فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و هشتم شماره 4 (پیاپی 89، زمستان 1401)

The Baghamshah Formation (Middle Jurassic) at the Senj stratigraphic section, northeastern Tabas, central Iran, consists of diverse and relatively well-preserved palynomorphs, including spore and pollen of land plants, microscopic algae, acritarchs, Tasmanites, fungal spores, foraminiferal test linings and dinoflagellate cysts. The miospores are attributed to the Pterophyta (11%), Lycophyta (1%), Coniferophyta (80%), Cycadophyta (3%) and Pteridospermophyta (5%). Among the miospores, the maximum frequency is related to Classopollis from the Chirolpidiaceae family of conifers. The abundance of Classopollis in the studied samples may represent the abundance of Chirolpidiaceae in the composition of vegetation nearby the sedimentary environment, the abundance of produced pollen, and/or the vicinity of the habitat of the parent plants to the depositional environment. Previous investigations about the environment of the Chirolpidiaceae family indicate the predominance of hot and dry climates. The abundance of Botryococcus algae separately or attached to Classopollis also supports this type of weather. The dominant size of the miospores in the stratigraphic section (25–35 µm) indicates the transport by a wind from highland to lowland. Based on the model of Sporomorph EcoGroups (SEGs), miospores typifying all the six plant communities are present in the studied strata. The palaeoclimate study was determined by the pattern of relative abundance of drier/wetter and warmer/cooler elements. The consequences of these calculations approve the hot and dry climatic conditions during the accumulation of the strata examined.

The Lower Cambrian Barut Formation is one of the most important lithostratigraphic units in reconstructing the paleogeography of northern Iran during the early Cambrian time. Herein, we present detailed facies analysis data of this formation in the Barut Aghaji Section in southwest Zanjan to analyze the palaeoenvironment. The Barut Formation in this section consists of about 500 m thick mixed siliciclastics and carbonate rocks and its upper and lower contacts with both Soltanieh and Zaigun formations are gradational. Seven recognized lithofacies/microfacies include: red, fine- to medium-grained arkosic sandstone containing physical and biogenic tidal indicators (F1), red to green, finely laminated mudrock containing tidal biogenic structures (F2), dolomitic stromatolite boundstone (F3), dolomitic mudstone with evidence of former evaporites (F4), dolomitic thrombolite boundstone (F5), carbonate breccia/conglomerate (F6), and dolomitic oncoid wackestone (F7). These facies are arranged in shallowing-up cycles consisting of mixed flat sandstones overlain by mud flat mudrocks and supratidal carbonates. Evidence of evaporite minerals in the Barut Formation along with other contemporaneous early Cambrian evaporite basins in the Middle East, India and Pakistan, indicates a dry and warm palaeo climate during the deposition of the sediments.

Qazvin alluvial fan is the largest alluvial fan in the northern margin of the Qazvin Plain. This research focuses on describing and interpreting the origin of the sediments and facies model of this alluvial fan using 24 sediment samples from 11 sections and two surface samples. The results of facies granulometry show that the size of the sediments of the alluvial fan shows wide variations from gravel to clay, and the texture of the sediments of this alluvial fan is mainly gravel, gravelly sand and sandy gravel with very poorly sorting and fine skewness. The sedimentary rock fragments are mostly igneous and limestone. Facies study led to the determination of eight facies including coarse to medium-grained lithofacies (Gmp, Gcp, Gcp-Gmp/Sm, Gmg, Glns, Spl, and Sm), and calcrete facies (P) which grouped into two facies association. The results of this study show that the Qazvin alluvial fan can be considered a waterlaid-dominated alluvial fan due to the superiority of fluvial facies and the absence of the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red matrix-supported gravel.

Stratigraphic and sedimentology studies have been carried out on sixty-nine rock samples related to the one hundred fifteen meters thickness of the Dalichai and Lar formations in the southeast of Zanjan. The carbonate layers of the Dalichai Formation with seventy-eight meters thickness overlay the strata of the Shemshak Group/Formation (the boundary has been covered) and are overlaid by thirty-seven meters thickness of carbonate layers of the Lar Formation with gradual boundary in this area. There are some sedimentological changes in the succession across the Dalichai-Lar formations boundary such as color changes, bedding thickness changes from medium to thick, disappearance of Thalassinoides facies, chert nodules, and Ammonite/Belemnite facies and finally changes in microfacies from mudstone to the wackestone/packstone (deeper to the shallower). The Lar Formation is the youngest formation in this area that has been covered by the Quaternary sediments. Five lithofacies have been identified based on field and microscopic studies: 1- Pelloidal packstone with intraclasts, 2- Pellet/oncoid wackestone/packstone, 3- Mudstone with Thalassinoides, 4- Bositra buchi pelagic packstone and 5- Pelagic mudstone that shows basin and outer ramp as depositional environments for the Dalichai and Lar formations in this section. Field and facies studies show a deepening upward trend to the middle parts of the section (upper parts of the Dalichai Formation) and followed by shallowing upward trend to the upper parts (Lar Formation) of the section.

Sequence stratigraphy is a branch of stratigraphy that can enable us to correlate deposits with considerable accuracy. This research aims to investigate the role of fossils in the recognition of system tracts and sequence boundaries along succession using microfacies features. To achieve this aim, we studied the Qom Formation at the Qasr-e-Bahram section located in the south of Garmsar. This formation is mainly composed of argillaceous limestones, limestones, and marls, overlies the Lower Red Formation, and lies under the Upper Red Formation disconformably. Based on paleontological studies, the suggested age is the Late Aquitanian to Burdigalian (Early Miocene). The microfacies analysis indicates a variety of facies and environments (lagoon, carbonate barrier, and open marine). The significant presence of red algal with other reef-forming elements within microfacies as well as the presence of turbidite facies probably implies a shelf carbonate platform. According to geological field and laboratory studies, deposits of the Qom Formation include four third-order depositional sequences, and the presence and abundance of fossils such as foraminifera, algae, bryozoans, and corals were useful tools in identifying the systems tracts and their boundaries.

The Shahbazan Formation is dated to the middle to late Eocene age, after the Pyrenean orogenic phase. Following the progression of seawater, it was deposited in the Lorestan subzone and the folded Zagros basin. The lithology of this formation is composed of weathered white to thick-bedded, porous, and sugar textured, brown dolostones and dolomitic limestones. The thickness of this formation at the Darabi, Maleh Kuh, Langar, and Chenareh sections is 289, 269, 309.7, and 294 meters, respectively. In the Darabi, Maleh Kuh, and Langar sections, the lower boundary of the Shahbazan Formation is disconformity with the Kashkan Formation and overlain by the Asmari Formation with discontinuity. Furthermore, only in the Chenareh section does the Shahbazan Formation overlies conformably on the Pabdeh Formation and is overlined with a disconformity surface by the Asmari Formation. Microfacies studies revealed 12 microfacies within the Chenareh, Langar, Poshtejangal (Darabi section), and Maleh Kuh anticlines, deposited in five sedimentary environments (facies belts), including open marine A, bioclastic shoal B, lagoon C, tidal zone D, and supratidal F. These environments are part of a ramp-type carbonate platform with a uniform slope in the inner and middle ramp.