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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]

Abstract: Studies of the Mesozoic and Cenozoic sequence crossed by the Barreiro-4 borehole provide an improved understanding of the organic matter deposited in the Lower Tagus sub-basin (Lusitanian Basin, Portugal) and the implications for the potential source rock and depositional environment. This study focused on 43 samples (Middle Jurassic to Neogene) that were subjected to palynofacies and organic geochemistry analyses (Total Organic Carbon, Rock-Eval pyrolysis and molecular biomarker analysis). The palynofacies data indicate that the sequence contains mainly phytoclasts (non-opaque phytoclasts). However, the Middle Jurassic samples are dominated by Amorphous Organic Matter (AOM). Continental and/or marine palynomorphs are present in all the samples. The Cretaceous samples are characterized by small amounts of kerogen that have high contents of solid bitumen. The Total Organic Carbon (TOC) content is generally less than 1 wt.%. The Rock-Eval S1 and S2 parameters vary from 0.01 to 3.50 mgHC/g rock and 0.15 to 34.03 mgHC/g rock, respectively, with the highest values corresponding to the Cretaceous samples. The hydrogen index (HI) and oxygen index (OI) values range from 35 to 552 mgHC/g TOC and 4 to 180 mgHC/g TOC, respectively. The T max values range from 416 to 437 °C. The biomarker analysis showed that n-alkanes with 15–30 carbon atoms are present and usually have a unimodal distribution with a predominance of low to medium molecular weight compounds. The CPI values range between 0.63 and 3.65, and the pristane/phytane ratios vary between 0.48 and 1.64, indicating alternation of oxic–anoxic conditions along the sequence. The distribution of terpanes shows small amounts of tricyclic and tetracyclic terpanes in most of the samples (except for some Cretaceous samples) and a predominance of pentacyclic terpanes. The amount of 17α (H),22,29,30-trisnorhopane (Tm) usually exceeds the amount of 18α (H),22,29,30-trinorneohopane (Ts). The 20S/(20S + 20R) and αββ/(ααα + αββ) ratios of the C29 steranes generally have values below the range of equilibrium, indicating an immature stage of the OM. [Copyright &y& Elsevier]

Abstract: A Middle–Upper Jurassic sedimentary succession has been cut by the Ramalhal-1 borehole in the Bombarral sub-basin (Lusitanian Basin, Portugal). The succession comprises the Brenha, Montejunto, Abadia and Lourinhã Formations, which are composed of limestones, marls, sandstones and clays. The main objective of this study was to characterize the organic matter using palynofacies and geochemical analyses to determine the depositional paleoenvironments and the hydrocarbon generation potential. The Total Organic Carbon content is generally less than 1wt.% but reaches 4.1wt.% in one sample, due to the presence of perhydrous coal. The Rock-Eval pyrolysis results reveal lower values HI, usually nether to 100mgHC/gTOC, showing that the studied samples have type III kerogen and a low potential for oil generation. The Tmax values (varies between 319 and 443°C) and biomarker data obtained for these samples indicate a maturation ranging between immature and, eventually, mature. The palynofacies data indicate predominance of the Phytoclast group (>80%), with different degradation degrees and a modest contribution of Palynomorph group, especially sporomorphs, and the Amorphous Organic Matter (AOM) group. Solid bitumen was observed in some samples from the Montejunto and Brenha Formations. Determining the relative percentages of the kerogen groups allowed for the identification of seven intervals that established variations in the depositional environment. [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 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]

The unusual occurrence of calcretes and prominent organic matter in the Middle Jurassic (Lower Bathonian, Serra de Aire Formation) of the Lusitanian Basin of western Portugal (Western Iberian Margin) revealed a complex palimpsest exposure record, here interpreted as reflecting hydrological changes caused by phases of emergence and immersion. It serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions. The exposure-dominated facies association grades upwards into peritidal and lagoonal limestones, and the interval is assigned to the regressive peak of a Transgressive-Regressive Facies Cycle (2nd order) of the thick Middle Jurassic carbonate ramp succession. The Galinha Quarry, Fátima region, NE of Lisbon, a type section for this lowstand assemblage, exhibits varied calcretes, with black-clasts, interbedded with, and grading into: organic-rich marly/clayey seams and lenses, locally with carbonate nodules; carbonates with evaporite traces; microbial laminites; black-clast and fenestral limestones; some lithofacies are dolomitized. The palynofacies contains phytoclasts associated with less refractory, more prone to degradation components, which suggests natural combustion/pyrolysis (wild fires). The lowstand surface represents a low relief landscape with small depressions/ponds bordering a more distal marginal-littoral setting; the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating, very shallow water bodies and water table. Coeval climatic regime was a seasonally dry/wet one, with dry/semi-arid phases dominating over the sub-humid, as shown by the combined record of intense calcrete development, rhizogenic structures, microbial mats, brecciation, desiccation, evaporites and wild fire evidence. However, sea level rise caused changes to shallow, sea-water influenced restricted lagoonal-peritidal settings. Comparisons and differences with modern and ancient coast marginal carbonates are made to provide a guide to the variability in such lowstand deposystems in the stratigraphic record. [ABSTRACT FROM AUTHOR]

The study of the organic matter present in sedimentary rocks is fundamental for the characterization of the potential source rocks as well as to define the depositional paleoenvironments. Parameters of organic petrology and organic geochemistry, and their variations along sedimentary successions are essential tools to achieve these goals. Two borehole successions (Freixial-1 and Benfeito-1) from Arruda sub-basin (Lusitanian Basin), that comprise siliciclastic–carbonate deposits of Jurassic age, have been studied in order to characterize the organic matter and its vertical variability as well as its hydrocarbon potential. Palynofacies and geochemical data indicate both, marine (including zooclasts) and terrestrial organic matter where the phytoclasts predominated despite an important contribution of the amorphous organic matter (AOM). Different types of solid bitumen were observed. Most of the analyzed samples have total organic carbon content (TOC) lower than 1 wt.% and Hydrogen Index (HI) values lower than 100 mgHC/g TOC, revealing types III and IV kerogen. However, one set of samples exhibit TOC values higher than 1 wt.% and higher HI values depicting a type II kerogen. The biomarker data showed a dominance of n -alkanes with 15–30 carbon atoms having a unimodal distribution. Pristane/Phytane ratio varies between 0.04 and 1.84 indicating an alternation of oxic–anoxic conditions along the sequences. Typical terpane distributions are characterized by the presence of tricyclic and tetracyclic terpanes as well as pentacyclic terpanes (rare in carbonated samples from Freixial-1 borehole). The amount of 17α (H),22,29,30-trisnorhopane (Tm) usually exceeds the amount of 18α (H),22,29,30-trinorneohopane (Ts). The values of the ratio 22S/(22S + 22R) epimers of C32 homohopanes revealed that most samples reached equilibrium values. The 20S/(20S + 20R) and ββ/(αα + ββ) isomerization ratios in C29 sterane, calculated for the studied samples, range between 0.19–0.61 and 0.20–0.70, respectively, with several samples reaching the equilibrium values. The vitrinite reflectance values are higher than 0.5% indicating that the organic matter reached the oil generation window. According to the data obtained in this study, the Abadia, Montejunto, Cabaços and Brenha Formations can be considered potential source rocks of hydrocarbons (gas and/or oil) in this section of the Lusitanian Basin. [ABSTRACT FROM AUTHOR]

The main goal of this study was to quantitatively and qualitatively characterize the sedimentary organic matter (OM) and demonstrate the usefulness of geochemistry and palynofacies analysis for obtaining paleoenvironmental data for the Holocene in southernmost Brazil. The results indicate that during the time interval from 10,586 cal yr BP to the present, the study area housed a wetland characterized by different hydrologic regimes. The basal peaty deposits correspond to a phase influenced mainly by the groundwater table, whereas the upper deposits composed of silty organic mud indicate fluvial influence related to river overflow events. In a similar manner, the TOC (total organic carbon) and TS (total sulfur) contents are higher in the basal portion of the profile, decreasing toward the top. These findings could be related to granulometry alterations that are linked to hydrologic regimes or anthropogenic interference in the landscape dynamics. Anomalous TS content observed in one of the samples might be due to an external source and perhaps related to the presence of thermal springs in the region. These types of areas have potential as a modern reference that can be applied in the reconstruction of past analogous environments such as coal deposits associated with fluvial paleoenvironments. [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]