FACIES AND DEPOSITIONAL ENVIRONMENTS OF INJANA FORMATION IN ZAWITA, AMADIA AND ZAKHO AREAS, NORTHERN IRAQ

Abstract

This study deals with facies analysis and depositional environments of Injana Formation (Upper Miocene) in Zawita, Amadiya and Zakho areas. The lower part of the formation at Zakho and Zawita comprises reddish brown mudstone and greenish grey marl representing mudflats (transitional environments). At Amadiya logged succession some coarsening upwards successions are recorded at the lower part representing deltaic environment. The upper part, which is the major part, consists principally of repeated fining-upwards succession nested above each other in a general coarsening upwards in the sand fraction. The Injana Formation comprises seven lithofacies which form eight facies associations. Mudflats and deltaic facies association represent the transitional environments and are of relatively limited thickness and restricted to the lower part only of the formation. Channel floor, point bar, chute and chute bars, abandoned channel, crevasse splay and interchannel floodbasin facies associations represent the high-sinuosity stream (meandering river) forming most of the upper part of the logged successions.The fining-upwards succession starts with a scour surface at the base of current bedded fine to coarse sandstone with occasional intraformational conglomerates followed by mudstone. In the logged successions, five basic architectural elements are identified: Downstream accretion, Lateral accretion, Floodplain fines, Crevasse splay and Abandoned channel elements. Facies analysis revealed that the upper part of the Injana Formation represents fluviatile deposits basically meandering river system (high – sinuosity streams).