فصلنامه زمین شناسی ایران
پیاپی 60 (زمستان 1400)

In this research, biostratigraphic studies of the Gurpi Formation were carried out at the Chenareh section (Lorestan Zone). The thickness of Gurpi Formation at the studied section is 140 m and consists of limestobe, marly limestone and marl. The Gurpi Formation conformablely (with significant lithological changes) underlies the white limestones of the Ilam Formation and is covered by the sandstone of the Amiran Formation. On the basis of the recognized planktonic foraminifera, 7 biozone were reported as follows: Globotruncanita elevata Partial range Zone (Early Campanian), Globotruncana ventricosa Interval Zone (Middle to Late Campanian), Radotruncana calcarata Total Range Zone (Late Campanian), Globotruncanella havanensis Partial Range Zone (Late Campanian), Globotruncana aegyptiaca Interval Zone (Late Campanian), Gansserina gansseri Interval Zone (Late Campanian-Early Masstrichtian), Contusotruncana contusa  Interval Zone (Late Masstrichtian). In the studied section, the Seymareh and Imam Hassan sections are not observed, unlike other sections in the Lorestan basin. The thickness of this formation in Chenareh anticline is much less than other sections in the adjacent areas.

Oilgocene-Miocene celestite occurrences are observed across the carbonate-evaporite formations of Asmari and Gachsaran in the Zagros fold - thrust belt. The aim of this research is the study of fluid inclusions in our celestite deposits (Tortab, Tarak, Likak and Babamohamad) to reveal the nature of ore-forming fluids. Abundant structures including: geodic and vein-like structures as open-space filling along with replacement textures like mosaic and vein-like in a carbonate matrix are present. Moreover, celestite, calcite, gypsum and anhydrite are observed as the major minerals in this deposits. Based on petrographic studies, 5 groups of fluid inclusions were recognised, which are categorized as: Liquid mono phase (L), vapour mono phase (V), liquid-rich two phase (LV), vapor-rich two phase (VL) and multi-phase fluids (LVS). The results obtained from the study of microthermometry data show 134.3 to 291.8°C as homogenisation temperatures and salinities of 2.5-18.17 wt%, NaCl equ, all are involved in forming celestite. Based on the results of microthermometry data, it can be deduced that formation mechanism of celestite is resulted from reaction between fluid and rocks of the area. Moreover, tectonic activities such as uplift and diagenesis of beds along with dissolution of minerals have caused release of strontium in the fluids responsible for ore-forming. This has generally undertaken by two fluids of meteoric and brine origins over different stages of ore-formation, replacing anhydrite with strontium at high temperatures during late- diagenetic and epigenetic processes.

The Gorgan-Aqghala-Aliabad plain, which is located in Southwestern part of Western Kopet dagh, has experienced subsidence in last decades. One of the effective techniques in subsidence assessment is Interferometric Synthetic Aperture Radar (InSAR) technique which is an effective and fast method with high coverage area and high spatial resolution. In this research, the above mentioned plain is selected to determine the subsidence pattern and its relationship with structures and abnormal water consumtion from aquifers, with using integration of InSAR techniques outputs and extracted subsurface data. The results show that some parts of this plain are undergone uplift with a rate of +19.0 mm/yr, whereas, the subsidence is located predominantly in two strips with strikes N40-50 (14.0 km width) and N-S (9.0 km width) with a rate of -9.0 to -14.7 mm/yr. Investigation on subsidence patterns - structures relationship demonstrated that these subsiding strips are correlated with previously determined subsurface structures. Considering the relationship between subsidence-uplift patterns with water wells in the area shows that subsidence pattern continues in the area where there is no exploiting water well. Inversely, in the areas with densely located exploiting water wells, uplift took place. Therefore, these results show that subsidence-uplift patterns of Gorgan-Aqghala-Aliabad plain are dominantly controlled by structures and to a lesser extent by abnormal exploiting from aquifers.

Rock units in the Madabad celestite deposit are composed of medium to thick-bedded and massive limestone interlayered with marly limestone and marl units of the Qom Formation (lower Miocene). Mineralization occurs as lens-shaped orebody, hosted by limestone units of member of the Qom Formation usually crosscutting bedding of the host rocks. Three stages of mineralization occurred in the Madabad deposit. The first stage is characterized by calcite formation during syn-depositional to syn-diagenesis processes. The second stage is related to hydrothermal processes that are distinguished by formation of fine-grained and sugary crystals of massive stage-1 celestite, vein-veinlets of coarse-grained stage-2 celestite along with minor strontianite and barite, coarse-grained euhedral crystals of stage-3 celestite with vug infilling texture, and finally late-stage quartz and calcite vein-veinlets. Stage three includes supergene processes. Hydrothermal alteration includes dolomitization, calcitization and silicification. Celestite along with minor strontianite and barite are ore minerals, and calcite, dolomite, quartz and iron oxides-hydroxides are gangue minerals at Madabad. The ore minerals show vein-veinlets, vug infilling, brecciated and cataclastic textures. Microthermometric measurements of two-phase liquid-rich fluid inclusions hosted in celestite II indicate that salinities values range from 6 to 18 wt.% NaCl equiv. (avg. 10.6 wt.% NaCl equiv.). These inclusions have homogenization temperatures range from 248 to 365 °C, with an average of 278 °C. These data indicate a minimum trapping depth of 510 m for the Madabad deposit. Sr was originated from evaporate units within the marly parts of the Qom Formation and volcanic units of the Karaj Formation. Characteristics of the Madabad deposit are similar to epigenetic replacement celestite deposits.

By stating the fundamental differences between terrestrial and detrital facies, this paper emphasizes on the limitations of provenance studies in terrestrial facies. Considering the presence of coarse-, medium- and fine-grained facies in most of terrestrial sedimentary sequences, the differences in textural and mineralogical characteristics, their study methods and possible differences in the provenance of these facies, the basic and necessary steps in studying these facies for determining the sedimentary provenance was investigated. In explaining these steps, some examples from terrestrial formations of Central Iran (Upper Red Formation) and north west of Iran (Zivar Formation) are presented. The role of diagenesis, structural deformation and paleogeography in the provenance study and their importance in this type of studies are explained. Finally, it is discussed how to proof the accuracy of the interpretations for the studied sedimentary sequences.

Via combining the geological, geochronological data with archaeological and historical data synthesis, it is shown that the northern part of the central plateau of Iran corresponded to a large lake, at the very end of the Pleistocene-early Holocene period.The morphological and stratigraphic markers of this ancient lake are still visible in some areas of the central plateau of Iran, especially in the Kavir desert, the Qom-Aran desert and the region of Masileh.The Paleo shorelines located at altitude of ~1100 m found in many places around the current Great Kavir depression is one of the most important signs that confirms the existence of an integrated lake, especially during the younger Dryas.Our geochronological data suggest that between the beginning of the Holocene (~11.5 ka) and 8 ka, the lake level gradually decreased by 250 m, to reach the altitude of 850 m.It is suggested that the cause of this lowering is the evaporation due to warmer and drier climate.
According to absolute archaeological dating, the northern part of the Central Plateau has been inhabited by human communities for 50,000 years. From early Holocene; the first sedentary communities around 9,000 years ago provided the structure of rural communities in this part of Iran. From an environmental point of view, part of the water resources of these ancient settlements originated from the mountains of southern Alborz. Based on the newly found evidence of the present article, it can be assumed that in the current location of the Great Central Desert in the ancient world, freshwater lake or lakes provided suitable habitat, rich in biological resources, for prehistoric inhabitants.