NEOGENE STRATIGRAPHY OF THE İZMİR -OUTER- BAY ISLANDS

Year 2016, Volume: 152 Issue: 152, 1 - 24, 25.05.2016

Fikret Göktaş

https://doi.org/10.19111/bmre.86643

Cited By: 2

Abstract

The volcaniclastics, derived from calcalkaline acidic-intermediate volcanism in the region during late Early Miocene, and lacustrine deposits of Middle Miocene and alkaline volcanics are exposed on Uzun Ada , Hekim Adası, Çiçek Adası and Karantina Adası  in the Outer Gulf of Izmir. Kocadağ volcaniclastics derived from Kocadağ volcanism, by extruding mainly calcalkaline andesitic-dacitic products during Late Early Miocene, represents the exposed oldest rock unit. The volcaniclastic succession extending in the north of Uzun Ada is composed of pyroclastics in ignimbrite and blocky ash flow facieses, and epiclastics in volcanic mass flow (lahar) facies. Foça tuff, represented by rhyolitic ignimbrites, originated from an area around Foça and moving to an area around Uzun Ada, emplaced onto the Kocadağ volcaniclastics in two main explosive stages. The Değirmentepe Member alluvial deposits composed of coarse volcanic detritus were deposited during a inactive period between the explosion stages.  A K/Ar age of 16.0 Ma was obtained from a rhyolite dome, which shows lateral relationship with the correlant ignimbrites in Foça Peninsula, and so it is considered that Foça tuff emplaced onto the region at the end of late Early Miocene. Lacustrine-dominated Middle Miocene succession, which overlies the Foça tuff unconformably, differentiated as the Urla group. Urla group consists of alluvial Beşiktepe Formation, the Pırnallı island  volcaniclastics, which is composed of sublacustrine volcanic density-flow deposits and felsic ignimbrites, Hekim Adası basalt comprising basic volcanics and lacustrine Urla limestone, respectively from bottom to top. Beşiktepe Formation only exposed on Uzun Ada, overlies the Foça tuff with an unconformity indicating a basin margin deposition during the Middle Miocene. Pırnallı island volcaniclastic succession, which its lower boundary does not expose within the area on Hekim Adası and Çiçek Adaları, is mainly composed of epiclastics deposited by the dynamics of sublacustrine gravity flow and includes trachytic ignimbrite layers in various welding degrees. The main lithologic components of Pırnallı island volcaniclastics derived from alkaline trachytic volcanism, which was active during the Middle Miocene in Menteş Yarımadası (peninsula). The eruption center of Hekim Adası basalt intruding as a sill to the bottom of Urla limestone succession is on Hekim Adası. Along the upper contact of the basalt intruding backshore deposits at the bottom of Urla limestone, the peperites occurred reflecting the interaction between molten lava and unconsolidated sediment. A K/Ar age of 14,8±0,8 Ma is obtained from the basic lavas called as trachybasalt and basaltic trachyandesite according to the major element composition. Hekim Adası basalt, which exposed at the center of Foça Depression, can be correlated with both the Ilıpınar basalt in Foça Yarımadası the Ovacık basalt in Urla basin with respect to chrono- and lithostratigraphy. Urla limestone succession, which transgressively overlies Hekim Adası basalt, begins with backshore mudstones, continues with foreshore deposits comprising stromatolitic oncoids and algal bioclasts and lasts with cherty limestones. 

Keywords

Gulf of Izmir, Neogene Stratigraphy, Middle Miocene Deposition, Alkaline Basic Volcanism, K/Ar Geochronology

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