Sedimentology and geochemistry of the Jurassic system in northern Iraq: Implications for paleoenvironmental reconstruction, provenance and tectonic setting

Abstract

This cumulative thesis presents pioneering studies on the paleoclimate, paleosalinity and paleoredox conditions, prevailing during the Jurassic period in northern Iraq, based on a variety of proxies. To this end, several research studies were performed, divided into five individual chapters, four of which were already published in international peer-reviewed journals, while a fifth manuscript will be submitted for publication in due course. <br /> The areas of study were located in northern Iraq and involved detailed examination and analysis of six formations in total. From base to top, these are the Early Jurassic-age Sarki and Sehkaniyan formations, the Middle Jurassic-age Sargelu Formation, the Late Jurassic-age Naokelekan and Barsarin formations, and the Late Jurassic-Early Cretaceous-age Chia Gara Formation. The lithologies present are mainly carbonate rocks (limestones, dolomitic limestones and dolomites), sporadic shale units, in addition to some solid bitumens which were observed from the Sargelu and Naokelekan formations in the Banik area. The formations were examined in three different locations (i.e., the Banik, Warte and Ranya areas) within the three governorates of the Kurdistan region (i.e., Duhok, Erbil and Sulaimaniyah). <br /> Chapter 1 provides an introduction to the areas of study as well as the individual formations. It also outlines the regional geology of northern Iraq. This is followed by Chapter 2 which focusses on a more detailed description of the Early Jurassic- to Early Cretaceous-age formations of northern Iraq. The calcareous nannofossils of the entire Jurassic system from the Warte area in northern Iraq were recorded and analyzed for the first time. The results were used to determine the stratigraphic position of the lower and upper boundaries of the Middle Jurassic in the Warte succession. In addition, calcareous nannofossil data were integrated with geochemical analyses to reconstruct the paleoecological and paleoclimatic conditions of the Jurassic-Lower Cretaceous succession of the region. Chapter 2 was published in the peer-reviewed journal Geosciences in 2022. <br /> Chapter 3 presents the first broad comparative study of the mineralogical and geochemical features of the Early Jurassic-Early Cretaceous-age Sarki, Sehkanyian, Sargelu, Naokelekan, Barsarin and Chia Gara formations from the Ranya section with the same formations from the Warte section (both sections are located in northeastern Iraq). The aim of this study was to reconstruct the paleoclimate, paleosalinity and paleoredox conditions which were active during the deposition of the Early Jurassic-Early Cretaceous-age sedimentary successions in the area. In addition, the results were used to evaluate the variations and/or similarities in the paleoenvironmental conditions that prevailed during the Early Jurassic-Early Cretaceous times across the region of northern Iraq. Chapter 3 was published in the peer-reviewed journal Marine and Petroleum Geology in 2023. <br /> Chapter 4 presents a comprehensive examination of the petrography and microfacies of the carbonates from the Middle to Upper Jurassic succession (i.e., Sargelu and Naokelekan formations) from the Banik area in northernmost Iraq. The results were subsequently compared with data on the geochemistry of the shale rocks from the same formations, with the aim of providing important information regarding evaporation proxies, paleoredox and diagenetic conditions, that can be integrated into new depositional paleoenvironments for the area. Chapter 4 was published in the peer-reviewed journal Neues Jahrbuch für Geologie und Paläontologie in 2020. <br /> A detailed study of the solid bitumens present in the Middle Jurassic-Late Jurassic-age Sargelu and Naokelekan formations in the Banik area and which, to date, have never been studied, formed the basis of Chapter 5. This study aimed to propose possible depositional paleoenvironments of the solid bitumens and their host rocks by examining a range of paleoredox proxies and isotopic geochemistry. Furthermore, the results from the geochemical data were integrated with the vitrinite reflectance results in order to reconstruct the accumulation process of the solid bitumens and to interpret their origin. Chapter 5 was published in the peer-reviewed journal Arabian Journal of Geosciences in 2021. <br /> Chapter 6 comprises a detailed mineralogical and geochemical examination of the shales from the Early Jurassic-Early Cretaceous-age formations of the Warte and Ranya sections in northern Iraq. The aim of this study was to determine the provenance of the mud-size sediments as well as the tectonic setting. Chapter 6 is currently being prepared as a manuscript for submission. <br /> The final chapter – Chapter 7 – presents a summary of the various aspects of the thesis. In summary, these studies provide important information which is highly relevant for any future hydrocarbon exploration in the region of northern Iraq; they will pave the way for future work in this respect, since the Jurassic system in Iraq is – as noted - highly promising and harbors great potential.