Yilmaz, Cemil; Kandemir, Raif

The Gümüşhane Mesozoic Basin is characterized by Lower-Middle Jurassic volcanic-siliciclastic sediments (Şenköy Formation), Upper Jurassic-Cenomanian platform carbonates (Berdiga Formation) and Upper Cretaceous turbidites (Kermutdere Formation). Four extensional periods (Lias-Dogger, Turonian-Coniacian, Late Campanian (?) and Early (?) Maastrichtian) separated by two quiet tectonic periods (early Malm-Cenomanian and Santonian-Campanian) have been defined in this sequence. The previous studies suggested that Mesozoic basins only formed by extensional movements in the middle Cretaceous. Three extensional periods seperated by two quiet periods from the Cenomanian to the end of the Maastrichtian in Gümüşhane and NE Turkey were firstly proved by sedimentological findings in this study. The definition of these periods depends on features such as (1) neptunian dykes in different levels, (2) shallow marine limestone, (3) thinning-and-fining-upward sequences, (4) mixed faunal assemblages, (5) micro-turbiditic structures, (6) syn-sedimentary fault, (7) grabens, half-grabens, (8) pelagic limestone, (9) calciturbidites, (10) laterally and vertically rapid changes of the thickness and facies, (11) platform-to-basin transition and (12) monogenic breccias.

Eyüboǧlu, Yener; Bektaş, Osman; Şeren, Aysel; Maden, Nafiz; Özer, Rahşan; Jacoby, Wolfgang R.

The Eastern Pontide magmatic arc (NE Turkey) was rifted by the polyphase extensional tectonic regimes in the Early Jurassic. While alternated volcanics and siliciclastic sedimentary rocks accumulated during the episodic tectonic subsidences, thermal subsidence is manifested by sedimentation of the red pelagic limestones of the Ammonitico Rosso during the Pliensbachian. The trends of the Liassic basins extending in NW-SE, E-W, NE-SW directions coincide with the gravity and magnetic lineament anomalies and corresponding fault zones that are responsible for the paleotectonic and neotectonic evolutions of the Eastern Pontide magmatic arc. These mutual relationships suggest that the faults making up the architecture of the Liassic basins might have operated during the Paleozoic, Mesozoic and Cenozoic times in different manners. Neptunian dikes, filled by the early rift siliciclastic and following fossiliferous red pelagic limestone implying the repeated extensional tectonic regimes, are also parallel to the main extensions of the Liassic basins. The poles of the contemporaneous neptunian dikes suggesting two or three extensional conjugate fracture systems are in accordance with the dip directions of the rift sediments accumulated in the same conjugate normal fault systems. Assuming that the Liassic basins with Ammonitico Rosso are coeval, multi-armed rift basins might have opened by the mode of the three-directional extension rather than reactivation of faults in the different times.