西非与南美东部的关联盆地的对比，基于构地质学和地层学的分析

摘要

In this work, the main evidence and conclusions regarding the geological links betweenthe basins of South American margin (Espirito Santos basin, Pelotas basin & Coloradobasin) with the conjugate margin of Western African (Kwanza basin, Walvis basin &Orange basin) Many research works have been done in both margins of South Atlanticand Western African like sedimentation history and tectonic evolution.However, thereare some cognition needs to be unified, and some geologic problems need to be furtherresearched, such as the deposition of salt, extension of the basin, and the sedimentationhistory along the comparative basins.These basins were formed during the breakup of Gondwana, while the South AtlanticOcean started to open during the Late Cretaceous at ca.131.7Ma, thesedimentationhistory between the Late Jurassic and present are broadly similar on both margins, wherethese basins are filled with the Cretaceous, Tertiary and the Quaternary sediments.However, the sediment of the Late Jurassic only deposit at Colorado basin in SouthAmerican margin and at Kwanza basin and Orange basin in Westem African margin.Sedimentation proceeded from the depositionof continental pre-and syn-rift facies,through syn-rifi lacustrine, the turbiditic and transgressive shales, to shallow marinecarbonates and evaporitic units before the deposition of a post rift marine transgressiveand regressive sequence.During the opening of the South Atlantic Ocean there were some major events (i.e,the Parana & Etendeka volcanic plume, salt deposition before the opening of SouthAtlantic), these events at these two margins could be well matched.Tectonically, SouthAtlantic Ocean are divided into four major segments from South to North: the Falklandsegment, the South segment, the Central segment and the Equatorial segment.SouthAtlantic Ocean contains two kinds of passive margins which are the thick crust volcanicmargin and the thin-crust non-volcanic margin.The volcanic passive margins contain theLarge Igneous Province (LIPs).The Florianopolis Fracture zone (South segment) which characterize the Seawarddipping reflectors (SDRs), and the volcanic distributed along the South Atlantic in thearea with length of hundreds of km and width of overl 5kin.The basins developed in thesouthern margin recorded the LIPs and SDRs.The most parts of the two margins are builton the block faulted continental crust (what does this mean) marked bythe hinge zones,which are parallel along the coast or sub parallel to the ancient orogenic belts.While thestrata deposited on both margins during the rifting are similar, the Evaporite sequencesare formed in central segment on both margins.Resulted in several kilometers ofmudstone and sandstone, alluvial and marine shelf origins were deposited in bothmargins.During the Cenozoic, the sedimentation rates are increased and the sediments inthe study area are characterized by intercalated (marine clay, chalk, mudstone) andvolcanic beds.The continental extension between West Africaand Brazil was directly or indirectlyresponsible in the development within the pre-salt sag basin, and also for thedevelopment of evaporates at the central segment in the South Atlantic Ocean which isimportant in the petroleum researches.The initial halite and anhydrite depositionoccurred in the Espirito Santos of North East Brazil during ca.124.8 Ma, closely followedby the depositionwithin the Kwanza basin.All these evidence strongly supports initial rifting in the South Atlantic, after the timewhen separation of Brazil and Africa started.The initial phase of the East-westextensionin South Atlantic rift basins occurred from ca.140Ma of earliest Cretaceous to ca.127Maat Hauterivian.The second phase started from ca.126Ma of late Hauterivian ca.121Ma ofearliest Aptianis characterized by the rapid lithospheric weakening.The last phase wasstarted from ca.120 Ma with a breakup of the South Atlantic Ocean basins.

目录

声明

Acknowledgement

Abstract

Index

1．Introduction

1．1 Significance of the study

1．2 Previous study and Existing problems

1．3 Idea to solve the problems

1．4 Expected results

2．Geological setting and Tectonics

2．1 Geology of the South America

2．2 Geology of the West Africa

2．3 Tectonics

2．4 Magmatism

2．5 Opening of South Atlantic

2．6 Bathymetry of South Atlantic

3．Basin Stratigraphy

3．1 Espirito Santos Basin

3．2 Pelotas Basin

3．3 Colorado basin

3．4 Kwanza Basin

3．5 Walvis basin

3．6 Orange basin

3．7 Facies distribution

4．Evolution of South Atlantic spreading till Mesozoic

4．1 Evolution of Marginal Basins inferred from Balanced Section

4．1．1 Espirito Santos—-Kwanza basin

4．1．2 Pelotas—Walvis basin

4．1．3 Colorado—Orange basin

4．2 Evolution of Proto basin distribution

4．3 Topography of hotspot mountain chain

5．Discussion

5．1 Difference between the segments of South Atlantic Ocean

5．2 Mechanism of Salt deposition

5．3 Extension of the Basins

6．Conclusion

References