Z Kiadaliri; M.R Majidifard
Abstract
The Lower- Middle Jurassic strata are well developed in northeast of Jajarm (E Alborz). At the study section, the Shemshak Group has a maximum thickness of 585 m, consisting of grey silty sandstones and light- green siltstones with brown sandstones, subdivided into 3 formations ofAlasht, Shirindasht ...
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The Lower- Middle Jurassic strata are well developed in northeast of Jajarm (E Alborz). At the study section, the Shemshak Group has a maximum thickness of 585 m, consisting of grey silty sandstones and light- green siltstones with brown sandstones, subdivided into 3 formations ofAlasht, Shirindasht and Fillzamin.The lower boundary of the Shemshak Group at Golbini sectionwith the red bauxite horizon of the underlying Elikah Formation is disconformity due to the EarlyCimmerian tectonic event.Its upper boundary with marly limestone and marl of the Dalichai Formation is disconformity, too. In the Shemshak Group at the study section, summing up 186 fossil specimens were collected, among which the ammonoids with 67 specimens clearly predominate and belonging to 6 biozones (ThouarsenseZone, Pseudoradiosa Zone,Aalensis zone, Opalinum Zone, Murchisonaezone, ConcavumZone) have been recognized. Based on the ammonite fauna, the age of the Shemshak Group in the investigated area ranges from the Upper Toarcian to Upper Aalenian. Paleobiogeographically, the fauna shows close relationship to Northwestern Europe and Sub-Mediterranean regions. This indicates a paleogeographical position of the area at the northern Tethys during the Lower-Middle Jurassic.
M. Paknia; Habib Alimohammadian; M. R. Majidifard; J. Sabouri; A. Aghanabat
Abstract
The Golbini section comprising of continuous succession of sediments ranging in age from Triassic – Jurassic formations, is situated at 35 Km north – east of Jajarm city. On the bases of studies on Dalichai Formation at this section and at about Middle Jurassic (Bathonian–Callovian ...
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The Golbini section comprising of continuous succession of sediments ranging in age from Triassic – Jurassic formations, is situated at 35 Km north – east of Jajarm city. On the bases of studies on Dalichai Formation at this section and at about Middle Jurassic (Bathonian–Callovian boundary), 3 Member, 31 Genus and 13 species of Ammonite, has been identified. For paleomagnetic analysis, with the help of portable coring machine, the total number of 155 oriented core samples were collected from limestone and clayey– limestone of this section. Then the samples were prepared for paleomagnetic analysis at Environmental and Paleomagnetic Laboratory based at Geological Survey of Iran, Tehran, Iran. The conducted paleomagnetic analysis include measurement of NRM, Susceptibility, Thermal and AF demagnetizing, Virtual Geomagnetic Polarity (VGP), identification of normal and reversal magnetic polarities and calculation of sedimentation rate. The obtained paleomagnetic results then composed with GPTS and also with proposed Bathonian–Callovian boundaries in Russia and Germany. This comparison reveals that the magnetic polarity of Golbini section is co-relatable with GPTS and also with Bathonian–Callovian boundary in Russia and Germany.
D. Esmaeily; A. Esna Ashari; H. Rahimpour Bonab
Abstract
Study of source rock materials in Jajarm bauxite deposit is the main subject of this study to show its origin. From bottom to top, this deposit consists of lower argillaceous layer, argillaceous bauxite, hard bauxite and upper kaolinite units. Correlation coefficients and scatter ...
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Study of source rock materials in Jajarm bauxite deposit is the main subject of this study to show its origin. From bottom to top, this deposit consists of lower argillaceous layer, argillaceous bauxite, hard bauxite and upper kaolinite units. Correlation coefficients and scatter diagrams of immobile elements in these four layers, demonstrate an early homogenous origin at the beginning of the bauxite formation. Accordingly, source materials were separated slowly due to the different conditions dominated in different parts of the deposit. Difference in drainage conditions and leaching of some elements from upper part and their re-deposition in lower parts of the deposit are the main reasons for hard bauxite separation from argillaceous one. Formation of the lower argillaceous layer, located between argillaceous bauxite and carbonate footwall is due to the direct contact of the argillaceous bauxite and carbonate footwall and also difference in drainage rate in contact area of the two layers. Geochemical evidence also depicts that upper kaolinite formation is the result of the silica leaching from upper horizons and its re-deposition in hard bauxites. Compositional comparison of studied samples with chondrite and upper continental crust demonstrates the effect of both of the basic and sedimentary rocks in evolution of the Jajarm bauxite. Formation of this deposit can be considered as a result of the alteration of the primitive laterite in an area close to the current location of the deposit. During alteration and transportation bauxite is deposited on the karstic topography and then some continental sediment was added to it.
