Depositional Record最新文献

The regressive surface of marine erosion is a key stratigraphic discontinuity used to identify episodes of forced regression in marine strata. Typically, it marks the base of shallow-marine (e.g. shoreface and deltaic) deposits eroding over relatively deeper-water (e.g. shelf and prodelta) lithofacies. While well-documented in marginal-marine areas, its occurrence in offshore or strait settings dominated by tidal currents is less understood. This study investigates lower Pleistocene outcrops in the Plio-Quaternary Siderno Basin, Calabria, southern Italy, where tidal sand ridges developed in a Mediterranean strait. High-resolution drone images reveal a basinward-dipping basal surface marking the onset of tidally dominated sedimentation. This discontinuity separates underlying shelf fines from overlying cross-stratified, tidal bioclastic/siliciclastic arenites, indicating a prolonged period of marine regression in a strait setting. The stratal architecture of the ridges shows cross-strata aggradation in up-dip sections, transitioning down-dip into balanced aggrading/prograding strata, and further basinward into markedly prograding deposits. These features are interpreted to reflect an initial phase of normal regression, evolving into forced regression. This latter stage is characterised by a progressive deepening of the basal discontinuity, causing more erosional effects on the underlying beds, with a vertical basinward fall of about 60 m over 2 km. Internal foreset geometry (two-dimensional vs. three-dimensional cross strata) and their vertical and lateral repetition indicate stages of equilibrium and disequilibrium for tidal bedforms, reflecting varying current speeds and water depth changes. The regressive surface of marine erosion here is formed by tidal currents, rather than waves, suggesting a new type of sequence stratigraphic discontinuity associated with tide-dominated settings.

This contribution examines the climate variations reflected by a mainly lacustrine succession spanning from 17.73 to 14.0 Ma in north-east Iberia, thus encompassing the Miocene Climatic Optimum (MCO). The study is based on the δ¹³C and δ¹⁸O composition of an array of carbonate facies and marl samples, complemented with sedimentological analysis, illite crystallinity index and magnetic susceptibility data. The onset and ending of the MCO have been detected at ca 17.10-17.06 Ma and 14.56 Ma, roughly equivalent to the boundaries in the marine record, although with relatively short lags. The variability of the data series evidenced changes in humidity and air temperature through the MCO, some of which coincided with similar variations in other records. Specifically, an evolving positive shift in δ¹³C values, from 16.5 to 14.5 Ma, seems to fit the Monterey excursion observed in marine records. Likewise, increases in δ¹⁸O values between 16.8 and 16.5 Ma and between 14.85 and 14.56 Ma in the study succession concurred with warming intervals recorded in palaeosols of Central Europe, emphasising the coincidence with the temperature maximum at ca 16.6 Ma. A general decline in temperature and an increase in humidity are detected from 14.56 Ma, both with steeper trends until 14.41 Ma then more gradual onwards, indicating the beginning of the Middle Miocene Climatic Transition. These results shed light upon the tightly coincidental features between terrestrial and marine records over those time intervals and, more importantly, highlight the earlier warming and the faster cooling experienced by the lake system as compared with the marine record. These findings provide further evidence to help infer palaeoclimate conditions on a much broader reach than the regional context.

Mineralogy and texture of diagenetic phases in the Aptian Pre-Salt Barra Velha Formation are described, quantified and compared by facies and structural setting to understand their spatial and temporal distribution, and to develop predictive concepts for their genesis. This study examined data from eight wells from one oil-field in the Santos Basin. Calcite is the most abundant mineral and occurs with fibro-radial texture as spherulites and shrubs and sparse microcrystalline mudstone. The δ¹⁸O values from calcite spherulites and shrubs suggest water of similar composition and temperature, but they have different δ¹³C values. Mudstones show lower δ¹⁸O, suggesting warmer lake water and/or lower evaporation, whereas δ¹³C values indicate a variable, but commonly strong influence of biogenic CO₂. Dolomite with rhombohedral habit was the first to precipitate, followed by lamellar, saddle and anhedral varieties. Rhombohedral dolomites show a positive δ¹³C-δ¹⁸O correlation and a similar range in values to spherulites and shrubs, suggesting similar lake water. The lamellar dolomite is related to biofilms, whereas anhedral dolomite is attributed to mixing of pore and meteoric waters. Lamellar and anhedral dolomites have similar isotopic values, precipitating after rhombohedral dolomite in slightly warmer and/or less evaporatively concentrated pore water. Saddle dolomite is related to hydrothermal fluids that percolated the formation during early diagenesis. Silica occurs as replacement of primary calcite and Mg-clay, but also as a cement and more rarely as a depositional chert. Both dolomite and silica display a complex range of petrographic textures, many of which are facies dependent. This study focusses on the most important phases of the paragenetic sequence that took place pre-burial and are (1) formation of Mg-clay, calcite spherulites and shrubs, (2) partial dolomitisation of shrubs and spherulites and precipitation of rhombohedral and lamellar dolomites, (3) precipitation of saddle dolomite, matrix and carbonate dissolution and (4) anhedral dolomite and all textures of precipitated or substituted silica.

Facies, microfacies and stable isotope analyses of limestone beds in the northernmost Ñirihuau Basin, North Patagonian Andes, Argentina, document and constrain the past hydrological, sedimentological and climate conditions that prevailed during the deposition of a lacustrine system between ca 15 and 13 Ma. This palaeoenvironment is recorded in the middle section of the Ñirihuau Formation, which holds significance because: (1) It was deposited during a transition from an extensional to a compressional tectonic regime; (2) it spans the Middle Miocene Climatic Optimum and the beginning of the Middle Miocene Climatic Transition; and (3) it contains limestone beds interbedded within a 600 m thick interval of mudstones and siltstones, along with intercalated sandstone and volcaniclastic bodies. Two detailed sedimentary logs were surveyed along the Arroyo Las Bayas, at the western and eastern flank of the David Syncline. Limestones from both stratigraphic sections were sampled as well as isolated limestone beds from two other sites. One facies association was defined and interpreted as a perennial lake associated with a deltaic system and dominated by detrital clastic material. It comprises Facies 1 (Marginal lacustrine) and Facies 2 (Lower delta plain); in both, the presence of grainstones and calcimudstones stands out. Through petrography and cathodoluminescence studies of these continental carbonates, nine microfacies were identified: (a) Intraclastic grainstone, (b) Homogeneous calcimudstone, (c) Silty grainstone, (d) Disrupted micrite, (e) Birds eye micrite, (f) Bioclastic mudstone, (g) Calcimudstone with sparse detrital grains, (h) Fenestral micrite, (i) Stromatolitic boundstone. These indicate mainly bio-induced subaqueous carbonate precipitation and subordinate deposition by tractive flows with short-distance transport on a littoral lacustrine environment. Most of these microfacies exhibit very early diagenesis (eogenesis) effects. These features, and the geochemistry results, indicate that they were deposited in a palaeolake system under temperate to warm and humid conditions.

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.

In the Early to Middle Miocene, the post-orogenic intramontane lacustrine Sinj Basin that belonged to the Dinarides Lake System evolved in the area of the External Dinarides. A composite 770 m thick stratigraphic column was measured spanning the basin's stratigraphy. Eight facies were differentiated. Four facies are almost entirely composed of freshwater carbonate deposits. Carbonate facies are divided into calcareous mudstone, charophytic micritic limestone, calcisiltite and coquina facies. They are interpreted to belong to a prograding carbonate bench on a gently inclined lake margin. In addition, tuff/clays, carbonate conglomerate, carbonate breccia and coal were differentiated. The tuff/clays are the result of remote volcanic eruptions, while the coarse-grained sediments belong to subaqueous shallow stream channels or were deposited by gravity flows. The coal at the top of the measured succession, mostly of allochthonous origin, was deposited as a fen forest peat, representing the final stage of the lake. The formation of the Sinj Basin might have been triggered by dissolution of Permo-Triassic evaporites, within the mostly carbonate basement but also by breakdown and collapse of Mesozoic and Palaeogene carbonate rocks and coalescence of contiguous sinkholes. The non-tectonic interpretation of the basin genesis is a novel hypothesis explaining the origin of one of the Dinarides intramontane basins and is in contrast to previous considerations that evolution of the Sinj Basin was controlled by strike-slip or extensional tectonics.

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.