Ferruginous oolitic limestone in Shishtu Formation (Late Devonian) and the role of Microbial activities in their formation

نوع مقاله : بدون عنوان

نویسندگان

محمودی قرائی محمودی قرائی

عاشوری Reza عاشوری

محمد خانه باد

عباس قادری

10.22067/sed.facies.v2i1.1073

چکیده

Ferruginous shallow marine limestones of Late Devonian age -mainly Famennian- are widely distributed across central and eastern Iran. The iron, almost hematite, is concentrated in oolitic and skeletal grainstones, skeletal packstones and rarely in lime-mudstones. Hematite occurred as clay coatings on various allochems (ooids, bioclasts and intraclasts), and also as finely dispersed clays within micritic beds. Most grains are concentrically laminated with alternations on ferruginous clays and micro-laminae suggesting that the clays were syndepositionally formed on grain surfaces. The ferruginous beds are commonly associated with ooides and oncoides. The planar to wavy and sometimes discontinuous laminae with individual thickness of 2 to 5 m resemble oncolitic microbialites. The microbial tubules from laminae show several concentric layer of stepwise growth around a core. Micro-morphological and mineralogical characteristics suggest biogenic factors are essential for the formation of ferruginous grains.

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