Secondary Porosity in Sandstones

Öz

Secondary porosity play an important role in the diagenesis of some sandstones. Studies after 1970's have shown that more than half of the porosity in sandstones is secondary in origin. Chemical. Physicochemical, biochemical, physical and biophysical presses result in secondary porosity through leaching and shrinkage of rock constituents or through the opening and shrinkage of rock constituents or through the opening of fractures. Secondary porosity can originate anywhere in the diagenetic history. Most of secondary porosity in ancient sandstones formed as a result of mesogenetic leaching of the carbonate minerals such as calcite, dolomite and siderite. Secondary porosity resulting from the dissolution of unstable framework or cement, such as feldspar, carbonate, sulfate or rock fragment is common in sandstone. Recognition of secondary porosity should be based on multiple evidence because monfractured secondary porosity often mimics primary porosity. Petrographic criteria for recognizing secondary porosity include partial dissolution, molds, inomogeneus packing, oversized pores, carrodedr grains, intraconstituent pores and fractured grains.

Anahtar Kelimeler

• Sandstone
• Secondary Porosity
• Metamorphism

Kumtaşlarındaki İkincil Gözeneklilik

Öz

İkincil gözeneklilik kumtaşlarının diyajenezinde önemli rol oynar. 1970'lerden sonra yapılan araştırmalar kumtaşlarındaki gözenekliliğin yarısından çoğunun ikincil kökeni olduğunu göstermiştir; Kimyasal, fiziksel, fizikokimyasal, biokimyasal ve biyofiziksel prosesler sonucu ikincil gözeneklilik kumtaşlarındaki çimento ya da tanelerin çözünmesi, buruşması, oyulması ve çatlak-kırık oluşması şeklinde gelişir. İkincil gözeneklilik sedimentlerin depolanmasından hemen sonra ve matemorfizma öncesi herhangi bir zamanda oluşabilir. Yaşlı kumtaşlarında ikincil gözenekliliğin büyük bir kısmı kalsit, dolomit ve siderit gibi karbonat minerallerinin mezojenetik olarak çözünmesi sonucu oluşur. Feldispat, karbonat, sülfat ya da kaya ç parçacıları gibi duraylı olmayan sedimenter tane ya da çimentonun çözünmesi veya çatlaklanması sonucu oluşan ikincil gözeneklilik kumtaşlarında oldukça yaygındır. Çatlaklanma dışındaki ikincil gözenekliliğin birçok açıdan birincil gözenekliliğe benzemesi, ikincil gözenekliliğin tanımlanmasında birden fazla belirtinin bulunmasını gerektirir. Kısmi çözülme, mold, homojen olmayan paketlenme, aşırı boyutlu boşluk, sıralanmış gözenekler, kemirilmiş taneler, tane içi gözeneklilik, kırılmış ya da çatlaklanmış taneler ikincil gözenekliliğin tanımlanmasında kullanılan petrografik belirtilerdir.

Anahtar Kelimeler

• Kumtaşı
• İkincil Gözeneklilik
• Metamorfizma

Kaynakça

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