Geochemical and palynological analyses of the Serikagni Formation, Sinjar, Iraq

Abstract

Serikagni Formation (lower–middle Miocene) was studied at four outcrop sections within Sinjar Anticline, Para (the western plunge), Jaddala, Sinjar, (Southern limb), and Noaniaa (Northern limb) of Sinjar Mountain, which is part of foothill zone in northwest Iraq. This formation is composed of Globigerina limestone, marly limestone intercalated with marl, deposited in quiet, deep marine environment. Palynological analyses and the percentages of palynological matter were determined. Palynofacies analysis was recorded for paleoenvironmental interpretation. Mineralogical investigations and petrographical analyses were done. Geochemical analyses for the determination of the major constituents (CaO, MgO, and I.R.),the secondary constituents (SiO2, Al2O3, Fe2O3, Na2O, K2O, and trace elements (Sr, Mn, Cu, Zn, Co, Cr, Pb) in the rock samples were accomplished. The calcite is the predominant mineral which is mostly of micrite types as well as spary calcite. The insoluble residue (I.R.) has negative correlation with the carbonate percentages in the rock formation as observed by the XRD analyses. Clay minerals show low occurrence represented by palygorskite, montmorillonite, and sepiolite. Geochemical differences can be noticed between the limy and marly facies constituting the same formation. Differences are also observed between the geochemistry and mineralogy of the four studied localities such as the relatively more pure limestone in Jaddala and Para sections than Sinjar and Noaniaa sections which indicate the higher percentages of marly limestone. This is believed to be due to the geographic location of these sections within the main depositional environment, as well as the consequences of sea level fluctuation. Two palynofacies (PF-1) and (PF-2) were identified. Palynomorphs are more numerous with high percentages (>80%) of amorphous organic matter (AOM) is present in the PF-1. The lithological association of this palynofacies is limestone and marly limestone. This palynofacies 1, indicate the deep marine depositional environment. The second palynofacies (PF-2) reflect low quantities (less than 40%) of AOM, with increase of phytoclasts (translucent-type) to more than 30% and the miospores (small spores and pollen grains) to more than 20%. The lithological association of this palynofacies is marl and marly limestone. This palynofacies 2, indicate the nearshore and shallow marine depositional environment.