This PDF file includes: Methods: Collection and Processing SOM Text Figs. DR1 to DR7 Tables DR1 to DR3 References Methods: Core Collection and Processing The cores were collected using an underwater pneumatic hammer attached by airhoses to a tending compressor at the surface and operated by divers below (Fig. DR1). Once drilled, the cores were capped and removed using airlift bags. After collection, each core was photographed, described, and sampled at 1 cm intervals (unless sediment character required larger intervals), and subsampled for granulometry, micropaleontological analysis, and dating (Figs. DR2-DR6, Table DR1 and DR2). Chronological ages were based on (depending on availability in core) ceramics, OSL, and C14 (Tables DR1 and DR2). Granulometry was completed using Laser particle Analyzers (on a Beckman laser Coulter counter and Malvern Multisizer). Values from Malvern Multisizer varied from Beckman by a maximum of +/-1%. Micropaleontological collection, analysis, and statistics were based on the methods of Fishbein and Patterson (1).
18During the late glacial, marine isotope Stage 2, the Marmara Sea transformed into a 19 brackish lake as global sea level fell below the sill in the Dardanelles Strait. A record of the 20 basin's reconnection to the global ocean is preserved in its sediments permitting the extraction of 21 the paleoceanographic and paleoclimatic history of the region. The goal of this study is to 22 develop a high-resolution record of the lacustrine to marine transition of Marmara Sea in order to 23 2 reconstruct regional and global climatic events at a millennial scale. For this purpose, we mapped 24 the paleoshorelines of Marmara Sea along the northern, eastern, and southern shelves at 25Çekmece, Prince Islands, and Imrali, using data from multibeam bathymetry, high-resolution 26 subbottom profiling (chirp) and ten sediment cores. Detailed sedimentologic, biostratigraphic 27 (foraminifers, mollusk, diatoms), X-ray fluorescence geochemical scanning, and oxygen and 28 carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided 29 evidence for cold and dry conditions prior to 15 ka BP, warm conditions of the Bolling-Allerod 30 from ~15 to 13 ka BP, a rapid marine incursion at 12 ka BP, still stand of Marmara Sea and 31 sediment reworking of the paleoshorelines during the Younger Dryas at ~11.5 to 10.5 ka BP, and 32 development of strong stratification and influx of nutrients as Black Sea waters spilled into 33 Marmara Sea at 9.2 ka BP. Stable environmental conditions developed in Marmara Sea after 6.0 34 ka BP as sea-level reached its present shoreline and the basin floors filled with sediments 35 achieving their present configuration. 36 37
Figure 1. Location map showing harbor ruins and excavation sites outside of harbor (W4: 677079, 3598186; W6: 677100, 3598300; W7: 677045, 3598318). Insets show regional tectonic framework of eastern Mediterranean (bottom left) and layout of Herod's harbor (upper right). ABSTRACTUnderwater geoarchaeological excavations on the shallow shelf (ϳ10 m depth) at Caesarea, Israel, have documented a tsunami that struck and damaged the ancient harbor at Caesarea. Talmudic sources record a tsunami that struck on 13 December A.D. 115, impacting Caesarea and Yavne. The tsunami was probably triggered by an earthquake that destroyed Antioch, and was generated somewhere on the Cyprian Arc fault system. The tsunami deposit consisted of an ϳ0.5-m-thick bed of reverse-graded shells, coarse sand, pebbles, and pottery deposited over a large area outside of the harbor. The lower portion of the deposit was composed of angular shell fragments, and the upper portion of whole convex-up Glycymeris spp. shells. The sequence records tsunami downcutting (ϳ1 m) into shelf sands, with the return flow sorting and depositing angular shell fragments followed by oriented whole shells. Radiocarbon dating of articulated Glycymeris shells, and optically stimulated luminescence (OSL) dates, constrain the age of the deposit to between the first century B.C. and the second century A.D., and point to the tsunami of A.D. 115 as the most likely candidate for the event, and the probable cause of the harbor destruction.
The recent PRISMED II geophysical survey has documented various styles of salt tectonics in and around the Nile deep-sea fan (Eastern Mediterranean Sea). The first main type of salt-related structures comprises listric normal growth faults and grabens, trending roughly perpendicular to the slope line of the Nile Cone. These faults and associated salt structures result from thin-skinned extension, driven by gravity gliding and spreading as a result of sediment loading of the Plio-Quaternary overburden above the Messinian evaporites, which acted as a décollement layer. The second major type of salt structures consists of lineaments that obliquely intersect the continental slope of the Nile deep-sea fan. These structures may have had some strike-slip movement, and salt diapirs grew reactively or were deformed by fault-block movement. In the western distal part of the Nile deep-sea fan, compressional tectonics of the adjacent Mediterranean Ridge caused the formation of a series of salt-cored folds and reverse faults above the Messinian evaporites. In the eastern distal part of the Nile Cone, sediment progradation progressively expelled salt northward, first forming small folds and tight diapirs, then a scarp of 400 m height around the Eratosthenes Seamount, corresponding to the basinward limit of salt deformation.
S U M M A R YWe report the results of experiments on the initiation of subduction, using stratified analogue models in a large centrifuge, where the experiments are driven only by the enhanced gravity of the centrifuge without the effect of external lateral stresses. The scaled density of the stratified components resembles that of the asthenosphere and the continental and oceanic lithospheres. The experiments demonstrate that under the effect of enhanced gravity, the layers simulating the oceanic lithosphere detach from the front of the 'continental lithosphere' and plunge under it, pushing the more pliable asthenosphere downwards. Simultaneously, the 'continental lithosphere' is thrust over the downgoing slab; where friction is low, the 'continental lithosphere' extends considerably so that the 'ductile continental lithosphere' is exposed in some places. The rate of thrusting of the experimental continental slab over the oceanic one, as well as the amount of extension of the overriding slab and the extent of the rollback of the subduction zone that follows the initial lithospheric detachment, are controlled by friction and density differences between the subducting and the overthrust slabs. The analogue experiments emphasize the role of lateral density variations in incipient subduction and the effect of differential seismic friction along the subduction plane on the evolution of subduction zones, their shape and the evolution of their backarc basins. The morphological resemblance of the experimental results to various subduction systems seems to support their applicability to real subduction systems.
The onset of subduction at passive margins has been extensively investigated and debated. However, the force constellations and mechanisms that enable the development of a subduction system from a passive margin remain unclear. This study presents new insights into the conditions and processes by which lateral density differences between oceanic and continental lithospheres in passive margins may lead to initiation of a low‐angle subduction system. The presented study consists of (1) analytical calculations of flow fields generated in passive margins, and (2) analogue experiments of mature passive margins performed in a centrifuge. The analytical formulation predicts temporal and spatial evolution of an interface between the oceanic and continental lithospheres, and demonstrates that oceanic underthrusting may occur by rotation of this interface. The analogue experiments show that incipient subduction may develop by ductile deformation within the lithosphere, involving no sliding along the ocean‐continent interface, so that the frictional resistance between the plates need not be overcome. The force induced by the negative buoyancy of the oceanic plate with respect to the asthenosphere, is found to be in some cases irrelevant to subduction nucleation. Results of both the analogue experiments and the analytical calculation are compared to the south‐east Australian passive margin, and show an excellent fit to its geometry and stress distribution. The proposed mechanism is also applied to the only two cases of subduction of Atlantic tectonic system, the Lesser‐Antilles and the South Sandwich subduction systems.
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