Search

The Aptian-Albian sedimentary record of the Parnaíba Basin (NE Brazil), represented by the Codó and Itapecuru formations, is characterized by near-shore, shallow marine, and fluvio-lacustrine clastic sediments deposited in a large shallow sag basin that developed during the breakup of northwestern Gondwana associated with the early opening stages of the South Atlantic. This study aims to precisely characterize the nature, variability, paleoenvironmental significance and preservation conditions of the organic matter of the Aptian-Albian succession of the 2-TV-1-MA borehole (270 m). With these premises, organic petrographic and geochemical techniques were applied for the definition of the organic facies, allowing a better understanding of the Parnaíba Basin evolution during the Aptian-Albian interval. The 2-TV-1-MA borehole presents, at the base, a lacustrine system, with a high contribution of continental components deposited in a high energy, oxic environment, with incipient marine influence. This is intercalated by periods of restriction, with deposition occurring in a dysoxic-anoxic, low energy environment, with high contribution of higher plants. To the top, a relative decrease in the water-column leads to an increase in restriction, the emplacement of a stratified water-column, and the development of microbial mats. This is topped by a return to a high energy, oxic environment, with marine influence, and dominance of higher plants organic components. • Four depositional systems have been proposed for the 2-TV-1-MA well core. • A first marine influence in the initial stages of deposition of the Codó Fm. • Organic-rich levels with terrestrially-derived AOM coeval with OAE 1b. [ABSTRACT FROM AUTHOR]

The early Toarcian is marked worldwide by major environmental changes that resulted in organic-rich black shale deposition, the Toarcian Oceanic Anoxic Event (T-OAE). This organic-rich sedimentation is particularly recorded in the Grands Causses (GCB) and Quercy (QB) basins. The main objectives of this study are the characterization, through organic petrology and geochemistry techniques, of the organic matter (OM) of the late Pliensbachian – early Toarcian sedimentary successions of these basins and the definition of the organic facies, assessing their implications in the evolution of depositional paleoenvironments. In the GCB sedimentation occurred, during the late Pliensbachian, in a well oxygenated water body (Total Organic Carbon - TOC 0.6 wt.% and low Amorphous Organic Matter - AOM) proximal to the terrestrial source area (high terrestrial contribution) with marine influence. In the lattermost Pliensbachian a shallowing of the water column is observed with decrease of marine influence and separation from the terrestrial source area (TOC 0.9 wt.%, AOM and zooclasts co-dominate) under an arid climate ( Classopollis ssp.). From the Tenuicostatum to early Serpentinum chronozones a restricted and stagnated environment (TOC 5.7 wt.%, AOM dominates) is implemented. From middle to late Serpentinum Chronozone the reestablishment of the oxygen levels (decrease in TOC and AOM) takes place, as well as paleoceanographic circulation patterns. In the QB, the late Pliensbachian to earliest Toarcian is characterized by low TOC (0.2 wt.%) with sedimentation occurring in a shallow oxygenated proximal water body (amorphous Hydrozoans dominate) separated from the terrestrial source area with arid climate ( Classopollis ssp.), and with episodes of emersion. From the Semicelatum Subchronozone to Serpentinum Chronozone the development of dysoxic to anoxic conditions (TOC 4.2 wt.%) takes place, associated with water column stratification and more effective non-carbonate sedimentation, and with an increase in water level. For the lattermost Serpentinum Chronozone shallowing of a more oxidizing water body, with some oxygen depletion still present is proposed. The differences in these paleoenvironmental depositional contexts further demonstrate that, although the T-OAE has a global character, local control mechanisms in these basins play a pivotal role. Furthermore, the first occurrence of Hydrozoans, namely its free-swimming medusoid forms, is described in organopalynological preparations of sediments from the Pliensbachian–Toarcian and their first paleoenvironmental application in a palynofacies based study is made. [ABSTRACT FROM AUTHOR]

The Middle-Upper Jurassic transition is a geodynamic benchmark in the evolutionary history of several peri-Atlantic basins. Contrary to the vast Tethyan and peri-Tethyan areas, in the Lusitanian Basin (Portugal), this interval corresponds to a major basin-wide disconformity preceded by a complex forced regression that induced sharp facies variations across the depositional systems. The Middle Jurassic units below are fully marine, whereas the Upper Jurassic sediments (Lower?-Middle Oxfordian), correspond to freshwater/brackish lacustrine, grading into punctuated brackish-restricted lagoonal and shallow-marine paleoenvironments. This study presents total organic carbon and palynofacies data of 34 samples (total analyzed thickness about 85 m) collected from three key sections encompassing the Middle-Upper Jurassic transition in the central-northern sector of the Lusitanian Basin. The palynofacies of the analyzed part of Middle Jurassic units (Cabo Mondego Formation) are characteristic of marine environments at their base, evidencing upwards a regressive trend of the depositional systems. Total organic carbon content is generally low, reaching up to 1.94 wt%. The Upper Jurassic Cabaços Formation presents kerogen assemblages mostly of continental origin, although punctuated by minor intervals of marine influence. Total organic carbon content is more variable, reaching up to 30.56 wt%. Intraclasts of re-deposited fragments of microbial mats were found incorporated in the kerogen assemblages, which point to highly dynamic erosional and depositional processes. Diversity of Botryococcus sp. occurrences was confirmed as an indicator of the degree of paleoenvironmental stability. The vertical distribution and comparison of the kerogen assemblages of the different sections indicate major changes of these parameters among relatively close settings and along narrow vertical intervals, attesting to the high sedimentary dynamics observed in the Lusitanian Basin. [ABSTRACT FROM AUTHOR]

Abstract: A high-resolution study (n=66) was conducted on Late Permian coal measures of the Bowen Basin, Australia, to observe palynofacies changes during peat accumulation over time. Palynofacies were determined using polytopic vector analysis (PVA) to derive end members with variable compositions that reflected fine scale environmental changes, within and between seams, of the Kaloola Member. Palynofacies reflect a three-stage succession within the palaeo- peat-forming environments from stable, anoxic conditions at the base, progressing to variable, oxic conditions toward the top of each seam. In cases where a seam was capped by tuff, rather than siliciclastic sediment, anoxic conditions similar to the bottom of each seam occurred. The results corroborate previous interpretations of palaeofloral communities and provide a new palynofacies model that integrates environmental progression within the coal seams in the Late Permian coal measures of the Bowen Basin. A complementary study of palynological assemblages recognised a shift from Dulhuntyspora sp., to Protohaploxypinus sp. in the lower Kaloola Member, indicating a change in pollen/spore source. Associations between dispersed palynomorphs and coal phyterals of parent flora remain tenuous beyond class rank, due to poor preservation and taxonomic bias inherent within the sample space. This is the first such palynofacies study to be conducted in the Bowen–Sydney–Gunnedah basin complex, thus opening the way for future work examining regional changes in palynofacies, expressed in both coal and siliciclastic sediments. [Copyright &y& Elsevier]

Abstract: In order to place information from palynofacies variations in a sequence stratigraphic context, palynofacies analyses for wells GTP-17-SE and GTP-24-SE from the Sergipe Basin, was integrated with sequence stratigraphy. Previous works assigned the succession to two second-order sequences, K50 and K60, the last being subdivided into systems tracts KM1 and KM2 (third-order sequences). By combining lithofacies data and gamma-ray logs from the studied wells with palynofacies and paleoecological data, the succession was subdivided into third-order sequences and correlated with the integrated sequence stratigraphic framework. The K50 sequence shows a slightly transgressive upward trend. The sequence boundaries of K50 are marked by major peaks in abundance of phytoplankton and amorphous organic matter and in the gamma-ray. KM1 sequence starts below of the boundary between Muribeca and Riachuelo Formations. This sequence was subdivided into three parasequences. The first transgressive systems tract is supported by a marked increase in Palynological Marine Index and amorphous organic matter values, and the phytoclast relative abundance shows a progressive decrease. The upper boundaries are marked by maximum flooding surface characterized by high abundances of dinoflagellate cysts. The boundaries are also marked by an abrupt decrease of phytoclasts, which is best observed in well GTP-24-SE. The highstand systems tract is characterized by an increase in amount of phytoclast particles, a clear decrease in amorphous organic matter percentage values and moderate values that tend to increase upwards of the Palynological Marine Index. The upper boundary of this sequence is marked by a peak of dinoflagellate cysts indicating the transgressive surface. In well GTP-24-SE, the boundary is placed at the base of an abrupt lithological change, from calcilutites to dark shales. The second transgressive systems tract is based on a marked increase in Palynological Marine Index and amorphous organic matter percentage values, together with the clear decrease in phytoclast particles. These are observed clearly in well GTP-24-SE, especially the decrease of phytoclasts. The top of these parasequences is distinguished on the basis of the peaks of Palynological Marine Index indicating the maximum flooding surface. In well GTP-24-SE, the lowest abundances of the phytoclast group are recorded at the maximum flooding surface. The KM2 sequence interpreted previously as a highstand systems tract is confirmed herein, on the basis of palynofacies. [Copyright &y& Elsevier]

Abstract: Palynofacies analyses were carried out on 272 core samples from two wells (GTP-17-SE and GTP-24-SE) in the Sergipe Basin, with the aim of reconstructing the paleoenvironments of the upper Aptian–middle Albian. For the palynofacies analysis the kerogen categories were counted and subjected to cluster analyses. For detailed environmental analysis, kerogen distribution trends and parameters were applied, based on percentages of kerogen categories. Total organic carbon analysis was also used. The stratigraphic distribution of palynofacies associations that defined eight palynofacies units in well GTP-17-SE and ten in well GTP-24- SE reflects a continuous terrestrial influx throughout the succession. Amorphous organic matter (AOM) and palynomorph groups show moderate to high percentages, especially in well GTP-24-SE. The increase in relative abundance of these groups suggests that a long-term a transgression and/or a decreasing terrestrial influx occurred in the area. From the bottom to top six depositional environments were identified in wells GTP-17-SE and GTP-24, respectively, and they reflect the progressive increase in marine influence as the basin evolved. Brackish lagoon conditions changed to more open marine conditions as sea level changed during the separation of South America from Africa. [Copyright &y& Elsevier]

The Cenomanian—Turonian boundary is marked by worldwide paleoenvironmental and paleoceanographical changes that are associated with a perturbation of the global carbon cycle and black shale deposition, called the Oceanic Anoxic Event 2 (OAE2). The objective of this study is to precisely characterize the nature of the organic matter, its variability, paleoenvironmental significance and the preservation conditions of two areas located along the northwest African Shelf where large-scale organic carbon burial contributed significantly to the global carbon burial associated with OAE2. With these premises, an organic petrographic and geochemical approach to the Cenomanian—Turonian record of the Moroccan Atlantic coast allowed the definition of the variability of the organic facies and the paleoenvironmental characterization of the upper Cenomanian—lower Turonian sediments of the Agadir section (Agadir Basin) and of the lower Turonian record of the Amma Fatma section (Tarfaya Basin). At Agadir, the marine microplankton dominated assemblages, with variable degree of amorphization, allowed the characterization of a transgressive-regressive cycle during the upper Cenomanian followed, during the lower Turonian, by a drowning event with establishment of a deep platform environment (under reducing conditions, increase in EFU, EFV, EFMo). The base of the succession (base of W. archaeocretacea biozone) and the top of the upper Cenomanian are characterized by two sea-level lowstands, and a high energy oxic environment, that culminate in emersion surfaces (high EFMn and low organic matter preservation). The organic facies in the lower Turonian of Amma Fatma is largely dominated by bacterial material (probably derived from sulfur bacteria), indicating an outer shelf setting, with some degree of restriction, under euxinic conditions (high EFMo) and high primary productivity (high EFCu, EFNi, EFZn). Differences in terms of the redox conditions between the two basins during the lower Turonian were determined, with anoxia prevailing at Agadir, while euxinic conditions are established at Tarfaya. These are explained by different oceanic circulation patterns, with the mixing of Tethyan waters at Agadir. High primary productivity is recorded at both locations, possibly promoted by the occurrence of upwelling currents. This study further corroborates a delay in the anoxia in Agadir, that during the isotopic excursion of OAE2 only reaches slight dysoxia (upper Cenomanian), and the maintenance of reducing conditions in Tarfaya post-OAE2. • Paleoenvironmental conditions during Cenomanian—Turonian at Agadir and Tarfaya. • Bacterial material in the organic facies of the Amma Fatma section. • Different redox conditions in the Agadir and Tarfaya basins during the lower Turonian. • Global vs local control mechanisms on the OAE2 organic record are highlighted. • Corroborates delay of anoxia in shallow water marginal environments during OAE2. [ABSTRACT FROM AUTHOR]

The Cenomanian-Turonian boundary is marked by global sea-level highstands and one of the warmest periods of the Mesozoic, with high p CO 2 levels linked to a massive magmatic episode. This is associated with the establishment of a worldwide marine anoxia, the deposition of organic-rich facies and disturbances of the global carbon cycle, the so-called Oceanic Anoxic Event 2 (OAE2). The Pont d'Issole section's (Subalpine Basin, SE France) sedimentary succession represents the reference record of OAE2 in the Tethyan domain, although its organic fraction is extremely poorly studied. Therefore, the main objectives of this study are the characterization of the Pont d'Issole section's organic matter (OM) for paleoenvironmental interpretation and the assessment of the OM thermal maturity using organic petrology and organic geochemistry techniques. The organic record characterizes a shallowing-up marine system with varying redox and restriction conditions, associated with periods of stratified oxygen regimen. It displays the presence of two OM enrichment episodes with different paleoenvironmental and geodynamic contexts. The first OM enrichment episode (Unit Th1) is thought to be associated with the global mechanisms that trigger OAE2 and is characterized by a palynofacies association co-dominated by amorphous OM and marine microplankton, reflecting a context of high sea-level. This is followed by the Plenus Cold Event (Unit Th2), characterized by a decrease in amorphous OM and increase in marine microplankton, representing a reoxygenation associated with an increase in water level, and an apparent decrease in temperature (disappearance of Classopollis sp.). The second OM enrichment episode (Unit Th3 and base of Unit Th4) is characterized by an association dominated by amorphous OM, the occurrence of freshwater microplankton, and the development of a restricted environment with low sea level. These depositional conditions are thought to be connected to the beginning phases of basin closure, promoted by the regional tectonic framework (compressive trend between Africa and Europe). The molecular fraction showed the presence of unsaturated compounds, monoaromatic steranes, monoaromatic anthrasteroids and the biological ββ hopanes, indicating a low thermal evolution for the OM. This is corroborated by biomarkers ratios and organic petrographic data, namely vitrinite reflectance (0.29% R r). The presence of Paleozoic reworked OM in the samples was also identified presenting a more complex thermal history than the Cretaceous OM. This OM is possibly related to the subaerial erosion of Hercynian Massifs. • Depositional paleoenvironmental conditions during CTB at Pont d'Issole section. • Global vs local control mechanisms on the OAE2 organic record are highlighted. • Identification of the presence of Paleozoic reworked organic matter at Pont d'Issole. [ABSTRACT FROM AUTHOR]

The Pliensbachian–Toarcian (Lower Jurassic) in the Lusitanian Basin (Portugal) is particularly well exposed through marl-limestone alternations very rich in nektonic and benthonic macrofauna. In the general context of Toarcian Oceanic Anoxic Event (T-OAE), the Lower Toarcian (Polymorphum and Levisoni ammonite zones) marks important sedimentological changes in the marine paleoenvironment. To better understand the paleoenvironmental changes that occurred during the latest Pliensbachian–early Toarcian, a high-resolution study of organic matter was undertaken in the Alcabideque section, in the northern sector of the basin. Based on the analysis of 14 samples from a section 20 m thick, this study involved organic geochemistry [total organic carbon (TOC), sulfur and biomarkers] and palynofacies. The results confirm that sediments are particularly poor in organic matter, with the highest TOC values reaching 0.41 wt.% around the top of Polymorphum Zone. The palynofacies analysis provides evidence that the organic matter largely consists of particles belonging to phytoclasts and palynomorphs groups. The phytoclasts present were generally degraded and oxidized, with significant representation in the Emaciatum and Polymorphum zones. The palynomorphs were mainly composed by sporomorphs, with a sporadic increase in marine palynomorphs (mainly dinocysts) at the top of the Emaciatum and Polymorphum zones. Continental organic matter was predominant at the base of Levisoni Zone (T-OAE), through the deposition of brownish marls (Chocolate Marls), which was confirmed by the occurrence of tetrads and polyads (pollen grain agglomerates), and by biomarkers, with the major presence of long-chain n -alkanes, n- alkane C17, C20 tricyclic terpane, C24 tetracyclic terpane and C29 regular sterane. The gammacerane index shows a peak at the top of Polymorphum Zone, clearly associated with the increase of marine palynomorphs and the maximum marine influence in the series. [ABSTRACT FROM AUTHOR]

Gaiteiros-1 borehole, located in the central Lusitanian Basin (Portugal), drilled a continuous Jurassic (Hettangian to Kimmeridgian) sedimentary sequence. Forty-one samples were selected for this study to characterize the dispersed organic matter and its vertical variation along Gaiteiros-1 borehole and to evaluate the environmental changes based on palynofacies and bulk geochemistry analyses. Gaiteiros-1 borehole lithological sequence is characterized by a low organic carbon content, which varies between 0.10 wt% and 0.83 wt%, in Candeeiros carbonates and Lower Jurassic Coimbra Formation, respectively. The insoluble residue content indicate a carbonated character in almost the entire sequence, except for Kimmeridgian samples. The palynofacies analysis evidences the presence of the main groups of kerogen (Phytoclats, Amorphous and Palynomorphs) with a dominance of the amorphous group in the carbonated samples and phytoclasts in Kimmeridgian detritic samples. Different types of amorphous particles were identified, suggesting periods of reworking by bacterial activity and primary bioproductivity in depleted oxygen environments. Despite the dominance of amorphous particles, the kerogen groups vertical variation provides information that reveals changes in the depositional environment. The kerogen assemblage of the Candeeiros facies suggests a stratified water column, with well-oxygenated layers, responsible for high primary productivity periods, which allowed for the development of zooplankton, preserved in the form of zooclasts fragments and foraminiferal test-linings. The contribution of the Palynomorph group is scarce during the Lower-Middle Jurassic but increases in the Upper Jurassic. This modification in the kerogen assemblage reflects changes in the sea level, oxygenation conditions, climate and proximity to the terrestrial source area. The presence of Coleochaete -like freshwater algae was detected for the first time in the Lusitanian Basin, suggesting more restrictive conditions during the Late Oxfordian. During the Kimmeridgian, the amorphous material disappears and phytoclasts, mainly opaque phytoclasts, come to dominate the kerogen assemblage, as a result of terrigenous sediments input, due to the great proximity to the terrestrial source area. • Palynofacies are reported for Gaiteiros-1 sedimentary sequence (Lusitanian Basin). • Monotonous carbonated record dominated by amorphous organic matter. • Non-carbonate sedimentation characterized by terrestrial organic matter. • Different depositional environments, from carbonate platform to fluvio-deltaic. • Coleochaete algae: first occurrence in the Jurassic fossil record. [ABSTRACT FROM AUTHOR]

The Toarcian Oceanic Anoxic Event (TOAE) is characterised by a perturbation of the global carbon cycle and the widespread deposition of organic matter (OM)-rich strata/sediments in the northern areas of the West Tethys Shelf, in several northern European epicontinental basins. Contrariwise, in the southern areas of the West Tethys Shelf such as western and southern Iberian, and northern Gondwana margins, OM-rich strata/sediments are spatially and temporally restricted. To better understand the relationship between OM production, depositional conditions, and palaeoceanographic controls on the occurrence of OM-rich facies in the northern Iberian margin, we collected and analysed 18 samples from the Rodiles section (Asturian Basin) for geochemical (total organic carbon-TOC, total sulfur-TS, δ13C Kerogen , and δ13C Wood) and palynofacies analysis. The studied upper Pliensbachian–lower Toarcian succession has TOC values reaching up to 2.9 wt%. The relative dominance of non-opaque phytoclasts and the δ13C Kerogen values (average of ~ −24‰) in the lowermost Toarcian (Tenuicostatum Zone) agrees with previous interpretations indicating that this area was located in a dominantly winter-wet climate zone. A change in the kerogen assemblages is observed at the Tenuicostatum/Serpentinum zones boundary (onset of TOAE), related to an increase in amorphous OM (AOM). A slight increase in non-opaque phytoclasts and terrestrial palynomorphs, and a negative δ13C Kerogen excursion (reaching −31.5‰) is recorded in the same interval. These observations suggest a increase in continental weathering and fluvial runoff associated with more humid conditions, likely resulting in increased superficial productivity and deposition and preservation of OM under, at least, suboxic conditions. Above the TOAE interval, the δ13C Kerogen record (values around −24‰) and the drastic drop in TOC and AOM content indicate that bottom water oxygenation improved after the TOAE. Our results demonstrate a link between early Toarcian climate dynamics and the deposition of OM-rich strata/sediments. • Organic matter-rich sediments occur in the Asturian Basin. • The studied kerogen assemblages are mostly of terrestrial affinity. • Increase in abundances of TOC, amorphous and terrestrial organic matter during TOAE. • Improved bottom water oxygenation caused decline in TOC and amorphous organic matter after TOAE. • A link between kerogen assemblages, δ13C Kerogen and winter-wet climate is demonstrated. [ABSTRACT FROM AUTHOR]

Lakes can be classified as open, semi-closed, and closed based on the balance between accommodation space and sediment–water fill. Different lake types can coexist in adjacent basins and rapidly change throughout time from one type to another. Understanding the processes that result from shifts in a lake's hydrological properties can be challenging, as well as characterizing its sedimentary products. The Aptian Codó Formation, in the Parnaíba Basin, north–northeast Brazil, contains in its record a complex facies succession deposited in a continental lacustrine system. In order to better understand the depositional aspects of different lake types, we characterized the lower portion of the Codó Formation using a multi-proxy approach. We combined litho- and microfacies analysis, ichnology, bulk chemical data, mineralogy, isotopic geochemistry, and organic matter analysis in the recently drilled, fully recovered borehole, 2-CO-1-MA. We defined eight lithofacies: bioturbated siltstones, dark gray mudstones, laminites, stratiform and domal stromatolites, heterolites rich in ostracods and organic muddy, and anhydrite and gypsum rocks. The isotopic data and the palynofacies analysis pointed out the existence of restricted conditions (TOC up to 19.6 wt%) with intermittent connections with seawater. Integrating all techniques, we interpreted five depositional stages: expanded lake, brackish ephemeral lake, perennial shallow lake, evaporitic sabkha, and stratified lake. These stages were influenced by the relation between inflow and evaporation rate, which were the main controls on sedimentation in the lacustrine-sabkha system studied. Our findings provide a detailed description and interpretation of the paleoenvironmental conditions related to the alternation from open to closed lakes, combining sedimentological, geochemical, and palynological characteristics of an inland lake system. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the relationship between early Toarcian climatic events and the composition of kerogen assemblages in the Lusitanian Basin (Portugal). In particular, we aim to understand how the Pliensbachian–Toarcian Event (Pl–Toa Event) and Toarcian Oceanic Anoxic Event (TOAE) affected the continental areas of the western Iberian margin and how possible variations in continental sources of organic matter (OM) were expressed in marginal-marine and hemipelagic depositional environments during the early Toarcian. We present here a characterisation [total organic carbon (TOC), total sulphur (TS), δ13C in kerogen concentrate (δ13C Kerogen), and palynofacies] of kerogen assemblages from several uppermost Pliensbachian (emaciatum ammonite Zone)–lower Toarcian sections in the Lusitanian Basin (western Iberian margin), including the Peniche section, which contains the Toarcian GSSP. In all sections, TOC concentration is low (average 0.4 wt.%), with the highest values reaching up to 2.1 wt.% in a discrete level located approximately 10.5 m above the base of the levisoni Zone at Peniche. The TOAE negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni Zone throughout the basin. Palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity, with the dominance of the Phytoclast Group and terrestrial palynomorphs, and with punctual increases in amorphous organic matter, freshwater (e.g. Botryococcus sp.) and marine microplankton (dinoflagellate cysts, acritarchs, and prasinophyte algae) in specific stratigraphic intervals. A change in palynofacies assemblages associated with the TOAE is observed around the base of levisoni Zone. Although with slight differences between sections, the TOAE interval records an increase in non-opaque, translucent, phytoclasts (NOP) and cuticle fragments, and is also associated with an increased contribution of terrestrial palynomorphs (increase in sporomorphs and Classopollis in tetrads and agglomerates) and decrease in marine palynomorphs. The increases in NOP and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial OM into marine environments during the early Toarcian, especially during the TOAE, in the western Iberian margin. Understanding the impact of the early Toarcian climatic events on land-based ecosystems may provide important insights into current climate change. • The Lower Jurassic in the Lusitanian Basin is mainly organic matter lean. • The studied kerogen assemblages are mostly of terrestrial affinity. • A link between kerogen assemblages and climate conditions is demonstrated. • During the TOAE δ13C negative trend an increase in terrestrial particles is observed. • A gradual re-establishment of the depositional conditions after TOAE is observed. [ABSTRACT FROM AUTHOR]

The investigation of the relationship between paleoenvironmental conditions and distribution and relative abundance of specific saturated and aromatic hydrocarbons was the main objective of this study, thus marking the parameters, which were most sensitive to environmental changes. Insights on the type, generative potential, and maturity of organic matter (OM), as well as paleoclimate conditions, along with the reconstruction of depositional settings of the northwest part of the Toplica basin (Serbia), were provided. Organic petrographic, palynofacies, organic geochemical, mineralogical, and XRF analyses were carried out to investigate 40 sediment samples of the Prebreza and Čučale sedimentary units. Investigated samples were deposited in the saline and anoxic environment, under semi-arid to semi-humid/humid climate conditions, along with the constant inflow of volcanoclastic material. The predominance of δ-methyltrimethyltridecil chroman (δ-MTTC) within euxinic portions of the stratified water column was associated with an increase in salinity, which was noticed for sediments of the Prebreza unit. Sediments from this stratigraphic unit showed a higher contribution of algae precursor, whereas sediments of the Čučale unit suggested higher participation of microbiologically reworked OM. Most of the samples contained oil-prone kerogen type II. Maturity of the OM for sediments of the Prebreza unit ranged from immature to early-mature, while for samples of the Čučale unit varied from early-mature to mature stages. Distribution of hopane biomarkers typical for crude oil indicated that depth of 1 km was a boundary for the genesis of thermodynamic, more stable compounds. A significant portion of semifusinite was correlated with the paleofire event, which affected the distribution of n -alkanes. The high production of hydrocarbons was related to volcanic activity. Parameters, which proved to be highly susceptible at the stratigraphic boundary between the Prebreza and Čučale units, were C-value, S/H, α-MTTC, δ-MTTC, β-/γ-MTTC, and (1,3- + 1,6-)/(1,4 + 1,5-DMC), respectively. • The Prebreza and Čučale units are deposited in two distinct paleoenvironments. • Most of the samples contain oil-prone kerogen type II and cover a wide maturity span. • Analcime in the borehole is related to the constant inflow of volcanoclastic material. • δ-MTTC predominance is related to the higher salt content in the Prebreza unit. • Significant alteration of some parameters is observed at the stratigraphic boundary. [ABSTRACT FROM AUTHOR]

The Early Toarcian Oceanic Anoxic Event (T-OAE) is characterised by major palaeoenvironmental and palaeoceanographical changes (ocean anoxia, global warming, ocean acidification, among other), and a severe perturbation of the global carbon cycle. Although widespread oceanic anoxia was a significant control on the occurrence of organic-rich facies during the T-OAE in several locations of the northern Tethyan margin, the effects of anoxia, oceanic productivity, and dilution are poorly understood in other worldwide locations, such as the southern Tethyan and Iberian margins. In this study, we report new geochemical [total organic carbon (TOC), total sulphur (TS), total carbonate content (CaCO 3), δ13C from kerogen isolates (δ13C Kerogen)], palynofacies and thermal maturation data from the Upper Pliensbachian–Lower Toarcian successions in La Cerradura and Fuente Vidriera, External Subbetic domain, Betic Cordillera (SE Spain). The obtained results indicate that these successions have low TOC contents (~ 0.3 wt.%), with TOC reaching up to 0.46 wt.% around the Polymorphum–Serpentinum ammonite zone boundary in La Cerradura. δ13C Kerogen negative carbon isotope excursions (CIE) are observed at the base of the Polymorphum Zone, the Pliensbachian–Toarcian Event (Pl-Toa), and base of the Serpentinum Zone (T-OAE). Overall, the low maturity kerogen assemblages are dominated by terrestrial OM and with a minor marine component. Small increments in terrestrial OM, non-opaque phytoclasts, and palynomorphs are observed just before and during the T-OAE in the studied area. During the Early Toarcian, in the External Subbetic domain, accumulation and preservation of OM was low and with a significant terrestrial contribution, similarly to other locations around the southern margins of Iberia and Tethys. The dominance of the opaque phytoclast subgroup, the occurrence of Classopollis , and the relatively more positive δ13C of terrestrial kerogen suggest that OM was mostly sourced from an area characterised by a semi-arid climate (i.e. with pronounced arid periods) during most of the Polymorphum Zone. The T-OAE negative CIE is accompanied by an increase in terrestrial OM, with a slight increase in the non-opaque phytoclast subgroup and terrestrial palynomorph subgroup. The increase of non-opaque phytoclast and terrestrial palynomorphs are in line with the posited enhancements of the hydrological cycle and export of terrestrial OM into marine environments during the T-OAE. This study suggests a link between 13C fractionation during photosynthesis in C3 plants and climate during the Early Toarcian. This link suggests coupling of the water and terrestrial carbon cycles before and during the T-OAE. • Early Toarcian sediment successions of the External Subbetic are mainly organic matter lean. • The studied palynofacies assemblages suggest a dominantly semi-arid climate. • During the T-OAE, an increase in land plant-derived organic matter is observed. • A link between 13C fractionation during photosynthesis in C3 plants and climate during the Early Toarcian is suggested here. [ABSTRACT FROM AUTHOR]