This work deals with the geological, petrographic and paleoenvironmental research of carbonate reefs deposits found on Tambaba Formation (Eocene), that occur in a restrict region on the south portion of Paraíba basin along Conde city, Paraíba state, and in elongated bioconstructions which are parallel to the coastal zone, called Jacumã-Carapibús, Tabatinga, Coqueirinhos and Tambaba. Based on macroscopic lithological aspects and geometric and stratigraphic patterns three stages of reef accretion were recognized: colonization (bafflestone lithofacies), diversification (framestone lithofacies) and domination (bindstone lithofacies) associated to the reef superimposed surfaces (stratified boundstone lithofacies) correspond to reef core, while the rudstone lithofacies corresponds to fore reef. The biotic macroscopic content is poorly preserved, possibly due to the diagenetic processes (dolomitization and dissolution) and weathering, including four scleractinian corals, two bivalves, one gastropod, one rhodophyta algae, and an ichnospecie. The petrographic study defined the microfacies fossiliferous dolomudstone on the layers related to the reef core- colonization stage, fossiliferous dolowackestone, fossiliferous dolopackstone, doloframestone and peloidal dolobindstone on the reef core- diversification stage, terrigenous dolomudstone corresponding to reef superimposed surfaces, dolorudstone and dolofloatstone with intraclasts on fore reef deposits, and peloidal fossiliferous dolowackestone on the reef core of domination stage. The allochemical elements are represented by fragments of Rhodophyta and Chlorophyta calcareous algae, porifera, corals, bivalves, gastropods, echinoids and trace fossils. The genesis of this reef system is related to a very shallow platform during a transgressive pulse where the deposition of calcareous levels from the reef core and hardground levels (reef superimposed surfaces) are related to subsidence and uplifting of the hanging wall of a half-graben system.
|
