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Supplemental material, sj-pdf-1-eea-10.1177_0144598720949584 for Evaluation of the hydrocarbon generation potential of the Pimenteiras Formation, Parnaiba Basin (Brazil) based on total organic carbon content and Rock-Eval pyrolysis data by Agostinho Mussa, Wolfgang Kalkreuth, Ana Maria Pimentel Mizusaki, Marleny Blanco González, Tais Freitas da Silva and Marcos Müller Bicca in Energy Exploration & Exploitation

Geochronology has became a powerfull tool for diagenetic studies in siliciclastic rocks as it supply parameters for the definition of their depositional or diagenetic ages. This development occurred particularly in the last decades, with analytical techniques improvements and application of oil exploration. Sandstones are important hydrocarbon reservoir-rocks in many basins of the world. Sandstones devoid of fossils with defined ages lack precise chronostratigraphic definition. Such lack of definition limits the precision of the generation-migration-accumulation models developed for the exploration and exploitation of these reservoirs. However, many sandstones contain diagenetic minerals which represent the possibility of dating the deposition of these sandstones, or episodic diagenetic fluid migration through radiometric 40K-40Ar, 40Ar-39Ar and 87Rb-87Sr methods. In the present work, we show that these methods have been successfully applied to samples of reservoirsandstones all over the world. The improvement of the radiometric methods applied to sedimentary rocks yielded significant results concerning depositional or diagenetic ages.

Coastal-eolian sabkha sandstones from different ages and basins show similar diagenetic patterns, which understanding is important for their evaluation as geochemical systems and as hydrocarbon reservoirs. The Carboniferous sandstones of the Juruá Formation (Solimões Basin) are one of the most important gas reservoirs of Brazil. The sandstones and interbedded mudrocks, evaporites and dolostones were deposited within a coastal sabkha environment with pervasive eolian reworking, under increasing marine influence, and hot and dry climate. Four stacked drying/wetting upward cycles were identified, with sabkha facies in the base overlain by eolian deposits, followed again by sabkha deposits, commonly eroded by the next cycle. Eolian dune and sandsheet sandstones are the best reservoirs. The diagenetic evolution and the relationships among diagenesis, depositional facies and stratigraphic unit boundaries show similarities with other coastal-eolian sabkha sandstones. The eodiagenesis is characterized by mechanical compaction, hematite and infiltrated clay coatings, framboidal pyrite, microcrystalline and blocky dolomite. Mesodiagenesis comprises chemical compaction, K-feldspar and quartz overgrowths, poikilotopic anhydrite, feldspar dissolution and albitization, illite and chlorite authigenesis, and late quartz, Fedolomite/ ankerite, calcite and siderite. Localized telogenetic effects include oxidation of ferroan constituents and kaolinite precipitation. Blocky dolomite and quartz cementation, and chemical compaction through intergranular and stylolitic pressure dissolution are more abundant in the non-eolian sandstones. Microcrystalline pore-filling and pore-lining dolomite, and patchy, poikilotopic, post-compactional anhydrite cementation, mostly close to the contacts with interbedded evaporites, are more abundant in the eolian sandstones. These diagenetic patterns are similar to those of the Rotliegend Group in northern Germany and in the North Sea, of the Norphlet and Tensleep Formations in USA, of the Muschelkalk Formation in Spain, and of the Monte Alegre Formation from the Amazonas Basin, northern Brazil. The similarities among the diagenetic histories of these coastal-eolian sabkha sandstones are ascribed to their similar patterns of stratigraphic organization (intercalated evaporite and carbonate beds) and of composition and circulation of pore fluids.

This paper presents the results of a study performed on bedload samples from the Salso Creek in the Porto Alegre City (Rio Grande do Sul State) rural area where agricultural and pastoral activities are carried out within urban areas. Sediment sampling took place on the 16th September 2001 (winter) and 21th January 2002 (summer), at five sites along the Salso Creek. The Salso Creek bed load changes from granules and pebbles (upstream reaches), through coarse- to medium-grained sand (mid reaches) to fine-to very fine-grained sand in the Salso Creek mouth region. Organic matter content increases throughout the summer low discharge due to the accumulation of the suspended load on the creek bed surface. Grains larger then 0.062 mm feature the following estimated mineralogical composition: feldspar (55-50%), quartz (30-40%), opaque (5-10%) and acessory (5-10%) minerals. Among the finegrained sediments (< 0.062 mm) kaolinite dominates being followed by a minor amount of muscovite/illite as well as quartz, feldspar and smectite traces. The chemical composition of the fine-grained sediments reveals that, among the major (Al, Fe, Mn, Ca, Mg, Na and K) and trace (Cr, Cu, Ni, Pb and Zn) analyzed elements, the Al content is high, probably a result of the kaolinite-rich (Al4(Si4O10)(OH)8) composition of the fine-grained fraction. GeoAccumulation Index calculation shows no significant accumulation of any of the analyzed elements within the finegrained fraction, hence indicating slightly to moderately polluted sediments. On the other hand Contamination Factor computation for the sediments fine-grained fraction pointed out a Cu, Ni and Zn enrichment, indicating considerable to high contamination, especially for those places directly under domestic sewerage influence. These elements are probably being concentrated in the fine-grained fraction of the bed load.

In many cases, when dealing with argillaceous fine-grained sedimentary rocks, the isotopic ages obtained from Rb–Sr whole-rock isochron calculations are of geological significance, despite the fact that the initial conditions of Sr isotopic homogenization are not fulfilled. To explain this, a mechanical mixing during deposition has been suggested, leading to an aggregate of mixed material with fairly uniform 87Sr/86Sr values, whatever Rb/Sr ratio is found in the analysed samples. This investigation of the behaviour of Rb and Sr during sedimentation and early diagenesis, involves study of more than 60 samples of fine-grained recent sediments from selected coastal localities of Brazil. The results indicate that pelitic samples from some recent to present-day transitional or shallow marine environments, such as the Jacarepagu´a tidal flat and the Amazonas River mouth, where halmirolysis could have occurred, may produce nearly horizontal best-fit lines in a Rb–Sr isochron diagram. Moreover, the initial isotopic 87Sr/86Sr ratios appear to be well above 0.710. In open marine environments, such as the Campos Basin, where sampling was spread over more than 100 metres, exchanges between the argillaceous sediments and seawater potentially happen at low temperature, inducing a reduction of the 87Sr/86Sr isotopic composition of the sediments to nearly 0.710. An almost horizontal best-fit line is produced for the entire stratigraphic section, independent of the sedimentation age. We believe that in similar environments such ‘zero age isochrons’ are maintained for some time, testifying to exchanges between the sediment and the interstitial fluids, before the onset of burial diagenesis. The above described studies on fine-grained and recent argillaceous sediments seem to confirm the production of horizontal best-fit lines in isochron diagrams, justifying the application of the Rb–Sr whole-rock method to pelitic sedimentary rocks. The nature of the material is critical. The pelitic sediments to be analysed should contain only very limited amounts of coarse clastic material (especially feldspars and mica fragments) and consist mainly of fine clay minerals in which smectites, illite and mixed layers illite–smectite largely predominate.

Coastal-eolian sabkha sandstones from different ages and basins show similar diagenetic patterns, which understanding is important for their evaluation as geochemical systems and as hydrocarbon reservoirs. The Carboniferous sandstones of the Juruá Formation (Solimões Basin) are one of the most important gas reservoirs of Brazil. The sandstones and interbedded mudrocks, evaporites and dolostones were deposited within a coastal sabkha environment with pervasive eolian reworking, under increasing marine influence, and hot and dry climate. Four stacked drying/wetting upward cycles were identified, with sabkha facies in the base overlain by eolian deposits, followed again by sabkha deposits, commonly eroded by the next cycle. Eolian dune and sandsheet sandstones are the best reservoirs. The diagenetic evolution and the relationships among diagenesis, depositional facies and stratigraphic unit boundaries show similarities with other coastal-eolian sabkha sandstones. The eodiagenesis is characterized by mechanical compaction, hematite and infiltrated clay coatings, framboidal pyrite, microcrystalline and blocky dolomite. Mesodiagenesis comprises chemical compaction, K-feldspar and quartz overgrowths, poikilotopic anhydrite, feldspar dissolution and albitization, illite and chlorite authigenesis, and late quartz, Fedolomite/ ankerite, calcite and siderite. Localized telogenetic effects include oxidation of ferroan constituents and kaolinite precipitation. Blocky dolomite and quartz cementation, and chemical compaction through intergranular and stylolitic pressure dissolution are more abundant in the non-eolian sandstones. Microcrystalline pore-filling and pore-lining dolomite, and patchy, poikilotopic, post-compactional anhydrite cementation, mostly close to the contacts with interbedded evaporites, are more abundant in the eolian sandstones. These diagenetic patterns are similar to those of the Rotliegend Group in northern Germany and in the North Sea, of the Norphlet and Tensleep Formations in USA, of the Muschelkalk Formation in Spain, and of the Monte Alegre Formation from the Amazonas Basin, northern Brazil. The similarities among the diagenetic histories of these coastal-eolian sabkha sandstones are ascribed to their similar patterns of stratigraphic organization (intercalated evaporite and carbonate beds) and of composition and circulation of pore fluids.

The Rb-Sr and Sm-Nd isotopic systems are ideal in constraining the provenance of fine-grained clastic rocks. This is particularly true for continental, fluvio-lacustrine, sedimentary units deposited under semi-arid climate conditions, where mechanical desintegration of source rocks dominates the weathering processes. Three sets of red-colored, continental siltstones of the Camaquã Group (Early Paleozoic, southern Brazil) were analyzed for these isotopic systems, providing important data for the understanding of the provenance pattern of the Santa Bárbara (lower) and Guaritas (upper) formations. The results of six samples from the finer-grained portion of Sequence I of Santa Bárbara Formation (SEI samples) suggest provenance predominantly from the adjacent volcanic units (Hilário and Acampamento Velho formations), with subordinated contribution of monzonites (Arroio do Jaques) and metamorphic rocks (Cambaizinho), reflecting eastward paleoflow. Three samples from the outcrop area of the Santa Bárbara Formation east of Caçapava do Sul (SBG samples) reveal a similar provenance pattern, with a more effective contribution of felsic ignimbrites of the Acampamento Velho Formation as source rock. On the other hand, eight samples from the Guaritas Formation, obtained near Santana da Boa Vista (GUA samples), show anomalously high 87Rb/86Sr and 87Sr/86Sr ratios, suggesting more potassic source rocks. The values find correspondence mainly in the syn-transcurrent metagranites Quitéria, Arroio Francisquinho and Cordilheira (older than 600Ma), felsic lavas of the Acampamento Velho Formation (poorly exposed in the area), orogenic (Pinheiro Machado) and post-orogenic (Encruzilhada do Sul) intrusive suites. Other presently exposed units, such as the Encantadas Gneiss (older and more mafic) and the Porongos metasedimentary rocks (also older Nd signature) would have been buried or unavailable for erosion during the deposition of the Guaritas samples.

The Rb-Sr and Sm-Nd isotopic systems are ideal in constraining the provenance of fine-grained clastic rocks. This is particularly true for continental, fluvio-lacustrine, sedimentary units deposited under semi-arid climate conditions, where mechanical desintegration of source rocks dominates the weathering processes. Three sets of red-colored, continental siltstones of the Camaquã Group (Early Paleozoic, southern Brazil) were analyzed for these isotopic systems, providing important data for the understanding of the provenance pattern of the Santa Bárbara (lower) and Guaritas (upper) formations. The results of six samples from the finer-grained portion of Sequence I of Santa Bárbara Formation (SEI samples) suggest provenance predominantly from the adjacent volcanic units (Hilário and Acampamento Velho formations), with subordinated contribution of monzonites (Arroio do Jaques) and metamorphic rocks (Cambaizinho), reflecting eastward paleoflow. Three samples from the outcrop area of the Santa Bárbara Formation east of Caçapava do Sul (SBG samples) reveal a similar provenance pattern, with a more effective contribution of felsic ignimbrites of the Acampamento Velho Formation as source rock. On the other hand, eight samples from the Guaritas Formation, obtained near Santana da Boa Vista (GUA samples), show anomalously high 87Rb/86Sr and 87Sr/86Sr ratios, suggesting more potassic source rocks. The values find correspondence mainly in the syn-transcurrent metagranites Quitéria, Arroio Francisquinho and Cordilheira (older than 600Ma), felsic lavas of the Acampamento Velho Formation (poorly exposed in the area), orogenic (Pinheiro Machado) and post-orogenic (Encruzilhada do Sul) intrusive suites. Other presently exposed units, such as the Encantadas Gneiss (older and more mafic) and the Porongos metasedimentary rocks (also older Nd signature) would have been buried or unavailable for erosion during the deposition of the Guaritas samples.

The alluvial fan deposits of Early Paleozoic Santa Bárbara Formation, located in Sul-rio-grandense Shield area of southernmost Brazil, have been analyzed here in terms of facies associations and tectonic significance. The investigated unit comprises conglomerates, sandstones, and siltstones, deposited probably under continental semi-arid climate conditions, in the post-collisional stages of Neoproterozoic Brasiliano/Pan-African Cycle. The location of the alluvial deposits suggests that the depositional locus of this sedimentary unit should probably consist of an individual and restricted fault-bounded basin, named here Santa Bárbara Basin. Its settling was controlled by the extensional and strike-slip reactivation of NE, NW, and N-S structures inherited from Brasiliano/Pan-African Cycle. Alluvial deposits located in the southwestern and northwestern borders show dominance of sheetflood processes in the alluvial fans deposition. On the other hand, the eastern border of Santa Bárbara Basin, named the “Caçapava paleohigh”, comprises the coarser alluvial deposits, with major occurrence of debris-flow features. This fact suggests a possible asymmetry of this basin. These eastern border deposits reveal, in the clast composition of the conglomerates, three main phases of denudation of “Caçapava paleohigh”. The basal conglomerates reflect a stage when this important topographic high was covered by andesites and metasedimentary rocks. Stratigraphically above, metavolcanic fragments compose the coarse deposits, while at the top of the package the conglomerate framework consists mainly of granitic clasts. This third stage reflects the exposure of the deeper parts of “Caçapava paleohigh”, and it can be positioned at the base of the unconformable Sequence III of Santa Bárbara Formation. The total inversion of braided fluvial axial filling system and the occurrence of intrabasinal debris-flow deposits suggest a strong tectonic event and possibly a significant time span at the base of Sequence III.a

Fresh shale samples taken from a well-known outcrop section of the Silurian Vila Maria Formation, located on the northeastern margin of the Paraná Basin (Três Barras Farm, Goiás State, central-western Brazil), have been analysed for both palynological and radiometric age determinations. The rocks yielded a fairly diverse, age-definitive cryptospore assemblage, and the same samples proved suitable for Rb–Sr analysis, despite Silurian sedimentary rocks being rarely suited to radiometric dating techniques. This study thus introduces an alternative, independent method for estimating the minimum depositional age of the Vila Maria Formation. The Rb–Sr age value has been calculated via an isochron diagram that yields 435.9±7.8 Ma. Accordingly, the latter value is interpreted as the minimum depositional age of the analysed Vila Maria strata, implying their deposition during Llandovery times. This concurs with the palynological results, which indicate an age no older than Early Silurian and, more particularly, favour an Early to Middle Llandovery (Rhuddanian–Early Aeronian) attribution.