نشریه رسوب شناسی کاربردی
پیاپی 4 (پاییز و زمستان 1393)

In this study, Heavy metal contents from outlet of the Anzali Lagoon were measured to assess the level and sources of possible contamination. The sediment samples were collected from 15 stations in the study area. Physico-chemical properties of the sediments were determined. Two instrumental methods of analysis were applied; powder X-ray diffraction to determine clay mineralogy and ICP-OES to determine bulk metal content of the samples. Eight metals (Cd, Cu, Ni, Pb, Cr, Ti, V, and Zn) concentrations were investigated in the surface sediments. The level of pollution attributed to heavy metals was assessed by several pollution indicators including the index of geo-accumulation (Igeo), Enrichment factor (EF) and pollution load index (PLI). The result of Igeo showed that the contamination degree of Cd and Cr ranged from unpolluted to moderately polluted in the most stations and show highest pollution compared to other metals. The EF results show moderate enrichment for Pb (in A1 and A2 sample stations), Cr (in A12 sample station), Cu (in A1 sample station) and Zn (in A1 and A15 sample stations). The values of PLI in most stations are > 1, so they are polluted, but the noticeable value of PLI is 3.12 which related to A12 sample station and other values varied between 0.48-1.51. Cluster Analysis (CA) and Principle Component Analysis (PCA) indicated that Cd, Pb, Zn, and Cu pollutions are mainly originated by anthropogenic sources while other metals have a lithogenic sources. The main sources of contamination in study area are produced by industrial activities and shipping.

The purpose of this study was to interpret depositional environment and the most effective diagenetic processes on the reservoir quality of the Asmari Formation in wells no. 3 and 6 in the Ramin Oil Field in the north Dezful embayment. Petrographic examination of 230 thin sections led to identification of 12 sedimentary facies deposited in five sub-environmentsincluding tidal flat, lagoon, shoal, open marine and outer ramp, where sedimentation took place in a homoclinal carbonate ramp. In addition, petrographic studies show a wide range of diagenetic processes affected these rocks but three processes including cementation, dolomitization and dissolution are the most important processes affecting reservoir properties of the studied formation. Dissolution and dolomitization processes with a higher frequency than the cementation process are mostly have affected the mud supported and peloidal facies and led to enhancement of the effective porosity (more than 12 %) and permeability (with a K more than 1 mD) as well as increased reservoir quality. On the other hand, cementation process led to a reduction of reservoir quality (with a PHIE less than 12 % Kless than 0.1 mD and SWE more than 0.6) in some parts of the succession (especially in well No. 3).Generally, shallow and mostly mud-supported facies are more abundant than other facies (with a frequency about 60%) and more affected by dissolution and dolomitization processes that played an important role in the increasing of reservoir quality of studied carbonate in the Asmari Formation in Ramin oilfield.

Limestones of Elika Formation, were deposited in some part of the Alborz range during sea-level rise of early Triassic. The Elika Formation in Kelarize consists of two members. The lower members (lower Triassic) has been mostly deposited during storm and quiet periods, while the upper member (Middle Triassic) has been exclusively deposited during quiet periods. Thickness of the Elika Formation at the Kelarize section is up to192 m. The Elika Formation in the Study area, is unconformably overlain by the Shemshak Formation. Petrography and microfacies of the Elika Formation indicate that the calcareous microfacies are deposited in four depositional sub-environments including, open marine, bar, lagoons and tidal flat. Sedimentary environment of this formation in Kelarize section is very similar to the recent carbonate basins. These sediments are deposited in a homoclinal ramp. Based on field observations, thin sections study and sedimentary facies, 3 third-order sequences were recognized. Each sequence consists of a few shallowing upward para-sequence.

The Amiran Fm. (Mastrichtian- Paleocene in age) was deposited in the Zagros basin. This Fm. Comprises variegated shale beds in the Lorestan province. As presumably the majority of the formation was deposited in a deep marine environment, it is expected to find organic-rich facies within fine- grained facies of the Amiran. Fm. Hence, attempts were made to evaluate hydrocarbon potential of the Am. Fm. in this region. For this purpose, an outcrop of the Amiran Fm. in northern flank of the Amiran anticline was investigated and 52 samples were collected, of which12 samples, particularly of dark color fine-grained facies were selected for geochemical analysis. These samples were analyzed by Rock-Eval Pyrolysis type III in Research Instituteof Petroleum Industry (RIPI). Geochemical analysis revealed that TOC content of the 55% samples is less than 0.5 Wt %.Other parameters such as S1, S2, S1 + S2 suggest weak hydrocarbon production. Results also revealed that the Amiran Fm. predominatly copmrises kerogen types III and IV. The HI vs. Tmax cross-plot and PI vs. Tmax show that 73% of the samples fall in catagenesis stage. According to Jone’s diagram, the Amiran Fm. represents various organic facies including (BC, CD and D). Various organic facies may imply mixing of land-derived OM with autochthonous OM during turbidity currents, which intermittently occurred within the basin. Hence, we purpose that organic facies of the Amiran Fm. were deposited in oxic to suboxic conditions during relative see- level fall.

Permian rocks of Bagh-e-Vang section with the age of Bolorian-Dorashamian (Jamal Formation) consist of carbonate rocks. These rocks overlie Sardar and underlie Sorkh Shale formations. Petrographic studies show that these rocks can be divided into 13 calcareous microfacies. Integration and results of microscopic studies and field evidence have demonstrated that the mentioned calcareous microfacies have deposited in 4 sub-environment of shore, lagoon, bar and open sea. The lack of build-up, slump and flows resulting from turbidity is an indication that Permian carbonate platform of Bagh-e-Vang section is of homoclinal ramp type. The formation and development of this carbonate platform is simultaneous with sea transgression in Belorian. Based on field observations, thin sections study and sedimentary facies, 2 third-order sequences and 1 second-order sequences were recognized. Each sequence consists of a few shallowing upward para-sequence.These sequences with both type 1 and 2 sequence boundaries are recognized in carbonat deposits.The Upper Permian sequences in the study area are correlated global sea – leve curve.

The original mineralogy of carbonate- evaporite series of Kangan and Dalan formations in central Persian Gulf area has been determined in this study. Uranium and strontium elemental concentrations were determined in the samples of two wells using inductively coupled plasma tool. The concentrations of these two elements show the same variations in the studied formations. Comparison of these elements with uranium wire line data showed the same trend. As both uranium and strontium preferentially enrich in aragonite other than calcite, they can be used for determination of the original mineralogy of carbonate deposits. The results showed that in the end-Permian time, there was an aragonite sea stage that was favorable of life for carbonate secreting organisms. After that, an equilibrium condition was dominated with simultaneous precipitation of aragonite and calcite. At the end-Permian time just below the Permian-Triassic boundary, there was an acidic condition that was hostile to life. Comparing this period with other sections withcomplete end-Permian record showed that there is a gap in these sediments. Using carbon- hydrogen- uranium and oxygen system, anoxic conditions determined at the later stage. These results show that combination of acidic and anoxic conditions made a serious problem for life at the end-Permian time in central Persian Gulf area at the time of deposition.