Depositional Record最新文献

The basal Taebaek Group (Myeonsan and Myobong formations) illustrates second-order transgression on the eastern Sino-Korean Block during the early–middle Cambrian (Stage 3?–Wuliuan). The irregular palaeotopography of Precambrian basement led to the development of localised alluvial fans and fan deltas. As transgression continued, tidally influenced estuarine and associated shallow subtidal flats developed. Continued transgression resulted in a relatively deep subtidal environment, with postulated carbonate shoals serving as barriers. Stacking of facies indicates a general deepening-upward trend, transitioning from terrestrial–nearshore to marine environments dominated by tidal effects. The study area subsequently experienced shallowing, leading to the emergence of tidal inlet and dune environments. Siliciclastic input was attenuated, facilitating the development of carbonate shoal complexes. The overall transgressive succession of the basal Taebaek Group aligns with similar sequences observed in the Sino-Korean Block and western Laurentia, where the lowermost Cambrian strata which formed in various depositional environments on the uneven basement rocks were followed by extensive tide-dominated siliciclastic successions. These successions were then overlain by epeiric carbonate platforms that developed synchronously across the area as siliciclastic input diminished with the continued transgression. This comparison demonstrates that the transgressive sequences in the Sino-Korean Block and western Laurentia can be understood within a framework that explains how extensive Cambrian carbonate platforms initially developed due to a second-order eustatic sea-level rise during the Cambrian greenhouse period.

Striated grooves in tool marks are common at the base of sandstones, especially in deep-marine successions, but their use in physical-process and environmental reconstruction is underdeveloped. To fill this gap in knowledge, striations in the central groove of chevron marks and in chevron-less groove marks were formed in the laboratory by dragging tools armoured with silt, sand or gravel across muddy substrates. These experiments simulated the formation of striated grooves by armoured mud clasts carried at the base of quasi-laminar and fully laminar debris flows, aiming to: (1) delineate the bed shear strengths for the formation of striated grooves at different armour sediment sizes; (2) examine how the preservation potential of striated grooves depends on clay bed rheology and size of armour sediment and (3) discuss how the pre-lithification clay bed consolidation state and size of armour sediment can be reconstructed from striated grooves in the geological record. The experimental results revealed that tools with small-diameter silt and sand armours dragged along soft beds lack striations or, at best, leave poorly defined striations, whereas firm beds and gravel armours exhibit well-defined striations. The spacing of striations formed by gravel clasts corresponds well with the clast diameter, implying that striation spacing is a good proxy for the diameter of armoured gravel under natural conditions. In contrast, the spacing of striae formed by sand armours is greater than the grain diameter, suggesting that the spacing of fine striations can only be used to predict a maximum armour sand size. A comparison of different processes of formation of armoured mud clasts demonstrated that the armouring of mud clasts most probably happens after incorporation of the clasts by erosion into the head of the debris flow and subsequent movement across a loose sandy or gravelly bed surface.

In numerous carbonate reservoirs in the Middle East, peloidal packstone-grainstones are rock types with excellent pore storage potential in micritised microporous grains. However, the origin of the micro-porosity and associated micro-spar remains unclear, and one hypothesis is that both micro-spar and porosity originate from early marine micritisation and were later altered during subsequent diagenesis (i.e. cementation recrystallisation). The south-eastern coast of the Arabian Gulf is recognised as a modern, albeit miniature, depositional setting analogue to Mesozoic carbonate sequences that form the supergiant reservoirs of the Middle East. Using optical microscopy, backscattered scanning electron microscopy and carbon and oxygen stable isotope analysis the present study aims to document the nature of internal microstructures of micritic envelopes and peloids from the surface sediments of various sub-environments of the Abu Dhabi Lagoon. Results highlight a high degree of diversity and heterogeneities of most micritic envelopes and peloids observed across the sub-environments. First, carbonate grains from ooid and bioclastic shoals show the simpler micritic envelopes. Here, micritic envelopes and peloids show sparse microborings filled with banded radial aragonite cement, a pattern of production of cryptocrystalline texture (e.g. micritisation) that is similar to the sequence of micritisation observed in the modern sediment of the Great Bahama Bank. Conversely, in the subtidal and intertidal zones with mangroves or seagrass, the micritic envelopes and peloids are much more complex and show multiple generations of microborings that are either empty or filled with carbonate materials of varying types (i.e. various cements, fragments, etc.).

The export of neritic material from the top of carbonate platforms is a key process in the construction of their slopes. However, our knowledge of the supply pattern of materials from platforms is dominantly based on platforms lying in the euphotic zone during the present sea-level highstand. This is a somewhat biased perspective as through geological time not all platforms were euphotic. The Saya de Malha Bank in the Mascarene Plateau is an example of a modern mesophotic carbonate platform, and as such, its flooding and export patterns differ from those of euphotic ones. Using cores collected on the western slope of the Saya de Malha Bank, the export patterns of the platform since the last glacial maximum were explored. Material on the platform edge is winnowed and transported to the slope by multiple possible processes. The material on the platform is a combination of high and low magnesium calcite as well as high and low strontium aragonite, integrating pelagic and neritic sources. The ratio of these constituents varies over time with changes in the platform production capability as it was flooded and drowned during the Holocene transgression. The material from the platform is transported in both confined flows, mainly during lowstands, and unconfined flows, mainly during late transgression and early highstand. In the present state of the highstand, supply may have diminished, leading to erosion of the canyon shoulders.

This paper presents the results of the interpretation of a set of high-resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North-Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea-level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave-ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane-derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.

This paper contributes to an understanding of the tectono-sedimentary evolution of the South Pyrenean foreland system by reviewing the chronostratigraphic framework of the basin infill in its eastern sector. Six sections are analysed and cross-correlated to build a 6.5 km thick composite magnetostratigraphy that represents the complete record of the Cadí Nappe in the Ripoll Syncline. New and previous magnetostratigraphic sections are integrated with available biostratigraphy to provide a new age calibration of the sedimentary succession of the Cadí Nappe, encompassing from Palaeocene to Middle Lutetian age. The proposed correlation with the Geomagnetic Polarity Time Scale aims at best reconcile magnetostratigraphic data with the regional biochronology built on the marine Shallow Benthic Zonation (SBZ biozones), the continental mammalian biochronology (MP levels) and the newly collected charophyte data. A subsidence analysis was performed on the calibrated composite succession, resulting in two well-defined intervals bounded by a hiatus. A Palaeocene to Early Eocene interval with low (11–21 cm/kyr) total subsidence rates, and an Early to Middle Eocene interval, characterised by high (70–75 cm/kyr) total subsidence rates. The detailed trends in both subsidence and sedimentation mark the development and evolution of the foreland depozones, from distal foreland depozones to foredeep and wedge-top depozones, relative to the emplacement of the Pedraforca Nappe and Cadí Thrust Nappe. The most pronounced sedimentary shift in the Cadí Nappe occurred at 49 Ma, with the rapid drowning of the carbonate platforms and its transition into talus and deep basinal environments. Carbonate platforms collapsed and resedimented on the talus of the elongated trough, newly formed parallel to the orogenic front. This marked the onset of tectonic subsidence triggered by the submarine emplacement of the Lower Pedraforca Nappe. The emersion of the orogenic wedge drove the entry of siliciclastics, lagged by 1 Myr, into the Ripoll Trough. The foredeep filled rapidly (5.5 km thickness in less than 7 Myr) compared to other South Pyrenean regions, favoured by its semi-enclosed palaeogeography. The emplacement of the Vallfogona Thrust as early as the Middle Lutetian (43 Ma) brought the Cadi Nappe into a wedge-top setting. However, the Ripoll growth syncline continued acting as a temporary sink for alluvial sedimentation while a foredeep developed further south in the autochthonous Ebro Basin. The flexural response of the Iberian plate to the tectonic thickening of the Axial Zone counterbalanced for a period the local uplift of the Cadi Nappe, providing accommodation space for the top sediments filling the Ripoll Syncline.

The Triassic red beds of the Tabular Cover of the Iberian Meseta are an excellent reservoir outcrop analogue, a direct consequence of high-quality exposures, which offer exceptional three-dimensional outcrops, as well as a wide variability of depositional environments. Fluvial and transitional with tide-influenced and wave-influenced settings are recognised. Three point bar geobodies of similar scale, but influenced by different processes, were selected from this succession. Point bar geobody 1 was influenced by purely fluvial processes while geobodies 2 and 3 were tide-influenced. Both types of geobody were developed as point bar deposits in sinuous channels. A fully integrated study was carried out on these geobodies, utilising both outcrop and subsurface-based approaches, to characterise the key differences between fluvial and tidal point bars in the sedimentary record. The outcrop-based component involved traditional field data collection methods alongside digital techniques and data capture, including the use of digital outcrop models. Additionally, subsurface-based methods were employed, utilising core and wireline logs obtained from wells drilled in close proximity to the outcrop. The integration of these approaches aims to accurately differentiate the depositional settings of the three different geobodies, which while apparently very similar in many key respects also exhibit considerable differences when considered from the perspective of subsurface management of potentially similar geobodies. This study also emphasises the need to clearly distinguish high-sinuosity deposits based on their depositional sub-environment in order to properly evaluate their potential for subsurface management. Additionally, it highlights the presence and importance of internal baffles that may well influence fluid migration and indeed even compartmentalise geobodies. Three point bar geobodies of similar scale, but influenced by different processes, have been selected in this succession. A fully integrated study was carried out on these geobodies, utilising both outcrop-based and subsurface-based approaches, to characterise the key differences between fluvial and tidal point bars in the sedimentary record.

The lake-basin-type model classified the stratigraphic record of ancient lake systems according to rates of potential accommodation relative to sediment + water supply. The model convolved all modes and paths of water supply (direct fall, surficial, subsurface) with amounts and types of sediment supply (clastic, biogenic, chemical) into a single basin-filling volume term (sediment + water); its major strength was its widespread applicability. This was supported by subsequent investigations confirming the utility of this approach, but it also revealed some important limitations due to simplifications in the original model. The model has been expanded here to address all inland waters (lakes, ponds, wetlands, playas) as well as adding two major subdivisions of the sediment + water term: (1) water supply paths and (2) the volume of water supply relative to sediment supply. Water supply flow paths in the subsurface are subdivided into ‘throughflow’, ‘recharge’ and ‘discharge’. Each of these groundwater hydrology states can be defined quite precisely by the ratio of net outflow to inflow, from persistently open to consistently closed. These paths can be deciphered using stable carbonate and oxygen isotope composition of primary lacustrine limestones, detailed sedimentology, stratigraphy, palaeontology and mineralogy. Distinguishing water supply paths provides additional insights into playa systems and the occurrence and character of evaporites and carbonates. The volume ratio of water to sediment supply most directly influences the water depths of lakes, ponds and wetlands, which affect water body hydrodynamics and ecosystem behaviour as well as the details of stratal stacking and depositional sequences. It helps fine-tune estimates of the distribution of sediment texture, bedding, composition and organic matter content. The aim of this contribution is to address questions about the fundamental types of inland water bodies and to explain the new lake-basin subtypes and provide examples that illustrate their potential to enable higher-resolution, robust analysis of inland water systems and their stratigraphic records.

Jurassic and Palaeocene tidal deposits of the epeiric Western Interior Sea in Wyoming, USA, differ significantly due to their contrasting climates and tectonic, geographic and depositional settings. Tidally generated, cross-bedded sandstone bodies contained by incisions are common to both settings and can potentially be uncritically attributed to marine flooding of fluvial systems. Key differences in lithology, ichnology and relationships with surrounding sediment reveal fundamentally different depositional settings, however. The Jurassic system occupied a low accommodation, semi-arid environment, with geographically open shorelines as relative sea-level fell, creating an unconformable contact with the underlying, storm wave-dominated shelf and shoreface deposits. Siliciclastic, intertidal flats formed adjacent to coastal aeolian and fluvial environments during brief turnarounds from the degradational (forced regressive) to aggradational and retrogradational (transgressive) system tract. Basinward of these environments, metre to decimetre-scale cross-bedded, bioclastic, subtidal compound dunes and tidal inlet complexes accumulated in areas of minimal clastic flux and within incisions created by submarine tidal currents. By contrast, the Palaeocene tidal systems formed in a high accommodation, subtropical setting, as rising sea levels forced the fluvial to marine transition zone landward and flooded coastal swamps, forming geographically irregular, back-barrier complexes and tidally influenced fluvial systems. High volumes of siliciclastics, terrigenous organic material and freshwater were delivered by the rivers and created physicochemical stress on the marine embayments. Sandy tidal flat deposits accumulated in lagoons and interdistributary bays, but unlike the Jurassic examples, they do not mark a turnaround from the falling stage to the transgressive system tract. The potential preservation window for tidalites is significantly greater vertically in the aggradational to retrogradational setting than in the degradational system due to greater accommodation. The preservation window is vertically smaller, but areally greater in the Jurassic, forced regressive system because of basinward enhancement of tidal currents driven by complex palaeobathymetry caused by tectonic activity of local pre-Laramide uplifts.

Mass movements are common on the continental slope, affecting not only the subsequent sea floor morphology but often substantially modifying the underlying deposits. Various styles of substrate interaction have been recognised, representing the various degrees of involvement of the underlying material and its incorporation into the mass movement. This work presents a new style of basal interaction not previously described. Based on the morphology of the basal surface of a mass transport deposit, this can be recognised both in seismic data and in an outcrop analogue. A subsurface example, from an ca 100 m thick mass transport deposit located in Santos Basin, offshore Brazil, displays a basal surface with spoon-shaped scours or scoops. These scoops are of the order of tens up to 400 m in maximum dimension, where masses of underlying sediment have been removed and incorporated into the mass movement. Outcrops used for this work are located in La Rioja Province, Western Argentina, where the study involves a well-exposed ca 200 m thick mass transport deposit that crops out continuously over 7 km. Its basal surface is incised irregularly into the underlying sandstones, incorporating the blocks of sandstone into the mass movement. The striking similarities observed between outcrop examples and the northern Santos Basin suggest that they can be effective analogues, facilitating a comprehensive understanding of mass transport deposit dynamics across diverse basin environments.