Ilgar A.,General Directorate of Mineral Research and Exploration MTA
Turkish Journal of Earth Sciences | Year: 2014
The middle Miocene shallow-marine siliciclastic succession in the Sinop Peninsula, north-central Turkey, bears a wellpreserved sedimentary record of syndepositional deformation associated with the buried escarpment of an oblique-slip dextral reverse fault and attributed to seismotectonic activity. The deposition occurred in a marginal trough at the edge of a tectonically inverted retroarc foreland basin of the Central Pontides. The synsedimentary deformation involved contemporaneous shoreface deposits and their consolidated, weakly cemented littoral substrate. Deformation features include neptunian dykes, convolute stratification, plumose transposition structure, injection dykes, diapirs, and large sandstone blocks dislodged from the fault escarpment. The genetic sequence of deformation structures deciphered from the outcrop section indicates 3 main episodes of seismotectonic activity associated with the fault and separated by renewed sediment accumulation. The first episode formed a surface rupture equal to about a third of the total minimum vertical displacement, estimated at ~5.5 m, with a detachment of a large sandstone block from the fault scarp. The second episode is inferred to have involved at least 2 closely consecutive earthquakes, which caused partial liquefaction and fluidization of footwall sediment. The last episode of fault activity caused detachment of an even larger sandstone block and was followed by abrupt basin subsidence, possibly accompanied by a minor tsunami. The seismotectonic events postdated the Pontide orogen and are considered to represent an early phase of neotectonic activity in the north-central Turkey, heralding the development of the North Anatolian Fault Zone. Similar deformation features associated with fault escarpments are potentially common in the stratigraphic record, but may have been lumped with fault breccias or talus deposits and escaped recognition. The study ofers detailed sedimentological criteria for the recognition of syndepositional seismotectonic activity. © TÜBİTAK.
Akbayram K.,General Directorate of Mineral Research and Exploration MTA |
Sorlien C.C.,University of California at Santa Barbara |
Okay A.I.,Technical University of Istanbul
Tectonophysics | Year: 2015
The North Anatolian Fault (NAF) splits into two major branches in northwestern Turkey with most of the present strain accumulation and Holocene displacement being along the northern branch (NAF-N). Estimates of total offset along the NAF-N range between 4km and 70km in the Marmara Sea region. These different estimates lead to different interpretations on the formation of Marmara Sea basins. In this study, we use Cretaceous faults sub-perpendicular to the NAF-N as precise offset markers. Based on these faults, as well as the offset of the Middle Eocene volcanic belt, we report a minimum 52±1km cumulative dextral displacement along the NAF-N east of Marmara Sea near 31°E longitude. The displacement of the Middle Eocene volcanic belt shows that the offset is post-Middle Eocene. If we assume an additional 15km dextral displacement on the second strand of the NAF-N (Düzce fault), the total offset along the NAF-N can be estimated as ~67km in the Eastern Marmara region. Adding the published offsets that range from 16 to 26km on the Southern Branch of the NAF give a total offset estimate of whole NAF zone as 88±5km in the eastern Marmara region. The GPS velocity estimate indicates ~23mmyr-1 of total plate motion across and near eastern Marmara Sea that would take 3.9 million years to accumulate 88km of displacement on the NAF. Additionally, the Anatolian Plate would not have instantaneously accelerated to its modern rate of motion. Thus, initiation of transform displacement must somewhat pre-date 3.9Ma. © 2015 Elsevier B.V.
Kozlu H.,General Directorate of Mineral Research and Exploration MTA |
Prichard H.,University of Cardiff |
Melcher F.,University of Leoben |
Fisher P.,University of Cardiff |
And 2 more authors.
Ore Geology Reviews | Year: 2014
The high-Al chromitite-bearing stratigraphic levels (Cr# ranges from 0.38 to 0.47) are located at the mantle/crust transition zone (MTZ) and in the cumulate dunites in the Berit ophiolite in SE Turkey. Iridium group elements-IPGE (Ir, Os and Ru) and related mineralisation were previously reported from ophiolitic high-Cr chromitites in the Berit-Elbistan area. Palladium group elements - PPGE (Pt, Pd and Rh) and associated mineralisation are predominantly found in the high-Al chromitites and they are presented in this study for the first time. Our results indicate that IPGE-enriched phases of the PGMs such as laurite are present in both the PPGE-enriched and the PPGE-poor chromitites in Berit.The high-Al chromitite chondrite normalised patterns in the Berit ophiolite show an enrichment of PPGE, with values of up to 1700. ppb Pt and up to 4469. ppb Pd. During their occurrence sulphur saturation is consistent with the production of minor quantities of base metal sulphides (BMS) which took place in the form of droplets enclosed in chromite, commonly with PPGE-enriched patterns. These PPGM assemblages include Pd-Pt-tellurides, sperrylite, platarsite, Pd-antimonide, Pd-Sb-As, and Pt-Pd-Cu-Au- alloys. The PPGE enrichment in the Berit ophiolite is unusual, and the presence of such occurrences is known only in a few other ophiolites worldwide.The geochemical evolution of the high Cr# ratios of the high-Cr chromitites indicates an origin due to high degrees of partial melting, whereas the high-Al chromitites indicate lower degrees of partial melting. Both high-degree and low-degree melts may have been fluxed through the upper mantle, either synchronously or possibly with a hiatus between the generation of different melts. © 2013 Elsevier B.V.
Demircan H.,General Directorate of Mineral Research and Exploration MTA
Comptes Rendus - Palevol | Year: 2012
Bioerosion is a common process in hard substrates. This study introduces an example from the rocky palaeoshore cropping out at a sea cliff on the Bozcaada Island. It includes bioerosion trace fossils preserved in limestone boulders of the shallow marine and lacustrine Alcitepe Formation of Late Miocene age. The ichnotaxa include borings produced by duraphagous drillers (Oichnus isp.), phonorids (cf. Conchotrema isp.), clionid sponges (Entobia cf. goniodes, Entobia geometrica, Entobia laquea, Entobia ovula, E. cf. solaris, Entobia isp.), endolithic bivalves (Gastrochaenolites torpedo, Gastrochaenolites lapidicus, Gastrochaenolites isp., Phrixichnus isp.), polychaete annelids (Maeandropolydora isp., Maeandropolydora sulcans, Maeandropolydora decipiens, Caulostrepsis taeniola, Caulostrepsis isp.), echinoids (cf. Circolites isp.) and spinculid worms (cf. Trypanites isp.). Barnacles are also common as encrusters. The borings can be ascribed to the Gastrochaenolites-Entobia assemblage, which is typical of Neogene rocky-shores. They belong to the Entobia ichnofacies indicating various conditions of light, energy, and depth. Therefore they can reveal environmental changes and play an important role in forming palaeo-rocky shores and wave-cut platforms during marine trangressive events. © 2012 Académie des sciences.
Ilgar A.,General Directorate of Mineral Research and Exploration MTA
Sedimentary Geology | Year: 2015
This study from the Central Pontide Miocene foredeep basin compares the local record of relative sea-level changes at the Turkish southern periphery of the Eastern Paratethys with the general Paratethyan eustatic history. Detailed sedimentary facies analysis is used to decipher high-resolution sequence stratigraphy of the basin-fill succession. The Tarkhanian-Chokrakian Sinop Formation overlies directly the pre-Cenozoic bedrock and consists of neritic to littoral, foreshore and barrier-lagoon deposits, which form transgressive-regressive parasequences with estimated time spans of ca. 60 to 700. ka. The overlying Konkian-Bessarabian Gelincik Formation occurs as the infill of fluvial valleys, up to >. 120. m deep, which were incised during the Karaganian and filled with deltaic to non-deltaic bayhead shoreline deposits passing up-valley into alluvium. The valley-fill deposits form parasequences with an estimated mean time span of ca. 300. ka, organized into a lower regressive and an upper transgressive set. These 1st-order parasequences consist of smaller, 2nd-order parasequences with an estimated mean time span of ca. 5. ka.All the main mid-Miocene Paratethyan eustatic events are recognizable in the basin-fill succession, although their record appears to have been modulated by the local tectonism and high rate of post-orogenic sediment supply. The signal of 3rd-order eustatic cycles is recorded on a stratigraphic scale of parasequence sets. The 1st-order parasequences are attributed to pulses of the basin subsidence, which was initially driven by the thrust loading of the collapsing Pontide orogen and later by the neotectonic inception of the strike-slip North Anatolian Fault System. The 2nd-order parasequences represent minor subsidence pulses and/or the Milankovitch eustatic cycles. The study shows how a comparative analysis of local sequence stratigraphy and eustatic sea-level record can serve to recognize the relative role of eustasy, tectonics and sediment supply in a sedimentary basin. © 2014 Elsevier B.V.