Comparing of Holocene sedimentary facies between Hoz-e-Soltan and Garmsar Playas

IntroductionExaminations of sedimentological and mineralogical characteristics of the closed-basin cores due to the very high susceptibility to precipitation and evaporation balance are beneficial for determination and evolution of late Quaternary sedimentary specification. Orogenic movements and volcanic eruptions at the end of Cretaceous and early Eocene led to formation of Eocene volcanics in the north and some central parts of Iran. As a result of faulting which took place following the volcanism at this area, a graben was formed. This graben formed a closed basin such as Hoz-e-Soltan and Garmsar Playa, which has since become partially filled with interbedded clastic and evaporite sediments. Hoz-e-Soltan Lake with 195 km2 catchment area located at 85 km of southwest of Tehran-Qom highway, in Central Part of Iran. It is sited between 34º 56´ and 35º 31´ north and 50º 53´ and 51º 20´ east at western-north of Hoz-e-Masileh. It is surrounded by Ali-Abad and kushk-e-Nosrat mountains in north and northeast, Manzarieh and Chahar mountains in west and Mohammad-Abad and Badamcheh mountains in south and southeast. The Garmsar Playa, with an area of 700 km2, is located in the north of Central Iran and adjacent to the southern slopes of Central Alborz Mountains (north of Iran). The altitude of the studied area is 750-760 meters above sea level. The geology of the highlands flanking the Garmsar Basin comprises mainly Tertiary sedimentary rocks. Within the Tertiary sedimentary sequence, the Oligocene-Miocene rocks and salt diapirs, which are widely exposed in the north and west, are mainly composed of siliciclastics and evaporites, which are an important source rocks for the Garmsar Playa. The present research is aimed to separate sedimentary sub-environments of Hoz-e-Soltan and Garmsar Playas and it is based on study of sedimentary cores and sedimentary and mineralogical evidencens.
Materials and methodsIn the research, 9 cores were obtained from Hoz-e-Soltan Playa using a handy auger in Feb 2010. Sampling from surface down to 20 cm depth of Garmsar Playa was done. The core samples were then dissected in halves longitudinally, underneath the sediments, Playa environment was detected. In total, 113 samples of sedimentary facies related to Hoz-e-Soltan Playa and 30 samples from Garmsar Playa were prepared and then analyzed using grain and mineral analytical methods such as granulometery and mineralogy. Samples were dried in an oven at 60 ̊C for 48 hours in laboratory. Analysis of particles ˃63μ and ˂63μ was performed by using a wet Vibratory Sieve Shaker and Laser Particle Sizer, respectively. Also the analyses of all clastic, carbonate and evaporite minerals were determined semi-quantitative. Field studies of the Garmsar Playa were conducted in 2008 and 2009. Depositional environment, minerals, color, grain size and other distinctive features were noted. Over forty sediment samples were collected from the Playa surface to 25 cm below the surface. X-Ray Diffraction analyses were performed for more than 20 samples. All of analyses were done in the laboratory of Geological Survey of Iran and Kansaran Binaloud laboratory.
Results and discussionAfter obtaining the results of different laboratory studies such as granulometery, mineralogy, scanning electron microscope, morphometry and morphoscopy from 1 core (HS4) and processing the data, final investigations were done. Sediments in the central part of both Playas is almost entirely chemical (evaporite and carbonate) and in the margin of the Lake is clastic-chemical. Between the carbonate minerals, calcite is the most abundant mineral as cement in the alluvial fans and sand dunes. Quartz and calcite dominated in mud flat and saline mud flat sub-environments of Hoz-e-Soltan Playa. The clastic fraction of the Hoz-e-Soltan Playa sediment consists of quartz, feldspar and clay minerals such as kaolinite and illite, but other minerals such as muscovite, magnetite, hematite, amphibole, and pyroxene were found. Hoz-e-Soltan evaporite minerals include calcite, gypsum, halite, bassanite, thernadite, carnalite along with minor volumes of polyhalite and hexahydrite. Halite is the most abundant lithofacies in the basin. There are two main types of halite: massive halite and hopper halite. Gypsum is in the lens form, semi-translucent prismatic crystals in white, grey and yellowish brown colors. Halite and gypsum dominated in salt pan and ephemeral Lake sub-environment. From north to south, the Garmsar Basin comprises a variety of environments and their deposits including a big alluvial fan, ephemeral fluvial rivers and Playa. Their sediments generally rang from gravel size in the north through sand to mud size in the south. The Garmsar Playa comprises a variety of sub-environments, including gravel/sand sheets, dry mud flat, saline mud flat and saline pan. The sediments found in saline pans consist of alternating layers of crystalline salts and siliciclastic-rich mud. The mineralogy of salt deposits depends on the composition of the inflow waters and ground water discharge. In Garmsar Playa, various evaporite minerals such as halite, gypsum and carnalite were indentified. Halite is the dominant evaporite mineral in the studied area. The salt crusts of Garmsar Playa are characterized by elongate halite crystals chevron and other forms of crystals. Continued dissolution and reprecipition of halite and other soluble salts in the vadose and capillary portion of the crust can destroy much of the initial aligned chevron texture. Complete desiccation of the pan causes the halite crust to break up into polygons and tepees.
ConclusionThe type of sediments in both Playas includ slightly gravelly sandy mud, slightly gravelly muddy sand, mud, sandy mud and muddy sand. In the Hoz-e-Soltan Playa, there are three facies: clastic, carbonate and evaporite. In Garmsar Playa there are three facies: siliceous clastic, mixture of siliceous clastic with evaporative and evaporite. The minerals of the Hoz-e-Soltan Playa are quartz, feldspar, clay minerals, calcite and rarelt aragonite, gypsum, halite, anhydrite, basanite, tenardite, carnalite, polyhalite, thenardite and hexahydrite were found in Hoz-e-Soltan Playa. The minerals of Garmsar Playa are halite, gypsum, calcite, bassanite, carnalite, carnalite ammonium, sylvite, chloride magnesium potash quartz, albite, anortite, muscovite, chlorite and illite. Mud cracks, Aeolian sands, tepees and cauliflower surfaces are the commonest recognized features in both Playas. Sub-environments of both Playas include (from outer parts to inner parts) aluviall fan, snady flat, dry mud flat, saline mud flat, salt pan and ephemeral Lake. Most of the saline pan surface is covered by halite. These sedimentary sub-environments are based on changing of sedimentary environment according affected by climate change in Holocene.