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 hierarchies of the stratigraphic discontinuity surfaces observed in ancient tidalites are qualitatively assessed, aiming to evaluate their role as possible preferential conduits for fluid migration. Three outcrop examples are presented from microtidal settings of southern Italy: (i) siliciclastic tidalites consisting of quartz-rich cross-stratified sandstones generated by strong two-directional tidal currents flowing along a tidal strait; (ii) carbonate tidalites, which accumulated in a Cretaceous lagoon and tidal flat where peritidal cycles formed vertically-stacked sequences of biopeloidal and fenestral packstones, wackestones and bindstones during repeated phases of Milankovitch-scale sea-level changes; (iii) mixed, siliciclastic-bioclastic tidalites, deposited in a bay and recording offshore-transition, to shoreface wave-dominated and tide-influenced environments. Observations made during this study suggest that fluid movement can be controlled by the presence of main bounding surfaces that occur at different dimensions, from large (hectometre)-scale, to medium (decametre)-scale, to smaller (metre)-scales. These surfaces produced either by depositional or erosional processes, are characterised by different features and geometries in siliciclastic, carbonate and mixed siliciclastic-bioclastic tidalites arguably revealing complex internal pathways for fluid flows. These results suggest that fluids propagating along the main discontinuities follow a dominant sub-horizontal direction of propagation, associated with minor sub-vertical movements, due to local internal surface geometries and interconnections and a general lack of fractures. This surface-based approach to the study of fluid-flow transmission within stratified rocks represents a conceptual attempt to predict fluid mobility and reservoir potential in tidalite-bearing siliciclastic, carbonate and mixed reservoir rocks.

Submarine channels are conduits for the transfer of material to deep water by sediment gravity flows. Some channels clearly show meandering patterns in planform that have attracted comparisons with fluvial systems. Many submarine channels, however, are aggradational. Transitions from meandering (at grade) channels to aggradational channels have been described in the subsurface, from seismic data. A field example is presented here in which these meandering and aggradational states may alternate several times during the overall development of a fourth-order sequence before the system is temporarily or permanently abandoned. This implies a change in flow state from one where successive flows behave similarly over extended periods, to one in which the flow parameters are progressively changing. The cause of these cyclic changes is unclear. The generation of sedimentary architectures so strikingly comparable to those of meandering fluvial systems provides strong evidence in favour of stably stratified, essentially two-layer flows, in which the lower high-density part is channel-confined, with a normal (i.e. fluvial-like) secondary circulation, and the upper, low-density part extends onto the overbank regions adjacent to the channel, with minimal mixing and entrainment. Such flows are described as subcritical, in line with published experimental and numerical work, allowing that the critical Froude number in such settings may not be unity. The switch to an aggradational state may be linked to changes in flow criticality, but the ultimate driver for these alternations in flow properties remains unknown.

Cretaceous cyclic peritidal carbonates form the bulk of the Apulia Region in Italy and represent the vestiges of the Apulia Carbonate Platform. To show from a sequence stratigraphic perspective the architecture of peritidal carbonates, the 17 m thick Albian Giovinazzo sea-cliff section was studied at a centimetre detail, aiming to: (i) describe cyclic facies organisation in beds and bedsets; (ii) reconstruct the relative sea-level curve and its evolution over time; (iii) interpret the long-term evolution of the accommodation space in terms of sequence stratigraphy. The hierarchical stacking pattern of facies in beds and bedsets reveals Milankovitch cyclicity. As a working hypothesis, elementary sequences are assumed to represent the precession cycle (ca 20 kyr) and small-scale and medium-scale sequences the short (ca 100 kyr) and long (ca 400 kyr) eccentricity cycles, respectively. Four different types of elementary sequences (condensed, catch-down, catch-up and give-up) are recognised and interpreted in terms of relative sea-level changes to reconstruct the relative sea-level curve of the entire succession. The envelope of the reconstructed relative sea-level curve is used to represent the long-term accommodation change on the platform, which covers a time span of approximately 1.8 Myr. Most of this time was spent in subaerial exposure, as approximately 1.2 Myr was predicted to be condensed in a stratigraphic interval encompassing both the sequence-boundary zone/falling stage deposits and the lowstand deposits. Moreover, it was interpreted that about two-third of the total thickness of the succession was formed in only 280 kyr and consisted of both transgressive and maximum-flooding deposits. The main implication of this study is that unconformities do not necessarily correspond to single surfaces but, rather, to very amalgamated intervals or unconformity zones. Moreover, based on biostratigraphic constraints, there is a correlation between the unconformity zone of the studied succession and the third-order KAl4 sequence boundary of the Cretaceous eustatic cycle chart.

The present study examines the stratigraphy of two sandspits that both appeared and developed since the middle of the 17th century during the Little Ice Age. The Arçay spit is located along the macrotidal Atlantic coast in South-West France with a maximum tidal range of 6.5 m. The Pointe du Banc in the English Channel, North-West France, is located in a hypertidal coastal setting with a tidal range of up to 14 m. The evolution of the two spit systems has been compared using historical maps, ground penetrating radar data and facies analysis and geochronological data from sediment cores. The Pointe du Banc spit developed between 1650 and 1750 CE, in a dominant seaward direction while the main mode of construction of the Arçay spit was in a longshore direction. It is proposed that this difference relates to sediment supply and coastline morphology. At the Pointe du Banc spit, the large tidal range causes a long wind fetch and sustained aeolian sediment supply. Moreover, the spit is located at the apex of a large-scale embayment where sediment transport from north and south converges. Combined, these factors result in a positive sediment budget and seaward shoreline progradation. At the Arçay spit, high wave obliquity results in a large littoral drift and sustained longshore spit construction. At both locations, low gradient shorefaces may have favoured a net landward-directed sediment flux that supply sand to the foreshore.

The Río Alías Strait developed in the Early Pliocene as a narrow marine corridor at the connection of the microtidal Mediterranean Sea and the north-eastern margin of the Almería-Níjar Basin in the eastern Betic Cordillera (South-East Spain). The orientation and topography of the strait were controlled by the transpressive Carboneras and Polopos/South Cabrera fault systems. Ten sedimentary facies occur in the up to 150 m thick mixed biogenic carbonate-terrigenous succession distinguished on the basis of their lithology, components, grain size, stratal geometries and sedimentary structures, which were observed in seven sections at well-exposed outcrops of four sectors. The sedimentary record of the Río Alías Strait reflects the morphological constraints, which conditioned its sedimentary dynamics and facies distribution. Even in this microtidal setting, tidal current amplification through narrow constrictions produced thick accumulations of large cross-stratified bodies up to 15 m thick formed by the opposite migration of three-dimensional simple and compound dunes. The Río Alías Strait reconstruction shows: (1) a very narrow constriction in the central sector from which “constriction-related deltas” (CRDs) formed in the flood downstream (westward) and ebb (upstream) directions and (2) a relatively deep depression (>65 m water depth) separating the eastern and central-east sectors, where tidal current energy was attenuated and dunes were not generated. The closure of the strait resulted from the tectonic uplift of the antecedent upland of Sierra Cabrera at the northern side, which promoted the southward progradation of deltaic systems over the strait. The Río Alías Strait represents the only clear record of a microtidal strait in the Betic Cordillera since the Miocene. The case study presented here improves existing models on the sedimentary dynamics of ancient tidal-dominated straits by expanding the knowledge on their spatial environment variability.

The Selendi Basin developed as a supradetachment basin on the Simav detachment fault in response to the continental extension in western Turkey (Türkiye) and the associated Menderes Massif uplift. Process-based facies analyses were used to define and interpret the depositional evolution of the lacustrine Selendi Basin. The Early-Middle Miocene deposits are composed of stream-dominated alluvial fans, foreshore, shoreface, shoal-water delta and offshore transition facies assemblages, which are laterally and vertically transitional throughout the succession. The alluvial fan and nearshore deposits reveal that the topography of the basin floor and the coastal plain was gently inclined. Shoal-water deltas, 70–250 cm thick, in the delta complex reflect comparable water depths and a relative rise in lake level, ultimately attributable to basin subsidence. Shallow environmental conditions prevailed during the basin's evolution, as evidenced by widespread nearshore deposits along its southern margin. The facies assemblages forming the basin's southern part show a predominantly aggradational stacking pattern, recording a balance between the sediment supply and a steadily growing basin accommodation. The balanced fill deposition and aggradational stacking pattern of the sedimentary facies associations indicate that the rate of basin subsidence and the uplift of the Menderes Massif was relatively consistent. This study shows that the intensity of a synsedimentary fault system, especially one leading to basin opening, plays a crucial role in controlling the architecture and sedimentary facies of the basin succession, both by creating accommodation and by filling it.

Deep-water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep-water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep-marine systems. Less documented are carbonate-rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep-water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate-rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow-water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast-supported conglomeratic division (Division I), an intermediate matrix-supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep-water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally-supplied carbonate-rich megaflows that eroded and incorporated the substrate during transport.