پژوهش های چینه نگاری و رسوب شناسی (مجله پژوهشی علوم پایه دانشگاه اصفهان)
سال:1403 | دوره: | شماره: |تعداد مقالات:4

The shale-marlstone interval of the upper Aitamir-lower Abderaz formations in the southeastern part of the Kopet-Dagh Basin was investigated using planktonic foraminiferal studies to determine how surface and water column characteristics of the basin were influenced by Cenomanian/Turonian (C/T) boundary conditions. Three planktonic foraminiferal biozones (upper part of the Rotlipora cushmani Total Range Zone, Whiteinella archaeocretacea Interval Zone, and lower part of the Helvetoglobotruncana helvetica Total Range Zone) have been identified in the studied section, which suggests a late Cenomanian–early Turonian age for this interval. The Aitamir-Abderaz boundary is supposed to be conformable in this section because of the presence of all the C/T boundary planktonic foraminiferal biozones and no evidence of subaerial exposure in the field. The presence of benthic foraminifera throughout the studied section indicates that the anoxic event 2 (OAE2) interval in this succession has never experienced a complete oxygen depletion at the bottom water. However, the low diversity of planktonic foraminifera and low abundance of specialized species indicate more stressful conditions due to intensified weathering and higher productivity (eutrophic conditions) during the OAE2 interval. This interval is punctuated by a transient period with higher diversity of planktonic foraminifera and more abundance of specialized species at the upper part of R. cushmani biozone-lower part of W. archaeocretacea biozone. This interval can correspond to the “Plenus Cold Event” and demonstrates more stable and oligotrophic conditions across the OAE2.

This research aims to investigate the hydrogeochemical changes and brine evolution process in dry areas, using the Bajestan Playa as a case study. The Bajestan playa is one of the largest playas in the Middle East, located in northeastern Iran within the Central Iran Plate. The playa is surrounded by volcanoclastic rocks and has an arcuate shape with a gentle slope from the margins to the center. The climate of the region is arid and the area belongs to the “D” type in Geomorphological classification. We collected and analyzed 35 samples by the XRF method in September 1998. The results showed that group (1) potassium, calcium, sulfate and magnesium ions; Group (2) of chlorine and sodium ions and group (3) of carbonate and bicarbonate were formed. The spatial distribution of elements indicated that group (1) elements were more prevalent in the south and central parts of the area, group (2) elements were more abundant in the north and east parts, and group (3) elements were more dominant in the west part. The current facies of the playa brine is magnesium sulfate, and the possible evolution paths are I, II, IIIA, IIIB, IIIC. Therefore, we can expect sodium chloride facies for the playa brine in the future. We concluded that the origin and evolution of water resources were the main factors affecting the hydrogeochemical changes of the Bajestan Playa brine.

The present study aims to identify and examine gravel-sized ventifacts in the vicinity of Abdia village, located in the southern part of the city of Damghan. To collect samples required for the present study, an area approximately four km wide was logged. Nearly 200 gravel-sized ventifacts with an average size of 36 mm in diameter were collected from above-ground surfaces. The ventifacts collected for the present study were found within unconsolidated sedimentary structures. The identification of a variety of ventifacts including rubbing pits, vortex pits, facets such as dreikanters and einkanters, spheroid ventifacts, and worm-shaped gravels (rillstones) distinguishes the study as there have been no previous reports on the aforementioned ventifacts in Iran. The data analysis also shows that the studied area had a different, moist climate in the late Pleistocene–early Quaternary(?). However, the passage of time along with the formation of a dune and desert pavement in the area has brought an arid climate with strong winds, which is an appropriate environment for the formation of gravel-sized ventifacts.

The Middle to Late Paleogene Zagros sedimentary basin witnessed the development of carbonate platforms teeming with large benthic foraminifera (LBF), exemplified by the Jahrum and Asmari formations in Fars Province, SW Iran. The LBF assemblage is dominated by Nummulites and Orbitolites, accompanied by smaller benthic foraminifera. In the present study, microfacies analysis, palaeoenvironmental reconstruction, and interpretation of depositional sequences/cycles in the late Eocene Jahrum and lower Miocene Asmari carbonates were conducted on the subsurface section of the Kuh-e-Mond Oil Field, located in Coastal Fars Province, within the Zagros Foreland Basin. The studied wells, designated as MD-07, MD-06, and MD-02, exhibit respective thicknesses of 33 to 130 m for the Asmari Formation and 382 to 517 m for the Jahrum Formation. The interpretation of facies suggests that these intervals precipitated along a low-angle ramp-type platform in a shallow-water setting. Nine distinct microfacies have been identified, representing tidal flats, lagoons, platform margins, and shallow open marine sub-environments. Based on the integration of petrographic studies and petrophysical logs (Gamma-ray log), three depositional sequences or cycles within the Jahrum Formation (SQ A, SQ B, SQ C) in the MD-07 well, and one depositional sequence or cycle within the Asmari Formation (SQ D) have been identified in the MD-07, MD-06, and MD-02 wells. These determined depositional sequences/cycles are not only influenced by global sea level fluctuations but also impacted by the regional tectonic history, including uplift and subsidence rates.