F. Shirezade Esfahani; A. Bayet-Goll; N. Kohansal Ghadimvand; A. Kangazian; A. Akbari Mohammadi; M. Sadri
Abstract
The carbonate successions (Tournaisian-Visean) exposed in the Tang-e-Darchaleh and Banarizeh sections from Sanandaj-Sirjan Zone (SSZ), Iran, have been used to generate a facies model. From the analysis of facies and their associations, four depositional zones are recognized on the Tournaisian-Visean ...
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The carbonate successions (Tournaisian-Visean) exposed in the Tang-e-Darchaleh and Banarizeh sections from Sanandaj-Sirjan Zone (SSZ), Iran, have been used to generate a facies model. From the analysis of facies and their associations, four depositional zones are recognized on the Tournaisian-Visean ramp: basinal environments, outer ramp (FA1 and FA2; deep subtidal associations), mid ramp (FA3, FA4 and FA6; shallow subtidal to lower intetidal associations), and inner ramp (FA5; shoal). The gradual transitions between facies and facies associations, as well as the depositional profile of the shelf transect indicate a low gradient ramp. The observed sedimentary features in the facies associations portray a transgressive, proximal-to-distal, wave-dominated combined flow marine ramp sequence, as recorded in stratigraphic changes in character of storm bed sequences and the spatial arrangement of types of storm bed along the depth related environmental gradients. This study suggests that during the Lower Carboniferous, a broad shelfal platform covered the southern margin of the Palaeotethys, which was characterized by dominantly shallow carbonate ramp.
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.
