Luís Vítor Duarte

University of Coimbra | UC · Department of Earth Sciences

The goal of this study is to assess the spatial variability of the terrestrial gamma dose rate (TGDR) across the major lithostratigraphic units of the Lusitanian Basin. For this purpose, over 485 field measurements of the TGDR were carried out in the three reference sections with a total thickness of 232 m. The variability of the measured TGDR values compares with those obtained from aerial and ground surveys carried on in the same lithostratigraphic units outcropping along several thousands of square metres. Due to the high variability of TGDR, which implies a high variability of the radioisotopes content in the rocks, an extremely detailed, cost-demanding, sampling campaign would be needed towards a proper estimate of the geogenic radon potential. However, as the range of variation of the TGDR measured in the reference sections (tens of meters scale) is similar to that calculated in the surface of the same geological units (thousands of meters scale) this suggests that sampling along reference sections can be a suitable method for the estimation of the radiometric signature of sedimentary units and should be preferred over sampling along spatial grids. As the contents of the radioisotopes in sedimentary rocks are strongly controlled by lithology, a possible solution for a proper estimation of the geogenic radon risk potential would be the aggregation of data according to the bedrock properties, mainly lithology.

The Lusitanian Basin is located in central western Portugal and is filled mainly with marine Jurassic sediments. Here, the Lower Jurassic is particularly well developed and characterized by marl-limestone alternations. Dinoflagellate cysts are reliable palaeoecological indicators and the goal of this work is to describe the pre and post T-OAE dinoflagellate cyst assemblages. The Pliensbachian and Toarcian succession in the Lusitanian Basin is characterised by relatively low dinoflagellate cyst diversity; fifteen taxa were encountered. Only seven genera were recorded, these are Luehndea, Mancodinium, Mendicodinium, Nannoceratopsis, Scriniocassis, Sentusidinium and Valvaeodinium (Fig. 1). The dinoflagellate cyst diversity in the upper Pliensbachian of the Lusitanian Basin is relatively low. In terms of abundances, dinoflagellate cysts are moderately rare in the Amaltheus margaritatus ammonite biozone, but increased markedly within the Emaciaticeras emaciatum ammonite biozone. Both abundances and diversity increased in the earliest Toarcian Dactylioceras polymorphum ammonite biozone. Luehndea spinosa dominates the palynofloras at the uppermost Pliensbachian – lower Toarcian interval (upper Emaciaticeras emaciatum and Dactylioceras polymorphum ammonite biozones). These acmes may reflect optimal abiotic conditions, particularly temperature, oxygen levels and salinity, prior to the start of T-OAE. Above the Dactylioceras polymorphum ammonite biozone, overall dinoflagellate cyst abundances are markedly reduced due to the palaeoenvironmental perturbations caused by the T-OAE and the recovery from this event. At the base of Hildaites levisoni ammonite biozone, the Luehndea spinosa extinction is recorded together with a general disappearance episode in the dinoflagellate cysts assemblage (e.g. Nannoceratopsis spp.). These bioevents, probably, were caused by the palaeoenvironmental changes associated with the T-OAE. Only Mancodinium semitabulatum is consistently relatively common. The recovery of dinoflagellates after the T-OAE at the Lusitanian Basin was extremely slow and somewhat indistinct. The apparently unaffected dinoflagellate cyst associations of the high northerly latitudes and a slow recovery in southern Europe, for example in Portugal and Italy, appears to be a coherent trend.

Body size is a determinant key of how organisms interact with their environment as it constrains in important ways ecological and physiological traits and it can be modulated by environmental stressors. Body size reduction has been seen as an important response to climate warming and it has been suggested for multiple mass extinction events including the Pliensbachian - Toarcian crisis (Morten & Twitchett, 2007). This interval is characterized by palaeoenvironmental perturbations and their impact on marine biota, associated with rapid warming, anoxia, and the consequent deposition of organic-rich sediments. As a working hypothesis, we aim to assess the existence of a belemnite body size reduction across the Pliensbachian – Toarcian boundary considering different levels of organization (individuals, populations and communities). The ultimate hypothesis to test is the link between belemnites body size dynamics and the increasing seawater temperatures (Suan et al., 2008) related with the volcanic activity in the Karoo-Ferrar igneous province, recognized in the Lusitanian Basin as peaks in mercury concentration occurring during the Pliensbachian-Toarcian boundary and during the Toarcian Oceanic Anoxic Event (Percival et al., 2015). For this study, we focused on the Peniche section (Lusitanian Basin, Portugal), the Toarcian GSSP (Global Boundary Stratotype Section and Point) (Rocha et al., 2016). From the Emaciatum Zone (uppermost Pliensbachian) – Levisoni Zone (uppermost lower Toarcian) interval more than 450 complete belemnites rostra were collected. The geometric mean was calculated as a proxy for belemnites body size taking into account post-phragmocone length, height and width at the protoconch level. A statistically significant reduction in belemnites body size was recognized across the Pliensbachian-Toarcian boundary at the assemblage level (i.e. community level of organization). From the analysis of the different taxa recorded, it seems that adult specimens of Pseudohastites longiformis are driving the body size pattern observed. Multiple regression analysis, taking into account palaeotemperature (δ18O as a proxy), volcanic activity peaks (mercury concentration as a proxy) and/or perturbations of the carbon cycle (δ13C as a proxy), indicates that seawater temperature best explains the pattern in body size changes. However, the synergy with other related stressors cannot always be discarded

The Lower Jurassic of the Lusitanian Basin (Portugal) contains three well characterized organic-rich intervals: the Coimbra Formation (Unit F), Água de Ma- deiros Formation (Polvoeira Member) and Vale das Fontes Formation (Marly limestones with organic-rich facies Member). These units are dated from the Sinemurian–Pliensbachian and are regarded as potential hydrocarbon source rocks. These specific stratigraphic (source rock) intervals have not yet been identified in the offshore areas of the Portuguese margin, mostly due to the inadequate stratigraphic definition in the several wells drilled in the basin. In this work, we compare detailed gamma-ray profiles from 11 onshore outcrops and 7 offshore wells. Our objectives are: i) to recognise Lower Jurassic units and organic-rich intervals in offshore areas of the basin, ii) to delineate their lateral extension, and iii) to improve the overall stratigraphic definition of the Lower Jurassic in the Lusitanian Basin.

Lower and Middle Jurassic successions along the Western Portuguese coast contain several carbonated units that comprise a large lithological variation. A project is currently running to evaluate the geological factors that control the natural radiation background in the Portuguese territory. Included in this project, a gamma-ray survey was carried out in different carbonate lithofacies cropping out in the Figueira da Foz, São Pedro de Moel, and Peniche coastal areas. The results are expressed as total gamma field and K, U and Th concentrations. The lithofacies shown different frequency patterns in the three coastal sectors. The São Pedro de Moel coastal area shows the highest variability and, in all the sectors, the argillaceous lithologies and organic-rich facies increase the radiation background.

Lower Jurassic (Sinemurian–Pliensbachian) successions cropping out in onshore areas of the Lusitanian Basin provide detailed information of three well characterized organic-rich intervals: i) the Unit F from the Coimbra Formation, ii) the Polvoeira Member of the Água de Madeiros Formation, and the iii) Marly Limestones with Organic-rich Facies (MLOF) Member of the Vale das Fontes Formation. Despite decades of research, these source rocks have not yet been properly identified and characterized in terms of extension and thickness in the basin's offshore. This paper compares detailed gamma-ray (GR) profiles from onshore outcrops (Coimbra, Montemor-o-Velho, Figueira da Foz, Monte Real, São Pedro de Moel and Peniche regions) with seven offshore wells. Our objective is to recognise Lower Jurassic organic-rich intervals in offshore areas of the basin, highlighting their lateral extension and improving the overall stratigraphic definition of the Lower Jurassic in the Lusitanian Basin. GR field measurements indicate that the highest GR values and U contents are consistently observed in the organic-rich intervals, reaching up to 134 API and 9.0 ppm of U. In contrast, the lowest API and U contents were determined in dominantly calcareous units, ranging between 5-34 API and 0.1-1.4 ppm, respectively. Wireline gamma-ray logs show a good correspondence between field patterns and offshore well logs, recognizing the organic-rich intervals in offshore areas. The highest GR values are interpreted to be linked with the 2nd- and 3rd-order maximum flooding intervals previously recognised in the Sinemurian–Pliensbachian successions in the western Iberian margin. Detailed GR maps linked to maximum flooding intervals highlight the variation of the vertical and lateral distributions of the organic-rich units in offshore areas of the Lusitanian Basin.

Body size is a determinant key of how organisms interact with their environment as it constrains in important ways ecological and physiological traits and it can be modulated by environmental stressors. Body size reduction has been seen as an important response to climate warming and it has been suggested for multiple mass extinction events including the Pliensbachian-Toarcian (Pli-Toa) crisis. This interval is characterized by palaeoenvironmental perturbations, namely rapid warming, anoxia, and perturbations of the carbon cycle, and their impact on marine biota. These perturbations have been associated with volcanic activity in the Karoo-Ferrar igneous province. For this study, we focused on the Peniche section (Lusitanian Basin, Portugal), where the effects the T-OAE, namely anoxia, were not so dramatically felted, in contrast with NW European sections (e.g. Cleveland Basin). Mercury concentration peaks are recorded across the studied interval, alongside with increasing seawater temperatures, and interpreted as an effect of distal volcanic activity pulses. From the Emaciatum Zone (uppermost Pliensbachian)-Levisoni Zone (uppermost lower Toarcian), 930 belemnites rostra were collected. Post-phragmocone length was used as a proxy for belemnites body size. As a working hypothesis, we aim to assess the existence of a belemnite body size reduction across the Pli-Toa boundary at different levels of organization (individuals, populations and communities). The ultimate hypothesis to test is the link between belemnites body size dynamics and temperature related stressors. A statistically significant reduction in belemnites body size was recognized across the PliensbachianToarcian boundary at the assemblage level (i.e. community level of organization). From the analysis of the different taxa recorded, it seems that adult specimens of Pseudohastites longiformis are driving the body size pattern observed. Multiple regression analyses, taking into account paleotemperature (δ 18 O as a proxy), volcanic activity peaks (mercury concentration as a proxy) and/or perturbations of the carbon cycle (δ 13 C as a proxy), indicate that seawater temperature best explains the pattern in body size changes. However, the synergy with other related stressors cannot always be discarded.

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.

Body size is a determinant key of how organisms interact with their environment as it constrains in important ways ecological and physiological traits and it can be modulated by environmental stressors. Body size reduction has been seen as an important response to climate warming and it has been suggested for multiple mass extinction events including the Pliensbachian - Toarcian crisis (MORTEN & TWITCHETT 2009). This interval is characterized by palaeoenvironmental perturbations and their impact on marine biota, associated with rapid warming, anoxia, and the consequent deposition of organic-rich sediments. As a working hypothesis, we aim to assess the existence of a belemnite body size reduction across the Pliensbachian – Toarcian boundary considering different levels of organization (individuals, populations and communities). The ultimate hypothesis to test is the link between belemnites body size dynamics and the increasing seawater temperatures (SUAN et al. 2008) related with the volcanic activity in the Karoo-Ferrar igneous province, recognized in the Lusitanian Basin as peaks in mercury concentration occurring during the Pliensbachian-Toarcian boundary and during the Toarcian Oceanic Anoxic Event (PERCIVAL et al. 2015). For this study, we focused on the Peniche section (Lusitanian Basin, Portugal), the Toarcian GSSP (Global Boundary Stratotype Section and Point, ROCHA et al. 2016). From the Emaciatum Zone (uppermost Pliensbachian) - Levisoni Zone (uppermost lower Toarcian) interval more than 450 complete belemnites rostra were collected. The geometric mean was calculated as a proxy for belemnites body size taking into account post-phragmocone length, height and width at the protoconch level. A statistically significant reduction in belemnites body size was recognized across the Pliensbachian- Toarcian boundary. Regarding the uppermost Polymorphum - Levisoni zones interval, a dramatic decrease on belemnites abundance and diversity occurs, including a barren interval ranging from the base until the medium/upper part of Levisoni Zone. However, a body size increase seems to be recognized within Toarcian beds (uppermost Polymorphum - Levisoni zones), despite the reduced sample size. This body size changes were recognized in several organizational levels, such as community level, population and individual. Aiming to assess the mechanisms behind this body size dynamics, we performed a multiple regression analysis testing several models taking into account paleotemperature (δ18O as a proxy) and volcanic activity peaks (mercury concentration as a proxy). Increasing seawater temperatures seems to have been the cause of the trend observed. However, no relationship between body size and the concentration of mercury in the sediment could be established. This contribution was supported by the German Research Foundation (DFG; project number: 269895748; grant number: Ba 5148/1-1). This is a contribution to the DFG Research Unit FOR 2332 "Temperature-Related Stresses as a Unifying Principle in Ancient Extinctions (TERSANE).

A comprehensive investigation of the Early Jurassic stratigraphical palynology of the Lusitanian Basin in western Portugal was undertaken, with most emphasis placed on dinoflagellate cysts. A total of 214 samples from an upper Sinemurian to upper Toarcian composite section based on six successions were examined. The Sinemurian material examined was barren of dinoflagellate cysts; however, the Pliensbachian and Toarcian successions are characterised by relatively low diversities where Luehndea spinosa, Mancodinium semitabulatum, Mendicodinium microscabratum, Nannoceratopsis gracilis, Nannoceratopsis senex, and Scriniocassis priscus are relatively common and biostratigraphically significant. Luehndea spinosa dominates the lowermost Toarcian (Dactylioceras polymorphum ammonite Biozone), and is an index species. At the base of the Hildaites levisoni ammonite Biozone, the effects of the Toarcian-Oceanic Anoxic Event (T-OAE) caused Luehndea spinosa to become extinct. At the same time, dinoflagellate cyst abundance and diversity markedly decreased. After the T-OAE, during the middle and late Toarcian, phytoplankton recovery was prolonged and slow in the Lusitanian Basin. The Luehndea spinosa and Mendicodinium microscabratum dinoflagellate cyst biozones are defined, both of which are subdivided into two dinoflagellate cyst subbiozones.

Thermal maturity of late Pliensbachian-early Toarcian organic-rich sediments in the Grands Causses (Suèges section), Quercy (Caylus section) and Pyrenean (Pont de Suert section) basins was determined through multiple parameters, including Spore Coloration Index (SCI), hydroid random reflectance (HRr) and spectral fluorescence of Tasmanites algae (λmax). The main objective of this study is to test the effectiveness and make comparisons of organic matter thermal maturity in these three sections by different techniques and particularly hydroid reflectance. For the Suèges section SCI presented a value of 3.5–4.0. HRr ranges between 0.36% and 0.47%, which corresponds to 0.45%–0.52% VReq, and shows a good correlation with SCI values. Spectral fluorescence analysis presents a λmax of 560 nm for most samples. The fluorescence spectral maximum seems to be redshifted in comparison to other thermal maturity parameters. The Caylus section exhibited SCI of 3.5–4.0. HRr ranges between 0.32% and 0.50% corresponding to 0.42%–0.54% VReq. Spectral fluorescence analysis points out a λmax of 560 nm, displaying a good correlation with SCI. When Req values determined through SCI are compared with equivalent vitrinite reflectance values determined through λmax, a redshift of the fluorescence spectrum maximum is detected. For the Pont de Suert section SCI ranges between 8.0-8.5 and 8.5–9.0. HRr varies between 0.85% and 1.18% which corresponds to 0.76%–0.98% VReq. Even though there are lower values than those obtained by SCI, VReq is reliable and acceptable to determine the thermal evolution stage. Furthermore, HRr values also present a good correlation with SCI. These data indicate that the majority of the samples from the Suèges and Caylus sections are in the immature to early mature evolution stages and Pont de Suert section samples are in late mature to early overmature evolution stages for liquid hydrocarbons generation, supporting a very similar thermal evolution for the Grands Causses and Quercy basins and an entirely different thermal history for the Pyrenean Basin. This is in accordance with the similar tectonic and sedimentary context of the Quercy and Grands Causses basins. The Pont de Suert section, located near the collision front of the Pyrenees mountains, records a more complex sedimentary and tectonic history. In addition, this study presents the first reflectance data for Jurassic hydroids, which show a good correlation with other rank parameters.

Major changes in ostracod assemblages have been recorded in the Lower Jurassic of Western Tethys related to biotic crises of the Pliensbachian-Toarcian boundary and the Polymorphum-Levisoni boundary (Toarcian Oceanic Anoxic Event). The study is focused on the ostracods assemblages from Benzerka section (Traras Mountains, Algeria) and their comparison with sections from External Subbetic and Algarve Basin (South Iberian Palaeomargin). Three stratigraphic intervals coincident with the ammonite zones have been differentiated with important fluctuations in the composition of ostracod assemblages. In the ostracod assemblages from the Traras Mountains the turnover related to this benthic biotic crisis is shown by assemblages previous to the biotic crisis (uppermost Pliensbachian) mainly composed by families Healdiidae and Cytherellidae to assemblages just after the T-OAE (upper part of the Levisoni Zone) with assemblages dominated by families Protocytheridae and Polycopidae and the extinction of family Healdiidae (suborder Metacopina). The Toarcian Oceanic Anoxic Event (T-OAE) probably resulted in restricted conditions but a barren interval due to oxygen-depleted conditions in this setting is not recorded. In this context, the change of components of ostracod assemblages looks gradual. In the Southiberian Palaeomargin, represented by the External Subbetic the turnover of ostracods assemblages is also recorded but the families involved are different than in Traras Mountains. Therefore, different phases have been differentiated in the ostracod turnover occurring from Upper Pliensbachian (assemblages dominated by families Pontocyprididae, Healdiidae and Bairdiidae) to end of Lower Toarcian (assemblages dominated by family Cytherellidae and the extinction of family Healdiidae). In the Algarve Basin the families Healdiidae and Bairdiidae were dominant previously to the Toarcian Oceanic Anoxic Event. Differences in the composition of ostracod assemblages between Traras Mountains and External Subbetic may be related to the fragmentation of these palaeomargins related to early stages of rifting in the Western Tethys. Moreover, the incidence of oxygen-depleted conditions was higher in External Subbetic than in Traras Mountains where some ostracod genera survive during the biotic crisis.

A formal lithostratigraphic framework is proposed for the Lower Jurassic dolomitic-limestone succession of Lusitanian Basin, cropping out in the Coimbra-Penela region (western-central Portugal). In this proximal domain of the basin, the Coimbra Formation (Early to Late Sinemurian) and the S. Miguel Formation (Late Sinemurian to Early Pliensbachian) were defined and characterized in according with the normative imposed by the International Stratigraphic Guide. In turn, the Coimbra Formation is subdivided into two members: the Vila Seca Member, at the base, and the Casa do Sal Member, at the top. The proposed units locally reach a combined total thickness of ca. 110 m. The available biostratigraphic references of ammonites and of benthic fauna, by comparison with the profiles from the distal domain (S. Pedro de Moel and Peniche), allow the interpretation of an original regional correlative framework.

The uppermost Pliensbachian and lower Toarcian (Lower Jurassic) succession exposed at Peniche in the central part of the Lusitanian Basin, western Portugal, was examined for palynomorphs. The 45 samples span the Emaciaticeras emaciatum, Dactylioceras polymorphum and Hildaites levisoni ammonite biozones (ABs), and the succession includes the Global Stratotype Section and Point (GSSP) for the Toarcian Stage and the Toarcian Oceanic Anoxic Event (T-OAE). A low diversity dinoflagellate cyst flora, typical of the Sub-Boreal Realm, was recovered from the Emaciaticeras emaciatum and Dactylioceras polymorphum ABs. The dominant element is the cold water species Luehndea spinosa, which is an index for the Pliensbachian to earliest Toarcian, and is thought to have migrated from the more northerly Boreal Realm. Prior to the T-OAE, dinoflagellates thrived in the Lusitanian Basin, except during a brief warm period in the earliest Toarcian. Despite the latter, the recovery from this event was relatively rapid and was characterised by a return to relatively cool temperatures. The Hildaites levisoni AB at Peniche represents the T-OAE and the overlying strata, and is characterised by a profound reduction in dinoflagellate cyst relative abundances. This dinoflagellate cyst ‘blackout’, and the associated rise of prasinophytes, reflects significant environmental stress, such as marine anoxia, elevated temperatures and reduced salinity, with the former two probably being most important. The low proportions of dinoflagellate cysts following the T-OAE indicates a protracted recovery phase from the bottom and water column anoxia developed throughout the Lusitanian Basin.

The Lusitanian Basin is a marginal depocentre located in central western Portugal, and the basin fill is mainly Jurassic. The uppermost Pliensbachian and Toarcian succession comprises the Lemede and São Gião formations, characterized by marl-limestone alternations. The Cabo Carvoeiro Formation constitutes the Toarcian at Peniche. In the Lusitanian Basin, the T-OAE and a sudden rise in marine palaeotemperatures were confidently identified using carbon and oxygen isotopes (Hesselbo et al., 2007; Suan et al., 2008; Pittet et al., 2014). The aim of this work is to study the T-OAE in the Lusitanian Basin, in terms of the palynological response, especially of the marine palynoflora. The growth and distribution of dinoflagellates is influenced by several ecological factors, such as temperature, sunlight, nutrients, salinity, ocean currents, water depth and, thus, are reliable palaeoecological indicators. Three sections were sampled: Peniche (the Toarcian GSSP), Maria Pares and Vale das Fontes. In total, 103 samples were studied. The material spans the Emaciaticeras emaciatum (uppermost Pliensbachian), Dactylioceras polymorphum, Hildaites levisoni and Hildoceras bifrons ammonite biozones. Dinoflagellate cysts, acritarchs, prasinophytes, foraminiferal test linings and terrestrial palynomorphs were documented. A low diversity assemblage of dinoflagellate cysts, typical of the Lower Jurassic, was recorded. Prior to the T-OAE, in the Emaciaticeras emaciatum and Dactylioceras polymorphum ammonites biozones, dinoflagellates thrived throughout the Lusitanian Basin. This interval was dominated by the cool water dinoflagellate cyst Luehndea spinosa. The T-OAE is represented at the Hildaites levisoni ammonite biozone, and this event caused the extinction of Luehndea spinosa. During and following this perturbation, Mancodinium semitabulatum and Mendicodinium spp. were the only dinoflagellate cysts recorded. The T-OAE is characterised by a virtual ‘blackout’ of dinoflagellate cysts, which were largely replaced by opportunistic prasinophytes, such as Tasmanites spp. and clumps of Halosphaeropsis liassica.

During the Callovian, dinoflagellate cysts underwent a significant diversification, where many genera and species emerged. The main aim of this work is to document the Callovian dinoflagellate cyst record in the Cabo Mondego section, Lusitanian Basin, Portugal, in order to contribute to the biostratigraphy and palaeobiology/palaeoecology of this area, and to compare with coeval successions. The Lusitanian Basin is a marginal depocentre located in central western Portugal, and the basin fill is mainly Jurassic. The Cabo Mondego section, located in the western Lusitanian Basin, comprises a well exposed upper Toarcian to Callovian succession of marine marl and limestone interbeds of the Cabo Mondego Formation. This section was sampled for palynomorphs and here we present preliminary dinoflagellate cyst data from the uppermost Bathonian and Callovian. In general, the dinoflagellate cysts were abundant and relatively well preserved. The most significant taxa are Adnatosphaeridium caulleryi, Batiacasphaera sp., Chytroeisphaeridia chytroeides, Compositosphaeridium polonicum, Ctenidodinium spp., Ellipsoidictyum spp., Endoscrinium acroferum, Gonyaulacysta spp., Impletosphaeridium sp., Korystocysta spp., Meiourogonyaulax spp., Pareodinia ceratophora, Sentusidinium spp., Systematophora spp., Tubotuberella dangeardii and Wanaea acollaris. This record compare well with Bathonian and Callovian assemblages elsewhere in Europe.

The elemental geochemistry of ancient shallow-marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways. Complex multi-parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the Lusitanian Basin (Ericeira, Portugal) are presented and interpreted. The section comprises marly, carbonate, and sandstone-rich coastal-marine deposits of early Albian to early Cenomanian age. Principal component analysis of bulk elemental abundance (Ca, Mg, Sr, Fe, and Mn) lead to define four geochemical clusters based on common elemental attributes. Siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration, but still preserve information on paleoshoreline position. Mixed carbonate-siliciclastics and limestone facies bear evidence for relative sea-level position and relevant paleoclimatic information in their elemental record. Accordingly, mid-Albian mixed carbonate-siliciclastic deposits present variable degrees of continental influx. Specifically, a sharp increase of Fe and Mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands. The progressive transition towards more marine conditions is accompanied by higher Ca and Sr content and represented by limestone facies corresponding to a higher sea-level position during late Albian to early Cenomanian times. Moreover, this facies records a trend towards warmer and more arid conditions. Early diagenetic stabilization and /or dissolution of aragonite into low-Mg calcite can account for major elemental variations, including higher Sr content strongly coupled with Ca content, along with lower Mg, Fe and Mn concentrations. Data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits, when combined with conventional sedimentology and thin section petrography, allow for elaborate conclusions on their depositional environment and diagenetic pathways. Cored wells and facies-specific reservoir properties can be addressed by these methodologies, able to detect and quantify changes in patterns. Both industry and academy can therefore benefit from approaching such a complex interplay.

The Early Toarcian (Early Jurassic) global marine mass extinction is associated with one of the most important environmental perturbations of the Mesozoic, the Toarcian Oceanic Anoxic Event (T-OAE), usually interpreted as a global oceanic anoxic event. In the Lusitanian Basin (LB) — one of the reference areas for the study of the T-OAE — despite an elevated extinction rate among marine invertebrates, the anoxia hypothesis has been discarded based on geochemical and isotopic data. In the Fonte Coberta section the T-OAE is characterised by the extinction of the previously well-represented brachiopod taxa, a decreased abundance of ammonoids, and the establishment of a well-developed endobenthic community mainly composed by Thalassinoides tracemaker, which indicates favourable environmental parameters at least for this community. Thus, the palaeoenvironmental changes associated with the T-OAE event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance; yet they exert a major effect on the behaviour and palaeobiology of tracemakers. The Thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval, tied to behavioural adaptations to nutrient availability and/or substrate firmness. Smaller burrow diameters are registered at the base of the T-OAE, and then an increase is observed during the T-OAE. This could be associated with a palaeobiological response (Lilliput effect) to palaeoecological changes at the beginning of the T-OAE, followed by a progressive change to pre-event environmental parameters. This study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer, as reflected by variations in significant features of Thalassinoides architecture.

Summary of raw data collected

Seeking to identify the oils groups accumulated in the Jurassic of the Lusitanian Basin and the source rock of each group, stable carbon isotope and gas chromatography coupled with mass spectrometry analyses were performed in oils and oil shows from the main discoveries, and on representative organic extracts from the potential source rocks, selected based on previous works and data obtained by total organic carbon and Rock-Eval pyrolysis techniques. The geochemical comparison between the oils, and between the oils and the organic extracts, allowed the identification of three oil groups, whose differences depend on their source rocks: oils generated at the Coimbra Formation (lower-upper Sinemurian) and accumulated in the same formation and in the Água de Madeiros Formation (upper Sinemurian-lower Pliensbachian) in the northern sector of the basin; oils originated from the top of the Cabaços Formation (middle Oxfordian) and accumulated in the Montejunto (middle-upper Oxfordian) and Abadia (lower-upper Kimmeridgian) formations, in the central and southern sectors of the basin; and oil generated and accumulated at the base of the Montejunto Formation in the central sector of the basin. The geochemical correlations between the oils and the organic extracts allowed the identification of the source rocks of the different accumulations of the Jurassic succession, allowing further guidance to the petroleum exploration in the Lusitanian Basin.

A macroinvertebrate assemblage has been studied from the Thin Nodular Limestones Member (TNL) of the Fonte Coberta section (Lusitanian Basin, Portugal), giving special attention to its trace fossils. The assemblage was studied to analyse the influence of the Toarcian Oceanic Anoxic Event (T-OAE) on the macroinvertebrate community. The TNL consists of thin alternations of marl/limestone and nodular limestone beds, showing clear differentiations from bottom to top. Integrative analysis of the macrofossil assemblage for the studied interval, conducted for the first time in the Lusitanian Basin, reveals three major features: (1) abundant trace fossils with dominance or near exclusiveness of Thalassinoides, and a local record of Spongeliomorpha; (2) scarcity, but not extinction, of ammonoids; and (3) the absence of previously abundant brachiopods. The findings reveal a selective incidence of the T-OAE on the macrobenthic community, with a major influence (extinction) of brachiopods, severe changes (diminution in abundance and diversity) on ammonoids and a minor effect on macrobenthic tracemakers. A complex relationship between different palaeoenvironmental conditions during the T-OAE can be interpreted, discarding anoxic conditions in the seafloor, although low oxygen conditions in the water column are a possibility. The increase in seawater temperature and availability of nutrients on the seafloor would have played an influential role.

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth's oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO 2) leading to termination of an OAE after B1 Myr. Wildfire is highly responsive to changes in pO 2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained B800 kyr enhancement of fire-activity beginning B1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted pO 2 variations, and we argue this was primarily driven by increased pO 2. Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising pO 2 may have aided in terminating the T-OAE.

A aula de campo representa um tipo de estratégia não-formal com grande e comprovada importância em Ciências Naturais, podendo-se aplicar na exploração de múltiplas atividades práticas e experimentais com conteúdos paleontológicos, relacionados com os programas dos ensinos Básico e Secundário. Todavia, o contexto atual destes graus de ensino carece de promover esta estratégia de modo satisfatório, faltando situações exemplo relacionadas com a Geologia de Portugal, em que existam materiais didáticos preparados adequadamente e à disposição do professor. No presente estudo é proposta uma ficha de atividades bastante exaustiva, após validação por especialistas, dizendo respeito à praia da Leirosa, situada num troço de litoral a sul da Figueira da Foz. Nesta ficha de campo são explorados conceitos relacionados com os processos de fossilização, sobretudo processos biostratonómicos ligados à dinâmica sedimentar numa praia arenosa e modelada pela dinâmica sedimentar, integrando-os com outros aspetos intrínsecos à evolução holocénica do litoral.

The Peniche Peninsula shows the most continuous carbonate sedimentary succession of the Jurassic in Portugal. In this paper, supported by several important scientific arguments from the different domains of Sedimentary Geology, we highlight this locality as a focal point to understand the Early Jurassic time interval. Among several other themes we emphasize the definition of the Toarcian GSSP, the discussion around the Early Toarcian oceanic anoxic event and the organic-rich deposition occurred in the Sinemurian- Pliensbachian of the Peniche Peninsula section. These key geological themes have been the focus of significant educational/scientific outreach, involving Geology promotion activities directed towards different audiences, on a local and international scale.

A formal lithostratigraphic framework is proposed for the Lower Jurassic dolomitic-limestone succession of Lusitanian Basin, cropping out in the Coimbra-Penela region (western-central Portugal). In this proximal domain of the basin, the Coimbra Formation (Early to Late Sinemurian) and the S. Miguel Formation (Late Sinemurian to Early Pliensbachian) were defined and characterized in according with the normative imposed by the International Stratigraphic Guide. In turn, the Coimbra Formation is subdivided into two members: the Vila Seca Member, at the base, and the Casa do Sal Member, at the top. The proposed units locally reach a combined total thickness of ca. 110 m. The available biostratigraphic references of ammonites and of benthic fauna, by comparison with the profiles from the distal domain (S. Pedro de Moel and Peniche), allow the interpretation of an original regional correlative framework. Keywords: Coimbra Formation, S. Miguel Formation, lithostratigraphy, Sinemurian-Early Pliensbachian, Lusitanian Basin.

Dactylioceras (Eodactylites). The Pliensbachian/ Toarcian boundary (PLB/TOA) is contained in a continuous section forming over 450m of carbonate-rich sediments. Tectonics, syn-sedimentary disturbance, metamorphism or significant diagenesis do not significantly affect this area. At the PLB/TOA, no vertical facies changes, stratigraphical gaps or hiatuses have been recorded. The base of the Toarcian Stage is marked in the bed 15e by the first occurrence of D. (E.) simplex, co-occurring with D. (E.) pseudocommune and D. (E.) 460 Articles

Available information on the production and emanation of radon gas in sedimentary rocks is scarce. In the present work, 121 samples of siliciclastics and carbonates of Lower– Middle Jurassic to Lower Cretaceous of the Lusitanian Basin (western Portugal) were selected. Sandstones, lutites, dolo- stones, limestones and marls are included in the sample set. These rocks are associated with different facies deposited on different depositional environments, from fluvial to deeper marine environments. In each sample, the activity of 226Ra, the radon per unit mass activity as well as its emanation coefficient were determined. Variability is significant for all 3 parameters, ranging from 4.7 to 98 Bq · kg−1 in the case of 226Ra, 0.3 to 18.6 Bq · kg−1 for emanated radon and 0.01–0.47 for the coefficient of emanation. The radon source is lowest in the dolostones and the limestones and higher in the lutites. Marls and sandstones fall in the intermediate part of the spectrum. The same trend was detected for radon emanation, with very low values in the carbonates. The emanation coeficient is higher in marls and sandstones. Density measurements are ongoing to allow a precise cal- culation of the radon production rate of these sedimentary rocks.

Vale das Fontes were sampled. The material spans the Dactylioceras polymorphum, Hildaites levisoni and Hildoceras bifrons ammonite biozones. The taxa encountered were Mancodinium semitabulatum, Mendicodinium microscabratum, Mendicodinium spinosum subsp. spinosum, Mendicodinium sp., Nannoceratopsis ambonis, Nannoceratopsis gracilis, Nannoceratopsis senex and Sriniocassis weberi. The samples produced relatively low diversity dinoflagellate cyst floras which are typical of those from coeval European successions. The most abundant species is Luehndea spinosa. Dinoflagellate cysts typically dominate throughout the Dactylioceras polymorphum ammonite biozone; they significantly decreased in relative proportions after the T-OAE in the overlying Hildaites levisoni and Hildoceras bifrons ammonite biozones. The T-OAE in the Lusitanian Basin is characterised by a sudden decline in dinoflagellate cyst abundance and diversity. During and following the T-OAE, Mancodinium semitabulatum and Mendicodinium spp. were the only dinoflagellate cysts recorded. In the Lusitanian Basin, the T-OAE caused the extinction of Luehndea spinosa in the lowermost Hildaites levisoni ammonite biozone. This bioevent and the general 'blackout' of dinoflagellate cysts during the T-OAE, and their low recovery following the event, are indicative that dinoflagellate populations were responding to a major palaeoenvironmental change.

Lower Toarcian sections from Lusitanian Basin were sampled. The material spans the Dactylioceras polymorphum, Hildaites levisoni and Hildoceras bifrons ammonite biozones. The taxa encountered were Mancodinium semitabulatum, Mendicodinium microscabratum, Mendicodinium spinosum subsp. spinosum, Mendicodinium sp., Nannoceratopsis ambonis, Nannoceratopsis gracilis, Nannoceratopsis senex and Sriniocassis weberi. The samples produced relatively low diversity dinoflagellate cyst floras which are typical of those from coeval European successions. The most abundant species is Luehndea spinosa. Dinoflagellate cysts typically dominate throughout the Dactylioceras polymorphum ammonite biozone; they significantly decreased in relative proportions after the T-OAE in the overlying Hildaites levisoni and Hildoceras bifrons ammonite biozones. The T-OAE in the Lusitanian Basin is characterised by a sudden decline in dinoflagellate cyst abundance and diversity. During and following the T-OAE, Mancodinium semitabulatum and Mendicodinium spp. were the only dinoflagellate cysts recorded. In the Lusitanian Basin, the T-OAE caused the extinction of Luehndea spinosa in the lowermost Hildaites levisoni ammonite biozone. This bioevent and the general 'blackout' of dinoflagellate cysts during the T-OAE, and their low recovery following the event, are indicative that dinoflagellate populations were responding to a major palaeoenvironmental change.

Due to the multiple controlling factors involved, it is a challenging task to identify and quantify the processes influencing the distribution and heterogeneity of marine organic-rich rocks. To improve our understanding of these deposits, we model their burial history and stratigraphic evolution as well as processes linked to marine organic matter history throughout the Lower Jurassic in of the Northern Lusitanian Basin (Western Iberian Margin). This 15 Ma-long interval is modelled using 100-kyr time steps to simulate lithologies and organic matter heterogeneity as layers with a thickness of 2 to 5 m, depending on the sedimentation rate in the basin. The model is calibrated by well and outcrop data which provide structural and biostratigraphic constraints, as well as information on the depositional facies and geochemistry of the sediments. The results show that the presence of organic-rich intervals is linked to first-order variations in the basin geometry and sedimentation rates. Without considering any variation of primary productivity or oxygen content in surface sea-waters, the parameters of basin geometry and sedimentation rate are sufficient to predict the main characteristics of source rocks, i.e. their occurrence, thickness and mineralogy at the basin-scale. However, to fit the measured organic carbon contents, we need to take account of other parameters such as variations of primary productivity or changes in dissolved oxygen concentration. This article is protected by copyright. All rights reserved.

The nautiloids assigned to the genera Cenoceras, Ophionautilus and Digonioceras of the Universidad Complutense de Madrid and the Instituto Geológico y Minero de España, Spain, and the Universidade de Coimbra and the Instituto Geológico e Mineiro de Portugal, Portugal, obtained from the Toarcian of the Iberian Peninsula have been studied and classified. As a result, new representatives of the species Cenoceras fontannesi, C. semistriatum, C. robustum, C. jourdani, C. astacoides, C. toarcense, C. ciryi, C.? beirense, Ophionautilus sp., Digonioceras sp. 1 and D. sp. 2 have been identified and described. Additionally, the holotype of C. fontannesi has been refigured, and the neotype of C.? beirense has been designated and figured. Although some of these species have already been cited in the literature, most of them have never been previously clearly described or illustrated, and their stratigraphic distributions have not been determined accurately for this region. Therefore, the present work, joined to that recently presented by the same authors on the new genus Ligeiceras, constitutes a notable advance to classify and to group these scarcely-known Toarcian cephalopods in South-western Europe. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

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.

After the palaeoecological study based on foraminiferal assemblages from the Peniche section, belonging to uppermost Pliensbachian-lower Toarcian interval, this work aims to study the impact of the Toarcian Oceanic Anoxic Event on foraminifera test-sizes. Opportunistic forms (Reinholdella and Eoguttulina) usually record lower values in terms of test dimension in contrast with the specialist forms (Marginulina and Astacolus), specially during Levisoni Zone. Reinholdella proliferation in the fine fraction during the lower part of Levisoni Zone is a response to the stressing environmental conditions due to the Toarcian Oceanic Anoxic Event known as the Lilliput effect.

Abstract Dolomitization is the most significant syndepositional and diagenetic process within the early Lower Jurassic shallow-marine carbonate succession cropping out in the eastern part of the Lusitanian Basin (Portugal). In this proximal domain, the Coimbra Formation (lower Sinemurian) overlies a Hettangian muddy-evaporitic complex and is composed of several dolomitic facies types, with few thick sandy-argillaceous/shale interbeds. New and detailed sedimentological field analytical work coupled with sequential analysis, allow defining a coastal/peritidal depositional system, which includes environments ranging from tidal flat-protected lagoon to relatively higher-energy, more open-marine influenced (shoal) conditions, for the Coimbra Formation. Field observations show that a first phase of laterally continuous stratabound dolomitization (the subject of this study) is crosscut by a second phase of fracture-related dolomitization (sometimes with associated dedolomitization). Based on petrographic evidence, carbon/oxygen stable isotope signatures and stratigraphic distribution, three types of penecontemporaneous dolomite were differentiated and interpreted: tidal flat dolomite, seepage reflux matrix dolomite and burrow dolomite. The δ13C and δ18O records of most dolomites fall within the range of expected values for early Jurassic seawater, supporting the inference that this was the fluid responsible for dolomitization. The positive covariation between δ18O and δ13C may indicate diagenetic alterations or multistage dolomitization, or a dolomitization by mixed solutions. The low values of δ18O are inconsistent with a strictly evaporitic hypersaline sabkha-environment. Furthermore, no massive evaporite deposits are associated with the Coimbra Formation. Considering all the faciological and sedimentological aspects of this unit, the most appropriate model to explain a pervasive syndepositional (or early diagenetic) dolomitization is the “penesaline-type” model, in the sense of a semi-restricted carbonate platform, under semiarid and slightly hypersaline conditions. During relative sea-level rising periods, the more open coastal/peritidal system would allow free water-exchange between the more proximal environments and the open sea. Under these conditions, stronger tides/storm waves provide the water recharge for the tidal flat, subsequent fluid concentration (by evaporation) and formation of fine dolomite crusts at the flat surface, with possible microbial/bacterial associated activity. Along the lower intertidal and shallow-subtidal zones, ichnofossil burrow dolomitization may occur. During the relative sea-level drop periods, the development of subtidal sand-shoals limited seawater exchange between the ocean and the lagoon, with the latter becoming a penesaline environment. Hypersaline to mesohaline brines reflux would occur, favoring the formation of shallower dolomitized horizons, controlled by base-level high-frequency fluctuations. The underlying sandy-argillaceous/shale bodies operated as aquitards, converting the downward circulation into a stratification-parallel reflux. Hardground and subaqueous erosive surfaces of previous cycles can have acted as barriers to penetration of fluids into greater depth and/or facilitated a lateral circulation, both leading to massive-stratiform dolomitization. It is likely that all these mechanisms were working in parallel, simultaneously or alternately.

This is the first ecostratigraphic and palaeoecological analysis of the benthic foraminiferal assemblages, defined as morphogroups, in the Pliensbachian–Toarcian transition and the Toarcian Oceanic Anoxic Event (T-OAE) of the Peniche section, the Toarcian Global Boundary Stratotype Section and Point. Foraminiferal assemblages from the uppermost Pliensbachian (Emaciatum Zone) reveal the presence of a stable benthic environment, with good oxygen and availability of trophic resources, as evidenced by the high diversity of specialists. The Pliensbachian–Toarcian transition reveals high foraminifera abundance, mainly specialists, although it is considered a slightly condensed interval. The base of the Levisoni Zone shows dramatic changes in life-style of foraminifera (increase of epifauna and potentially deep infauna), an increase in opportunistic forms, and a decrease in diversity. These changes suggest unfavourable conditions, related to food availability diminution and depleted oxygenation, corresponding to the beginning of the δ13C negative excursion. Palaeoenvironmental conditions become severe in the lower to middle Levisoni Zone, where there is a barren interval for foraminifera, coincident with the highest values of total organic carbon. After this interval, foraminiferal assemblages experienced a recovery with increasing diversity and occurrence of specialists, consistent with a well oxygenated environment and good food availability. These changes observed in benthic foraminiferal fauna from the Peniche section through the uppermost Pliensbachian–Lower Toarcian are comparable to what was reported previously on ostracods, brachiopods and calcareous nannofossils. Foraminiferal assemblages from Peniche section are comparable to other Tethyan (Spain, Italy, North Africa) and NW European sections (England) from the same stratigraphic interval, with the suborder Lagenina dominating the assemblages.

Late Toarcian–Aalenian brachiopod assemblages recorded in different basins located in and around Iberia present a pattern of spatial and temporal distribution which enables two palaeobiogeographic biochoremas to be differentiated: the Iberian-Atlantic District (IAD), which includes the Lusitanian Basin, Asturias and the Basque- Cantabrian Basin, on one hand, and the Iberian-Mediterranean District (IMD); the latter basically comprises the Iberian Range and the Tortosa Platform of the Catalonian Basin. Changes in the composition of the assemblages throughout the stratigraphical interval studied have enabled three main stages characterizing each palaeobiochorema to be recognized. The first two assemblages reflect gradual individualization and isolation, with frequent endemisms. These two stages correspond to the IAD1, IAD2, IMD1 and to the IMD2 assemblages respectively. As fromthe Pseudoradiosa Chronozone, and during the Aalensis and Opalinum chronozones, an increase in communication between the two districts can be observed, as well as between these and other remote areas. This stage is represented by the IAD3 and the IMD3 assemblages. Some of the brachiopods colonizing the districts are widely dispersed due to their capacity for expansion: they have been found in other Tethysian basins. Other species are exclusive to the district basins and appear to have originated in the areas close to them. For the latter species the existence of two different “evolutionary factories” is proposed: one that supplies species to the IAD, mainly from generic stocks as Neozeilleria, Soaresirhynchia or Praemonticlarella; and another for the species reaching the basins of the IMD, clearly shared by other European and North African basins. The Atlantic “evolutionary factory” remains active until the Aalenian and part of the Early Bajocian, while the Mediterranean is diluted since the Aalenian.

The Lower Jurassic carbonate series of the Lusitanian Basin (Portugal), due to their remarkable exposure and high quality outcrops, are currently regarded as a pivotal point to the comprehension of the less-known offshore basins located along the Atlantic Margin. This study presents a detailed sedimentological and biostratigraphical framework and the carbon and oxygen isotopic record of one of the main organic-rich intervals of the Lusitanian Basin, the marly limestones with organic-rich facies member of the Vale das Fontes Formation (Pliensbachian). We report the occurrence of secular δ¹³C trend of the Lusitanian Basin concordant with the (second-order) Pliensbachian transgressive–regressive facies cycle. An overall increase in carbon isotopic record with transgression, reaching its maximum just above the maximum flooding interval and enhanced organic matter preservation is also observed. When compared with the defined third-order sequences, a transient δ¹³C increase during the onset of transgression is recognizable. Higher frequency variations in the carbon isotopic record can possibly be traced along the offshore studied sections and are interpreted to be the reflections of local controls which may eventually outpace the regional variation.

This study shows preliminary data from gamma-ray spectrometry measurements (total count, K, Th and U concentrations) performed in the Jurassic basal units cropping out in the Lusitanian Basin (Portugal), namely in the Pereiros and Coimbra formations. The study was developed in the northern sector of the basin, involving reference stratigraphic sections in the Castelo Viegas, Lamas, Vila Seca, Penela and Cabanas-Brenha regions. Preliminary results clearly demonstrate differentiation of the spectral range between the two units, with the Pereiros formation, due the mixed and complex sedimentary and lithological character (sandstones to dolostones), to show spectrometric values with larger variability as evidenced (average values) in sandstones (369 cps); presenting the maximum values of K (6.2%), U (8.6 ppm) and Th (25.6 ppm)), lutites (328 cps), sandy dolostones (288 cps) and micritic dolostones (147 cps). Dolostones and dolomitic limestones of Coimbra formation present a decreasing vertical trend in the total count of gamma spectrometry, showing in the eastern part of the basin an average value of 126 cps and 96 cps in the western region.

This study shows preliminary data from gamma-ray spectrometry measurements (total count, K, Th and U concentrations) performed in the Jurassic basal units cropping out in the Lusitanian Basin (Portugal), namely in the Pereiros and Coimbra formations. The study was developed in the northern sector of the basin, involving reference stratigraphic sections in the Castelo Viegas, Lamas, Vila Seca, Penela and Cabanas-Brenha regions. Preliminary results clearly demonstrate differentiation of the spectral range between the two units, with the Pereiros formation, due the mixed and complex sedimentary and lithological character (sandstones to dolostones), to show spectrometric values with larger variability as evidenced (average values) in sandstones (369 cps); presenting the maximum values of K (6.2%), U (8.6 ppm) and Th (25.6 ppm)), lutites (328 cps), sandy dolostones (288 cps) and micritic dolostones (147 cps). Dolostones and dolomitic limestones of Coimbra formation present a decreasing vertical trend in the total count of gamma spectrometry, showing in the eastern part of the basin an average value of 126 cps and 96 cps in the western region.

Neste trabalho apresenta-se um estudo de alta resolução estratigráfica da matéria orgânica registada na sucessão margo-calcária do Toarciano inferior (base da Formação de S.Gião) do perfil de Alcabideque (Bacia Lusitânica), tendo como objetivo uma interpretação paleoambiental entre as cronozonas Polymorphum e Levisoni. Suportado na análise do carbono orgânico total (COT), enxofre (S), resíduo insolúvel (RI) e biomarcadores (n-alcanos, terpanos e esteranos) de 14 amostras de níveis margosos contidos no referido intervalo, a série estratigráfica apresenta valores de COT abaixo de 0,5% e máximo de S de 0,36%. Os valores máximos destes dois componentes geoquímicos são observados no topo da Zona Polymorphum, associados a um aumento do índice de gamacerano, o que sugere uma maior influência marinha da matéria orgânica. A base da Zona Levisoni, marcada no setor norte da Bacia Lusitânica por uma sedimentação fortemente argilosa (Margas Chocolate), mostra um aumento prenunciado dos valores de RI, n-alcano C27, terpano tríciclico C20, terpano tetracíclico C24 e esterano regular C29, o que indicia um ambiente marinho com forte influência continental. This work presents a high-resolution stratigraphic study of organic matter recorded in marly-limestone succession of lower Toarcian (base of S.Gião Formation) of Alcabideque section (Lusitanian Basin), having as objective a paleoenvironmental interpretation between Polymorphum and Levisoni chronozones. Supported on the analysis of total organic carbon (TOC), sulfur (S), insoluble residue (IR) and biomarkers (n-alkanes, terpanes and steranes) of 14 marly samples contained in the mentioned interval, the stratigraphic series present TOC and S values below 0.5 wt.% and 0.36 wt.%, respectively . The maximum values of these two geochemical components were observed at the top of Polymorphum Zone associated with an increase of gammacerane index, suggesting a greater marine influence of organic matter. The base of Levisoni Zone, marked in the northern sector of the Lusitanian Basin by a strongly argillaceous sedimentation (Chocolate Marls), reveals a pronounced increase of IR value, n-alkane C27, C20 tricyclic terpane, C24 tetracyclic terpane and C29 sterane, which indicates a marine environment with strong continental influence.

Neste trabalho apresenta-se um estudo de alta resolução estratigráfica da matéria orgânica registada na sucessão margo-calcária do Pliensbaquiano terminal – Toarciano inferior do perfil de Rodiles (Formação de Rodiles, Bacia das Astúrias), suportado na análise geoquímica orgânica (carbono orgânico total (COT) e enxofre (S)) e palinofácies (análise de componentes orgânicos particulados) de 15 amostras de níveis margosos contidos no referido intervalo. Numa série estratigráfica de clara natureza marinha, os resultados obtidos confirmam não só os elevados valores de COT (acima de 2%), já anteriormente referenciados para o limite entre as zonas Tenuicostatum – Serpentium, facto que é acompanhado por um incremento em S (máximo de 3,59%), como evidenciam valores de COT acima de 1% para a Zona Spinatum. O querogénio é dominado em toda a sucessão por fitoclastos, com exceção dos níveis mais ricos em COT, onde existe um claro incremento de matéria orgânica amorfa (MOA). Uma análise mais detalhada desta MOA mostra, à semelhança dos fitoclastos, uma proveniência continental, cuja sedimentação terá sido favorecida por uma diminuição do oxigénio disponível no ambiente deposicional. This work presents a high-resolution stratigraphic study of organic matter recorded in marly-limestone succession of upper Pliensbachian - lower Toarcian from Rodiles section (Rodiles Formation, Asturian Basin), supported by organic geochemistry analysis (total organic carbon (TOC) and sulfur (S)) and palynofacies (analysis of particulate organic compounds) in 15 samples of marly levels. On a stratigraphic series of a clear marine origin, the results confirm not only high values of TOC (above 2 wt.%), previously referenced for the boundary between the Tenuicostatum – Serpentium zones, a fact which is accompanied by an increase in S (maximum of 3.59%), as show for the top of the Spinatum Zone values of TOC above 1%. Across the succession the kerogen is dominated by phytoclasts, with the exception to the richest in TOC levels where there is a clear increase of amorphous organic matter (AOM). A more detailed analysis of this AOM shows, akin to the phytoclasts, a continental provenance, in which sedimentation has been favored by a decrease in the availability of oxygen in the depositional environment.

The Pliensbachian-Toarcian (Pli-Toa) transition and the Toarcian Oceanic Anoxic Event (T-OAE) are two global episodes known by its palaeoenvironmental perturbations and their impact on marine biota. This work aims to contribute to the study of these two episodes in the Peniche section, where is defined the Toarcian Global Boundary Stratotype Section and Point (Rocha et al., 2013). The ecostratigraphic and palaeoecologic analysis of the benthic foraminiferal assemblages, through the definition of morphogroups in 39 marly samples, has allowed the interpretation of the Pli-Toa transition and the T-OAE biotic crisis evolution and the recovery of foraminiferal assemblages in the sea-bottom after this latter in the Lusitanian Basin. The foraminiferal assemblages of the uppermost Pliensbachian (Emaciatum Zone) reveals the presence of a stable benthic environment, with good oxygen and nutrient availability, as evidenced by the high diversity of K-strategists. The Pli-Toa transition reveals high foraminifera abundance once it’s considered a slightly condensed interval. The base of the Levisoni Zone shows dramatic changes in foraminifera’s life style (increase of the epifauna and potentially deep infauna), an increase in opportunistic forms and a diversity decrease. These changes suggest a nutrient availability and oxygenation degree diminution, which corresponds to the beginning of the δ13Ccarb negative excursion (Hesselbo et al., 2007). Palaeoenvironmental conditions become severe in lower to middle Levisoni Zone where there is a record of a barren interval for foraminifera, coincident with the highest values of Total Organic Carbon (Hesselbo et al., 2007). After this interval, foraminiferal fauna records a recovery with assemblages consistent with a well oxygenated environment and good nutrient availability. These changes in benthic foraminifera record through the uppermost Pliensbachian – lower Toarcian are comparable to what happens with other microfauna and macrofauna groups (ostracods, brachiopoda, calcareous nannofossils) already studied by other authors in the Peniche section (e.g. Pinto et al., 2006, Mattioli et al., 2008; Comas-Rengifo et al., 2015). Foraminiferal fauna from Peniche section is comparable to other tethyan sections (Spain, North Africa and United Kingdom) from the same stratigraphic interval, with the suborder Lagenina dominating the assemblages (eg. Herrero, 2006; Hylton, 2000; Reolid et al., 2014; Herrero & Ramírez, 2013; Reolid, 2014).

The Lower Jurassic in Lusitanian Basin is characterized by marl-limestone alternations, with some very organic-rich intervals. One of these intervals is recorded in the Upper Sinemurian–lowermost Pliensbachian, corresponding to the Água de Madeiros Formation. Based on 49 horizons with relevant organic content, in this work a multidisciplinary analysis of the organic-rich facies, supported by detailed macroscopy, existing total organic carbon data and major element geochemistry obtained by x-ray fluorescence is presented. In this work are defined four main organic-rich facies, which are mainly distinguished by the type of lamination and by TOC, CaO, SiO2 and Al2O3 contents. The strong positive correlation between these last oxides is demonstrative of a significant siliciclastic phase, dominated by clay minerals. The MgO is practically constant in great majority of the studied samples, with values below 2%, which corresponds to a very low dolomite expression.

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 strtigraphic development at lowstand surfaces in ther 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 Pliensbachian (Early Jurassic) hemipelagic carbonate series of the Lusitanian Basin (Portugal) are of major importance as this basin is located at a key position between the Tethyan and Boreal (North European) realms. One of the most conspicuous features of this basin is the organic-rich nature of most of the Margaritatus Chronozone hemipelagic deposits, with the occurrence of several well-defined regional black shales. The analysis of selected redox sensitive elements (V, Cr, Co, Ni, Mo, and U) from the worldwide reference section of Peniche indicates that in this basin most of the organic-rich facies of the Ibex–Margaritatus chronozones were deposited under an oxic–dysoxic regime, while the rare centimetre thick well-defined black shales were deposited and preserved under suboxic–anoxic, intermittently euxinic conditions. Based on the integration of sedimentological, biostratigraphical, geochemical, and organic petrographic evidence we suggest that these basinwide black shales, corresponding to widespread mucilage and microbial outbreaks, were driven by extreme climate warming coupled with high oceanic productivity and intermittently stratified epeiric seas. Regionally, these “hot snaps” may have promoted the observed rapid but short-lived expansion of Tethyan ammonites into Boreal domains or led to decrease benthic diversity. Ensuing cooling during the Margaritatus Chronozone was accompanied by southwards influx of northwards ammonite fauna or radiation of cyst forming dinoflagellates.

The Lower Jurassic of the Peniche region (Lusitanian Basin, Portugal) constitutes one of the most worldwide references concerning the stratigraphy of the Lower Toarcian. In fact, the Peniche Section is the unique candidate to the Toarcian Global Boundary Stratotype Section and Point and records some important evidences about the palaeoenvironmental perturbations associated to the Toarcian Oceanic Anoxic Event (T-OAE) (e.g. Hesselbo et al., 2007). Despite the large number of micropaleontological studies developed in this section (e.g. ostracods, calcareous nannofossils), any relevant study of benthic foraminifera has been presented, even to the whole basin scale. Thus, based on a detailed stratigraphic analysis that includes 39 marly samples of the Emaciatum (= Spinatum) – Levisoni (= Serpentinum) ammonite zone interval (around 37 m thick), the aim of this work is the study of the foraminiferal assemblages from the Pliensbachian-Toarcian boundary and across the T-OAE. The results and main conclusions of this preliminary study show three different stages: 1) The uppermost Pliensbachian (Emaciatum Zone) is characterized by foraminiferal assemblages with high diversity and abundance (foram/g) dominated by Marginulina, Lenticulina, Dentalina and Ammobaculites, suggesting well-oxygenation and nutrient availability. 2) The beginning of the Toarcian (Polymorphum Zone) evidences a drastic decrease of the diversity and abundance of the foraminiferal assemblages. 3) This trend continues in the Levisoni Zone with decreasing diversity and abundance (some barren samples are recorded), but opportunistic forms such as Epistomina and Lenticulina, occasionally proliferate. This evolution suggests a clear perturbation in the palaeocological conditions at the sea-bottom during the Early Toarcian, feature that is observed in other basins (see Reolid et al., 2012). The fluctuations of foraminiferal assemblages recorded across the studied interval seems to correlate with the previous sequence stratigraphic interpretation of the series (e.g. Duarte, 2007) and the proliferation of opportunistic forms in some levels could be a reflex of the turbiditic sedimentation that took place in this area during this period (Wright & Wilson, 1984), which promotes the oxygenation of the sea-bottom.

The Pliensbachain-Toarcian is particularly well represented in the Lusitanian Basin (central western Portugal), dominated by benthic and necktonic marl-limestone succession, well dated by ammonites. In this general context, and besides all aspects related to the Toarcian Oceanic Anoxic Event (T-OAE), the Polymorphum (=Tenuicosta-tum) – Levisoni (= Serpentinum) ammonite zone boundary marks one of the most sedimentological changes occurred in the whole basin (Duarte, 1997). Among all well known available sections for this interval (e.g. Peniche and Rabaçal), the Alcabideque section shows at the base of Levisoni Zone a singular record of brownish marls very poor in macrofauna (the " Chocolate Marls "), unit that is exclusive of northern part of the basin (see Pittet et al., 2014). With the aim to improve the understand about the sedimentary vertical changes occurred between the late Pliensbachian (Emaciatum Zone) and the base of Levisoni Zone, and to clarify the palaeoenvironment of such unit, we developed an organic facies analysis, including palynofacies and organic geochemistry [total organic carbon (TOC), sulfur and biomarkers]. Results confirm that sediments are particularly poor in organic matter, with the highest TOC value reaching 0.41 wt.% around the top of Polymorphum Zone. In the studied succession (around 20 m thick) the organic content is represented mainly by components from palynomorph (essentially sporomorphs) and phytoclast (both opaque and non-opaque) groups (>85%). A strong change occurs at the base of Chocolate Marls, through a clear increase of sporomorphs under the form of tetrads and agglomerates and the lowest occurrence (<2%) of amorphous organic matter, after a peak of this group and marine palynomorphs recorded at the top of Polymorphum Zone. This continental influence occurred at the base of Levisoni Zone is also confirmed by the η-alkanes distribution profile and several biomarkers such as isoprenoides, terpanes and steranes. With these data we emphasize the special sedimentation occurred in the Lusitanian Basin across the T-OAE, clarifying the sedimentary nature and the palaeoenvironmental significance of the " Chocolate Marls " , clearly associated with a drop in the sea level. This evidence agrees with the general interpretation presented by previous works about the sedimentary evolution of the whole Lower Toarcian of the western Iberian margin.

The Pliensbachain-Toarcian is particularly well represented in the Lusitanian Basin (central western Portugal), dominated by benthic and necktonic marl-limestone succession, well dated by ammonites. In this general context, and besides all aspects related to the Toarcian Oceanic Anoxic Event (T-OAE), the Polymorphum (=Tenuicosta-tum) – Levisoni (= Serpentinum) ammonite zone boundary marks one of the most sedimentological changes occurred in the whole basin (Duarte, 1997). Among all well known available sections for this interval (e.g. Peniche and Rabaçal), the Alcabideque section shows at the base of Levisoni Zone a singular record of brownish marls very poor in macrofauna (the " Chocolate Marls "), unit that is exclusive of northern part of the basin (see Pittet et al., 2014). With the aim to improve the understand about the sedimentary vertical changes occurred between the late Pliensbachian (Emaciatum Zone) and the base of Levisoni Zone, and to clarify the palaeoenvironment of such unit, we developed an organic facies analysis, including palynofacies and organic geochemistry [total organic carbon (TOC), sulfur and biomarkers]. Results confirm that sediments are particularly poor in organic matter, with the highest TOC value reaching 0.41 wt.% around the top of Polymorphum Zone. In the studied succession (around 20 m thick) the organic content is represented mainly by components from palynomorph (essentially sporomorphs) and phytoclast (both opaque and non-opaque) groups (>85%). A strong change occurs at the base of Chocolate Marls, through a clear increase of sporomorphs under the form of tetrads and agglomerates and the lowest occurrence (<2%) of amorphous organic matter, after a peak of this group and marine palynomorphs recorded at the top of Polymorphum Zone. This continental influence occurred at the base of Levisoni Zone is also confirmed by the η-alkanes distribution profile and several biomarkers such as isoprenoides, terpanes and steranes. With these data we emphasize the special sedimentation occurred in the Lusitanian Basin across the T-OAE, clarifying the sedimentary nature and the palaeoenvironmental significance of the " Chocolate Marls " , clearly associated with a drop in the sea level. This evidence agrees with the general interpretation presented by previous works about the sedimentary evolution of the whole Lower Toarcian of the western Iberian margin.

The Pliensbachain-Toarcian is particularly well represented in the Lusitanian Basin (central western Portugal), dominated by benthic and necktonic marl-limestone succession, well dated by ammonites. In this general context, and besides all aspects related to the Toarcian Oceanic Anoxic Event (T-OAE), the Polymorphum (=Tenuicosta-tum) – Levisoni (= Serpentinum) ammonite zone boundary marks one of the most sedimentological changes occurred in the whole basin (Duarte, 1997). Among all well known available sections for this interval (e.g. Peniche and Rabaçal), the Alcabideque section shows at the base of Levisoni Zone a singular record of brownish marls very poor in macrofauna (the " Chocolate Marls "), unit that is exclusive of northern part of the basin (see Pittet et al., 2014). With the aim to improve the understand about the sedimentary vertical changes occurred between the late Pliensbachian (Emaciatum Zone) and the base of Levisoni Zone, and to clarify the palaeoenvironment of such unit, we developed an organic facies analysis, including palynofacies and organic geochemistry [total organic carbon (TOC), sulfur and biomarkers]. Results confirm that sediments are particularly poor in organic matter, with the highest TOC value reaching 0.41 wt.% around the top of Polymorphum Zone. In the studied succession (around 20 m thick) the organic content is represented mainly by components from palynomorph (essentially sporomorphs) and phytoclast (both opaque and non-opaque) groups (>85%). A strong change occurs at the base of Chocolate Marls, through a clear increase of sporomorphs under the form of tetrads and agglomerates and the lowest occurrence (<2%) of amorphous organic matter, after a peak of this group and marine palynomorphs recorded at the top of Polymorphum Zone. This continental influence occurred at the base of Levisoni Zone is also confirmed by the η-alkanes distribution profile and several biomarkers such as isoprenoides, terpanes and steranes. With these data we emphasize the special sedimentation occurred in the Lusitanian Basin across the T-OAE, clarifying the sedimentary nature and the palaeoenvironmental significance of the " Chocolate Marls " , clearly associated with a drop in the sea level. This evidence agrees with the general interpretation presented by previous works about the sedimentary evolution of the whole Lower Toarcian of the western Iberian margin.

In the present paper we describe the distribution of brachiopods in the proposed Toarcian GSSP (Global Boundary Stratotype Section and Point) at Peniche. We differentiated four assemblages in the stratigraphic interval from the upper Emaciatum Zone of the Pliensbachian to the Levisoni Zone of the Toarcian. Assemblage 1 clearly presents Northwestern European affinities, with many species that are also present in Southern England. In the last levels of the Pliensbachian and in the Mirabile Subzone (the first level of the Toarcian), Assemblage 2 contains taxa that still present Northwestern European affinities, but with a more restricted, even endemic, distribution. The majority of the species in these levels are known from the Iberian Range in Spain and other neighboring basins. An important faunal change takes place in the Semicelatum Subzone, coinciding with the base of the Cabo Carvoeiro Formation, giving rise to Assemblage 3. In this assemblage we observed a clear decrease in the size of the specimens, coinciding with the establishment of the "Koninckella Fauna"; this fauna is found in several localities in both Northwestern European and Mediterranean areas where the paleoenvironment is relatively deep or poorly oxygenated. Brachiopods disappear in Peniche just above the Polymorphum - Levisoni zonal boundary, as has been observed in several other localities in Western Tethys. Their renewal is marked by the presence of Soaresirhychia bouchardi several meters above the extinction level, constituting Assemblage 4.

Sinemurian ostracodes from the Lusitanian Basin (western Portugal, Iberian Peninsula) were studied using twelve samples from the marl-limestone succession of the Coimbra Formation at S. Pedro de Moel, north of Lisbon. The detailed taxonomical study identified 11 genera and 14 species, among which 3 are new species: Phraterfabanella boomeri Cabral and Colin n. sp., Klieana? coimbraensis Cabral and Colin n. sp. and "Klinglerella" roselinae Cabral and Colin n. sp. The recognized ostracode species are particularly similar to those described from the uppermostHettangian-Sinemurian offshore Southwest Ireland (Fastnet Basin) and France (Normandy, Central France and Quercy). Overall, the assemblages include four brackish species (one clearly dominant) and ten marine species. The paleoecological analysis of the assemblages allowed a detailed paleoenvironmental reconstruction, reflecting frequent variations from brackish to restricted marine to slightly more open marine settings, which is supported by sedimentological and other paleontological data.

This work presents a high-resolution stratigraphic study of the organic matter preserved in a marly-limestone succession of the Upper Pliensbachian - Lower Toarcian from Rodiles section (Rodiles Formation, Asturian Basin), supported by organic geochemistry data [total organic carbon (TOC) and total sulfur (St)] and palynofacies in 15 samples of marly levels. Results confirm not only high values of TOC (above 2 wt. %), previously reported for the boundary between the Tenuicostatum - Serpentium zones, accompanied by an increase in St (maximum of 3.59 %), and show values of TOC above 1% for the top of the Spinatum Zone. Across the studied section the kerogen is dominated by tissues derived from higher plants (phytoclasts), with the exception of the richest TOC levels where there is a clear increase of amorphous organic matter (AOM). A more detailed analysis of this AOM shows, as the phytoclasts, a continental provenance, in which preservation has been favored by a decrease of oxygen availability in the depositional environment.

This study shows preliminary data from natural gamma-ray spectrometry measurements (total counts, K, Th and U contents) carried out in outcrops of the Jurassic basal units in the Lusitanian Basin (Portugal), namely in the Pereiros and Coimbra formations. The study was developed in the northern sector of the basin, involving reference stratigraphic sections in the Castelo Viegas, Lamas, Vila Seca, Penela and Cabanas-Brenha regions. Preliminary results clearly demonstrate differentiation of the spectral range between the two units. The Pereiros formation, due its mixed and complex sedimentary and lithological character (sandstones to dolostones), shows largest variability of the spectrometric data, with average of the total counts being higher in sandstones (369 cps) and decreasing in lutites (to 328 cps) and dolostones (288 cps in the sandy dolostones and 147 cps in micritic dolostones) and maximum contents of K (6.2 %), U (8.6 ppm) and Th (25.6 ppm). Dolostones and dolomitic limestones of Coimbra formation present a decreasing vertical trend in the total counts of gamma-ray spectrometry, showing, for the same parameter, in the eastern part of the basin, an average value of 126 cps and 96 cps in the western region.

The Lower Jurassic interval is characterized in the Lusitanian Basin by marl-limestone alternations with some very organic-rich intervals. One of these intervals is recorded in the Upper Sinemurian-lowermost Pliensbachian, corresponding to the Água de Madeiros Formation. Based on 49 horizons with relevant organic content, a multidisciplinary analysis of the organic-rich facies is presented in this work, supported by detailed macroscopic analysis, pre-existing total organic carbon data (TOC) and major element geochemistry obtained by x-ray fluorescence. In this work, four main organic-rich facies are defined, which are mainly distinguished by the type of lamination and by the TOC, CaO, SiO2 and Al2O3 contents (%). The strong positive correlation between the last oxides is indicative of a significant siliciclastic phase, dominated by clay minerals. MgO is practically constant in the great majority of the studied samples, with values below 2%, which corresponds to a very low dolomite expression.

In order to identify the source rock of the oil found in the Benfeito-1 well (Montejunto region) geochemical analyses were carried out on rocks from this well, belonging to the Santo António - Candeeiros (Moleanos Member equivalent, Callovian), Cabaços (lower? - middle Oxfordian) and Montejunto (middle - upper Oxfordian) formations, on rocks of the Cabaços Formation sampled in the Cabaços reference section and on oil recovered in the well from Montejunto Formation. The data obtained by determination of total organic carbon and Rock-Eval pyrolysis allowed to recognize that the levels with the highest concentration of organic matter rich in hydrogen occur in the reference section of Cabaços Formation and in the Montejunto Formation in Benfeito-1 well. Data of stable carbon isotopes and biomarkers enabled to establish that the Benfeito-1 well oil was generated and accumulated in Montejunto Formation. The oil-source rock correlation allows further understanding of a model to explain the generation, migration and accumulation of the hydrocarbons identified on the well Benfeito-1 drilled in the southern flank of the Montejunto structure.

Angola shows a large number of natural beauties that result from its wide range geodiversity, revealing a high geotouristic potential. Despite these important attributes, the geological knowledge of these sites is low. Based on the recent contest “Seven Natural Wonders of Angola” and in field work recently developed in the west and southwestern Angola, we characterize and summarize the geological information associated with four locations, where high landscape and iconographic values have been recognized. They are the Leba Mountain, Egito-Praia, Sassa Caves and Binga Waterfalls, localities that are included in the Namibe-Huíla, Benguela and Kwanza Sul Provinces. These geosites, framed by different geomorphological features, have their common feature in the carbonate sedimentary record, from the dolomitic Proterozoic of Humpata Plateau to the Cretaceous deposits of the Benguela Basin. With this new information we intend to enhance and promote the geological knowledge of these singular sites of Angola.