Stratigraphy and paleontology of Miocene strata in the Southwest of Zanjan

Document Type : Original Article

Authors

1 Department of Geology, Faculty of Science, University of Zanjan, Zanjan, Iran

2 Department of Geology, Faculty of Science, University of Zanjan, Zanjan, Iran,

Abstract

Introduction
Qom formation in type section in the South of Qom city (Dobaradar, Dochah, Mil, Naraghi, Khorabad and Shorab areas) has been divided to six members (a-f) (Furer and Soder, 1955). Lower Miocene age and carbonate shelf as sedimentary environment have been proposed for these strata in the previous studies (Alipour et al, 1395). Moreover, carbonate shelf as sedimentary environment has been proposed for marly strata in the upper parts of this section (Rabbani et al, 1399).
Materials and methods
Studied section is located in the Southwest of Zanjan provience (near Qamchoghai village). We can use Zanjan to Halab main road (about 40km) to access this area at the right of the road near the Zarrinabad factory. Forty-two samples from one hundred and forty-three meters of strata have been studied. All samples have been documented in Paleontology Laboratory in the University of Zanjan.
Results and discussion
Thick bedded limestones are cropping out at the base of the section that overlay the red bedded strata (lower red Formation equivalent) (Alipour et al, 1395) by disconformity boundary. Theses thick bedded strata are overlayed by marl and argillaceous limestone strata (the most upper parts of Qom Formation) by conformity boundary that gradually turned to the lower most parts of the Upper Red Formation (gypsum) in the upper parts of the section. Microfacies analysis and field studies proposed open carbonate shelf as sedimentary environment for these strata (Rabbani et al, 1399). Also, Alipour et al. (1395) believes that carbonate shelf can be consider as sedimentary environment for the f member of Qom Formation in this section.
Biostratigraphy
In order to relative dating of these strata, formainifera and macrofossils content have been studied. Sixteen species of foraminifera and one species of echinoderms have been identified. Some sponges have been reported for the first time from this section. Based on index fossils (specifically Borelis melo curdica and Pericosmus latus), Burdigalian age can be proposed for these strata.
Conclusion
Paleontological studies on thin section samples lead to identify sixteen species of foraminifera fossil that based on occurrence of Borelis melo curdica (as index foraminifera fossil), one biostratigraphic zone has been identified that proposed Burdigalian age for the studied strata. Also, presence of Pericosmus latus (as index echinoid fossil) confirm the Lower/Middle Miocene age for these strata. Some of sponges fossils related to the Hexactinellidea have been reported from the Qom Formation in this section for the first time.

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Main Subjects

References

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