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The Cambrian pre-salt dolomite sequence in the Tarim Basin is a target zone of great strategic significance for hydrocarbon exploration in the basin. Using the results of the interpretation of 3D seismic data from Lunnan and 2D seismic data covering the whole basin, and based on a synthesis of outcrop data, drilling data, well logs, core data, and thin-section data, and the findings from previous studies, this paper studies the characteristics of the facies of the Middle–Lower Cambrian in the platform area in the Tarim Basin, the formation and evolution of platform margins, and the sedimentary characteristics, lithofacies, and paleogeographic characteristics of the Middle–Lower Cambrian series. Based on the types of lithofacies and the seismic facies analysis, the sedimentary facies of the Middle–Lower Cambrian strata can be classified into the five types. From bottom to top, the Middle–Lower Cambrian have experienced several development stages, including the deposition of continental shelf sediments of the Yuertusi Formation, gently sloping non-rimmed platform margin sediments of the Xiaoerbulake Formation, weakly rimmed platform margin sediments of the Wusongger and Shayilike formations, and strongly rimmed platform margin sediments of the Awatage Formation. In each stage, the platform margin shifted further east relative to its location in the previous stage. Based on these results and previous studies, the lithofacies and paleogeography maps of the Middle–Lower Cambrian in the Tarim Basin are modified, and the implications for hydrocarbon exploration in this area are discussed. [ABSTRACT FROM AUTHOR]

The internal structure and architecture of evaporite sequences is often overlooked, with attention frequently concentrating on the external geometries that salt bodies form. The availability of extensive 3D seismic data affords the opportunity to interpret the internal structures within these evaporite sequences and comprehensively characterise the different structural facies over large areas. This paper concentrates on the Zechstein Supergroup evaporite deposits within the Southern North Sea of the United Kingdom's Continental Shelf. This analysis of the internal structural complexity and stratigraphic heterogeneity utilises 26,000 km2 of 3D seismic data together with over 96 wells from the Southern North Sea. Characterisation of the different structural facies present was undertaken alongside mapping their spatial distribution to understand the relationship they have with one another and the structural evolution that may have been taken. This work has (1) characterised and mapped six different internal structural facies present within the Zechstein with increasing levels of deformation; (2) shown the internal lithological heterogeneity is indicative of variations in the vertical strength profile of layered evaporite sequences; (3) discontinuous high‐amplitude reflections within the Zechstein are as a result of the geometries being too steeply dipping for the seismic data to image; and (4) the ability to possibly predict the internal heterogeneity of areas of poorly imaged salt, such as within large diapiric salt structures, from surrounding structural facies. These findings suggest that there is significant internal complexity even within areas of the basin with minor mobilisation to the external salt geometry. [ABSTRACT FROM AUTHOR]

Green marine clays, known as glaucony and verdine facies, are unique iron-rich minerals typically found in shallow marine sedimentary environments covering large areas of continental shelves today. While on some occasions they have been used effectively as paleoenvironmental indicators associated with transgressive and highstand system tracts, their occurrence can vary in different sedimentary environments. This paper aims to provide a review of the nomenclature and mineralogical composition of these facies, their habits and morphologies, as well as the physico-chemical characteristics of their genesis. This includes water depth, temperature, and geochemical factors that influence the local environments and characteristics of their formation. The article also presents examples from the NW Galician Continental Shelf and discusses the variety of mechanisms behind their genesis and evolution, as well as the challenges surrounding their chronology. Comparisons are drawn with the old facies (ironstone), which can occur in a wider range of marine environments and are sometimes found alongside glaucony and verdine facies in ancient deposits. This highlights the importance of accurately reconstructing the environment of each deposit. The literature reveals many exceptions in relation to the zonal and bathymetric distribution, sedimentation rates, age, etc. of these facies, emphasizing the need for further investigation into their genesis in current and ancient environments. Such research would provide valuable insights for paleogeographic, paleoenvironmental, and stratigraphic interpretations. [ABSTRACT FROM AUTHOR]

& Olariu, C. (2018) Mixed-energy process interactions read from a compound-clinoform delta (paleo-orinoco Delta, Trinidad): preservation of river and tide signals by mud-induced wave damping. Keywords: hydrodynamics; sedimentology; shallow-marine EN hydrodynamics sedimentology shallow-marine 206 212 7 05/30/23 20230401 NES 230401 Sketch diagram illustrating the various hydrodynamic processes occurring in coastal to shelf environments, with numbers referring to articles from this issue. Furthermore, certain systems are or were dominated by a single depositional process, yet their deposits lack any characteristics commonly assigned to such systems: for example, the Venice lagoon is tide-dominated, yet no tidal rhythmites are preserved in the sediments (Ghinassi et al., [19]). [Extracted from the article]

Shelf-edge deltas play a critical role in shelf-margin accretion and deepwater sediment delivery, yet much remains to be understood about the detailed linkage between shelf edge and slope sedimentation. The shelf edge separates the flat-lying shelf from steeper slope regions, and is observable in seismic data and continuous outcrops; however, it is commonly obscured in non-continuous outcrops. Defining this zone is essential because it segregates areas dominated by shelf currents from those governed by gravity-driven processes. Understanding this linkage is paramount for predicting and characterizing associated deepwater reservoirs. In the Tanqua Karoo Basin, the Permian Kookfontein Formation shelf-slope clinothems are well-exposed for 21 km along depositional strike and dip. Two independent methods identified the shelf-edge position, indicating that it is defined by: (i) a transition from predominantly shelf-current to gravitational deposits; (ii) an increase in soft-sediment deformation; (iii) a significant gradient increase; and (iv) clinothem thickening. A quantitative approach was used to assess the impact of process-regime variability along the shelf edge on downslope sedimentation. Facies proportions were quantified from sedimentary logs and photographic panels, and integrated with mapped key surfaces to construct a stratigraphic grid. Spatial variability in facies proportions highlights two types of shelf-edge depositional zones within the same shelf-edge delta. Where deposition occurred in fluvial-dominated zones, the slope is sand rich, channelized with channels widening downslope, and rich in collapse features. Where deltaic deposits indicate considerable tidal reworking, the deposits are thin and pinch-out close to the shelf edge, and the slope is sand poor and lacks channelization. Amplification of tidal energy, and decrease in fluvial drive on the shelf, coincides with a decrease in mouth bar and shelf-edge collapse, and a lack of channelization on the slope. This analysis suggests that process-regime variability along the shelf edge exercised significant control on shelf-edge progradation, slope channelization and deepwater sediment delivery. [ABSTRACT FROM AUTHOR]

Kakanui volcaniclastic deposits on the South Island of New Zealand are the remnants of two late Eocene to early Oligocene Surtseyan-type cones. Eruptive-dominated material of the (i) stratified tuff and lapilli tuff, and (ii) lapilli tuff breccia lithofacies and post-eruptive debris of the (iii) shell-rich tuff and lapilli tuff, and (iv) chaotic and cross-bedded tuff and lapilli tuff lithofacies compose the deposits. The 9–250 m thick stratified tuff and lapilli tuff contains grain-flow deposits originating from low-volume tephra jets and local thinning and fining upward sequences that formed from density currents during sustained uprush. The lapilli tuff breccia, up to 4.5 m thick, contains inward-dipping beds deposited via debris flows along inner-cone walls. Burrows and articulated shells in the 2–4 m thick shell-rich tuff and lapilli tuff indicate volcanic quiescence and low sedimentation rates, whereas shell fragments upsection signal increased wave and current activity. Burrows, pyrite concretions, and mudstone in the lower part of the 26 m thick chaotic tuff and lapilli tuff indicate suspension deposition and cessation in pyroclastic volcanism. High-angle trough cross-beds and limestone rip-up fragments upsection are consistent with wave-induced current reworking. The depositional model involves a Surtseyan-type eruption on a continental shelf, followed by colonization of organisms on the tops of planed-off cones. The Kakanui deposits comprise a cluster of cones constituting part of a late Eocene – early Oligocene monogenetic volcanic field. The Kakanui succession provides an opportunity to study deposits that form from explosive subaqueous pyroclastic eruptions and wave-dominated deposition and erosion. Les dépôts volcanoclastiques Kakanui de l’Île du Sud de la Nouvelle-Zélande sont les lambeaux d’érosion de deux cônes de type surtseyen datant de l’Éocène tardif à l’Oligocène précoce. Les dépôts sont composés principalement de matériaux éruptifs composés (i) de tufs stratifiés et de tufs à lapilli et (ii) de lithofaciès de brèches de tuf à lapilli et de débris post-éruption composés (iii) de tufs coquilliers et de tufs à lapilli et (iv) de tufs chaotiques et à laminations croisées et de facies de tufs à lapilli. Le tuf stratifié et à lapilli d’une épaisseur de 9 à 250 mètres contient des dépôts d’écoulement de grains provenant de jets de tephra à faible volume et des séquences qui s’amincissent et dont les grains deviennent plus fins vers le sommet; ces séquences proviennent de courants de densité présents durant la montée soutenue de la lave. Les brèches de tuf à lapilli, atteignant des épaisseurs de 4,5 m contiennent des lits à pendage retourné déposés par des écoulements de débris le long des murs internes du cône. Des tunnels et des coquillages articulés dans le tuf riche en coquillages, d’une épaisseur de 2 à 4 m, combinés au tuf à lapilli, indiquent un volcan au repos et de faibles taux de sédimentation. Par contre, des fragments de coquillages dans le haut de la section sont un indice de plus de vagues et de courants. Les tunnels, les concrétions de pyrite et les mudstones dans la partie inférieure du tuf chaotique d’une épaisseur de 26 m et le tuf à lapilli indiquent une déposition de la matière en suspension et l’arrêt du volcanisme pyroclastique. Les lits à stratification entrecroisée dont l’angle est élevé et des fragments de calcaire arrachés concordent avec un remaniement par un courant induit par les vagues. Le modèle de déposition implique une éruption de type surtseyen sur un plateau continental, suivie d’une colonisation d’organismes sur les sommets des cônes tronqués. Les dépôts Kakanui comprennent une grappe de cônes qui font partie d’un champ volcanique monogénique datant de l’Éocène tardif – Oligocène précoce. La suite Kakanui fournit la possibilité d’étudier des dépôts qui se sont formés à partir d’éruptions explosives pyroclastiques subaquatiques et de déposition dominée par les vagues et par l’érosion. [ABSTRACT FROM AUTHOR]

Jeju Island is a Quaternary shield volcano built upon the Yellow Sea continental shelf off the Korean Peninsula. Decades of borehole drilling reveals that the shield-forming lavas of the island are underlain by extensive hydrovolcanic deposits (the Seoguipo Formation), which are about 100 m thick and show diverse depositional features. This study provides criteria for distinguishing between hydrovolcanic deposits formed by primary (pyroclastic) and secondary (resedimentation) processes in subaerial and submarine settings based on the observations of several selected cores from the formation. Five facies associations are identified, including: (i) primary hydrovolcanic deposits formed by pyroclastic surges and co-surge fallouts in tuff rings (facies association PHTR); (ii) primary hydrovolcanic deposits formed by Surtseyan fallout and related pyroclastic transport processes in tuff cones (facies association PHTC); (iii) secondary hydrovolcanic deposits formed by debris flows, hyperconcentrated flood flows, sheet floods and rill flows in subaerial settings (facies association RHAE); (iv) secondary hydrovolcanic deposits formed in submarine settings under the influence of waves, tides and occasional mass flows (facies association RHMAR); and (v) non-volcaniclastic and fine-grained deposits formed in nearshore to offshore settings (facies association NVMAR). The primary hydrovolcanic facies associations (PHTR and PHTC) are distinguished from one another on the basis of distinct lithofacies characteristics and vertical sequence profiles. These facies differ from the secondary hydrovolcanic and non-volcaniclastic facies associations (RHAE, RHMAR and NVMAR) because of their distinctive sedimentary structures, textures and compositions. The depositional processes and settings of some massive and crudely stratified volcaniclastic deposits, which occur in many facies associations, could not be discriminated unambiguously even with microscopic observations. Nevertheless, these facies associations could generally be distinguished because they occur typically in packets or sequences, several metres to tens of metres thick and bounded by distinct stratigraphic discontinuities, and comprise generally distinct sets of lithofacies. The overall characteristics of the Seoguipo Formation suggest that it is composed of numerous superposed phreatomagmatic volcanoes intercalated with marine or non-marine, volcaniclastic or non-volcaniclastic deposits. Widespread and continual hydrovolcanic activity, together with volcaniclastic sedimentation, is inferred to have persisted for more than a million years in Jeju Island under the influence of fluctuating Quaternary sea-levels, before effusion of the shield-forming lavas. Extensive distribution of hydrovolcanic deposits in the subsurface of Jeju Island highlights that there can be significant differences in the eruption style, growth history and internal structure between shelfal shield volcanoes and oceanic island volcanoes. [ABSTRACT FROM AUTHOR]

Palaeogene passive margin sediments on the US mid-Atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate–siliciclastic shelves. This study utilizes well cuttings, outcrop, core, and seismic data to document temporal and spatial variations in admixed bryozoan-rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone. This zone was situated between north-flowing, warm waters of the ancestral Gulf Stream (carbonate dominated settings) and south-flowing, cold waters of the ancestral Labrador Current (siliciclastic dominated settings). Some degree of mixing of carbonates and siliciclastics occurs in all facies; however, siliciclastic-prone sediments predominate in nearshore settings, while carbonate-prone sediments are more common in more open marine settings of the inner shelf break and deep shelf. A distinctive dual-break shelf depositional profile originated following a major Late Cretaceous to Palaeocene transgression that drowned the earlier shallow platform. This profile was characterized by prominent mid-shelf break dividing the shallow shelf from the deep shelf and a major continental shelf/slope break. Incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin. Storm wave base also contributed to the preservation of the dual-break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid-shelf break. Sediment fines in deep shelf facies were produced in place, transported downdip from the shallow shelf by storm ebb currents and boundary currents, and reworked from adjacent areas of the deep shelf by strike-parallel boundary currents. Regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf, with warmer waters and more humid climates favouring carbonate deposition and cooler, more arid conditions favouring glaucony and siliciclastic dominated deposition. Continuous wave and current sweeping of the shallow shelf favoured deposition of mud-lean facies across much of the shallow shelf. Skeletal components in much of the carbonate-rich strata formed in warm, nutrient-rich subtropical waters, as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages. These indicators of warm water deposition within the bryozoan-mollusk-rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage; such facies generally are associated with cooler water depositional settings. [ABSTRACT FROM AUTHOR]