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Miocene
Kinds of Miocene Selected AbstractsTHE RESERVOIR POTENTIAL OF MIOCENE CARBONATE ROCKS IN THE ASKALE AND HINIS-MUS-VAN SUB-BASINS, EAST ANATOLIA, TURKEYJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2003A. G. Büyükutku Lower-middle Miocene limestones in East Anatolia (eastern Turkey) assigned to the Adilcevaz Formation were studied using core and cuttings data from eight wells in the Tertiary Askale and Hinis-Mus-Van sub-basins. Their depositional environment, diagenetic characteristics and reservoir quality are reviewed. The Adilcevaz Formation carbonates are up to 225m thick. Abundant bioclasts are dominated by corals, encrusting red algae, bryozoans, and benthonic and planktonic foraminifera. Reef-core, fore-reef and back-reef facies were recognized. The preservation of primary porosity is generally poor as a result of late calcite cementation. Porosity is mainly present as moulds, vugs and interparticle types, which are best developed in the fore-reef and reef-core facies. However these pores are poorly connected and permeability is generally less than 0.1 mD. In contrast to coeval limestones of similiar facies in Iran, Iraq and other parts of the Middle East, the Adilcevaz Formation has little reservoir potential. [source] A NEW AMPHICYONINE (CARNIVORA: AMPHICYONIDAE) FROM THE UPPER MIOCENE OF BATALLONES-1, MADRID, SPAINPALAEONTOLOGY, Issue 4 2008STÉPHANE PEIGNÉ Abstract:, The vertebrate community of the late Miocene locality of Batallones-1, Madrid Province, Spain, is mainly composed of mammals of the order Carnivora, which represents 98 per cent of the total number of macro-mammal fossils. Here, we describe craniodental remains of approximately 12 individuals of a new, highly specialized member of the Amphicyonidae, previously assigned to Amphicyon sp. cf. A. castellanus. A phylogenetic analysis of Amphicyoninae shows that this new form, named Magericyon anceps gen. et sp. nov., is markedly distinct from all other known Amphicyoninae, specifically in its hypercarnivorous features (strongly compressed upper canines, absence of dP1/dp1 and P2/p2, single-rooted p3, absence of a metaconid on the lower molars, and reduction of M2 relative to M1). [source] TRACING BACK THE ORIGIN OF THE INDO-PACIFIC MOLLUSC FAUNA: BASAL TRIDACNINAE FROM THE OLIGOCENE AND MIOCENE OF THE SULTANATE OF OMANPALAEONTOLOGY, Issue 1 2008MATHIAS HARZHAUSER Abstract:, Two new tridacnine species are described from the Chattian and Aquitanian of the Arabian Peninsula. For these, the new names Omanidacna eos gen. et sp. nov. and Tridacna evae sp. nov. are erected. Omanidacna is interpreted as an Oligocene ancestor of Hippopus, being the oldest record of this tridacnine lineage. The Aquitanian Tridacna evae is the first occurrence of the genus Tridacna. These Arabian taxa imply that the modern tridacnine lineages are rooted in the Palaeogene and early Neogene of the East African-Arabian Province, although their Eocene ancestors, such as Byssocardium, are Western Tethyan taxa. During the Neogene they successfully settled the Indo-Polynesian Province and became typical elements of the entire Indo-West Pacific Region. The tridacnines are thus an example of a successive transformation and gradual eastward dispersal of an originally Tethyan element contributing to late Neogene diversity in the Indo-West Pacific. [source] NEW SPECIES OF PARAPHIOMYS (RODENTIA, THRYONOMYIDAE) FROM THE LOWER MIOCENE OF AS-SARRAR, SAUDI ARABIAPALAEONTOLOGY, Issue 2 2005RAQUEL LÓPEZ ANTOÑANZAS Abstract:, The family Thryonomyidae is represented in the Lower Miocene of Saudi Arabia by a single species, Paraphiomys knolli sp. nov. This new taxon differs from all other thryonomyids in being small, lower molars having a short metalophulid II and an isolated anterolabial cuspid, and upper molars being antero-posteriorly compressed and pentalophodont. A cladistic analysis involving all extinct and extant species of thryonomyids is provided. Paraphiomys knolli branches as the sister-species of Paraphiomys pigotti, type species of the genus. [source] Quantitative reconstruction of Late Cenozoic landscapes: a case study in the Sierra de Atapuerca (Burgos, Spain)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2008Alfonso Benito-Calvo Abstract We have developed a method to reconstruct palaeorelief by means of detailed geomorphological and geological studies, geostatistical tools, GIS and a DEM. This method has been applied to the Sierra de Atapuerca (NE Duero Basin, Burgos, Spain), allowing us to model a three-dimensional reconstruction of the relief evolution from the Middle Miocene to the present. The modelling procedure is based on geostatistical recovery of the palaeosurfaces characteristic of each geomorphological evolution stage, using polynomial regressions, trend surfaces and kriging. The modelling of morphology trends has been useful in establishing new geological and geomorphological relationships in the geodynamic evolution of this basin, such as uplift quantification, correlation of erosion surfaces and sedimentary units, and the evolution of fluvial base levels. The palaeosurface reconstruction together with an analysis of the slope retreat have allowed us to reconstruct the palaeoreliefs that define the Late Cenozoic landscape evolution of this area, where the Lower and Middle Pleistocene archaeopalaeontological sites of the Sierra de Atapuerca are located. Copyright © 2007 John Wiley & Sons, Ltd. [source] Geochronological evidence for pervasive Miocene weathering, Minas Gerais, BrazilEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2004Isabela de O. Carmo Abstract 40Ar/39Ar laser incremental-heating analyses of 22 individual grains of supergene cryptomelane from three weathering pro,les, up to 400 km apart, in the Rio Doce valley and Barbacena regions at Minas Gerais, Brazil, show that the formation of weathering pro,les in these regions is contemporaneous, suggesting a strong weathering event in the Middle to Late Miocene (10,8 Ma). The preservation of these Miocene samples at or near the present surface suggests that either erosion rates have been very low in the region since the Miocene or that a much thicker weathering mantle was present in the region originally. Assuming a constant thickness of weathering pro,les in the region throughout the Tertiary, we may calculate weathering front propagation rates of 4,8 m Myr,1 during the past 10 Ma. Copyright © 2004 John Wiley & Sons, Ltd. [source] Tooth row counts, vicariance, and the distribution of the sand tiger shark Carcharias taurusECOGRAPHY, Issue 5 2003Luis O. Lucifora Geographic variation in tooth row counts among sand tiger sharks Carcharias taurus (Chondrichthyes), from the SW Atlantic, NW Atlantic and the East China Sea is analyzed in this paper. We found significant differences between sand tigers from the SW Atlantic (Southern Hemisphere population) and each of the other two (Northern Hemisphere) regions in the number of upper lateral tooth rows, and between individuals from the SW Atlantic and the East China Sea in the total number of upper tooth rows. Sand tiger sharks from the two Northern Hemisphere populations did not differ in any of the studied variables. Our results agree with comparisons of vertebral counts between sand tiger sharks from Southern and Northern Hemispheres. Both lines of evidence suggest that Southern and Northern Hemisphere populations of C. taurus were isolated to a larger extent than populations of the Northern Hemisphere. The fossil record of the genus Carcharias begins in the Early Cretaceous and C. taurus is certainly known since the Late Miocene. During the Miocene, the Tethys Sea separating northern and southern land masses was still present and it provided a continuous temperate shallow sea that could allow dispersal of sand tiger sharks along Northern Hemisphere seas. Independent observations on the distribution and evolutionary history of the genera Myripristis, Neoniphon, Sargocentron and Aphanius, and genetic studies on the temperate shark genus Mustelus that indicate a close relationship between the Indo-Pacific M. manazo and the Mediterranean M. asterias suggest that this hypothesis is plausible and deserves to be tested. [source] Subsurface microbiology and biogeochemistry of a deep, cold-water carbonate mound from the Porcupine Seabight (IODP Expedition 307)ENVIRONMENTAL MICROBIOLOGY, Issue 1 2009Gordon Webster Summary The Porcupine Seabight Challenger Mound is the first carbonate mound to be drilled (,270 m) and analyzed in detail microbiologically and biogeochemically. Two mound sites and a non-mound Reference site were analyzed with a range of molecular techniques [catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH), quantitative PCR (16S rRNA and functional genes, dsrA and mcrA), and 16S rRNA gene PCR-DGGE] to assess prokaryotic diversity, and this was compared with the distribution of total and culturable cell counts, radiotracer activity measurements and geochemistry. There was a significant and active prokaryotic community both within and beneath the carbonate mound. Although total cell numbers at certain depths were lower than the global average for other subseafloor sediments and prokaryotic activities were relatively low (iron and sulfate reduction, acetate oxidation, methanogenesis) they were significantly enhanced compared with the Reference site. In addition, there was some stimulation of prokaryotic activity in the deepest sediments (Miocene, > 10 Ma) including potential for anaerobic oxidation of methane activity below the mound base. Both Bacteria and Archaea were present, with neither dominant, and these were related to sequences commonly found in other subseafloor sediments. With an estimate of some 1600 mounds in the Porcupine Basin alone, carbonate mounds may represent a significant prokaryotic subseafloor habitat. [source] EVOLUTION OF SUBTERRANEAN DIVING BEETLES (COLEOPTERA: DYTISCIDAE HYDROPORINI, BIDESSINI) IN THE ARID ZONE OF AUSTRALIAEVOLUTION, Issue 12 2003Remko Leys Abstract Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification. [source] Rudabánya: A late miocene subtropical swamp deposit with evidence of the origin of the African apes and humansEVOLUTIONARY ANTHROPOLOGY, Issue 2 2002László Kordos Abstract Rudabánya, a rich late Miocene fossil site in northern central Hungary, has yielded an abundant record of fossil primates, including the primitive catarrhine Anapithecus and the early great ape Dryopithecus. While the affinities of Anapithecus are not clear, Dryopithecus is clearly a great ape sharing numerous characteristics of its dental, cranial and postcranial anatomy with living great apes. Like all Miocene hominids (great apes and humans), Dryopithecus is more primitive in a number of ways than any living hominid, which is probably related to the passage of time since the divergence of the various lineages of living hominids, allowing for similar refinements in morphology and adaptation to take place independently. On the other hand, Dryopithecus (and Ouranopithecus) share derived characters with hominines (African apes and humans), and Sivapithecus (and Ankarapithecus) share derived characters with orangutans, thus dating the split between pongines and hominines to a time before the evolution of these fossil great apes. Pongines and hominines follow similar fates in the late Miocene, the pongines moving south into Southeast Asia from southern or eastern Asia and the hominines moving south into East Africa from the Mediterranean region, between 6 to 9 Ma. [source] SYNTHESIS: Evolutionary history of Pacific salmon in dynamic environmentsEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 2 2008Robin S. Waples Abstract Contemporary evolution of Pacific salmon (Oncorhynchus spp.) is best viewed in the context of the evolutionary history of the species and the dynamic ecosystems they inhabit. Speciation was complete by the late Miocene, leaving c. six million years for intraspecific diversification. Following the most recent glacial maximum, large areas became available for recolonization. Current intraspecific diversity is thus the product of recent evolution overlaid onto divergent historical lineages forged during recurrent episodes of Pleistocene glaciation. In northwestern North America, dominant habitat features have been relatively stable for the past 5000 years, but salmon ecosystems remain dynamic because of disturbance regimes (volcanic eruptions, landslides, wildfires, floods, variations in marine and freshwater productivity) that occur on a variety of temporal and spatial scales. These disturbances both create selective pressures for adaptive responses by salmon and inhibit long-term divergence by periodically extirpating local populations and creating episodic dispersal events that erode emerging differences. Recent anthropogenic changes are replicated pervasively across the landscape and interrupt processes that allow natural habitat recovery. If anthropogenic changes can be shaped to produce disturbance regimes that more closely mimic (in both space and time) those under which the species evolved, Pacific salmon should be well-equipped to deal with future challenges, just as they have throughout their evolutionary history. [source] Piceoxylon pseudotsugae GOTHAN emend.FEDDES REPERTORIUM, Issue 1 2001Deutschland, VAN DER BURGH aus dem Obermiozän von Ottendorf-Okrilla bei Dresden 1987 konnte im Westteil der Kiesgrube Ottendorf-Okrilla (höheres Obermiozän) aus Tonen mit kohligen Schmitzen ein 1,14 m langer Stammrest geborgen werden. Er wird als Piceoxylon pseudotsugae Gothan 1906 emend, van der Burgh (1973) bestimmt. Das fossile Holz zeigt große Ähnlichkeit mit der heute noch im pazifischen Nordamerika beheimateten Pseudotsuga menziesii (Mirb.) Franco. Xylotomische Nachweise dieser Art sind bis heute nur wenige bekannt. Sie stammen aus Nordamerika, Deutschland (Rheinland), Österreich und Slask (Schlesien/Polen). Zu der anatomischen Beschreibung des Holzes wird die Ökologie der rezenten und die Paläookologie der fossilen Pseudotsuga diskutiert. Piceoxylon pseudotsugae Gothan emend. Van der Burgh from the Upper Miocene from Ottendorf-Okrilla near Dresden, Germany. A fossil wood, collected in Ottendorf-Okrilla by H. Kubasch, Kamenz, is described in this paper. It is identified by the first author as Piceoxylon pseudotsugae Gothan 1906 emend, van der Burgh 1973 because of its clear spiral thickenings in the tracheids (early and late wood) together with vertical and horizontal resin ducts. Tertiary wood assigned to this species is up till now only known from a few localities in North America and Europe (Rheinland/Germany, Austria, Silesia/Poland). The recent comparable species, Pseudotsuga menziesii (Mirb.) Franco, is known from a wide variety of localities in North America, with a very variable range concerning temperature. It is a tree of well drained, slightly acidic soils, preferably on sedimentary rocks with a volcanic or glacial origin. In the Tertiary of Europe this tree is also known from brown coal deposits. Therefore, for the Tertiary species a habitat in swamp environment must be added. [source] Lebensspuren holzzerstörender Organismen an fossilen Hölzern aus dem Tertiär der Insel Lesbos, GriechenlandFOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 1 2001Herbert Süss Abstract Lebensspuren (Schadbilder) holzzerstörender Organismen an fossilen Holzresten aus dem Untermiozän von Lesbos (Griechenland) werden beschrieben. Von pflanzlichen Holzzerstörern konnten Bakterien, imperfekte Pilze, Weiß- und Braunfäulepilze und in das Holz eingewachsene Wurzeln nachgewiesen werden. Von tierischen Holzzerstörern wurden Termitenfraß, durch Pflanzensauger (Homopteren) verursachtes Wundgewebe, Larvenfraß der Kambium-Minierfliege Palaeophytobia (Agromyzidae, Diptera) und Fraßgänge mit Koprolithen verschiedener Käferarten (Anobiiden?) und Milben (Acari) gefunden. Außerdem werden durch Kristallisationsvorgänge im Holz verursachte kugelförmige Gebilde beschrieben. Traces of wood destroying organisms on fossil wood from the Lower Miocene of Lesbos (Greece) are described. Among nonanimal wood destroyers evidence is presented of bacteria, Fungi imperfecti, whiterot and brownrot fungus and penetrating roots. Animal wood destroyers include termite feeding traces, wound tissues produced by plant suckers (Homoptera), larval feeding traces of the cambium miner Palaeophytobia (Agromyzidae, Diptera) and feeding channels, with coprolites, of several beetle species (Anobiidae?) and Mites (Acari). In addition globe-like structures produced in the wood through crystallization processes are described. [source] Ribosomal RNA gene fragments from fossilized cyanobacteria identified in primary gypsum from the late Miocene, ItalyGEOBIOLOGY, Issue 2 2010G. PANIERI Earth scientists have searched for signs of microscopic life in ancient samples of permafrost, ice, deep-sea sediments, amber, salt and chert. Until now, evidence of cyanobacteria has not been reported in any studies of ancient DNA older than a few thousand years. Here, we investigate morphologically, biochemically and genetically primary evaporites deposited in situ during the late Miocene (Messinian) Salinity Crisis from the north-eastern Apennines of Italy. The evaporites contain fossilized bacterial structures having identical morphological forms as modern microbes. We successfully extracted and amplified genetic material belonging to ancient cyanobacteria from gypsum crystals dating back to 5.910,5.816 Ma, when the Mediterranean became a giant hypersaline brine pool. This finding represents the oldest ancient cyanobacterial DNA to date. Our clone library and its phylogenetic comparison with present cyanobacterial populations point to a marine origin for the depositional basin. This investigation opens the possibility of including fossil cyanobacterial DNA into the palaeo-reconstruction of various environments and could also be used to quantify the ecological importance of cyanobacteria through geological time. These genetic markers serve as biosignatures providing important clues about ancient life and begin a new discussion concerning the debate on the origin of late Miocene evaporites in the Mediterranean. [source] Origin and geochemistry of Miocene marine evaporites associated with red beds: Great Kavir Basin, Central IranGEOLOGICAL JOURNAL, Issue 1 2007Hossain Rahimpour-Bonab Abstract During the Cenozoic numerous shallow epicontinental evaporite basins formed due to tectonic movements in the Northern Province of the Central Iran Tectonic Zone (the Great Kavir Basin). During the Miocene, due to sea-level fluctuations, thick sequences of evaporites and carbonates accumulated in these basins that subsequently were overlain by continental red beds. Development of halite evaporites with substantial thickness in this area implies inflow of seawater along the narrow continental rift axis. The early ocean basin development was initiated in Early Eocene time and continued up to the Middle Miocene in the isolated failed rift arms. Competition between marine and non-marine environments, at the edge of the encroaching sea, produced several sequences of both abrupt and gradual transition from continental wadi sediments to marginal marine evaporites in the studied area. These evaporites show well-preserved textures indicative of relatively shallow-brine pools. The high Br content of these evaporites indicates marine-derived parent brines that were under the sporadic influence of freshening by meteoric water or replenishing seawater. However, the association of hopper and cornet textures denotes stratified brine that filled a relatively large pool and prevented rapid variations in the Br profile. Unstable basin conditions that triggered modification of parent brine chemistry prevailed in this basin and caused variable distribution patterns for different elements in the chloride units. The presence of sylvite and the absence of Mg-sulphate/chlorides in the paragenetic sequence indicate SO4,depleted parent brine in the studied sequence. Petrographic examinations along with geochemical analyses on these potash-bearing halites reveal parental brines which were a mixture of seawater and CaCl2 -rich brines. The source of CaCl2 -rich brines is ascribed to the presence of local rift systems in the Great Kavir Basin up to the end of the Early Miocene. Copyright © 2007 John Wiley & Sons, Ltd. [source] Stratigraphy and volcanology of the Türkbükü volcanics: products of a stratovolcano in the Bodrum Peninsula, SW AnatoliaGEOLOGICAL JOURNAL, Issue 2 2006Zekiye Karacik Abstract The Middle-Upper Miocene Bodrum magmatic complex of the Aegean region, southwestern Turkey, is mainly represented by intermediate stocks, lavas, pyroclastic and volcaniclastic deposits. Monzonitic stocks and connected porphyry intrusions and extrusions are the first products of the magmatism. These are followed by a volcanic succession consisting of andesitic-latitic lavas, autobrecciated lavas, pyroclastic and volcaniclastic deposits. The final stage is represented by basaltic and basaltic andesitic flows and dykes intruded into previous units. The volcanic succession crops out in the northern part of the Bodrum peninsula. In the lower part of this succession are widespread pyroclastic deposits, composed of pyroclastic fall and flow units, alternating with epiclastic deposits. Grain size, volume and thickness of the pyroclastic deposits were mainly controlled by the type, magnitude and intensity of the eruption. Further up the section, there are two horizons of debris avalanche deposits forming the coarsest and thickest deposits of the volcaniclastic succession. The debris avalanche deposits indicate at least two different flank collapses coeval with the volcanism. The stratigraphy and map pattern of these volcanic units imply that the northern part of the Bodrum peninsula was the north-facing flank of a stratovolcano during the mid-Late Miocene. Copyright © 2006 John Wiley & Sons, Ltd. [source] Evidence for two episodes of volcanism in the Bigadiç borate basin and tectonic implications for western TurkeyGEOLOGICAL JOURNAL, Issue 5 2005Fuat Erkül Abstract Western Turkey has been dominated by N,S extension since the Early Miocene. The timing and cause of this N,S extension and related basin formation have been the subject of much debate, but new data from the Bigadiç borate basin provide insights that may solve this controversy. The basin is located in the Bornova Flysch Zone, which is thought to have formed as a major NE-trending transform zone during Late Cretaceous-Palaeocene collisional Tethyan orogenesis and later reactivated as a transfer zone of weakness, and which separates two orogenic domains having different structural evolutions. Volcanism in the Bigadiç area is characterized by two rock units that are separated by an angular unconformity. These are: (1) the Kocaiskan volcanites that gives K/Ar ages of 23,Ma, and (2) the Bigadiç volcano-sedimentary succession that yields ages of 20.6 to 17.8,Ma. Both units are unconformably overlain by Upper Miocene-Pliocene continental deposits. The Kocaiskan volcanites are related to the first episode of volcanic activity and comprise thick volcanogenic sedimentary rocks derived from subaerial andesitic intrusions, domes, lava flows and pyroclastic rocks. The second episode of volcanic activity, represented by basaltic to rhyolitic lavas and pyroclastic rocks, accompanied lacustrine,evaporitic sedimentation. Dacitic to rhyolitic volcanic rocks, called the S,nd,rg, volcanites, comprise NE-trending intrusions producing lava flows, ignimbrites, ash-fall deposits and associated volcanogenic sedimentary rocks. Other NE-trending olivine basaltic (Gölcük basalt) and trachyandesitic (Kay,rlar volcanites) intrusions and lava flows were synchronously emplaced into the lacustrine sediments. The intrusions typically display peperitic rocks along their contacts with the sedimentary rocks. It is important to note that the Gölcük basalt described here is the first recorded Early Miocene alkali basalt in western Turkey. The oldest volcanic episode occurred in the NE-trending zone when the region was still experiencing N,S compression. The angular unconformity between the two volcanic episodes marks an abrupt transition from N,S collision-related convergence to N,S extension related to retreat of the Aegean subduction zone to the south along an extensional detachment. Thrust faults with top-to-the-north sense of shear and a series of anticlines and synclines with subvertical NE-striking axial planes observed in the Bigadiç volcano-sedimentary succession suggest that NW,SE compression was reactivated following sedimentation. Geochemical data from the Bigadiç area also support the validity of the extensional regime, which was characterized by a bimodal volcanism related to extrusion of coeval alkaline and calc-alkaline volcanic rocks during the second volcanic episode. The formation of alkaline volcanic rocks dated as 19.7,±,0.4,Ma can be related directly to the onset of the N,S extensional regime in western Turkey. Copyright © 2005 John Wiley & Sons, Ltd. [source] Major neotectonic features of eastern Marmara region, Turkey: development of the Adapazar,,Karasu corridor and its tectonic significanceGEOLOGICAL JOURNAL, Issue 2 2004nç Yi Abstract Eastern Marmara region consists of three different morphotectonic units: Thrace,Kocaeli Peneplain (TKP) and Çamda,,Akçakoca Highland (ÇAH) in the north, and Armutlu,Almac,k Highland in the south of the North Anatolian Fault Zone (NAFZ). The geologic-morphologic data and seismic profiles from the Sakarya River offshore indicate that the boundary between the TKP in the west and ÇAH in the east is a previously unrecognized major NNE,SSW-trending strike-slip fault zone with reverse component. The fault zone is a distinct morphotectonic corridor herein named the Adapazar,,Karasu corridor (AKC) that runs along the Sakarya River Valley and extends to its submarine canyon along the southern margin of the Black Sea in the north. It formed as a transfer fault zone between the TKP and ÇAH during the Late Miocene; the former has been experiencing extensional forces and the latter compressional forces since then. East,West-trending segments of the NAFZ cuts the NE,SW-trending AKC and their activity has resulted in the formation of a distinct fault-bounded morphology, which is characterized by alternating E,W highlands and lowlands in the AKC. Furthermore, this activity has resulted in the downward motion of an ancient delta and submarine canyon of the Sakarya River in the northern block of the NAFZ below sea level so that the waters of the Black Sea invaded them. The NE,SW-trending faults in the AKC were reactivated with the development of the NAFZ in the Late Pliocene, which then caused block motions and microseismic activities throughout the AKC. Copyright © 2004 John Wiley & Sons, Ltd. [source] Insights into biaxial extensional tectonics: an examplefrom the Sand,kl, Graben, West Anatolia, TurkeyGEOLOGICAL JOURNAL, Issue 1 2003Mustafa Cihan Abstract West Anatolia, together with the Aegean Sea and the easternmost part of Europe, is one of the best examples of continental extensional tectonics. It is a complex area bounded by the Aegean,Cyprus Arc to the south and the North Anatolian Fault Zone (NAFZ) to the north. Within this complex and enigmatic framework, the Sand,kl, Graben (10,km wide, 30,km long) has formed at the eastern continuation of the Western Anatolian extensional province at the north-northwestward edge of the Isparta Angle. Recent studies have suggested that the horst,graben structures in West Anatolia formed in two distinct extensional phases. According to this model the first phase of extension commenced in the Early,Middle Miocene and the last, which is accepted as the onset of neotectonic regime, in Early Pliocene. However, it is controversial whether two-phase extension was separated by a short period of erosion or compression during Late Miocene,Early Pliocene. Both field observations and kinematic analysis imply that the Sand,kl, Graben has existed since the Late Pliocene, with biaxial extension on its margins which does not necessarily indicate rotation of regional stress distribution in time. Although the graben formed later in the neotectonic period, the commencement of extension in the area could be Early Pliocene (c. 5,Ma) following a severe but short time of erosion at the end of Late Miocene. The onset of the extensional regime might be due to the initiation of westward motion of Anatolian Platelet along the NAFZ that could be triggered by the higher rate of subduction at the east Aegean,Cyprus Arc in the south of the Aegean Sea. Copyright © 2003 John Wiley & Sons, Ltd. [source] The Romagna Apennines, Italy: an eroded duplexGEOLOGICAL JOURNAL, Issue 1 2001A. Cerrina Feroni Abstract The study of clast composition carried out on the alluvial gravels of the Romagna Apennines of northern Italy has provided evidence for an extensive covering of allochthonous units (Ligurian nappe and Epiligurian succession) above the Miocene foredeep deposits (Marnoso-Arenacea Formation), which has been subsequently eroded during the Late Miocene,Pleistocene uplift. This result is confirmed by the burial history outlined in the Marnoso-Arenacea Formation through vitrinite reflectance and apatite fission-track analyses. The Romagna Apennines represent, therefore, a regional tectonic window where the thrust system that displaced the Marnoso-Arenacea Formation crops out. The geometric relations between this thrust system and the basal thrust of the Ligurian nappe, exposed at the boundaries of the Romagna Apennines (Sillaro Zone and Val Marecchia klippe), are consistent with a duplex structure. Thus, the Romagna Apennines thrust system is an eroded duplex. The duplex roof-thrust corresponds to the surface of the synsedimentary overthrust of the Ligurian nappe on the Marnoso-Arenacea Formation; the floor-thrust is located in the pelagic pre-foredeep deposits (Schlier Formation). Copyright © 2001 John Wiley & Sons, Ltd. [source] A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New ZealandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Donna Eberhart-Phillips Summary The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S,P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130 km are included, parts of the model are well-resolved to depths of 100 km. The crustal features are generally consistent with geology. The low velocity in the upper 10 km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40 km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4 km s,1 at 15 km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80 km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate. [source] Small mammal (rodents and lagomorphs) European biogeography from the Late Oligocene to the mid PlioceneGLOBAL ECOLOGY, Issue 4 2007Olivier Maridet ABSTRACT Aim, To analyse the fossil species assemblages of rodents and lagomorphs from the European Neogene in order to assess what factors control small mammal biogeography at a deep-time evolutionary time-scale. Location, Western Europe: 626 fossil-bearing localities located within 31 regions and distributed among 18 successive biochronological units ranging from c. 27 Ma (million years ago; Late Oligocene) to c. 3 Ma (mid Pliocene). Methods, Taxonomically homogenized pooled regional assemblages are compared using the Raup and Crick index of faunal similarity; then, the inferred similarity matrices are visualized as neighbour-joining trees and by projecting the statistically significant interregional similarities and dissimilarities onto palaeogeographical maps. The inferred biogeographical patterns are analysed and discussed in the light of known palaeogeographical and palaeoclimatic events. Results, Successive time intervals with distinct biogeographical contexts are identified. Prior to c. 18 Ma (Late Oligocene and Early Miocene), a relative faunal homogeneity (high interregional connectivity) is observed all over Europe, a time when major geographical barriers and a weak climatic gradient are known. Then, from the beginning of the Middle Miocene onwards, the biogeography is marked by a significant decrease in interregional faunal affinities which matches a drastic global climatic degradation and leads, in the Late Miocene (c. 11 Ma), to a marked latitudinal pattern of small mammal distribution. In spite of a short rehomogenization around the Miocene/Pliocene boundary (6,4 Ma), the biogeography of small mammals in the mid Pliocene (c. 3 Ma) finally closely reflects the extant situation. Main conclusions, The resulting biogeographical evolutionary scheme indicates that the extant endemic situation has deep historical roots corresponding to global tectonic and climatic events acting as primary drivers of long-term changes. The correlation of biogeographical events with climatic changes emphasizes the prevalent role of the climate over geography in generating heterogeneous biogeographical patterns at the continental scale. [source] Tectonic control of erosion and sedimentation in the Amazon Basin of BoliviaHYDROLOGICAL PROCESSES, Issue 22 2009Patrice Baby Abstract The western Amazon drainage basin, which extends from southern Colombia to northern Bolivia, comprises the Cordillera Oriental of the Andes and its adjacent foreland basin system. In northern Bolivia, the orogenic wedge of the eastern Andes is very large, and its forward propagation controls the morphology of the Madeira drainage basin. We consider here the erosion and sedimentation mass balance in this part of the Amazon Basin, estimated on the basis of recent sediment yield data, within the current tectonic and geomorphic framework. The total suspended sediment (TSS) flux exported from the present orogenic wedge of northern Bolivia has been estimated at 500,600 million t year,1. More than 50% of the total sediment load crossing the Madeira foreland basin system is deposited. The rest of the sediments (less than 46%) reaches the eastern Amazon Basin, bypassing the Brazilian craton to the north. The average mass of sediment that has been deposited from the late Miocene to the present in the Madeira foreland basin sedimentation system is less than that intercepted today, by a factor of about 2·4. These results can be interpreted as an increase in Bolivian foreland basin flexural subsidence over time, associated with crust thickening and orogenic loading, and accentuated by the growing mass of retained sediments. They are consistent with the uplift rates of the Cordillera Oriental, obtained from fission-track dating, which began increasing significantly around 10,15 Ma. Copyright © 2009 John Wiley & Sons, Ltd. [source] A dwarf species of the Phalacrocoracoidea (cormorants and anhingas) from the early Miocene of GermanyIBIS, Issue 2 2009GERALD MAYR A tarsometatarsus of a diminutive representative of the Phalacrocoracoidea, the clade including the Phalacrocoracidae (cormorants) and Anhingidae (anhingas), is described from the early Miocene of Germany. The fossil is assigned to a new species Limicorallus (?) carbunculus, and closely resembles the tarsometatarsus of extant Phalacrocoracidae in overall morphology. Limicorallus (?) carbunculus is the smallest representative of the Phalacrocoracoidea, reaching only two-thirds the size of the extant Pygmy Cormorant Phalacrocorax pygmeus. By significantly lowering the minimum size of the Phalacrocoracoidea, this new species adds to our knowledge of the early diversity of this clade. [source] A stem lineage representative of buttonquails from the Lower Oligocene of Germany , fossil evidence for a charadriiform origin of the TurnicidaeIBIS, Issue 4 2007GERALD MAYR A new species of the charadriiform taxon Turnipax Mayr, 2000 is described from the Lower Oligocene fossil site Frauenweiler in southern Germany. The postcranial skeleton assigned to Turnipax oechslerorum sp. nov. is very well preserved and allows the recognition of significant, previously unknown osteological details of Turnipax, especially concerning the wing and pectoral girdle bones. We provide evidence that Turnipax is a stem lineage representative of the Turnicidae (buttonquails) and synonymize Turnipacidae Mayr, 2000 with Turnicidae Gray, 1840. Turnipax is the earliest fossil representative of the Turnicidae, which otherwise have no Paleogene fossil record. Because recent molecular studies support a charadriiform origin of buttonquails, the mosaic distribution in the skeleton of Turnipax of derived features of the Turnicidae and non-turnicid charadriiform birds is of particular interest. Turnipax exhibits a more plesiomorphic morphology than extant Turnicidae, and we assume that its habitat and way of living differed from that of crown group Turnicidae, which may not have diversified before the spread of grasslands during the Oligocene and Miocene. [source] Structure of Sumatra and its implications for the tectonic assembly of Southeast Asia and the destruction of PaleotethysISLAND ARC, Issue 1 2009Anthony J. Barber Abstract It is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous,Early Permian ,pebbly mudstones' interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar. [source] Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructionsISLAND ARC, Issue 4 2006Ken Sawada Abstract Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo-Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (,13C) of kerogen macerals increased from ,28, to ,25, from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C4 plants into southwest Japan. The timing was concordant with that of the expansion of C4 plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C27,C29) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates-dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C26 norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of ,13C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C4 plants was possibly associated with the high production of diatom in the shallow-marine areas of the paleo-Japan Sea during the Neogene Period. [source] Evolution of an accretionary complex along the north arm of the Island of Sulawesi, IndonesiaISLAND ARC, Issue 1 2004Yusuf Surachman Djajadihardja Abstract Seismic reflections across the accretionary prism of the North Sulawesi provide excellent images of the various structural domains landward of the frontal thrust. The structural domain in the accretionary prism area of the North Sulawesi Trench can be divided into four zones: (i) trench area; (ii) Zone A; (iii) Zone B; and (iv) Zone C. Zone A is an active imbrication zone where a decollement is well imaged. Zone B is dominated by out-of-sequence thrusts and small slope basins. Zone C is structurally high in the forearc basin, overlain by a thick sedimentary sequence. The subducted and accreted sedimentary packages are separated by the decollement. Topography of the oceanic basement is rough, both in the basin and beneath the wedge. The accretionary prism along the North Sulawesi Trench grew because of the collision between eastern Sulawesi and the Bangai,Sula microcontinent along the Sorong Fault in the middle Miocene. This collision produced a large rotation of the north arm of Sulawesi Island. Rotation and northward movement of the north arm of Sulawesi may have resulted in southward subduction and development of the accretionary wedge along North Sulawesi. Lateral variations are wider in the western areas relative to the eastern areas. This is due to greater convergence rates in the western area: 5 km/My for the west and 1.5 km/My for the east. An accretionary prism model indicates that the initiation of growth of the accretionary prism in the North Sulawesi Trench occurred approximately 5 Ma. A comparison between the North Sulawesi accretionary prism and the Nankai accretionary prism of Japan reveals similar internal structures, suggesting similar mechanical processes and structural evolution. [source] Long-term changes in distribution and chemistry of middle Miocene to Quaternary volcanism in the Chokai-Kurikoma area across the Northeast Japan ArcISLAND ARC, Issue 1 2004Hirofumi Kondo Abstract To understand the characteristics of long-term spatial and temporal variation in volcanism within a volcanic arc undergoing constant subduction since the cessation of back-arc opening, a detailed investigation of middle Miocene to Quaternary volcanism was carried out within the Chokai-Kurikoma area of the Northeast Japan Arc. This study involved a survey of available literature, with new K,Ar and fission track dating, and chemical analyses. Since 14 Ma, volcanism has occurred within the Chokai-Kurikoma area in specific areas with a ,branch-like' pattern, showing an east,west trend. This is in marked contrast to the widespread distribution of volcanism with a north,south trend in the 20,14 Ma period. The east,west- trending ,branches' are characterized by regular intervals (50,100 km) of magmatism along the arc. These branches since 14 Ma are remarkably discrepant to the general northwest,southeast or north-northeast,south-southwest direction of the crustal structures that have controlled Neogene to Quaternary tectonic movements in northeast Japan. In addition, evidence indicating clustering and focusing of volcanism into smaller regions since 14 Ma was verified. Comparison of the distribution and chemistry of volcanic rocks for three principal volcanic stages (11,8, 6,3 and 2,0 Ma) revealed that widely but sparsely distributed volcanic rocks had almost the same level of alkali and incompatible element concentrations throughout the area (with the exception of Zr) in the 11,8 Ma stage. However, through the 6,3 Ma stage to the 2,0 Ma stage, the concentration level in the back-arc cluster increased, while that in the volcanic front cluster remained almost constant. Therefore, the degree of partial melting has decreased, most likely with a simultaneous increase in the depth of magma segregation within the back-arc zone, whereas within the volcanic front zone, the conditions of magma generation have changed little over the three stages. In conclusion, the evolution of the thermal structure within the mantle wedge across the arc since 14 Ma has reduced the extent of ascending mantle diapirs into smaller fields. This has resulted in the tendency for the distribution of volcanism to become localized and concentrated into more specific areas in the form of clusters from the late Miocene to Quaternary. [source] Rock magnetism and paleomagnetic stratigraphy of forearc sediments of the Japan Trench, ODP Sites 1150 and 1151ISLAND ARC, Issue 1 2004Toshiya Kanamatsu Abstract Magnetic measurements were carried out to investigate rock magnetic properties and paleomagnetic directions of late and middle Miocene sediments recovered from the land side of the Japan Trench during the Ocean Drilling Program Leg 186. Because the low coercive component in natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization shows that the drilling-induced magnetization is severe in the sections obtained by the advanced hydraulic piston coring method, careful analyses of demagnetization of NRM using the ,demagnetization plane' were carried out to decompose the direction and intensity. Magnetostratigraphic correlation down to the upper Miocene, supplemented by biostratigraphic data, revealed that the sedimentation rates are characterized by drastic changes, with the early Pliocene having the highest rate. This high sedimentation rate is related to the subsidence of the southern deep-sea terrace of the Japan Trench. [source] | |||||||||||||||||||||||||||||||||||||