USE OF PALEOMAGNETIC EVIDENCES FOR SOME TECTONIC IMPLICATIONS OF AQRA LIMESTONE OUTCROPS NORTHEASTERN IRAQ Emad H. Al-Khersan, Basim R. Hijab & Ezzadin N. Baban (original) (raw)
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Remanent Magnetization in the Proterozoic Basement Rocks of Iraq: the Southern Desert in Focus
Research Sequare, 2023
Utilizing aeromagnetic data, this research examines basement rocks in Iraq, focusing on the southwestern part, known as the Southern Desert. The basement has particular importance since it is deep and has not been discovered directly yet. The purpose of this study is to outline regions of remanent magnetization, which have lithological, structural, and tectonic implementations using a recently proposed method by Smith et al. (2022) that transforms the magnetic data to the pole and vertical dip and subsequently estimates the apparent magnetic susceptibility. The results show the presence of remanent magnetization in the basement with different shapes and spatial extensions that predominately aligns in northwest-southeast and north-south directions in accordance with basement inherited weak zones. Further, these occurrences lie in particular tectonic zones and sub-zones. The results in the Southern Desert are consistent with a previous study that used two-dimensional forward modeling and mentioned remanent magnetization in two north-south-trending zones. Concerning the origin of the reversely magnetized bodies in Iraq, their distribution may suggest either faulting in a basement terrane (of reverse magnetization) with different displacement or intrusions of basic rocks within structural basins that are resulting from extensional tectonics.
A palaeomagnetic survey of Dinantian limestones in the Craven basin shows that limestones of Arundian/Holkerian and Asbian age (Skibeden Shales-with-limestones and Draughton Limestone) in the Skipton Anticline area have anomalous directions of magnetization. Although some of the Asbian limestones in this area are proximal turbidites, none of the sampled horizons are conglomeratic or intraclastic limestones and the anomalous directions cannot be accounted for by the derivation of previously lithified (and magnetized) clasts. The anomalous direction also occurs in non-turbiditic Arundian/Holkerian limestones which supports this contention. The directional characteristics of the NRM indicate that the limestones in this area have suffered partial to complete remagnetization. The remagnetization is characterised by the presence of a normal component of magnetization superimposed on an original reversed component. However, some specimens have Lower Carboniferous directions of magnetization which suggests that the remagnetization effect is inhomogeneously distributed throughout the limestones. The remagnetization process stopped prior to the Permo-Carboniferous folding of the area and was probably associated with diagenetic processes such as dolomitization and silicification which took place in the Skipton area prior to the deposition of the Bowland Shales in Brigantian times. The Pendleside Limestone in the Thornton Anticline area is the lateral correlative of the Draughton Limestone but shows completely different palaeomagnetic results. The results agree closely with known Lower Carboniferous directions and it is concluded that these limestones retain their original magnetization. A detailed study of a 40 m section of alternating limestones with shales shows that all the limestone beds are reversely magnetized, a feature taken to indicate that the late Asbian geomagnetic field was reversed for prolonged periods.
2018
Rock magnetic properties have been investigated across the Paleocene/Eocene boundary in two distally separate sections of Paleogene marine sedimentary rocks from Iraq, namely the Sinjar and the Shaqlawa sections. The sediments at the studied sections belong to the Aaliji and the Kolosh formations respectively, which were previously examined for their biostratigraphy by the authors using planktonic and benthonic foraminifera to delineate the Paleocene/Eocene (P/E) transition. Measured magnetic properties include; bulk magnetic susceptibility, hysteresis cycles, isothermal remnant magnetization (IRM) acquisition, and thermomagnetic curves analysis. Rock-magnetic results (i.e. low magnetic coercivity component) indicate greigite as the main magnetic phase at Aaliji rocks, while a mixture of magnetite and greigite with high magnetic coercivity has been observed at Kolosh clastics. Magnetic susceptibility is induced by related to both biogenic minerals (mainly at Aaliji Formation) and transported terrigenous material sources. Multi varied magnitude phases of high bulk rock magnetic susceptibility observed in both formations along PETM lithosomes are attributed to two sources: greigite or biogenic iron oxides source and increase in terrigenous discharge source as inferred by anoxic to suboxic iron-sulfate-reducing conditions and lithological change respectively. Both sources referred to some of environmental conditions associated with Paleocene-Eocene thermal maximum events such as methane dissociation, water stratification, enhanced hydrological and weathering cycles.
Paleomagnetism of Abu Aggag and Sabaya Formations at Kalabsha, South Western Desert of Egypt
2015
Two profiles have been sampled from the Nubia Sandstone at Aswan, south Western Desert: The 1st profile has been taken from Abu Aggag Formation and the 2nd one was from Sabaya Formation (23.25 oN, 32.75 oE). 136 oriented cores (from 9 sites) have been sampled. Abu Aggag Formation is of Late Cretaceous (Turonian) and Sabaya Formation is of Early Cretaceous (Albian-Cenomanian). The studied rocks are subjected to rock magnetic measurements as well as demagnetization treatment. It has been found that hematite is the main magnetic mineral in both formations. Four profile sections (normal polarity) from Abu Aggag Formation, yielded a magnetic component with D = 352.7 , I = 36.6 with [U+F061]95 = 5.2 and the corresponding pole lies at lat. = 82.8 N and long. = 283.1 E. Five profile sections (normal polarity) from Sabaya Formation, yielded a magnetic component with D = 348.6 , I = 33.3 with [U+F061]95 = 5.8 and the corresponding pole lies at lat. = 78.3 N and long. = 280.4 E. The obtained p...