Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Deposition of Stratiform Celestite of Aftar Region, West of Semnan

Document Type : Original Research Paper

Authors
Kamaledin Bazargani Guilani 1
Mohammad Sadegh Rabbani 2
1 Department of Geology, Faculty of Science, Tehran University, Tehran, Iran
2 Department of Chemistry, Faculty of Science, Tehran University, Tehran, Iran
Abstract
The sequence of sedimentary rocks of Aftar syncline (35 Km west of Semnan) be longs to Karadj, Semnan and Kond formations. Celestite occurs at the lower part of the Kond formation. The Kond formation itself is mainly made of gypsum, limestone and sandy limestone deposited in an evaporitic environment.  Based on the type of fossils found in the limestones of the Kond formation, the age of this sequence is attributed to upper Eocene.  The formation was formed during a slow and fluctuating subsidence in an evaporitic shallow basin.  The layered, rhythmic and elongated lenticular celestite crystals are positioned parallel to the general bedding of the sequence and formed at early principal diagenetic stage.  Two forms of celestite crystals are distinguished: a) long automorphic, to xenomorphic, slabs, and b) elongated lenticular gypsum pseudomorphs.  The act of silicification, at late diagenetic stages, affected the celestite bearing layers more than other layers.  Based on the shape and arrangement of celestite in the evaporitic sequence the genesis of major portion is believed to be diagenetic; while a small portion has been probably formed synsedimentarily by saturation of strontium ions in solutions of evaporitic environment.  It seems that strontium sulphate (celestite) was formed due to the abundant gypsum in shallow evaporitic environment.  Furthermore; celestite could have been formed due to the migration of strontium ions from lower layers (Semnan and Karadj formations) or by transport of the ions by meteoric fluids.  Relatively high strontium ion content of the Semnan and Karadj formations suggests a high probability of ion supply to form celestite from these formations.
Keywords
celestite
diagenesis
Aftar
Semnan
stratiform
Kond formation
upper Eocene
gypsum
strontium

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 14, Issue 55
Spring 2005, Vol.14, No. 55
Spring 2005
Pages 30-41