ABSTRACT: Main Geological Provinces and Distribution of the Rift Phase Sediments in the Eastern and Southeastern Continental Margins, Brazil
DIAS, JEFFERSON LUIZ, Petrobras, Rio de Janeiro, Brazil
The analysis of seismic, gravimetric, magnetometric, and well data available on the eastern and southeastern Brazilian continental margins allowed an overview of the distribution of the Early Cretaceous sediments of the Rift Phase. The western limit of the rift is defined by a shelf edge in the southeastern continental margin and by normal faults in the eastern continental margin. The eastern limit of the rift phase sediments is more difficult to establish owing to scarce geophysical data.
The Mesozoic-Cenozoic sequence of volcanic and sedimentary rocks was subdivided into six geological provinces in order to identify the areas where the rift can be best investigated with geophysical data. Four provinces are located over continental/transitional crust: (1) Tertiary province (TP), where tertiary sediments overlie the PreCambrian Basement and where the sediments of the rift phase are not expected to be present; (2) Aptian province (AP), where Aptian sediments not included in the rift phase overlie the basement and are covered by a thick package of Late Cretaceous and Tertiary sediments; (3) Mapped Rift province (MRP), where sediments of the Early Cretaceous Rift Phase overlie the basement or Jurassic sediments and are covered by a thick package of Late Cretaceous and Tert ary post-rift sediments. In this province the relative small thickness of Aptian evaporites (tens of meters) favor the mapping of the underlying sediments. The majority of oil and gas fields discovered by Petrobras is located in the MRP province; (4) Salt Domes province (SDP), where the presence of a thick package (up to 4000 m) of Aptian evaporites mask the seismic resolution of the rift section. Its eastern limit corresponds to the contact between continental/transitional and oceanic crusts.
The last two provinces are not located entirely over continental crust: (5) Abrolhos and Royal Charlote Volcanic Complexes province (VCP), where a thick package of Cenozoic rocks is interbedded into the sedimentary section: and (6) Oceanic Crust province (OCP), where the oceanic crust probably is covered by post-Aptian sedimentary rocks.
AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)