ABSTRACTThe east-west trending Taurides form a curved area in central eastern Anatolia known as the Gürün Curl. In order to understand the origin of the Gürün Curl and Tauride evolution in general, the results of a new field study of this region have been synthesized together with previously published data. We suggest that the geodynamic evolution of the area began with the likely presence of a Tethys Ocean transform fault. This fault separated the Taurides into the Akdere Sector in the west and the Munzur Sector in the east in the Late Cretaceous. During the late Santonian–early Campanian, ophiolites obducted onto the Munzur Sector, while platform sediments continued to accumulate in the Akdere Sector. This was followed by the development of an Andean-type arc-type magmatism (the Baskil Arc) during the early–middle Campanian in the Munzur Sector. Continued closure of the Tethys led to the collision of the Bitlis Massif in the south of the Munzur Sector in the Campanian. This, in turn, resulted in continental subduction and slab roll-back that was controlled by a Subduction Transform Edge Propagator (STEP) Fault that lay on the original transform fault between the Akdere and Munzur sectors. Because the subducted slab was free at its western corner, the western edge rolled back faster than in the east, leading to an asymmetrical extensional regime on the upper plate that created the late Campanian Hekimhan Basin. While these geodynamic events were taking place in the Munzur Sector, the Akdere Sector was in a platform setting. During the Palaeocene, the Late Mesozoic units of the Akdere Sector began to overthrust on the Hekimhan Basin and the ophiolites. Following the Palaeocene, all these tectonostratigraphic units were covered by Eocene sediments around the Gürün Curl of which the modern appearance was completed by the Miocene to Recent movements along the strike-slip faults.KEYWORDS: AnatoliaTauridesHekimhan BasinLate CretaceousGürün Curl AcknowledgmentsThis study was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK), the Department of Scientific Research Projects of Dokuz Eylül University, and the Turkish Academy of Sciences (TÜBA-GEBİP). We would like to extend our gratitude to Dr. Fatih Karaoğlan for his valuable assistance in interpreting the zircon age data.Disclosure statementNo potential conflict of interest was reported by the author(s).Supplementary materialSupplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2258393Additional informationFundingThe Scientific and Technological Research Council of Türkiye - TÜBİTAK (grant number: ÇAYDAG-119Y187); Department of Scientific Research Projects of Dokuz Eylül University (grant number: 2019.KB.FEN.006); Turkish Academy of Sciences - TÜBA-GEBİP (TÜBA-GEBİP/2018).
Bey Dağları Otoktonu’nun doğu bölümüne karşılık gelen Katran Dağ alanında sığ denizel Jura-Kretase karbonat istifi en üstte orta-geç Senomaniyen yaşlı bol rudistli platform kireçtaşları (Yağca Köy Formasyonu) ile temsil edilir. Platform kenarı ortamında çökelmiş kireçtaşlarında daha derin ortamı işaret eden planktonik foraminifer ve kalsisifer içeren en az üç farklı mikritik neptüniyen dayk dolgusu tanımlanmıştır. D2 ve D3 dolgularında tanımlanan planktonik foraminifer toplulukları, dolguların geç Koniasiyen-Santoniyen ve en geç Kampaniyen-Maastrihtiyen’de gerçekleştiğini gösterir. D2 dolgusundan daha önce gerçekleşen D1 dolgusunun yaşı planktonik foraminifer içermemesi nedeniyle belirlenememektedir. Benzer şekilde, neritik kireçtaşları veya D2 dolgusundan oluşan yan kayacı kesen D4, D5 ve D6 dolguları da karakteristik planktonik foraminifer içermemeleri nedeniyle yaşlandırılamamaktadır. Ancak, özellikle D4 dolgusunun bazı bölümlerinin fasiyes özellikleri D3 dolgusu ile az çok benzerdir. D2 ve D3 dolgularında tanımlanan fasiyes ve planktonik foraminifer toplulukları Bey Dağları Otoktonu’nun kuzey bölümünde yaygın yüzlekleri bulunan pelajik istifler ile oldukça benzerdir. Bu veri platformun kuzey bölümünde gözlenen pelajikleşmenin platformun doğu bölümünde de gerçekleştiğini gösterir. Platformun doğu bölümünde, Santoniyen sonrası ve Maastrihtiyen sonunda gerçekleşen aşınma dönemlerinde pelajik istifler aşınmış olmalıdır. Neptüniyen dayk dolguları çoğunlukla genleşme tektoniğine bağlı olarak gelişen platform boğulmaları ile ilişkili olmaları nedeniyle, platformun bu bölümünün de kuzey bölümde olduğu gibi geç Koniasiyen-Santoniyen ve en geç Kampaniyen-Maastrihtiyen’de boğulduğunu gösterir.
Identification of the benthonic foraminiferal assemblages from ten stratigraphic sections from the inner platform limestones of the Middle Cenomanian−Coniacian successions of the Bey Dağları carbonate platform (BDCP) allowed the recognition of one biozone and two subzones. The lower part of the platform limestones (Middle−Upper Cenomanian) is represented by relatively rich benthonic foraminiferal assemblages, while the upper part (Turonian−Coniacian) contains poor assemblages. The benthonic foraminiferal assemblages determined in the BDCP are dominated by long-ranging species. The shorter-ranging, stratigraphical index species have been selected to date the Upper Cretaceous platform limestones of the BDCP based on the distributions of the species in the circum-Mediterranean region. The Pseudolituonella reicheli-Pseudorhapydionina dubia Concurrent Range Zone is defined from the Middle−Upper Cenomanian platform limestones. The biozone includes the Cisalveolina lehneri Subzone and the Coxites zubairensis Subzone of Middle Cenomanian and Upper Cenomanian age respectively. The first occurrences of Moncharmontia apenninica-compressa and Pseudocyclammina sphaeroidea indicate the Late Turonian and the Coniacian respectively. The spread of hemipelagic limestones in the BDCP during the Coniacian shows that neritic accumulation on the BDCP persisted from the Middle Cenomanian to the Coniacian. These data indicate that the global sea level rise at the Cenomanian−Turonian boundary, which caused the general demise of many Tethyan carbonate platforms, did not result in deepening on the BDCP.
The Ankara region (central Türkiye) comprises a part of the Sakarya Terrane and the accretionary remnants inherited from the Izmir-Ankara-Erzincan (IAE) branch of the Northern Neotethys. The Sakarya Terrane is characterized by a pre-Jurassic basement overlain by Jurassic-Cretaceous sedimentary assemblages, collectively known as the Sakarya Continent Cover. In this study, we aim to elucidate the Jurassic-Cretaceous evolution of the Sakarya Terrane through detailed geological mapping in the regions of Haymana, Yakacık, north of Alagöz and west of Memlik, located to the west and southwest of Ankara city, central Türkiye. By analyzing radiolarian and planktonic foraminiferal assemblages, we provide precise dating for three key lithological units: the Soğukçam Limestone Group (part of the Sakarya Continent Cover), the Elmadağ Olistostrome, and the Unaz Formation (from the overlying units). The oldest rock unit exposed in the Haymana region, south of Ankara city, is the Bilecik Limestone Group, consisting of Tithonian to lower Berriasian platform carbonates. A drowning unconformity separates the Bilecik Limestone Group from the overlying middle Berriasian-uppermost Albian Soğukçam Limestone Group, which has been elevated to "group" status in this study. The Soğukçam Limestone Group is subdivided into two formations -the Seyran Formation and the Akkaya Formation- separated by a disconformity surface. The Seyran Formation, at the base, consists of middle Berriasian limestone breccia in a micritic pelagic matrix, and upper Berriasian-lower Aptian micritic clayey, cherty pelagic limestones with abundant and diverse radiolarians in its upper part. The disconformity between the Seyran and Akkaya formations represents a small depositional gap corresponding to the middle to late Aptian. The lower part of the Akkaya Formation contains lower to middle Albian debris flow deposits while the upper part is composed of clayey pelagic limestones rich in glauconite and planktonic foraminifers, dating to the latest Albian. Overall, the Akkaya Formation is roughly assigned to the Albian stage. The Akkaya Formation within the Soğukçam Limestone Group is unconformably overlain by the Coniacian Elmadağ Olistostrome, which also covers the ophiolitic mélange of the IAE Ocean (containing Turonian radiolarian blocks) to the west of the Memlik region. The basal part of the Elmadağ Olistostrome is characterized by an unstratified, loosely-packed, gray- to beige-colored carbonate matrix, while its upper part features stratified, highly-sheared gray- to beige-colored clayey carbonate/marl matrix with embedded carbonate blocks. These blocks, dated through radiolarians and planktonic foraminifers, range from the early Callovian to Coniacian. These blocks, observed in the Haymana, north of Alagöz, and Yakacık regions, primarily originated from the underlying Soğukçam Limestone Group. The Elmadağ Olistostrome was likely deposited in a peripheral foreland flysch basin, resembling trench-like settings, in front of the southward-moving nappes derived from the Neotethys Intra-Pontide Ocean. This olistostrome is unconformably overlain by the Unaz Formation, which represents the lowermost unit of the fore-arc basin within the Galatean Arc and is present in all four studied regions. The Unaz Formation mainly consists of thin-bedded, gray- to red-colored clayey limestones with abundant planktonic foraminifers, along with red- to pink-colored marls. In the northern part (west of Memlik), the Unaz Formation also includes basal clastics. Based on its characteristic planktonic foraminiferal assemblages, the formation is dated to the late Santonian and correlates well with the type locality in the Pontides, northwestern Türkiye. Following this sequence, a brief period of continental arc magmatism occurred in the Santonian-Campanian, accompanied by the deposition of fore-arc sediments (the Haymana Formation, consisting of clastics) during the Campanian-Maastrichtian interval. In this study, an abundant, well-preserved, and diverse radiolarian microfauna (146 taxa, including fourteen new species and four new subspecies from the early Hauterivian to early Aptian, Early Cretaceous) were recovered from the clayey micritic limestones of the Seyran Formation in the Soğukçam Limestone Group. The vertical distributions of these radiolarians and their age correlations with previous studies are also documented.
The Bornova Flysch Zone (BFZ), located between the Menderes Massif and the İzmir-Ankara Suture in westernmost Anatolia (Turkey), forms the westernmost part of the Anatolide-Taurides. The BFZ comprises intensely sheared Upper Cretaceous-Palaeocene matrix and blocks of various origins. The matrix of the BFZ is mainly made up of unfossiliferous flysch-type sediments (alternations of sandstones and shales). In Bornova (İzmir, western Turkey) and its surroundings, these clastics locally include planktic foraminifera-bearing pelagic micritic limestone and calcareous shale lenses and interbeds (Beytitepe Limestone). As a result of studies focusing on the planktic foraminifera-bearing pelagic interlayers in three areas (Gökdere, Işıklar and Kocaçay areas) around Bornova, a detailed planktic foraminiferal biostratigraphy of the rocks is documented for the first time. The thickness of the laminated micritic limestones attains 360 m in the Gökdere area. Occurrences of late Maastrichtian species such as Abathomphalus mayaroensis (Bolli), Contusotruncana contusa (Cushman), Globotruncanita conica (White) and Racemiguembelina fructicosa (Egger) within planktic foraminifera assemblages obtained from the laminated micritic limestones and red calcareous shales in the three areas suggest a late Maastrichtian age for these rocks. The occurrence of various species of Globanomalina, Morozovella, Igorina and Parasubbotina within the calcareous shales in the Işıklar area suggests a late Palaeocene age. The Kocaçay area has well-preserved outcrops showing the stratigraphy of the matrix, despite the more complex geology. The upper Maastrichtian laminated micritic limestones are gradationally overlain by upper Maastrichtian calcareous shales. The calcareous shales are represented by rich planktic foraminiferal assemblages and include blocks derived from laminated micritic limestones. The upper Mastrichtian calcareous shales are overlain by Palaeocene red calcareous shales. Poor assemblages including Parasubbotina varianta (Subbotina), Subbotina triangularis (White), Subbotina cf. velascoensis (Cushman), Globanomalina compressa (Plummer) and Globanomalina planoconica (Subbotina) indicate a late Palaeocene age for the lower part and a latest Palaeocene age for the upper part of the calcareous shale sequence. Therefore, the age of conglomerates and flysch overlying the calcareous shales should be latest Palaeocene or younger in the Kocaçay area.
