The characteristics and evolution of accommodation zone in Xihu Sag, East China Sea Shelf Basin

<p>Accommodation zone is an important deformation structure in sedimentary basin, which is significant to understanding the basin structure. The formation and evolution of the Xihu Sag is controlled by the NNE-striking faults, whereas the NNE-striking deformation is offset by the NW-striking accommodation zone. However, the structure and evolution of the accommodation zone are poorly known. Based on the dips and activation rates of related NNE-striking faults on two sides of the NW-striking accommodation zone, 8 styles of NW-striking accommodation zones are divided in this sag, including the synthetic approaching style, synthetic broken line style, synthetic overlapping style, reverse approaching style, reverse broken line style, composite approaching style, composite broken line style, composite overlapping style. The relative accommodation ratio of the accommodation zone can be reflected by the difference-value of the faults activation rate of the NNE-striking faults. The results show that: (1) the most of the NW-striking accommodation zones formed at Early Cretaceous with low relative accommodation ratio, and reached its peak at Eocene, and disappeared at Late Oligocene. (2) The temporal and spatial differences of the NW-striking accommodation zones are very common in the Xihu Sag. Spatially, the accommodation zones are mainly developed in the western slope of Xihu Sag, and rarely developed in the middle and eastern of the Xihu Sag. Temporally, the accommodation zones developed in the northern area of the western slope of the Xihu Sag during the early stage, whereas, these zones migrated to the southern area of the western slope of the Xihu Sag during the late stage. This study on the tectonic evolution of the accommodation zone provides significant support to the study on the tectonic evolution of the Xihu sag.</p>

THE MISSING SOFT LINK? EVIDENCE FOR MARGINAL FAULT INTERACTION AT THE SOUTHERN MARGIN OF GERANEIA MOUNTAINS, CENTRAL GREECE

We examine the structure of the southern faulted margin of Geraneia Mountains, controlled by two marginal faults, namely the Loutraki and Kakia Skala Faults, which have been active in the Quaternary; however, Holocene activity on these structures has not been verified. Structural observations at the probable overlap zone between these two faults, suggest that they became soft-linked, or linkage ended at its early stage, before activity migrated basinwards, with consequent footwall backtilt. The affinity of the kinematics in the accommodation zone with the present-day extensional stress field might hint at possible Late Quaternary activity on these two major faults.

Accommodation zones and tectono-stratigraphy of the Gulf of Suez, Egypt: A contribution from aeromagnetic analysis

ABSTRACT This paper starts with an up-to-date literature review of the pre-rift, syn-rift and post-rift stratigraphy of the Gulf of Suez. The geometry and depth of the Proterozoic basement is not generally known due to poor seismic images below the Upper Miocene evaporites (including massive rock salt) and clastics. The pre-rift Paleozoic to Early Oligocene succession shows that several local basins (c. 10s of km in extent) occur in the Gulf, with thick sedimentary sections (e.g. c. 3,000 m for Paleozoic and 1,000 m for Jurassic and Lower Cretaceous). The origin and distribution of these basins is not well understood and the presence of similar pre-rift basins in the southern Gulf is not known to occur. The syn-rift Late Oligocene to Middle Miocene and post-rift Late Miocene – Pliocene successions are widely distributed within the rift basin and reach a thickness in excess of 5,000 m. In order to visualize the grain and relative relief of the Proterozoic basement, a series of aeromagnetic images are shown in this paper. The images include Total Magnetic Intensity (TMI), Reduced-to-Pole (RTP), filtered regional and structural RTP, and Second Vertical Derivative (SVD). The paper also shows a three-dimensional visualization image of the magnetic basement that highlights the distribution of the basins in the Gulf. The magnetic lows do not generally trend along the Suez (NNW-trending Clysmic) Fault, but instead show highly variable orientations attributed to a complex pattern of criss-crossing faults. In particular, two areas were selected to interpret the geometry and depth of the basement. The first area covered the northern Zaafarana Accommodation Zone and involved modeling five aeromagnetic profiles. The Zone was interpreted as an EW-trending basement plateau bounded by basins that are c. 8,000 m deep. The second modeled area (four profiles) covered the southern Morgan Accommodation Zone. This zone was interpreted as an ENE-trending plateau of similar relief to the Zaafarana Zone. The Morgan Zone is terminated in the eastern Gulf by the 8,000-m-deep Morgan Basin. The very deep basins surrounding the two plateaus may contain both pre-rift and syn-rift source rocks, from which the numerous surrounding petroleum fields were sourced.