The First Record of Eotrigonobalanus Furcinervis (Fagaceae) from the Oligocene of the Thrace Basin, Western Turkey

Eotrigonobalanus furcinervis was recorded for the first time from the Oligocene sediments of the Thrace Basin. The species was discovered in the upper part of the Danişmen Formation from the Marmaraereglisi Area, southeastern the Basin. Eotrigonobalanus furcinervis appeared in large numbers early during the early Paleocene–late Oligocene localities in Europe; especially in Thrace of Greece, Bulgaria, Germany, Czech Republic, Hungary and Romania. Therefore, this data is valuable as the first recording for Thrace Basin.

Paleogene extension in the Northern Aegean: Colluvial/debris flow deposits of the Early-Middle Eocene in NW Thrace Basin, Turkey

The Thrace Basin consists of Paleogene–Neogene deposits that lie in the lowland south of the Strandja highlands in NW Turkey, where metagranitic and metasedimentary rocks occur. The Akalan Formation consisting of colluvial fan/debris flow deposits represents the base of the sequence in the northern Thrace basin where it is bounded by a right lateral strike-slip oblique fault called “The Western Strandja Fault Zone”. This formation exhibits a coarse-grained, angular and grain-supported character close to the fault zone which has releasing-bends. Fine-grained, rounded, and matrix-supported sediments occur away from the contact. During this study, the Akalan Formation is described for the first time as having larger benthic foraminifera (LBF) of Coskinolina sp of Ypresian–Lutetian, Nummulites obesus of early Lutetian, Dictyoconus egyptiensis of Lutetian, Orbitolites sp. of Ypresian–Bartonian, Miliola sp of early–middle Eocene, Idalina grelaudae of early Lutetian–Priabonian, Ammobaculites agglutinans, Amphimorphina crassa, Dentalina sp., Nodosaria sp., Operculina sp., Lenticulina sp., Quinqueloculina sp. and Amphistegina sp. of Eocene. This unit passes upward with a conformity into reefal limestones of the middle/late Eocene–early Oligocene Soğucak Formation. At times, the limestone overlies the conformity, there is an indication of a prograding sedimentary sequence. The new stratigraphic, paleontological, sedimentological and structural findings related to the NW Thrace Basin suggest a strong transtensional/extensional tectonic control for the initial Paleogene sedimentary deposition during the Ypresian–Lutetian period as shown by fossil content of the Akalan Formation. Right lateral-slip extensional tectonics appears to have had activity during the middle–late Eocene transgressive deposition of the Soğucak Formation when the basin became deepened and enlarged.

Late oligocene–early miocene shortening in the Thrace Basin, northern Aegean

Late Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.

Timing and rate of exhumation of Central Sredna Gora Zone basement, Bulgaria

<p>Sredna Gora Zone in Bulgaria is confined between the Balkan fold-thrust belt to the north and the Rhodope metamorphic complex to the south. The pre-Mesozoic basement of the central parts of the zone consists of Variscan high-grade metamorphic rocks intruded by Late Carboniferous granitoid plutons. They are transgressively overlaid by Triassic epicontinental, arc-related Upper Cretaceous volcaniclastic and Paleocene continental deposits. The Paleogene-Neogene sediments of the Thrace basin cover unconformably the older rock sequences. The zone experienced several compressional and extensional events during the Alpine time followed by post-orogenic extension in the Cenozoic.</p><p>We performed apatite fission-track analysis on rocks from the central, topographically highest parts of the Sredna Gora Zone in order to constrain the cooling history of the Variscan basement. With this aim four granitic samples were collected at different altitude (between 565 and 1604 m) from the tectonically uninterrupted section along the slope of Sredna Gora Mountains. The samples were processed and analyzed in the newly established Low-Temperature Thermochronology Laboratory in Bulgaria using LA-ICP-MS technique.</p><p>The samples yield apatite FT ages between 41.6 ± 2.6 (the highermost sample) and 39.4 ± 3.1 (the lowermost sample). The obtained confined mean tracks lengths are between 12.81 and 14.06 µm with standard deviation between 0.99 and 2.11 µm. The Dpar values vary from 1.75 µm to 1.46 µm (with standard deviation of approx. 0.20 µm).</p><p>The obtained positive age-altitude correlation suggests indeed that the studied part of the basement has cooled as one single block. The apparent exhumation rate is estimated to 0.46 mm/year. However, the positive Dpar-age correlation implies that the age dispersion could be influenced by apatite kinetic variability and hence relatively different closure temperature for the analysed samples may be suggested. Therefore, we consider the estimated apparent exhumation rate as only the minimum possible rate. The thermal models of the analysed samples (using HeFTy software) also show moderate cooling rates in the period between 45 and 35 Ma. This cooling could be related to the period of post-orogenic denudation and extension during the Eocene, associated with formation of the Thrace basin to the south-southeast. This extensional event, known from the whole Balkan Peninsula, is well documented in the neighbouring Balkan fold-thrust belt and the Rhodope metamorphic complex from where much faster exhumation rates were reported.</p><p> </p><p><strong>Acknowledgements</strong>. The study is supported by the grant 04/9 funded by the National Science Fund, Ministry of Education and Science, Bulgaria.</p>

Uncovering the impact of Gokceada Volcanic Zone on pressure and temperature conditions of Thrace Basin in the Northern Aegean Sea using 1D basin modelling and seismic velocity extraction

<p>Tectonic evolution of Thrace Basin in the offshore area surrounding the Gokceada island has been widely studied except for pressure and temperature conditions. This study aims to fill this scientific gap while introducing the discovery of NW-SE oriented Gokceada Volcanic Zone, represented by extinct volcano geometries and chaotic seismic facies on seismic sections. Presence of such a significant heat source causes inevitable effects on pressure-temperature behaviour that might manifest itself as abrupt changes and makes the understanding of petroleum system essential. Hence, an integrated workflow involving seismic & well log interpretation, post-drill ppfg & temperature analysis, conversion of interval velocities into a 3D pore pressure model and 1D basin modelling has been conducted for the first time. 1D models focus especially on the oldest sedimentary unit of gas prone Thrace Basin, known as Early-Mid Eocene aged Karaagac Formation in the Northern Aegean region.</p><p><br>Basin analysis has yielded unique results by providing clues to better understand pore pressure mechanism and maturity rate of the Karaagac Formation, including type-III Eocene shales. The shallower parts of the Karaagac Formation, dominated by the Eocene deltaic succession, is in main oil window. On the other hand, between 4-5 km. depth at where the Eocene shales exist, maturity rate reaches late oil-wet gas. Maturity profile also suggests that entrance to the early oil window is at 38-35 Ma, corresponding to the Oligocene. It can be claimed that high burial rates caused fast maturation which can also be supported by the sedimentation rates, calculated approximately as 450 m/Ma. The post-collisional extensional regime in the Early-Mid Eocene, characterised by wedge-shaped growth strata on seismic sections, can be considered as the main reason for the high sedimentation rates. Thus, it can be proposed that the main causes for increasing pore pressures are disequilibrium compaction and possibly hydrocarbon generation process.</p><p><br>Gokceada Volcanic Zone can be suggested as another driving force of fast maturation. Temperature profiles of two wells exhibit a significant increase towards the volcanic zone. In terms of geothermal gradients, the abrupt changes resulted with temperature fluctuations. Gradient values change between 35-45 <sup>0</sup>C/km during Eocene-Oligocene at when the basin has experienced severe volcanism due to the crustal thinning. By the ongoing burial, values decrease and approach present-day conditions, ranging between 25-35 <sup>0</sup>C/km. Present day temperatures reach at least 150-160 <sup>0</sup>C interval for the deepest part of the basin.</p><p><br>Unlike the temperatures, pore pressures slightly decrease along the volcanic zone. This trend can be related to low porosities of products of intrusions and extrusions. For a better comparison of pressure conditions, a pore pressure cube has been reflected on the seismic sections. According to the model, present-day pressure values range between 5000-12000 psi in the Karaagac Formation. A very similar pressure profile has been illustrated by burial history charts and post-drill ppfg graphs as well. Although different inputs were used, outcomes of all methods validate each other. Therefore, findings of this study can act as a reliable foundation for pore pressure prediction and static temperature prognosis in the area.</p>

Foraminifera of shallow and very shallow facies from the upper Eocene–lower Oligocene Kazandere Member, Soğucak Formation, Thrace Basin, northwest Turkey

The middle−upper Eocene to lower Oligocene Kazandere Limestone Member of the Soğucak Formation is widely represented in the Thrace Basin and rich in shallow-water marine foraminifera. Very shallow-water Priabonian facies described here include Borelis vonderschimitti, Borelis laxispira sp. nov., Chapmanina gassinensis, Chapmanina elongate sp. nov., Pfendericonusglobulus sp. nov., Orbitolites minimus,Coscinospira sp. Last occurrences of the aforementioned Priabonian species and first appearances of the shallow-water marine Rupelian species Nummulites fichteli, Nummulites vascus and Operculina complanata define the Eocene−Oligocene boundary in the new Kazandere Member at the northeast Thrace Basin.