Search

The Jurassic-Cretaceous transition was marked by the fragmentation of the West Gondwana supercontinent and consequent opening of the Atlantic Ocean. This event resulted in extensive lava flows in the central portion of West Gondwana, composing the Central Atlantic Magmatic Province. In the Parnaíba Basin (NE Brazil), a large lacustrine system succeeded this event; nevertheless, the post-CAMP scenario and the influence of the decreasing isotherms in the Mesozoic sedimentation are poorly understood. In this sense, cyclostratigraphy and outcrop-based facies analysis were carried out in the lacustrine stratigraphic record, allowing the recognition of four paleoenvironments: central lake, sheet-like delta front, lakeshore and ephemeral fluvial channels, mainly organized in shallowing upward cycles. The upsection transition of thin black shales and limestones to thick oxidized mudstones and stratified sandstones reflects the evolution of underfilled to overfilled lake settings. The lacustrine succession is organized in four major depositional cycles, characterized by millimeter to centimeter-scale cycles, bounded by unconformities or flooding surfaces. The cycles define a retrogradational-progradational-retrogradational stacking pattern, with random and frequent changes in lithology and cycle thickness. Cyclostratigraphic data suggest that the upward increasing accommodation space was controlled by the post-CAMP thermal subsidence, as well as shifts in sedimentary supply and water inflow/outflow. The time span of this subsidence phase lasted from even before the CAMP magmatism (~200 Ma), affecting the whole deposition of the lacustrine succession, and was interrupted by the Cretaceous magmatic event (~126 Ma). Subsidence was also enhanced by crustal loading associated with thick subsurface Jurassic intrusions and probably influenced the whole basin, in consequence of flexural effects. • A lacustrine depositional system is defined by cyclostratigraphy and facies analysis. • Facies are mainly organized in shallowing upward cycles. • The lacustrine succession evolves from an underfilled to an overfilled lake system. • The cycles define increasing accommodation space upsection. • Geological and geophysical data suggest a post-CAMP thermal subsidence. [ABSTRACT FROM AUTHOR]

The transgressive-regressive events due to changes in the eustatic sea level represent the occurrence of an epeiric sea in Western Gondwana. This event is recorded in the carbonate-siliciclastic succession exposed in the central portion of the Parnaiba Basin, Northern Brazil, mainly represented by densely fossiliferous deposits, with mollusks, brachiopods, corals and microfossils, related to the upper member of the Piauí Formation. Outcrop-based facies/microfacies and stratigraphic analysis of this succession allowed the individualization of two facies associations (FA), representative of a shallow carbonate platform system adjacent to a coastal dune field. The FA1– dune field/interdune, comprises well sorted, intensely biortubated, fine to medium-grained sandstone with even parallel and tabular cross stratification, as well as translatent climbing ripple cross-lamination. FA2-shallow sea deposits consist of fossiliferous pelletal carbonate and microspar carbonate layers, laterally continuous for hundreds of meters, interbedded with centimetric beds and lenses of organic shale with small pyrite crystals. Covariant values of positive δ18O carb and negative δ13C carb for the carbonate profiles, together with intense substitution of primary constituents by dolomite and an abundance of associated organic matter contributed towards determining an organogenic dolomitization model. Although the Pennsylvanian records a long icehouse event, glacioeustatic fluctuations were common during the Moscovian and Kasimovian. The icehouse periods contributed to the semi-arid to desert conditions that shaped the aeolic environments of the Piauí Formation. Later greenhouse events favored a rise in the sea level and development of an extensive epicontinental Pennsylvanian sea that extended throughout Western Gondwana called the Itaituba-Piauí sea in this paper, which connected the Andean, Solimões, Amazonas and Parnaíba basins. • Carbonate-clastic sedimentation in the Penssylvanian of Parnaíba Basin. • Coastal wind dunes from the top of the Piauí Formation. • Piauí Formation evidences the epicontinental sea in West Gondwana. • Dolomitization and δ13C carb and δ18O carb of shallow sea carbonates in the Piauí Formation. • The carbonate factory on the great lakes/sea were ceased. [ABSTRACT FROM AUTHOR]

The Permian Period of the Parnaíba Basin, northern Brazil, represented here by deposits from the Pedra de Fogo Formation, records important events that occurred in Western Gondwana near its boundary with the Mesozoic Era. The analysis of outcrop based facies from the Permian Pedra de Fogo Formation, which is 100 m thick, carried out along the eastern and western borders of the Parnaiba Basin, allowed the identification of eleven sedimentary facies, which were grouped into three distinct facies associations (FA), representative of a shallow lacustrine system associated with mudflats and ephemeral rivers. Bioturbation, desiccation cracks, silcretes and various siliceous concretions characterize the Pedra de Fogo deposits. The FA1 mudflat deposits occur predominantly at the base of the Pedra de Fogo Formation and consist of laminated claystone/mudstone, mudcrack-bearing sandstones/mudstones and sandstones exhibiting cross-lamination, massive and megaripple bedding. Popcorn-like silicified nodules and casts indicate evaporite deposits. Other common features are silica concretions, silicified tepees and silcretes. FA2 represents nearshore deposits and consists of fine-grained sandstones with evenly parallel lamination, climbing ripple cross-lamination, massive and megaripple bedding and mudstone/siltstone showing evenly parallel lamination. FA3 refers to wadi/inundite deposits, generally organized as fining-upward cycles of metric size, composed of conglomerates and medium-grained pebbly sandstones showing massive bedding and cross-stratification, as well as claystone/siltstone showing evenly parallel to undulate lamination. Scour-and-fill features are isolated in predominantly tabular deposits composed of mudstones interbedded with fine to medium-grained sandstones showing planar to slightly undulate lamination. Silicified plant remains previously classified as belonging to the Psaronius genus found in the uppermost levels of the Pedra de Fogo Formation, near the contact with the Motuca Formation, are considered here as excellent biostratigraphic markers. Fish remains, ostracods, bryozoans and scolecodonts represent other fossils that are present in the succession. Mudflat deposits developed in an arid and hot climate probably in the Early Permian. Semi-arid conditions prevailed in the Middle Permian allowing the proliferation of fauna and flora in adjacent humid regions and onto the lake margin. The climate variation was responsible for the contraction and expansion phases of the lake, fed by sporadic sheet floods carrying plant remains. The reestablishment of the arid climate, at the end of Permian, marks the final sedimentation of the Pedra de Fogo Formation, linked to the consolidation of the Pangaea Supercontinent. This last event was concomitant with the deposition of the Motuca Formation red beds and the development of extensive ergs related to the Triassic Sambaíba Formation in Western Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: Event Layers in Neoproterozoic cap carbonates of Brazil's southwestern Amazon Craton record post-Marinoan synsedimentary seismicity. The 35 m-thick cap carbonates overlie glaciogenic sediments related to the Marinoan glaciation (635 Ma) and are comprised of two units: the lower cap consists of dolomite (∼15 m thick) and the upper cap is limestone (∼25 m thick). The cap dolomite includes pinkish crystalline dolostone with even parallel lamination, stratiform stromatolites, eventual tube structures and megaripple bedded peloidal dolostone interpreted as shallow (euphotic) platform deposits. The cap limestone onlaps the cap dolomite and consists of red marl, gray to black bituminous lime mudstone, bituminous shale with abundant calcite crystal fans (pseudomorphs after aragonite) and even parallel lamination interpreted as moderately deep to deep platform deposits. Five successive events of synsedimentary deformation were recognized in the cap carbonates exposed at Mirassol d'Oeste and Tangará da Serra, in Central Brazil: Event 1 – large to small-scale load cast structures in the contact between dolostones and glaciogenic sediments; Event 2 – stromatolitic lamination truncated by tube structures; Event 3 – vertical to subvertical fractures and faults, and large-scale synclines and anticlines with chevron folds; Event 4 – conglomerate and breccia filling neptunian dykes limited by undeformed beds; and Event 5 – slump and sliding deposits found only in the upper part of the cap limestone. Event 1 was produced by hydroplastic dynamics likely induced by isostatic rebound during ice cap melting in the final stages of the Marinoan glaciation. Events 2 and 5 are autocyclic in nature, and related to depositional processes. Event 2 is linked to fluid and methane escape from organic degradation of microbial mats and domes that formed tubestones; Event 5 is associated to collapse and sliding/slumping in the platform and slope. The reliable orientations of synsedimentary faults, and fractures and folds of events 3 and 4 are consistent with regional extensional tectonics associated with earthquakes that triggered sediment deformation. The 200 km that separate the occurrences of cap carbonates suggest that important seismic events took place during the early Ediacaran in the southern Amazon Craton. [Copyright &y& Elsevier]

Samples from outcrops of the Miocene Solimoes and Barreiras formations from the central and coastal Amazon regions of Brazil were analyzed palynologically. Assemblages of fossil fungi were identified, and are described herein, and their relevance to paleoenvironmental and paleoclimatic studies in tropical regions discussed. The fungal assemblage comprises four spore groups, 19 species belonging to 12 genera. Additionally, two new species are proposed. The samples from the Solimoes Formation contain the following taxa: Mediaverrunites elsikii, Mediaverrunites mulleri, Monoporisporites sp., Fusiformisporites crabbii, and Multicellites cingulatus. The presence of these suggests river channel margins colonized by freshwater vegetation, where seasonal fluctuations of water table and rainfall produce wetter substrates. The samples from the Barreiras Formation showed higher species and generic diversity than those from the Solimoes Formation with Hypoxylonites minutus, Hypoxylonsporites ater, Hypoxylonites sp., the new species Inapertisporites multiporus n. sp., Pluricellaesporites regularis, Lacrimasporonites levis, Monoporisporites annulatus, Spirotremesporites simplex, Dyadosporites novus, Dyadosporites sp., and Multicellaesporites attenuates. All of these correspond to parasitic fungi from a range of from tropical wetlands. Spegazzinites sp. and Dicellaesporites aculeolatus, good indicators of marine influence and mangrove presence, were also identified in the samples from the Barreiras Formation. Furthermore, the fungal spore taxa Inapertisporites multiporus, Mediaverrunites elsikii, Mediaverrunites mulleri, Pluricellaesporites regularis, and Spirotremesporites simplex serve as stratigraphic indicators when combined with miospore index taxa such as Crassoretitriletes vanraadshooveni, Grimsdalea magnaclavata and Fenestrites longispinosus indicating a Miocene age for these sediments in the Amazon region. [ABSTRACT FROM AUTHOR]

The opening of the Central Atlantic Ocean was accompanied by ascending plume zones that generated large igneous provinces (LIPs), such as the Central Atlantic Magmatic Province (CAMP), with voluminous lava flows and outpourings. One of the best records of the CAMP in the West Gondwana is the Jurassic volcanic-sedimentary succession exposed in the western Parnaíba Basin, northern Brazil. Diagenetic and hydrothermal processes are discussed, focusing on the lava-sediment interaction. The siliciclastic sediments called "intertrap deposits" record a wet desert system characterized by fluvial-aeolian and shallow lake deposits engulfed by lavas of the CAMP at approximately 200–202 Ma. The facies and petrographic studies, based on a drill core and outcrops, led to the interpretation of the palaeoenvironmental and diagenetic evolution of the intertrap deposits. The intertrap deposits are sandwiched by basalts and may be organized in seven sedimentary facies, grouped into two facies associations: 1) ephemeral braided river deposits (FA1), which consist of medium- to coarse-grained pebbly sandstone with poorly sorted angular to sub-rounded grains (basaltic fragments and quartz) and low-angle cross-bedding, even-parallel stratification, and trough cross-stratification, and 2) pond/shallow lake deposits (FA2) composed of tabular beds of sandstone/siltstone rhythmite and laminated mudstone. The main architectural elements of intertrap deposits are 1) channels on volcanic substrate, 2) sand sheets deposited over pre-existent lava topography, 3) tabular beds with laminated rhythmites, and 4) sand-filled fissures/fractures and clastic dykes. The intensification of magmatic processes due to the disruption of Pangaea promoted the formation of extensive volcanic plains, whereas wet desert settings were developed during the quiescent intervals between lava flow episodes. Fluvial channels with subaqueous dunes and sand sheets were incised into the basaltic substrate. The abandoned fluvial plains were affected by flash floods that promoted mechanical infiltration of clays, forming coatings over grains. The heat flow and hydrothermal activity of volcanic rocks increased the devitrification of glassy clasts, releasing silica and precipitating low-temperature authigenic mineral assemblages. The most common pore-filling process was the massive precipitation of early diagenetic-hydrothermal minerals, including smectite, chalcedony, poikilotopic zeolite, megaquartz, and haematite, which partially obliterated the primary porosity and permeability. These exceptional conditions of cementation triggered by basalt eruptions precluded the modification of a primary framework by late stages (post-Jurassic) burial diagenesis. The intertrap sandstones represent the last lava-sediment interaction related to the CAMP recorded in West Gondwana. • Pangaea breakup caused the installation of large volcanic plains in West Gondwana. • Wet desert settings developed during the quiescent intervals between lava flows. • The first description of CAMP-related lava-sediment interaction for the West Gondwana. • Basaltic hydrothermalism overtook the diagenetic history of the intertrap sandstone. • Heat flow-induced devitrification amplified silica release and authigenesis. [ABSTRACT FROM AUTHOR]

• The occurrence of giant stromatolites within extreme palaeoceanographic and palaeoenvironmental changes provides an opportunity to understand the interaction between biological and sedimentological processes. • The transition from stratiform to domal morphology reflects the progressive deepening of the platform, concomitant with increases in microbial activity. • The progressive generation of accommodation space related to sea-level rises and glacial isostatic adjustment (GIA) caused subsidence in the coastal zone, as proposed by the Snowball Earth hypothesis. • The decline in microbial communities in carbonate platform caused by the massive influx of siliciclastic sediments in a mixed water setting, influenced by intense turbidity and continuous burial of the communities. Giant domal stromatolites associated with vertical tubestone are reported for the first time in the Marinoan (635 Ma) Puga cap dolostone on the southern Amazon Craton, Brazil. The well-preserved giant domal mounds reach 12 m in diameter and 10 m in height, forming laterally continuous biostromes of at least 200 m. The giant mounds occur mainly on the top cap carbonate succession overlying stratiform stromatolites directly underlying glacial diamictites marking the Cryogenian-Ediacaran boundary. We discuss the sedimentological and biological conditions during the greenhouse period that led to the development of these exceptional stromatolitic features. The microbial communities primordially colonized the diamictite substrate, forming stratiform bioconstructions in a shallow platform under hypersaline calm water conditions. The transition from stratiform to domal morphology reflects the progressive deepening of the platform, concomitant with increases in microbial activity. The high production and pre-lithification of carbonate muds, that formed a rigid load-resistant framework, allowed for the accumulation by vertical accretion, increasing the potential for preservation of giant mounds. The progressive generation of accommodation space related to sea-level rises and glacial isostatic adjustment (GIA) caused subsidence in the coastal zone, as proposed by the Snowball Earth hypothesis. The maximum flooding was associated with an increase in siliciclastic inflow, causing burial of microbial communities and the demise of giant stromatolites. The succession was succeeded by the deposition of long-term transgressive lime mud in a CaCO 3 -oversaturated sea. The giant stromatolites consist of a new element of the Marinoan Puga cap carbonate and provide essential insights to enlarge the discussion about the biological and sedimentological interaction that occurred on post-glacial carbonate platforms worldwide. [ABSTRACT FROM AUTHOR]

The low-latitude Marinoan glaciation (635 Ma) record in the southern Amazon Craton has been one of the most important sites with strong evidence for the Neoproterozoic Snowball Earth hypothesis. In Central Brazil, the 50-m-thick carbonate succession of the post-Marinoan cap carbonate exposed in the Tangará da Serra region, Central Brazil, represents a complementary section of the classical occurrence of the Puga cap carbonate in Mirassol d'Oeste region, that overlies glaciogenic deposits marking the well-preserved Cryogenian-Ediacaran boundary in South America. The 8-m-thick cap dolostone that represents the Mirassol d'Oeste Formation consists of pinkish microcrystalline peloidal dolomudstone, exhibiting even parallel to low-angle lamination locally tubestone, and megaripple bedded dolopackstone. The cap dolostone is succeeded upsection by the cap cementstone limestone (basal Guia Formation), comprising laminated lime mudstone rich in silt-sized terrigenous grains (quartz), and subordinately bituminous shale, dolomitic marls, intraformational breccias, and abundant calcite crystal fans and crusts. Crystal fans occur in isolated and decimetre-scale arrays and are considered aragonite pseudomorphs. Primary precipitation of dolomite, crystal fans, and micrite and the formation of tubestone are related to depositional processes. The cap dolostone was affected by the neomorphism of the dolomicrite, development of vug and intercrystalline porosity, euhedral dolomite precipitation, synsedimentary fracturing, calcite and quartz precipitation, chemical compaction, Fe-oxide substitution, and precipitation. The diagenetic processes of the cap cementstone limestone were pyrite precipitation, calcite cementation, neomorphism of micrite and crystal fan, partial crystal fan dissolution, dolomitization, chemical compaction, fracturing, ferrous dolomite and calcite precipitation, pyrite (pseudomorph) and micrite replacement with Fe-oxide and replacement of rhombohedral dolomite by Mn-oxides. Hydrocarbons are rare and its migration represents the last diagenetic event being found: 1) in fractures and interpeloidal, vug and intercrystalline pores (~2%) with low permeability and connectivity of the cap dolostone; and 2) in intercrystalline pores, fractures, and rare pores in crystal fans of the cap cementstone limestone. During the post-Marinoan sea-level rise occurred the establishment of a shallow to moderately deep microbially induced dolomitic platform locally influenced by storm-action. The progressive transgression led the implantation of a deep anoxic and CaCO3-oversaturated aragonitic platform. The similarities of cap carbonate microfacies among the post-Marinoan succession worldwide reflects an extraordinary and non-recurring global precipitation event in geological history. In contrast, besides the majority of cap carbonate have the same textural and compositional framework, the diagenetic history seems to be regional and completely dependent on the tectonic, thermal, and burial history of the depositional basins where they were deposited. [ABSTRACT FROM AUTHOR]

Glacial strata are excellent stratigraphic markers in Paleozoic basins worldwide. The eastern Parnaíba Basin in northern Brazil is a highly favorable setting for studying episodes related to the Ordovician-Silurian glaciation. Previous studies in this region led to the recognition of unequivocally glaciogenic sediments associated with pre- and postglacial deposits, favoring the understanding of lower Paleozoic events that occurred in West Gondwana. Outcrop-based facies and stratigraphic analyses of the ~170 m-thick siliciclastic succession of the Serra Grande Group indicate fluvial, glacial, and coastal depositional systems. Seventeen sedimentary facies are grouped into seven facies associations (FAs): FA1, interpreted as intermediary sheet braided plain deposits that consist of tabular cross-bedded coarse-grained sandstones and conglomerates; FA2-FA4, which correspond to subaqueous glacial deposits comprising massive to stratified diamictites, cross-laminated sandstones, diamictites and organic matter-rich black shales with dumpstone and dropstone structures; FA5-FA6, constituting organic matter-rich black shales, fine- to medium-grained sandstones with sigmoidal cross-bedding and occurrences of the ichnotaxon Arthrophycus interpreted as delta front deposits; and FA7, composed of medium- to coarse-grained pebbly sandstones interpreted as channelized braided plain deposits. This interpretation partially confirms the previous paleoenvironmental interpretation discounting the presence of subaerial alluvial fan and outwash plain deposits for this unit. The sequence stratigraphy of the Serra Grande Group is refined mainly using the coherent interpretation of the key surfaces and comparing the systems tracts with the global sea-level curve, providing a more robust third-order sequential evolutionary model that includes three depositional sequences. The Middle Ordovician sheet braided deposits are the lowstand sediments of Sequence 1 truncated by an extensive unconformity that possibly removed the transgressive and highstand strata. This unconformity generated by glacial dynamics represents 23 Myr during the Late Ordovician to early Silurian. The second sequence started with the advance of ice sheets in marginal areas of the basin, causing the deposition of ablation diamicton during the lowstand. The postglacial transgression is marked by ice-rafted debris from icebergs deposited onto organic matter-rich mud in the shoreface-offshore zone. The maximum flooding during the middle to late Silurian was succeeded by the highstand phase marked by the progradation of deltaic deposits. Biological activity is marked by the presence of polychaetes that reworked the marine seafloor. The Early Devonian featured extensive sea-level fall and renewed continental drainage with the formation of a braided plain marking a lowstand phase of Sequence 3. These new interpretations allow the global correlation of the Serra Grande Group and provide an improved understanding of the role of ice sheets and postglacial transgressions that affected West Gondwana during the Ordovician-Silurian periods. [ABSTRACT FROM AUTHOR]

Provenance analyses are highly affected by transport, depositional and diagenetic processes, as well as the grain size chosen for evaluation. In order to avoid misleading data, provenance research requires multi-approach techniques. In this work, a set of widespread methods were applied to investigate a debatable stratigraphic interval in the Parnaíba Basin, northeastern Brazil. Discontinuous exposures and fault displacements result in enigmatic stratigraphic relations in the Mesozoic portion of this basin. This succession consists of the lacustrine sandstones and shales of the Pastos Bons Formation and aeolian sandstones of the Corda Formation, composing the Mearim Group, and fluvial conglomerates and sandstones of the Grajaú Formation. The provenance was studied through sandstone petrography, quartz petrography, hot cathodoluminescence and heavy minerals analyses. Sandstones from Mearim Group plotted in recycled orogenic and craton interior fields, whereas quartz petrography and cathodoluminescence constrained predominantly volcanic sources. The heavy minerals assemblages of the lacustrine and aeolian deposits are very similar, whereas the fluvial succession presents texturally immature grains and anomalous high hornblende content. Additionally, ZTR, GZi and RZi indexes are higher for lacustrine and aeolian deposits, and lower for fluvial beds. These data indicate polycyclic minerals and mixed sources for Mesozoic sandstones of the Parnaíba Basin. The Mearim Group presents both volcanic contribution, probably supplied by basalts from the Central Atlantic Magmatic Province (CAMP), and low to medium-grade metapelitic heavy minerals assemblage. Heavy minerals were probably supplied by Neoproterozoic metapelites from the Ceará Central Domain (Ceará Group?), Borborema Province. Conversely, heavy minerals of the Grajaú Formation were derived from I-type Brazilian granites, incompatible with the Mearim Group. These data provided new stratigraphic relations for the Mesozoic deposits of the Parnaíba Basin and implications for the evolution of this basin. • Stratigraphic positioning of a debatable Mesozoic succession is investigated. • Petrographic data indicate recycled orogenic and craton interior sources. • We distinguish and separate the Mearim Group units from the Grajaú Formation. • Neoproterozoic metapelites and CAMP basalts sourced the Mearim Group. • Provenance data suggest shift source areas or unroofing of common source areas. [ABSTRACT FROM AUTHOR]

The Tamengo Formation corresponds to one of the most complete records of Ediacaran carbonate deposits in South America that contains Cloudina and Corumbella calcified exoskeletons macroscopic fossils. With the objective of characterizing its paleoenvironment, a total of ten sedimentary facies indicative of a carbonate platform were identified. In the outer ramp region there are massive mudstones, massive marl to claystones, and shales. In the mid-ramp there are facies that are storm-dominated with swaley/hummocky cross-stratified grainstone, tangential cross-bedding grainstone, massive bioclastic grainstone and massive marl to claystone. Lastly, in the inner ramp portion there are massive intraclastic grainstone, massive intraclastic rudstone, massive oolitic grainstone and laminate mudstone/shale rhythmite, and microbial textures are present at the base of the rhythmites, indicative of a back-ramp environment. Faciology data indicate that the Cloudinas inhabited a protected environment between oolitic bars in the inner ramp and back-ramp. These organisms were periodically transported and reworked by waves generated by storms in the mid-ramp and outer ramp zones. The positive values for δ13C in carbonates (1,5 to 5,4‰) and δ15N (between 3,5 and 4,5‰) of deposits with Cloudina indicate a marine paleoenvironment with shallow, hot, and oxygenated waters with a high productivity of organic matter. In this context, the facies analyses and stratigraphy, aided by C, O, and N isotopes from the Tamengo Formation in outcrops from the Corumbá regions in the southwest of Brazil allows for the reconstruction of an Ediacaran carbonate ramp and inferences about the habitat of Cloudina , thus increasing understanding of this important chapter of Earth history. • Ten sedimentary facies grouped into four facies associations that indicate a storm-dominated carbonate ramp. • Cloudina inhabited a back-ramp environment protected from wave action by oolitic bars of the inner ramp. • Eventually Cloudina was transported to the mid-ramp to outer ramp zones where it was subjected to reworking by storm waves. [ABSTRACT FROM AUTHOR]

Zeolite cement is one of the main components of the Jurassic to Lower Cretaceous fluvial-aeolian succession in the Parnaiba Basin, northeastern Brazil. Core and outcrop-based stratigraphic analyses permitted the paleo-environmental and diagenetic interpretation of aeolian sandstone and showed the influence of the volcanic substrate in the origin of the zeolite cement. The substrate is represented by an extensive volcanic plain developed in the last stages of the Central Atlantic Magmatic Province (CAMP) in West Gondwana. The siliciclastic deposits consist of dune field, sand sheet and wadi deposit facies associations. The zeolite cement of the aeolian succession forms poikilotopic crystals with anomalous up to 50% modal content. X-ray diffraction and SEM/EDS/CL analyses showed laumontite and Ca-stilbite exhibiting, respectively, massive and radial textures. During eodiagenesis, the main processes included clay infiltration linked to water table fluctuations and flash flood events, producing clay coatings and displacive stilbite cementation. Massive laumontite cementation and smectite-chlorite conversion occurred in the mesodiagenesis, while in the final stages, the zeolite was partially replaced by calcite cement. Telodiagenesis is recorded by iron exsudation and the corrosion of clay films. Several processes can be inferred to explain the origin of the zeolite cement in the Jurassic-Lower Cretaceous sandstone of the Parnaiba Basin. After the first magmatic pulse (Triassic magmatism), the zeolite-bearing basalts were submitted to chemical weathering, causing cation leaching. Afterwards, the deposition of aeolian sands related to a wet desert system occurred above this weathered substrate. Fractured basaltic substrate favored the release of ions to the surface, with fluids enriched in sodium and calcium that percolated the permeable aeolian sandstone beds during the diagenesis. Furthermore, zeolite cement is geographically associated with the volcanic substrate in the western Parnaíba Basin. However, it is absent in the eastern part, where the aeolianites overlie sedimentary rocks. We suggest that the system was thermally reactivated by the last thermal CAMP phase, with basalt emplacement in the eastern Parnaiba Basin linked to the opening of the Equatorial Atlantic Ocean (Cretaceous magmatism). The progressive heating towards the western part of the basin triggered fluids convection, and the enrichment in ions such as Ca2+, Si4+, Na+, Al3+, HCO− 3 and SO 4 2−, promoting optimal conditions for zeolite crystal growth (100 °C–300 °C). Sandstone textural aspects, as well as extensional faults and fractures allowed fluids migration resulting in the massive poikilotopic zeolite cementation, characterizing one of the most singular features of the diagenetic history of the West Gondwana record. Unlabelled Image • Genesis of poikilotopic zeolite cement in aeolian sandstones is investigated. • Zeolites occur in anomalous content in aeolianites from Mesozoic of Parnaíba Basin. • Zeolite only occurs associated with a weathered volcanic substrate. • These deposits are influenced by heat propagation due to CAMP emplacement. [ABSTRACT FROM AUTHOR]

The demise of the carbonate platform in the Brazilian Equatorial Margin has been related to the progradation of massive siliciclastic inflow from the Cratonic Amazon River during the middle Miocene. The sediment plume did not influence the eastern portion of this drainage, including the Bragantina Platform andthe Marajó Basin, the onshore Pará-Maranhão Basin. The provenance signatures of these tectonic segments have been demonstrated in siliciclastic coastal deposits of the Barreiras Formation, whose progradation caused the suppression of the Oligocene-Miocene carbonate platform. Our provenance study is based on clast morphology, quartz cathodoluminescence, and heavy minerals of mainly Barreiras alluvial-fluvial deposits, using new and published facies data. This study opens a window of opportunity to investigate, for the first time, the proximal facies combined with paleocurrents exposed only in this area of Brazil. The restricted occurrence of proximal facies indicates an exceptional potential for preservation related to subsiding regions generated by reactivated faults in the Gurupi Belt. Provenance data indicate the strong influence of metamorphic source rocks with minor volcanic and plutonic contributions from the southeastern and southern of the Bragantina Platform and eastern Marajo Basin. Respectively, two heavy minerals assemblages were found: 1) staurolite, metamorphic quartz, and angular clasts; and 2) abundant zircon, kyanite, tourmaline, mixed quartz (metamorphic, plutonic, and volcanic), and rounded clasts. The assemblages are associated with São Luís Craton, mainly crystalline rocks from Gurupi Belt. In addition, the proximal facies of the Bragantina Platform provide rich staurolite concentration and angular clasts indicating near source area; the uplifted Marajó Basin during the middle Miocene contributed with reworked sediments containing rounded clasts and ultrastable minerals related to Silurian-Cretaceous rocks. This work complements the previous paleoenvironmental reconstruction for the Barreiras deposits, including the most robust proximal facies interpretation contributing to understanding sediment dispersion during the middle Miocene, reinforcing previously defined source areas. • Alluvial fan deposits are definitively included in the middle Miocene Barreiras facies model. • The Barreiras delta spread across different geotectonic segments in eastern Amazonia. • Proterozoic, Paleozoic, and Mesozoic source rocks supplied the Barreiras fan delta.. • The Oligocene-Miocene Cratonic Amazon River never influenced the Barreiras fan delta. [ABSTRACT FROM AUTHOR]

The lateral and vertical distribution of sedimentary facies and ichnofacies in lacustrine systems records sensitive climatic variations and rates of subsidence. The Upper Jurassic–Lower Cretaceous lacustrine system of the Pastos Bons Formation in the Parnaíba Basin, northeastern Brazil, is an excellent opportunity to evaluate the depositional history of the post-CAMP thermal subsidence. This subsidence event succeeded the voluminous emplacement of mafic magma linked to the Central Atlantic magmatic province (CAMP), ∼201 Ma, forming a large subsiding area in West Gondwana. In this sense, this paper developed outcrop-based facies and ichnofacies analysis, allowing the interpretation of two depositional phases and four facies associations (FAs): 1) The lower depositional phase comprises lacustrine deposits showing an aggradational stacking pattern. FA1 - central lake records fibrous gypsum interbedded with fossiliferous shale beds, forming shallowing-upward cycles. 2) The upper depositional phase reveals a fluvio-lacustrine succession, forming a progradational stacking pattern. Central lake (FA1) comprises laminated mudstone and sandstone beds hosting a suite representative of Mermia ichnofacies, forming coarsening-upward cycles. Lakeshore (FA2) comprising mudstone beds, limestone lenses, and sandstone beds hosting a suite representative of Scoyenia ichnofacies, forming shallowing-upward cycles; and conglomerate lenses overlaid by sandstone beds hosting a suite representative of Skolithos ichnofacies, forming fining-upward cycles. A braided fluvial system (FA3) comprises conglomerate and sandstone beds, forming fining-upward cycles. Delta front (FA4) comprises mudstone lenses and sandstone beds hosting a suite representative of Skolithos ichnofacies, organized in coarsening-upward cycles. The fluvial discharge and wave activity oxygenated the water lake in the progradational phase, creating chemical and biological conditions that allowed the establishment of the epifaunal and infaunal benthic communities, represented by the well-preserved ichnological record. The decrease of the post-CAMP thermal subsidence rates (accommodation potential) related with the increase of the wet periods to the top of the succession (sedimentary supply) indicate a depositional evolution from underfilled to overfilled lake basin, during Upper Jurassic–Lower Cretaceous, in West Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: Palynostratigraphic and sedimentary facies analyses were made on sedimentary deposits from the left bank of the Solimões River, southwest of Manaus, State of Amazonas, Brazil. These provided the age-dating and subdivision of a post-Cretaceous stratigraphic succession in the Amazonas Basin. The Novo Remanso Formation is subdivided into upper and lower units, and delineated by discontinuous surfaces at its top and bottom. The formation consists primarily of sandstones and minor mudstones and conglomerates, reflecting fluvial channel, point bar and floodplain facies of a fluvial meandering paleosystem. Fairly well-preserved palynoflora was recovered from four palynologically productive samples collected in a local irregular concentration of gray clay deposits, rich in organic material and fossilized wood, at the top of the Novo Remanso Formation upper unit. The palynoflora is dominated by terrestrial spores and pollen grains, and is characterized by abundant angiosperm pollen grains (Tricolpites, Grimsdalea, Perisyncolporites, Tricolporites and Malvacearumpollis). Trilete spores are almost as abundant as the angiosperm pollen, and are represented mainly by the genera Deltoidospora, Verrutriletes, and Hamulatisporis. Gymnosperm pollen is scarce. The presence of the index species Grimsdalea magnaclavata Germeraad et al. (1968) indicates that these deposits belong to the Middle Miocene homonymous palynozone (Lorente, 1986; Hoorn, 1993; Jaramillo et al., 2011). Sedimentological characteristics (poorly sorted, angular to sub-angular, fine to very-coarse quartz sands facies) are typical of the Novo Remanso Formation upper part. These are associated with a paleoflow to the NE-E and SE-E, and with an entirely lowland-derived palinofloristic content with no Andean ferns and gymnosperms representatives. All together, this suggests a cratonic origin for this Middle Miocene fluvial paleosystem, which was probably born in the Purus Arch eastern flank and areas surrounding the crystalline. The palynological analysis results presented herein are the first direct and unequivocal evidence of the occurrence of Middle Miocene deposits in the central part of the Amazonas Basin. They also provide new perspectives for intra- and interbasin correlations, as well as paleogeographic and paleoenvironmental interpretations for the later deposition stages in the northern Brazilian sedimentary basins. [Copyright &y& Elsevier]

• Microbial laminites compose a great part of the Dolostone Cap Carbonate. • Microbialites are related to the origin of typical sedimentary structures of the Marinoan. • Bathymetry and energy were responsible for the end of microbialites. • The end of the Microbialites changed the main means of carbonate precipitation. At the margin of the Amazon Craton (west-central Brazil), the Mirassol D'Oeste Formation comprises an emblematic, 16 m-thick Marinoan cap dolostone deposited directly upon diamictites of the Puga Formation. Laterally continuous and morphologically simple microbialites, a common component of Marinoan cap carbonates, begin two meters above the base of the formation and continue upwards as stratiform, domical and irregular wavy microbial laminate boundstones for approximately 10 m. These microbialites consist of alternating thin and thick laminae of peloids (micritized remains of microbial colonies) and subordinate micrite with spar-filled fenestrae that differ in the greater relative abundance of fenestrae in the thicker laminae. The microbialites developed profusely in a calm platformal environment below storm-wave base level, but within the photoic zone, without any contribution of siliciclastics, the Waxing phase of growth. Vertical dolomicrite-filled tubestone structures up to 10 m, occupy the apical portion of the broad domical microbial laminites, Confined percolation of fluids seems the most plausible hypothesis for their origin. The wanning phase began in the final meter of the boundstone consists of irregularly wavy microbial laminites indicating prolonged oscillatory wave-action, followed by dolomitic peloidal grainstone-packstone with megaripple and millimetric macropeloids generated by oscillatory wave action during tradewinds. The hydrodynamic change and a rising sea level put an end to microbialite deposition in the Mirassol D'Oeste cap carbonate. [ABSTRACT FROM AUTHOR]

Upper Devonian-Lower Carboniferous deposits in north Brazil show a postglacial transgressive event characterized by the formation of thick layers of gray to black shales. In the Parnaíba Basin, the shales of the Longá Formation overlap the Upper Famennian non-marine glacial deposits of the Cabeças Formation marked by a ravinement surface. The Longá shales exhibit wavy-lenticular beddings in their base, grading to gray-black shales locally interbedded with thin layers of sandstones with hummocky cross-stratification and megaripple bedding. These deposits were interpreted as having formed in shallow marine upper offshore to lower shoreface with episodic storm events. The organic matter analysis of the outcropping Longá shales using Total Organic Carbon (TOC), Rock-Eval pyrolysis, and biomarkers provide several geochemical parameters for the interpretation of the paleoenvironment, the origin of the organic matter and its thermal maturation. The Longá shales presented low TOC contents (less than 1%), very low numbers of free hydrocarbons (S1), and potential generators (S2). The maximum pyrolysis temperature (Tmax), as well as the thermal maturation biomarker parameters, indicate that the Longá shales are immature. The values of pristane/n-C 17 , phytane/n-C 18 , Hydrogen Index (HI) and Oxygen Index (OI) suggest kerogen types III and IV, which are formed from conical land leaves, needles, and plant waxes; this interpretation is also supported by total sulfur (TS) < 0.2 wt%, terrigenous/aquatic ratio (TAR), C 29 -sterol, hopane/sterane and Methylphenanthrene (MPs). This organic matter was deposited in an epeiric sea with shallow water, oxidizing conditions, normal salinity, and low temperatures prevalence. • The Longá shales record the postglacial transgressive event of D-C Boundary of South America. • Longá Formation is composed by wave- and storm-dominated marine systems. • The organic poor-shales were deposited in a marine environment under oxic and normal salinity with high terrestrial organic matter input. • The organic matter is immature forming kerogen type III and IV from land plant. • The Longá shales are correlated with other Devonian shales of Western Gondwana intracratonic basins. [ABSTRACT FROM AUTHOR]

Fossil bonanzas called Konservat Lagerstätten provide geological windows to the ecology of ancient life communities. These deposits often occur as cluster of fossil localities with similar geographic locations, geological ages and facies, as the fossils were generally preserved during special periods and large-scale events in Earth history within environments with exceptional taphonomic conditions. This work applied petrological and geochemical analyses to evaluate the taphonomic pathway of a Konservat Lagerstätten in the Muzinho Shale, Upper Jurassic-Lower Cretaceous of the Parnaíba Basin, northeastern Brazil. These lacustrine deposits include interbedded limestones and fossiliferous black shales deposited in anoxic, non-euxinic and saline environment. Black shales contain articulated skeletons of fish fossils, characterised by three-dimensional preservation of the skeletal tissue. The polytypical assemblage includes diverse ontogenetic stages and is concentrated in a specific stratigraphic level. Mass mortality was triggered by anoxia probably established by stratified water column, high C flux and thermocline demise. The specimens are encased in kerogen-bearing siliciclastic laminae and cementstone microfacies, both microbially-induced. The fossils were cemented by eodiagenetic poikilotopic calcite that filled the skeletal articulation, including bone trabeculae and voids originally filled by bone marrow. The short distance, similar fossil assemblages, ages and coincident palaeoenvironments suggest that Muzinho Shale (Parnaíba Basin) and Crato Formation (Araripe Basin) compose a cluster of exceptional preservation in West Gondwana. Lava flows and outgassing related to the Central Atlantic Magmatic Province (CAMP) resulted in the subaereal exposure of volcanic plains, acid rains and subsequent CO 2 greenhouse crisis. CAMP-magmatism was especially voluminous in northern Brazilian basins, enhancing nutrient-rich waters and lacustrine eutrophication due to intensified chemical weathering in this area. Probably, other Konservat Lagerstätten remain unreported in West Gondwana. Despite similar causative events, the individual taphonomic pathways of Muzinho Shale and Crato Formation are very different, suggesting that in these cases local phenomena affected authigenesis and diagenesis. • Exceptionally preserved fossils are evaluated through petrography and geochemistry. • Three-dimensional preservation of bone tissue allows proposing a new Lagerstätte. • CAMP-related magmatism and intensified chemical weathering triggered eutrophication. • Similar location and geological data suggest clusters of exceptional preservation. • Despite similar taphonomic pathways, autogenic factors control fossildiagenesis. [ABSTRACT FROM AUTHOR]