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Abstract In the Amazonian lowlands, the shift from a large wetland dominated by flooded forests (Várzea) to the modern incised valleys bounded by extensive areas of non-flooded forests (Terra Firme) is considered a key driver of the Amazonian mega-biodiversity. Dating the sedimentary beds covered by Terra Firme forest is crucial to constrain the timing of such landscape change. Here we determined the formation ages of widespread regions of Terra Firme substrates in central Amazonian lowlands combining optically stimulated luminescence (OSL) dating, magnetostratigraphy and palinostratigraphy. Our data suggest a very dynamic fluvial system leading to a recent expansion of Terra Firme forests and retraction of Várzea forests during the late Pleistocene. The shift from an extensively flooded to non-flooded surface resulted from river incision around 45-35 ka, which potentially influenced the distribution of taxa by expanding available habitat, creating new barriers to dispersal, or changing the permeability of previous barriers. Transitions between flooded and non-flooded landscapes may have driven diversification and caused changes to species distributions, contributing to the high species diversity and biogeographic patterns currently found in the region. The late Quaternary evolution of Terra Firme substrates reveals that physical landscape changes play a major role in shaping biotic habitats even in the 104–105 years time-scales. Highlights • We combined OSL dating, magnetostratigraphy, and palinostratigraphy to date sediments. • Widespread Varzea-like environment has developed from 250 to 45 ka. • The last expansion of Terra Firme forests and retraction of Várzea forests happened after 45 ka. • Fluvial changes appear to play a major role in the biodiversity during the Quaternary. [ABSTRACT FROM AUTHOR]

The thermal and diagenetic evolution of shale units has received renewed focus because of their emergence as unconventional hydrocarbon reservoirs. The Serra Alta Formation (SAF) is a Permian shale unit of the Paraná Basin, which is the largest South American cratonic basin. The SAF stands out as a pathway for aqueous fluids and hydrocarbon migration from the Irati organic-rich shales to the Pirambóia fluvial-eolian sandstone reservoirs. Vertical NNW and NNE opening fractures would be the main pathways for the migration of buried pore waters and aqueous fluids, besides the input of meteoric water. These fractures would be associated to the reactivation of basement discontinuities such as the Jacutinga (NE) and Guapiara (NW) faults. Thus, vertical NNE and NNW associated fractures would represent the main pathways for fluid migration in the studied area. The vertical calcite filled opening fractures from SAF record moderately low salinity (0–4.5 wt % of NaCl eq.) aqueous fluids, suggesting the input of meteoric water in the buried fracture system. Eutectic melting temperatures at −52±5 °C indicate an H 2 O + NaCl + CaCl 2 system with CaCl 2 or MgCl 2 in solution. Homogenization temperatures recorded in fluid inclusion assemblages (FIAs) of calcite filled opening fractures indicate that the SAF in the studied area reached temperatures above 200 °C, suitable for generation of gaseous hydrocarbons. The recorded paleotemperatures point to a thermal peak associated with Serra Geral volcanic event during the Early Cretaceous, with the thermal effect of volcanic rock cap possibly overcoming the effect of intrusive igneous bodies. The detection of methane in SAF shale pores indicates conditions for hydrocarbon generation. However, additionally studies are necessary to confirm the thermogenic and/or biogenic origin of the methane within the SAF. [ABSTRACT FROM AUTHOR]

The Amazon region hosts the world's largest watershed spanning from high elevation Andean terrains to lowland cratonic shield areas in tropical South America. This study explores variations in optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) signals in suspended silt and riverbed sands retrieved from major Amazon rivers. These rivers drain Pre-Cambrian to Cenozoic source rocks in areas with contrasting denudation rates. In contrast to the previous studies, we do not observe an increase in the OSL sensitivity of quartz with transport distance; for example, Tapajós and Xingu Rivers show more sensitive quartz than Solimões and Madeira Rivers, even though the latter have a significantly larger catchment area and longer sediment transport distance. Interestingly, high sensitivity quartz is observed in rivers draining relatively stable Central Brazil and Guiana shield areas (denudation rate ξ = 0.04 mm yr − 1 ), while low sensitivity quartz occurs in less stable Andean terrains ( ξ = 0.24 mm yr − 1 ). An apparent linear correlation between quartz OSL sensitivity and denudation rate suggests that OSL sensitivity may be used as a proxy for erosion rates in the Amazon basin. Furthermore, luminescence sensitivity measured in sand or silt arises from the same mineral components (quartz and feldspar) and clearly discriminates between Andean and shield sediments, avoiding the grain size bias in provenance analysis. These results have implications for using luminescence sensitivity as a proxy for Andean and shield contributions in the stratigraphic record, providing a new tool to reconstruct past drainage configurations within the Amazon basin. [ABSTRACT FROM AUTHOR]

Robust chronologies for Quaternary fluvial carbonate sediments (tufas) from Brazil are still challenging. We obtain Optically Stimulated Luminescence (OSL) ages of Brazilian tufa deposits using the Single Aliquot Regeneration (SAR) dose protocol applied to single grains and multigrain aliquots of quartz extracted from tufa matrix. Additionally, radiocarbon ( 14 C) ages were obtained for the carbonate matrix and organic matter from tufas. The methodology was applied in samples from tufa deposits in southwestern and southeastern regions with Quaternary carbonate deposition. Equivalent doses distributions have overdispersion between 19% and 81%, indicating that the studied samples comprise well bleached as well as poorly bleached sediments. The quartz grains extracted from the studied tufas show an OSL signal dominated by the fast component and reliable dose response curves, with saturation doses (2 D 0 ) ranging from 35 to 210 Gy. Most of the samples has low radiation dose rates (0.40 ± 0.02 to 0.78 ± 0.05 Gy/ka), with variation in the water content due to compaction and matrix recrystallization, being the major factors that could induce dose rate changes through time. Hard tufa samples with intense carbonate cementation show quartz OSL ages from 51.9 ± 4.8 to 150.3 ± 35.9 years. These ages are much older than the radiocarbon ages of the carbonate matrix and organic matter. The OSL ages of soft tufa samples related with the active fluvial system ranged from 0.8 ± 0.1 to 5.5 ± 0.4 years and are in the same interval of radiocarbon ages presented in the previous works. We interpret that carbonate recrystallization or uptake of organic matter after tufa formation are responsible for the younger radiocarbon ages compared to quartz OSL ages in the older tufa samples. For these samples, age differences vary up to tens of thousands years between deposition of quartz grains and the last episode of carbonate recrystallization or organic matter uptake. Consequently we believe that the obtained OSL ages are the best estimates for the starting deposition time of the studied tufa samples. [ABSTRACT FROM AUTHOR]

The Paraná Basin, southern Brazil, has an atypical thermal and fluid history due to the occurrence of an episodic continental flood volcanism during the Early Cretaceous. So far, there are few data about the influence of this volcanic event on the paleotemperatures and paleofluids of the Paraná Basin sedimentary rocks. The Teresina Formation in the northern flank of the Ponta Grossa dyke swarm hosts high concentration of subsurface igneous rock bodies (sills and dykes), besides its covering by a hundreds meter thick volcanic rock cap. In this study, we used fluid inclusion analysis performed in horizontal and vertical calcite veins from the Teresina Formation and from a Late Cretaceous basic dyke to estimate paleotemperatures and to characterize the composition of diagenetic paleofluids. Homogenization temperatures of requilibrated fluid inclusions show that the Teresina Formation reached temperatures above 200 °C. Horizontal parallel bedding calcite veins from the Teresina Formation record low to high salinity (2–26 wt.% NaCl eq.) aqueous paleofluids. The prevalence of high salinity fluid inclusions associated with light hydrocarbon fluid inclusions indicates deep buried fluids. Fluid inclusions in vertical calcite vein from basic dyke comprise only low salinity aqueous fluids (0–3 wt.% eq.NaCl) interpreted as dominated by meteoric water. The recorded paleotemperatures are attributed to the heating by the Paraná volcanic event during the Early Cretaceous, with the thermal effect of the volcanic rock cap surpassing the effect of nearby sills and dykes. Estimated paleotemperatures higher than 200 °C would allow the generation of light liquid and gaseous hydrocarbons. Overpressured compartments in the Teresina Formation allowed the expulsion of buried pore fluids (high salinity aqueous fluids and hydrocarbons) to fracture systems, where they mixed with meteoric water. The input of meteoric water through fracture systems connected with the surface favored hydrocarbons degradation in the early stages of source rock maturation during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Abstract: The thermoluminescence (TL) characteristics of quartz are highly dependent of its thermal history. Based on the enhancement of quartz luminescence occurred after heating, some authors proposed to use quartz TL to recover thermal events that affected quartz crystals. However, little is know about the influence of the temperature of quartz crystallization on its TL characteristics. In the present study, we evaluate the TL sensitivity and dose–response curves of hydrothermal and metamorphic quartz with crystallization temperatures from 209 ± 15 to 633 ± 27 °C determined through fluid inclusion and mineral chemistry analysis. The studied crystals present a cooling thermal history, which allow the acquiring of their natural TL without influence of heating after crystallization. The TL curves of the studied samples present two main components formed by different peaks overlapped around 110 °C and 200–400 °C. The TL sensitivity in the 200–400 °C region increases linearly with the temperature of quartz crystallization. No relationship was observed between temperatures of quartz crystallization and saturation doses (<100 Gy). The elevated TL sensitivity of the high temperature quartz is attributed to the control exerted by the temperature of crystallization on the substitution of Si4+ by ions such as Al3+ and Ti4+, which produce defects responsible for luminescence phenomena. The linear relationship observed between TL in the 200–400 °C region and crystallization temperature has potential use as a quartz geothermometer. The relative abundance of quartz in the earth crust and the easiness to measure TL are advantageous in relation to geothermometry methods based on chemistry of other minerals. [ABSTRACT FROM AUTHOR]

Abstract: The stratigraphic subdivision and correlation of dune deposits is difficult, especially when age datings are not available. A better understanding of the controls on texture and composition of eolian sands is necessary to interpret ancient eolian sediments. The Imbituba–Jaguaruna coastal zone (Southern Brazil, 28°–29° S) stands out due to its four well-preserved Late Pleistocene (eolian generation 1) to Holocene eolian units (eolian generations 2, 3, and 4). In this study, we evaluate the grain-size and heavy-mineral characteristics of the Imbituba–Jaguaruna eolian units through statistical analysis of hundreds of sediment samples. Grain-size parameters and heavy-mineral content allow us to distinguish the Pleistocene from the Holocene units. The grain size displays a pattern of fining and better sorting from generation 1 (older) to 4 (younger), whereas the content of mechanically stable (dense and hard) heavy minerals decreases from eolian generation 1 to 4. The variation in grain size and heavy-mineral content records shifts in the origin and balance (input versus output) of eolian sediment supply attributable mainly to relative sea-level changes. Dunefields submitted to relative sea-level lowstand conditions (eolian generation 1) are characterized by lower accumulation rates and intense post-depositional dissection by fluvial incision. Low accumulation rates favor deflation in the eolian system, which promotes concentration of denser and stable heavy minerals (increase of ZTR index) as well as coarsening of eolian sands. Dissection involves the selective removal of finer sediments and less dense heavy minerals to the coastal source area. Under a high rate of relative sea-level rise and transgression (eolian generation 2), coastal erosion prevents deflation through high input of sediments to the coastal eolian source. This condition favors dunefield growth. Coastal erosion feeds sand from local sources to the eolian system, including sands from previous dunefields (eolian generation 1) and from drowned incised valleys. Therefore, dunefields corresponding to transgressive phases inherit the grain-size and heavy-mineral characteristics of previous dunefields, leading to selective enrichment of finer sands and lighter minerals. Eolian generations 3 and 4 developed during a regressive-progradational phase (Holocene relative sea level highstand). The high rate of sediment supply during the highstand phase prevents deflation. The lack of coastal erosion favors sediment supply from distal sources (fluvial sediments rich in unstable heavy minerals). Thus, dunefields of transgressive and highstand systems tracts may be distinguished from dunefields of the lowstand systems tract through high rates of accumulation (low deflation) in the former. The sediment source of the transgressive dunefields (high input of previously deposited coastal sands) differs from that of the highstand dunefields (high input of fluvial distal sands). Based on this case study, we propose a general framework for the relation between relative sea level, sediment supply and the texture and mineralogy of eolian sediments deposited in siliciclastic wet coastal zones similar to the Imbituba–Jaguaruna coast. [Copyright &y& Elsevier]

Abstract: Middle to Late Holocene barriers are conspicuous landforms in southeastern and southern Brazilian regions. The barriers in the coastal zones of northern Santa Catarina, Paraná and São Paulo states (27°19′–24°00′S) are formed mainly by beach ridge alignments and many barriers present foredune and blowout alignments in their seaward portion. The development of these eolian landforms appears to record a regional shift in coastal dynamics and barrier building. In this context, the Ilha Comprida barrier stands out for its well-developed and well-preserved foredunes and blowouts. Based on the presence or not and type of eolian landforms, the Ilha Comprida barrier can be divided seaward into inner, middle and outer units. The inner unit is formed entirely by beach ridges. The middle unit comprises a narrow belt of blowouts (up to 15m high) aligned alongshore. Blowout lobes pointing NNW are indicative of their generation by southern winds. The outer unit is represented by low (≤1m high) active or stabilized foredunes and a small transgressive dunefield (∼1km2). Twenty-seven luminescence ages (SAR protocol) obtained for the beach ridges, foredunes, and blowouts of these three units allow definition of a precise chronology of these landforms and calculation of rates of coastal progradation. The inner unit presents ages greater than 1004±88 years. The blowouts of the middle unit show ages from 575±47 to 172±18 years. The ages of the outer unit are less than 108±10 years. Rates of coastal progradation for the inner and outer units are 0.71–0.82m/year and 0.86–2.23m/year, respectively. The main phase of blowout development correlates well with the Little Ice Age (LIA) climatic event. These results indicate that southern winds in subtropical Brazil became increasingly more intense and/or frequent during the LIA. These conditions persist to the present and are responsible for the development of the eolian landforms in the outer unit. Thus, barrier geomorphology can record global climatic events. The sensitivity of barrier systems in subtropical Brazil to Late Holocene climate changes was favored by the relative sea level stillstand during this time. Luminescence dating makes it possible to analyze barrier geomorphology during Late Holocene climate changes operating on timescales of a hundred to thousand years. These results improve our knowledge of barrier building and will help in the evaluation of the impact of future climate changes on coastal settings. [Copyright &y& Elsevier]

Abstract: The Late Quaternary coastal eolian deposits of the Imbituba–Laguna region (Santa Catarina State, southern Brazil) comprise two “eolian depositional sequences”, separated by an unconformity. The older eolian sequence, A, is correlated to the relative sea level rise of the Last Interglacial period. The eolian sequence B was initiated during the relative sea level rise in the post-glacial period and extends up to active dunefields. The correspondence between the two eolian depositional episodes represented by these sequences and the relative sea level highstand phases is confirmed by thermoluminescence and optically stimulated luminescence dating. This correspondence is explained by a conceptual model that links the availability of coastal sediments for eolian transport with relative sea level changes. The link between relative sea level changes and coastal eolian sedimentation can be used to integrate coastal eolian systems to the sequence stratigraphy model. [Copyright &y& Elsevier]

We investigated the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of quartz from sediments and parent rocks across South America. OSL and TL sensitivities were compared with the characteristic dose of dose response curves. Additionally, we estimated electron trap parameters of quartz from sediments with contrasting OSL sensitivities. Our results show that the natural sensitivities of quartz OSL (initial 0.8 s) and TL (110 °C peak) are positively correlated and range over six and four orders of magnitude respectively. The corresponding characteristic doses range from around 30 Gy–3000 Gy for dose response curves described by a single exponential function. Quartz from igneous and metamorphic rocks and Andean short-transported sediments report low-sensitivity OSL and high characteristic dose. The studied initial OSL signal has significant contribution of medium and slow components in quartz from rocks and Andean short-transported sediments, while in quartz from Brazilian long-transported sediments, the initial OSL signal is dominated by the fast component. The trend of sensitivity increase and characteristic dose decrease is attributed to the relative contribution of medium and low components to the initial OSL emission. Regarding the electron trap parameters, high, medium and low sensitivity quartz has statistically similar values of the activation energy and the frequency factor, but both parameters have larger variations in medium and low sensitivity quartz. • The OSL and TL properties of quartz from rocks and sediments were characterized. • Quartz from longer-transported sediments has higher OSL and TL sensitivities. • Higher OSL sensitivity implies dose response curves with lower characteristic dose. • Trap parameters of medium and low sensitivity quartz suggest non-fast components. [ABSTRACT FROM AUTHOR]

Abstract: Barrier development during the Holocene is studied using the example of the Ilha Comprida, Southeastern Brazil. Aerial photos, facies analysis, and optically stimulated luminescence dating are used to define the barrier emergence and evolution. Optically stimulated luminescence ages and facies successions indicate that the Ilha Comprida probably began as a Holocene transgressive barrier island 6000years ago, just before the last relative sea-level maximum. Since then the barrier has progradated through the addition of curved beach ridges. Based on beach ridge alignments, six units of growth are identified with two growth directions, transverse and longitudinal. Rates of progradation with transverse growth vary from 0.13 to 4.6m/year. Rates of longitudinal growth to NE range from 5.2 to 30m/year. Variation in coastal progradation rates and sediment retention during the last 6000years is compared with climate, physiography and relative sea-level changes. The physiography, represented by pre-Cenozoic hills, is the major control on sediment retention and alternation between longitudinal and transverse growth. Climate variations, such as the Little Ice Age event, apparently control the formation of ridges types: beach ridges, foredunes, and blowouts. These results allow the use of the Ilha Comprida Barrier as an example to analyze the major controls on barriers progradation. [Copyright &y& Elsevier]

Brazilian shale formations are potential biogenic gas systems that are still poorly understood. Organic-rich shales from Ponta Grossa (Devonian, Paraná Basin), Irati (Permian, Paraná Basin) and Tremembé (Paleogene, Taubaté Basin) Formations were analyzed in order to evaluate their biogenic methane (CH 4 ) generation potential and to constrain environmental and geological conditions that may affect methanogenic metabolism. Additionally, the generation potential of carbon dioxide (CO 2 ) was evaluated in combination with CH 4 to constrain Brazilian organic-rich shales as sources of greenhouse gas to the atmosphere. Twenty-four shale samples were used for batch incubations in dry and wet conditions and after headspace refilling and acetic acid addition during one year. Physico-chemical parameters such as Total Organic Carbon (TOC), specific surface area and pore volume were characterized in order to understand general geologic controls on CH 4 and CO 2 production. Biogenic gas generation rates in dry tests reached up to 3.17 ml/t·d (milliliter per ton of shale per day) for CH 4 and 2.45 × 10 3 ml/t·d for CO 2 during the first 30 days, with wet samples producing about 54% more CH 4 and 151% more CO 2 than dry samples. Headspace refilling did not demonstrate significant changes on production rates, while acetic acid addition restarted or increased CH 4 and CO 2 production rates in several microcosms. Shales from the Irati Formation showed the highest methane production rates for both dry and wet tests, with unusual ranges of δ 13 C CH4 and δ 13 C CO2 that may be linked to hydrocarbon biodegradation. The studied shale formations have different pore volume and specific surface area, but without significant influence over biogenic methane generation. [ABSTRACT FROM AUTHOR]

Abstract: Ilha Comprida is a regressive barrier island located in southeastern Brazil that was formed essentially by Quaternary sandy sediments. Ilha Comprida sediments were analyzed to assess heavy mineral indices and grain size variables. The spatial variation of heavy minerals and grain size was interpreted in terms of the present barrier dynamics and the barrier’s evolution since the Middle Holocene. These analyses allowed for the identification of the main factors and processes that control the variation of heavy minerals and grain size on the barrier. Rutile and zircon (RZi) and tourmaline and hornblende (THi) are significantly sensitive to provenance and exhibit the contributions of the Ribeira de Iguape River sediments, which reach the coast next to the northeastern end of Ilha Comprida. In addition to the influence of provenance, TZi responds mainly to hydraulic sorting processes. This agrees with a sediment transport pattern characterized by a divergence of two resultant net alongshore drifts southwest of the barrier. The sediments from the Ribeira de Iguape River reach the barrier directly through the river mouth and indirectly after temporary storage in the inner shelf. The combination of grain size and heavy mineral analyses is a reliable method for determining sediment transport patterns and provenance. [ABSTRACT FROM AUTHOR]

Lipid biomarker proxies from terrigenous sediments have been extensively used to understand variations in paleoenvironmental conditions, but many of the mechanisms affecting these proxies during riverine transport are still poorly understood. Here, we analyze glycerol dialkyl glycerol tetraether (GDGT) distributions and n- alkane isotopic compositions of soils and sediments from the Amazon River Basin. Our dataset includes suspended sediments of the Amazon River and its main tributaries, as well as soils and sediments of the Xingu River, a large clearwater tributary draining the easternmost part of the Amazon River Basin. Our sampling design aimed at understanding the processes behind spatially distinct GDGT distributions and n -alkane isotopic signatures across lowland Amazonia. Gradual changes in the fractional abundances of isoprenoid GDGTs and in 5- and 6- methyl branched GDGT ratios in suspended sediments of the Amazon River towards its mouth suggest that riverine production is an increasingly important control on the distribution of GDGTs in the lower parts of the system, while values from the western parts are more in line with a dominant soil sourcing. In the Xingu River, indices based on the fractional abundances of branched GDGTs and long-chain n- alkanes demonstrate a strong contribution of terrestrial organic material during the high-water season and an important aquatic component during low-water season. Meanwhile, average stable carbon (δ13C) and hydrogen (δD) isotopic signatures of long-chain n- alkanes in soils, riverbed and suspended sediments of the Xingu River are similar and reinforce the relatively conservative behaviour of these proxies within large river systems. The average compound-specific δ13C signatures of sediments in the Xingu River are within the expected range for C 3 vegetation and do not seem to capture the signals from the nearby deforested areas. n- Alkanes δD signals in the Xingu Basin are similar to values obtained in the Amazon River mouth and indicate that n- alkanes sourced from easternmost Amazonian lowlands may predominate over signals from western areas. [Display omitted] [ABSTRACT FROM AUTHOR]

The increasing global demand for natural gas and petroleum byproducts is turning organic-rich shales into an important target for hydrocarbon exploration and production. Current understanding about hydrocarbon generation in unconventional plays, such as oil shales and gas shales, is still evolving, especially in sedimentary basins where hydrocarbon generation is influenced by magmatism. This is the case for the Permian oil shales of the Irati Formation in the Paraná Basin, southern South America. The Irati shales are considered an atypical petroleum system due to thermal effects of the Paraná Large Igneous Province (LIP) emplaced during the Early Cretaceous. In this context, the focus of this study was to characterize the thermal conditions of hydrocarbon generation in the Irati Formation as well as the composition of related aqueous diagenetic fluids. The kerogen from the Irati organic-rich shales has an aromaticity around 30% (ƒ ar ≈ 30%), as determined by carbon nuclear magnetic resonance (13C-NMR), and vitrinite reflectance (R o) of around 0.6%. Fluid inclusions in calcite and quartz veins present aqueous fluids with salinity of 0–5 wt% of NaCl equivalent and homogenization temperatures greater than 250 °C. Hydrocarbon fluid inclusions were classified as black oil through their vapor fraction volumes (F v = 1.6–9.1%) and homogenization temperatures (Th) in the 60–80 °C range. Methane (CH 4) or carbon dioxide (CO 2) fluid inclusions were absent within the analyzed calcite and quartz veins. The PVT model for trapped fluid inclusions suggests a shallow hydrocarbon petroleum system (≈2.5 km depth) active during the Early Cretaceous, synchronous with the Paraná LIP. • Low salinity fluids have contributed to the formation of calcite and quartz veins. • Paleotemperatures and composition of hydrocarbons were reported by fluid inclusions. • Vitrinite reflectance and kerogen aromaticity report oil-window maturities. • The maturity of the Irati Formation shales was controlled essentially by burial. • Liquid hydrocarbons were classified as black oil due to their Fv and Th parameters. [ABSTRACT FROM AUTHOR]

The Permian Irati Formation in Brazil hosts organic-rich shales and heavy hydrocarbons suitable for biogenic production of methane (CH 4) and carbon dioxide (CO 2). In this study, shale samples from the Irati Formation were used in laboratory incubation experiments performed under different temperatures (22 °C, 50 °C, 70 °C and 80 °C) to evaluate the generation of CH 4 and CO 2 under thermal conditions compatible with biodegradation in shallow gas systems (<80 °C). Despite our laboratory experiments do not represent natural subsurface temperature conditions, it is observed that the concentrations of CH 4 and CO 2 increase when shale samples are incubated under temperature higher than 22 °C. Samples incubated at 80 °C presented a maximum CH 4 yield of 2.45 ml/t.d (milliliter per ton of shale per day) compared to 0.49 ml/t.d at 22 °C, 1.75 ml/t.d at 50 °C and 2.09 ml/t.d at 70 °C. The same trend of increasing production rates with higher temperatures was observed for CO 2 , with maximum potential production observed under a laboratory temperature of 80 °C, reaching 23.47 ml/t.d. Stable carbon isotopes (δ13C) on CH 4 and CO 2 suggest a mixture of thermogenic and secondary microbial gas. However, the measured CH 4 and CO 2 can be generated through methanogenic degradation of heavy hydrocarbons present in the studied shales, difficulting the use of carbon isotope composition to discriminate between biogenic and thermogenic gases. The studied shale samples showed significant differences in CH 4 and CO 2 production rates, which are possibly related to the major elements composition of the mineral matrix. Higher CH 4 and CO 2 production rates occurred in samples with higher amount of sulfur. Besides sulfur, we highlight that others soluble elements in the mineral matrix, such as Ca and Mg, can play an important role for the generation of biogenic CH 4 and CO 2. The present work intends to alert for the importance of thermal conditions as well as the geochemical composition of the mineral matrix to build conceptual models about shallow gas systems, acting on organic-rich shales in sedimentary basins. • The temperature stands out as the factor that most affects the biogenic generation of CH 4 and CO 2. • Biogenic generation of gases in shale units is most efficient under high temperature conditions, up to at least 80 °C. • The composition of the mineral matrix plays an important role in the biogenic generation of CH 4 and CO 2 : • Environments with high sulfur content, at high temperatures, potentiates the biogenic generation of CH 4. [ABSTRACT FROM AUTHOR]