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The Upper Jurassic Garedu Red Bed Formation of the northern Tabas Block: elucidating Late Cimmerian tectonics in east-Central Iran
International Journal of Earth Sciences ( IF 1.8 ) Pub Date : 2021-02-17 , DOI: 10.1007/s00531-021-01988-z
Markus Wilmsen , Franz Theodor Fürsich , Kazem Seyed-Emami , Mahmoud Reza Majidifard

The Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine limestones of the Esfandiar Subgroup (Callovian–Oxfordian) and is assigned to the Kimmeridgian–Tithonian. In the lower part, it consists of pebble- to boulder-sized conglomerates/breccias composed of limestone clasts intercalated with calcareous sandstones, litho-/bioclastic rudstones and lacustrine carbonates. Up-section, sharp-based pebbly sandstones and red silt-/fine-grained sandstones of braided river origin predominate. Palaeocurrent data suggest a principal sediment transport from west to east and a lateral interfingering of the GRBF with marine greenish marls of the Korond Formation at the eastern margin of the Tabas Block. Westwards, the GRBF grades into the playa deposits of the Magu Gypsum Formation. Red colours and common calcretes suggest arid to semi-arid climatic conditions. The onset of Garedu Red Bed deposition indicates a major geodynamic change with the onset of compressive tectonics of the Late Cimmerian Tectonic Event (LCTE), being strongest at the eastern margin of the northern Tabas Block. When traced southwards, the same tectonic event is expressed by extension, indicating a shift in tectonic style along the boundary fault between the Tabas and Lut blocks. The complex Upper Jurassic facies distribution as well as the spatio-temporal changes in tectonic regime along the block-bounding faults are explained by the onset of counterclockwise vertical-axis rotation of the CEIM in the Kimmeridgian. The block boundaries accommodated the rotation by right-lateral strike slip, transpressional in today’s northern and transtensional in today’s southern segments of the block-bounding faults. Rotation occurred within bracketing transcurrent faults and continued into the Early Cretaceous, finally resulting in the opening of narrow oceanic basins encircling the CEIM. Palaeogeographically, the GRBF is part of a suite of red bed formations not only present on the CEIM, but also along the Sanandaj-Sirjan Zone (NW Iran), in northeastern Iran and beyond, indicating inter-regional tectonic instability, uplift and erosion under (semi-)arid climatic conditions across the Jurassic–Cretaceous boundary. Thus, even if our geodynamic model successfully explains Late Jurassic tectonic rotations, fault motions and facies distribution for the CEIM, the basic cause of the LCTE still remains enigmatic.



中文翻译:

塔巴斯块北部的上侏罗统加里杜红床组:阐明了伊朗中东部的晚西密尔构造

塔巴斯地区北部(中东部伊朗微大陆,CEIM)的加里杜红层形成(GRBF)是岩性变化的,最大厚度为500米,主要为大陆单元。它逐渐或不一致地停留在Esfandiar子群(Callovian–Oxfordian)的海洋石灰石上,并被分配给Kimmeridgian–Tithonian。在下部,它是由卵石到砾石大小的砾岩/角砾岩组成的,砾岩/角砾岩由石灰岩碎屑和钙质砂岩,岩石/生物碎屑的rutstone和碳酸盐湖相碳酸盐组成。辫状河起源的上层断层以锋利的卵石砂岩和红色粉砂/细粒砂岩为主。古流变数据表明,主要的泥沙运移是从西向东,GRBF与塔巴巴斯地块东缘的科隆组的海洋绿色泥灰岩横向交插。向西,GRBF分为马古石膏组的普拉亚沉积。红色和普通碎石提示干旱至半干旱气候条件。Garedu红层沉积的开始表明,随着晚Cimmerian构造事件(LCTE)压缩构造的开始,地球动力学发生了重大变化,在北部塔巴斯地块的东部边缘最为强烈。向南追溯时,同一构造事件通过扩展来表示,表明构造样式沿塔巴斯区块与卢特区块之间的边界断层发生了变化。CEIM在Kimmeridgian的逆时针垂直轴旋转的开始解释了复杂的上侏罗纪相分布以及沿着块体边界断裂的构造状态的时空变化。块体边界适应了右旋走滑的旋转,在今天的北部断层是压性的,而在今天的南部断层是张性的。旋转发生在包围横流断层的内部,并一直持续到白垩纪早期,最终导致围绕CEIM的狭窄海洋盆地的开放。在古地理上,GRBF是CEIM以及伊朗东北及其他地区的Sanandaj-Sirjan区(伊朗西北部),以及伊朗东北部及周边地区一系列红层形成的一部分,表明区域间构造不稳定,侏罗纪-白垩纪边界的(半)气候条件下的隆升和侵蚀。因此,即使我们的地球动力学模型成功解释了CEIM的晚侏罗世构造旋转,断层运动和相分布,LCTE的基本原因仍然是未知的。

更新日期:2021-02-17
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