Crato Formation Research Articles

Chemical and mineral comparison of fossil insect cuticles from Crato Konservat Lagerstätte, Lower Cretaceous of Brazil

The Crato Formation palaeoentomofauna from the Lower Cretaceous (Aptian) of northeast Brazil is extremely well preserved. Crato insects are often complete with abdomen, thorax, head, legs, wings articulated and fragile cuticle details observed at the macro and micro scale. The Crato Formation stands out for the high diversity of fossil insects with at least 386 described species, so far. We investigate the preservation pathways through SEM–EDS and Raman spectroscopy, which give fundamental insights regarding the understanding of this complex theme. Our study compared cuticle soft-tissue preservation of Ensifera in different layers of the Crato limestone. The results of our analyses confirmed that the anaerobic bacterial respiration processes influenced the labile-tissues preservation. Ensifera fossils display preservational stages ranging from kerogenization to pyritization. Kerogenization represents the partial or complete chemical transformation of organic material into aliphatic and cyclic hydrocarbons in situ during mesodiagenesis, while pyritization occurs during the decaying of carcass in the early diagenesis. Here, we followed the previous hypothesis of fish tissue preservation that these processes are governed principally by variations in the positioning and residence time of the carcasses in different microbial zones within the sediment column. Besides early/mesodiagenetic modifications, oxidation processes during recent weathering led to some mineral transformations that played a key role in the preservation of Ensifera.

Taphonomy of lacustrine fish fossils of the Parnaíba Basin, northeastern Brazil: Spatial and causative relations of Konservat Lagerstätten in West Gondwana during Jurassic-Cretaceous

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 CO2 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.

New species of Myrmicium Westwood (Psedosiricidae = Myrmiciidae: Hymenoptera, Insecta) from the Early Cretaceous (Aptian) of the Araripe Basin, Brazil.

This paper records the first occurrence of the genus Myrmicium Westwood, 1854 in the Cretaceous of Gondwana and describes it as a new species Myrmicium araripterum sp. nov, based on the most complete specimen of this genus yet known, which represents the largest specimen of the grade "Symphyta" ever found in the Crato Formation.

Remarkable fossil crickets preservation from Crato Formation (Aptian, Araripe Basin), a Lagerstätten from Brazil

The paleoentomofauna recorded in the Crato Formation laminated limestones (Araripe Basin, Aptian) represents one of the most important Konservat-Lagerstätten deposits globally documented. Among the insects, the high morphological fidelity, abundance and diversity of the Grylloidea superfamily allows a more refined study of the external and internal cuticular morpho-anatomical features and preserved soft tissues. Scanning electron microscope analysis with coupled energy dispersion x-ray spectroscopy (SEM/EDS) show that the carcasses of the grylloids are predominantly replaced by three distinct mineral phases with occurrence of features hardly preserved in the fossil record such as the ommatidia's polygonal facets of compound eyes, cuticular layers differentiation (epi and procuticle), internal anatomical microstructures of digestive tract, ovarian fragments, eggs, and visceral and locomotor muscle tissues. The identification of significant microbial evidence associated with the cricket's carcasses allow us to interpret that the main factor responsible for the exceptional cricket's preservation is the influence of microbial mats in the fossilization process.

Biomarker signatures of Cretaceous Gondwana amber from Ipubi Formation (Araripe Basin, Brazil) and their palaeobotanical significance

An amber (UFRPE 5037), from the black shales of the Ipubi Formation, Araripe Basin (Brazil), has been analyzed to understand its organic geochemical characteristics and possible botanical source using gas chromatography–mass spectrometry (GC–MS). The analyses carried out detected monoterpenes, hydrocarbonic sesquiterpenes, and aliphatic diterpanes like abietanes and norabietanes, as well as aromatic diterpanes such as simonellite, norsimonellite, retene, hinokiol, ferruginol and dehydroabietic acid. Such a combination of components is mainly known to have originated from gymnosperms. The individual identification of diterpenoids allowed the suggestion of Cheirolepidiaceae or Podocarpaceae families as possible amber producers, pointing to a flora similar to the underlying Crato Formation. Therefore, UFRPE 5037 consists on the first amber record in the Ipubi Formation, allowing the acquisition of important information regarding the botanical sources associated to new Brazilian amber occurrence described here.

Phytogeographical implications of the probable occurrence of the gnetalean plant Welwitschiophyllum in the Late Cretaceous (Cenomanian) of Africa

A new fossil plant specimen, identified as a probable leaf of Welwitschiophyllum Dilcher et al. (2005) is reported from the Gara Sbaa Member of the? Lower Cenomanian to Turonian Akrabou Formation of south east Morocco. Previously Welwitschiophyllum was only known from the Early Cretaceous of Brazil, and this discovery considerably extends its temporal and geographical ranges. It is identified on account of its characteristic elongate shape, entire margins, parallel venation and an arcuate margin of the base. The new specimen expands our knowledge of the poorly-known Gara Sbaa florule, and is the first possible gnetophyte recorded from this locality, adding crucial knowledge to African Cretaceous floral diversity. Comparison with similar leaf types from the Aptian-aged Nova Olinda Member of the Crato Formation of north east Brazil hint at a xerophytic or perhaps halophilic floral province in equatorial Gondwana prior to the opening of the South Atlantic Ocean. This province is at least 3500 km from north to south.

Cratonaia novaolindensis gen. et sp. nov. (Unionida, Silesunionoidea) from the Aptian of Brazil (Araripe Basin), and its implications for the early evolution of freshwater mussels

The fossil-rich carbonate deposits of the Aptian Crato Formation, Araripe Basin (Brazil) are one of the main Cretaceous Konservat-Lagerstätten of Gondwana, and have come to fame globally. However, information on fossils from deposits other than the famous laminites of the basal part of the unit is scarce. Herein, we describe the first bivalves of the suborder Silesunionidina Skawina and Dzik, 2011 in the order Unionida Gray, 1854 from South America. The specimens were collected from a 0.3–1-m-thick grey to yellow mudstone interval located 0.3 m above the laminated limestones of the lower part of the Crato Formation at Nova Olinda, State of Ceará. They comprise exquisite composite, internal and external moulds, preserving key anatomical characters. Based on the analysis of muscle scars, hinge and ornamentation, these bivalves are here assigned to a new genus and species, Cratonaia novaolindensis gen. et sp. nov. The presence of a series of small pedal elevator scars linearly arranged on the external wall of the umbonal cavity indicates that this is a member of the suborder Silesunionidina. The new form is the by far youngest representative of this group. Closely related bivalves were previously reported from Triassic deposits of Australia, Africa, Europe and potentially India. Detailed stratigraphic, sedimentological and taphonomic observations indicate that the new taxon thrived in a freshwater lake. The occurrence of Silesunionoidea in the Lower Cretaceous of South America indicates that the condition of the musculature in Mesozoic freshwater mussels needs to be established to assign them confidently at family level.

Anti-inflammatory actions of marine natural products; the impact on molecular markers of innate immune responses

In this work we study two types of wood fossils (Gymnosperms, Araucariaceae) from the Crato Formation of Araripe Basin in Brazil, from the Cretaceous Period. The samples were characterized by Raman and infrared spectroscopies, X-ray diffraction and scanning electron microscopy. The results obtained by different techniques showed that although the rocks surrounding the fossils have predominantly the same constitution – calcite – however, the formation processes of these types of wood fossils are quite different. One of the fossils, denominated as light wood, is predominantly composed of gypsum, while the other fossil, the dark wood, is rich in amorphous carbon, possibly the kerogen type. Implications relative to the environment where the plants lived millions years ago are also given. Finally, the results highlight the constitution of one of the most important paleontological sites of the Cretaceous Period in the South America.

New gomphaeschnid dragonflies (Odonata: Anisoptera: Aeshnoptera) from mid-Cretaceous Burmese amber

A new true dragonfly, named Kachinaeshna zhuoi Zheng, Nel and Wang, gen. et sp. nov., is described from Cretaceous Burmese amber representing the second gomphaeschnaoidine from this deposit. Kachinaeshna Zheng, Nel and Wang, gen. nov. differs from other Gomphaeschnaoidinae in: the absence of an elongate distal paranal cell, directly basal of the anal loop, in the hindwing; a distinct curvature of RP2; and a curve of RP1 at the pterostigmal brace. The gomphaeschnaoidine dragonflies were previously only recorded from the Lower Cretaceous and mainly from the upper Aptian Crato Formation of Brazil. Based on the true dragonfly fossils found in Burmese amber, a possible late Early Cretaceous age is supported for Burmese amber.

A new genus of pipimorph frog (Anura) from the Early Cretaceous Crato Formation (Aptian) and the evolution of South American tongueless frogs

Pipimorpha is a clade of tongueless anurans with a wide fossil record. Furthermore, the oldest South American fossils come from the Late Cretaceous (Cenomanian) of Patagonia, Argentina. The aim of the present contribution is to describe a new genus and species of Pipimorpha from the Crato Formation (Aptian, Early Cretaceous), Araripe Basin, Brazil. The new specimen consists of a nearly complete skeleton that shows several anatomical similarities with other fossils from South America. Phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic South American clade. Further, some traditional groupings within Pipimorpha were not recognized. The new phylogenetic analysis reinforces previous biogeographical hypotheses sustaining dispersal of pipimorph between Africa and South America through an island chain or continental bridge across the Atlantic Ocean.

Architectural and facies characterization of the Aptian fluvial Barbalha Formation, Araripe Basin, NE Brazil

Abstract The Aptian Barbalha Formation records the beginning of the post-rift stage of the Araripe Basin. It consists predominantly of sandstones and mudstones interbedded with thin layers of bituminous black shales and conglomerates. The depositional and architectural features of the alluvial succession of the Barbalha Formation were characterized by detailed study and descriptions of the selected outcrops and analysis of well core data. In this study, two main depositional sequences were identified. The lower depositional sequence is more than 100 m thick and comprises a vertical facies succession composed of amalgamated, multistorey, braided fluvial channel sandstone bodies overlain by a widespread lacustrine black shale up to 10 m thick. The lacustrine black shales–carbonate mixed interval is known as the Batateira Beds and constitutes a regionally important stratigraphic correlation marker in the basin. This interval records the establishment of a large lake that experienced severe water-level fluctuations and anoxic events. The upper depositional sequence is 60–95 m thick, and mainly consists of thin, yellowish, medium- to fine-grained sandstones and variegated shales. The upper sequence rests unconformably on the lacustrine black shales of the Batateira Beds. Thin and discontinuous conglomerate beds at the base of the upper sequence laterally grade into coarse-grained sandstones. These coarse-grained sandstones are overlain by interbedded sandstones and mudstones organized in fluvial cycles. The upper and lower sequences of the Barbalha Formation are separated by an erosive unconformity, traceable throughout the study area, formed during a period of stratigraphic base-level lowering. This surface marks a change in the lower sequence from a dominantly fluvial depositional style, with amalgamated multistorey braided fluvial channel sand bodies, to a lacustrine system in the top to an eminently fluvial sedimentation, which in the basal section comprises amalgamated, multistorey, braided fluvial channel sand bodies, and in the superior section the amalgamated fluvial channels are overlain by floodplain and overbank sandstone bodies with fixed fluvial channel deposits, interpreted as a suspended-load-dominated fluvial system in the upper sequence. This change in the depositional style is accompanied by a reduction in grain size and a change in the fluvial regime, suggesting that the drainage system was restructured due to tectonic movements in the basin and climatic variations. In addition to the restructuring of the drainage basin, the characteristics of the discharge of the river system have changed, probably because of the more humid climatic conditions that dominated during the deposition of the upper sequence. The fluvial deposition in the lower sequence is associated with more ephemeral river systems, while the facies architecture of the upper sequence is associated with perennial systems and is suggestive of a suspended-load-dominated fluvial system. This fluvial system is capped by lacustrine deposits of the Crato Formation. The upper sequence grades upwards into the Crato Formation. The boundary between these two units is delineated by the presence of greenish calciferous shales that are covered by lacustrine laminated limestones and shales of Neoaptian age. Palaeocurrent readings from the fluvial deposits of both sequences display a consistent palaeoflow to the SE. Sedimentological and palaeontological evidence indicates a tectonic control on sedimentation and humid to subhumid climate conditions.

Microfacies and diagenetic evolution of the limestones of the upper part of the Crato Formation, Araripe Basin, northeastern Brazil

Abstract This paper presents the results of a petrographic and diagenetic study of the laminated limestones of the upper part of the Aptian to Albian Crato Formation, northeast of Brazil. The applied techniques were optical microscopy, cathodoluminescence and scanning electron microscopy (SEM) coupled to a wavelength-dispersive spectrometer (WDS). Petrographic analysis has revealed that most of the laminated limestones are calcilutites with a dominance of a micritic matrix, indicating a low-energy depositional environment. Microstructures such as microfaults, microfractures, microslumps, and loop bedding were observed. Based on textural, structural and paleontological features, seven microfacies were recognized: massive limestone, limestone with parallel laminations, limestone with undulated laminations, limestone with slumps, limestone with loop bedding, limestone with ostracods and limestone with peloids. In addition, the processes of cementation, dissolution, replacement, recrystallization and compaction, which are related to different diagenetic stages, were also recognized. The diagenetic constituents found in the sections include calcite, pyrite, silica and sulfates. We can conclude that a large part of the microstructures (microfaults, microfractures, microslumps and loop bedding) can be related to local seismicity, probably due to the reactivation of the Patos Shear Zone. The diagenetic constituents indicate an early to late diagenesis (eogenetic, mesogenetic and telogenetic stage).

Throwing light on an uncommon preservation of Blattodea from the Crato Formation (Araripe Basin, Cretaceous), Brazil

Fossilization results from several physical-chemical-geological processes. Original labile and non-bioclastic structures rarely survive throughout this process. In particular, the Crato Formation (Araripe Basin) is one of the most significant Cretaceous Konservat- Lagerstatten due to its well-preserved invertebrates, mainly three-dimensional insects. In general, Crato insects exhibit brown-orange color, constituted by goethite or hematite replacements. In this context, we used the scanning electron microscopy coupled to energy dispersive spectrometer and Raman spectroscopy to analyze Araripeblatta dornellesae, a 115 million-years-old fossil from Crato Formation, Araripe Basin. Our results show that a dark-color material rather than the brown-orange pattern preserve this specimen. The carbon is restricted to the fossil imprint, indicating some retention of the original organic remains. In addition, the presence of original organic components allowed to approach the biochemical aspects further than simple morphology, as well as to elucidate the taphonomical complexity involved in this preservation style.

A representative of the modern leafhopper subfamily Ledrinae in mid-Cretaceous Burmese amber (Hemiptera, Cicadellidae)

The Cicadellidae, one of largest insect families, is highly diversified in its living groups; fossils of this family, however, are poorly documented. Up to now, only three modern cicadellid subfamilies have been reported from the late Mesozoic, represented by five monotypic genera. We herein erect a new taxon, Qilia regilla gen. et sp. nov., from mid-Cretaceous Burmese amber, and tentatively ascribe it to Ledrinae: Paracarsonini. The new genus differs distinctly from other Paracarsonini from the Crato Formation of Brazil in having the head with the apex of the anterior margin acute; the antennae located relatively far away from the postclypeus; crossveins from RA to the anterior margin of the wing absent, resulting in a long and unbroken anterior cell; the terminal branches of RA and MP reduced in number; and crossveins (ir and rp-mp) weakly expressed. The results of the present study greatly expand the paleogeography of modern Ledrinae in the late Mesozoic, and also add some significant information to our knowledge of the diversity, distribution and evolution of early leafhoppers.

On the status of Araripegryllus romualdoi (Insecta: Orthoptera: Grylloidea) from the Cretaceous Santana Formation of Brazil.

The fossil cricket Araripegryllus romualdoi was described by Freitas et al. (2016) based on a single, very poorly preserved specimen from the Romualdo Member of the Lower Cretaceous Santana Formation; a deposit famed for the exceptional preservation of vertebrates in carbonate concretions (Martill, 1996, 2007). While abundant and diverse in the underlying Crato Formation (Martill et al., 2007 and contributions therein), fossil insects had not been reported from the Santana Formation prior to Freitas et al.'s paper. The occurrence of an insect in the Santana Formation is certainly noteworthy, but the description of a new species and its placement in the genus Araripegryllus are problematic, primarily because of the very poor preservation of the specimen. Here, problems associated with the diagnosis and placement of A. romualdoi are outlined, and the species declared a nomen dubium.

A new cheirolepidiaceous conifer Pseudofrenelopsis salesii sp. nov. from the Early Cretaceous of Brazil (Romualdo Formation, Araripe Basin): Paleoecological and taphonomic significance

Pseudofrenelopsis is a genus of the conifer family Cheirolepidiaceae, whose temporal distribution was restricted to the Early Cretaceous. Its set of features correspond to adaptive responses to rather unstable and stressful environmental conditions, such as aridity and/or groundwater salinity. In this paper, we describe Pseudofrenelopsis salesii sp. nov. from the Albian Romualdo Formation of the Araripe Basin, northeastern Brazil, based on anatomical analyses of the stem and leaf epidermis of a new specimen using scanning electron microscopy. The unique combination of features of P. salesii sp. nov., such as internodes of uniform sizes, completely sunken stomatal apparatuses, non-papillate subsidiary cells, and multi-layered hypodermis, distinguishes it from the remaining species of the genus, including Pseudofrenelopsis capillata from the late Aptian Crato Formation of the same basin. The new fossil species represents both an additional record of Cheirolepidiaceae in the Araripe Basin and the first representative of Pseudofrenelopsis formally described from the Romualdo Formation.

Publisher's note

Abstract The fossil dragonfly is a perfect model to study past biogeography. Araripegomphidae is an ancient Gondwanan family comprising the sole genus Araripegomphus previously from the Crato Formation (Upper Aptian) of Brazil. For the first time, a non-rock find, Araripegomphus shai sp. nov., is here described from mid-Cretaceous Burmese amber. This rare araripegomphid dragonfly extends the range of Araripegomphus to the west Burma block.

The palate and choanae structure of theSusisuchusanatoceps(Crocodyliformes, Eusuchia): phylogenetic implications

Crocodyliformes is a group with a broad fossil record, in which several morphological changes have been documented. Among known transformations the most iconic is perhaps the series of changes seen in the structural evolution of the choanae. The change in the position of the choanae was important during the evolutionary history of the Crocodyliformes. This structure is relevant in the phylogenetic position of many crocodyliforms. The new skull of Susisuchus anatoceps from the Crato Formation of the Santana Group (Lower Cretaceous) is described and the preservation in the ventral view allows character encoding not yet observed for the species. The new specimen shows a typical eusuchian palate for Susisuchus anatoceps, in which the choana is fully enclosed by the pterygoid. The Susisuchidae clade has been placed in different phylogenetic positions: as a sister group of Eusuchia, advanced Neosuchia and in Eusuchia. In Isisfordia there are reports that the choana of this taxon is or is not fully enclosed by the pterygoid. The encoding of the ventral characters of S. anatoceps places Susisuchidae in Eusuchia. However, this position must be further studied, since the matrices showed fragility in the reconstitution of the Neosuchia–Eusuchia transition.

Quantifying aperture, spacing and fracture intensity in a carbonate reservoir analogue: Crato Formation, NE Brazil

Abstract The characterization of fracture networks in carbonate reservoirs represents a primary approach to understand the processes of fluid flow. The study of outcrop analogues has been used to enhance the understanding of the relative contribution of fracture networks to reservoir permeability. The outcrop data can overcome scale limitations and/or lack of consistency of subsurface datasets (e.g. seismic, well logs, and cores). This paper presents the fracture characterization of the Aptian-Albian lacustrine laminites of Crato Formation (Araripe Basin, NE Brazil), which have been investigated as an analogue to some of the observed carbonate facies present in the pre-salt reservoir sequence of the Brazilian marginal basins. In order to provide fracture attributes for Discrete Fracture Network (DFN) modelling we investigate spacing and aperture distribution, length and intensity of fractures based on the use of traditional scanline (macro and microscale) method. The main fractures identified in the Crato Formation are shear and extensional fractures and with stylolites also present. In this study, we focused on vertical veins, which strike in two principal directions, NNW-SSE (Set 1), NE-SW (Set 2), and are filled or partially filled by calcite or gypsum. The relationship between length and aperture of vertical veins is linear. Apertures and spacings of fractures in both sets 1 and 2 follow power law and lognormal cumulative frequency distribution functions, respectively. Fractures of Set 2 are more likely to be clustered than are fractures of Set 1, which have a wider kinematic aperture. This structural database can be used to populate computational models that consider the widespread fracture system in the fluid flow simulation of carbonate reservoirs.

Stratigraphic Relations of the Ipubi Formation: Siliciclastic-Evaporitic Succession of the Araripe Basin.

The Ipubi Formation represents the Aptian-Albian siliciclastic-evaporitic succession of Araripe Basin, NE Brazil. This succession comprises siliciclastic rocks (bituminous shales and claystones) and evaporites (gypsum and secondary anhydrite) and represents part of the lacustrine-shallow marine post-rift phase I. This study used sequence stratigraphy concepts to define the relations between changes in the relative lake level and the formation of Ipubi deposits. Results show that the organic-rich shales of the Ipubi Formation formed during a transgressive pulse that covered large areas of the proximal domains. These deposits overlie a regional unconformity that marks the end of the deposition of the underlying Crato Formation. A High Stand stage that followed the transgression influenced the formation of evaporitic deposits. Climate conditions played a major role in influencing the triggering and stopping of evaporite deposition. Thus, a new relative lake level fall event caused the exposure of the Ipubi Formation deposits, and created another regional subaerial unconformity accompanied by widespread karstification of evaporite beds. A posterior transgression caused the deposition of siliciclastic rocks of the Romualdo Formation over the Ipubi Formation strata, and also promoted a new event of karstification of the Ipubi upper evaporite beds.