Depositional Record最新文献

The Loza-Portilla Formation consists of 100–300 m of alluvial siliciclastics and palustrine-lacustrine carbonates and minor evaporites, infilling a tectonically active syncline basin (Miranda-Trebiño Basin, Basque-Cantabrian Pyrenees), which developed over the south Pyrenean Thrust Front during middle to late Eocene times. Detailed facies characterisation and correlation allowed the reconstruction of the stratigraphic architecture of the formation, which consists of three unconformity-bounded depositional sequences, representative of three successive phases of carbonate lake development. A model of low-energy shallow lake with ramp margins and wide palustrine fringes fits well with the architecture of the three stacked carbonate-dominated sequences, with stratal architectures characteristic of shallow balanced-fill lake basins. A range of limestones representative of different palustrine and lacustrine environments is distinguished, commonly arranged in metre-thick facies sequences and cycles reflecting water-level changes and marked shoreline shifts, likely associated with prevailing tectonic and climate conditions. Compressional tectonism and associated halokinetic movements exerted major control on depositional trends and distribution of the main depocentres. The Loza-Portilla Formation is of major palaeogeographical significance in the tecto-sedimentary evolution of the Pyrenean domain, labelling the first phase of uplift and emersion that affected large areas of the Basque-Cantabrian (western) Pyrenees, prior to end-Eocene generalised continentalisation.

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.

Kimmeridgian limestone (KL) strata are one of the best examples of peritidal carbonates that record palaeogeographical and palaeoclimate conditions in the Eastern Pontides, Eastern Black Sea region. These Kimmeridgian limestone strata consist of well-preserved dark grey lime-mudstones that serve as essential archives for various geochemical proxies. This study presents new data on trace elements, rare earth elements and stable isotopes (δ¹⁸O, δ¹³C) to enhance our understanding of the palaeoclimate, weathering patterns, salinity, redox conditions and productivity during the deposition of these strata. Furthermore, organic chemistry data, including total organic carbon, Rock-Eval (S1, S2, S3, HI, OI) and production index, are presented to discuss their hydrocarbon potential. The Kimmeridgian limestone strata exhibit relatively high total organic carbon content (0.16–0.22%) with an average of 0.19%, δ¹⁸O values ranging from −2.12 to −0.69‰, and δ¹³C values ranging from 1.42 to 2.09‰. Additionally, they display distinct rare earth element characteristics such as low La/Yb_N (0.64–1.00) ratios, varying Gd*/Gd (0.54–1.16) ratios, high Eu/Eu* (1.19–1.84) ratios and Ce/Ce* (0.91–1.16) ratios. The Kimmeridgian limestone strata also exhibit chondritic Y/Ho (30.48) and Zr/Hf (40.35) ratios, relatively high redox-sensitive element values, low Ga/Rb (0.10–1.10; an average of 0.29) ratios and high K₂O/Al₂O₃ ratios (0.2–0.40; an average of 0.27). According to the geochemical results of this study that are integrated with published stratigraphy and palaeontological data, the Kimmeridgian limestone strata are interpreted as having been deposited in a shallow subtidal lagoon environment or a partly protected interior ramp setting. Although sea-level fluctuations influenced the palaeoenvironmental changes, ocean circulation along the inner platform supplied nutrients to the basin. The possible occurrence of low-temperature water/rock interaction under reduced oxygen conditions contributed to additional element flux. Palaeoclimate indices suggest the existence of an aridification event, wherein arid climate played an important role in low weathering input, organic matter source, productivity, evaporation and salinity enhancement. The climate, accompanied by sedimentary factors, facilitated enhanced productivity, a balanced sedimentation rate and the preservation of organic matter under reducing conditions. Contrary to the anticipated outcome, considering the high productivity and anoxic depositional conditions suggested by microfacies and inorganic geochemical results, the over-maturation processes have resulted in a notable decline in the organic matter content and hydrocarbon potential of the samples.

Facies models for basin-plain turbidite systems often depict very simplistic event-bed geometries that are tabular at the kilometre scale. However, recent studies have demonstrated more complex facies architectures, including rapid changes in event-bed thickness and facies composition. This lateral event-bed heterogeneity can have a significant impact on reservoir heterogeneity prediction in basin-plain turbidite systems developed for hydrocarbon production, carbon sequestration or geothermal energy. Coastal outcrops on the Gaspé Peninsula in Quebec expose the Middle Ordovician Cloridorme Formation, a synorogenic ‘flysch’ turbidite system developed in the Taconic foreland basin. The formation is interpreted to occupy a basin-floor position due to long-distance (tens of kilometres) correlations of bedsets in the direction of palaeocurrent. This outcrop-based study of the Cloridorme Formation utilises drone photogrammetry, centimetre-scale graphic logs and handheld gamma ray scintillometry data to better understand the detailed turbidite and hybrid event-bed architecture in a basin-plain setting. While most beds in this outcrop study can be traced for 500 m or more in a downcurrent direction, these results indicate significant intra-bed and inter-bed lateral complexity, including changes in bed thickness, grain-size distribution and mud content. The quantification of these lateral changes and comparison with other well-constrained outcrop analogues refines the environment of the Cloridorme Formation and aids in the prediction of subsurface heterogeneity in conventional and unconventional hydrocarbon reservoir systems through reservoir model parameterisation, as well as the characterisation of lateral heterogeneity important for horizontal-well geosteering and completion strategies.

The formation of calcareous coated grains like ooids and oncoids have been extensively researched. In contrast, the origin and genesis of ferruginous coated grains are less clear. Radically different processes like surficial weathering, hydrothermal exhalation and microbial activity have been advocated for the source of iron and the development of coatings. Modern examples are sparse and from marine environments affected by igneous activity. This study presents the features of ferruginous coated grains found in freshwater lacustrine–palustrine deposits of the Lower Jurassic syn-rift strata of the Pranhita–Godavari Basin, India. The coated grains occur in metre-thick lenticular bodies of nodular limestones enclosed in black mudstones containing plant debris and sulphates (gypsum and baryte). In the nodular limestones, sand-size coated grains, along with chert and quartz grains, float in a micritic groundmass. Angular quartz grains embedded in dark, amorphous haematite–goethite constitute the nuclei of the coated grains. Cortices comprise numerous, thin, wavy laminae of goethite with trapped detrital grains. These coated grains are typically devoid of carbonates, although the outermost part of the cortex is replaced by calcite spars to varying extent. The black mudstone-nodular limestone association occurs in between siliciclastic lacustrine deposits (laminated red and green mudstones) below, and the palustrine limestones-green shale association above. The palustrine limestones contain remains of aquatic organisms, evidence of desiccation, paedogenesis, microbial-mat formation, chert, baryte and gypsum layers. A few decimetre-scale, wedge-shaped, flood-derived cross-bedded sandstones occur locally. Due to the proximity of the depositional area to the marginal fault system of the rift basin and association of the limestones containing coated grains with sub-aerially weathered microbialites, these ferruginous coated grains are ideally poised for a comparative assessment of various hypotheses of solute supply and precipitation. Based on field, microscopic and chemical characteristics, it is possible to conclude that microbially mediated precipitation in hydrothermal (hot spring)-influenced pools is the most probable origin for these ferruginous coated grains.

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.