فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و سوم شماره 3 (پیاپی 68، پاییز 1396)

Sporomorph EcoGroups data and the relevant plant communities are considered as a possible routine used to draw palaeoecological inferences for their host strata. Occurrence of high abundant, diversity and well preserved miospores in the Dalichai Formation of the central and eastern Alborz Ranges allows for this method to be used to obtain certain palaeoecological implications of its depositional environment. The misopores are classified as Sporomorph EcoGroups (SEGs) that with reference to their parent plants each indicate particular palaeocological specifications.
According to the SEG data derived from study of the Dalichai Formation's palynological assemblages, declination of miospores representing Upland/Lowland plant communities and the proliferation of those characterizing Lowland/Coastal-Tidal plant associations is interpreted to signify relatively low sea level and sedimentaion in a marginal marine setting.
Furthermore, the ratio of wetter/drier and warmer/cooler elements suggests deposition under a moist, ±warm climate during the Middle Jurassic in central and eastern Alborz Mountains. Notable abundance of the fern spores in the palynofloras studied tends to support this palaeoclimate generalization.

Early to Middle Cambrian successions exposed at the Shirgesht area, Tabas Block of central Iran has yielded a high diversity and abundant ichnofossils with arthropod trackways. These trace fossils contain diverse ethological patterns, including furrowing or crawling (Cruziana), resting (Rusophycus), walking (Diplichnites), sideways grazing (Dimorphichnus) and swimming grazing (Monomorphichnus). The assemblage of trace fossils reported from the Early to Middle Cambrian of the Tabas Block, has a significant stratigraphic importance as they provide evidence regarding the developmental patterns during the early phase of life on earth. Stratigraphically, trace fossils studies is significant for defining the age of the unfossiliferous Cambrian successions of the Tabas Block from Central Iran where typical diagnostic trilobite fauna is absent. According to Cruziana ichnostratigraphy and comparsion the Lalun ichnofauna with other examples from similar age, the present assemblage could represent the late Early to Middle Cambrian. The distribution of trace fossils in the Early to Middle Cambrian successions reflects the paleoecological conditions including the availability of oxygen and nutrient influx. Hwever, the diversity and abundance of infauna, smaller trace fossil size, sporadic distributions of burrowing and lower intensities of bioturbation of trace fossil suite and the presences of evidence of predominance of trilobite trace fossils with morphologically simple represents a stressed expression of the ichnofacies and ichnologically stressed environment during deposition such as estuary.

The present study is an attempt to biostratigraphically classify the rocks of Gurpi Formation at Samand Anticline with the help of calcareous nannofossils. The succession measures 197 meters in thickness and consists of shale, marl and marly limestone. A total of 96 species belonging to 45 genera of calcareous nannofossils have been identified whose distribution points to delineation of 11 international biozones. Consequently, the rocks of Gurpi Formation are attributed to middle Campanian through late Paleocene (Selandian) time and the K/Pg boundary interval is found to be continuous. Taking into account the absence of nannofossil biozones NP2-NP4 as well as the sedimentological evidence observed, the non-deposition event at the boundary interval has occurred later than the previously thought time identified on the basis of planktic foraminifera.
Consequently, the rocks of Gurpi Formation are attributed to middle Campanian through late Paleocene (Selandian) time and the K/Pg boundary interval is found to be continuous. Taking into account the absence of nannofossil biozones NP2-NP4 as well as the sedimentological evidence observed, the non-deposition event at the boundary interval has occurred later than the previously thought time identified on the basis of planktic foraminifera.

The Permo-Triassic Dalan-Kangan and upper Jurassic Arab formations are important carbonate-evaporate reservoirs resulted from depositional and diagenetic heterogeneities. The objectives of the study are comparison precursor mineralogy, identification of dominant pore types and clarify the role of diagenetic processes on petrophysical characteristics and reservoir quality of the Dalan-Kangan and Arab formations in the Persian Gulf. To achieve this goal core description and petrographic study and core poroperm data from two hydrocarbon fields in the Persian Gulf were integrated. Pore system studies show that different pore types contribute to the fluid flow and production within the Dalan-Kangan and Arab formations. These pore types are inter-granular, intercrystalline, touch and non-touch vugs and microspores. The initial mineralogy of the components had a significant effect on pores system distribution and trend of the diagenesis of the two studied intervals. During the Permo-Triassic and upper Jurassic, the composition of ocean waters has been suitable for deposition of non-skeletal components with aragonite and calcite mineralogy, respectively. Thus, moldic pores in the Dalan and Kangan reservoirs and intercrystalline and inter-granular pores in the Arab Formation occur as the dominant pore types. In Dalan and Kangan formations, micropores are more frequent than the Arab Formation, which is attributed to the dominance of mud-dominated facies during the Permo-Triassic periods. Detailed diagenetic studies indicate that the studied intervals were exposed to dissolution, cementation, anhydrite mineralization, dolomitization, physical and chemical compaction and fracturing after deposition. Dissolution, anhydrite mineralization and cementation seem to have exerted the main effect on pore system properties

In order to study biostratigraphy of the Pabdeh Formation in southwest of Ilam, Marbera section was selected. In this section, Pabdeh Formation is mainly consists of marls, shale and marly limestones. The study of calcareous nannofossils led to the recognition of 72 species and 26 genera. According to the first and last occurrence of index species and based on Martini (1971) zonation, the following biozones are identified:, Tribrachiatus contortus Zone (NP10), Discoaster binodosus Zone (NP11), Tribrachiatus orthostylus Zone (NP12), Discoaster lodoensis Zone (NP13), Discoaster sunlodoensis Zone (NP14), Nannotetrina fulgens zone (NP15), Discoaster tanii nodifer Zone (NP16), Discoaster saipanensis Zone (NP17), Chiasmolithus oamaruensis Zone (NP18), Isthmolithus recurvus Zone (NP19), Sphenolithus pseudoradians Zone (NP20), Ericsonia Subdisticha zone (NP21), Helicosphaera reticulate Zone (NP22), Sphenolithus predistintus Zone (NP23), Sphenolithus distentus Zone (NP24), Sphenolithus ciperoensis Zone (NP25). As a result of this study and based on the obtained biozones, the age of Pabdeh Formation in southwest of Ilam, is Early Eocene (Ypresian) to Late Oligocene (Chattian).

A relatively complete succession of Viséan to Serpukhovian rocks is exposed in the northern Alborz, where two sections Naserabad and Dozdehban have been selected for their biostratigraphic interest. The archaediscoids are probably the best stratigraphical microfossils during the Viséan and Serpukhovian. In this study, the archaediscoids of northern Alborz are analyzed owing to their potential in biostratigraphic and chronostratigraphic subdivisions. During the early Viséan, MFZ9 foraminiferal biozone, the proposed ancestor of the archaediscoids Lapparentidiscus appears followed by the massive occurrence of primitive archaediscids, defining the MFZ10 biozone. The MFZ11 can be well defined by the first occurrence of Uralodiscus rotundus. The base of MFZ12 of this area is characterized by the first occurrence of Nodosarchaediscus and the top by Paraarchaediscus at concavus-angulatus stage. The lower upper Viséan rocks might be absent from the northern Alborz, probably because a mid-Viséan tectonic event occurred in this area. The middle late Viséan (MFZ14) is dominated by the acme of Archaediscus at angulatus stage and archaediscoids with occluded and semi-occluded lumen as well as the first occurrence of Neoarchaediscus and Kasachstanodiscus. The Archaediscus/Paraarchaediscus at angulatus stage with transitional forms to the tenuis stage and Neoarchaediscus akchimensis mark the late late Viséan (lower MFZ15) in the succession. The lower Serpukhovian rocks (upper MFZ15) of the studied sections are characterized by occurrences of new large Kasachstanodiscus and Archaediscus and a significant decrease in Paraarchaediscus, Nodosarchaediscus and Archaediscus at angulatus stage. The late Serpukhovian (MFZ16) is marked by first occurrences of Brenckleina and Brenckleina rugosa.