Neotethyan tectonostratigraphic evolution of SE Anatolian basin, Türkiye

MUSTAFA TUNCER

Neotethyan tectonostratigraphic evolution of SE Anatolian basin, Türkiye

Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty Of Engineering, Department Of Geological Engineering, Turkey

Approval Date: 2023

Thesis Language: English

Student: MUSTAFA TUNCER

Supervisor: Nuretdin Kaymakci

Open Archive Collection: AVESIS Open Access Collection

Abstract:

The SE Anatolian basin constitutes the northern margin of the Arabian Plate in SE Türkiye and contains a continuous sedimentary succession from the pre-Cambrian to the recent. It has evolved mainly into four tectonic phases, the first phase includes the Pre-Cambrian to Permian continental platform stage that constitutes the core sequences of the Arabian platform and is represented by continental to shallow marine, and deep marine deposits, the second phase includes Triassic to Jurassic rift-drift stage of the Neotethys ocean and the basin acted as a passive margin during this stage and characterized by shallow marine deposits with occasional continental deposits in places. The third phase is represented by shallow marine and deep marine deposits and it involves the subduction of the Neotethys mainly during the late Cretaceous and ophiolite obduction at the rim of the Arabian Plate. The fourth sequence includes the terminal closure of the Neotethys and the collision of adjacent continental blocks. This sequence is represented by regressive deep marine to shallow marine and continental clastics. Overall Upper Cretaceous to Recent basin-fill units are characterized by northwards thickening wedge-shaped geometry such as Upper Cretaceous deep marine Kastel Formation, Upper Cretaceous-Paleocene deep marine Germav Formation, Lower Miocene shallow and deep marine deposits and Upper Miocene continental clastics. This northward thickening of the basin fill deposits suggests flexural basin development, rapid subsidence, and the creation of accommodation space in front of the thrust front mainly at its northern parts. Apart from the basin infill of the SE Anatolian basin, several allochthonous units such as the upper Cretaceous Karadut Complex and Koçali Ophiolite were emplaced mainly along the northern rim of the basin. These units are related to an accretionary prism growth during the subduction of the Neotethys oceanic lithosphere northwards. The obduction is associated with deep marine units accreted within the Karadut Complex and ophiolitic sequence fragments (Koçali Ophiolites) as well as fore-arc sequences developed piggyback at the top of the growing accretionary prism. They are characterized by regressive shallow marine to continental deposits accumulated at the top of the growing accretionary prism. A basin-wide shallowing and domination continental deposition almost everywhere in the basin is ascribed to dynamic topography resulting from shallow subduction due to the subduction of the mid-ocean ridge that caused regional uplift and subaerially emergence during the Lower Eocene. The Lower Miocene deep marine deposits in the northern parts of the basin become thinner towards the south in SE Türkiye. Abrupt southwards shift of depocenter, wedge-shape geometry, and facies associations and their distribution indicate peripheral foreland basin deposition as the continental collision took place. The northern boundary of the Arabian Plate considerably contributed to the development of an early Miocene flexural foreland basin. The Upper Miocene to recent sequences is characterized by continental deposits and they unconformably overlie all other units in the basin. The structures that shape the present tectonic scheme of the basin are dominated by compressional and contractional structures characterized dominantly by thrust faults and fault propagation folds, as well as strike-slip faults that largely accommodated translation of the thrust faults and folds. In addition, some of the structures are developed due to reactivation or inversion of pre-existing structures that developed mainly during the early Mesozoic opening of the Neotethys ocean. The Triassic-Jurassic normal faults are related to rifting of the Neotethys Ocean while the Late Cretaceous structures are mainly related to ophiolite obduction and thrusting. The late Eocene-to-late Miocene structures are related to accretionary wedge growth and the terminal collision-related thrusting and inversion mainly at the northern rim of the basin. Inversion structures further south of the rim involved the basement and resulted in fault-propagation folds related to the inversion of previous normal faults. One of the best examples of these structures is developed at the base of the Mardin high, Hazro area, Tavan, Sadak, Reşan, and Batman anticlines. In total 358 fault slip data collected from 26 different locations along the interpreted seismic lines, indicate that all of the faults that are interpreted in the seismic sections and exposed on the surface are characterized by almost vertical σ3 and horizontal σ1 orientations. However, the overall σ1 trend changes from NW-SE in the western part of the basin, while it is almost N-S in the center and NE-SW in the eastern part of the basin. This indicates northwards radial fanning of σ1 directions almost perpendicular to the Bitlis Suture Zone and the northern rim of the basin. The resulting structures are typical examples of south-verging thin-skinned deformation, manifested by imbricate thrust fault belts and fault propagation in a foreland setting. The basal decollement surface seems to be the Ordovician or Silurian mudstones and shales. Restored balanced cross sections indicate that the western part of the study area experienced a minimum of 32.31% shortening while the central part experienced 19,12% shortening and the eastern areas experienced 16,62% minimum total shortening. Additionally, the maximum and minimum ratios of shortening in sedimentary units are 9,09 % and 5,88 % at the east and the center, respectively.