bluuebunny/crossref_metadata_2025 huggingface dataset:
The provenance of sediments in the Barrême thrust-top basin, Haute-Provence, France
Authors: Evans Martin J. , Mange-Rajetzky Maria A.
Published: April 2008

This paper records the results of an integrated analysis of heavy minerals, sedimentary facies, palaeocurrents and structural data. The objective of the study was to evaluate the provenance of the sediments of the Barrême thrust-top basin. This basin contains a Late Eocene to Late Oligocene succession of shallow marine, alluvial and lacustrine sediments. Late Eocene marine transgression resulted in starvation of clastic supply to the basin hence the Calcaires Nummulitiques received only a limited influx of heavy minerals derived from local sedimentary sources, augmented by the first appearance of assemblages with andesitic affinities at
c.
42–41 Ma. Clastic members associated with the overlying Marnes Bleues record a significant diversification of provenance and sediment transport paths. Clastic detritus supplied to the shallow marine Grès de Ville were derived from Permo-Triassic sediments to the south. Conglomeratic submarine channels of the La Poste member mark the introduction of Alpine ophiolite-blueschist-derived minerals at
c.
37–35 Ma, eroded from the Embrun-Ubaya thrust complex to the NE. The deltaic St Lions member is dominated by volcaniclastic assemblages. Completing the marine fill, the shoreface Grès de Senez received detritus from the southerly Maures-Esterel crystalline massif.

The succeeding Oligocene continental sediments record an increasing supply of minerals from Alpine lithologies. The alluvial Molasse Rouge contains reworked sedimentary detritus, including material cannibalized from the underlying marine Tertiary, and first-cycle Alpine minerals. The succeeding lacustrine Série Saumon-Série Grise show the increasing diversity of Alpine suites. The youngest sediments, the fluvial Grès Verts, signal a major influx of Alpine-derived assemblages related to reactivation of the Embrun-Ubaye thrusts between
c.
28–27 and 25–24 Ma.
Evolution of the Devonian Hornelen Basin, west Norway: new constraints from petrological studies of metamorphic clasts
Authors: Cuthbert Simon J.
Published: April 2008

The Middle Devonian Hornelen Basin of western Norway is a continental fault-basin which formed during the late stages of the Caledonian orogeny, closely following the Late Silurian crustal thickening and high pressure metamophism responsible for the formation of eclogites in the adjacent Western Gneiss Region. Clasts from alluvial fan conglomerates which fringe the basin provide important constraints on the type of basin tectonism and the uplift history of this part of the orogen.

The clasts lack a petrographic linkage with the Western Gneiss Region (from which they are separated by a fault), but show a strong petrographic linkage with units of the allochthon (which lie unconformably below the basin fill). The clast sourceland had a similar metamorphic evolution to the allochthon, and both lack evidence for the high pressures recorded in the Western Gneiss Region. Both clasts and allochthon cooled through muscovite argon-retention temperatures about 40 Ma earlier than the Western Gneiss Region. Depth-time curves derived from isotopic and petrological results show that prior to basin initiation the Western Gneiss Region was uplifting faster than the clast source, but still lay at about 10 km depth during basin formation.

A tectonic scenario is suggested in which much of the uplift of the Western Gneiss Region took place before the deposition of the Hornelen Basin sediments, aided by crustal thinning along a major extensional mylonitic shear-zone. However, final exposure of this high-pressure metamorphic terrain only took place after the Hornelen Basin sediments were deposited, aided by uplift in the footwall of the basin sole fault.
Modern and ancient continental shelf anoxia: an overview
Authors: Tyson R. V. , Pearson T. H.
Published: April 2008

The characteristics of mid-latitude shelf seas are primarily controlled by seasonal cyclicity in wind-driven mixing. Seasonal dysoxic-anoxic conditions may occur in summer in salinity-stratified estuarine or pro-delta settings, or more extensively in those open shelf areas where a total depth of ≤60 m and the seasonal thermocline result in a bottom water layer ≤10 m thick. When bottom circulation is limited the oxygen stored in this layer may become periodically exhausted if climatic factors extend the stratified period to seven or more months, or if there is additional organic loading (via flagellate blooms and/or pollution). This causes widespread mortalities and a shift to soft-bodied, non-fossilizing benthic faunas. Our review supports seasonal dysoxia-anoxia as being the best model to account for the key characteristics of many ancient epeiric sea black shales. It would appear that the latter rarely represent true continuous anoxia except locally in more-confined deeper sub-basins.

We recommend that the following terms should be applied to environments, facies, or oxygenation levels: oxic (8.0–2.0 ml/l O
2
), dysoxic (2.0–0.2 ml/l), suboxic (0.2–0.0 ml/l) and anoxic (0.0 ml/l). The corresponding biofacies terms are: aerobic, dysaerobic, quasianaerobic (laminated, without macrofauna, but with in situ benthic microfauna) and anaerobic. Hypoxic and normoxic should only be used with regard to the physiological responses of living organisms.
Effects of hypoxia on continental shelf benthos: comparisons between the New York Bight and the Northern Gulf of Mexico
Authors: Boesch Donald F. , Rabalais Nancy N.
Published: April 2008

Depletion of dissolved oxygen to a point inducing mortality of bottom dwelling organisms (hypoxia) occurs in several continental shelf environments in Europe and North America and may have increased as a result of nutrient overenrichment due to human activities. Hypoxia in coastal waters results from plankton decomposition combined with a density stratification of the water column that hinders the oxygenation of bottom waters. Mass mortalities of benthic organisms have occurred as a result of extensive hypoxia on the inner continental shelves of the New York Bight and the northern Gulf of Mexico off Louisiana and Texas. Extensive hypoxia is rare in the New York Bight, and following catastrophic hypoxia in 1976, recovery of the benthic communities took more than two years. On the Louisiana-Texas shelf, large-scale hypoxia occurs virtually every year and recovery from this disturbance is rapid, because the community is kept in an early successional state by the annually recurring hypoxia.
A brief summary of hypoxia on the northern Gulf of Mexico continental shelf: 1985–1988
Authors: Rabalais Nancy N. , Turner R. Eugene , Wiseman William J. , Boesch Donald F.
Published: April 2008

Oxygen-deficient conditions occur from April to October on the inner to middle continental shelf of the northern Gulf of Mexico and may cover up to 9500 km
2
during mid-summer off the Louisiana coast. Hypoxic bottom waters are found in 5–60 m water depth, 5–60 km offshore and extend up to 20 m above the bottom. Salient forcing functions contributing to hypoxic water formation, maintenance and break-up are presented. Stratification is directly correlated with hypoxia in time and space, suggesting that reaeration of bottom waters is controlled by physical processes that are influenced by regional wind fields, river discharge and continental shelf scale currents. Phytoplankton biomass reaches the bottom waters in the hypoxic zones in large amounts (>5 µg/l), fueling water column and benthic respiration rates, but to a currently unknown degree. Increased nutrient loadings in the two major rivers and changes in the proportion of those nutrients essential to phytoplankton growth have probably changed both the phytoplankton community species composition and community production. It is not yet clear whether the extent and severity of hypoxia on the Louisiana continental shelf have changed as a result of these riverine water quality changes.
Recovery responses of two benthic assemblages following an acute hypoxic event on the Texas continental shelf, northwestern Gulf of Mexico
Authors: Harper Donald E. , McKinney Larry D. , Nance James M. , Salzer Robert R.
Published: April 2008

A hypoxic/anoxic event occurred in the northwestern Gulf of Mexico between May and July 1979. This event, associated with warm water temperatures, water column stratification and the decay of a phytoplankton bloom, led to the production of hydrogen sulphide which moved above the sediment—water interface and into the lower 2 metres of the water column. Regular monthly sampling at two sites (15 and 21 m depths) off Freeport, Texas, showed that abundances of benthic organisms declined precipitously during the event. Divers inspecting the study areas during the event observed ‘cottony’ mats, presumed to be sulphur bacteria colonies, covering large areas of bottom, and numerous bodies of dead benthic invertebrates.

Recovery of the two communities was markedly different. The assemblage in deeper water apparently stabilized within a year; the species of polychaetous annelids that were dominant before the event quickly returned to dominance and there was very little evidence of succession of different species during the recovery process. The shallower water assemblage, however, underwent a very different recovery process. Following the hypoxic event, polychaete dominance was greatly reduced, and there occurred successional dominance which involved several species in different taxa. Each of these species underwent a ‘bloom’ and constituted the numerical dominant for 1 to 3 months, and then declined and was replaced by another species’ ‘bloom’. This sequential dominance pattern persisted until about May 1981, two years after the hypoxic event, at which time polychates again became, and remained, numerically dominant.
Biofacial patterns in river-induced shelf anoxia
Authors: Van Der Zwaan G. J. , Jorissen F. J.
Published: April 2008

Three areas were studied to assess the effects of riverine input on the marine benthic ecosystem: the Adriatic Sea (with the Po river), the Orinoco-Paria shelf (with the Orinoco and Essequibo rivers) and the northern Gulf of Mexico (with the Mississippi and Rio Grande rivers). In all these areas, the interplay of river-discharge and subsequent transport by surface-water currents has resulted in the deposition of a zone with finegrained, organic-rich sediments parallel to the coast. The foraminiferal associations occupying these mud-belts indicate the occurrence of regular, widespread anoxic or dysoxic conditions at the sediment-water interface. Across the mud belt, benthic foraminifera display a very characteristic zonation, which is essentially the same in all areas studied. In the centre of the zone, low diversity and the presence of opportunistic species indicate a degree of stress. A model which describes the microhabitat occupation within these muddy zones is discussed in some detail. We conclude that the width of the shelf, together with the force of the long-shore current carrying the riverine products into the basin, are essential in determining the occurrence of dysoxic or anoxic conditions while the discharge volume of rivers is a subordinate factor. The chance of anoxia appears to be highest during periods of high sea level, leading to large shelf areas. A final conclusion is that benthic formainifera are excellent tools for determining the occurrence and degree of marine eutrophication induced by the input of polluted river waters.
River flow, phytoplankton production and oxygen depletion in Chesapeake Bay
Authors: Malone Thomas C.
Published: April 2008

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

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

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

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

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

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

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.
About this title
Authors: England W. A. , Fleet A. J.
Published: April 2008

Petroleum Migration
follows petroleum from its generation in source rocks through migration to the reservoir or the surface. The book is divided into 4 parts. Part 1 deals with both the generation of petroleum by the thermal breakdown of kerogen and the expulsion of the petroleum from the source rock. Part 2 considers secondary migration: the procesess which control petroleum behaviour during its movement through relatively permeable carrier beds from the mudrock sequences, which contain source intervals, to the reservoir in the structural culmination of the carrier bed or other trap. Part 3 contains case studies which show how understanding of generation, expulsion and secondary migration can be used to explain the distribution of oil and gas in a basin and therefore, to predict the nature of the petoleum in an undrilled prospect. Part 4 examines leakage from accumulations.
Evolution of the Triassic Hawasina Basin, Central Oman Mountains
Authors: Bernoulli D. , Weissert H. , Blome C. D.
Published: April 2008

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

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

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

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

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

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

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.
The evolution of the Oman Mountains Foreland Basin
Authors: Warburton J. , Burnhill T. J. , Graham R. H. , Isaac K. P.
Published: April 2008

The Late Cretaceous fill of the Oman Mountains foredeep is subdivided into four sub-sequences using seismic stratigraphic principles based on seismic, well and outcrop data. Sub-sequence FD-a (Late Coniacian to Early Santonian) was overriden by the Hawasina allochthon on the sea bed of the foredeep. FD-b (Early to Late Santonian) was deposited during thrusting and slices of foredeep sediment were tectonically accreted onto the allochthon during the final stages of thrusting. FD-c and FD-d (Late Santonian to Late Coniacian) were deposited after the emplacement of the allochthon into the foredeep. Subsidence curves for the foredeep area show that an emergent peripheral bulge bounded the cratonic side of the foredeep throughout the Late Cretaceous. There is no evidence that the forebulge migrated with time ahead of the advancing Hawasina thrust sheets. Instead the bulge remained in situ while the basin narrowed during thrusting. During the Maastrichtian, after infill of the foredeep, the Oman Mountains area subsided beneath sea level. Clastic supply from the drowned hinterland ceased and carbonate deposition followed. The main Oman Mountain building episode was during the Late Miocene when continent-continent collision occurred in the Zagros Mountains.
Structures associated with nappe emplacement and culmination collapse in the Central Oman Mountains
Authors: Coffield D. Q.
Published: April 2008

The Fanjah Saddle, in the Central Oman Mountains, forms a structural and topographic depression between two major culminations which expose parautochthonous rocks in windows through the overlying allochthon. Two styles of normal faulting are present in the culminations: high-angle faults which dip toward the saddle core and cut the plunging noses of the culminations, and low-angle faults around the culmination flanks which include bedding-parallel detachments, reactivated thrust planes and surge zones. This second set of faults verge down-dip radially away from the culmination flanks.

The high-angle normal faults are interpreted to be accommodation structures resulting from the differential uplift of the parautochthon between the culminations and the saddle. The low-angle normal faults are interpreted to be gravity-driven culmination collapse structures resulting from oversteepening of the culmination flanks.

Post-orogenic late Campanian to Maastrichtian sediments adjacent to the culminations indicate that the culminations were initialy emergent during this time, acting as a clastic source. These same sediments, and the underlying nappe pile, are folded by compression from displacements on the normal faults which implies culmination uplift was reactivated after the Maastrichtian, possibly during post-middle Eocene Zagros orogeny.
Maastrichtian to early Tertiary stratigraphy and palaeogeography of the Central and Northern Oman Mountains
Authors: Nolan S. C. , Skelton P. W. , Clissold B. P. , Smewing J. D.
Published: April 2008

Maastrichtian to Tertiary sedimentary rocks outcrop extensively around the periphery of the Oman Mountains. They form part of a geologically distinct suite of strata deposited after obduction of the Semail ophiolite and thrusting of the Hawasina and Sumeini imbricates onto the eastern edge of the Arabian plate. The lithostratigraphy of Maastrichtian and early Tertiary rocks of the central and northern Oman Mountains is revised and a number of new formations are erected. The proto-Oman Mountains were emergent in the early Maastrichtian and were subject to subaerial erosion and weathering. NW and W of the mountains, gradual subsidence followed during the Maastrichtian, allowing for formation of a transgressive, onlapping sequence represented by the Qahlah (fluviatile to shallow marine terrigenous clastics) and Simsima (shallow shelf carbonate) Formations. More rapid subsidence NE of the mountains produced fan delta and submarine debris flow/turbidite apron sequences comprising the Al Khawd and Thaqab Formations respectively. A low-angle unconformity separates Tertiary strata from older units. During the Palaeogene, basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins NW (Muthaymimah Formation) and NNE (Ruwaydah Formation) of the Oman Mountains. Elsewhere, shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the Palaeogene. The Palaeocene and early Eocene is represented by the Jafnayn Limestone Formation. This is succeeded and overlapped by a variety of later Eocene units. ENE and E of the mountains early Eocene regression is marked by restricted facies of the Rusayl Formation. Overlying the Rusayl Formation are shallow, open shelf limestones of the Seeb Formation which is rich in alveolinid and nummulitic foraminifera. On the Arabian side of the mountains the Rusayl Formation is not developed and the Jafnayn Formation is succeeded either by the Seeb Formation or fine-grained, faunally restricted limestones and marls of the Fahud Beds, which represent intra-shelf facies.
Cenozoic alluvial fan systems of interior Oman: palaeoenvironmental reconstruction based on discrimination of palaeochannels using remotely sensed data
Authors: Maizels J. , McBean C.
Published: April 2008

Sequences of exhumed, superimposed palaeochannel generations exposed on a Cenozoic alluvial fan in interior Oman are discriminated using a range of different remote sensing techniques. While lithological composition has been demonstrated to vary systematically with relative age of the deposit, ground radiometry has confirmed a relationship between spectral response and percentage cherts in the alluvial deposits. This relationship has allowed up to 14 palaeochannel generations to be discriminated from tonal contrasts on black and white air photographs, and up to five generations on black and white air photo mosaics and SIR-A imagery, and on Landsat MSS false colour imagery. Mapping of successive palaeochannel generations has highlighted the contrasts in channel extent, morphology and pattern during long-term evolution of the fan. These changes in palaeochannel characteristics are interpreted in terms of changes in humidity and continentality of the catchment, changes in eustatic level and in the watertable, and progressive expansion of the drainage network during the Cenozoic.
Structures in the Huqf-Haushi Uplift, east Central Oman
Authors: Ries A. C. , Shackleton R. M.
Published: April 2008

The extensive, very gentle Huqf-Haushi Uplift shows the effects of intraplate deformation from Infracambrian times onwards. The Uplift itself, apparently complementary to subsidence of the Ghaba Salt Basin to the west and the Masirah Trough to the east, began in the Infracambrian and continued intermittently until the Late Cretaceous. Local open folds are shown to be Palaeozoic, probably pre-Ordovician. The main deformation in the Uplift is by faulting. Two closely related sets, one NNE-SSW, the other N-S are essentially strike-slip in sense. The NNE-SSW faults, associated with half-domes and with folds making a small angle clockwise from the faults, are transpressional left-lateral strike-slip faults and the N-S set are probably also mainly left-lateral strike-slip faults. The array of faults is associated with the Masirah Fault, itself interpreted as a left-lateral transform fault. The faulting occurred in the Late Cretaceous. Subsequent deformation was slight.
The structure of Masirah Island, Oman
Authors: Moseley F.
Published: April 2008

The Masirah Ophiolite, extending over 1000 km
2
and now believed to be of Tithonian age, is cut by an extensive melange of uncertain age. The melange has been interpreted as representing a former transform fault zone. Later pre-Tertiary cross-cutting tectonic zones exist, within which ophiolite units have been tilted to the vertical and strongly folded. In one zone there are granites with continental affinities suggesting that Masirah was thrust against continental Arabia, probably late in the Cretaceous. Limestone of presumed early Tertiary age rests with strong unconformity upon the ophiolite, and is itself folded and faulted.
Tectonics of the Masirah Fault Zone and eastern Oman
Authors: Shackleton R. M. , Ries A. C.
Published: April 2008

Previously known but undescribed ophiolites on Ras Madrakah and Ras Jibsch and the ophiolite forming Masirah Island define an upthrust linear zone now separated from the Oman continental margin by the Masirah Fault. West of this, in the Batain coast, are the allochthonous Batain Melange and the Hawasina Complex of Mesozoic basinal deposits, mainly cherts. The Melange, like the Semail Melange with which it is correlated, contains ophiolite and Permian limestone exotics with Tethyan faunas. These allochthonous rocks are intensely deformed by WNW-vergent thrusts and folds. This Batain fold and thrust belt widens and becomes more complex northwards. It appears to have been continuous with the deformation south of the Semail Ophiolite, although now separated by the Jebel Ja’alan Uplift. The tectonics are intrepreted to be the result firstly of northward motion, along the Masirah Fault, of the Helmand Block of Afghanistan, away from the Oman continental coast, and during this motion, upthrust of the Masirah Ophiolite. Then, later in the Cretaceous, southwestward obduction of oceanic coast, including the Semail Ophiolite and the Masirah Ophiolite Zone, onto the Arabian continental plate. The oblique obduction across the NNE-trending Batain margin produced the Batain fold and thrust belt and reversed the strike-slip motion on the Masirah Fault.
Neogene tectonics and sedimentation of the SE Oman continental margin: results from ODP Leg 117
Authors: Prell Warren L. ,   shipboard party of ODP Leg 117
Published: April 2008

The primary objective of Leg 117 of the Ocean Drilling Program was to test ideas about the origin and variability of the Asian summer monsoon and its influence on depositional patterns and the oxygen minimum zone (OMZ) in the northwestern Indian Ocean. The western Arabian Sea currently is characterized by intense summer monsoonal upwelling that induces high primary productivity and distinctive planktonic assemblages. The planktonic indicators of upwelling conditions, as well as aeolian detritus from deserts and highlands of adjacent lands, are preserved in the sediments deposited on the Owen Ridge and the Oman Margin. A second objective was to resolve questions about the tectonic history of the Owen Ridge and Oman Margin.
Inter-relationship of Makran-Oman Mountains belts of convergence
Authors: Glennie K. W. , Hughes Clarke M. W. , Boeuf M. G. A. , Pilaar W. F. H. , Reinhardt B. M.
Published: April 2008

Mid Permian rifting and crustal separation along the northern margin of Arabia led to initiation of the Neo-Tethys ocean and deposition of sediments typified by the Hawasina. Subsequently, the Neo-Tethyan oceanic crust was consumed in a late Cretaceous subduction zone, generally easterly dipping in the Oman sector, and its sedimentary cover built up an accretion wedge (Hawasina; Coloured Melange) until the late Campanian, when the buoyant crust of the Arabian continental margin seemingly choked the subduction process.

Continuing convergence caused increased activity on, or the creation of, another subduction trench running between and extending south and east of the Central Iran-Lut and Sanandaj-Sirjan microcontinents (the proto-Makran trench). The resulting crustal relaxation on the earlier subduction site permitted uplift of the half-buried Oman continental margin; the overlying Hawasina and former hanging wall of Semail ophiolite then spread gravitationally further onto the Arabian shelf.

The Makran accretion wedge of Mesozoic Coloured Melange-type rocks and a thick pile of Maastrichtian to Eocene flysch underlies an ophiolitic hanging wall. Post-Eocene collisions between Arabia, Eurasia and intervening microcontinents resulted in: movement of the Naiband Fault in Iran and associated change in trend of the main subduction trench from NW-SE to E-W; thrusting of the Kahnu-Daragar and Alpine-type ophiolite over the SE Sanandaj-Sirjan Zone and rotation of part of its basement; westward thrusting of Musandam, and was associated with the Oligocene uplift of the Oman Mountains. The Zagros plicate folds began their main development in the Pliocene. Continent-continent collision has not occurred between Oman and the Makran.