Search

ABSTRACT 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.

Reports on Cretaceous charcoals are relatively common on a global scale and have been increasing in recent years. Fossil charcoal from the Early Cretaceous mostly belongs to conifers (and other gymnosperms) and ferns whereas angiosperms become more common only during the Late Cretaceous. However, so far, reports of Cretaceous macroscopic charcoal are rare (three) for South America. Here, charcoal is identified from the Crato, Ipubi and Romualdo formations of the Early Cretaceous Santana Group within the Araripe Basin, Brazil. The presence of charcoal provides for the first time compelling evidence for the repeated occurrence of Early Cretaceous palaeo-wildfires in this region. The charred wood remains were identified as belonging to gymnosperms, which were important components of the palaeoflora during the Cretaceous in Northeast Brazil. The results presented here provide additional evidence for the occurrence of palaeo-wildfires in Northern Gondwana during the Early Cretaceous, increasing our understanding for the relevance of such events and their influence on palaeoenvironmental dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Geochimica Brasiliensis is the property of Sociedade Brasileira de Geoquimica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Ipubi Formation in the Araripe Basin (Northeast Brazil) has evaporite-lutite successions rich in gypsum, a mineral of great regional economic relevance, a highlighted stratigraphic mark, and also a natural boundary for underlying successions potentially analogous to “Pre-Salt” hydrocarbon reservoirs of the Brazilian coastal basins. In this study, syngenetic and diagenetic aspects of the Ipubi Formation at Santana do Cariri (Ceará State) were investigated by means of facies analysis, petrography, and mineralogical/chemical analyses of evaporites and shales. The results show that the contact relationship between evaporites and marly shales, without signs of subaerial exposure and laterally adjacent, was associated with shallow, calm and somewhat anoxic waterbodies, locally salt-supersaturated (brines) but under seasonal variations of water levels. This scenario could have shared place with hydrothermal phenomena in a playa lake depositional system. Regarding diagenesis, although there is evidence supporting pseudomorphic replacement of gypsum by anhydrite, the burial of the Ipubi Formation would have been limited due to the frequent occurrence of gypsum without any trace of chemical replacement. [ABSTRACT FROM AUTHOR]

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. • Geochemical Biomarkers. • Chemotaxonomical interpretation of Brazilian ambers. • Amber Ipubi Formation. [ABSTRACT FROM AUTHOR]