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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]

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

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