Document Type : Original Research Paper

Authors

1 Ph.D., Department of Geology, Islamic Azad university Science and Research Branch, Tehran, Iran

2 Professor, Islamic Azad university South Tehran Branch, Tehran, Iran

3 Professor, Department of Geology, Islamic Azad university Science and Research Branch, Tehran, Iran

Abstract

In this paper the Fajan Formation of Paleocene age with a thickness of 172.5 meters is studied in northwest Shahroud (Eastern Alborz). Main lithology of this formation, at the studied section, consists of conglomerate and sandstone. The formation disconforably overlain  upper Cretaceous limestones and its upper boundry with Ziarat limestone of Eocene age is of transitional type. Dominant lithology of mentioned formation, at the studied section, consists of polymodal and polymictic orthoconglomerate which contains rounded to subrounded grains. These clastic grains are generally oval to spherical in shape and originated from limestone, sandstone and chert materials. Paleocene Conglomerate is characterized by two distinc lithofacies: clast-supported massive gravel (Gcm) and clast-supported horizontally stratified gravel (Gh) which are formed in a braided river system. This subject is interpreted by evidances as condensed texture gravels, imbrication fabric that indicate on one hand paleocurrent, non-existence of fossil by reason of oxidation conditions of sedimentary environment, sandstone lenses that have through cross bedding (St) and existence of gravels that are mostly rounded to subrounded and denote distance from origin. Abundant bed load mostly rang in size from pebble to cobble and partially boulder, gravelly beds with long extended lateral spread and lack of flood plain muddy sediments,  are reasons in distinguish between recognized sedimentary environment and meandering river. The studied Sandstone layers are described by ripple marked sand (Sr) and planar-cross-bedded sand (Sp) which  contain  sublitharenite and quartzarenite type are deposited in tide-dominated deltaic system.Interpretation criteria are propounded by means of interference ripple mark that prove direction change of  current bearing clastic particles, rounded to subrounded   sands that can present repeated reworking of grains after deposition in sedimentary environment, well sorting, high textural maturity, insignificant  matrix as criterion in distinction specified delta from other deltaic environments and herringbone cross bedding which is the most important evidence of tidal currents.

Keywords

Burley, S. D. and Worden, R. H. 2003- Sandstone Diagenesis: Recent and Ancient, Blackwell Publishing, 649 p.
Colombera, L., Mountney, N. P. and McCaffrey, W. D., 2013- A quantitative approach to fluvial facies models: Methods and example results, International Association of Sedimentologists, pp 1526-1558.
Dellenbach, J., 1964- Contrbution a l`etude geologique de la region situee a l`est de Tehran. Strasbourg, 120 p.
Folk, R. L., 1980- Petrology of sedimentary rocks: Hemphill Publication Co., Austin, Texas, 182p.
Kostic, B., Becht, A. and Aigner, T., 2005- 3-D sedimentary architecture of a Quaternary gravel delta (SW-Germany): Implication for hydrostratigraphy. Sedimentary geology, 181: 143-171.
Mial, A. D., 1996 - The Geology of  Fluvial Deposits: Sedimentary Facies, Basin Analysis, and Petroleum Geology. Springer, 582 p.
Nichols, G., 2009- Sedimentology and Stratigraphy, Wiley-Blackwell, Second Edition, 419 p.
Omali, A. O., Imasuen, O. I. and Okiotor, M. E., 2011- Sedimentological characterictics of Lokoja Sandstone exposed at Mount Patti, Bida Basin, Nigeria. Advances in Applied Science Reserch, vol 2, pp 227-245.
Reineck. H. E. and Singh, I. B., 1985- Depositional Sedimentary Environment, Springer- Verlag, 439 p.
Reynaud, J. Y., Ferrandina, M., Santiago, M., Thinon, I., Andre, J. P., Barthet, Y. and Tessier, B., 2013- From non-tidal to tide-dominated strait: The Miocene Bonifacio Basin, Southern Corsica, International Association of Sedimentalogists, Sedimentology, vol 60, pp 599-623.
Roberts, E. M., 2007- Facies architecture and depositional environments of the Upper Cretaceous Kaiparowits Formation, Southern Utah, Sedimentary Geology, Vol. pp 197-215.
Sarker, M. H., Hugue I., Alam, M. and Koudstaal, R., 2003- Rivers, chars and chars deweller of Bangladesh. Int. J. River Basin Manag.,vol 1, pp 61-80.
Steiger, R., 1966- Die geologie der Weat-Firuzkuh area (Zentral Elburs /Iran). Mitteilung geologisches Institut, ETH-Zurich, 145p.
Stow, A. V., 2003- Sedimentary Rocks in the Field ( A Colour Guide ), Manson Publishing, 322 p.
Tucker, M. E., 2001- Sedimentary Petrology. Third Edition, Blackwell, Oxford, 272 p.