AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Reconstructing Aptian Evaporite Basin Geometry: Implications for Pre-evaporite Facies Distribution in the Santos and Campos Basins, Brazil
(1) Chevron Energy Technology Company, Houston, TX.
(2) Chevron Africa & Latin America Exploration & Production, Houston, TX.
We determine original evaporite basin geometry of the Campos and Santos Basins of Brazil using different, yet complimentary approaches which include 2D restorations and 3D isostatic calculations. Original evaporite distribution records the last vestige of rift tectonics and provides a snapshot of the rift morphology in its final stages. When coupled to the distribution of early synrift deposits, the evolution of structurally-controlled accommodation space begins to take shape. Using published accounts bracketing the age of salt and earlier deposits, our reconstruction suggests that rifting here can be divided into three tectono-stratigraphic intervals with different structurally induced basin accommodation rates.
In our model, extensional deformation of the Campos and Santos Basins spanned a period of about 20 Ma. During the first 6-7 Ma or so (Early Rift interval), Barremian basin capacity develops rather uniformly and is dominated by locally derived continental siliciclastic and volcaniclastic deposits in fluvial, alluvial, and lacustrine depositional environments. Onset of Aptian deposition marks an approximately 12 Ma transitional period of mixed carbonate and siliciclastic deposition as structural basin integration develops (Middle Rift interval). During this interval, basin stratigraphy becomes dominated by lacustrine to restricted marine carbonates interbedded with hydrocarbon source intervals. Molluscan coquinas lower in the section transition upward into microbial carbonates. Alluvial conglomerates interfinger with these carbonate reservoirs in the Campos Basin and are present locally in the Santos Basin. Completion of basin integration climaxes in a dramatic increase in basin capacity enabling the bulk of evaporite deposition (Late Rift interval).