Arabian Platform Research Articles

Oceanic crust generation in an island arc tectonic setting, SE Anatolian orogenic belt (Turkey)

A number of Late Cretaceous ophiolitic bodies are located between the metamorphic massifs of the southeast Anatolian orogenic system. One of them, the Göksun ophiolite (northern Kahramanmaraş), which crops out in a tectonic window bounded by the Malatya metamorphic units on both the north and south, is located in the EW-trending nappe zone of the southeast Anatolian orogenic belt between Göksun and Afşin (northern Kahramanmaraş). It consists of ultramafic–mafic cumulates, isotropic gabbro, a sheeted dyke complex, plagiogranite, volcanic rocks and associated volcanosedimentary units. The ophiolitic rocks and the tectonically overlying Malatya–Keban metamorphic units were intruded by syn-collisional granitoids (∼ 85 Ma). The volcanic units are characterized by a wide spectrum of rocks ranging in composition from basalt to rhyolite. The sheeted dykes consist of diabase and microdiorite, whereas the isotropic gabbros consist of gabbro, diorite and quartzdiorite. The magmatic rocks in the Göksun ophiolite are part of a co-magmatic differentiated series of subalkaline tholeiites. Selective enrichment of some LIL elements (Rb, Ba, K, Sr and Th) and depletion of the HFS elements (Nb, Ta, Ti, Zr) relative to N-MORB are the main features of the upper crustal rocks. The presence of negative anomalies for Ta, Nb, Ti, the ratios of selected trace elements (Nb/Th, Th/Yb, Ta/Yb) and normalized REE patterns all are indicative of a subduction-related environment. All the geochemical evidence both from the volcanic rocks and the deeper levels (sheeted dykes and isotropic gabbro) show that the Göksun ophiolite formed during the mature stage of a suprasubduction zone (SSZ) tectonic setting in the southern branch of the Neotethyan ocean between the Malatya–Keban platform to the north and the Arabian platform to the south during Late Cretaceous times. Geological, geochronological and petrological data on the Göksun ophiolite and the Baskil magmatic arc suggest that there were two subduction zones, the first one dipping beneath the Malatya–Keban platform, generating the Baskil magmatic arc and the second one further south within the ocean basin, generating the Göksun ophiolite in a suprasubduction zone environment.

The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin

According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indo-Arabian margin in the south. Igneous remnants of this opening are exposed in Oman within either the Hawasina nappes or the para-autochtonous Arabian platform exposed in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three groups have been distinguished. Group 1 is tholeiitic and characterized by low TiO2 and incompatible trace element contents, and a large range of εNdi values. Group 1 basalts are associated with distal sediments and plot near the boundary of or within the MORB field in the Pb–Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in εNdi–(206Pb/204Pb)i diagram. Group 2 basalts are alkaline and differ from Group 1 ones by their higher TiO2, La and Nb contents, and lower and more homogeneous εNdi values (+3 to +5). Group 2 volcanics are similar to alkali basalts from oceanic islands and share with Group 1 similar initial Pb ratios. Group 3 consists of tholeiitic and alkali basalts which are interbedded either with carbonate-platform sediments from the Saih Hatat window or with distal sediments from the Hawasina Nappes. This group differs from Groups 1 and 2 by its low to negative εNdi (+1.6 to −2). Group 1 likely derived from the mixing of depleted and enriched sources while Group 2 derived exclusively from an enriched source. There is no indication that continental crust was involved in the genesis of both Groups 1 and 2. In contrast, the low to negative εNdi values of Group 3 suggest that the magmas of this group were contaminated by the Arabian continental crust during their ascent. The geochemical features of the Middle Permian plume-related basalts suggest thus that the basement of the Hawasina basin was not genuine oceanic crust but either the thinned Arabian rifted continental margin or the continent–ocean transition zone of the Neo-Tethys.

Regional seismic wave propagation (Lg and Sn) and Pn attenuation in the Arabian Plate and surrounding regions

Continuous recordings of 17 broadband and short-period digital seismic stations from a newly established seismological network in Saudi Arabia, along with digital recordings from the broadband stations of the GSN, MEDNET, GEOFON, a temporary array in Saudi Arabia, and temporary short period stations in Oman, were analysed to study the lithospheric structure of the Arabian Plate and surrounding regions. The Arabian Plate is surrounded by a variety of types of plate boundaries: continental collision (Zagros Belt and Bitlis Suture), continental transform (Dead Sea fault system), young seafloor spreading (Red Sea and the Gulf of Aden) and oceanic transform (Owen fracture zone). Also, there are many intraplate Cenozoic processes such as volcanic eruptions, faulting and folding that are taking place. We used this massive waveform database of more than 6200 regional seismograms to map zones of blockage, inefficient and efficient propagation of the Lg and Sn phases in the Middle East and East Africa. We observed Lg blockage across the Bitlis Suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. This is probably due to a major lateral change in the Lg crustal waveguide. We also observed inefficient Lg propagation along the Oman mountains. Blockage and inefficient Sn propagation is observed along and for a considerable distance to the east of the Dead Sea fault system and in the northern portion of the Arabian Plate (south of the Bitlis Suture). These mapped zones of high Sn attenuation, moreover, closely coincide with extensive Neogene and Quaternary volcanic activity. We have also carefully mapped the boundaries of the Sn blockage within the Turkish and Iranian plateaus. Furthermore, we observed Sn blockage across the Owen fracture zone and across some segments of the Red Sea. These regions of high Sn attenuation most probably have anomalously hot and possibly thin lithospheric mantle (i.e. mantle lid). A surprising result is the efficient propagation of Sn across a segment of the Red Sea, an indication that active seafloor spreading is not continuous along the axis of the Red Sea. We also investigated the attenuation of Pn phase (QPn) for 1–2 Hz along the Red Sea, the Dead Sea fault system, within the Arabian Shield and in the Arabian Platform. Consistent with the Sn attenuation, we observed low QPn values of 22 and 15 along the western coast of the Arabian Plate and along the Dead Sea fault system, respectively, for a frequency of 1.5 Hz. Higher QPn values of the order of 400 were observed within the Arabian Shield and Platform for the same frequency. Our results based on Sn and Pn observations along the western and northern portions of the Arabian Plate imply the presence of a major anomalously hot and thinned lithosphere in these regions that may be caused by the extensive upper mantle anomaly that appears to span most of East Africa and western Arabia.

The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin

According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indo-Arabian margin in the south. Igneous remnants of this opening are exposed in Oman within either the Hawasina nappes or the para-autochtonous Arabian platform exposed in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three groups have been distinguished. Group 1 is tholeiitic and characterized by low TiO 2 and incompatible trace element contents, and a large range of εNd i values. Group 1 basalts are associated with distal sediments and plot near the boundary of or within the MORB field in the Pb–Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in εNd i–( 206Pb/ 204Pb) i diagram. Group 2 basalts are alkaline and differ from Group 1 ones by their higher TiO 2, La and Nb contents, and lower and more homogeneous εNd i values (+3 to +5). Group 2 volcanics are similar to alkali basalts from oceanic islands and share with Group 1 similar initial Pb ratios. Group 3 consists of tholeiitic and alkali basalts which are interbedded either with carbonate-platform sediments from the Saih Hatat window or with distal sediments from the Hawasina Nappes. This group differs from Groups 1 and 2 by its low to negative εNd i (+1.6 to −2). Group 1 likely derived from the mixing of depleted and enriched sources while Group 2 derived exclusively from an enriched source. There is no indication that continental crust was involved in the genesis of both Groups 1 and 2. In contrast, the low to negative εNd i values of Group 3 suggest that the magmas of this group were contaminated by the Arabian continental crust during their ascent. The geochemical features of the Middle Permian plume-related basalts suggest thus that the basement of the Hawasina basin was not genuine oceanic crust but either the thinned Arabian rifted continental margin or the continent–ocean transition zone of the Neo-Tethys.

Stratigraphic architecture of the northern Oman continental margin - Mesozoic Hamrat Duru Group, Hawasina complex, Oman

ABSTRACT The Triassic to Late Cretaceous deep-marine sediments of the Hamrat Duru Group, Oman Mountains, represent a subunit of the Hawasina nappe-complex which was deposited in a deep marine basin. During the Late Cretaceous SSW-directed obduction of the Semail Ophiolite, the Hawasina complex was emplaced onto the autochthonous cover of the Arabian basement, while the original configuration of the basin was destroyed. New lithostratigraphic results and high-resolution radiolarian and conodont biostratigraphy lead to a revised stratigraphic scheme of the Hamrat Duru Group which conforms with the standard stratigraphical nomenclature. The Hamrat Duru Group is divided into six formations: (1) The Early Triassic (Olenekian) to Late Triassic (Upper Norian) Zulla Formation (Limestone and Shale Member, Sandstone and Shale Member, Radiolarian Chert Member and Halobia Limestone Member); (2) The Late Triassic (late Norian to Rhaetian) Al Ayn Formation; (3) The Early Jurassic (late Pliensbachian) to Middle Jurassic (early Callovian) Guwayza Formation (Tawi Sadh Member and Oolitic Limestone Member); (4) Middle Jurassic (Callovian) to Late Cretaceous (Cenomanian?) Sid’r Formation (Lower Member, Upper Member); (5) Late Cretaceous (Cenomanian? to Santonian?) Nayid Formation; and (6) Late Jurassic (early Callovian) to Early (Late?) Cretaceous Wahrah Formation. Most of the lithostratigraphic units (formations and members) show isochronous boundaries between the different outcrop areas. The stratigraphic architecture of the Hamrat Duru Group megasequence is controlled by alternating siliciclastic and carbonate sedimentation possibly related to the second-order sea-level variations. The sediments accumulated on the continental rise of the Arabian margin mostly by submarine sediment-gravity flows and hemipelagic to pelagic rainout. A close relationship of the evolution of the Arabian Platform and the adjoining slope and basinal environments is evident. Changes in carbonate supply, oceanographic circulation and/or variations in silica productivity resulted in two distinct phases of radiolarian sedimentation. The first phase corresponds to the Triassic late Anisian-early Norian time interval; the second started in the Early Jurassic late Pliensbachian and lasted, with some interruptions, up to the Late Cretaceous Coniacian. The litho- and biostratigraphic similarities between the Mesozoic Hamrat Duru Basin of the northern/central Oman Mountains and the Mesozoic Batain Basin of northeastern Oman are seen as related to Neo-Tethys-wide palaeoceanographic changes and suggest a strong interdependence of the two basins with the evolution of the Arabian Platform.

Eoalpine (Cretaceous) evolution of the Oman Tethyan continental margin: insights from a structural field study in Jabal Akhdar (Oman Mountains)

ABSTRACT A structural study in Jabal Akhdar (an autochthonous window in the Oman Mountains) shows that the thrusts and imbrications, mapped in the Permian-Cretaceous formations of the Arabian Platform, have a vergence top to the north-northeast and are associated with a regional cleavage resulting from a ductile shear deformation of the same vergence. This deformation affects the entire autochthonous unit, from the southwestern edge of Jabal Akhdar to the northeastern edge of Saih Hatat, with an increasing strain intensity towards the northeast. The same domain is also affected by a HP/LT metamorphism with a northeastward increase from chlorite facies to blueschist and eclogite facies, i.e. characteristic of a northeast-dipping subduction. However, the retrograde character of the metamorphic parageneses associated with the ductile shear, as well as its north-northeast vergence, indicate that this deformation is linked to the exhumation of the autochthon during the Campanian. These observations have been synthesised in a new lithospheric-scale interpretation of the geodynamic development of the North Oman continental margins during the middle to late Cretaceous. The sequential evolution along a transect passing from southwest of Jabal Akhdar to northeast of Muscat can be summarised as follows: An intra-continental subduction zone affected the autochthon of the Arabian Platform with a basal rupture lying in the proximal part of the continental margin, to the south of the northern edge of the carbonate platform. A North Muscat microplate was created between the intra-continental subduction zone and the intra-oceanic subduction that gave rise to the Samail Ophiolite; this microplate includes the outer part of the Arabian Platform, the continental slope and the entire Hawasina Basin. From Early Turonian to Late Santonian the obduction and the intra-continental subduction were coeval and parallel. The northeast edge of the North Muscat microplate plunged below the Samail Nappe whilst the emergent southwest part overthrust the innermost parts of the Arabian Platform. The leading edge of the Samail and Hawasina Nappes advanced across the southwestern border of the North Muscat microplate just before obduction and intra-continental subduction ceased at the Santonian–Campanian boundary. Towards the end of the intra-continental subduction, the lower part of the crust of the subducted autochthon delaminated the upper part, marking the first stage of the metamorphic rocks exhumation. From Early Campanian to Early Maastrichtian, the North Muscat microplate moved to the northeast, its northeastern edge sinking by gravity into the asthenosphere. The subducted autochthon rose up, and came into contact with the base of the obducted units. The resulting uplift of the ophiolite nappes produced its emergence and partial erosion. Local crustal thickening, related to the lithospheric delamination, caused doming at Saih Hatat and subsequent erosion that locally extended to the pre-Permian sedimentary basement during the Early Maastrichtian. The present day domal shape of Jabal Akhdar is however related to Tertiary tectonic events.

Variations of the Crustal Structure of Arabia

Data from the broadband seismic stations deployed in Saudi Arabia during 1996 made it possible to study the variation of surface wave dispersion of the Arabian plate as a function of azimuth. Careful selection of the paths from earthquakes associated with the boundaries of the Arabian plate was made, and the group velocities of the fundamental mode of both Love and Rayleigh waves along these paths were studied. Results show that the Arabian plate is characterized mainly by two different sets of similar group velocity curves that are related to the two major geological units, the Arabian shield and the Arabian platform. The group velocities along paths that traverse the eastern, northeastern, and northwestern regions of Arabia are found to be representative of the Arabian platform geologic province, and are slower than those along the Gulf of Aqaba, the southeastern and the southwestern paths, which in turn represent the Arabian shield geologic province. The group velocity data were inverted to obtain shear wave velocity structure models of both the shield and the platform regions. Damped least-squares inversions method that utilizes a differential rather than stochastic damping was used to obtain smooth shear wave velocity models. The resulting models are in good agreement with previous results obtained from tomographic inversion.

River terrace sequences in Turkey: sources of evidence for lateral variations in regional uplift

This paper reviews river terrace staircases in Turkey and examines their relation to regional uplift. Turkish fluvial records are shown to be similar to their counterparts in Europe, with aggradation concentrated in cold climatic stages, despite differences in present-day climate between these two regions. Furthermore, as in Europe, these Turkish river terrace sequences provide evidence for increases in regional uplift rates in the Late Pliocene and Middle Pleistocene. In both regions, this effect is unrelated to senses and rates of plate motion, being instead the result of crustal thickening caused by lower-crustal flow induced by surface processes. From the fluvial evidence, estimated amounts of regional uplift since the Miocene are typically c . 400 m in western Turkey and in the area of the border with Syria. However, they increase northward and eastward to c . 1 km or more in northeastern Turkey on this time-scale, reflecting the regional variations in mean altitude of the land surface. Estimated typical uplift rates during the Middle and Late Pleistocene have been c . 0.1 mm a −1 in the Arabian Platform and c . 0.2–0.3 mm a −1 in western and northern Turkey. These variations are interpreted as the isostatic response to lateral variations in erosion rates.

Rapid marine recovery after the end-Permian mass-extinction event in the absence of marine anoxia

A new Early Triassic marine fauna is described from the Central Oman Mountains. The fauna is Griesbachian in age, on the basis of abundant conodonts and ammonoids, and was deposited in an oxygenated seamount setting off the Arabian platform margin. It is the first Griesbachian assemblage from a well-oxygenated marine setting and thus provides a test for the hypothesis that widespread anoxia prevented rapid recovery. The earliest Griesbachian (parvus zone) contains a low-diversity benthic fauna dominated by the bivalves Promyalina and Claraia. A similar level of recovery characterizes the immediate postextinction interval worldwide. However, the middle upper Griesbachian sedimentary rocks (isarcica and carinata zones) contain an incredibly diverse benthic fauna of bivalves, gastropods, articulate brachiopods, a new undescribed crinoid, echinoids, and ostracods. This fauna is more diverse and ecologically complex than the typical middle to late Griesbachian faunas described from oxygen-restricted settings worldwide. The level of postextinction recovery observed in the Oman fauna is not recorded elsewhere until the Spathian. These data support the hypothesis that the apparent delay in recovery after the end-Permian extinction event was due to widespread and prolonged benthic oxygen restriction: in the absence of anoxia, marine recovery is much faster.

Middle Permian plume‐related magmatism of the Hawasina Nappes and the Arabian Platform: Implications on the evolution of the Neotethyan margin in Oman

Permian pillow basalts are commonly found in Oman either at the base of the Hawasina Nappes or within the Arabian Platform successions exposed in the Saih Hatat tectonic window. There is an ongoing debate on whether these lavas include normal mid‐oceanic ridge basalts (NMORB) witnessing the Permian opening of the Neotethys or if they are plume‐related magmas that are emplaced either on the Arabian Platform or on its thinned continental margin. We sampled these lavas from several paleontologically dated middle Permian sites. Four of them (Buday'ah, Rustaq, Al Ajal, and Wadi Wasit) are located within the Hawasina Nappes and are exposed as thrust slices overlain by the Samail Nappe, and one (Wadi Aday) is within the Arabian Platform units and is exposed in the Saih Hatat window. These lavas are associated with marine sediments deposited in environments ranging from proximal (Saih Hatat, Wadi Wasit, and base of the thrust pile of Al Ajal) to distal (Buday'ah, Rustaq, and top of the Al Ajal pile) with respect to the Arabian Platform. Major and trace element features of the basalts allow two groups to be recognized. Enriched high‐Ti basalts similar to alkali basalts from intracontinental traps, rifted continental zones, and oceanic islands are exposed in Wadi Aday, Wadi Wasit, and at the structural base of the Al Ajal pile. Moderately enriched to slightly depleted low‐Ti tholeiitic basalt magmas resembling the low‐Ti flood basalts and those from seaward dipping reflector sequences are represented in Wadi Al Hulw in Saih Hatat, Buday'ah, Rustaq, and at the top of the Al Ajal thrust pile. Both groups show distinct plume‐related trace element signatures, and they do not include typical NMORB. Although emplaced in shallow to deep submarine environments, these basalts provide no direct evidence for a Neotethyan seafloor‐spreading event in the Hawasina Basin. Instead, they were likely erupted through the crust of the already rifted and drowned Arabian continental margin. Thus, despite their characteristic plume‐related geochemical signatures, the middle Permian basalts from Oman were not likely emplaced during the evolution of a typical volcanic rifted margin. We suggest that they originated from a mantle plume which ascended beneath the Arabian passive margin well after the initiation of seafloor spreading of the Neotethys.

Seismological constraints on the crustal structure beneath the Zagros Mountain belt (Iran)

SUMMARY The Zagros Mountain belt of western Iran results from the collision of the Arabian and Central Iran continental blocks. The stage of the collision is unclear and the crustal structure of the Zagros is rather poorly known. In this study we investigate the velocity structure of the crust and upper mantle beneath the Ghir region located in the Central Zagros using data collected by a temporary local seismological network including a broad-band instrument. The structures of the sedimentary cover and the upper crystalline crust are estimated from the inversion of P and S traveltimes of local earthquakes recorded on a dense seismological network. The upper crust consists of an ∼11 km thick sedimentary layer (V p ∼ 4.70 km s −1 ) above a ∼8 km thick upper crystalline crust (V p ∼ 5.85 km s −1 ). The velocity of the lower crust and the depth of the Moho are found using receiver function analysis of teleseismic earthquakes. The lower crystalline crust is unusually slow (V p ∼ 6.5 km s −1 ) and ∼27 km thick. The upper bound for the total crustal thickness beneath the Ghir region is 46 ± 2 km. A comparison of the thickness of the crystalline crust of the Zagros with available information for the thickness of the crystalline crust of the Arabian Platform shows that, at present, the Zagros has a thinner crust. The current crustal thickness beneath the Zagros is comparable to the pre-collision crustal thickness of the Arabian Platform, suggesting that the Zagros is now in a very early stage of continental collision.

Aptian faulting in the Haushi-Huqf (Oman) and the tectonic evolution of the southeast Arabian platform-margin

ABSTRACT A major upper Aptian unconformity is recorded on the eastern Arabian Platform, between the lower Aptian Qishn limestone and the Albian Nahr Umr marls. The study of this hiatus, in the western homocline of the Haushi-Huqf Uplift (Eastern Central Oman) provides new data about the evolution of the eastern Arabian Platform during middle Cretaceous times. The limestones of the Qishn formed a shoaling sequence, mainly composed of matrix-rich, coarse-grained sediment with small rudistids and algal build-ups, that led to a subemergent environment. A third-order sequence is recognized in the Qishn platform carbonates, which is partitioned into three minor sequences. The Qishn carbonate was subjected to pre-lithification normal faulting. A thick ferrugineous crust (hardground) covered the top surface of the Qishn as well as the faultscarps before they were buried under the Albian Nahr Umr marls. The faults are dominantly NW-trending, SW-facing, normal faults. The significance of the faulting remains hypothetical. The syndiagenetic NW-SE normal faults may correspond to ‘en-echelon’ faults, combined with a sinistral movement of the Haushi-Nafun Fault (HNF). The HNF acted as a left-lateral, strike-slip fault during late Cretaceous, pre-Maastrichtian times. This movement possibly began earlier, during the late Aptian. It could be related to the dynamics of the eastern Arabian margin during the Cretaceous (Masirah transform margin). There are some indications testifying to the activity of the Masirah transform fault during the early-middle Cretaceous. The margin kinematics may be responsible for the reactivation of nearby large faults affecting the platform basement (for instance the HNF). A slight sinistral reactivation of the HNF may have induced the development of the Aptian NW-trending normal faults. Moreover, the occurrence of early Cretaceous strike-slip movements in the Arabian Platform have already been envisaged, at a plate-scale, as a consequence of the South Atlantic extension. On this assumption, the Aptian fault blocks may have resulted from the development of a sinistral transtension along the HNF.

Development of an Oblique Subduction Zone—Tectonic Evolution of the Tethys Suture Zone in Southeast Turkey

The Southeast Anatolian orogen, part of the Mediterranean-Himalayan orogenic belt, may be divided into three approximately E-W-trending zones. From south to north, they are the Arabian platform, an imbricated zone, and a nappe zone. The eastern part of the Arabian platform includes a lower Paleozoic to lower Miocene sedimentary sequence and ophiolitic rocks that were obducted on the platform during Late Cretaceous time. Also, in the eastern part of the nappe zone consisting of lower and upper nappe packages, three major Paleocene-Oligocene deformational phases occurred, related to late-early Paleocene-early Eocene, late Lutetian, and late Oligocene nappe emplacements. These amalgamated nappes collided with the Arabian plate and were welded onto it at the latest stage of the orogenic evolution during late early Miocene time. The imbricated zone consists of units that were compressed and sandwiched between the nappes and the Arabian platform. In the nappe and imbricated zones, various island-arc volcanics and associated units developed related to the northward subduction of Neotethys during the Late Cretaceous to the late Oligocene. The ages of volcanic units decrease from west to east. This reflects oblique subduction of the ocean floor; its remnant presently underlies the northerly nappes.

Tectonic evolution of the NE Palmyride mountain belt, Syria: the Bishri crustal block

Investigation of the Bishri block, centrally positioned amid the diverse tectonic and structural zones of Syria, reveals details of the intraplate Phanerozoic development of the northern Arabian platform. The Bishri block is a broad NE-plunging inverted basin located at the NE portion of the Palmyride mountain belt where the mountains intersect the Euphrates fault system. Well and seismic data show that subsidence and sedimentation in the Bishri area was generally continuous from Carboniferous to Paleocene time, with the Bishri block part of the extensive Palmyride–Sinjar trough. Major bounding faults and a rift-type environment are documented in the Permo-Triassic, Jurassic and Cretaceous. The present Bishri structural and topographic high has been formed through transpressive structural inversion since the Mid-Miocene; high-angle Mesozoic bounding normal faults now have net reverse offsets with a significant dextral strike-slip component. East of the Bishri block, towards the Euphrates fault system, NNW–SSE-striking normal faults exhibit less reverse movement. This deformation history correlates with the opening and closing of the nearby NeoTethys ocean that has driven the evolution of intracontinental Syria.

The Barremian-Aptian Evolution of The Eastern Arabian Carbonate Platform Margin (Northern Oman)

ABSTRACT Carbonate platform margins are sensitive recorders of changes in sea level and climate and can reveal the relative importance of global and regional controls on platform evolution. This paper focuses on the Barremian to Aptian interval (mid Cretaceous), which is known for climatic and environmental changes towards more intensified greenhouse conditions. The study area in the northern Oman mountains offers one of the very few locations where the Cretaceous carbonate margin of the Arabian Plate can be studied along continuous outcrops. Our detailed sedimentological and sequence stratigraphic model of the platform margin demonstrates how major environmental and ecological changes controlled the stratigraphic architecture. The Early Cretaceous platform margin shows high rates of progradation in Berriasian to Hauterivian times followed by lower rates and some aggradation in the Late Hauterivian to Barremian. High-energy bioclastic and oolitic sands were the dominant deposits at the margin. Turbidites were deposited at the slope and in the basin. The Early Aptian platform margin shows a marked change to purely aggradational geometries and a welldeveloped platform barrier that was formed mainly by microbial buildups. The sudden dominance in microbial activity led to cementation and stabilization of the margin and slope and, therefore, a decrease of downslope sediment transport by turbidites. In the Late Aptian, large parts of the Arabian craton were subaerially exposed and a fringing carbonate platform formed. Seven Barremian to Early Albian large-scale depositional sequences reflecting relative sea-level changes are identified on the basis of time lines constrained by physical correlation and biostratigraphy. The reconstruction of the margin geometries suggests that tectonic activity played an important role in the Early Aptian. This was most likely related to global plate reorganization that was accompanied by increased volcanic activity in many parts of the world. Along the northeastern Arabian platform the associated global changes in atmospheric and oceanic circulation are recorded with a change in platform-margin ecology from an ooid-bioclast dominated to a microbial dominated margin. Time-equivalent argillaceous deposits suggest an increase in rainfall and elevated input of nutrients onto the platform. This process contributed to the strongly diminished carbonate production by other organisms and favored microbial activity. The platform margin may thus represent a shallow-marine response to the Early Aptian global changes, commonly associated with an oceanic anoxic event in basinal environments.

Late Ordovician glaciation in southern Turkey

ABSTRACT We present a new survey of several Palaeozoic sections in both the Taurus range and the Border Folds that documents typical glacial features including a glacial pavement and striated dropstones (Halevikdere Formation) and demonstrates the former presence of an ice sheet in southern and south‐eastern Turkey. Evidence for the late Ashgill (Hirnantian) age of this episode is provided by macro‐ and microfossils found within the glacial formation. The extension of ice‐related deposits into the northernmost part of the Arabian Platform (Mardin region) implies a much wider distribution of the Ordovician ice sheet than was previously believed, and strongly suggests that southern Turkey lay close to Egypt during the Lower Palaeozoic.

A Broadband Seismic Deployment in Jordan

In 1983 a short-period seismic network was established in the Hashemite Kingdom of Jordan in cooperation with the United States Geological Survey (USGS). This network continues to operate under the direction of the Jordan Seismological Observatory (JSO) within the Natural Resources Authority (NRA). In 1998 two broadband seismic stations were deployed in Jordan as part of a cooperative project between JSO, USGS, and Lawrence Livermore National Laboratory (LLNL). The purpose of this deployment, which continues today, is to obtain long-period constraints on earthquake source parameters, improve estimates of magnitudes and crustal and upper-mantle structure, and obtain ground-truth data for nuclear explosion monitoring calibration. In this paper we demonstrate the value of the broadband instruments in Jordan by using the data to characterize earthquake and mining sources and estimate crustal structure using some simple examples. We also describe an openly available data product containing event-oriented waveforms for use by researchers. One station is located in southern Jordan near Hittiyah (HIT), and the other is located in northeastern Jordan near Ruweishid (RUW). Station locations are given in Table 1. Figure 1 shows the JSO/LLNL/USGS stations, stations from regional networks, various mines, and recorded seismicity in the region. The numerous short-period stations of the national networks in the region record the seismicity along the Gulf of Aqaba and the Dead Sea Transform. Only a few broadband stations are in the region outside of the Dead Sea Transform to make long-period observations of events and estimate source parameters and structure. The Geophysical Institute of Israel (GII) operates broadband stations along the Dead Sea Transform. King Abdulaziz City for Science and Technology (KACST, Saudi Arabia) operates broadband stations in the Gulf of Aqaba region. The broadband stations in Jordan provide an opportunity to sample the structure of the northwestern Arabian Platform. View this table: TABLE 1 Station Locations The …

Agriopleura Morphotypes of the Lower Aptian Shu’aiba Formation of Saudi Arabia

The Shu’aiba Formation of the Arabian Platform consists of Aptian carbonates in which rudists are important biocomponents. It is an important hydrocarbon reservoir. Semi quantitative micropalaeontologyand macropalaeontological observations from cores have enabled three-dimensional interpretation of biofacies and lithofacies that have guided optimal reservoir exploitation.In addition to the presence of Offneria murgensis MASSE, O. cf. nicolinae (MAINELLI), Glossomyophorus costatus MASSE et al., Oedomyophorus shaybahensis SKELTON, and Horiopleura cf. distefanoiBOEHM the Shu’aiba Formation contains Agriopleura cf. blumenbachi(STUDER) and A. cf. marticensis (d’ORBIGNY). Although species of Agriopleura are locally present over short sections below the Glossomyophorus costatus accumulations of the middle part of the formation, they are very well represented in its upper part, where they are typically associated with the moderately deep marine benthonic foraminifera Praechrysalidina infracretacea, Vercorsella arenata, Debarina hahounerensis and Palorbitolina lenticularis.Agriopleura cf. blumenbachi and A. cf. marticensis display contrastingmorphologies. Agriopleura cf. marticensis is cone-shaped, with a fixed valve expansion angle of 30–35º, and with average right valve dimensions of 3.5 cm length and 2.5 cm maximum diameter. A recently observed “clinger” form is, however, 70 cm long. A. cf. blumenbachiis elongate, almost tube-like, with a very low rate of fixed valve diameter increase, of less than 10º with average right valve dimensions of 6.5 cm length and 2.2 cm maximum diameter.The two forms are present in distinct biofacies. Both Agriopleura facies are considered to compose a single depositional cycle, and it is possible that the elongate shape of Agriopleura cf. blumenbachi is better adapted to the slightly higher rate of sedimentation associated with the relatively rapid sea level rise at the base of each new depositionalcycle. The cone-shape of A. cf. marticensis is possibly adapted to lower rates of sedimentation during the relatively slower rate of sea level rise, and ultimate fall of the upper part of each depositional cycle.

Paleomagnetic reconstruction of the Cenozoic evolution of the Eastern Mediterranean

A total of 113 paleomagnetic sites were sampled along an Anatolian S–N transect from the Arabian platform, the Hatay region, the Eastern Taurides, the Kirsehir block, the Sivas basin and the Eastern Pontides. Reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites, spanning in time from Paleocene to Miocene. In a general way, declinations are westerly deviated and inclinations are shallower than the geocentered dipole value at the present latitudes. When combined with previously published results, these data indicate that a large-scale counterclockwise rotation of Anatolia of some 25° has occurred since the Miocene. Assuming that the pole of rotation of Anatolia with respect to Europe has remained constant in time at the location given by MacClusky et al. [J. Geophys. Res. 105 (2000) 5695] on the basis of the geodetic data, this rotation implies that a large westward displacement (500 km at the average latitude of 40°) has taken place. Assuming that the rotation was initiated by the Arabia/Europe collision about 12 Ma ago, this corresponds to an average displacement of about 40 mm/year. Together with previous results from the western part of the Aegean arc, these results indicate that the main trends of the Cenozoic evolution of the Eastern Mediterranean appear to consist of two post-early Miocene rotations of opposite senses: a clockwise rotation of the western part of the Aegean [Tectonophysics 146 (1988) 183] around a pole situated in northern Albania, and a counterclockwise rotation around the pole given by McClusky et al. [J. Geophys. Res. 105 (2000) 5695]. Comparison with GPS data suggest that both rotations are still active today.

Subsidence modelling of the Arabian Platform from Permian to Paleogene outcrops

The burial history of Permian to Tertiary sediments of the Arabian Platform is deduced from quantitative subsidence analysis. This permits the reconstruction of both the sedimentary depositional history and geodynamic evolution of the southern Tethyan margin. Lithostratigraphic, biostratigraphic and sedimentologic outcrop data originate from, and were studied during, geological mapping in Central Arabia and the Oman Mountains. Correlations with two wells located in Central Arabia allow comparisons with subsurface modelling. In Saudi Arabia, the results of this extensive survey, over 1200 km long between lat. 18°N and 30°N, have been summarized in several synthetic profiles. Five profiles cover Permian, Triassic and Jurassic outcrops, and three profiles deal with Cretaceous and Cenozoic outcrops of Central Arabia. One synthetic section of the autochthonous series of the Oman Mountains allows correlation with the eastern area of the Arabian Peninsula. A structural reconstruction at the western edge of the Arabian Platform, from Late Permian to Late Jurassic times, is thus proposed along a north–south transect. The role of permanently active structural features that controlled sedimentation on the Arabian Platform is demonstrated for the first time. Subsidence modelling of the Permian to Jurassic succession of the Arabian Platform indicates several major tectonic events during the Late Permian, Early Triassic, Norian, Middle Toarcian and Dogger. However, eustasy controlled sedimentation during the Late Jurassic. Strongly combined tectonic and eustatic influences were active during Cretaceous and Early Cenozoic times.