Kandemir, Raif; Yilmaz, Cemil

Ammonitico Rosso type sediments (ARTS) form the bottom level of the Şenköy Formation in the Gümüşhane area. The formation accumulated in the rift-related basins triggered by extensional tectonic regimes in the Early Jurassic times. Six different sections were studied in this area in order to interpret the lithostratigraphy, facies, and deposition environments of the ARTS. Two basic lithofacies were distinguished, nodular-marly and nodular-calcareous. These facies provide useful information regarding depositional conditions in the area and environmental energy. These factors were mainly related to the relative sea-level that in turn was controlled by tectonic and eustasy conditions. In addition, seven different types of microfacies were recognized and described as a result of the detailed analysis of the sections. The results of the analysis show that these sediments in the Gümüşhane area were developed in transgressive phases/events. These sediments share characteristics with other peri-Mediterranean regions and sea-level curves, and show a similarity to the major transgressive pulse during the Pliensbachian stage. Deposition of ARTS was controlled by syn-depositional extensional movements, leading to their accumulation on top of tilted blocks, slopes and horsts in an open marine environment. The ARTS were developed during the rifting of the continental margins pointing up the phases of the Tethys opening. Neptunian dykes verifying this opening developed at different levels of the ARTS and were filled with overlying sediments. These results support the hypothesis that the ARTS were formed in tectonically active environments where extensional tectonic movements were continuously improved during the deposition of the ARTS.

Yilmaz, Cemil; Carannante, Gabriele; Kandemir, Raif

In the Gümüşhane region (NE Turkey), carbonate platform and basin deposits, crop out with excellent exposures. In this area, two localities (Mescitli-İkisu region, 10 km west of the Gümüş hane and Kale-Kilop region, 20 km southeast of the Gümüşhane), in which the related successions are particularly well exposed, have been studied in detail. The outcropping shallow water limestones of the Berdiga Formation (Eastern Pontides Carbonate Platform) were deposited during Late Jurassic-Cenomanian p.p. times in peritidal environments. The overlying Kermutdere Formation consists of monogenic breccias, calciturbidites, red pelagic limestone and siliciclastic turbidites, which were deposited in slope and basin environments. In the Gümüşhane region, the above Formations record the evolution from platform to basin settings in relation to an extensional regime set up in the Cenomanian. The tectonics-related drowning of the Eastern Pontides carbonate platform resulted in graben-semi graben basins in which deep marine sediments were deposited during Late Cretaceous times, having a wedge geometry.

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.

Steuber, Thomas; Yilmaz, Cemil; Löser, Hannes

Rudist communities that developed on the southern slope of the Pontid magmatic arc during the late Cretaceous thrived in a tectonically unstable setting, and in environments that were strongly influenced by siliciclastic sedimentation. Strontium isotope stratigraphy indicates an early Campanian age of the investigated association at Höbek Tepe, near Amasya. Stable isotope analyses of sclerochronological profiles of several shells of the three dominating hippuritid species yielded cyclic variations of δ18O that delineate seasonal variations in palaeotemperature. This allowed for the determination of individual life spans, skeletal growth rates and the reconstruction of the living growth fabric. Annual vertical shell growth of 35-40 mm was maintained by cylindrical morphotypes of Vaccinites ultimus during several successive years, while adult annual shell accretion of conical morphotypes was only 27 to 30 mm. Vertical growth of the co-occurring Yvaniella alpani was considerably slower and rarely exceeded 10mm/year. Differential growth rates of the two most abundant species, and morphological characters of Yvaniella which indicate that skeletal growth capacity was similar to sediment accumulation, allowed for a consistent reconstruction of the original growth fabric. CaCO3 production of the rudist communities amounted to 20 kg x year-1 x m-2 and contributed significantly to the sedimentary budget. Large-scale formation of fine-grained calcareous sediments by bioeroders occurred only in environments of less rapid burial, indicated by associations of slowly-growing geniculate rudist morphotypes and patellate corals. The implications of these results for the distribution of rudists and corals in Cretaceous shallow-marine environments are discussed.