), platform deposition was reestablished in Palaeocene-early Oligocene. Renewed compression after mid-Eocene resulted in folding and reverse faulting of the Dibba Zone and thrust culmination of the Musandam shelf carbonates, driven by incipient continent-continent collision in the Zagros area.
Structural style and domains of the Northern Oman Mountains (Oman and United Arab Emirates)
Authors: Dunne L. A. , Manoogian P. R. , Pierini D. F. 
Published: April 2008

Abstract
A variation in the style of compressional deformation is observed in the northern Oman Mountains. This variation is expressed by the relationship between two major structural levels. The shallower structural level comprises Tertiary (Pabdeh Group), Late Cretaceous (Aruma Group), and Mesozoic (Hawasina and Sumeini Groups) clastics and carbonates that have been extensively deformed by closely spaced, folded duplexes and imbricate fans. In response to the same compressional events, the deformation in the deeper portion of the section is charcterized by more widely spaced, high-angle reverse faults that are interpreted to merge at depth into a decollement surface. This reverse fault system creates large hanging wall anticlines of Middle (Wasia Group) to Early Cretaceous (Thamama Group) and older platform carbonates. The major differences in the structural styles of the two levels are probably related to lithologic variations of the major tectono-stratigraphic units in response to the compression and the large-scale dynamics of the thrust belt as a whole.
Structural linkage is expressed between the two levels by the spacial correlation of the culmination axes of the two levels. The variation in this linkage between the two levels in a strike orientation defines several domains that are separated by major structural discontinuities. These domains are interpreted to reflect differences in the interaction between the two structural levels during several compressional events. They are postulated to have been ultimately created in response to variations in the dynamics of the thrust belt related to the emplacement of the Semail Ophiolite onto the Arabian continental margin during the Late Cretaceous and subsequent reactivation during the Tertiary.
Seismic interpretation of the structure and stratigraphy of the Strait of Hormuz
Authors: Michaelis P. L. , Pauken R. J. 
Published: April 2008

Abstract
Multifold seismic data from the Strait of Hormuz display stratigraphy and structure typical of that found on the Musandam Peninsula to the south. The sedimentary section seen on the seismic and tied to nearby hydrocarbon exploration wells ranges in age from Early Cretaceous to Recent. The section is subdivided into three seismic stratigraphic sequences by two prominent unconformities; the lowermost is at the top of the Lower Cretaceous and the upper one is at the base of the Miocene. The unconformities appear to have been formed as a result of two episodes of compression in the region; one during the late Cretaceous and the other during Oligocene-Miocene time. A Prominent ‘hummocky’ surface is present on many of the seismic lines and is interpreted as the result of erosion of piggy-back nappes consisting of allochthonous Musandam Limestone thrust westward on the Tethyan continental margin, in this region, during the Late Cretaceous. Two alternative interpretations of the ‘hummocky’ surface are that it is (a) composed of Miocene Makran conglomerate and (b) Upper Cretaceous Coloured Melange. These models and seismic data may be useful in future attempts at linking the stratigraphy and structure of the Musandam Peninsula to that in the Zagros Fold Belt to the north as more data become available.
Structural evolution of the Suneinah Foreland, Central Oman Mountains
Authors: Boote D. R. D. , Mou D. , Waite R. I. 
Published: April 2008

Abstract
In the early Mesozoic, the Suneinah Foreland of the central Oman Mountains lay on the flank of a north facing Tethyan rift margin. By the end of the Middle Cretaceous, this had evolved into a carbonate dominated passive margin. Following regional uplift and erosion during the Turonian, it was downwarped, faulted and buried by a deeper water shale facies. At the beginning of the Campanian, the earlier Tethyan sea floor and continental rise prism were rapidly telescoped across the margin, loading and downflexing the crust to form the narrow Suneinah Foredeep and peripheral bulge beyond. By the end of the Cretaceous this foredeep had been filled with marls and coarse detritus shed from the adjacent allochthon, and during the Early Tertiary a transgression swept across and blanketed much of the eroded nappe surface. In the Late Oligocene-Middle Miocene the Arabian plate began to separate from Africa and move northeast towards the Eurasian crustal collage. The Musandam promontory acted as a spur or indentor on this advancing plate, focussing compression and transmitting it back along deep basement fractures in the old Tethyan rift domain. Intense transpressional deformation inverted the entire margin to form the modern Oman Mountains and a new foredeep along its western flank. Reactivated Mesozoic fault blocks fringing the inversion orogen in the Suneinah area, deformed fairly rigidly, but the more plastic Late Cretaceous and Tertiary section above was squeezed into sometimes quite spectacular high amplitude folds. With the onset of sea floor spreading in the Red Sea/Gulf of Aden and northerly movement of the Arabian plate along the Dead Sea transform during the Late Miocene-Pleistocene, tectonic intensity waned in the Oman Mountains and much of its earlier sedimentary cover was stripped off.