Combination of palynological evidences, magnetic susceptibility and eochemical analyses in sequence stratigraphy of the Abtalkh Formation (Turonian - Santonian), Kopeh-Dagh Basin, Northeastern Iran

The Abtalkh Formation in the Kopeh-Dagh basin in northeastern Iran with an age of Late Cretaceous (Turonian – Santonian) is selected to evaluate resolution of magnetic susceptibility for assessing sea level fluctuations. Thirty-nine shale samples were collected and studied for magnetic susceptibility and palynology. Assuming the average MS magnitude as the proxy for mean sea level, positive Magnetic Susceptibility (MS) values were considered to present sea level falls and negative values for sea level rises. Based on these data a curve showing water level fluctuations throughout the stratigraphic column was prepared which shows a general trend of regression from base to the top of the formation. To test accuracy of this method, magnetic susceptibility results were compared with those gained from palynology and palynofacies studies and with those from geochemical analyses. Based on the changes in palynological factors (e.g. the terrestrial/marine particles ratio, chorate/proximate, proximochorate, and cavate dinocysts ratio, differences in dinoflagellate assemblages, rarity and abundance of dinoflagellate groups), palynofacies and fossil contents, three Third-order sequences were differentiated, confirming the results gained from magnetic susceptibility method. In addition, the results gained from Rock-Eval pyrolysis indicate that the Abtalkh Formation at the type section was deposited under an oxic condition and confirm the results gained from palynology and magnetic susceptibility.