JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2009 | Volume:25 | Issue:1 (36)|Papers Count:8

In this study, 45 drilling cuttings of Pabdeh and Kazhdumi fomtations in Rag-e-Safid oilfield, in southern Dezful Embayment, were analyzed by Rock-Eval instruMent. Sz vs. TOC plot revealed that kerogen type in this oilfield predominantly is Type II. Significant Szadsorption by matrix in Pabdeh (2.5-4 mg HC/gr rock) and Kazhdumi (7-12 mg HC/gr rock) formations is due to low maturation as well as low gas-oil ratio potential factor. Amount of TOC directly influences the mineral matrix effect on hydrocarbon adsorption on Pabdeh Formation. Live organic carbon in Pabdeh and Kazhdumi formations was in the range 0.22-2.29% and 1.7-2.25% by weight, respectively, which showed said formations have fair to excellent potential for petroleum generation. Transformation ratio of kerogen in studied formations was low (0.07-0.15), so these formations have not generated significant amount of petroleum as is supported by low Tmax data. GORP factor in studied formations (0.2-0.5) reveal that their oil generation potential is higher than gas generation potential. Considering to iso TOCoil and TOCgas maps, when Pabdeh Formation was deposited, basin in northwest and southeast was deeper than central part of the oilfield.

Two stratigrphic sections from Dahu Fonnation (Early Cambrian), at Gezuieh and Dahuieh (type section) in E and SE Zarand, NW Kennan, with thickness of 227 and 240 meters respectively, were measured. These data have been used for interpretation of provenance of these siliciclastic sediments. Lithofacies, architectural elements and petrofacies analysis show that Dahu Fonnation has been deposited in meandering river system when the river was flowing from south toward the north. Provenance studies and depositional history, using petrography frameworks characteristics, paleocurrent analysis and tectonic setting (using the triangle diagram Qt-F-L and Qm-F-Lt), show that the sediments. of Dahu Fonnation may have been derived from alkali granite related to Pan-African orogeny from Saudia Arabian train. These sediments may have been deposited as post rift sediments in Kennan region. We hope that this infonnation can be used for paleogeographical reconstruction of the Early Cambrian time in local and regional scales.

The study area (Cheshmeh-Ali and its catchment area) is located in 32 km northwest of Damghan. The catchment area is mainly composed of thick-bedded and massive limestones of Lar Formation and thinbedded limestones and marly limestone of Dalichay Formation. In order to evaluate the effect of stratigraphy on karst development in the above-mentioned formations, the geology, the physical and chemical characteristics of water, and characteristics of input system in catchment area of the spring were studied. On the subject of physical and chemical characteristics of water, the discharge of spring, water temperature, electrical conductivity, pH, and dissolved carbon dioxide were measured in-situ and the major cations and anions measured in the lab. The above-mentioned measurements were carried out monthly during 2005-2006 water-year. According to the insignificant variability of all physical and chemical parameters of water and also the characteristics of the catchment area of the spring (i.e. the absence of important karst geomorphological features such as closed depression, sinkholes, large and deep solutional joints and fractures etc.) it may be argued that the aquifer feeding the Cheshme-Ali karst spring is dominated by diffuse flow system. Such a system in karstic aquifers indicates that the degree of karstification in the study area is low. According to the geology setting in the study area, the stratigraphy is one of the most important reasons for insignificant developing of karst in the catchment area of the Cheshmeh-Ali karst spring. Such that the Dalichay Formation (which is slightly suitable for karstification) is located between the thick-bedded and massive limestones of Lar Fbrmation (which is highly appropriate for developing karst) and the location of spring which results in a gradual groundwater flow from aquifer to the spring. The gradual groundwater flow from aquifer to the spring has prevented the developing of karst in the aquifer.

Ab-Talkh Formation (Campanian-Maastrichtian) is one of the lithostratigraphic units of the Kopeh-Dagh basin. Marine palynomorphs (Dinoflagellates) with good preservation are found in lower and middle parts in the type section while the upper part contains few palynomorphs. In the present article in addition to palynology, seven samples from the Ab Talkh Fonnation in type section were selected for geochemical analysis using Rock-Eval pyrolysis. Palynology slides indicate that the Ab-Talkh Fonnation at the type section was deposited in a proximal shelf to marginal basin and under an oxic, medium to high energy condition. The Rock-Eval pyrolysis results show that these samples haven't reached the catagenesis zone (Tmax higher than 435 degrees centigrades) so they are immature. These samples contain kerogen type III and have poor genetic potential of petroleum generation. It should be mentioned that results from Rock- Eval pyrolysis confinn palynological results.

Marun and Kupal oilfields situated in south east of Ahwaz city next to Agha Jari and Ahvaz oilfields are among the largest oilfields in the Dezful Embayment. Ham and Sarvak formations constitute the main reservoirs. In order to investigate geochemical characteristics, oil samples of Ham and Sarvak reservoirs studied by analyzing their physical and chemical properties. Investigation based on physical properties including sulfur content (%), nickel to vanadium ratio, API gravity and other physical properties suggest similar maturities for the oil samples. Biomarkers study of extracted Terpanes and Steranes of saturate section reveals that accumulated hydrocarbons in understudy reservoirs were originated from carbonate source rock. The kerogen of source rocks is possibly type II or mixed of type II and III. Biomarker investigation also detected that the candidate source rock(s) are thermally mature. Studying of Oleanane index reveals that oils in Marun and Kupal oilfields were originated from marine organic matter. It also shows a pre-Cretaceous source rock(s).

The Shahbazan Formation with the age of Middle Eocene to Late Eocene consists of dolomite, dolomitic limestone and marl sequence. The study area is located in the southwest of Iran in the Lorestan province. Based on field observations and petrographic studies (grain size and fabric), five different dolomite types are recognized. In the dolomicrite (dolomite I) due to the presence of evaporite mold, peloid grain and algal laminates, it has been concluded that dolomicrites were deposited in a tidal flat environment and secondary dolomite (II, III, IV and V) formed during shallow to deep burial diagenesis. In diagenetic environments, by increasing diagenetic processes, in dolomicrite, Mg, Fe and Mn value have been increased while the contents of Ca, Sr and Na decreased. According to change in mineralogy component and dissolution prossess in probable boundary between the Shahbazan and the Asmari Formations, the contents of Ca, Sr and Na have been increased and the value of Mg, Mn and Mn/Ca decreased. On the basis of cluster analysis, geochemical results of analyzed samples divided into four different groups that indicate different- characters of sedimentary environment.

The upper part of the Chamanbid Formation at the type section was studied for determination of paleoenvironmental changes by using palynomorphs and organic matter contents. Diverse and reasonably well preserved palynomorphs recorded in many samples. The upper part of the Chamanbid Formation consists of calcareous shale and limestone (ca. 240 m thick). Of 34 rock samples collected, 30 proved to be palynologicaly productive containing proximate dinoflagellate cysts, spores, pollen, foraminiferal test lining, SOM and wood debris which statically studied.Abundance of non-mature bladed form large brown wood debris, bright SOM, foraminiferal test linings and few numbers of proximate dinocysts indicate that the upper part of the formation deposited in a lagoon that witnessed intermittent marine incursions.

Four facies associations can be differentiated in the modem deposits of the lower reach of the Zayandeh river drainage basin in the south-east of Esfahan.They are debris-flow-dominated alluvial fan, stream-flow-dominated alluvial fan, lake and overbank. The first includes matrix-supported gravel facies (Gms) and massive muddy sand facies (Sms). The second consists of unstratified to crudely stratified facies (Gm), plannar cross-bedded facies (Gp), through crossbedded facies (Gt), and clast-supported gravel/conglomerate and trough cross-bedded facies (St). The third comprises red to purple massive mud facies (Fm) and yellow to greenish mud, interlayering with sand layers facies (Fsc). The forth includes matrix-free massive sand/sandstone facies (Sm) and laminated khaki mud facies (Fl).The quantitative summary of these facies emphasizes a periodic deposition in a semi-arid setting and ephemeral rainy conditions of deposition with dominance of low energy. Fluctuation in rainfall caused periodic change of the base level, which were reflected both in lacustrine deposits and in the deposits produced by the alluvial systems, particularly in the distal fan.