بررسی ویژگی‌های ژئومورفولوژی و هیدرولوژی مناظر کارستی جنوب کرمان

Investigating the geomorphological and hydrological characteristics of the karst landscapes of southern Kerman
Abstract

One of the most important factors in the formation of karst forms is the type of lithology. The existence of limestone is one of the necessary conditions for the formation of these shapes, but the different quality of different types of limestone has a great effect on the formation and development of these shapes. The process of karstization causes the creation of certain geomorphological forms, which are usually associated with the formation of cracks, channels and large dissolution holes. One of the most important types of formations in the southeast region of Iran are limestones. In the studied area, two-layer limestones belonging to the Oligomiocene period (equivalent to the Qom Formation) are outcropped. This karst mass has many springs and geomorphological forms, such as dolines, lapia, rain pits and dry valleys. The main goal of this research was to identify the karst forms of the region and the role of karst landscapes in the drainage of water and waste water into the hydrological system. For this purpose, fractures and lines have been extracted and analyzed using satellite images. According to the field visits, the carbonate units in the studied area have expanded a lot, many tectonic structures (fractures and faults) and karst geomorphological phenomena are clearly visible.

Introduction


Karst lands are characterized by enlarged dissolution cracks and channels of karst grooves whose development depends on the origin, structure and dimensions of these cracks (Keltat, 2008). (Ford, 2007: 675-684) describes dolines as a factor for identifying karst lands. In our country, despite the karst massifs in the Zagros, Alborz, Kepe Dagh and Central Iran and Persian Gulf islands, unfortunately, very little research has been done on the identification of karst roughness, managing the exploitation of karst water resources and their tourist attractions. The extent of limestone formations in Khorasan province is about 20,000 square kilometers, which belong to the Mesozoic era (Eshghi, 2003). The karst landscapes that are created here, in addition to tourist attractions, also have geomorphological and hydrological aspects. Also, due to the water reserves in such karst formations, they are considered as one of the important sources of drinking water for cities and surrounding rural areas, especially dry and water-scarce areas. Karst areas show significant biodiversity on the surface, underground and in the ecosystems associated with underground water. They are very vulnerable to pollution, as a result they need special protection (Ravbar and Goldscheider, 2007: 397-411). The review of various studies of karst aquifers shows the influence of factors such as surface geomorphology, physiography of the feeding basin, altitude, rainfall, temperature, tectonic status, geology on the hydrodynamic characteristics of karst aquifers. The purpose of this research is to investigate and identify the geomorphology, hydrogeology and petrology phenomena and characteristics of Do Sari limestone massif in the southeast of Jiroft Plain. This karst region is investigated for the first time in this research.

Materiel and method
The most important existing stratigraphic units of the studied area are OMm, OM1 and alluvial sediments (Qt) (Figure 2). The OMm unit consists of marl and marl limestone. This unit is considered equivalent to the lower red formation in the Urmia-Dakhter belt. This rock unit has low permeability and is placed under the OM1 unit. The border between these two units in the western part of the region is seen as a fault with a high slope. This fault has also created abysses. The lithology of the OM1 unit consists of rife limestone from the Oligomiocene period (equivalent to the Qom Limestone Formation). This unit is placed under the Neogene loose conglomerate which forms the bottom rock of Jiroft plain aquifer. The existence of many faults and cracks in the limestone unit OM1 and the penetration of water into it has caused the dissolution of these rocks. These limestones have water in their deep parts and have created springs in Do Sari area (Figure 3). The springs of Deh-Divan and Dosari are two of the most important springs in the limestones of the studied area. Alluvial sediments of the Quaternary period also include the products of weathering and destruction of limestone, marl and sediments that were transported by floods from the upstream areas. In this research, after conducting field visits to the area of karst geomorphological phenomena, faults and fractures were identified and their characteristics were measured. In order to investigate the hydrogeological characteristics of the karst springs of Deh-Divan, which has two series of statistics and information on the discharge and the chemical quality of the water of these springs, it has been used. These data have been measured seasonally by Kerman Regional Water Company. Data on discharge and chemical quality are available from 2018 to 2019. The discharge data of the springs along with the rainfall data have been used to investigate the temporal changes of the discharge of the springs and its relationship with the rainfall. The quality data of springs water has also been used to determine the chemical type and surface of water and the saturation profile of carbonate minerals and to examine its temporal changes. The saturation index indicates the state of yin balance of minerals and water in the aquifer. If the value of this index for a mineral is less than zero, the groundwater is in a saturated state with respect to that mineral, and the mineral in question will tend to settle and create sediment in the water environment. If the value of the saturation index for a mineral is less than zero, the groundwater is in an unsaturated state relative to that mineral. And the desired mineral dissolves in the aqueous environment. In this study, the isotopic data (18O, 2H, 3H and 14C) measured by the Iranian Water Resources Management Company in 2015 was also used. Considering the concentration of these isotopes in water, it is possible to comment on the age and retention time of water in the aquifer. In order to investigate the flow system in the karst aquifer of the study area, fractures and fault lines have also been studied. For this purpose, existing fractures, faults and lineaments have been identified and extracted using geological maps and satellite images.

Results


Based on field observations, carbonate units are widely spread in the region. The climate of the region is cold and dry and the region is tectonically active. There are many tectonic structures such as faults and all kinds of fractures, and most karst development has occurred along tensile fractures. A variety of karst geomorphological phenomena such as sinkholes, caves, karst springs, po noors, karst wells, dissolution holes and various karns can be seen in the area. The springs of the region are permanent floodwaters and are part of fault springs in terms of formation mechanism. These springs, which are the main drains, play a major role in the development of karst. Deh-Divan and Dosari springs have a diffusion flow regime and the water flows in a network of seams and fractures in the limestone mass. The water flow of Deh-Divan spring has a maximum threshold. During the occurrence of important rains (with more than the average monthly rainfall), the flow of this spring reaches its maximum value. As a result, more water flows towards the spring and causes more fluctuations in its water supply.

Keywords: geomorphology, karst, quality parameters, dosari limestone mass.