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<jats:title>ABSTRACT</jats:title><jats:p>Knowledge of the rifting and opening process of the Meso‐Tethys Ocean is important for understanding the evolution of the Tethys tectonic domain and for an in‐depth understanding of Tethys dynamics. Sedimentary rocks are faithful recorders of surface expressions of tectonic events and are thus expected to have recorded the rifting and opening of the Meso‐Tethys Ocean. This study presents petrography, sedimentology, zircon U–Pb geochronological data and Hf isotope data for the Carboniferous–Permian Shiquanhe stratigraphic succession in the Lhasa Terrane of the Tibetan Plateau. The data indicate that the 300 to 273 Ma Lagar and Angjie formations in the lower section of the Carboniferous–Permian Shiquanhe succession were deposited in the stable passive margin of northern Gondwana with sediment sources in Gondwanaland. However, the 273 to 252 Ma Xiala Formation in the upper section of the Carboniferous–Permian Shiquanhe succession was deposited in a tectonically active setting characterized by intense magmatic activity. Considering the transition from the Lagar and Angjie formations to the Xiala Formation, a significant change in depositional setting from tectonically stable to tectonically active occurred at <jats:italic>ca</jats:italic> 273 Ma. Similar Early–Middle Permian changes in depositional setting have also been identified in the South Qiangtang, Baoshan and Oman regions in the Tethyan tectonic domain. These widespread changes in depositional setting, together with Early–Middle Permian tectonic uplift and episodes of subsidence, as well as rift‐related magmatism in the South Qiangtang, Baoshan, Himalayan, Zagros, Oman and Turkey regions once located in northern Gondwana, constitute a complete record of continental rifting–ocean opening associated with the diachronous opening of the Meso‐Tethys Ocean during the Early–Middle Permian.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The deposits of the upper Neoproterozoic Zerrissene Group of central‐western Namibia represent a large siliciclastic deep‐water depositional system that showcases the intricacies of facies and architectural relationships from bed‐scale to fan‐system‐scale. The lack of vegetation in the Namib Desert and regular east–west repetition of folded stratigraphy (reflecting <jats:italic>ca</jats:italic> 50% tectonic shortening) provides quasi‐three‐dimensional exposure over a current area of approximately 2700 square kilometres. The Brak River Formation, the middle sand‐rich unit of the Zerrissene Group, consists of nearly 600 m of strata exposed in multiple parallel continuous outcrops up to <jats:italic>ca</jats:italic> 10 km in length and oriented obliquely to depositional dip. Ten stratigraphic sections are correlated <jats:italic>ca</jats:italic> 32 km (<jats:italic>ca</jats:italic> 64 km restored) across the basin and offer exposure comparable in scale to modern submarine fans. Six sedimentary facies are identified and grouped into four facies associations that represent axial‐to‐marginal portions of deep‐water lobes in an unconfined submarine fan system. Spatial facies patterns, regional thickness variations, and palaeocurrents indicate that Brak River Formation sediments were transported primarily from the north to south–south‐west through a trough‐like basin and deposited within an unconfined basin plain at the junction of the Adamastor and Khomas oceans. The unique outcrop exposure and extent permits the documentation of system‐scale architecture and basin configuration of the Brak River submarine fan system. A transition from the sand‐rich lower Brak River Formation to more intercalated mudstone‐dominated intervals in the middle and upper Brak River Formation is interpreted to record a change from aggradational to compensational stacking of lobe deposits. This records the evolution of a large submarine fan as it filled the subtle seafloor topography and became less confined at the system‐scale. The documentation of these deep‐water deposits from centimetre‐scale to basin‐scale provides a new model for a system with extensive long‐distance transport of sand‐rich sediment gravity flows to submarine lobes without apparent channelization.</jats:p>

<jats:title>Abstract</jats:title><jats:p>High‐Alpine regions are prone to a large variety of geohazards, among which earthquakes have the strongest impact on landscape and local population. Historic records indicate a moderate to high seismic activity in the northern, south‐western and central parts of Switzerland. In contrast, south‐eastern Switzerland has less historic earthquake chronicles due to the low population density, resulting in a poorly constrained seismic event catalogue. The aim of this study is to evaluate the palaeoseismic activity for south‐eastern Switzerland by using the sedimentary record of Lake Silvaplana in the Engadine Valley. A dense grid of high‐resolution two‐dimensional seismic profiles, high‐resolution bathymetry and a 10 m long sediment core from the deepest basin were used to investigate the stratigraphy of the lake sediments. The bathymetry reveals a flat basin, flanked by steep slopes to the north‐west and south‐east. The acoustic basement consists of four ridges, and gently‐dipping fans to the south‐west and north‐east. Expressions of slope failure can be identified in all domains of the lake floor and the subsurface data. Multiple coevally‐triggered chaotic mass‐flow deposits, overlain by megaturbidites with a coarse‐sand base, have been detected along ten horizons in the seismic data. The four most recent of these deposits are cored and radiocarbon dated to approximately 230, 310, 960 and 1330 cal yr BP, indicating four over‐regional seismic events that triggered large slope failures in Lake Silvaplana in the last 1400 years. Correlation with sediments of Lake Sils, Lake Como, Lake Iseo and Lake Ledro indicate within radiocarbon uncertainties a large earthquake around 1330 cal yr BP. Within their age ranges, the postulated earthquake at 310 cal yr BP (1640 CE) further correlates with a moment magnitude Mw <jats:italic>ca</jats:italic> 5.4 event in Ftan in 1622 CE, and the 960 cal yr BP (990 CE) earthquake correlates with a Mw <jats:italic>ca</jats:italic> 5.2 earthquake in Brescia in 1065 CE. Six mass‐movement deposits, also suggested to be caused by earthquakes, were not reached by the sediment core and have suggested ages between 7800 and 11300 cal yr BP. Thus, Lake Silvaplana sediments provide the first reliable record of seismic activity for the mid and Late Holocene in this region, likely related to the neotectonic activity of the Engadine Line, a major fault zone running along the main valley.</jats:p>

<jats:title>ABSTRACT</jats:title><jats:p>The Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southwards. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels lead to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity.</jats:p>

<jats:title>ABSTRACT</jats:title><jats:p>Fine sediment stored in the gravel bed is an important component of river systems. Current field protocols usually allow evaluation of the silt–clay fraction of fine sediment stocks only and neglect the sand fraction. This study proposes a new protocol to quantify fine sediment stocks, including the sand fraction inside the gravel bed matrix. Fine sediment stocks were sampled within patches of 0.30 m × 0.30 m on the dry gravel bed surface, separating the surface layer and the subsurface layer. The grain‐size distribution of the samples was obtained by field sieving (10 mm, 2 mm, 500 μm and 100 μm) over a bucket, using a known volume of water. The mass of the fraction below 100 μm was measured based on the concentration within the bucket. The local stocks were then integrated over the whole river reach by assigning local stocks to facies, in which fine sediment stocks were assumed to be homogeneously distributed. The methodology was applied to a 1 km long reach of the River Galabre (Southern French Alps), characterized by significant fine sediment stocks and upstream sediment input. Results from local measurements show a large amount of sand in both surface and subsurface layers. The quantity of sand can reach up to three times the quantity of silt–clay. An estimation of porosity showed that fine material may play an important role in structuring the bed, since porosity increases with increasing fine sediment content. The potential fine sediment stock that can be re‐suspended due to channel migration is found to be of the same order of magnitude as the sediment budget estimated from the measured flux in the upstream hydrometric station of the studied reach.</jats:p>

<jats:title>ABSTRACT</jats:title><jats:p>The Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Hummocky cross‐stratification is commonly observed in the marine offshore transition to lower shoreface environments. However, to date, the origins of hummocky cross‐stratification and its associated hummocky bedforms and hydrodynamic processes remain controversial and enigmatic. In the present study, a large‐scale flume experiment was conducted to study the formation of hummocky bedforms. In the central test area of the flume, combined flow with water waves, with period of 2 s and velocity of 0.34 m s<jats:sup>−1</jats:sup>, progressed at a right angle to a current with velocity of 0.17 m s<jats:sup>−1</jats:sup>, whereas a wave‐alone condition pertained upstream and downstream of the test area. The combined‐flow ripples in the test area had smaller dimensions than wave ripples, but their cross‐section geometries were very similar. Most importantly, the experimental results, for the first time, revealed that humps occur with lengths up to approximately 40 mm beneath combined flow ripples. The formation of these structures appears to relate to the enhanced turbulence for the combined flow, because the turbulence kinetic energy for combined flow was <jats:italic>ca</jats:italic> 50% higher than that under the wave‐only condition. Moreover, the observed small‐scale humps in the present experiment had comparable cross‐section geometries with hummock‐like bedforms previously reported in laboratories and fields under storm conditions. Additionally, these humps could scale up to large‐size hummocks under waves with longer period and faster velocity than the present conditions. The present experiment indicates that waves perpendicular to a current do generate hummock‐like structures in association with ripples and therefore provide a new perspective for future study of the origins of hummocky cross‐stratification.</jats:p>