Al-Juboury, Ali ¹ Al-Zoobay, Burkan²  and Al-Juwainy, Qais³

1.Research Center for Dams and Water Resources, Mosul University, Iraq

    alialjubory@yahoo.com

2.College of Science, Kirkuk University, Iraq

3.Northern Oil Company, Kirkuk, Iraq

Abstract  Albian shallow-water carbonates facies (Upper Qamchuqa Formation) and Cenomanian deep-water carbonates facies (Dokan Formation) are described on the basis of subsurface lithology, thin section and well log analyses of five boreholes in Kirkuk area within the Zagros foreland basin of Iraq. The Upper Qamchuqa Formation consists of conical orbitolinid-bearing platform carbonates, being the most common in addition to calcareous algae, miliolids and echinoderms. It grades into more basinal facies in the southeastern parts of the studied oilfield where it juxtaposed the Balambo Formation. These facies changes divided the study area laterally into three parts; the northwestern part in which neritic facies dominate, the central part in which a basinal influence is considerable; and the southeastern part that shows basinal mudstone type facies. The Dokan Formation consists of oligosteginal limestones with common calcispheres and foraminifera, deposited in sub-basinal environment. A sequence stratigraphic approach was applied to interpret the studied Albian-Cenomanian sequences that permitted delineation of several 3rd order and key surfaces. Tectono-sedimentary evolution of the area controls the distribution and geometry of the studied sequences. The biotic distribution was controlled largely by palaeoenvironmental changes, such as trophic level, agitation and clay influx as well as sedimentation controlled by variation in accommodation space.

Key Words: Cretaceous; Albian; Cenomanian; Carbonates; Iraq; facies

1. Introduction

Iraq constitutes a rich petroleum province within the Middle East where parts of the oil reserve are situated in the Cretaceous carbonate platform. The present work is concerned with the Albian-Cenomanian platform deposits at Kirkuk area, northeastern Iraq. This studied oilfield lies within the Zagros foreland basin, bordered on the northeast by the Zagros Mountains and on the southwest by the Arabian shield (Fig. 1A). Data were collected from five wells drilled in a limited sector corresponding to a northwest-southeast anticlinal structure situated in Kirkuk region (Fig. 1B). Analysis of facies variation in the depositional sequences, of the chosen time interval of this study that, led to interpretation of the paleoenvironmental changes and the ecological successions.

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