Browsing by Subject "Submarine geology"

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    Sequence stratigraphy, tectonics and depositional history in eastern Thrace Basin, NW Turkey
    (2000) Turgut S.; Eseller G.
    The eastern Thrace Basin forms the eastern portion of the Turkish Thrace Basin in NW Turkey. The pre-Tertiary crystalline basement shows platform and deep basin depositional morphology which results in facies pattern and thickness distribution localization during the early stages of basin development in Middle to Late Eocene time. Normal fault controlled early and lateral/reverse fault controlled later stage tectonic events characterize basin geometry and the present topography, respectively. The early stage normal faulting caused subsidence and sediment accumulation in the Late Eocene and Early Oligocene, while later stage tectonic events caused intense deformation and structuration in the Early to Middle Miocene. As a result, southeastern and northern regions were folded or uplifted and deeply eroded. Outcrop, well log, core and reflection seismic studies reveal that the sedimentary succession can be subdivided into five characteristic depositional sequences bounded at their base by unconformities. These unconformities were dated using paleontological data. The sequence boundaries, underlying consecutively Sequences-1, 2, 3, and 5 were dated at 39.5, 36, 30, and 25.5 Ma from older to young in order of succession, corresponding to the major erosional breaks between the Middle and Upper Eocene, the Upper Eocene and the Lower Oligocene, the Lower and Upper Oligocene, and the Upper Oligocene and the Lower Miocene. The sequence boundary underlying Sequence-4 was determined to lie within the Late Oligocene succession and, as an age designation could not be assigned, it was termed intra sequence boundary (ISB). The first two sequences correspond to relative sea level rises and a normal fault controlled tectonism coincides with them. Reefal carbonates, coarse grained clastics and marine shales, with abundant volcanic flows or layers represent the sedimentary facies of these two early sequences. The third and fourth sequences correspond to either a decreased relative rise of sea level or a relative still stand of sea level and a sediment-induced subsidence related to thermal relaxation provides accommodation. Prograding delta sediments of varying extent constitute the sedimentary packages of these two sequences. The Depositional Sequence-5, which makes up the uppermost part of the sedimentary succession in the basin, corresponds to a relative sea level fall and a tectonic style shaped by lateral and inversion faulting characterizes this period. Nonmarine alluvial fan, fluvial channel and various lagoonal deposits constitute the sedimentary facies of this last sequence. Porous reefal limestones and shallow marine beach sandstones of Sequence-1 and deltaic sandstones of Sequences-3 and 4 provide good reservoir rocks for the hydrocarbons produced in the study area. The marine shales and marls of the second and the third sequences provide good source rocks as they are rich in disseminated organic matter content. Although the non-marine alluvial and fluvial channel deposits of Sequence-5 are good reservoirs, they lack effective seals. The time interval in which Sequence-5 was deposited represents a period of major structural and trap development in the basin. (C) 2000 Elsevier Science Ltd. All rights reserved.; The eastern Thrace Basin forms the eastern portion of the Turkish Trace Basin ni NW Turkey. The pre-Tertiary crystalline basement shows platform and deep basin depositional morphology which results in facies pattern and thickness distribution localization during the early stages of basin development in Middle to late Eocene time. Normal fault-controlled-early and lateral/reverse fault-controlled-later stage tectonic events characterized basin geometry and the present topography, respectively. The early stage normal faulting caused subsidence and sediment accumulation in the Late Eocene and Early Oligocene, while later stage tectonic events caused intense deformation and structuration in the Early to Middle Miocene.
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    Geochemical characteristics of mafic lavas from the Neotethyan ophiolites in western Turkey: Implications for heterogeneous source contribution during variable stages of ocean crust generation
    (Cambridge University Press, 2008) Aldanmaz E.; Yaliniz M.K.; Güctekin A.; Göncüoǧlu M.C.
    The Late Triassic to Late Cretaceous age mafic lavas from the Neotethyan suture zone ophiolites in western Turkey exhibit a wide diversity of geochemical signatures, indicating derivation from extremely heterogeneous mantle sources. The rocks as a whole can be divided into three broad subdivisions based on their bulk-rock geochemical characteristics: (1) mid-ocean ridge basalts (MORB) that range in composition from light rare earth element (LREE)-depleted varieties (N-MORB; (La/Sm)N < 1) through transitional MORB to LREE enriched types (E-MORB; (La/Sm)N > 1); (2) the ocean island basalt (OIB)-type alkaline volcanic rocks with significant enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to normal mid-ocean ridge basalts (N-MORB); and (3) the supra-subduction zone (SSZ)-type tholeiites originated from arc mantle sources that are characterized by selective enrichments in fluid-soluble large ion lithophile elements (LILE) and LREE relative to the high field strength elements (HFSE). The formation of MORB tholeiites with variable enrichments and depletions in incompatible trace elements is probably related to the processes of crust generation along an oceanic spreading system, and the observed MORB-OIB associations can be modelled by heterogeneous source contribution and mixing of melts from chemically discrete sources from sub-lithospheric reservoirs. Evaluation of trace element systematics shows that the inferred heterogeneities within the mantle source regions are likely to have originated from continuous processes of formation and destruction of enriched mantle domains by long-term plate recycling, convective mixing and melt extraction. The origin of SSZ-type tholeiites with back-arc basin affinities, on the other hand, can be attributed to the later intra-oceanic subduction and plate convergence which led to the generation of supra-subduction-type oceanic crust as a consequence of imparting a certain extent of subduction component into the mantle melting region. Mixing of melts from a multiply depleted mantle source, which subsequently received variable re-enrichment with a subduction component, is suggested to explain the generation of supra-subduction-type oceanic crust. The geodynamic setting in which much of the SSZ-type ophiolitic extrusive rocks from western Turkey were generated can be described as an arc-basin system that is characterized by an oceanic lithosphere generation most probably associated with melting of mantle material along a supra-subduction-type spreading centre. © 2007 Cambridge University Press.