S Bayetgoll
Abstract
The integration of ichnologic data with sedimentology analyses allows for discrimination between delta and open marine deposits of the Nayband Formation (Upper Triassic) in the Central Iran, Kerman. Relying on the facies characteristics and stratal geometries, the siliciclastic successions are divided ...
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The integration of ichnologic data with sedimentology analyses allows for discrimination between delta and open marine deposits of the Nayband Formation (Upper Triassic) in the Central Iran, Kerman. Relying on the facies characteristics and stratal geometries, the siliciclastic successions are divided into two facies associations, FA (open marine), FB (fluvial-dominated delta). The river-dominated deltaic assemblage includes facies that have been deposited in prodelta, distal delta front, proximal delta front, and mouth bar environments. The overall sedimentological and ichnological characteristics suggest deposition facies association A within the river-dominated deltaic environment. The open-marine facies association includes facies that have been deposited in shelf-offshore, offshore transition, distal lower shoreface and proximal lower shoreface environments. Facies association A and B of the Nayband Formation display markedly different suites of ichnofossils throughout the different depositional subenvironments. The fluvial-dominated delta successions are characterized by numerous physical and chemical stresses that can strongly influence the behavior of burrowing organisms. Three trace fossil assemblages are identified in the fluvial-dominated delta deposits. High rates of fluvial discharge, high water turbidity, seasonally high rates of deposition and phytodetrital pulses in river-dominated deltas may cause marked variations in the temperature, oxygenation and salinity of the fluvial-dominated delta successions. All of these factors in combination lead to reduction in diversity and abundance of infauna, small trace fossil size, and sporadic distribution of burrowing and lower intensities of bioturbation of trace fossil suite of river-dominated deltaic successions. Open marine deposits contain ichnological signatures characterized by moderate to intense bioturbation, high assemblage diversities and larger trace fossil size compared with the river-dominated delta successions. The occurrence of diverse and robust trace fossil suites attributable to the Zoophycos, Cruziana and Skolithos ichnofacies point to unstressed environmental conditions in open marine setting.
M Mannani; M Yazdi
Abstract
The Nayband Formation in North of Isfahan includesfive Members: 1- Gelkan Member (marl and sandstone), 2- Bidestan Member (sandstone and reefal limestone), 3- Howz- e- Sheikh Member (marl and sandstone), 4- Howz- e- Khan Member (marl and reefal Limestone) and 5- Qadir Member (marl and sandstone). The ...
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The Nayband Formation in North of Isfahan includesfive Members: 1- Gelkan Member (marl and sandstone), 2- Bidestan Member (sandstone and reefal limestone), 3- Howz- e- Sheikh Member (marl and sandstone), 4- Howz- e- Khan Member (marl and reefal Limestone) and 5- Qadir Member (marl and sandstone). The biostromal limestones of Bidestan and Howz-e- Khan Members represent a typical known key bed in North of Isfahan. In Bidestan and Howz-e- Khan Members (Nayband Formation), coral reefs grow up and their distribution are significant in the biostromal limestone of Bidestan and Howz-e- Khan Members of Nayband Formation.Twelve genera and 31 species of Scleractinian corals were recognized in the sereefal members. They included: Reimani phylliidae, Margarophylliidae, Coryphylliidae, Cyclophyllidae, Astraeomorphidae, Pamiroseriidae, Stylophyllidae and Actinastraeidae families. According to the field observations and evidences, laboratory studies and analysis, measurements of the coral size and the destroyed epitecha of the corals, it could beguessed that Scleractinian corals survive below the storm wave base (about 20 meters depth) but they tolerated many storms. Morphology of Scleractinian corals of Late Triassic sea (North of Isfahan) indicates in adequate living conditions and high energy environment. Corals have major role in reconstruction of Paleoenviroment of the Late Triassic units of the North of Isfahan (Nayband Formation) in Dizlu section.
