Dolomitization mechanisms of Eocene Zagros carbonate platforms (an example from Shahbazan Formation, Amiran anticline, south of Lorestan)

Authors

1 Assoc. Prof., Dept., of Geology, Faculty of Science, Lorestan University, Khorramabad, Iran

2 Ph. D., student sedimentology and sedimentary rocks, Faculty of Science, Bu Ali Sina University, Hamedan, Iran, Expert of the Central Laboratory of Lorestan University, Khorramabad, Iran

Abstract

Shahbazan Formation is one of the Eocene carbonate units of Lorestan region. In present study, dolomitization models this formation were investigated by petrographic and geochemical (EDS) methods. The section under study is 71 m in the thickness and located at 65 km southwest of Khorramabad including carbonate and dolomitic carbonate rocks, and dolomite. The dolomites based on the texture are categorized into dolomicrite, dolomicrosparite, dolosparite, and filling of fractures, which except dolomicrite, the others are secondary. Dolomites of first type represent the formation in the tidal zone environment. In most cases, these dolomites are seen at the end of upwardly shallowing sequences, which indicate a drop in sea level. The secondary dolomites were formed in a shallow to medium burial digenesis environment as a result of seepage of evaporated basin floor sediments into the carbonate platform of the Shahbazan Formation. Low amounts of Fe and high amounts of Sr and Na in dolomicrites, high concentration of Fe and Mn in dolomicrosparites and doloasparites along with evidences such as algal laminae, intraclasts, fenestral porosity and absence of evaporate minerals indicate the formation of this dolomite from the model of tidal, seepage and the following shallow to medium burial. Low values of Sr and high concentration of Fe and Mn in coarse crystal dolomites can indicate the increase in the size of dolomite crystals and their recrystallization during burial. The absence of saddle dolomites probably indicates the non-interference of hydrothermal solutions and fluids during the process of dolomitization of Shahbazan Formation carbonates.

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History

  • Receive Date: 16 November 2023
  • Revise Date: 20 January 2024
  • Accept Date: 24 January 2024

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