Search

Changes in Earth’s eccentricity, obliquity, and precession can cause quasi-cyclic variations in Earth’s climate that may be preserved in sedimentary archives. Recent research has shown that shallow-marine paleoclimate archives in mid- to low-latitude regions have the potential to preserve changes in hydroclimate driven by precession, given sufficient space for sediment accumulation and a high sedimentation rate. Our integrated stratigraphic study of the Kueichulin Formation in Taiwan’s Western Foreland Basin (WFB) uses magnetostratigraphy, biostratigraphy and astrochronology to constrain time, with the aim to assess how the evolution of a rapidly uplifting mountain range affected the preservation of climate cycles in the shallow-marine record.Using time-series analysis of two sets of gamma-ray borehole data from the late Miocene to Pliocene Kueichulin Formation (WFB), we found that despite increasing monsoon intensities between 8 and 3 Ma, the preservation of precession-driven East Asian Summer Monsoon variability was low during the early stages of Taiwan orogenesis (before 5.4 Ma). Prior to 5.4 Ma, the Taiwan Strait had not yet formed. Consequently, the southeastern margin of Eurasia was open to the Pacific Ocean, and so the depositional environments in the WFB were susceptible to reworking by large waves. This led to the preservation of low-frequency eccentricity and obliquity, but not higher-frequency precession.Despite increasing basin subsidence from 5.4 to 4.9 Ma, the preservation of orbital oscillations is low. This is attributed to either low sedimentation rates at deeper water depths, which could obscure variations in sediment input or result in cycles below the resolution of the gamma-ray logging tool, or cycles not being detectible in the gamma-ray proxy record due to a lack of contrasting lithology. After 4.9 Ma and up to 3.2 Ma, the Taiwan orogen became the dominant sediment source for the WFB, and rapid growth of the orogen shielded the WFB from high-energy waves generated in the Pacific Ocean. The increased sediment influx and the formation of a semi-sheltered strait, combined with increased space for sediment accumulation in the WFB, resulted in enhanced preservation of precession-driven East Asian Summer Monsoon variability.

Sedimentologika is a community-driven Diamond Open Access scientific journal for the publication of work in the broad area of sedimentology and stratigraphy. The journal aims to provide a platform to the academic community and broader society, offering and guaranteeing permanent free publication and free access to peer-reviewed scientific studies focusing on all types of sedimentary processes, deposits, and environments across all spatial and temporal scales, on Earth or any other planetary body. It will publish high-quality research that will advance the field of sedimentary science (through multidisciplinarity, new teaching practices, tools and methods, and progress in accessibility to science). Sedimentologika is part of an ongoing broader Diamond Open Access movement in geosciences aspiring freedom from the financial barriers and pressures of private publishing houses, to provide direct and equal access to science for all citizens, scientists, and institutions worldwide. The published material will include research, review, methodology and opinion articles, which will be free to share, as the authors will retain the copyright on all the submitted material. Manuscripts will be published in English. Authors can attach a second abstract in the language of their choice, further allowing local communities, students, or decisional bodies to access, at least, a summary of the latest research, thus reducing potential language barriers. Sedimentologika follows Open Science principles to promote ethical dissemination and accessibility of science and knowledge, following high equity, diversity and inclusion standards. Sedimentologika emerged as a solution for the scientific community to sidestep structural inequality of the academic publishing system that is becoming financially unsustainable to its payers (authors, funding agencies), and to commit to bibliodiversity. The objective is to ensure that scientific findings remain accessible to all in order to keep advancing research and informing society on how we understand sedimentology and stratigraphy in the world around us. Sedimentologika is driven by the academic and scientific community for the community and society, promoting self-governance and adapting to the needs expressed by the community.

The late early Permian coincided with a short-lived cold episode in Western Australia, which occurred long after the demise of late Paleozoic ice sheets, and is manifested by conspicuous dropstones...

Coastal depositional systems are normally classified based on the relative input of wave, tide, and river processes. While wave- through to river-dominated environments are well characterized, environments along the wave-to-tide continuum are relatively poorly understood and this limits the reliability and utility of coastal classification schemes. Two tidal shoreface models, open-coast tidal flats (OCTF) and tidally modulated shorefaces (TMS), have been introduced for mixed wave-tide coastal settings. Following nearly two decades of research on tidal shorefaces, a number of significant insights have been derived, and these data are used here to develop a unified model for such systems. First, OCTFs are components of larger depositional environments, and in multiple published examples, OCTFs overlie offshore to lower shoreface successions that are similar to TMS. Consequently, we combine OCTFs and TMSs into a single tidal shoreface model where TMS (as originally described) and TMS-OCTF successions are considered as variants along the wave-tide continuum. Second, tidal shoreface successions are preferentially preserved in low- to moderate-wave energy environments and in progradational to aggradational systems. It is probably difficult to distinguish tidal shorefaces from their storm-dominated counterparts. Third, tidal shorefaces, including both TMSs and OCTFs, should exhibit tidally modulated storm deposits, reflecting variation in storm-wave energy at the sea floor resulting from the rising and falling tide. They may also exhibit interbedding of tidally generated structures (e.g. double mud drapes or bidirectional current ripples), deposited under fairweather conditions, and storm deposits (e.g. hummocky cross-stratification) through the lower shoreface and possibly into the upper shoreface.The development of the tidal shoreface model sheds light on the limitations of the presently accepted wave-tide-river classification scheme of coastal environments and a revised scheme is presented. In particular, tidal flats are components of larger depositional systems and can be identified in the rock record only in settings where intertidal and supratidal deposits are preserved; consequently, they should not represent the tide-dominated end-member of coastal systems. Instead, we suggest that tide-dominated embayments should occupy this apex. Tide-dominated embayments exhibit limited wave and river influence and include a wide range of geomorphological features typically associated with tidal processes, including tidal channels, bars and flats., Les systèmes de dépôts côtiers sont normalement classés en fonction de l’apport relatif des processus liés à la houle, aux marées et aux rivières. Si les environnements dominés par la houle et les rivières sont bien caractérisés, les environnements le long du continuum houle-marée sont relativement mal compris, ce qui limite la fiabilité et l’utilité des systèmes de classification des côtes. Deux modèles d’avant-plages tidales, les estrans ouverts (open-coast tidal flats; OCTF) et les avant-plages modulées par la marée (tidally modulated shoreface; TMS), ont été introduits pour les milieux côtiers mixtes, houle-marée. Suite à près de deux décennies de recherche sur les avant-plages tidales, un certain nombre d’informations importantes ont été obtenues et ces données sont utilisées ici pour développer un modèle unifié pour ces systèmes. Tout d’abord, les OCTF sont les composants de systèmes de dépôt plus vastes et, dans de nombreux exemples publiés, les OCTF recouvrent des successions sédimentaires allant du large à l’avant-plage inférieure, similaires à celle des TMS. Par conséquent, nous combinons les OCTF et les TMS en un seul modèle d’avant-plage tidale où les TMS (tel que décrit à l’origine) et les successions TMS-OCTF sont considérés comme des variantes le long du continuum houle-marée. Deuxièmement, les successions d’avant-plages tidales sont préférentiellement préservées dans des environnements ayant une houle faible à modérée et dans des systèmes progradant et aggradant. Il est probablement difficile de distinguer les avant-plages tidales de leurs homologues dominés par les tempêtes. Troisièmement, les avant-plages tidales, incluant à la fois les TMS et les OCTF devraient présenter des dépôts de tempête modulés par la marée, reflétant ainsi la variation de l’énergie des vagues de tempête sur le fond marin liée à la marée montante et descendante. Les avant-plages tidales peuvent également présenter une interstratification de structures générées par la marée (par exemple, des doubles drapages argileux ou des rides de courants bidirectionnelles) déposées pendant des conditions de beau temps, et des dépôts de tempête (par exemple, des stratifications en mamelons) au niveau de l’avant-plage inférieure et éventuellement de l’avant-plage supérieure.Le développement du modèle d’avant-plage tidale met en lumière les limites de la classification tripartite (houle-marée-rivière) des environnements côtiers actuellement acceptée et une classification révisée est présentée. En particulier, les OCTF et les estrans sont des composantes de systèmes dedépôt plus importants et ne peuvent être identifiés que dans le registre sédimentaire dans les milieux où les dépôts intertidaux et supratidaux sont préservés; par conséquent, ils ne devraient pas représenter le membre extrême des systèmes côtiers dominé par la marée. Nous suggérons plutôt que les baies dominées par la marée occupent cette place. Les baies dominées par les marées présentent une influence limitée des vagues et des rivières et comprennent un large éventail de caractéristiques géomorphologiques généralement associées aux processus de marée, notamment des chenaux, des barres et des platiers tidaux.

Tectonic activity in extensional basins has a profound control on accommodation and sediment supply through the interplay between footwall uplift and hanging-wall subsidence, and thus largely influences the three-dimensional architecture of syn-rift sequences. This is emphasized in areas close to major rift-border faults, where steep coastal reliefs and fluvial gradients produce compound facies zonation and stratigraphic styles with strong lateral variability. The lower Permian High Cliff Sandstone was deposited in an array of shallow marine environments along the margin of the northern Perth Basin during a protracted late Paleozoic rifting episode in Western Australian basins. The formation is composed of fluvio-deltaic and nearshore strata sharply overlying a thick succession of offshore mudstone that was deposited during a phase of tectonic quiescence. This basal contact likely reflects submarine erosion and is, therefore, interpreted as a regressive surface of marine erosion generated in response to forced regression. The facies arrangement consisting of interbedded sandstone, conglomerate, and heterolithic facies chiefly records the evolution of a low- to high-gradient paleoshoreline punctuated by coastal streams, steep sea cliffs, and back-barrier lagoons. Extraformational outsized clasts were probably emplaced by the erosion of exhumed basement and older sedimentary rocks through fluvial incision, wave sapping, or landsliding. The along-strike variability between low- and high-gradient shoreline deposits indicates a dynamic depositional setting with a complex tectonic influence. The basal regressive surface of marine erosion is attributed to footwall uplift during the early reactivation stage of basin-bounding normal faults and, therefore, records the initiation of a new syn-rift phase in the northern Perth Basin.

Throughout their long history, trilobites occupied various ecological niches, colonizing a wide variety of marine environments. However, the paleoecology of this group is mostly based on shelf–slope environments and less is known about their distribution in marginal environments. To understand how trilobite communities respond to a deltaic influence, we studied changes in the taxonomic composition and structure of a diverse and well-known Lower Ordovician olenid-dominated fauna from the Argentine Cordillera Oriental along a delta–marine gradient. Cluster analysis revealed two distinct associations, and ordination analysis revealed a clear biotic gradient within each. The ecological structure and diversity trends of both associations follow a predictable response to a depth-related gradient. Impoverished communities with a highly nested structure characterize the lower offshore, whereas rich and even communities occur in the upper offshore. The trend towards higher diversity and greater taxonomic turnover in shallower environments corresponds to greater habitat heterogeneity. Towards the other extreme, only the ubiquitous genus Jujuyaspis was a successful colonizer in deltaic settings. This marked contrast with the more diverse and abundant assemblages of fully marine deposits indicates stressful physiological conditions in marginal-marine environments, where alternating and contrasting normal-marine to brackish-water conditions and high input of siliciclastic material were among the key factors controlling the distribution of these early trilobite communities.

Shallow-marine sediment typically contains a mix of marine and terrestrial organic material (OM). Most terrestrial OM enters the ocean through rivers, and marine OM is incorporated into the sediment through both suspension settling of marine plankton and sediment reworking by tides and waves under fair-weather conditions. River-derived terrestrial OM is delivered year-round, although sediment and OM delivery from rivers is typically highest during extreme weather events that impact river catchments. In Taiwan, tropical cyclones (TCs) are the dominant extreme weather event, and 75% of all sediment delivered to the surrounding ocean occurs during TCs. Distinguishing between sediment deposited during TCs and that redistributed by tides and waves during fair-weather conditions can be approximated using δ13Corg values and C:N ratios of OM. Lower Pliocene shallow-marine sedimentary strata in the Western Foreland Basin of Taiwan rarely exhibit physical evidence of storm-dominated deposition. Instead they comprise completely bioturbated intervals that transition upward into strata dominated by tidally generated sedimentary structures, indicating extensive sediment reworking under fair-weather conditions. However, these strata contain OM that is effectively 100% terrestrial OM in sediment that accumulated in estimated water depths

Collision between the Philippine Sea Plate and the Eurasian Plate in the late Miocene-early Pliocene resulted in the uplift of Taiwan, and lithospheric flexure to the west formed the adjacent Western Foreland Basin (WFB). Petrographic studies of late Miocene to Recent sediment and sedimentary strata in the WFB indicate that Taiwan was the main sediment source to the WFB in the early- to mid-Pleistocene, and prior to this, sediments were assumed to be derived primarily from the Eurasian continent. However, uplift of Taiwan began significantly earlier, and sediment derived from the island should reflect the onset and acceleration of uplift and subsequent erosion.To resolve the timing of changes in sediment sources in the WFB, we present clay mineralogy, carbon and nitrogen geochemistry, and magnetic susceptibility data from the late Miocene to late Pliocene Kueichulin Fm that outcrops along the Da’an River in western Taiwan. This formation is composed of the lower Kuantaoshan Member, the middle Shihliufen Shale, and the upper Yutengping Sandstone. Clay mineralogy shows an upward increase in illite and illite crystallinity, and a decrease in chlorite and kaolinite starting at the base of the Shihliufen Shale, and this suggests that rapid erosion of Taiwan became a major sediment source to the WFB between the late Miocene and early Pliocene (Shihliufen Shale). δ13Corg­­­ and C/N ratios preserve the dominance of Taiwan-derived sediment in the early Pliocene where there is a marked change from dominantly marine- to dominantly terrestrially sourced carbon at the transition from the Shihliufen Shale to the overlying Yutengping Sandstone. Finally, a rapid decrease (>50%) in magnetic susceptibility across the Shihliufen/Yutengping boundary indicates a significant dilution of magnetic minerals deposited in the WFB by the high flux of non-magnetic minerals delivered from the Taiwan orogenic belt. Together, these datasets record a major shift in sediment source to the WFB during the late Miocene to early Pliocene, and that Taiwan became the dominant source of sediment supply to the WFB by the early Pliocene, approximately two million years earlier than previously thought.

Sedimentologika is a community-driven Diamond Open Access (DOA) scientific journal about sedimentology. The journal aims to create a place where people can publish their research and access scientific studies on all types of sedimentary processes, methods, deposits, and environments, across all spatial and temporal scales, on Earth or any other planetary body, for free. The published material will be free to share (i.e., no embargo period) since authors retain the copyright. Sedimentologika is driven by the community for the community and is part of a broader DOA movement in geosciences. Sedimentologika aspires at emancipating from the financial barriers associated to private publishing houses to provide direct and equal access to science to all citizens, scientists, and institutions all over the globe. This journal will be defined by Open Science principles to promote ethical dissemination of science and knowledge, following high equality, diversity, and inclusion standards. Each step of the review and publication process will be visible and easy to follow for authors, reviewers and the community. Sedimentologika will be launched by mid-2022 and we are always looking for motivated people keen on giving a little bit of their time to make Sedimentologika a viable and recognized peer-reviewed scientific journal. Interested in this initiative? Come discuss with us!

The stratigraphic records of shallow-marine environments are not commonly regarded as excellent climate archives because of their presumed temporal incompleteness. However, a recent study of lower Pleistocene strata in the Western Foreland Basin, Taiwan, reveals high-resolution records of past climate oscillations preserved within shallow-marine strata. Deriving such narratives is made possible because of the high accommodation and sedimentation rates in the basin, which enhanced the completeness of the stratigraphic record.Here, we astrochronologically tune the Chinshui Shale and the lower part of the Cholan Formation of the Western Foreland Basin from approximately 3.5 to 2 Ma. These strata are calibrated to global deep-sea stable oxygen isotope (δ18O) records with established time scales detailing global climate change during the studied time period. The Chinshui Shale is mudstone-dominated and was deposited mostly in offshore settings, while the Cholan Formation comprises mainly heterolithic strata deposited in shallower settings (i.e., offshore transition, nearshore) of the paleo-Taiwan Strait. The data used herein are two borehole gamma-ray profiles through the Chinshui Shale and the Cholan Formation that have a proximal-distal relation to Taiwan. High gamma-ray values reflect clay-rich intervals and correlate to lower values of δ18O in the global reference records. Low gamma-ray values point to sand-rich packages and correlate with higher values of δ18O.Preliminary results show that the alternating clay-rich to sand-rich deposits during the late Pliocene to early Pleistocene are orbitally paced. The results allow us to i) tune the upper Pliocene–lower Pleistocene Chinshui Shale and lower part of the Cholan Formation, ii) refine the magneto-biostratigraphic framework established for this time interval in the Western Foreland Basin of Taiwan, and iii) lay the groundwork for connecting climatic changes in Taiwan during this time period to the wider frame of global climate change.

The western Gondwana margin underwent a complex geodynamic history during the early Paleozoic, and major uncertainties remain as to the role of tectonism in sedimentary dynamics. This study focuses on the lower part Santa Rosita Formation and the coeval Guayoc Chico Group (Cordillera Oriental; Northwest Argentina), ranging from the late Cambrian (Furongian; Age 10) to Early Ordovician (early Tremadocian; Tr1). This stratigraphic interval has been previously interpreted as deposited in an extensional basin to a retro-arc basin without major regional tectonic-induced deformation during its deposition, only recording long-term relative sea-level fluctuations. Four areas (Sierra de Cajas, Angosto del Moreno, Quebrada de Trancas, and Quebrada de Moya) were chosen because they host the most complete and temporally well-constrained stratigraphic sections of the Cordillera Oriental. Throughout the stratigraphic sections, four main facies zones are described and attributed to deposition in estuarine, foreshore-shoreface, delta-front, and offshore environments. Trilobite biozones are used as the biostratigraphic framework. By integrating sedimentary facies analysis, biostratigraphy, and sequence stratigraphy from the four selected sections, a new scenario showcasing the evolution of the basin is proposed. This scenario interprets a tectonically induced deformation during the deposition of the Santa Rosita Formation and the coeval Guayoc Chico Group. The newly acquired sedimentological data show that physiographical changes took place during the Cambrian-Ordovician transition and are expressed in various localities. This major change is recorded in the stratigraphic architecture, where extensive wave-ravinement surfaces and sedimentary hiatus are the result of local, syn-depositional basement uplifts. The initiation of the Puna-Famatinian volcanic arc during the Early Ordovician on the western margin was likely responsible for deformation in the retro-arc basin and the proposed scenario is consistent with the stratigraphic evolution in other areas of the Cordillera Oriental (e.g., Sierra de Mojotoro) and the Sierra de Famatina. Therefore, this study helps to constrain the evolution of the western Gondwana margin during the early Paleozoic, showing changes in the stratigraphic architecture and basin evolution from an extensional to a retro-arc style.

The Chengjiang Biota is the earliest Phanerozoic soft-bodied fossil assemblage offering the most complete snapshot of Earth’s initial diversification, the Cambrian Explosion. Although palaeobiologic aspects of this biota are well understood, the precise sedimentary environment inhabited by this biota remains debated. Herein, we examine a non-weathered core from the Yu’anshan Formation including the interval preserving the Chengjiang Biota. Our data indicate that the succession was deposited as part of a delta influenced by storm floods (i.e., produced by upstream river floods resulting from ocean storms). Most Chengjiang animals lived in an oxygen and nutrient-rich delta front environment in which unstable salinity and high sedimentation rates were the main stressors. This unexpected finding allows for sophisticated ecological comparisons with other Burgess Shale-type deposits and emphasizes that the long-held view of Burgess Shale-type faunas as snapshots of stable distal shelf and slope communities needs to be revised based on recent sedimentologic advances.

The Pleistocene was a phase of global cooling of the Earth through which glacial-interglacial cycles occurred, and the growth and decay of the ice-sheets resulted in quasi-cyclic sea-level fluctuations driven by orbital forcing. Despite that summer insolation is mostly controlled by precession, the records of the glacial cycles showcase a significant periodicity of ~41 kyrs during the Early Pleistocene forced by Earth’s obliquity (tilt) that varies the latitudinal distribution of insolation especially in high latitudes. The dominance of obliquity over precession in marine archives is commonly attributed to the in-phase effect of obliquity-related insolation versus the opposite-phased influence of precession, which may cancel out the summer insolation signal received by the southern and northern hemispheres.Here, we present a clastic shallow marine record from the Cholan Formation (Early Pleistocene; Taiwan). Facies analysis indicates that quasi-cyclic deposition occurred in shoreface to offshore environments in the paleo-Taiwan Strait. The magnetobiostratigraphic framework indicates that the studied section occurs in the lower part of the Matuyama subchron (1.925 - 2.595 Ma) close to the lower limit of the Olduvai (1.925 Ma) normal polarity subchron. Comparison of the stratigraphy to a d18O isotope record of benthic foraminifera and orbital curves of precession and obliquity at the time of sediment accumulation reveals a good correlation between depositional cycles and the Northern Hemisphere summer insolation, demonstrating precession dominated sea-level fluctuations during the Early Pleistocene. These results underpin recent findings suggesting that d18O isotope records of benthic foraminifera have a more significant precession signal than previously described. This study also demonstrates that shallow-marine stratigraphic successions in high-accommodation and high-sedimentation basins can be outstanding climate archives, possibly even preserving sediment flux responding to half-precession cycles.

International audience; The Fezouata Biota in Morocco is the only Lower Ordovician Lagerstätte yielding a biologically diverse assemblage in a fully marine environment, whilst also containing organisms typical of Cambrian Burgess Shale-type (BST) ecosystems. Fossils from the Fezouata Shale share the same mode of preservation as Cambrian BST biotas defined by carbonaceous compressions and accessory authigenic mineralization. Most organisms of the Fezouata Biota were already dead and decaying on the seafloor when they were buried in-situ by occasional storm-induced deposits in an environment just below the storm-weather wave base. Pre-burial decay in the Fezouata Shale was responsible for the non-preservation of completely cellular organisms such as jellyfish. These conditions contrast with the processes described for soft-tissue preservation in the Burgess Shale (Canada) and the Chengjiang Biota (China). In these two Cambrian Lagerstätten, animals were transported alive or shortly after death by obrution events to an environment that was favorable for preservation. Despite preservational biases, the autochthonous assemblages of the Fezouata Shale offer a unique opportunity to decipher the structure of in-situ communities and ecological dynamics in Early Palaeozoic seas, when compared to the allochthonous communities of most Cambrian BST biotas.

The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The acritarchs can be assigned to the diagnostic messaoudensis-trifidum acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1-2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision. (C) 2016 Elsevier B.V. All rights reserved.

The characteristics of tropical cyclone (TC) deposits are highly variable, and in the shallow waters of straits their character has not been established. Multiple coarse-grained beds in lower Pliocene strata in the Western Foreland Basin of Taiwan are interpreted as TC deposits, and the sedimentology of these beds reflects evolving TC processes and storm stages. By comparing sedimentological data from these beds with previous research on TCs, and with analysis of TCs that cross Taiwan from east to west, a conceptual model is built for understanding deposition in the Taiwan Strait during tropical cyclones. Taiwan is impacted by more than three TCs per year, including more than two super-typhoons every 10 years. These storms can deliver immense volumes of rain over very short time periods and are associated with intense winds. During TCs, and in shallow water in the Taiwan Strait (10–35 m water depth), hyperpycnal discharge, strong bottom currents, and oscillatory wave motion all impact deposition. These processes are manifested in the resulting deposits, and we propose that the best sedimentological criteria for recognizing TC deposits, include: 1) a basal scour surface; 2) an absence of within-bed bioturbation; 3) trough cross-stratification that preserves multi-directional, mainly shore-parallel flow with a 180° change in flow direction; 4) preservation of oscillatory structures towards the top of the bed; and, 5) organic lamina and clasts throughout the bed. Mudstone intercalated with trough cross-stratification is also a useful indicator of TC deposition as it probably reflects wave- and current-redistribution of sediment delivered to the strait through hyperpycnal and hypopycnal discharge from rivers. Contemporaneous mud deposition within TC beds is manifested as mudstone drapes on foresets and toesets, and discontinuous mudstone beds between trough cross-stratified sandstone beds. While not all TC beds exhibit all sedimentological characteristics, we hypothesize that high-probability TC beds should show three or more of them.

The Cap Ferret sand spit is situated along the wave-dominated, tidally modulated Atlantic coast of western France, characterized by a semidiurnal macrotidal range. It displays peculiar dome-like bedforms that can be observed at low tide across the intertidal zone. These bedforms exhibit a wavelength of ca. 1.2 m and an elevation of ca. 30 cm. They occur only when the incident wave heights reach 1.5 a 2 m. The internal stratifications are characterized by swaley-like, sub-planar, oblique-tangential, oblique-tabular, as well as hummocky-like stratifications. The tabular and tangential stratifications comprise prograding oblique sets (defined as foresets and backsets) that almost always show variations in their steepness. Downcutting into the bottomsets of the oblique-tangential stratifications is common. The sets of laminae observed in the bedforms share common characteristics with those formed by supercritical flows in flume experiments of earlier studies. These peculiar bedforms are observed at the surf-swash transition zone where the backwash flow reaches supercritical conditions. This type of flow can explain their internal architecture but not their general dome-like (three-dimensional) morphology. Wave-wave interference induced by the geomorphology (i.e. tidal channel) of the coastal environment is proposed as explanation for the localized formation of such bedforms. This study highlights that the combination of supercritical flows occurring in the surf-swash transition zone and wave-wave interferences can generate dome-like bedforms in intertidal zones. Fil: Romain, Vaucher. Université Claude Bernard Lyon 1; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Pittet, Bernard. Université Claude Bernard Lyon 1; Francia Fil: Humbert, Thomas. Laboratoire D'acoustique de L'universite Du Maine; Francia Fil: Ferry, Serge. Universite Claude Bernard Lyon 1

The genusRhopalocystis(Eocrinoidea, Blastozoa) is characterized by both a short stratigraphic range (Fezouata Shale, middle Tremadocian to middle Floian, Lower Ordovician) and a reduced geographic extension (Agdz-Zagora area, central Anti-Atlas, Morocco). Since the original description of its type species (R. destombesiUbaghs, 1963), three successive revisions of the genusRhopalocystishave led to the erection of nine additional species. The morphological disparity within this genus is here critically reassessed on the basis of both historical material and new recently collected samples. The detailed examination of all specimens, coupled with morphometric and cladistic analyses, points toward a relatively strong support for five morphotypes. A systematic revision ofRhopalocystisis thus suggested, with only five valid taxa:R. destombesi, R. fragaChauvel, 1971, R. grandisChauvel, 1971, R. havlicekiChauvel, 1978, andR. zagoraensisChauvel, 1971. The five others are considered as junior synonyms (R. dehirensisChauvel and Régnault, 1986,R. lehmaniChauvel and Régnault, 1986,R. sp. A,R. sp. B, andR. sp. C).

International audience; Hybrid depositional systems are created by the interaction of two or more hydrodynamic processes that control facies distribution and their characteristics in terms of sedimentary structures and depositional geometry. The interaction of wave and tide both in the geological sedimentary record and modern environments has been rarely described in the literature. Mixed coastal environments are identified by the evidence of wave and tidal structures and are well identified in nearshore environments, while their recognition in lower shoreface-offshore environments lacks direct information from modern settings. Detailed field analyses of 10 stratigraphic sections of the Lower Ordovician succession (Fezouata and Zini formations; Anti-Atlas, Morocco) have allowed the definition of 14 facies, all grouped in four facies zones belonging to a storm-dominated, wave-dominated sedimentary siliciclastic system characterized by symmetrical ripples of various scales. Peculiar sedimentary organization and sedimentary structures are observed: (i) cyclical changes in size of sedimentary structures under fair-weather or storm-weather conditions; (ii) decimetre-deep erosional surfaces in swaley cross-stratifications; (iii) deep internal erosion within storm deposits; (iv) discontinuous sandstone layers in most depositional environments, and common deposition of sandstones with a limited lateral extension, interpreted to indicate that deposition at all scales (metric to kilometric) is discontinuous; (v) combined flow-oscillation ripples showing aggrading-prograding internal structures alternating with purely aggrading wave ripples; and (vi) foreshore environments characterized by alternating phases of deposition of parallel stratifications, small-scale and large-scale ripples and tens of metres-wide reactivation surfaces. These characteristics of deposition suggest that wave intensity during storm-weather or fair-weather conditions was continuously modulated by another controlling factor of the sedimentation: the tide. However, tidal structures are not recognized, because they were probably not preserved due to dominant action of storms and waves. A model of deposition is provided for this wave-dominated, tide-modulated sedimentary system recording proximal offshore to intertidal-foreshore environments, but lacking diagnostic tidal structures.

The Lower Ordovician Fezouata Konservat-Lagerstätte from southern Morocco has been one of the major palaeontological discoveries of the last decade. It provides a unique insight into one of the most critical periods in the evolution of marine life: the Cambrian–Ordovician transition. However, its potential for deciphering key trends in animal diversification was hitherto largely limited by major uncertainties concerning its stratigraphic position, age and environmental setting. Based on extensive fieldwork, fossil evidence, and facies recognition, our study provides clarification on these three crucial issues. Exceptional preservation is limited to two intervals within the Fezouata Shale. Graptolites indicate a late Tremadocian age for the Fezouata Konservat-Lagerstätte as a whole, which is supported by biostratigraphical evidence provided by acritarchs. Sedimentological features and reconstructed patterns of relative sea-level changes indicate relatively shallow-water environmental conditions, under distal storm influence, in an offshore to lower shoreface siliciclastic ramp setting. The Fezouata Biota represents a unique and exceptional window into the palaeobiodiversity in open-marine conditions, thus contrasting with the other Ordovician Konservat-Lagerstätten presently known. In our analyses of this new set of data, we pave the way for accurate temporal, faunal and environmental comparisons with other Lower Palaeozoic Konservat-Lagerstätten, and unlock the full potential of the Fezouata Biota to better understand the processes and scenarios of early animal radiations., This work is part of the ANR (Agence Nationale de la Recherche) research project entitled “The Rise of Animal Life (Cambrian–Ordovician): organisation and tempo” (grant number RALI 197) and of the CNRS-CNRST cooperation project VALORIZ (grant number 52943). J. C. G-M thanks MINECO (project CGL2012-39471) and P. V. R. the National Science Foundation (grant EAR 1053247) for financial support.

International audience; Trilobites are a major component of both biomineralized and soft-bodied assemblages of the Fezouata Biota, central Anti-Atlas, Morocco. Trilobite taxa of the Fezouata Shale (Tremadocian-Floian) in the Zagora area are typical of Lower Ordovician communities from shallow shelf environments, and show strong affinities with Early Ordovician assemblages from the Montagne Noire (southern France). Dramatic variations in both taxonomic composition and taphonomic attributes, together with the sedimentological facies changes, allow us to discriminate the palaeoenvironmental versus stratigraphic control on trilobite assemblages. Three communities are described along an onshore-offshore profile, namely the pilekiid-bavarillid, Agerina and raphiophorid biofacies. Additionally, three stratigraphic assemblages are identified: assemblage 1 is confined to the late Tremadocian, assemblage 2 ranges from late Tremadocian to middle Floian and assemblage 3 is restricted to the Floian. The higher diversity of some levels is explained by storm-induced inputs of debris from taxa living in adjacent environments. Additionally, control of relative seal level variation on some peculiarities of the trilobite fauna (specific endemicity, lack of some expected taxa) is evidenced in the Fezouata Shale. Finally, temporary dysoxic events are highlighted by preliminary geochemical analyses, probably allowing episodic exceptional preservation. (C) 2016 Elsevier B.V. All rights reserved.

In the central Anti-Atlas (Morocco; Zagora region), the Fezouata Shale has yielded an extraordinary fossil Lagerstatte documenting the initial stages of the Great Ordovician Biodiversification Event. This Lagerstatte contains abundant and exceptionally well-preserved fossils (EPF) exhibiting soft-bodied preservation as well as "hard", mineralized parts of extinct organisms. While soft-bodied preservation in the Fezouata Shale is confined to a few stratigraphic intervals, other fossiliferous intervals contain only Shelly fossils in sandstone lenses (SL). Placed in the context of a previously established depositional model, EPF are interpreted as autochthonous assemblages buried by storm deposits, close to storm wave-base. There, the current component of storms is reduced compared to proximal settings and weak oscillation is dominant resulting in the record of oscillation ripples. In contrast, bioclastic accumulations were generated upslope in shallower, more proximal lower shoreface environments. There, the current component of storms was significant, as suggested by the disarticulation of skeletal remains. Bioclastic materials are localized in SL, which are lenses a few tens of centimeters in thickness and a few meters in width and length. These lenses commonly display erosive bases and convex tops, resulting in a lobate or a channel-lobe morphology. A large amount of sediment was thus rapidly deposited, resulting in the rapid burial of allochthonous material across a strongly localized surface of the sea floor. Integrating both sedimentological and paleontological evidence, intervals yielding EPF are considered as Konservat-Lagerstatten (KsL), in contrast with bioclastic accumulations defined as Konzentrat-Lagerstatten (KzL). Thus, KsL assemblages are interpreted to approximate biocenoses, in which organisms experienced rapid burial by distal tempestites, while KzL assemblages more likely correspond to thanatocenoses, locally deposited by storm back-currents. Here, a genetic link between KsL and KzL is suggested within the Fezouata Shale. Both types of Lagersttitten were related to storm activity, but at different depths. (C) 2016 Elsevier B.V. All lights reserved.