Open‐coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open‐coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north‐eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave‐dominated or tide‐dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic hummocky cross‐stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky cross‐stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair‐weather wave base. However, in this model of an open‐coast tidal flat, hummocky cross‐stratification beds were found in very shallow waters above the fair‐weather wave base. Indeed, this depositional environment was characterized by: (i) fair‐weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these hummocky cross‐stratification deposits.

No abstract

Pão de Açúcar is certainly one of the most impressive and challenging hydrocarbon accumulations found in the prolific Campos Basin, offshore Brazil. This discovery opened a new frontier for exploration in Brazil’s ultradeep waters, in depths ranging from 2500 to 2900 m (8202 to 9514 ft). Pão de Açúcar is the third discovery made by a consortium integrated by Repsol Sinopec Brasil (operator), Statoil do Brasil, and Petrobras in the Concession BM-C-33, with estimated resources of 700 million bbl of light oil and 3 tcf of gas. This discovery is the result of the integrated work of a multidisciplinary international team using some of the most advanced technologies available today in the oil exploration industry in seismic imaging, drilling, formation evaluation, and fluid-rock sampling analysis. This discovery consists of a significant hydrocarbon column hosted within a unique reservoir made up of a variety of basic volcanic rocks overlain by pervasively silicified microbial carbonate platform/ramps, grading toward profundal lake facies. This chapter summarizes the main results of the exploration and ongoing appraisal work regarding this unique hydrocarbon accumulation, highlighting both the complexity of the discovered reservoirs and the operational and technical challenges faced, and still to overcome, before beginning production.

No abstract

No abstract