Crato Formation Research Articles

Sedimentary organic matter and paleoenvironmental reconstruction of the Santana Group (Lower Cretaceous), Araripe Basin, Northeast Brazil

Depositional controls of the Santana Group in the Araripe Basin are still being debated. The main controversial subject is their marine influence and paleoenvironmental evolution. In this study, palynofacies analysis was performed on 59 samples from one core drilled at Sítio Romualdo in the Araripe Basin to investigate sedimentary organic matter. Three palynofacies associations (structureless, continental particles, and aquatic + opaque) were identified. The Santana Group consist of Barbalha, Crato, Ipubi and Romualdo formations. Based on palynofacies associations we conclude that the depositional setting of the Barbalha Formation reflects a fluvially-fed lacustrine system under oxic conditions. The Crato Formation, associated with tidal flats, coastal lakes, and lagoons within an open bay environment, represents a bayhead delta system. The Ipubi Formation corresponds to a coastal plain typical of sabkha paleoenvironments, characterized by low energy under reducing conditions, during drier climate conditions. The Romualdo Formation records mainly an estuarine paleoenvironment characterized by dysoxic to anoxic conditions. The presence of palynomorph groups typifies a late Aptian age for the Santana Group, which is based on the range of guide species marked mainly by the presence of Sergipea variverrucata biozone (P-270), as well as the occurrence of Complicatisaccus cearensis and Equisetosporites maculosus. The identification of marine palynomorphs (dinoflagellate cysts Subtilisphaera and foraminiferal test linings) are indicative of several, local marine incursions.

A palaeoecological analysis of the Cretaceous (Aptian) insect fauna of the Crato Formation, Brazil

A rich insect fauna is found in the Cretaceous (Aptian) Nova Olinda Member of the Crato Formation in the Araripe Basin, northeastern Brazil. The Crato Formation was deposited close to the centre of the supercontinent Gondwana, prior to significant rifting. In this paper, we analyzed remains of 1135 insect specimens, representing 55 families, within two limestone facies of the Nova Olinda Member: pale yellow and dark gray limestones. We collected taphonomical data and assessed the paleoecological significance of insect faunas in terms of their distribution and interaction with the paleoenvironment. The insect fauna is dominanted by fully terrestrial taxa despite preservation in an aquatic paleoenvironment. Considering both facies, the distribution of insect families is similar throughout the Nova Olinda Member, which excludes possible overlapping of one entomofauna over another. The pale yellow limestones near the top of the section are richer in fossil insect content and show a higher incidence of aquatic and semiaquatic insects preserved in dorsoventral view compared to the dark gray limestones. This suggests that the Crato insects preserved in the pale yellow limestones experienced short transport distances or prolonged decay or both. In contrast, insects preserved in the dark gray limestones appear proportionally with higher degrees of disarticulation than those preserved in the pale yellow limestones, indicating that these insects underwent a higher degree of postmortem transport in the biostratinomic stage. Compared to descriptions of other Early Cretaceous assemblages, the taxonomic literature of Crato Paleoentomofauna shows distinct differences. The Yixian and Zaza formations are described as being dominated by beetles and wasps. The Crato Formation, however, is relatively richer in Paleoptera species. Both the sedimentary facies studied and the paleoentomological content reveal a complex ecosystem inserted in a depositional setting, similar to modern long-standing wetlands, and where periodically flooded zones were surrounded by dry lands with xeromorphic vegetation.

The effect of fracture networks on the vertical permeability of a tight carbonate reservoir analogue: laminites from the Crato Formation, NE Brazil

The structural characterization of fractures is crucial to understand the processes of fluid flow in tight reservoirs. This contribution focuses on the role played by vertical fractures on the permo-porosity properties of the Aptian tight carbonate sequence of the Crato Formation, Araripe Basin (NE Brazil). The study performed a structural analysis in two different scales: reservoir scale (approximately 19.000 m2) and outcrop scale (approximately 125 m2), focusing on the fracture networks in lacustrine laminates, which have been investigated as an analogue of carbonate facies observed within the pre-salt reservoir sequence of the marginal basins in Brazil. This study employed a combination of systematic outcrop-based fracture characterization involving digital outcrop models and mechanical stratigraphy analysis. To evaluate the influence of vertical fracture systems in the fracture porosity and the equivalent permeability we performed DFN (Discrete Fracture Network) models. We focused on vertical calcite-filled fractures, oriented in two principal directions: set 1 NNW-SSE and set 2 NE-SW. Each set shows different vertical linkage patterns due to the influence of the mechanical intervals. Results of the outcrop scale model show similar behaviour for both fracture porosity and equivalent permeability, indicating that storage capacity and fluid flow may not be affected by vertical linkage of fractures. The reservoir scale DFN models show that the fracture porosity was greater in models which consider through-going continuous fractures than in models that consider the segmentation (discontinuity) of vertical fractures. Considering the vertical connectivity of fractures, the equivalent horizontal permeability (Kxx and Kyy) showed similar values in both scale models. This implies that vertical segmentation of fractures does not impact fluid flow in horizontal directions. The calculated values of equivalent vertical fracture permeability (Kzz) at reservoir scale are one order of magnitude higher in the DFNs that consider continuous fractures. Our results suggested that vertically continuous fractures enhance preferential flow pathways allowing greater vertical fluid flow than segmented fracture networks in tight carbonate reservoirs.

Expanding the diversity of conifer xyloflora from Early Cretaceous Crato Fossil Lagerstätte, Brazil

Remains of gymnosperms are the most abundant plant macro-fossils in the outcrops of a fossil lagerstätte preserved in lacustrine limestones in the likely lower Aptian Crato Formation of the Araripe Basin in NE Brazil. However, the systematics of most fossil-taxa are mainly based on foliage and reproductive structures, whereas wood anatomy has rarely been used to study fossil plant diversity, despite the abundance of wood fragments. Here we describe a new fossil gymnosperm taxon based on anatomical characters of a well-preserved specimen from this lithostratigraphic unit. The new fossil-genus and fossil-species Cratoxylon placidoi gen. nov. et sp. nov. are established using characters of the secondary xylem and the bark, features that are also crucial for their affiliation into conifers. This finding reinforces the already known remarkable preservation potential of organisms in this konservat lagerstätte, since bark tissues are rarely preserved in the fossil record of Mesozoic gymnosperms. The results reveal the great potential of fossil woods for studying diversity of the Crato Formation flora and thus contribute to expand our knowledge on fossil vegetation in equatorial Gondwana during the early diversification of angiosperms.

Description of a new fossil Thelyphonida (Arachnida, Uropygi) and further record of Cratosolpuga wunderlichi Selden, in Selden and Shear, 1996 (Arachnida, Solifugae) from Crato Formation (Aptian/Albian), Araripe Basin, Brazil.

A new fossil species of whipscorpion, Mesoproctus rayoli n. sp., is described. The specimen originates from the Crato Formation, dating to the Lower Cretaceous (Aptian/Albian) period within the Araripe Sedimentary Basin. This species has been provisionally assigned to Mesoproctus Dunlop, 1998, as it represents the sole known Thelyphonida fossil genus discovered in South America and within Araripe Lagerstätte. The material underwent detailed description and illustration processes. Key diagnostic characters, such as body length, pedipalpal coxae apophysis, the form of the opisthosoma, and the length of leg IV, were meticulously examined. SEM methods were applied in this study. Through the detailed analysis, comparisons and differences to Mesoproctus rowlandi Dunlop, 1998 were made possible. Additionally, a well-preserved specimen of the rare camel spider, Cratosolpuga wunderlichi Selden, in Selden and Shear, 1996, was identified from the limestones of the Crato Formation. The newly discovered fossil specimen of Cratosolpuga wunderlichi suggests two characters not previously described: (i) a segmented tarsomere on leg IV; and (ii) a leg I with one tarsal claw.

Exceptionally well-preserved orthopteran proventriculi from the Cretaceous Crato Formation of Brazil

The Crato Formation (Santana Group, Araripe Basin, Brazil) bears a high abundance of fossils in exceptional state of preservation, with insects from the order Orthoptera standing out. However, so far, few studies have explored their preserved inner organs in detail. Here, we provide the first detailed description of fossilized proventriculi from nine Grylloidea (Orthoptera: Ensifera) specimens of the Crato Formation. In all analyzed specimens, the external cuticle of the abdomen is cracked exposing the proventriculi, which are preserved as a tridimensional organ with a globular body and a tubular neck, similar to that of modern crickets. However, in the globular region of all fossils analyzed there are 9–12 rows of parallel divisions, differing from the modern crickets which have, more frequently, six. SEM images of two specimens revealed the exceptional preservation of internal median teeth, folds, and microvilli texture preserved in the organ.

A new specimen of whip scorpion (Arachnida; Thelyphonida) from the Crato Formation, Lower Cretaceous of Brazil

Fossil whip scorpions (Thelyphonida) are extremely rare in the Crato Formation strata, Araripe Basin, Lower Cretaceous (Aptian) of Brazil. Only four specimens of whip scorpions have been described in this unit so far. All specimens have been assigned to the genus Mesoproctus Dunlop and only one species has been formally proposed, M. rowlandi Dunlop. For Mesozoic times, apart from Crato Formation, whip scorpions are only documented by two species in the amber deposits of the Hukawng Valley, northern Myanmar. In this scenario, each new discovery of Mesozoic whip scorpion is highly important. In addition, we present the first documented example of book lungs from a fossil whip scorpion. Here, we present and illustrate a new specimen of whip scorpion found in the Crato strata. Keywords: Crato arachnofauna, Uropypi, Mesoproctus, Aptian, Lagerstätten.

A new condensed freshwater-brackish water bivalve-dominated assemblage in the Aptian Crato Formation, Araripe Basin, NE Brazil and its paleoenvironmental significance

The known occurrences of Early Cretaceous freshwater bivalves in the Araripe Basin are confined to the 0.85- to 2-m-thick Caldas Bed of the Crato Formation. Herein, we record a new bivalve-dominated assemblage in a siltstone bed nearly 30 m below the upper boundary with the overlying Romualdo Formation. The assemblage is composed of ecologically incompatible bivalve mollusk species, being dominated by tiny individuals of Modiolus? sp., a brackish water form. These are directly associated with the freshwater bivalves Araripenaia elliptica and Monginellopsis bellaradiata, the latter two species commonly found in the Caldas Bed. Those bivalves are mixed with carbonized, partially comminuted plant remains. Specimens of Modiolus? sp. are usually articulated and are dispersed to loosely packed or forming cm-long clusters. A few shells of the freshwater forms are also articulated. The bivalves lived in a semi-confined embayment setting with fluctuating salinity. Background brackish water conditions must have existed long enough for the Modiolus? sp. larvae to settle and develop as juvenile individuals. Rapid salinity fluctuations associated with sea level and climate variations allowed A. elliptica and M. bellaradiata to thrive in the same area. Hence, the numerically dominant shells of the brackish water forms and the freshwater bivalves have been telescoped into the same bedding plane, generating an environmentally condensed, time-averaged benthic assemblage. Finally, the presence of these taxa considerably expands the vertical/temporal distribution of bivalve mollusks within the Crato Formation.

Ostracods from the Barbalha and Crato formations, Aptian of the Araripe Basin, northeast Brazil.

Ostracods have been widely used for biostratigraphic and paleoenvironmental purposes for the Lower Cretaceous deposits of northeastern interior Brazilian basins. The ostracods of the Romualdo and Crato formations of the Araripe Basin are particularly well known; however, the ones from the underlying Barbalha Formation are less so. Here we report 10 ostracod species, of which three are new, obtained from 56 samples of the Barbalha and Crato formations collected from boreholes 1PS-06-CE and 1PS-10-CE: Candonopsis? alagoensis Tomé et al., 2014, Brasacypris subovatum Do Carmo et al., 2013, Damonella medialtis sp. nov., Cypridea araripensis Silva, 1978, Pattersoncypris cf. P. angulata (Krömmelbein & Weber, 1971), Pattersoncypris micropapillosa Bate, 1972, Pattersoncypris salitrensis (Krömmelbein & Weber, 1971), Pattersoncypris trapezium sp. nov., Looneyellopsis? sagittensis sp. nov., and Theriosynoecum silvai (Silva, 1978). Preservation of this material was very good in the Crato Formation and the Batateira Beds, with numerous well-preserved juvenile carapaces down to the A-6 instar having been found in the latter. Conversely, preservation was very poor in the upper portion of the Barbalha Formation, from which mostly molds were recovered.

A new Gondwanan mayfly family from the Lower Cretaceous Crato Formation, Brazil (Ephemeroptera: Siphlonuroidea: Astraeopteridae fam. nov.)

The adult holotype of the fossil mayfly Astraeoptera cretacica Brandão et al. 2021 from the Cretaceous Crato Formation, Brazil, is reviewed and attributed to a new family Astraeopteridae fam. nov. Based on alate specimens, we also describe further new representatives of Astraeopteridae fam. nov., namely Astraeoptera vitrea sp. nov. and Astraeoptera oligovenata sp. nov., as well as the new genus and species Eosophobia acuta gen. et sp. nov. A subsequent character analysis of the new material suggests systematic affinities of Astraeopteridae fam. nov. with those extant families of Siphlonuroidea distributed in the Southern Hemisphere. These newly described fossil Siphlonuroidea from the Cretaceous of Brazil thus add to the biogeography and systematics of mayflies.

Mayfly larvae preservation from the Early Cretaceous of Brazilian Gondwana: Analogies with modern mats and other Lagerstätten

The Crato Formation paleoentomofauna is noticeable for its high abundance, diversity and morphological fidelity, so the preservational approach of the Ephemeroptera larvae fossils becomes relevant, since they are aquatic insects living in a lacustrine environment of one of the major terrestrial ecosystems of the Early Cretaceous in the Gondwana supercontinent. The mayfly larvae fossils were analyzed under a stereomicroscope and a scanning electron microscope with coupled x-ray spectroscopy (SEM/EDX) for morphological, textural and geochemical purposes. The microfabric analysis confirms the most recent hypothesis that the main factor responsible for the preservation of the Crato Formation fossils was the influence of the microbial mats on the fossilization process. The microscopic signatures left by the mats occur in the insect’s cuticle and internal parts, represented by micro cracks and wrinkles, micro spheres, filaments and mineralized EPS. These features have been compared in light with deposits containing Quaternary microbial mats in the Vermelha Lagoon and its associated salt pans, in Brazil. Also, we discussed our results with taphonomic data of other mayfly larvae fossils from the Lagerstätten La Huérguina (Spain) and Yixian (China) Formations, specifically in relation to the taphonomic settings regarding these Early Cretaceous ephemeropterans. This study corroborates to the idea of the fundamental role of the microbial mats in the exquisite preservation of the Crato Formation invertebrate fossils, with an approach that permits some fundamental paleoenvironmental and paleoclimatic inferences for the Aptian of the Araripe Basin, in Brazil.

Arlenea delicata gen. et sp. nov., a new ephedroid plant from the Early Cretaceous Crato Formation, Araripe Basin, Northeast Brazil

Ephedroid macrofossils have been widely documented in Cretaceous deposits, including numerous from the Lower Cretaceous Yixian Formation of NE China. However, few ephedroid macrofossils have been reported from South America. Herein, we describe a new plant of the family Ephedraceae, Arlenea delicata gen. et sp. nov., from the Lower Cretaceous Crato Formation of the Araripe Basin, Northeast Brazil, based on the vegetative and reproductive structures. It has the typical morphological characteristics of ephedroid plants, including fertile reproductive branches, opposite phyllotaxy, terminal female cones, a sympodial branching system, longitudinally striated internodes, and swollen nodes. Our new finding is unusual in having inner chlamydosperms subtended by two pairs of bracts, reproductive units connected to branches through swollen receptacles and a smooth seed surface. This new ephedroid taxon from the Crato Formation increases our understanding of plant diversity of this group during the Early Cretaceous. Furthermore, the general morphology (fleshy bracts and enlarged receptacles) of this new fossil discovery indicates that seeds of this plant may have been dispersed by animals such as pterosaurs (mainly the Tapejaridae) and birds (Enantiornithes and Ornituromorpha). If true, this would explain the cosmopolitan distribution of Ephedraceae in the Lower Cretaceous.

A new remarkable Early Cretaceous nelumbonaceous fossil bridges the gap between herbaceous aquatic and woody protealeans

Dating back to the late Early Cretaceous, the macrofossil record of the iconic lotus family (Nelumbonaceae) is one of the oldest of flowering plants and suggests that their unmistakable leaves and nutlets embedded in large pitted receptacular fruits evolved relatively little in the 100 million years since their first known appearance. Here we describe a new fossil from the late Barremian/Aptian Crato Formation flora (NE Brazil) with both vegetative and reproductive structures, Notocyamus hydrophobus gen. nov. et sp. nov., which is now the oldest and most complete fossil record of Nelumbonaceae. In addition, it displays a unique mosaic of ancestral and derived macro- and micromorphological traits that has never been documented before in this family. This new Brazilian fossil-species also provides a rare illustration of the potential morphological and anatomical transitions experienced by Nelumbonaceae prior to a long period of relative stasis. Its potential plesiomorphic and apomorphic features shared with Proteaceae and Platanaceae not only fill a major morphological gap within Proteales but also provide new support for their unexpected relationships first suggested by molecular phylogenies.

Stomatal numbers of Pseudofrenelopsis capillata (Cheirolepidiaceae, Coniferales) in the peri-equatorial late Aptian Crato Formation (Santana group, Araripe Basin, Brazil) and their paleoclimatic and paleoenvironmental significance

This study is the first contribution towards the estimation of paleoatmospheric carbon dioxide concentration (pCO2) from the paleoequatorial late Aptian Crato Formation (Santana Group, Araripe Basin, NE Brazil) based on stomatal numbers. Cuticular and epidermal silicon replicas of Pseudofrenelopsis capillata Sucerquia, Bernardes-de-Oliveira & Mohr (Cheirolepidiaceae, Coniferales) were observed under scanning electron microscopy to analyze their stomatal frequency and distribution for paleoatmospheric and paleoenvironmental inferences. Stomatal counting yielded a mean stomatal density (SD) and stomatal index (SI) of 68.8 mm−2 and 6.7. Based on the mean SI value of four modern nearest living equivalent (NLE) conifer species, the stomatal ratio (SR) was calculated to be 1.4. The paleoatmospheric pCO2 range was estimated to be between 514.9 ppmv (Recent standardization) and 1029.8 ppmv (Carboniferous standardization). These values were found to be consistent with results from the literature based on other latitudes in the Early Cretaceous and were discussed in the light of the paleoenvironmental context that prevailed around the peri-equatorial Crato paleolake, including the occurrence of stomatal clustering in the leaves of P. capillata.

A new dragonfly genus and species from the Crato Formation, with a revised phylogenetic study of the Mesozoic family Liupanshaniidae (Odonata: Aeshnoptera)

The fourth genus and species of the Cretaceous aeshnopteran family Liupanshaniidae discovered in the Aptian Crato Formation, is described and illustrated as Brasiliupanshania cretacica gen. et sp. nov. Its phylogenetic position within the Liupanshaniidae is investigated using parsimony analyses, and it was found nested within the Liupanshaniidae. The Gondwanan species of the family do not form a clade, but appears to be more closely related to various Laurasian clades, suggesting a very ancient Mesozoic diversification prior to Gondwana–Laurasia split.

Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

AbstractMany studies have improved our understanding of the mode of preservation at the Crato fossil Lagerstätte. The high degree of preservation of the Crato mineralized insects is thought to be a consequence of the diffusion of ions through carcasses and envelopment by bacteria that, in turn, created microenvironmental conditions that led to mineralization, mainly pyritization. Pyritized insects have been oxidized by in situ weathering to more stable oxide/hydroxy minerals during Quaternary time. This transformation is essential to maintain the palaeontological information acquired during microbially induced pyritization in an oxidizing atmosphere. However, intense weathering can diminish or obscure the morphological fidelity, and little attention has been paid to the post-diagenetic processes experienced by these fossils. Here, we aim to determine the degree of alteration undergone by Crato pyritized insects using the following combination of analytical tools: scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared and Raman spectroscopy. Our results show that well-preserved insects are preferentially replaced by haematite and poorly preserved fossils are replaced by goethite. In addition, we recorded three types of post-diagenetic alteration: insects with iron-oxide overgrowths; insects associated with black coatings, sometimes with the formation of dendrites; and insects preserved as an impression, where only the outline of the body remains. All of these alterations have the potential to distort or tarnish palaeontological information. Here, we measured the effects of such telodiagenetic alterations at macro and micro scales. Therefore, this taphonomic approach has wide applicability wherever fine-grained deposits bearing mineralized insects are found.

On the systematic position of Cretothereva (Diptera, Therevidae): criticism versus evidence

ABSTRACT An extinct genus and species of Diptera – Cretothereva antiqua – has recently been described from the Lower Cretaceous of Brazil (Crato Formation). The fossil has been assigned to the family Therevidae and, according to its authors, would represent the oldest known member of the family of the entire Therevoid clade, with important implications for the evolutionary history of the group. A recent paper written by several Diptera experts challenges the systematic position of Cretothereva antiqua, but without a detailed assessment of the evidences. The evidence for the systematic position of this important fossil is reassessed. We argue that criticism of scientific hypotheses must be based on formal discussion of evidence, not based only on conjecture.

Micro-tomographic analysis of a scorpion fossil from the Aptian Crato Formation of Northeastern Brazil

A scorpion fossil (Protoischnurus axelrodorum) from the Lower Cretaceous Crato Formation (Aptian, northeastern Brazil) is analyzed with computed microtomography. Its taphonomy and morphology is described and illustrated, a revised diagnosis of the genus is presented, and the phylogenetic relationships of this taxon are discussed. Protoischnurus belongs in the Scorpionoidea and is probably an early member of the Iurida crown group, possibly representing a stem hormurid.

Palynofacies analyses of Santana Group, upper Aptian of the Araripe Basin, northeast Brazil: Paleoenvironmental reconstruction

We present the paleoenvironmental analysis based on sedimentary organic matter (SOM) of alluvial-lacustrine-transitional deposits that crop out in the east portion of the Araripe Basin, Ceará State, Brazil. Samples were collected from the Barbalha, Crato, Ipubi and Romualdo formations, Santana Group. For the palynofacies analyses, the kerogen categories were counted and grouped. The described SOM were subdivided into six groups: Structureless, which consists of resin and amorphous organic matter (AOM); Terrigenous, which consists of non-opaque biostructured-phytoclast; Opaque, which consists of equidimensional, lath and corroded of black color; Sporomorphs, which consist of spores and pollen grains; Freshwater, constituted by Botryococcus and Pediastrum microplankton and Marine elements, represented by dinoflagellate cysts and foraminiferal lining. The stratigraphic distribution of the seven palynofacies reflects a change from fluvial system to a lacustrine environment, as well as the first marine incursion on Serra da Mãozinha section (Crato Formation). In the top of the Santana Group recorded a transition from a lacustrine environment close to a fluvio-deltaic source to an estuarine system, marked by the presence of Subtilisphaera, during the late Aptian. The palynological data presented indicates that the entire Santana Group is of Aptian age considering the conspicuous presence of Sergipea variverrucata in the sections.

The oldest Gondwanan fossil of Leiinae (Diptera, Mycetophilidae): Phylogenetic and evolutionary implications.

A fossil Mycetophilidae from the Aptian Crato Formation-Cretomanota gondwanica gen. nov., sp. nov.-is described, which is the first mycetophilid from the Crato Formation and corresponds to the oldest known fossil leiine and only the second Gondwanan fossil mycetophilid described so far. Cretomanota gondwanica and both species of Alavamanota Blagoderov and Arillo were added as terminals to the data matrix of a general phylogenetic analysis of the Mycetophilidae, and both fit into the Leiinae. Alavamanota is monophyletic, sister to the clade composed by Cretomanota and the extant genus Manota Williston. The biology of the extant members of this fungivorous family corroborates the reconstruction of the Crato palaeoenvironment as including woodlands with humid habitats and microhabitats. The presence of a Cretaceous member of the tribe Manotini at low latitudes in South America reinforces the hypothesis that the clade with all manotines except Leiella Edwards corresponds to a Lower Cretaceous offshoot from a group in southern Gondwana expanding its distribution to more northern areas into the Gondwana and into Laurasia.