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Book Chapter

Campos and Espirito Santo Basins, Offshore Brazil

By
Petrobras
Petrobras
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Published:
January 01, 1983

Abstract

Normal faults as shown in this seismic section display typical geometry. The fault geometry is characterized by the verticality at upper part (Upper Miocene), and by the concavity at the basal part, where the fault trace becomes asymptotic to the Aptian reflectors. These faults occur quite often in the Campos basin; the main faulting direction is northeast to southwest, which is in accordance to the present coast line, and to the hypothetic axis of the basin tilting.

The genesis of these faults is related to the tilting of the sedimentary basin and resulting movement of the Albian carbonatic sediments over the Aptian evaporites. in the Albian and Upper Cretaceous sequence, the reflectors clearly show the growth character of faults. Some of them were reactivated up to the Upper Miocene, generating compensating faults showing dip in opposite direction.

This seismic section shows various tectonic styles developed during the tecto-sedimentary evolution of the Espirito Santo basin.

First in the Neocomian, during the "rift valley phase," basement (horizon 1) was cut by normal faults in a general down-to-basin pattern, that formed horsts and grabens filled by syntectonic continental clastics.

This rift valley phase evolved, in the Aptian, to a "restricted sea phase" that progressively gave rise to a narrow sea, in the Albian/Cenomanian.

In the Aptian, evaporites (anhydride and halite; horizon 2) were deposited, while in Albian/Cenomanian time, fan deltas and alluvial fans interbedded limestones in a broad carbonate shelf. Close to the end of the Albian, there was significant oceanward tilting of this shelf, triggering gravity slide features (horizon 3) over the evaporitic surface, concomitantly with sedimentation.

The top of this section (horizon 4) is a well recognized limestone. Reactivated basement normal faults, as well as gravity faults, intersected part of the Albian/Cenomanian section.

During the third phase (Late Cretaceous/Early Tertiary) with increasing seaward tilting, the environment changed to open marine. Late Cretaceous slope shales were deposited and were covered, at the east side, by volcanic flows (horizon 5).

In Early Tertiary, a sandstone/shale sequence prograded over the onlapping slope sediments (horizon 6). A shallow water clastic/carbonatic shelf was then developed from Late Tertiary to Present. Horizon 7 represents a single carbonate layer comprised in this section.

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Contents

AAPG Studies in Geology

Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces

A. W. Bally
A. W. Bally
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American Association of Petroleum Geologists
Volume
15
ISBN electronic:
9781629810188
Publication date:
January 01, 1983

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