Green algae carbonate deposits in Lake Ganau, Kurdistan Region, Iraq

Characeae-derived carbonate deposits in Lake Ganau, Kurdistan
Region, Iraq

Polla Azad Khanaqa • Kamal Haji Karim •1   Volker Thiel

*1  Department of Geology,  University of Sulaimani


Received: 15 October 2012 / Accepted: 30 November 2012
   published In Journal of:  Facies,  Springer Verlag, Germany
Abstract

Characeae, a family of calcifying green algae,are common in carbonate-rich freshwaters. The southwestern
shoreline of Lake Ganau (Kurdistan Region, northeastern Iraq) harbors dense and thick mats of these algae (genus Chara). On the lake bottom and along the shore, carbonate sands and rocks rich in the remains of stems, branches, nodes, and whorls of Chara are deposited.These deposits show all stages of growth and degradation of characean algae, including replacement and lithification into limestone. The replacement of the fragments by fine grained
calcite preserved delicate microstructures of Chara, such as cortical walls, cell shape, inner and outer layers
of the stems, and reproductive organs. Based on roundness, sorting, the degree of lithification, and preserved microstructures of the grains (fragments), three facies were recognized. The first is represented by a newly formed lime sand facies showing elongated grains, poor sorting, and reduced roundness, with pristine preservation of characean surface microstructures. The second is a weathered lime sand facies, which shows better sorting and good roundness, whereas internal structures of characean fragments are still well preserved. The third is comprised of a lithified lime sand facies (grainstone), with very well sorted and rounded grains, and poorly preserved external and internal structures of the characeans. As compared to the newly formed lime sand facies, the grainstone facies shows an increase in grain size by more than 30 %, owing to precipitation of micritic lamina of possible microbial origin. Eventually, the Characeae-derived lime sands are lithified into oolitic limestones with sparry calcite cement, forming a grainstone microfacies. The present study has important implications for the interpretation of pre-Quaternary environments, as it records all stages of the fossilization process of characean green algae and highlights the role of these algae in the formation of oolitic carbonate rocks. Keywords Characeae  Chara  ooids  Green algae Carbonate sand  Freshwater carbonates  Facies.

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Note:

  In the full text,  The two  ages " Jurassic and Early Ctretaceous" are   written   in opposite coresponding sentences in the page 655, 2nd collumn, at begining of  second paragraph. Soory for this accidentally error