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.
N Abbassi; M Parvanehnezhad Shirazi; M.A Hosseinzadeh
Abstract
Albian–Cenomanian siliciclastic-carbonate sediments of northwest Rayen in south Kerman, southeast Iran (526 m) are classifiable to three informal units. Unit one includes conglomerates, sandstones and siltstones with limestone and marl intercalations. Unit two is composed of Orbitolina bearing ...
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Albian–Cenomanian siliciclastic-carbonate sediments of northwest Rayen in south Kerman, southeast Iran (526 m) are classifiable to three informal units. Unit one includes conglomerates, sandstones and siltstones with limestone and marl intercalations. Unit two is composed of Orbitolina bearing limestones with rudists, belemnoid and ammonite bioclasts. Alternations of pelagic limestones and sandstones formed the third unit. Assemblage of continental to marine trace fossils have been found in the first and third units of the studied section, that include Koilosoma isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Skolithos isp., Taenidium isp., and Thalassinoides suevicus. These trace fossils belongs to Scoyenia, Skolithos and Cruziana ichnofacies. Abundant Thalassinoides-Phycodes compound trace fossil, however have been found in the third unit. Box-worked Thalassinoides burrow system ends to multi- branched Phycodes borrows. This compound trace fossil is interpreted as feeding-domicile biogenic structure, so that Thalassinoides domichnium ends to Phycodes excavated feeding burrows. Compound Thalassinoides-Phycodes trace fossil extended in the deeper parts of offshore shelf sediments in the studied section. Based on ichnological data, it seems that Albian–Cenomanian sediments of northwest Rayen deposited in a deepening upward sequence.
A Bayat Gol; N Abbassi
Abstract
A detailed ichnological study on the Geirud Formation (Late Devonian-Early Carboniferous) from the Zaygon area, central Alborz shows a diverse trace fossils, which include 14 ichnogenera represented by 23 ichnospecies. These trace fossils contains various ethological patterns, such as domichnia, fodinichnia, ...
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A detailed ichnological study on the Geirud Formation (Late Devonian-Early Carboniferous) from the Zaygon area, central Alborz shows a diverse trace fossils, which include 14 ichnogenera represented by 23 ichnospecies. These trace fossils contains various ethological patterns, such as domichnia, fodinichnia, grazing, equilibrichnia, and fugichnia. These trace fossils are: Arenicolites, Asterosoma, Chondrites intricate, Chondrites targionii, Diplocraterion parallelum, Arenicolites isp., Asterosoma isp., Chondrites intricate, Chondrites targionii, Chondrites isp., Diplocraterion parallelum, Helminthoidichnites isp., Helminthopsis abeli, Helminthopsis isp., Palaeophycus heberti,Palaeophycus tubularis, Planolites beverleyensis, Planolites isp., Phycodes cf. palmatus, Rhizocorallium jenense, Rhizocorallium irregular, Rosselia soccialis, Taenidium serpentinum, Taenidium satanassi, Talassinoides horizntalis, Thalassinoides suevicus, Thalassinoides paradoxicus, Zoophycos isp. Studied beds consist by alternations of laminated mudstones and siltstones, and thick- to medium-bedded sandstones with wavy lamination. Hummocky, trough and low angle to planar cross-bedding are common in layers. It seems that these beds were deposited in the delta to open marine environments. Determined ichno-assemblage represents characteristic of a moderately shallow-marine environment, which effected occasionally by high-energy conditions. A trace fossil assemblage has been examined from the uppermost dark-colored shale layers of the Geirud Formation in the Devonian/Carboniferous (D-Ca) boundary. This assemblage include Chondrites targionii, Zoophycos isp., which involved by Hangenberg event.
N. Abbassi; A. H. Amini
Abstract
The Upper Miocene Upper Red Formation in the Evan-e-Key Section is composed of conglomerates, sandstones, mudstones, and thin lenses of evaporates (gypsum). The formation is dominated by gypsiferous mudstones and characterized by fining-up cycles in this area. The whole ...
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The Upper Miocene Upper Red Formation in the Evan-e-Key Section is composed of conglomerates, sandstones, mudstones, and thin lenses of evaporates (gypsum). The formation is dominated by gypsiferous mudstones and characterized by fining-up cycles in this area. The whole formation occurs as a fining upward megasequence, in which the sandy facies dominate the lower half and muddy facies the upper half. Gypsum layers, up to 10 meters thick, are locally observed in the basal part. The formation has suffered an extensive weathering in the region, as a result of which primary features (e.g. sedimentary structures, trace fossils) are partially obscured. In the sandy units of the middle part of the formation some vertebrate footprints are observed, which are locally deformed due to intensive weathering of the rocks. Two types of Carnivoripedida footprints however, are distinguished and described here, so that well preserved Chelipus isp. is related to Felidae. Depositional environments including alluvial fans with abundant debris flows, gravelly bed load braided systems with wide flood plains and local swamps provided a good opportunity for development of the track makers. The transverse and longitudinal bars within the channels, levees, and over-bank sub-environments were found more suitable for development and preservation of the footprints. Comparing with other sections of the formation (e.g. Qum area), desirable climate was found a major control on development of the vertebrate track maker in the Evan-e-key area.
N. Abbassi; A. Amini
Abstract
The Thalassinoides bearing calcareous sandstone and sandy limestones of Oligocene age unconformably overlay the Eocene volcaniclastic rocks and gradually pass into the lacustrine sediments (Miocene? in age) in the study area. These layers are dominated by Thalassinoides ...
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The Thalassinoides bearing calcareous sandstone and sandy limestones of Oligocene age unconformably overlay the Eocene volcaniclastic rocks and gradually pass into the lacustrine sediments (Miocene? in age) in the study area. These layers are dominated by Thalassinoides suevicus (Rieth 1932) in the Y shaped boxwork cylindrical and bifurcating burrows, which are mainly filled actively by trace maker(s). The bioturbations in the layers are categorized into five ichnofabric classes, which are equal to standard ichnofabric indexes of 1 to 5. Frequency of the ichnofabric classes are 40.37, 15.9, 8.85, 4.97 and 29.9 percents, respectively. Ichnofabric variations of the studied layers are arranged in seven bioturbated upward cycles, which are divided into two groups. The first group shows low ichnofabric fluctuations and a constancy in the bioturbation, where the second group shows high ichnofabrics fluctuations and variability in the bioturbation. Results from the study show that the Thalassinoides in the studied section formed in conditions similar to those of Cruziana and Glossifungites ichnofacies.
