Desikan RAMAKRISHNAN, Krishna Chandra TIWARI

Calcretized ferricretes around the Jaisalmer area, Thar Desert, India: Their chemistry, mineralogy, micromorphology and genesis

Ferrikirit, demir 'duricrustı', Hindistan çölündeki Jaisalmer civarında Tersiyer ve Mesozoyik yaşlı kayaçları üzerler. Ferrikiritler iki farklı güncel yüzey şekliyle birlikte gelişmişlerdir. En üstteki birim parçalanmış kayalık yapısal bir düzlük iken allttaki ferrikrit çakıllarından oluşan yumuşak bir kolluviyal düzeydir. Bu çalışma, arazi gözlemleri, mikromorfolojik özellikler ve toprak kimyasına bağlı olarak ferrikritlerin Waither profilinde olduğu gibi yerinde oluştuğunu rapor etmektedir. Takip eden dönemde gelişen tektonizma ve temel seviyedeki değişimler etkin olan bozuşma sürecini erozyona doğru değiştirmiştir. Erozyon safhaları röliyefde terslenmelere neden olmuş; öyleki etraflarındaki yumuşak materyallerin aşınıp taşınması sonucu daha alçak kesimlerdeki dayanımlı alanlar yüksek yapısal düzlükler, mesa ve 'butle' şeklinde korunmuşlardır. Nodüller ve pisolitlerin parçalanması, nodüllerin taşınip-ortadan kaldırılması ve oyuk-boşlukların oluşması 'duricrust'lar ile beraberindeki günlenme profillerinin parçalanmasını öne sürmektedir. Sonrasında gelişen iklim değişiklikleri - Neojen dönemindeki sıcak ve nemli koşullardan günümüzdeki sıcak fakat kuru koşullara doğru değişim - günlenme mekanizmalarında ferrikritleşmenden kalkeritleşme doğru bir değişime neden olmuştur. Sonuçta, üç kakeritleşme fazı parçalanmış ferrikrit profillerinin üzerine gelişmiştir.

Jaisalmer bölgesi kalsitleşmiş ferikretleri, Thar Çölü, Hindistan: Kimyası, mineralojisi, mikromorfolojisi ve oluşumu

Ferricrete, an iron duricrust, caps Tertiary and Mesozoic rocks around Jaisalmer in the Indian desert. These ferricretes are associated with two distinct present-day landforms. The upper unit is a high-level dissected, rocky structural plain and the lower one a colluvial flat with soft ferricrete gravels. This study pertains to the first situation wherein field observations, micromorphological features and regolith chemistry suggest an in situ origin for the ferricretes, as in the case of the Waither profile. Subsequent tectonism and changes in base level resulted in a shift in processes from weathering to erosion. Episodes of erosion resulted in inversion of relief whereby low but resistant areas with in situ weathering profiles remain as high-level structural plains, mesas and buttes after erosion of the softer material around them. Destruction of nodules and pisoliths, removal of nodules, and formation of cavities suggest destruction of duricrust and the associated weathering profile. A subsequent shift in climatic regime from warm humid conditions of the Neogene period to hot arid conditions of the present resulted in a change in the weathering processes from ferricretization to calcretization. In all, three phases of calcretization are superimposed on the dissected ferricrete profiles.

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