A Bayet-Goll; R Moussavi-Harami; A Mahboubi
Abstract
Carbonate deposits of members 1 to 2 of the Mila Group (Middle Cambrian) in Central Alborz that call the Deh-Sufiyan Formation in this research, were studied in Shahmirzad, Tueh-Darvar, Mila-Kuh and Deh-Molla sections. The Unit 2 of Deh-Sufiyan Formatrion in Central Alborz of Northern Iran consists mainly ...
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Carbonate deposits of members 1 to 2 of the Mila Group (Middle Cambrian) in Central Alborz that call the Deh-Sufiyan Formation in this research, were studied in Shahmirzad, Tueh-Darvar, Mila-Kuh and Deh-Molla sections. The Unit 2 of Deh-Sufiyan Formatrion in Central Alborz of Northern Iran consists mainly of shallow marine carbonates and contains a variety of limestone conglomerates. Limestone conglomerate is an important component of Unit 2 of Deh-Sufiyan Formatrion, but its origins remain enigmatic. These limestone conglomerates have a diverse set of characteristics that range from clast to matrix supported with scattered flat pebbles. These conglomerates are largely comprised of oligomictic, rounded lime–mudstone clasts of various sizes and shape (equant, oval, discoidal, tabular, and irregular). According to composition and characteristic sedimentary structures and fabric, limestone conglomerates in the Unit 2 of Deh-Sufiyan Formatrion consist of: (1) Intraformational limestone conglomerate beds were formed by depositional processes (2) Limestone pseudoconglomerate beds were produced by diagenetic processes. The common characteristics of the Unit 2 of Deh-Sufiyan Formatrion pseudoconglomerates, such as oligomictic lithology of lime–mudstone clasts, mosaic fabric, disorganized/edgewise fabric, variable and gradational fabric, transitions from adjacent or underlying facies and the complete lack of depositional structures, are typical of pseudoconglomerates formed by early diagenetic sediment deformation under shallow burial conditions. These characteristics are different from those of intraformational limestone conglomerate showing primary depositional features such as normal or inverse grading, internal stratification, (hummocky) cross-stratification and sharp erosional bases. Diagenetic conglomerates in ribbon rocks resulted from soft-sediment deformation of ribbon rocks during early diagenesis. In contrast, the dimension and thickness, sizes of the clasts, clast-rich beds, size ingredient of matrix, tendency to amalgamate with amalgamation scours within depositional conglomerates suggest that high energy and strong erosion above storm wave base was responsible for the disintegration of the carbonate material.
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.
A. Bayat Gol; N. Abbassi; A. Mahboubi; R. Moussavi-Harami; H. Amin Rasouli
Abstract
Some of Paleozoic sediments from Alborz and Central Iran subzones from Mid-Iran zone evaluated for distinction of Palaeophycus and Planolites ichnofossils. These sediments include Shale Member of Lalun Formation, Shirgesht Formation, member 5 of Mila Formation and Geiroud Formation. A diverse ichnofauna ...
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Some of Paleozoic sediments from Alborz and Central Iran subzones from Mid-Iran zone evaluated for distinction of Palaeophycus and Planolites ichnofossils. These sediments include Shale Member of Lalun Formation, Shirgesht Formation, member 5 of Mila Formation and Geiroud Formation. A diverse ichnofauna has been found in these Formations, so Planolites and Palaeophycus are abundant between them. Ichnotaxa diagnosis and some determination problems of these ichnogenera was discussed here. Overall characteristics of Palaeophycus suggest dwelling structure made by predator or suspension-feeder and passive sedimentation in the open burrow. Planolites, on the other hand imply active backfilling structure in ephemeral burrows, which constructed by a mobile deposite-feeder. Planolites include unlined burrows with infilled sediments differ texturally from host rock. Whereas Palaeophycus is lined burrow filled by same sediments of surrounding matrix. Accordingly, Palaeophycus assemblage members made by opportunistic communities with r-selected population strategies in physically-controlled and unstable environment, whereas ichnofossils of Planolites assemblage are related to benthic communities with displaying K-selected or climax strategies in the stable environments and rather predictable conditions. Recognized ichnospecies of Planolites are P. montanus, P. annularis, P. terraenovae and P.beverleyensis. and ichnospecies of Palaeophycus include P. heberti, P. tubularis, P. striatus. P. sulcatus and P. alternates.
