فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و ششم شماره 1 (پیاپی 78، بهار 1399)

In karstification phenomenon of carbonate formations various factors are involved which the most important of them are lithology, precipitation, stratigraphic characteristics, structural factors and the topography of the region. Thick and massive limestones have much higher potential for the development of karst and, as a result, the formation of karst features. In this research, four important karstic springs have been investigated, the name of these springs are Ravansar, Kabotarlaneh, Sahneh and Kashanbeh. The catchment areas of these springs are located in the different geological formations with various lithologies and ages. The discharge of springs and its variability depends significantly on the lithology of the aforementioned formations. The average annual discharge of the Ravansar, Darband Sahneh, Kashanbeh, and Kabotarlaneh springs in the hydrological year 2016–2017 is 1932, 462, 166 and 771 lit/s, respectively. Moreover, the coefficients of variation of these karst springs are 1.07, 0.30, 0.49 and 0.48 and the maximum to minimum ratio of these springs were calculated 20, 2, 7 and 4, respectively. The Ravansar and Kabotarlaneh springs have three discharge coefficients, while the springs of the Sahneh and Kashanbeh have two, which are related to stratigraphy and lithology of their basins. The largest of the aquifer storage from these springs is dedicated to the Ravansar spring, and the smallest is Kashanbeh; the discharge of these springs also confirms it.

Mighan playa in the central part of Arak watershed receives heavy elements from urban, industrial and agricultural activities. In order to evaluate the pollutants of Mighan playa, 29 sediment and soil samples were collected from playa and heavy metal concentrations were determined and compared with local and upper crust reference. The concentration of heavy metals in most samples is lower than their concentration in the crust reference. Individual contamination index, such as contamination factor, determined the degree of contamination in all samples medium for Cu and Cr and low grade for other elements. However, indices such as ecological risk, enrichment factor, and geo-accumulation index were low for all samples. Moreover, integrated indices such as sum of degree of pollution, ecological risk potential and Nemerow index for sum of elements indicate low degree of contamination. Municipal wastewater, industrial and agricultural wastewater are the most important source of heavy metals in the Mighan playa. Therefore, efforts should be taken to reduce heavy elements from pollutants, especially municipal sewage in the vicinity of the Mighan playa.

The Dalichai Formation at the Andariyeh stratigraphic section in the northeast of Andariyeh village, central Alborz Mountains, was studied by using analyses of the Sporomorph EcoGroups (SEGs) data and associated plant communities and palynofacies in order to determine its paleoecology conditions. The Sporomorph EcoGroups data from the Dalichai Formation's palynological assemblages, declination of miospores representing Upland/Lowland plant communities and proliferation of those characterizing Lowland/Coastal-Tidal plant associations interpreted to signify relatively low sea level and deposition in a marginal marine setting. Furthermore, the ratios of wetter/drier and warmer/cooler elements suggest deposition of the host strata under a moist, ±warm climate prevailing during the Middle Jurassic in central Alborz Mountains. The results of drawing diagrams of the palynofacies in the Andariyeh stratigraphic section, indicates that the Dalichai sediments accumulated in a dysoxic shallow marine environment with low sedimentation rate that corresponds well with its SEGs graphs.

In this research, Ordovician conodonts obtained from the sedimentary succession of the informal Katkoyeh formation is studied in a stratigraphic section at the south of Kuh-e-Bonorg, eastern flank of Kalmard Anticline in the west of Tabas (Central Iran). The formation which is partly equivalent to the succession of the Shirgesht Formation in Tabas Block is unconformably overlaid the Kalmard Formation (attributed to the Neoproterozoic) and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation with 214.8 meter thickness is divided into three lithostratigraphic members including the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shales interbedded with some dolomitic and calcareous sandstones, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). The section was sampled bed by bed for conodont studies so that 80 samples have been selected, however only seven of them were productive. Within the selected samples, six genera and 14 species of coniform and ramiform conodont elements are determined, a few of them are reporting for the first time from Iran. The obtained conodonts demonstrate the faunal assemblages equal to the proteus, elegans-evae and diprion Zones which confirm the age of Early Ordovician (late Tremadocian–Floian) for the studied section. The whole conodont material display a faunal affinity with the Baltoscandic and Argentina paleobiogeographic provinces.

 The biostratigraphy of Devonian–Carboniferous (D/C) boundary of Til-Abad section in Eastern alborz is carried out in this study. The studied section is located about 85 km of northeast Shahrud city and close to the Shahrud–Azadshahr road. The uppermost sediments of Devonian and lowermost Carboniferous strata in Til-Abad section (467 m thick) systematically studied and in general led to discrimination of seven following zonal boundaries: Bispathodus aculeatus aculeatus zone, Bispathodus costatus zone, Bispathodus ultimus zone, ?praesulcata zone, ckI, sulcate zone, typicus Zone and anchoralis- latus Zone. The D/C transition interval contains a bioclastic limestone and a coaly shale bed (3 cm thick) with interbedded of very thin gypsum layer. The first horizon of Carboniferous strata is begun with grey marls interbedding fossiliferous limestone. This unit has large amounts of very small corals and brachiopods with high preservation. Interpreted conodont data shows lack of kockeli Zone at the D/C boundary and Carboniferous deposits disconformably overlays the Devonian deposits of the Khoshyeilagh Formation.

In order to reconstruct the sedimentary environment of marly strata related to the upper parts of Qom Formation, one stratigraphic outcrop have been studied. Studied section is located in the Zarrin-Abad area (South of Zanjan) and is composed of 135 meters of marls and argillaceous limestones. Theses strata are limited by thick bedded limestone (related to the F Member of the Qom Formation) at the base. There is a thick bed of evaporate layer at the top of these strata with sharp boundary that can be stratigraphically related to the Upper Red Formation. Based on petrographic and texture studies, eight microfacies have been identified. These microfacies are related to the distal parts of inner shelf, patch reef, slope, toe of slop and deep shelf sub environments. Based on microfacies analysis we can propose an open shelf as sedimentary environment for these strata. Relative abundance of allochems show one cycle (rise and fall) in relative sea level along the stratigraphic column that can be correlated with eustasy curve.