Geochemistry of shales of the Qadir Member (Nayband Formation, Upper Triassic), East Central Iran (Tabas Block): implications for provenance and palaeogeography

Sponges, along with scleractinian corals, are among the main reef-building organisms in Triassic reefs. Hypercalcified groups, including the chambered sphinctozoans, and the unchambered inozoans, chaetetids, and spongiomorphids, represent the most abundant Triassic reef-building sponges. Earlier workers have described elements of the latter group as “hydrozoans.” Hexactinellid sponges, abundant in some Permian reefs (e.g., in Texas, Finks, 1960), are rarely known from similar Triassic deposits, in general (Tichy, 1975), and particularly from Upper Triassic stratigraphic units. Hexactinellid sponges have been sporadically reported from well-investigated Upper Triassic reefs in the western Tethyan region (e.g., Keupp et al., 1989). However, a variety of hexactinellid sponges have been reported from Upper Triassic deposits and reefal limestones of the northern and central Tethyan realm (Boiko, 1990; Wu, 1989; Wu and Xiao, 1989; Rigby et al., 1998).

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Wildfire Events at the Triassic-Jurassic Boundary of the Tabas Basin, Central Iran

10.21203/rs.3.rs-97849/v1 ◽

2020 ◽

Author(s):

Majid M Alipour ◽

Bahram Alizadeh ◽

AmirAbbas Jahangard ◽

AhmadReza GandomiSani

Keyword(s):

Major Change ◽

Lower Jurassic ◽

Upper Triassic ◽

Central Iran ◽

Sharp Boundary ◽

Depositional Settings ◽

Run Off ◽

Clastic Sediments ◽

Nayband Formation ◽

Microscopic Charcoal

Abstract This paper presents organic geochemical evidence pointing to the occurrence of wildfire events at the Triassic-Jurassic boundary in Central Iran. The studied outcrop section (the Kamarmacheh Kuh section) is comprised of the Upper Triassic Nayband Formation which passes conformably into the Lower Jurassic Ab-e-Haji Formation with no sharp boundary. Organic petrographical studies reveal a higher concentration of semi-fusinite macerals and microscopic charcoal at the boundary between studied formations. This observation can be an evidence for widespread wildfire events at the Triassic-Jurassic boundary of the studied area. Following these fires, vast areas of land were exposed for erosion and large volumes of clastic sediments were provided due to increased run-off. This agrees well with previous sedimentological and stratigraphical studies suggesting a major change in the depositional conditions from marine to non-marine at the Triassic-Jurassic boundary of the Tabas Basin. These findings can have important implications about paleo-depositional settings of the studied formations and the nature of the associated organic matter.

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Norian to Rhaetian scleractinian corals in the Ferdows Patch Reef (Nayband Formation, east central Iran)

Journal of Paleontology ◽

10.1666/12-001.1 ◽

2012 ◽

Vol 86 (5) ◽

pp. 801-812 ◽

Cited By ~ 1

Author(s):

Hannah M. E. Shepherd ◽

George D. Stanley ◽

Fatemeh Amirhassankhani

Keyword(s):

Patch Reef ◽

Scleractinian Corals ◽

Central Iran ◽

East Central ◽

Patch Reefs ◽

Faunal Assemblages ◽

New Information ◽

Nayband Formation ◽

The Subject ◽

Northeast Iran

The Nayband Formation is one of the best known sedimentary units in central Iran. The type section consists of a thick succession of shale, siltstone, reef limestone and sandstone that is subdivided into five distinct members: Gelkan, Bidestan, Hoz-e-Sheykh, Howz-e- Khan and Qadir. Abundant and well-preserved framework-building scleractinian corals are included among the macrofossils of the Nayband Formation; these corals characterize the formation and are the subject of this study. The Hassan-Abad section, located in northeast Iran in Lute Block (northwest of Ferdows city), was chosen for detailed study and sampling. Analysis of sedimentary lithofacies and faunal assemblages in the Bidestan and the Howz-e-khan members indicate both biostromal and biohermal characters for the former shallow-water patch reefs and support a Norian to Rhaetian age. The useful biostratigraphic hydrozoanHeterastridium conglobatumwas studied along with 14 taxa of scleractinian corals:Stylophyllopsis rudis, Distichophyllia norica, Paradistichophyllum dichotomum, Retiophyllia frechi, Retiophyllia norica, Retiophyllia robusta, Chondrocoenia schafhaeutli, Chondrocoenia ohmanni, Astraeomorpha crassisepta, Astraeomorpha confusa, Astraeomorpha minor, Procyclolites triadicus, Pamiroseris rectilamellosa,andEocomoseris ramosa. These fossils clarify the stratigraphy of the Nayband Formation, as well as provide new information on the patch reefs and the framework constructors of these reefs.

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