Preliminary results on the origin of dissolution pipes in coastal eolianites of Şile (İstanbul)

Yıl 2018, Sayı: 1, 67 - 79, 15.10.2018

Muhammed Zeynel Öztürk , Çağlar Çakır , Mustafa Avcıoğlu , Topçu Ahmet Ertek Nabi Evren Ahmet Evren Erginal

Öz

The origin of cylindrical and cone-shaped dissolution pipes commonly observed on coastal eolianites at tropical and Mediterranean coasts is still under debate. Such unusual paleokarstic landforms have been first recognized on Turkey’s coasts at Doğancılı village to the west of Şile, İstanbul. Main aim of this study is explain physical properties and development model of these forms. Pipes are carved into cross-bedded laminae of 5 m-thick oolitic eolianites and forms are seen along cliff surface located northern part of the eolianite. Depth and perimeter of 45 pipes which are good condition are measured via ruler. Based on measurements of 45 dissolution pipes along sea-faced cliffs where they are preserved, pipes have the maximum upper diameter of 60 cm and depth of 460 cm. The depth of some pipes reaches the boundary with the underlying paleosol. The vertical shape of these holes are not apparently controlled by the cross bedded laminae. Variability in dimension of forms might represent differences in generation of pipe formation. Composite forms formed by combination of closely-spaced pipes verged into the sharp-edged blocks, i.e. pinnacle, as result of the removal of side walls. These weathered holes in eolianite dated to late MIS6 and early MIS5 might have formed during more humid conditions succeeding hotter and drier conditions, favoring the deposition and cementation of eolianite sands. The lack of calcarete within the dissolution pipes reveals nonoccurrence of arid stages during their formation. Consequently, dissolution pipes are likely the result of covered fossil (covered) karst caused by infiltrated waters having more acidity due to soil CO2. The vertical dissolution taking place on macro pores were possibly caused by the effects of infiltrated waters, passing from plant roots to preferred flow paths in vadose zone. 

Anahtar Kelimeler

Dissolution pipes, Vertical waethering, Eolianite, Şile

ŞİLE (İSTANBUL) EOLİNİTLERİNDEKİ ÇÖZÜNME BORULARININ KÖKENİ ÜZERİNE ÖN BULGULAR

Öz

Tropikal kıyılar ile Akdeniz kuşağı kıyılarındaki karbonat eolinitlerinde yaygın olarak gözlenen silindir ve konik şekilli dikey ayrışma borularının oluşumu halen tartışmalıdır. Bu tür nadir paleo-kıyı karstı şekilleri, Türkiye kıyılarından ilk kez Şile (İstanbul) batısındaki Doğancılı kıyı zonunda, 5 metre kalınlıktaki çapraz laminalı oolitik eolinit tabakaları içinde tespit edilmiştir. Bu çalışmanın temel amacı eolinit kütlesi içerisinde gelişmiş bu şekillerin fiziksel özelliklerinin ve gelişim modelinin ortaya konulmasıdır. Eolinitin kuzey kesimindeki falez yüzeyi boyunca çok fazla sayıda ayrışma borusu gelişmiştir. Bu şekillerden bozulmamış olan 45 tanesinden şerit metre yardımıyla derinlik, ve çap ölçümleri yapılmıştır. Ölçümlerine göre, çözünme borularının maksimum ağız çapı 60 cm ve derinliği 460 cm'dir.  Bazı şekillerde derinlik, eolinitin örttüğü paleosol katmanı ile olan dokanağa kadar yaklaşır. Şekiller çapraz tabakalı eolinit içerisinde gelişmiş olmakla birlikte dikey formları üzerinde çapraz laminasyonun kontrolü yoktur. Boyutlardaki değişkenlik, şekillerin oluşum evrelerinin farklılığı ile ilgili olmalıdır. Birbirine yakın gelişmiş olan çözünme borularının birleşmesiyle bileşik formlar oluşmuş, yan duvarların ortadan kalkması sonucu borular "pinnacle" denilen münferit keskin kenarlı bloklara dönüşmüşlerdir. Denizel izotop dönemi (MIS) 6 sonu ile MIS 5e başlarına tarihlendirilen eolinitler üzerinde gelişmiş bu şekiller, eoliyen kumlarının oluşumu ve çimentolanmasının gerçekleştiği daha sıcak ve kurak koşulları izleyen nemli koşullar altında gelişmiş olmalıdır. Borular içinde kalker kabuk gözlenmemesi, oluşumları esnasında kurak evrelerin yaşanmadığını açıklar. Sonuç olarak çözünme boruları organik maddece zengin topraktan derine sızan CO2 ile asitliği artmış suların yol açtığı erime sonucu fosil (örtülü) karst olarak gelişmiş olmalıdır. Çözünme yüzeyde bitki köklerinden vadoz zondaki tercihi akış kanallarına aktarılarak makro gözenekler boyunca derine ilerlemiştir.

Anahtar Kelimeler

Ayrışma boruları, Dikey ayrışma, Eolinit, Şile

Kaynakça

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