bluuebunny/crossref_metadata_2025 huggingface dataset:
Spreading-rate parameters in ocean crust: analogue for ophiolite?
Authors: Flower M. F. J.
Published: April 2008

Geophysical and petrologic studies of ocean crust generated at different spreading rates reveal specific rate-dependent characteristics, e.g. relative thickness of eruptive and intrusive crustal layers, stability of axial magma reservoirs in time and space, and pressure-temperature regimes for magma fractionation. Petrogenetic interpretation of whole-rock and glass selvedge compositional variation in basalts from different spreading axes reflects these relations. Inverse correlation of plagioclase accumulation (separately from mafic phases) and increasing spreading rate is attributed to the predominance of polybaric fractionation system at slow-spreading ridge axes, in contrast to low pressure, isobaric, systems at fast-spreading axes. Evidence for ‘cryptocumulates’ (aphyric lavas showing mass-balance attributes of cumulates) at axes of intermediate spreading rate, appears to reflect a combination of slow-spreading character (e.g. plagioclase accumulation) with fast-spreading character (e.g. relatively ‘open’ magma supply). It is desirable to monitor these effects on low-
K
D
incompatible-elements variation, and to test the applicability of spreading-rate parameters on ophiolite lava associations of ‘oceanic’ affinity.
The structure of the oceanic upper mantle and lower crust as deduced from the northern section of the Oman ophiolite
Authors: Smewing J. D. , Christensen N. I. , Bartholomew I. D. , Browning P.
Published: April 2008

The lowermost 7 km of the Oman ophiolite consist of harzburgite, dunite and minor lherzolite of mantle origin overlain by layered gabbros and peridotites of the lower oceanic crust. Detailed structural measurements along three traverses through the ophiolite, complemented by olivine petrofabric determinations on oriented specimens from these traverses, reveal the following geometrical parameters of the spreading process:

(i)

The ultramafic rocks of the mantle sequence have all suffered deformation by simple shear at temperatures exceeding 950°C beneath a spreading ridge.

(ii)

The tectonite fabric which characterizes the mantle sequence passes upwards with no change in orientation or intensity into the layered gabbros and peridotites at the base of the crust.

(iii)

The sense of shear and type of slip system vary at random with depth, reinforcing petrological arguments that the Oman mantle sequence results from the juxtaposition of various mantle ‘packages’ equilibrated at different depths beneath the ridge.

(iv)

No unique kinematic model for the ophiolite can be formulated from the structural data of the three traverses; each traverse has a distinctive geometrical arrangement of the various structural elements relative to the reconstructed ridge directions. Dispersed mineral-layering planes indicate closing directions of magma chambers strung along the ridge.
Intraoceanic tectonism on the Gorringe Bank: observations by submersible
Authors: Auzende J. M. , Ceuleneer G. , Cornen G. , Juteau T. , Lagabrielle Y. , Lensch G. , Mevel C. , Nicolas A. , Prichard H. , Ribeiro A. , Ruellan E. , Vanney J. R.
Published: April 2008

The Gorringe Bank is a 200 km long structure, oriented NE-SW, located at the eastern end of the Azores-Gibraltar line, at the Europe-Africa boundary. It consists of two mounts, Mount Gettysburg at the SW (−25 m) and Mount Ormond at the NE (−100 m). Previous works have shown that it corresponds to a section in oceanic mantle and crust.

A recent expedition of the submersible SP 3000 CYANA (May-June 1981) has allowed us:

(i)

to confirm that Mount Gettysburg essentially consists of largely serpentinized peridotites. The study of two oriented samples collected
in situ
allows some inferences about the kinematics of emplacement for these ultramafics;

(ii)

to show that Mount Ormond is mostly composed of various gabbros corresponding to different stages of differentiation. All the samples are more or less recrystallized and display strong deformation from high-temperature mylonitization to low-temperature brecciation. Such a ubiquitous deformation is not common in ophiolite complexes and may be linked with the location of the bank at the Europe-Africa plate boundary;

(iii)

to observe two generations of undeformed dykes cutting the Ormond gabbros: the first one of dolerites genetically linked with the gabbros, the second of alkaline rocks, feeders of the more recent alkaline volcanics capping the mount.
Oxygen-isotope and geochemical characterization of hydrothermal alteration in ophiolite complexes and modern oceanic crust
Authors: Stakes D. S. , Taylor H. P. , Fisher R. L.
Published: April 2008

Stable isotopic, geochemical, and mineralogic variations in plutonic and hypabyssal rocks from oceanic crust (mainly from the Indian Ocean) and ophiolitic terranes (principally the Semail complex, Oman) are very similar. Several stages of seawater-oceanic crust interaction are recognized in these gabbros and diabases. Isotopic and chemical compositions of secondary mineral assemblages reflect changing temperatures and water-rock ratios, and record the effects of (i) pervasive seawater-hydrothermal circulation associated with the main stage of crustal formation at an oceanic spreading centre, (ii) subsequent alteration associated with off-axis volcanism (upper pillow-lava sequences), and (iii) progressively lower-temperature alteration associated with hydrothermal ‘ageing’ of the oceanic crust. Along the contact between the high-level, isotropic gabbro of the ophiolite, and the overlying sheeted dyke complex, repeated stoping of hydrothermally altered roof rocks into the magma chamber appears to be a ubiquitous process. Stoping is a maximum where the roof is intruded by large (off-axis) gabbro-diorite-plagiogranite bodies which may be 60% xenoliths. Abundant quartz-epidote-sulphide veins originate near these silicic intrusions and alter the overlying sheeted dyke complex. Diabase from the sheeted dyke complex in Oman, typically much more altered than dredged oceanic rocks of similar texture, exhibits the integrated effects of both the axis and off-axis hydrothermal systems.
Chemical and isotopic heterogeneities in orogenic and ophiolitic peridotites
Authors: Menzies M. A.
Published: April 2008

Rare-earth element (REE) and isotopic analysis of clinopyroxenes from orogenic and ophiolitic peridotites reveal a complex multi-stage origin resulting in chemical and isotopic heterogeneity in the upper mantle. The bulk of the pyroxenes plot within the ‘mantle array’ in a region characterized by mantle depleted in light REE for much of Earth’s history. Interestingly the majority of the pyroxenes separated from orogenic and ophiolitic peridotites have ɛ
Nd
and ɛ
Sr
= MORB. As a consequence of such isotopic (and REE) characteristics the mantle sections of ophiolites are not believed to be related to the overlying plutonic and volcanic rocks by a simple parent-daughter melting relationship.
Emplacement of ophiolitic rocks in forearc areas: Examples from central Japan and Izu-Mariana-Yap island arc system
Authors: Ogawa Y. , Naka J.
Published: April 2008

Recent results of ocean dredging of ophiolitic rocks in forearc areas in the west Pacific region are summarized and discussed together with the field data in the ophiolitic belts in the Setogawa and Mineoka forearc belts in central Japan. Metamorphism, deformation and sedimentation of the dismembered ophiolites in these regions indicate that they were emplaced at first in transform-fault areas or oceanic fracture zones, and they became the subsequent zones of initiation of subduction. Sometimes the mass of dismembered ophiolite was tectonically and sedimentarily mixed with island-arc materials and incorporated into the forearc belts during subsequent forearc tectonics.
Ophiolites: Figments of Oceanic Lithosphere?
Authors: Hall R.
Published: April 2008

To resolve the problem of what a particular ophiolite represents it is necessary to look both at the ophiolite and at the rocks surrounding it: those immediately adjacent to the ophiolite and those of the region. Detailed geochemical and petrological studies are unlikely, on their own, to contribute to an understanding of the tectonic setting of ophiolite formation, nor of emplacement. Evidence from ophiolite complexes of the Mesozoic Arabian margin is inconsistent with the view that they originated at the spreading centre of a major ocean, or in back-arc basins. Instead, it is argued that these ophiolites represent discontinuous ‘oceanic’ rifts formed
within
the Arabian passive margin. Metamorphism of rocks beneath the ophiolite is considered to mark extension of the margin associated with the formation of these oceanic rifts in the late Cretaceous. These ophiolites do not mark a major suture and the true suture lies to the north of the ophiolite zone.
A review of fine-grained sediment origins, characteristics, transport and deposition
Authors: Gorsline D. S.
Published: April 2008

Fine-grained sediments and sedimentary rocks make up as much as 75% of the present and past sedimentary records. River discharge is the largest single source of fine-grained material, followed by biological, volcanic and aeolian sources. The composition, texture and bulk properties that characterize different sediment facies are controlled primarily by climate, tectonics, sediment supply, oceanic dispersal systems and biological activity.

Fine sediments are transported into deep water by low-concentration nepheloid plumes, turbidity currents of a range of concentrations, flows and mass-movements. Mass-movement may be the major process delivering fine-grained sediment to the deep-sea floor over long time periods. Abyssal plains, the end of the passive margin transport system, are more affected by turbidity currents. Much bottom current reworking of sediments occurs at all depths in the ocean with results that may be very subtle. In shallower waters, balances between supply and dispersal may allow for the accumulation of mud belts on shelves and much fine sediments passes through such systems. Organic matter concentrations in fine sediment may be more a function of accumulation rates of organic versus terrigenous matter than local biological productivity.

Fine-grained sediments require the application of methodology and results of a broad range of scientific disciplines. Effective understanding of the fine record will require interaction between several sciences.
Sedimentation in the southern Cape Verde Basin: regional observations by long-range sidescan sonar
Authors: Kidd R. B. , Searle R. C.
Published: April 2008

A long-range sidescan sonar survey of the lower continental rise in the Cape Verde Basin has detected a dominant acoustic facies characterized by lineated backscattering patterns. These are interpreted as the sedimentary expression of turbidity current pathways across the area. Primary sediment transport directions can be interpreted from the backscattering patterns. Towards the north and west sediment distribution is increasingly affected by abyssal hill topography, either exposed oceanic basement features or hills draped with pelagic sediment.
Fine-grained turbidites and associated mass-flow deposits in the Ulleung (Tsushima) Back-arc Basin, East Sea (Sea of Japan)
Authors: Chough S. K.
Published: April 2008

Acoustically laminated Quaternary deposits (up to 800 m thick) dominated by turbidites overlie transparent hemipelagic sediments (Pliocene and older) in the Ulleung (Tsushima) Basin. The topmost layer in sediment cores is post-glacial hemipelagic sediment, about 2 m thick, underlain largely by a repetitive sequence of fine-grained, thinly- or un-laminated turbidites. Coarse-grained, graded and plane-laminated units rarely occur. Turbidites in the Ulleung Basin were accumulated at a rate of about 12 cm/10
3
years. The turbidites in the centre of the Ulleung Basin correspond to slump, slide and debris-flow deposits on the slope and base-of-slope environments. It suggests that the mass-flow processes occur successively from a broad, linear source on the prograding shelf break. Sediments originated from the adjoining margins of the Korean Peninsula and north western Honshu. Turbidites deposited during the major volcanic eruptions were derived from the Oki Spur and San-in coast, whereas those deposited between the volcanic events were mainly from the stable craton of the eastern margin of the Korean Peninsula.
Late Quaternary calcareous clayey-silty muds in the Obock Trough (Gulf of Aden): hemipelagites or fine-grained turbidites?
Authors: Faugères J.-C. , Cremer M. , Gonthier E. , Noel M. , Poutiers J.
Published: April 2008

Three cores have allowed us to survey Holocene deposits in a trough of the Gulf of Aden ridge. Within this particular environment (steep slopes, tectonic and volcanic activity) sediments are fine-grained, apparently homogeneous calcareous muds, rich in clay and planktonic microfossils: these features suggest that they are hemipelagic deposits. However, high sedimentation rates (20 to 50 cm/1000 yrs), lateral variation, and the occurrence of dynamic sedimentary structures (visible on X-radiographs and in thin sections), suggest that they have been emplaced mainly by gravity currents. These reworked hemipelagic materials are deposited on the shelf edge and on the trough slopes. This is confirmed by the sequential arrangement of sedimentary characteristics, as shown by analysis of microstructures, microfacies, carbonates, clay minerals, grain-size and other components.

Two types of sequences have been observed; the first we call the ‘type sequence’. This commonly overlies an erosional surface and comprises three divisions from bottom to the top:
Division I
(equivalent to Piper’s E1 division); mud with 8–10% sand fraction, rich in biogenic tests which occur as well-sorted horizontal laminae.

Division II
(equivalent to Piper’s E2 and E3 divisions); mud with low sand fraction (1%), very poor in biogenic material, no lamination, but horizontal orientation of silt-sized bioclasts.

Division III
(equivalent to Piper’s E2 and E3 divisions); mud with low sand fraction (1%), very poor in biogenic material, no lamination, but horizontal orientation of silt-sized bioclasts.

Division III
(equivalent to Piper’s F division); mud with low sandy fraction, poorly-sorted biogenic material, no dynamic sedimentary structures.

The second type of sequence is less common and comprises two divisions:

Division I’a
; very thin layer (millimetric), rich in terrigenous silt, which scours underlying sediment and shows horizontal, oblique and cross lamination.

Division I’b
; mud with low biogenic sand content, showing horizontal more or less clear and irregularly-distributed lamination.

These two sequences correspond to divisions E and F defined by Bouma (1962) and Piper (1978) in terrigenous turbidite sequences. The ‘type sequence’ is comparable to turbiditic sequences described in pelagic or hemipelagic material, deposited in similar morpho-tectonic environments (e.g. the eastern Mediterranean Sea or Mid Atlantic Ridge fracture zone).
Contourite facies of the Faro Drift, Gulf of Cadiz
Authors: Gonthier E. G. , Faugères J.-C. , Stow D. A. V.
Published: April 2008

The Faro Drift is an elongate sediment body (50 km long, 300 m thick) that parallels the northern margin of the Gulf of Cadiz south of Portugal. On the basis of location, morphology and seismic character of the drift together with bottom photographs, sediment distribution and the known regional oceanography, we can be certain that the Faro Drift was constructed by bottom currents related to the deep outflow of Mediterranean water. Detailed study of a closely-spaced suite of cores has therefore allowed characterization of the sediments into three contourite facies: sands and silts, mottled silts and muds, and homogeneous muds. The first is equivalent to the sandy contourites and the two others to the muddy contourites of earlier studies. These three facies are arranged in irregular vertical ‘sequences’ that reflect long-term variations in bottom current velocity. They are distinctly different from typical fine-grained turbidite and hemipelagite facies.
The role of canyons in late Quaternary deposition on the United States mid-Atlantic continental rise
Authors: McGregor B. A. , Nelsen T. A. , Stubblefield W. L. , Merrill G. F.
Published: April 2008

The continental margin in the US mid-Atlantic region is dissected by many downslope-trending canyons, extending from near or at the shelf-edge out onto the rise. Sediments from the shelf and slope are transported seaward through the canyon system to the rise. Sand-size material from the shelf is introduced by means of spillover into the canyons and onto the upper slope. A dendritic gully system dissecting the entire slope also provides pathways for slope sediments, mainly silts and clays, to be introduced into the canyons. Distinct grain-size distributions of the shelf sands which are interbedded or mixed with the fine-grained sediments of the slope and rise can be used as tracers for transport pathways on the continental margin. Canyon erosion on the rise also may provide a local source of sediment which must be considered. Sand-size-sediment distribution and DSRV Alvin observations show that erosion and deposition take place periodically in the mid-Atlantic canyons and on the rise seaward of New Jersey and Delaware.
Continental source area contributions to fine-grained sediments on the Oregon and Washington continental slope
Authors: Krissek L. A.
Published: April 2008

Chemical and quantitative mineral abundance data for the 2–20 μm fraction of 78 samples from the Oregon-Washington continental slope have been modelled using linear programming to estimate sediment contributions from continental source areas and evaluate the effects of mixing material derived from these sources on the formation of hemipelagic sediments. The mineral data distinguish three source areas, while the chemical data define only two. Results from the two data sets indicate similar patterns and magnitudes of source area influence on the continental margin.

The contributions are used to construct a sediment budget for 2–20 μm-sized sediments on the continental slope. The slope sediments contain approximately 47% Columbia River, 32% Klamath Mountain, and 21% California Coast Range material. Approximately 25–50% of the Columbia River, 29–46% of the Klamath Mountain, and 7–12% of the California Coast Range annual suspended sediment input is retained on the slope, indicating that the slope acts as a more effective trap of 2–20 μm material from proximal than distal source areas. This study also demonstrates the importance of multiple sediment sources and sediment mixing in the formation of hemipelagic sediments on a continental margin.
Studies of fine-grained sediment transport processes and products in the California Continental Borderland
Authors: Gorsline D. S. , Kolpack R. L. , Karl H. A. , Drake D. E. , Thornton S. E. , Schwalbach J. R. , Savrda C. E. , Fleischer P.
Published: April 2008

The California Continental Borderland contains a series of margin basins which are sediment traps at increasing distance from the principal terrigenous and biological sediment sources located in the northern coastal areas. Terrigenous sediments are contributed during a short winter season from small steep coastal drainages. Sand content can be as much as 30–40% of the total contributed load. Silts and clays are sorted out of the river input by coastal wave action and distributed offshore by the seasonal ocean circulation systems. Suspended sediment moves to the basin floors via nepheloid plumes that are generated in the well mixed coastal waters and move offshore with the currents as surface, mid-depth and bottom turbid plumes. During times of low suspensate content in the dry season, lateral transport is dominant. At times of high sediment input and higher concentrations of fine suspensates in the coastal waters, cascading to successively deeper pycnoclines becomes an important process. Resuspension of fine sediments from the outer shelf substrate and the axes of submarine canyons by internal waves and tidally generated currents also contributes to the load of the bottom nepheloid plumes.

Large semi-fixed seasonal eddies in the Borderland surface circulation hold the suspended load in the northern sector of the borderland for several days to weeks. Zooplankters have ample opportunity to filter out this material and aggregate it into faecal pellets which rapidly fall to the local basin floors. The removal is sufficiently effective so as to deposit a minimum of 60% of the continental contribution within the northern inner zone of the borderland. High sedimentation rates in these basins promote mass-movement and also decrease the already low oxygen contents of basin floor water as a result of oxidation of the organic fraction of the suspended load. Primary sedimentation structures are preserved in these anaerobic basin floor environments. Mass-movements initiate mud turbidity currents that move to the central basin floors. Mass-movements include creep and sliding of thin sheets from low angle slopes. These effects are amplified following exceptional floods at intervals of around 30 years.
Fine-grained sediments associated with fan lobes: Santa Paula Creek, California
Authors: Bourrouilh R. , Gorsline D. S.
Published: April 2008

Plio-Pleistocene slumps, debris-flow deposits, turbidites and hemipelagic sediments accumulated in the Ventura Basin to thicknesses of almost 2 km. The section exposed along Santa Paula Creek, California, contains at least six units of thick sandstones and conglomerates that represent fan lobes deposited at times of either tectonic pulses or minor climatic changes. Sections exposed in Adams Creek about 5 km west of the Santa Paula section suggest that the Santa Paula section was located on the fringes of these lobes. Gross sedimentation rates for the entire section are of the order of 1 m/1000 yrs. This is similar to the accumulation rates in the contemporary Santa Barbara Basin. The bulk of the intervening mudstones, siltstones and fine sandstones are thin-bedded (less than 10 cm thick) and represent interdistributary and basin plain facies. Mudstones are often laminated and the relatively sparse evidence of bioturbation suggests that the basin bottom waters were anoxic. Open connection over sills is evidenced by the discovery of the skeletal parts of a whale. The section illustrates the structures and associations of fine-grained sediments in a deep-water turbidite basin of high accumulation rate.
Hemipelagic chalks in a clastic submarine fan sequence: Miocene SW Turkey
Authors: Hayward A. B.
Published: April 2008

The Miocene Salir Formation in SW Turkey is a 500 m thick dominantly terrigenous clastic succession deposited by turbidity currents and other mass-flow mechanisms on a series of small submarine fans. During intervals of non-clastic deposition hemipelagic chalk horizons up to 60 mm thick accumulated.

The chalks comprise disseminated planktonic and small benthonic foraminifera dispersed in a micrite matrix with abundant poorly preserved coccolith plates and other nannoplankton fragments. Biogenic sand and silt-sized particles form up to 20% of the rock. Carbonate content ranges from 55% to 95%. The non-carbonate component comprises dispersed clay platelets and in some beds silt-sized particles. The chalks range from structureless homogeneous units, to beds which show a wide range of sedimentary structures which suggest reworking of the slowly deposited hemipelagic ooze by bottom currents of fluctuating velocity.

The lateral and vertical distribution of the hemipelagic chalks reflects the area on the submarine fan on which they were deposited. Areas away from the main locus of deposition, for example interchannel areas in proximal sequences, and inactive mid-fan areas are characterized by frequent and often thick chalk beds. In active mid-fan and inner-fan channel areas hemipelagic chalks are scarce or absent.
Source rock potential of Bahamian Trough carbonates
Authors: Crevello P. D. , Patton J. W. , Oesleby T. W. , Schlager W. , Droxler A.
Published: April 2008

The organic content of fine-grained carbonate muds deposited in the intraplatform basins and canyons of the Bahamas range between 0.1 and 2.6% total organic carbon (TOC). Geochemical analyses suggest some of these muds are a potential source for hydrocarbon. Interbedded with the carbonate muds are porous carbonate sands and gravels which can serve as local reservoirs or serve as conduits for hydrocarbons to migrate into carbonate slope and platform reservoir facies.

Ingeneral, periplatform oozes are lean (generally less than 0.5 to 1% TOC) whereas green muds, very likely the products of turbidity currents, have higher organic contents (0.5 to more than 2.5% TOC), but values of TOC vary considerably both within and between study areas. Tongue of the Ocean and Exuma Sound are less than 80 km apart but their average TOC values differ markedly, 1% and 0.33% respectively. Higher sedimentation rates in the Tongue of the Ocean are thought, in part, to be responsible for better preservation of organic matter.

In Tongue of the Ocean, cyclic variations in TOC are correlated with fluctuations of sea-level. High stands of sea-level are recorded by aragonite-rich muds with TOC on the average 0.5% higher than the calcitic periplatform oozes deposited during low stands of sea-level. Organic fractions of green muds have δ
13
C values (−16.4‰ to −13.9‰ vs PDB) which are similar to platform carbonates, whereas lighter δ
13
C values of periplatform oozes reflect mixing of organic material derived from platform and pelagic sources.

Rock-Eval analysis shows that the periplatform oozes are relatively rich in oxygen; this, along with their low organic contents, results in a poor source rock potential. The green muds range between type II (mixed gas and oil potential) and III (gas potential) source rocks, which, through favourable maturation, should generate hydrocarbons. Gas chromatographic analysis of organic matter evolved at relatively low temperatures (300°C) demonstrated that these immature sediments underwent vapourization and thermal cracking of relatively heat-sensitive or thermally labile material.
Sapropels and organic-rich variants in the Mediterranean: sequence development and classification
Authors: Anastasakis George C. , Stanley Daniel Jean
Published: April 2008

Sapropel is the term often applied in a general manner to dark, organic-rich layers of late Quaternary age in the eastern Mediterranean. The DSDP Leg 42A studies have more precisely defined sapropel layers as those containing more than 2.0% organic carbon by weight, and sapropelic layers as those that contain between 0.5 and 2.0% organic carbon. The present study further focuses on extensive vertical and lateral petrological variations of these and associated organic-rich layers. Herein the different sediment lithofacies that form both sapropel and sapropelic sequences in radiocarbon-dated cores distributed throughout the basin are defined. Organic carbon and carbonate carbon content and their ratio are useful criteria; some sedimentary structures and textures also help define sediment types.

The recognition of the dominant vertical successions of lithofacies that form typical sapropel and sapropelic sequences is important; these provide further evidence that favour marked episodic water mass stratification and associated stagnation. The lithofacies succession typically includes the following, from base up: greyish mud becoming darker upward and passing into a grey ooze which is separated from the overlying dark grey to black sapropel (or sapropelic) layer by a sharp contact; the latter layer, in turn, is topped by a thin grey ooze and an orange-brown oxidized layer. These sediments, poor in benthonic faunas, are interbedded within lighter, well-oxygenated open marine lithofacies.

Sapropel and sapropelic sequences comprise sediment types which are largely hemipelagic in origin (suspension settling through the water column); variations within such vertical successions may be directly related to palaeoceanographic events. Regional study, however, reveals numerous variations displayed by these two sequences, and thus further classification of the different organic-rich layers is needed. Lithofacies members are sometimes absent, or poorly developed, or repeated as a result of transport processes (mostly gravity-flow mechanisms) and/or specific oceanographic conditions affecting a depositional site. On the basis of the above, we identify episapropel and episapropelic sequences. These are defined as highly irregular sequences which include sediment types that are locally introduced by sediment gravity-flows, commonly mud-carrying turbidity currents. A more accurate assessment of the diverse organic-rich sequences in cores across the basin helps us to better understand the nature of short-term stagnation-oxygenation cycles that affected the eastern Mediterranean, and may also shed light on some black shales of open marine origin preserved in the rock record.
Bioturbation in deep-sea fine-grained sediments: influence of sediment texture, turbidite frequency and rates of environmental change
Authors: Wetzel A.
Published: April 2008

In the deep sea, burrowing infauna can adapt to variation in sediment texture within < 100–300 years. When there is continuous sedimentation, a continuous bioturbation process also takes place and the biogenic trace association found in the fossil record may be dominated by deeply penetrating burrows. A low-diversity trace fossil association (
Zoophycos
ichnofacies) is typical. On the other hand, when turbidites interrupt the continuous bioturbation process, a highly diverse trace fossil association is often found in the fossil state that also contains highly organized near-surface traces (
Nereites
ichnofacies). This biotope is usually controlled by the non-turbiditic sedimentation rate and the recurrence time of turbidites. Biogenic trace assemblages are mainly controlled by the nature of sedimentation and other environmental conditions rather than by water depth. Therefore, the widely accepted use of trace fossils as palaeobathymetric indicators in the deep sea may be restricted.
Submarine volcaniclastic rocks
Authors: Fisher Richard V.
Published: April 2008

The type, relative abundance and stratigraphical relationships of volcanic rocks that comprise island volcanoes are a function of (i) depth of extrusion beneath water, (ii) magma composition, and (iii) lava-water interactions. The water depth at which explosions can occur is called the pressure compensation level (PCL) and is variable. Explosive eruptions that occur above the PCL and below sealevel can give rise to abundant hydroclastic and pyroclastic debris. Below the PCL, clastic material cannot form explosively; it forms from lava by thermal shock. The volcaniclastic products are widely dispersed in basins adjacent to extrusion sources by three principal kinds of marine transport processes. These are slides, sediment gravity flows and suspension fallout. Volcaniclastic debris can be derived in subaqueous and subaerial-to-subaqueous environments (i) directly from eruptions, (ii) from remobilization of juvenile volcaniclastics, or (iii) from epiclastic material which initially develops above sealevel.

Sediment gravity flows (fluids driven by sediment motion) exhibit the phenomenon of
flow transformation
. This term is used here for the process by which (i) sediment gravity flow behaviour changes from turbulent to laminar, or vice versa, within the body of a flow, (ii) flows separate into laminar and turbulent parts by gravity, and (iii) flows separate by turbulent mixing with ambient fluid into turbulent and laminar parts. Dominant kinds of subaqueous volcaniclastic sediment gravity flows are debris flows, hot or cold pyroclastic flows and turbidites. Fine grained material can be thrown into suspension locally during flow transformations or underwater eruptions, but thin, regionally distributed subaqueous fallout tephra is mostly derived from siliceous Plinian eruptions.
Intersection of a marginal basin with a continent: structure and sediments of the Bay of Plenty, New Zealand
Authors: Lewis K. B. , Pantin H. M.
Published: April 2008

West of the Kermadec Trench and Arc, the Havre Trough is an actively spreading, oceanic marginal basin. Bathymetric, magnetic and seismic data indicate that it terminates against the lower slope off the Bay of Plenty, North Island, New Zealand. It is replaced on the adjacent upper slope, and on land, by the ensialic marginal basin known as the Taupo Volcanic Zone, which is part of the Hikurangi Plate Boundary System. The Taupo Volcanic Zone is offset about 50 km eastwards from the Havre Trough, by transform faults on the middle and lower slope. It is intersected on the upper slope, and its bounding faults are offset, by the northern end of the North Island Shear Belt.

The central part of the Bay of Plenty, which is crossed by the marginal basins, is characterized by a network of active faults, and by arc and back-arc volcanism. Sedimentation here is highly variable and the result of local balances between a continuous, rapid, terrigenous supply from rising, frontal ridge mountains to the E, and an intermittent supply of mainly rhyolitic, pyroclastic debris from the Taupo Volcanic Zone. This contrasts with the smooth, non-volcanic, eastern side of the bay where there is a sigmoidal, prograding shelf and slope of terrigenous silt on the northward plunging frontal ridge. It also contrasts with the western side of the bay where an extinct, Upper Miocene to Lower Pleistocene, arc-back-arc system has been eroded and is covered by a veneer of relict gravel and volcanogenic sand on the shelf, and buried by sandy mud on the slope.
The Hercynian Geanticline of Helez and the Late Palaeozoic history of the Levant
Authors: Gvirtzman Gdaliahu , Weissbrod Tuvia
Published: April 2008

The presence of a large structure of Late Palaeozoic age has been deduced from analysis of Palaeozoic columnar sections from the Levant countries, Israel, Jordan, Egypt, Saudi Arabia and Syria. This structure, which was uplifted and truncated in two phases, pre-Carboniferous and pre-Permian, is here termed the Geanticline of Helez and is related to Hercynian movements. Permian to Triassic sediments overlie the Precambrian basement at its crest, whereas on the flanks of the structure, Palaeozoic sediments from Cambrian to Carboniferous in age wedge out gradually towards the culmination. Similar Hercynian geanticlines are known from the Hazro-Singar area near the Syrian-Turkish border, from Ennedi- Al Awaynat near the Libyan-Egyptian-Sudanese border, as well as elsewhere in North Africa. The culmination of the structure, some 500 km in diameter, extends over a large area of Israel, Sinai and Jordan. The flanks of the geanticline, originally dome-shaped, could be identified only in three directions. The missing northwestern flank, dipping towards the southeastern corner of the Mediterranean Sea, was probably removed during rifting and spreading from Late Triassic to Late Cretaceous times and may be located today in the Antalya area or elsewhere in Turkey. Its original location is today occupied by the Mesozoic basaltic ocean-floor of the Neo-Tethys, which is assumed to underlie the Levantine Basin of the Mediterranean.
Structural history of the Antalya Complex in the ‘Isparta angle’, Southwest Turkey
Authors: Waldron J. W. F.
Published: April 2008

The Isparta angle is the north-pointing cusp where the arc of the Hellenides meets that of the Taurides in southwestern Turkey. The Antalya Complex is an assemblage of allochthonous deep- to shallow-water Mesozoic sedimentary rocks and ophiolite fragments present at the centre of the angle, surrounded by massive platform carbonate units, also of Mesozoic age.

Structural mapping of the folded and faulted Antalya Complex in the Eǧridir region at the centre of the Isparta angle indicates at least two major episodes of deformation. An earlier phase, probably latest Cretaceous in age, resulted in the thrusting of deep-water sediments over shelf-edge units which originally lay to the northeast. Subsequent southwest-vergent folding and thrusting in the Tertiary era locally reversed the earlier stacking order. Regularly imbricated thrust complexes were converted into chaotic mélange-like terrains.

The sedimentary cover was shortened by at least 72% as a cumulative result of these events. Palinspastic reconstruction of the Antalya Complex sedimentary basin indicates a wide original separation of the carbonate platform units on the east and west limbs of the Isparta angle, with at least one smaller platform between. These units were therefore probably separate carbonate banks, analogous to the present-day Bahama Banks.
Fossil and K-Ar data for the age of the Antalya complex, S W Turkey
Authors: Yılmaz Pınar O.
Published: April 2008

The Antalya Complex of southwestern Turkey contains, from west to east, the autochthonous Mesozoic-Cenozoic platform carbonates of the Bey Daǧları massif and three allochthonous units: the Kumluca complex of imbricated Mesozoic continentalmargin sedimentary rocks; units of the Late Cretaceous Alakır Çay ophiolite sequence and the Late Cretaceous Tekirova partial ophiolite sequence; and the Teke-Tahtalı Daǧ unit of Palaeozoic-Mesozoic sedimentary rocks originating on continental crust. The allochthonous units are overlain by conglomerates containing Maastrichtian clasts, ophiolitic olistostromes and locally by pelagic marls bearing Lower Miocene foraminifera. Samples from the Alakır Çay and Tekirova ophiolites have been isotopically dated. These ages cluster in the latest Cretaceous.

Fossils from pelagic sediments interbedded with pillowed basalt flows yielded ages of Late Triassic-Jurassic and Late Jurassic-Early Cretaceous, indicating intermittent volcanic activity through Mesozoic time. It is believed that the ophiolites of the Alakır Çay and Tekirova unit were formed in the same basin but were emplaced during separate events.
HP/LT metamorphism and the structure of the Alanya Massif, Southern Turkey: an allochthonous composite tectonic sheet
Authors: Okay A. I. , Özgül N.
Published: April 2008

The southern part of the Alanya Massif is made up of three superposed, relatively flat-lying, crystalline nappes (Alanya Nappes), which tectonically overlie the largely sedimentary lithologies of the Antalya Unit (= Antalya Complex). The predominantly Mesozoic continental margin type lithologies of the Antalya Unit outcrop beneath the Alanya Nappes in a large tectonic window.

The structurally lowest of the Alanya Nappes (Mahmutlar Nappe) consists of a heterogeneous series of shales, sandstones, dolomites, limestones and quartzites all metamorphosed under greenschist facies conditions. At least part of the sequence is Permian in age. The intermediate Nappe (Sugözü Nappe) is made up of garnet-micaschists which contain bands and lenses of eclogites and blueschist metabasites. Petrographic study has shown that rocks of the Sugözü Nappe have undergone initial HP/LT metamorphism followed by greenschist facies metamorphism. The greenschist overprint has destroyed most of the primary HP/LT mineral assemblages. The structurally highest of the Alanya Nappes (Yumrudaǧ Nappe) consists of a thick Permian carbonate sequence underlain by a relatively thin schist unit metamorphosed under lower greenschist facies conditions.

The absence of HP/LT metamorphism in the structurally lowest and highest of the Alanya Nappes, and the greenschist facies metamorphism which has affected all three nappes indicate that the initial HP/LT metamorphism of the Sugözü Nappe was succeeded by the tectonic stacking of the Alanya Nappes, greenschist facies metamorphism and deformation. In post-Maastrichtian times the Alanya Nappes, which were by then welded into one unit, were thrust over the sedimentary rocks of the Antalya Unit. The final thrusting of the Alanya Nappes and the underlying Antalya Unit over the Tauride carbonate platform occurred before the Middle Eocene.
The significance of Crete for the evolution of the Eastern Mediterranean
Authors: Hall Robert , Audley-Charles M. G. , Carter D. J.
Published: April 2008

The Hellenic Arc is a convergent zone extending between Greece and Turkey associated with northward subduction of the African plate under the Aegean. The isopic zones of Greece are usually shown to extend parallel to the arc through Crete, implying that the present convergent pattern is long established. However, although Crete is situated in the centre of the Hellenic fore-arc the elongation of the island parallel to the arc is not due to convergence but to late Cenozoic regional extension. Our work in Crete indicates that Tertiary facies belts were orientated approximately N-S and that initial convergence in the region was oblique to the present arc. The Upper Nappes of Crete record two major deformational phases: D1 produced N-S folds and D2 produced E-W folds, whereas the lowest unit on Crete, the Plattenkalk Series, records only the D2 phase.

We suggest that Crete records the Mesozoic extensional, and Tertiary compressional, history of the Apulian continental margin. Eocene E-W compression (D1) caused stacking of the Upper Nappes and HP/LT metamorphism. Oligocene N-S compression (D2) caused thrusting of the Upper Nappes onto the Plattenalk Series, and initiated the present convergent pattern which is unrelated to the earlier history of the region.
The significance of deformation associated with blueschist facies metamorphism on the Aegean island of Syros
Authors: Ridley John
Published: April 2008

A thorough examination of the syn-metamorphic minor structures in the blueschists of the Aegean island of Syros allows a determination of the kinetics and nature of the deformation. The deformation is essentially related to ductile thrusting at up to 45 km depth.

The change in fold geometry with orientation, and the presence of a locally developed mineral lineation at a high-angle to the fold axes give two independent determinations of the direction of thrusting. The direction, 130 ± 10°, suggests a link between the tectonism here and that in the Izmir-Ankara zone of mainland Turkey.

The nature of the small-scale asymmetrical folding indicates shortening of the pile parallel to this thrust displacement. This, together with the suggestion from the metamorphic textures of increasing pressure and temperature during deformation suggest that the deformation is related to burial and is compressional, and hence is presumably related to a major collision event.
Metamorphosed ophiolitic rocks from the Serbo-Macedonian Massif, near Lake Volvi, North-east Greece
Authors: Dixon J. E. , Dimitriadis S.
Published: April 2008

The paper describes preliminary results from the 120 sq km Volvi mafic complex within the Greek Serbo-Macedonian Massif. We conclude from published information and isotopic ages that the central and eastern part of the Massif (basement and Triassic/Jurassic cover) were affected by an amphibolite-facies regional metamorphic and deformational event in the Late Jurassic-Early Cretaceous. Delayed uplift from this same event may explain Tertiary ages from Kerdilion migmatites. The Volvi complex may thus be A: pre-Mesozoic ‘basement’, or B: an
in situ
Mesozoic rift complex
or
C: a Mesozoic collisional suture remnant. Field, microprobe and XRF data appear to fit model B best. Though deformed, the complex has recognisable 100% sheeted-dyke tracts and substantial areas of undeformed gabbro at lower structural levels. Deformation began before the end of magmatic activity: late sheets of pegmatic gabbro cut deformed dykes; late dykes cut sheared gabbro. Assemblages are of high-grade amphibolite facies and give garnet-hornblende temperatures of 750°C, significantly higher than inferred for staurolite-garnet schists outside the complex. Geochemically, the basaltic rocks show LIL enrichment and are intermediate between ‘alkalic’ and ‘above-subduction-zone’ in character. The complex may relate to Mesozoic rift-basins identified in E. Serbia, but is not thought to be a Palaeotethyan remnant.
Sapropelic layers in the NW Aegean Sea
Authors: Cramp A. , Collins M. B. , Wakefield S. J. , Banner F. T.
Published: April 2008

The present study examines sapropelic layers and associated sediments in the NW Aegean Sea, based upon the analysis of cores collected during the 7/78 cruise of the R.R.S.
Shackleton
.

Preliminary sedimentological analyses of some of the cores, including the use of X-ray techniques, did not at first detect either a sapropel or a sapropelic layer (defined as >2% and 0.5 – 2.0% organic carbon, respectively—Sigl
et al.
1978) in the sediment. Further investigations, including the analysis of organic carbon, on twelve of these cores have demonstrated the presence of horizons relatively rich in organic carbon. These horizons contain up to approximately 1.0% organic carbon and could be regarded as sapropelic layers. The horizons vary between 26 and 33 cm in thickness and are found at depths of 25 to 100 cm below the sediment-water interface, in cores which range from 101 to 240 cm in length.

Organic carbon profiles are presented, together with a discussion of the corresponding X-ray analysis and a preliminary note on the biogenic contributions to these sediments.
Neogene to Quaternary geodynamics of the area of the Ionian Sea and surrounding land masses
Authors: Fabricius Frank H.
Published: April 2008

Investigations in the north-eastern and central Ionian Sea document important palaeogeographic and palaeoceanographic changes since Neogene time. These findings support the model of shallow basinal evaporation during Messinian time. On this basis the rate of subsidence of the Ionian Sea is calculated for the last 6 Ma, at about 1 m per 1000 years for basinal settings and half this for marginal settings.

Elevated terraces corresponding to high glacio-eustatic stages in the Quaternary are frequent on Mediterranean coasts at heights up to more than 150 m above present sea level. Together with elevated marine deposits of Pliocene age, they testify to general coastal uplift. These epeirogenic tectonics are interpreted as compensation for the subsidence of Mediterranean basins.

In its present general form the Mediterranean Sea has existed since Pliocene time. The first indications of the foundering of the Ionian basin are Messinian evaporites. The formation of such huge basins is interpreted as the result of the transformation of former continental crust to ‘intermediate’ or ‘oceanized’ crust. The important fast vertical tectonics of the margins of ‘Mediterranean type’ differ considerably from those of the Atlantic or Pacific type.
Clastic facies models and facies analysis
Authors: Anderton R.
Published: April 2008

The term facies is used either descriptively, for a certain volume of sediment, or interpretatively for the inferred depositional environment of that sediment. Facies models are intellectual aids to the understanding of sedimentary environments and the origin of ancient sedimentary rocks. Many different models can be constructed to explain a given set of data, depending on which aspect of the facies requires the most illumination and on the types of techniques used in the analysis.

When dealing with ancient rocks, facies modelling is the last stage in the process of facies analysis which consists of the detailed description of exposed or cored sediments, their classification into objectively defined facies, the compilation of the characteristics of each facies, the deduction of the processes of deposition of each facies, the examination of the spatial relationships between facies and the recognition of facies associations, the interpretation of the overall depositional environment of the association and the detailed interpretation and modelling of individual facies. Short cuts can lead to fallacious interpretations. Reliable facies models cannot be produced without careful facies analysis. A facies model may be plausible, yet totally inapplicable to the facies from which it was supposedly derived.