Mn Distribution in the Carbonate Fraction of Shallow Marine Lithofacies, Lower Miocene,Wadi Fuhaimi and Anah town (Western Iraq)

Abstract

Chemical determinations of Mn on (48) samples of carbonate rocks from Cenozoic Euphrates sequence of Wadi Fuhaimi and Anah town (Western Iraq) have been carried out. From the relationships between Mn content on one hand, the mineralogy and depositional environments on the other, the following conclusions can be drawn: (1) Mn appears to be mainly associated with carbonate fraction. (2) The low Mn content of the shallow water formation reflects the original carbonate phase, mainly aragonite; sharply higher Mn content has been found in deeper sea formation, in origin essentially calcitic. (3) Preferential substitution of manganese for calcium in the rhombohedral structure of calcite. (4) Diagenetic processes, particularly dolomitization, do not appear to have seriously modified the original Mn content. (5) The relatively high Mn content in some stratigraphic levels could be related to periods of intensive weathering and /or to a larger availability of Mn+2, due to more reducing sea water conditions.