The Upper Jurassic Garedu Red Bed Formation of the northern Tabas Block: elucidating Late Cimmerian tectonics in east-Central Iran

Abstract

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.

Depositional and thermal history of a continental, coal-bearing Middle Jurassic succession from Iran: Hojedk Formation, northern Tabas Block

“…This explains the complex facies distribution and the spatio-temporal changes in the tectonic regime of the faults, and is seen as the starting signal for the Late Cimmerian tectonic event (Wilmsen et al . 2021). This anticlockwise rotation of the CEIM comprises in total a 135° movement in two phases (latest Jurassic to Early Cretaceous and Middle–Late Miocene) in order to transfer the Yazd, Tabas and Lut blocks into their present north–south-oriented positions (Mattei et al .…”

“…2009; Wilmsen et al . 2021). Thus, we intend to elucidate the significance of the Hojedk Formation for the geodynamic evolution of the Central-East Iranian Microcontinent (CEIM) during the early Middle Jurassic in the run-up to the Mid-Cimmerian tectonic event.…”

Youngest Cretaceous dinosaur tracksite from the Middle East (Maastrichtian, Farrokhi Formation, Central Iran)

“…After its welding to Eurasia, the Iran Plate remained a tectonically highly mobile area in Jurassic times (e.g. Fürsich et al 2003;Seyed-Emami et al 2004;Taheri et al 2009;Salehi et al 2018;Wilmsen et al 2021). During the Early Cretaceous, strongly subsiding marginal oceans formed around the CEIM (Tirrul et al 1983;Babazadeh and De Wever 2004;Nasrabady et al 2011;Kazemi et al 2019;Pirnia et al 2020), probably in response to counterclockwise vertical-axis rotation of the microplate (e.g.…”

“…During the Early Cretaceous, strongly subsiding marginal oceans formed around the CEIM (Tirrul et al 1983;Babazadeh and De Wever 2004;Nasrabady et al 2011;Kazemi et al 2019;Pirnia et al 2020), probably in response to counterclockwise vertical-axis rotation of the microplate (e.g. Soffel et al 1996;Alavi et al 1997;Besse et al 1998;Cifelli et al 2013;Mattei et al 2015;Wilmsen et al 2021) and the break-up of deep-seated faults along its margins. The convergence of Arabia and Eurasia led to the closure of the narrow oceanic basins fringing the CEIM during the latest Cretaceous to Paleogene (e.g.…”

Cimmerian metamorphism and post Mid-Cimmerian exhumation in Central Iran: Insights from in-situ Rb/Sr and U/Pb dating

“…This phase of rapid subsidence is observed across all of northeast Iran and is interpreted as crustal extension across rotating blocks to explain the great magnitude of relative deepening (Fürsich et al, 2009b;Wilmsen et al, 2009b,a). A less well-constrained Late-Cimmerian event occurred during the Late Jurassic (∼145 Ma), mostly across Central Iran (Zanchi et al, 2009b;Wilmsen et al, 2015Wilmsen et al, , 2021. This event is possibly related to the opening and closure of the Iranian back-arc basins at the rear of the large-scale subduction zone of the Neotethys (Rossetti et al, 2010;Agard et al, 2011).…”