Archaediscoid foraminifers and their significance in biostratigraphy and chronostratigraphy of the lower Carboniferous deposits, a case study on the northern Alborz

• Main Authors: Keyvan Zandkarimi, Bahram Najafian, Hossein Mosaddegh
• Format: Article
• Language: fas
• Published: University of Isfahan 2017-11-01
• Series: Journal of Stratigraphy and Sedimentology Researches
• Subjects: archaediscoids; Biostratigraphy; chronostratigraphy; Viséan; Serpukhovian
• Online Access: http://jssr.ui.ac.ir/article_22228_2205c2c39de04a7601e2cb28b21e13a8.pdf

A relatively complete succession of Viséan to Serpukhovian rocks is exposed in the northern Alborz, where two sections Naserabad and Dozdehban have been selected for their biostratigraphic interest. The archaediscoids are probably the best stratigraphical microfossils during the Viséan and Serpukhovian. In this study, the archaediscoids of northern Alborz are analyzed owing to their potential in biostratigraphic and chronostratigraphic subdivisions. During the early Viséan, MFZ9 foraminiferal biozone, the proposed ancestor of the archaediscoids Lapparentidiscus appears followed by the massive occurrence of primitive archaediscids, defining the MFZ10 biozone. The MFZ11 can be well defined by the first occurrence of Uralodiscus rotundus. The base of MFZ12 of this area is characterized by the first occurrence of Nodosarchaediscus and the top by Paraarchaediscus at concavus-angulatus stage. The lower upper Viséan rocks might be absent from the northern Alborz, probably because a mid-Viséan tectonic event occurred in this area. The middle late Viséan (MFZ14) is dominated by the acme of Archaediscus at angulatus stage and archaediscoids with occluded and semi-occluded lumen as well as the first occurrence of Neoarchaediscus and Kasachstanodiscus. The Archaediscus/Paraarchaediscus at angulatus stage with transitional forms to the tenuis stage and Neoarchaediscus akchimensis mark the late late Viséan (lower MFZ15) in the succession. The lower Serpukhovian rocks (upper MFZ15) of the studied sections are characterized by occurrences of new large Kasachstanodiscus and Archaediscus and a significant decrease in Paraarchaediscus, Nodosarchaediscus and Archaediscus at angulatus stage. The late Serpukhovian (MFZ16) is marked by first occurrences of Brenckleina and Brenckleina rugosa.