JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2011 | Volume:27 | Issue:2 (43)|Papers Count:10

In order to understand facies belts, depositional environment, original carbonate mineralogy, paleotemperature and diagenetic environment, 624 m of the Garau Formation (Neocomian-Aptian) in type section (SW flank of Kabirkuh Anticline, in Lurestan province) was investigated by petrographic and geochemical analyses. Lower boundary of this formation is not exposed in the type section, but it overlies the Gotnia Formation in well no. 1 of Kabir Kuh and overlain by the Sarvak Formation. It is believed that the Garau Formation is a source rock in the Zagros Basin. Facies studies led to the recognition of deep marine facies belt. Absence of turbidite deposits and reefal facies and existence of peloid facies indicate that the Garau Formation was deposited in a carbonate ramp environment. Major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the Garau Formation. Elemental evidences (such as high Sr value) and oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy of this formation. Major and minor elements and carbon and oxygen isotope values (variations of Sr/Ca and 18O values versus Mn) suggest that diagenetic alteration occurred in an open diagenetic system. Temperature calculation based on the oxygen isotope value of the least-altered samples, using Anderson and Arthur (1983) equation, indicates that paleotemperature was 29.2oC.

Diverse and reasonably well preserved palynofloras including 148 species, dominated by¬ microphytoplankton cysts (acritarchs and prasinophyte phycomata) and spore assemblages, occur in most of surface samples of the Geirud Formation at the Dehmolla section; scolecodonts and chitinozoans are also represented as subordinate components. Co-occurrence of marine and terrestrial palynomorphs clearly indicates deposition in a marginal marine setting. Vertical distribution pattern of spores permits erection of two local assemblage zones in the material studied (here informally termed assemblage zones I and II). Occurrence in assemblage zone I of such distinctive spores as Grandispora inculta, Cymbosporites catillus, Geminospora lemurata, Teichertospora iberica, Laevigatosporites ovatus, Densosporites spitsbergensis, Punctatisporites labiatus, Retusotriletes rugulatus, R. pychovii, R. dubiosus, Dictyotriletes australis, Diducites mucronatus, Archaeoperisaccus sp., Stenozonotriletes conformis, and Ancyrospora ancyrea collectively denotes an early Late Devonian (Frasnian) age; the assemblage appears to be compatible with the ovalis-bulliferus and parts of the optivus-triangulatus and torquata-gracilis Assembalge Zones of the Old Red Sandstone Continent (ORSC). The succeeding assemblage II embracing Retispora lepidophyta, Vallatisporites hystricosus, V. vallatus, Verruciretusispora loboziakii, Punctatisporites planus, Densosporites rarispinosus, and Grandispora facilis correlates with the pusillites-lepidophyta, flexuosa-cornuta, and  torquata-gracilis (partial) Assemblage Zones of the ORSC and is ascribed to late Late Devonian (Famennian). Additionally, a barren interval (20 m thick) devoid of any palynomorphs can also be identified in the basal, mostly red conglomerates and coarse-grained sandstones of the section studied. Co-occurrence of spore assemblages with such globally index microphytoplankton cysts as Cymatiosphaera perimembrana, Daillydium pentaster, Unellium lunatum, U. piriforme, Chomotriletes vedugensis, Crassiangulina sp. cf. C. tesselita corroborates the Late Devonian (Frasnian-Famennian) age assignment which is in general agreement with the faunal evidence. Affinity, diversity, and abundance of spores in the palynofloras investigated imply that contemporaneous coastal vegetation was probably diverse and likely dominated by lycopsids, filicopsids, and archaeopterid progymnosperms.

Aitamir Formation (Albian-Cenomanian) crops out in the Kopet-Dagh basin in north-east Iran. It is mainly composed of sandstone, shale, siltstone, and several carbonate beds. In siliciclastic sediments of the Aitamir Formation, mud beds show a significant decrease in bioturbations with respect to sandstone beds. Based on ichnofossils studies, nine trace fossils were identified in sandstone, siltstone and carbonate beds which include of Thalassinoides suevicus and Thalassinoides isp. (Glossifungites ichnofacies), Ophiomorpha nodosa, Palaeophycus tubularis, Skolithos isp. (Skolithos ichnofacies) and Thalassinoides isp., Planolites isp., Cylindrichnous concentricus, Chondrites isp., Ophiomorpha nodosa, Palaeophycus tubularis and Teichichnus isp. (Cruziana ichnofacies). Skolithos ichnofacies formed in high energy condition with respect to Cruziana ichnofacies and Glossifungites ichnofacies. Skolithos ichnofacies with low diversity, Skolithos isp. and vertical orientation Ophiomorpha present in well sorted and  trough- hummocky cross bedded sandy substrate. This ichnofacies indicates of high energy barrier complex. Whereas Cruziana ichnofacies and Glossifungites ichnofacies with higher diversity and mainly horizontal to slightly oblique, trace fossils in sandy substrate with moderate sorting are formed in low energy condition in shoreface environment. Sedimentary evidences and investigated ichnofacies in vertical succession show that sandstones in the lower portion of the Aitamir Formation formed in barrier complex and sandstones sediment in upper portion deposited in shoreface environments.

Dariyan Formation is one of the most important hydrocarbon reservoirs of the South Pars gas field. Since abundance of Orbitolina family in these strata, our microfacies analyses are mainly based on their paleoecological characteristics. As shown by microfacies analysis in the SPOa and SPOb wells, depsoitinal and textural nature of the Dariyan Formation in this field are entirely different from its type section and the other parts of the Zagros Basin. Detialed sedimentological studies of this unit, its comparison with the Shuaiba Formation (equivalent of the Dariyan Formation in Arabian countries) in the north dome and compilation of these data with the paleogeographic features of Aptian, all are representing a regional carbonate ramp that was bordering an intrashelf leeward flank (leeward ramp) Employing different techniques, sequence stratigraphic study is carried out. In this approach facies association variations along with the gamma ray data and biota response to the sea-level fluctuations, are complied to recognize different system tracts in each well. This approach gives a good perspective for reservoir engineering. Vertical facies changes in the Darian Formation show that, on the whole, these strata represent a third order sequence and a HST that belongs to the lower unit.

Asteroids (a group of sea stars) were important members of the marine benthos from the Early Ordovician to Recent as is demonstrated by the occurrence of isolated ossicles in many marine types of sediment. Nonetheless, there is no report of these fossils from Late Cretaceous successions of Iran. Identified specimen in this research belongs to Metopaster parkinsoni, Family Goniasteridae and Order Valvatida that is reporting for the first time from Iran and Asia and the reason of its importance is that this specimen is the most eastern Metopaster fossil in Tethys Realm that is figured out until now. This species is obtained from second chalky limestone unit of Abderaz Formation in Padeha section, east of Kopet-Dagh Basin, northeast of Iran. Its well preservation permits to see all of necessary parameters for identification of shape, amount, size, elongation, ornamentation on marginal ossicles and the ossicular angel. Moreover, there are some bite marks of Late Cretaceous predators or scavengers on the surface of marginal ossicles that show the first evidences of biostratinomic process next to and after the death, before final burial. Before this, M. parkinsoni is identified in most of Late Cretaceous chalky limestone throughout the world, especially Paris Basin and England (Seaford Formation) and its uttermost abundance is in Micraster coranguinum Biozone, comprise Coniacian-Santonian boundary. Second chalky limestone unit of Abderaz Formation in Padeha section had mentioned species is equal to Seaford Formation of England and encompass the Coniacian-Santonian boundary.

1D modeling of oil generation is one of the methods used in petroleum system investigations. The candidate source rocks in the Pazanan field were subjected to 1D thermal modeling in order to investigate their maturation history and hydrocarbon generation. Oil generation modeling of the Pabdeh, Kazhdumi, Garau and Sargelu source rocks were constructed, in the Pazanan anticline and also in southern and northern synclines. Based on the investigation done during this study, it is evident, that there are significant differences between oil generations in the drilled wells in comparison to the adjacent synclines. These differences indicate that for example the Pabdeh Formation in Pazanan anticline is not reached to oil generation, while it is in peak of oil generation in northern syncline.The obtained oil generation history of source rocks during this study showed that quantity of oil generated of the Pabdeh and Kazdumi source rocks in synclines are more than anticline. In addition the oil generated from Garau and Sargelu formations is more than that of Pabdeh and Kazdumi source rocks.

Water seepage through foundation and abutments of dams is one of the most important parameters in design and construction of dams. Seepage endangers stability of dam in addition to lose reserved water. For this purpose, studies are done about permeability of the dam site rock masses and the sealing methods. Moreover, seepage of Tangab dam is discussed as a case study in this article. Based on the geological studies, three types of rock masses, i.e., Ilam-Sarvak, Kazhdomi and crushed zone, are distinguished in the study area. Kazhdomi Formation consisting of shale and shaly limestone underlies by Ilam-Sarvak limy formations. The crushed zone is located between these two rock units. Water seepage was evaluated according to the water pressure tests (lugeon) on these formations’ outcrops in the left and right abutments. Permeability of the rock masses interpreted based on secondary permeability index (SPI) considering the result of lugeon tests and the drilled core properties. Out of these three rock types, the crashed zone has the highest permeability, and Kazhdomi formation has the lowest permeability. In SPI classification, shale and shaly limestone of Kazhdomi Formation set on high class and need no improvement. But other rock masses need sealing due to the high permeability. Kazhdomi Formation can be counted as impervious bed to the dam site, thus grout curtain should extend to this formation. Results of the studies indicate that except of some cases, there is a reasonable correlation between SPI and RQD values. According to these results, type and composition of grout is suggested for construction of the grout curtain. The results also show that maximum value of water seepage occurs in the right abutment and if the grouting is successful, the seepage will decrease significantly.