Marine invertebrate fossils have long been
considered important tools for age dating and
stratigraphic interpretation of the Paleogene
deposits of Central Asia, however information has not yet been provided from the
Kopet-Dagh Basin (NE Iran). In this research,
fossiliferous horizons of the Chehelkaman
Formation at the Sheikh and Ghaleh-Zou
sections (which have never been recognized
previously), both in the Sheikh Syncline area,
are discussed. These sedimentary beds overlay
the terrestrial siliciclastic Pesteligh Formation
and are the first evidence of marine flooding
of the Paleogene transgression in the central Kopet-Dagh. Systematic paleontological
studies of molluscan fossils in this succession
led to the identification of ten genera, twelve
species and two subspecies of bivalves and five
genera and five species of gastropods. The
assemblage belongs to four different fossiliferous horizons: (1) Turritellidae Dominated
Assemblage (TDA), (2) Pycnodonte – Turkostrea
horizon, (3) Cordiopsis - Cardium horizon and (4)
Globularia shell beds in the Sheikh section and
only TDA horizon in the Ghaleh-Zou section.
The age of the whole succession, based on
Cordiopsis subathooensis – Turritella subathooensis
Zone co-occurrence with nannofossil zones
NP12 and NP13, is Late Ypresian (early middle
Cuisian). The TDA in both sections confirms
the abundance of nutrients and their bimodal
orientation demonstrates effects of oscillatory
waves rather than unidirectional paleo-currents. High rates of bioerosion, encrustation,
fragmentation, disarticulation and corrosion of
the shells in the Pycnodonte – Turkostrea horizon
reveals high volumes of nutrients and energy-rich conditions. This interval, overlain by
the Cordiopsis – Cardium horizon in a pavement
arrangement, represents the stable conditions
after a storm. The Globularia shell beds interbedded with marly beds indicate stability and a
deepening trend of the environment, terminating to deeper marine shales and marls of the
Khang