Eurasia Basin and Gakkel Ridge, Arctic Ocean: Crustal asymmetry, ultra-slow spreading and continental rifting revealed by new seismic data

High Arctic new seismic data, collected by Russian Federation from 2011 to 2014, and additional geological and geophysical information, are used to interpret the basement and sedimentary structure of central and eastern Eurasia Basin, the Gakkel Ridge, and their transition into the Laptev Sea. We find that significant changes in basement topography occur in Nansen Basin at C20 (43.43 Ma) and in the Amundsen basins at C21 (45.7 Ma), and in both basins at C13 (33 Ma). A long seismic profile, that documents for the first time the structure of conjugate flanks and their margins in the central-eastern Eurasia Basin, confirms that oceanic accretion was asymmetric, with 10% less crust developed in the Amundsen Basin since continental break-up. In the eastern Amundsen Basin, we observe mid-ocean ridge uplift since C13 (33 Ma). We identify four distinct sedimentary packages in the Eurasia Basin: Early to Mid Eocene (c. 56 to 45.7 Ma), Mid Eocene to Early Oligocene (45.7 to 33.2 Ma), Early Oligocene to Early Miocene (33.2 to 19.7) and Early Miocene to Present (19.7 to 0 Ma); they are linked to the oceanic lithosphere age determined from magnetic data. The deepest part of the Gakkel Ridge (5215 m), situated close to the easternmost part of this mid ocean ridge, is imaged for the first time by seismic data that reveals volcanic constructions within the older axial ridges and on the flanks. Gakkel Ridge's asymmetric flanks with shallow, regularly-spaced, and rugged structure, typical to ultra-slow spreading ridges, imply periodicity of tectonic phases. The Khatanga-Lomonosov Fault between Lomonosov Ridge and the Laptev Sea region, is identified on few seismic profiles; kinematic models predict that it may have been active only for a maximum of 10 myr after continental break-up

Bulgaria: sea-level change and submerged settlements on the Black Sea

The Black Sea is recognised as having great potential for the preservation of submerged prehistoric sites because of the large area of land exposed on the continental shelf at lowest sea levels, especially along its western and north-western coastlines. However, very few have been discovered to date, and those that are known are located in Bulgaria. Because of the complexities associated with the periodic isolation of the Black Sea from the Mediterranean and its reconnection, offshore research has tended to focus on geological and geophysical investigation of inundation history, with unresolved and strongly-held disagreements about the timing and rapidity of sea level rise at the end of the Last Glacial and its potential human impact. In Bulgaria, a rich concentration of underwater prehistoric sites has been discovered thanks to dredging activities earlier in the 20th century and a long tradition of underwater archaeological investigations going back to the 1970s. These demonstrate the presence of substantial in situ village settlements of Eneolithic and Early Bronze Age date in shallow water (< 10 m), with excellent preservation of large ceramic assemblages, wooden structures, and faunal and palynological data on palaeodiet and palaeoeconomy. More recently, large scale marine-geological and archaeological projects have begun, aimed at integrating shallow-water inshore investigations with offshore survey in deeper water