Neogene Sedimentary Basins Research Articles

Oblique rifting triggered by slab tearing: the case of the Alboran rifted margin in the eastern Betics

Abstract. The tectonic evolution of highly oblique continental margins that result from extension above lithospheric subduction–transform edge propagator (STEP) faults is poorly understood. Here, we investigate the case of the Alboran margin in the eastern Betics characterized by crustal thinning of 15–10 km, oblique to the direction of slab retreat. The current deformation patterns indicate that oblique rifting is underway. However, it is unclear whether these conditions are those that prevailed during the formation of the metamorphic domes and intramontane basins. We review the temporal and spatial evolution of Neogene sedimentary basins and brittle deformation in the eastern Betics and exploit offshore seismic reflection lines to propose a crustal-scale section across the oblique margin. The history of sediment infill and rates of subsidence combined with the analyses of fault slip data confirm that brittle extension oriented from north 20∘ E to E–W occurred during an interval spanning from the Serravallian–early Tortonian to the late Tortonian (14–8 Ma). This extension is associated with both normal and strike-slip regimes and the evolution of the strike-slip fault zones flanking the metamorphic domes. The transtensional model forms a coherent scheme linking the ductile deformation associated with metamorphic domes and the formation of E–W- and NW–SE- or NNW–SSE-directed sedimentary basins in the brittle upper crust during the Tortonian. The oblique extension, which is closely associated with STEP faulting, occurred during the regional convergence between Africa and Iberia since the Miocene. Only recently, around 8 Ma, has slab detachment started to migrate westward, leading to tectonic inversion in the eastern Betics. Such a type of narrow oblique-rifted margin associated with transform-like plate boundaries is not unique but is expected to be hardly preserved in the geological record due to the transient nature of retreating subduction systems.

Bio-Geochemical Processes: Insights from Fe-Mn Mineralization in the Aegean Sea (Greece)

In this study, we have compiled new and existing mineralogical and geochemical data on Fe-Mn mineralization from the Aegean region [Attica (Grammatiko, Legrena, and Varnavas), Evia and Milos islands], aiming to provide new insights on the genesis of Fe-Mn mineralization in that region and its potential environmental implications. A common feature of those deposits is the relatively low Cr, Co, V, Ni, Mo, and Cd content, whereas Ba, As, W, Cu, Pb, and Zn show remarkably variable values. The Mn-Fe deposits from Milos exhibit the highest tungsten content, while a positive trend between MnO and W, combined with a negative trend between MnO and Fe2O3 suggests the preference of W to Mn-minerals. The occurrence of bacterio-morphic Fe-Mn-oxides/hydroxides within Mn-Fe mineralizations in the studied region, indicates the important role of micro-organisms into redox reactions. Moreover, the presence of micro-organisms in the Fe-Mn-deposits, reflecting the presence of organic matter confirms a shallow marine environment for their deposition. A salient feature of the Varnavas and Milos Mn-Fe ores is the presence of sodium chloride coated fossilized micro-organisms, suggesting development from a solution containing relatively high Na and Cl concentrations. Furthermore, from an environmental point of view, consideration is given to the bioavailability of elements such as As, Pb, and W, related to the above-mentioned mineralizations. The high bio-accumulation factor for W (Wplant/Wsoil × 100) recorded in the Neogene sedimentary basins of Attica, related to the Grammatiko Fe-Mn mineralization, reflects the high W mobility under alkaline conditions and the potential environmental impact of similar deposits with elevated W content.

Occurrence, Origin and Health Hazards of High Fluoride Waters in the Western Part of the Neogene Sedimentary Basin in Opole Province, Poland

High fluoride content exceeding permissible limits for drinking water and causing numerous incidents of fluorosis disease in the population of Nysa town was the reason for the closure of the deepest wells in the western part of the Neogene groundwater basin Paczków-Niemodlin in the Opole region in Poland. Hydrochemical studies conducted by the Polish Geological Institute – National Research Institute resulted in the recognition and extent of fluoride anomaly in the groundwater extracted from the Neogene basin in southern Poland. The studies provided a comprehensive recognition of hydrogeological and chemical conditions of the aquifer located in the Neogene basin characterized by a series of fine-grained sands within a series of clays. The content of fluoride in groundwater is high; the average is 2.1 mg/L, maximum value reached 11.5 mg/l, exceeding several times the permissible limit for drinking waters (1.5 mg/L). The main objective of this study was to determine the source of high concentrations of fluoride in groundwater in the western part of Paczków-Niemodlin basin where the highest concentrations were observed. The investigations confirmed the increase in fluoride content with the decreasing altitude of the aquifers. Various factors that may form the chemistry of these groundwater were analyzed. The most probable source of high fluoride content in groundwater in this basin is their long-term contact with Precambrian and Palaeozoic igneous and metamorphic rocks containing fluorine-rich minerals along with the location near large fault zones, which may be privileged water flowpaths from greater depths.

Plio-Quaternary Volcanism in Northeastern Morocco: Petrography and Geochemistry of Outcrops with High Geothermal Potential

Cenozoic volcanic activity in Morocco started in the Miocene and proceeded, after a short break, during Pliocene and Quaternary. Calc-alkaline magmatic activity occurred first and was accompanied by the eruption of transitional lavas, followed by Plio-Quaternary alkali basaltic activity, which was emplaced within Neogene sedimentary basins of the Rif belt and its foreland. From calc-alkaline to alkaline magmatism, passing through a transitional term, volcanic activities in Morocco formed magnificent outcrops, very diversified in their affinities, their mineral compositions and their geochemistry. The petrographic study and geochemistry of Plio-quaternary volcanic rocks in the areas with high geothermal potential in northeast of Morocco show a dominance of Na-rich basaltic rocks (basanites, basalts, tephrites and basaltic trachy-andesites), followed by trachy-andesites. Most of the samples exhibit an enrichment of large-ion lithophile elements (LILEs) over high-field-strength elements (HFSEs). These results were used to test the global model of Circum-Mediterranean Anorogenic Cenozoic Igneous Province (CiMACI) and the regional model of [1].

Shallow S-Wave Velocity Structure in the Middle-Chelif Basin, Algeria, Using Ambient Vibration Single-Station and Array Measurements

In order to better assess the seismic hazard in the northern region of Algeria, the shear-wave velocity structure in the Middle-Chelif Basin is estimated using ambient vibration single-station and array measurements. The Middle-Chelif Basin is located in the central part of the Chelif Basin, the largest of the Neogene sedimentary basins in northern Algeria. This basin hosts the El-Asnam fault, one of the most important active faults in the Mediterranean area. In this seismically active region, most towns and villages are built on large unconsolidated sedimentary covers. Application of the horizontal-to-vertical spectral ratio (HVSR) technique at 164 sites, and frequency–wavenumber (F–K) analysis at 7 other sites, allowed for the estimation of the ground resonance frequencies, shear-wave velocity profiles, and sedimentary cover thicknesses. The electrical resistivity tomography method was used at some sites to further constrain the thickness of the superficial sedimentary layers. The soil resonance frequencies range from 0.75 Hz to 12 Hz and the maximum frequency peak amplitude is 6.2. The structure of the estimated shear-wave velocities is presented in some places as 2D profiles to help interpret the existing faults. The ambient vibration data allowed us to estimate the maximum depth in the Middle-Chelif Basin, which is 760 m near the city of El-Abadia.

Diagenetic study on the Neogene sedimentary basin as paleoenvironmental proxy data for an offshore CO2 storage project in Pohang Basin, South Korea

As the importance of reducing greenhouse gas emissions has attracted much attention, Pohang Basin has been identified as a CO2 geological sequestration test site in Korea. This study aims to provide a better understanding of the diagenetic history of Pohang Basin through mineralogical and microstructural analyses, with a focus on tectonic evolution in the reservoirs offshore of the Pohang Basin during the East Sea (Sea of Japan) opening in the Miocene. We focused on two sections in the core that are considered to be target layers for CO2 storage. Samples were analyzed for texture observation and chemical analysis. The major mineral components include quartz, feldspar, illite, chlorite, kaolinite and calcite, and the minor mineral components include pyrite, siderite, iron oxide, and titanium oxide. The detrital grains are composed of quartz and feldspar, and the primary pore is cemented with kaolinite (I), calcite, pyrite and chlorite. The analyzed chlorites are differentiated into five types by their textural characteristics, such as pore-filling (PF), pore-filling with kaolinite (PF-k), pore-lining (PL), replaced (RD), and detrital (DA) chlorites, and they were all categorized as either brunsvigite, diabantite, or ripidolite. Generally, the dissolution of feldspar is observed for all samples. The diagenetic temperature is estimated by chlorite geothermometry to be 170 °C on average, which is higher than the present temperature of Pohang Basin (55–60 °C). Considering all results together, the target layers have undergone diagenetic processes from early diagenesis (eogenesis) to late diagenesis (mesogenesis) and uplift-related diagenesis (telogenesis). After sedimentation of the Pohang Basin, kaolinite (I), calcite, and pyrite were cemented in the pore, and detrital mica was replaced with chlorite. As the burial depth increased, the dissolution of feldspar advanced. The high temperature resulting from the chlorite geothermometry could be influenced by the burial heat as source. Also, the Neogene volcanism and related tectonics (known as Eoil Orogeny) could become a heat source capable of high temperatures, and a high geothermal gradient and tectonically compressional environment may have influenced fluid flow. After the uplift, kaolinite (II) was precipitated in both an intergranular pore and intragranular pore as a result of dissolution. The effects of diagenesis, such as cementation and dissolution, in CO2 reservoir rocks, could be an important factor in assessing the appropriacy of predicting potential charge after injection in carbon capture and storage project.

Estimation of Bouguer correction density based on underground and surface gravity measurements and precise modelling of topographic effects – two case studies from Slovakia

Abstract We present a simple and straightforward method for estimating the mean density of topographic masses based on underground gravity measurements along with topography modelling. Two examples under different conditions are given, the first coming from a railway tunnel passing through a Mesozoic karst area and the second from an active coal mine situated in a Neogene sedimentary basin. Relative gravity measurements were processed and corrected by topographic effect modelling based on high-precision airborne LiDAR-derived elevation models. In addition, detailed mining tunnel gravimetric modelling based on terrestrial laser scanning data is presented. Resulted mean (bulk) densities are compared with those obtained from detailed surface gravity measurements as well as with available rock-samples density analysis.

From mountain summits to roots: Crustal structure of the Eastern Alps and Bohemian Massif along longitude 13.3°E

The crustal structure of the Eastern Alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth. Of particular interest are the nature of a previously proposed Moho gap south and east of the Tauern Window, the plate tectonic affinity of the steeply dipping Eastern Alpine slab, and the relationship of the Alps to the Neogene sedimentary basins and the Bohemian Massif. To address these questions, we use various seismological approaches based on converted waves from the temporary passive experiment EASI (Eastern Alpine Seismic Investigation), a complementary experiment of the AlpArray project. The EASI is a densely spaced, 540 km long seismic network along 13.3°E we operated for more than a year. The uppermost-crustal structures in and near the Alps exhibit dipping layers and/or tilted anisotropy that correlate well with surface geology observations. The Moho, despite its variable appearance, is clearly identified along most of the swath. The Variscan lithospheric blocks beneath the Bohemian Massif are imaged with sub-vertical boundaries. Beneath the Eastern Alps, the shape of the Moho is consistent with bi-vergent orogenic thickening, with a steeper and deeper-reaching Adriatic plate plunging northwards beneath the European plate in the north. At the junction of these plates at depth, around the previously proposed Moho gap, the root of the Eastern Alps is a broad trough characterized by a zone of low velocity-gradient that is up to 20 km thick, transitioning between crust and mantle. Our receiver-function results corroborate earlier lithosphere-upper mantle seismic tomography images, and highlight the Adriatic affinity of the Eastern Alpine slab. The zigzag deployment pattern of stations in the EASI experiment also allows distinction of short-wavelength variations perpendicular to the profile, both within the shallow and the deep crust. This underlines the importance of applying 3D imaging in complex geodynamic systems.

Core Complex Segmentation in North Aegean, A Dynamic View

AbstractThe core complexes of the North Aegean result from the gravity spreading of a thrust wedge, driven by the Hellenic slab rollback, since middle Eocene. The development of the Southern Rhodope Core Complex occurred in two stages: (i) core complex exhumation accommodated by the Kerdylion detachment and (ii) steep normal faulting controlling the deposition of Neogene sedimentary basins that segmented the core complex. Both stages have been controlled by a clockwise rotation of the detachment hanging wall. The bulk amount of extension along the Aegean coastline in Northern Greece reached 120 km. The transition between the two stages occurred in middle Miocene due to an increase in extensional displacement by a factor 5. This transition between two different modes of extension, from localized detachment (i.e., core complex mode) to distributed steep normal faulting (i.e., wide rift mode), occurred at Aegean scale as a result of an acceleration of slab rollback. The Neogene basins emplaced close to the detachment, where brittle upper crust was thin (around 7 km) but containing weak marble layers allowing the formation of ramp‐flat extensional systems with rollover‐type basin fill. Since Pliocene, the stretching direction changed, from NE‐SW to NS, due to the propagation of the North Anatolian Fault in the North Aegean domain.

Neogene evolution of the north-eastern Tibetan Plateau based on sedimentary, paleoclimatic and tectonic evidence

In this study, the development of the north-eastern Tibetan Plateau is investigated via an integrated study of the sedimentology, magnetostratigraphy, palaeogeography, and cross-section comparisons of the Neogene sedimentary basins of the Tibetan Plateau. From 23 to 17 Ma, this region was characterized by widespread angular unconformities and a sedimentary hiatus, indicating the comprehensive uplift of the plateau. The tectonic event that created the Tibetan Plateau triggered the evolution of sedimentary basins. During the Middle Miocene climatic optimum event, the growing Qilian Shan formed a barrier, leading to cooler and drier conditions on the western side of the mountain. However, humid and warm conditions persisted on the eastern side of the range. After this event, this region was influenced by a global cooling trend and enhanced tectonic activity in the north-eastern Tibetan Plateau. At approximately 10–8 Ma, sedimentary data, which were consistent with low-temperature thermochronological records, indicated the inversion of the surrounding mountains and rapid exhumation of the Laji Shan. Since 5.0–3.6 Ma, these intermontane basins gradually shrank and disappeared due to the overall uplift of the Tibetan Plateau and the accelerated global cooling trend and were associated with unconformities and growth strata that formed during stepwise-north-eastward thrusting tectonism.

EFFECTS OF SLAB ROLLBACK ACCELERATION ON AEGEAN EXTENSION

Aegean extension is a process driven by slab rollback that, since 45 Ma, shows a twostage evolution. From Middle Eocene to Middle Miocene it is accommodated by localized deformation leading to i) the exhumation of high-pressure metamorphic rocks from mantle to crustal depths, ii) the exhumation of high-temperature rocks in core complexes and iii) the deposition of Paleogene sedimentary basins. Since Middle Miocene, extension is distributed over the whole Aegean domain giving a widespread development of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry and kinematics of ductile deformation, paleomagnetic data and available tomographic models. The restorationmodel shows that the rate of trench retreat was around 0.6 cm/y during the first 30 My and then accelerated up to 3.2 cm/y during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, which occurred in Middle Miocene correlates with the acceleration of trench retreat and is more likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral NE-SW strike-slip faults during the second stage of Aegean extension, since Middle Miocene, is illustrated by the 450 Km-long fault, recently put in evidence, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene,almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean. This raises a fundamental issue concerning the dynamic relationship between slab tearing and Anatolia displacement.

堆積盆地の発生・発達過程の研究 : 秩父盆地西縁における解析

堆積盆地の発生・発達過程の研究 : 秩父盆地西縁における解析

The two-stage Aegean extension, from localized to distributed, a result of slab rollback acceleration

Back-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to (i) the exhumation of high-pressure metamorphic rocks to crustal depths, (ii) the exhumation of high-temperature metamorphic rocks in core complexes, and (iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry, and kinematics of ductile deformation, paleomagnetic data, and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/year during the first 30 My and then accelerated up to 3.2 cm/year during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral northeast–southwest strike-slip faults, since Middle Miocene, is illustrated by the 450 km long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in Western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean.

Spatial characteristics of the Pliocene to modern alluvial fan successions in the uplifted sedimentary basins of Almería, SE Spain: review and regional synthesis

Abstract Conventional sedimentological models of alluvial fan sequences tend to be based on fans in subsiding sedimentary basins. Fans in uplifting terrains are rather different. We examined the sequence of fan delta and alluvial fan deposition from the Pliocene to the Late Quaternary in the uplifting terrain of the Neogene sedimentary basins of Almería, Betic Cordillera, SE Spain. There were three phases of fan deposition, each yielding particular morpho-sedimentological characteristics and each having distinctive spatial distributions. The first phase was the Pliocene fan deltas, deposited where the larger river systems entered the receding early Pliocene seas. This phase was followed during the late Pliocene–Early Pleistocene by a phase of extensive alluvial fan deposition extending from the mountain fronts to the basin centres. Continued uplift occurred during the Pleistocene, resulting in incision of the drainage network and dissection of the Plio-Pleistocene fan systems. The third phase, during the Quaternary, involved much smaller mountain front alluvial fans set well below the Plio-Pleistocene fans, except in local areas of tectonic subsidence where extensive fans were formed. The older fans exhibit stacked sedimentary successions with very little evidence of sustained vertical incision. However, the Quaternary fans show much evidence of sustained incision between major aggradational phases, often resulting in inset rather than stacked stratigraphic relationships. We interpret this to imply that, although the tectonic context was the primary temporal control on variations within the older fan successions, within the Quaternary fans the overall tectonic control has been modified by responses to the Quaternary climatic sequence.

Late Neogene oroclinal bending in the central Taurides: A record of terminal eastward subduction in southern Turkey?

The Tauride fold-thrusts belt formed during ∼S–N convergence between Africa and Eurasia since Cretaceous time. The western end of the central Taurides strike NW–SE, highly obliquely to the overall convergence direction, and connect to the NE–SW Beydağları–Lycian Nappe flank of the western Taurides, forming the so-called ‘Isparta Angle’. In Neogene time, the western and central Taurides and the inner part of the Isparta Angle became overlain by Neogene sedimentary basins including Manavgat, Köprüçay and Aksu, characterized by marine clastics and carbonates. The eastern limb of the Isparta Angle experienced multidirectional Miocene to Present extension, whereas E–W shortening affected the marine sedimentary basins in the heart of the Isparta Angle. To quantitatively reconstruct the Neogene kinematic evolution of the Taurides, towards restoring the subduction system accommodating Africa–Eurasia convergence, we paleomagnetically assess if and when vertical axis rotations affected the Manavgat, Köprüçay, and Aksu basins in Early Miocene to Pliocene times. We show that the northern Köprüçay Basin rotated ∼20–30° clockwise, the Manavgat Basin underwent ∼25–35° counterclockwise rotation, and the Aksu Basin underwent no rotation since the Early-Middle Miocene. It was previously shown that the Beydağları region underwent a post-Middle Miocene ∼20° counterclockwise rotation. These results show that the prominent oroclinal salient geometry of the western Taurides thus acquired, at least in part, since Miocene times, that the Köprüçay Basin rotated relative to the Aksu Basin along the Aksu thrust, and that the Beydağları platform rotated relative to the Aksu Basin along the Bucak thrust, which must have both been active until Late Neogene time. This synchronous E–W shortening in the heart of the Isparta Angle, and multidirectional extension in its eastern limb may be explained by relative westward retreat of an eastward dipping subducting Antalya slab that has previously been imaged by seismic tomography and a Benioff zone. The Neogene Bucak thrust west of the Aksu Basin may represent the most recent surface expression of the Antalya subduction zone.

Geophysical analysis of fault geometry and volcanic activity in the Erzincan Basin, Central Turkey: Complex evolution of a mature pull-apart basin

The Erzincan Basin is one of several Neogene sedimentary basins developed by prolonged right-lateral strike-slip along the North Anatolian Fault Zone (NAFZ), the intracontinental transform defining the present boundary between the Eurasian Plate to the north and accreted Anatolian terranes to the south. The basin has a strong asymmetry and young (<780ka) volcanic centers with widespread development of cross faults defining an advanced phase of pull-apart basin evolution. To isolate faults with no surface geomorphic or morphotectonic signatures in the young sedimentary cover, continuous magnetic profiles were conducted together with detailed interpretation of the regional Bouguer gravity map. This geophysical approach combined with surface mapping defines a fault geometry highlighting a series of buried structures including a fracture system 0.2–2.35km wide which conforms to the volcanic lineaments seen at the surface. A model is developed for the evolution of the Erzincan Basin with a history commencing as a simple pull-apart by right-lateral strike-slip on the developing NAFZ, probably in Early Pliocene times. Subsequent interaction with a major left-lateral (Ovacık) fault (OF) caused the focus of motion on the NAFZ to shift to the southwest and develop a complex fishbone fracture system. This became the focus of volcanic activity on three lineaments which migrated progressively southwards toward the axis of the basin. Continuing motion on the OF transformed the south east margin of the basin into an extensional zone and the tectonic history of the basin has been further complicated by its proximity to a major transform intersection between the NAFZ and OF. The signatures of recent volcanism and the development of cross faults on which much activity is now concentrated define a mature pull-apart advancing toward extinction.

Emplacement of the Cabezo María lamproite volcano (Miocene, SE Spain)

Lamproite volcanoes are uncommon in the geological record but are exceptionally well preserved in the Betic Cordilleras of SE Spain, where they erupted during the Late Miocene (Tortonian to Messinian stages). The parent melts are thought to have been channelled through major lithospheric faults to erupt at or near the faulted margins of Neogene sedimentary basins. Lamproite magmas are thought to be relatively CO2-poor (<1 wt %) and are typically characterised by an effusive eruption style and the development of lava lakes and scoria cones. Cabezo Maria is a relatively small (∼550 m diameter) lamproite volcano that was emplaced within the shallow-water marine-influenced Vera Basin. The lamproites are compositionally similar to those of the Roman Province and generally less potassic (K2O<5 wt%) than other (ultra-) potassic rocks in SE Spain (e.g. Cancarix, Fortuna). The initial eruption stages were dominated by explosive magma-water interactions and the formation of peperites. These are characterised by angular fragments of glassy lamproite lavas (and isolated lobes) incorporated in sediments, locally showing the effects of thermal metamorphism. Further, elutriation pipes and ‘jigsaw-fit’ textures are observed in the peperites. The lavas and peperites are overlain by outward-dipping well-stratified scoria deposits defining part of a cinder cone, which is inferred to have emerged above sea level. Steep internal contacts with inward-dipping, structureless breccias likely represent the inner wall deposits of a central conduit. The deposits are cross-cut by late-stage dykes, which supplied fissure eruptions of geochemically similar lavas capping the scoria cone. The transition from explosive to effusive behaviour may reflect the decreased availability of water, possibly due to downward migration of the feeder conduit below the level of water-saturated sediments.

Sedimentary development of the Oligocene Karsantı Basin, southern Turkey, in its regional tectonic setting

Following Late Cretaceous ophiolite and melange emplacement within the Tauride belt several Neogene sedimentary basins of variable size were formed along the southern flank of the Taurus continent in southern Turkey. These include the Pozantı and Karsantı Basins and the regional scale Çukurova Basin Complex, extending southwestwards into the Cilicia-Kyrenia Basin. The Karsantı Basin is bounded by the regional scale sinistral Ecemiş Fault Zone to the west, the East Anatolian Fault Zone to the southeast and the Negoene Adana Basin to the south. Deformed Palaeozoic and Mesozoic rock units that display an irregular palaeotopography form the basement of the Karsantı Basin. These units are overlain by an allochthonous Kızıldağ melange and by thrust slices of basic/ultrabasic ophiolitic rocks (Faraşa ophiolites) that were emplaced in this region during the Late Maastrichtian. The Karsantı Basin was formed during the Oligocene above the thrust sheets. The Karsantı Basin disconformably overlies the ophiolitic nappes and is interpreted as a N–S trending half graben which was probably most active following the deposition of lacustrine sediments during the late Oligocene. The main Karsantı Basin infill is represented by four lithological units: 1. Alluvial fan deposits (A1), 2. shallow-marine deposits (A2), 3. lacustrine deposits (A3), and 4. fluvial deposits (A4). These sediments were deposited during the Oligocene, prior to the initiation of the main Adana Basin, which formed in a separate intermontane setting. The Karsantı Basin fill is unconformably overlain by early Miocene sediments of the Neogene Adana basin.

A Miocene onset of the modern extensional regime in the Isparta Angle: constraints from the Yalvaç Basin (southwest Turkey)

The pre-Neogene Tauride fold-and-thrust belt, comprising Cretaceous ophiolites and metamorphic rocks and non-metamorphic carbonate thrust slices in southern Turkey, is flanked and overlain by Neogene sedimentary basins. These include poorly studied intra-montane basins including the Yalvac Basin. In this paper, we study the stratigraphy, sedimentology and structure of the Yalvac Basin, which has a Middle Miocene and younger stratigraphy. Our results show that the basin formed as a result of multi-directional extension, with NE–SW to E–W extension dominating over subordinate NW–SE to N–S extension. We show that faults bounding the modern basin also governed basin formation, with proximal facies close to the basin margins grading upwards and basinwards into lacustrine deposits representing the local depocentre. The Yalvac Basin was a local basin, but a similar, contemporaneous history recently reconstructed from the Altinapa Basin, ~100 km to the south, shows that multi-directional extension dominated by E–W extension was a regional phenomenon. Extension is still active today, and we conclude that this tectonic regime in the study area has prevailed since Middle Miocene times. Previously documented E–W shortening in the Isparta Angle along the Aksu Thrust, ~100 km to the southwest of our study area, is synchronous with the extensional history documented here, and E–W extension to its east shows that Anatolian westwards push is likely not the cause. Synchronous E–W shortening in the heart and E–W extension in the east of the Isparta Angle may be explained by an eastwards-dipping subduction zone previously documented with seismic tomography and earthquake hypocentres. We suggest that this slab surfaces along the Aksu thrust and creates E–W overriding plate extension in the east of the Isparta Angle. Neogene and modern Anatolian geodynamics may thus have been driven by an Aegean, Antalya and Cyprus slab segment that each had their own specific evolution.

Magnetic properties of siliceous marine sediments in Northern Hokkaido, Japan: a quantitative tectono‐sedimentological study of basins along an active margin

AbstractThe formation processes of the late Neogene sedimentary basins in Northern Hokkaido have been investigated on the basis of rock magnetism, structural geology and numerical modelling. Untilted site‐mean directions of remanent magnetization of the Wakkanai Formation, obtained from oriented core samples in Horonobe, suggest remarkable counterclockwise block rotation (ca. 70°) since the late Neogene. Uniform microscopic fabric of the siliceous sediments was inferred from the alignment of the principal axes of the anisotropy of magnetic susceptibility (AMS). After correction for tectonic rotation, the maximum axis of AMS, which reflects the sedimentary fabric of the dominant paramagnetic minerals, is in an E‐W direction, which is concordant with the influx direction of diatomaceous particles into the N‐S elongate sedimentary basins. The difference in the bulk initial magnetic susceptibility of the siliceous sediments of the Wakkanai Formation between the depocenter of the basin and its peripheral part implies that terrigenous non‐magnetic fraction has been sorted out during transportation of the detrital grains as gravity flows. As for the development mechanism of the N‐S elongate late Neogene basins in Northern Hokkaido, their depocenter arrangement and subsidence pattern indicates dextral motions upon a longitudinal fault zone along the Eurasian convergent margin. Dislocation modelling was adopted to explain vertical displacement and rotational motion around the study area and successfully restored the deformation pattern based on the assumption of dextral slip at a left‐stepping part of a strand of the transcurrent fault.