نشریه رخساره های رسوبی
پیاپی 1 (زمستان 1387)

Dorouneh Fault System، as an active fault in Iranian Plateau، plays an important role in deformation and geomorphology of the region. This fault has caused some earthquakes in the 20th century. Detail study of Dourouneh fault's seismic characteristics indicates that in spite of Dorouneh Fault's high movement in Recent time، number of earthquakes and their magnitude is low that may be resultant of low slip rate، long recurrence interval and occurrence of creep on the fault. On the other hand، there are some witnesses that are indication of earthquake occurrence along Dourouneh fault which are accompanied with surface rupture.

In this paper، the results of evaluation of earthquakes site effect using the microtremor measurement، which have been obtained from 200 points in Mashhad city، are presented. Also by combination of the iso-resonance period and soil texture map، the ground classifieation map has produced according to the Iranian code of practice for seismic resistant design of buildings (2800 standard). This map shows that the resonance period of ground increase from south and west toward the center and east of city. But it decreases toward the north near Mashhad north fault in Khajeh Rabi area. Based on the Iranian 2800 standard، the south and south western parts of Mashhad city are classified in IB and IIB، while the central classified in IIIB، north part classified in IIB and limited area in east and north- east have a IV classes.

Based on enormous gas reserves and good potential for production from oil-bearing layers (Upper Dariyan، Lower Dariyan and Sarvak Formations)، South Pars Field is one of the most important hydrocarbon reserves in the Iran. The goal of this study is to determine the geochemical properties، such as quantity، quality and thermal maturity of the organic matters، of possible source rocks that might have a role in generation of hydrocarbon in the past. Therefore، core and cutting samples of the Surmeh، Fahliyan and Gadvan Formations from three exploratory oil wells in the South Pars Field، namely A، B and C، were analyzed using Rock-Eval pyrolysis and burial history reconstruction. The results of Rock-Eval pyrolysis show that such beds are not good sources and have poor to fair content of organic matter in which the total organic carbon richness (TOC) ranged between 0. 1 and 0. 64 Wt%. These three formations generally contain kerogen type II and III. Most of the studied samples are mainly gas-oil-prone organic matter (OM) with hydrogen index (HI) ranged between 150 and 300، associated with gas prone (OM) of (HI) 300. The maturity of these source beds ranges from immature to early mature-oil window in these three wells، as inferred from the production index (PI)، Tmax. Thus، no potential gas/oil source intervals were encountered in three wells. Burial history reconstruction indicates that at the end of the Cretaceous time، Permian to Cretaceous sediments remained immature in the Qatar Arch. Therefore، Surmeh، Fahliyan and Gadvan Formations could not be the source rock of the oils in this field.

Based on planktonic foraminifera، biozonations were identified in the Gurpi Formation northeast of Kabirkuh. These biozonations were correlated with those of Elkef in Tunisia and other Tethyan areas in low latitute. A very close similarity and relationship found between sections of west and southeast Tethys with the Gurpi Formation at the studied section.

The oldest exposed rocks، to the north of intrusive rocks and in Eastern Bajestan، are meta-chert، slate، quartzite، thin-bedded crystalline limestone and meta-argillite. They are exposed، to the north of intrusive rocks and in eastern Bajestan. Since both Sardar Formation (Carboniferous) and Jamal Formation (Permian)، close to this association، are not metamorphosed، therefore the regional metamorphism and the rocks must be older than Carboniferous. The sedimentary units are: Sardar Formation (Carboniferous)، Jamal Formation (Permian)، Sorkh Shale and Shotori Formations (Triassic)، K1، K2، K3 (Cretaceous) and lithostratigraph-ically equivalent to Kerman conglomerate (Cretaceous-Paleocene) are exposed in this area. Based on relative age، magmatism in eastern Bajestan and Taherabad started after Late Cretaceous and it has been active and repeated during Tertiary time. At least، three episodes of volcanic activities are recognized in this area. The first stage was mainly volcanic flow with mafic composition and minor intermediate. The second episode was mainly intermediate in composition. The third stage was changed to acid-intermediate in composition. Since the plutonic rocks intruded the volcanic rocks، therefore they may be Oligo-Miocene age. Bajestan intrusive rocks are granite-granodiorite-quartz monzonite. Taherabad intrusive rocks are diorite-quartz diorite- monzonite-latite. Bajestan intrusive rocks with magnetic susceptibility less than 20 ×10-5 SI are reduced type (ilmenite series) and Taherabad with susceptibility more than 100 ×10-5 SI are oxidized type (magnetite series). Based on geochemical analysis including trace elements، REE and (Sr87/Sr86) i = 0. 71، Bajestan intrusive rocks formed in continental collision zone and the magma has crustal origin. Taherabad intrusive rocks were formed in subduction zone and magma originated from oceanic crust. Taherabad intrusive rock has exploration potential for Cu-Au.

Kashmar Plain in the north eastern part of Central Iranian Kavir Catchment is one of the important and agricultural prosperity plain in Khorasan-e-Razavi Province. This plain located in a semi-arid to arid area. In the last decades، fast agricultural expansion coupled with rapid population growth has tremendously increased pressure on the ground water resources. Over-exploitation of the ground water resources leads to a decline of ground water levels as 0. 8 m/year and the total depletion in ground water resource is estimated to be about 121. 4 milion m3. Increasing in pumping rate of ground water resources has led to decline in ground water level and the plain listed as a critical plain in the province. Declining of groundwater and existing of fine-grained soil in Azim-Abad، Zaher-Abad، Zafar-rod Firooz-Abad، Kalatahshadi and Kondor villages have caused aquifer compaction and land subsidence in this area. This paper deals with the relation between declining of ground water level، earth-fissure and land subsidence based on the available data in this part of the plain.

The lower parts of Kashafrud Formation in Qara Gheitan Section is dominated by shale and fine siliciclastic facies، where carbonate concretions and thin bedded of sandstones are found useful indicators for environmental analysis. Sedimentological characteristics of the shale and their abundance as well as Helminthopsis trace fossil content indicate that they may have formed under deep marine conditions، where interpretation of relative sea-level change for deeper parts of the basin is rather complicated. Carbonate concretions in this formation are found eodiagenetic on the basis of their calcite content (radial calcimetry)، morphology (spherical)، and stratigraphic position (parallel to bedding). Detrital calcite، quartz and feldspar found in the concretions are similar to the hosting shales. The hosting shale is marked by abundant illite، kaolinite، and cholorite. The concretions are thought to be developed soon after deposition of sediment، in high stand period، during which no/minor sediments where derived from the land. Interaction of sea water with newly deposited sediments led to the enrichment of some parts by calcite (concretions). Hence، the concretion rich horizons are good indicators for determination of high-stand period (mfs)، therefore the sandy sheets within the shaly horizons، turbidites، indicate the low-stand period in the basin، during which sediment supply from the land was significant.