scholarly journals Basin evolution, configuration styles, and hydrocarbon accumulation of the South Atlantic conjugate margins

2019 ◽  
Vol 37 (3) ◽  
pp. 992-1008
Author(s):  
Zhixin Wen ◽  
Shu Jiang ◽  
Chengpeng Song ◽  
Zhaoming Wang ◽  
Zhengjun He
Keyword(s):  
Marine Sediments ◽  
Fracture Zone ◽  
South Atlantic ◽  
Source Rocks ◽  
Basin Evolution ◽  
The South ◽  
Passive Margins ◽  
Marine Shale ◽  
Lacustrine Shale ◽  
Northern Segment

The basins of the South Atlantic passive margins are filled with early rifting stage lacustrine sediments (Barremian, 129–125 Ma), transitional lacustrine and marine sediments (Aptian, 125–113 Ma), and drift stage marine sediments since early Cretaceous (Albian, 113 Ma). The South Atlantic margins can be divided into three segments by the Rio Grande Fracture Zone and the Ascension Fracture Zone according to variations in the basin evolution history and configuration style. The lacustrine shale and marine shale source rocks are developed in the rift stage and drift (post-rift) stage in the South Atlantic passive margins, respectively. The southern segment of the margins is dominated by the lacustrine sedimentary filling in the rifted stage overlain by a thin marine sag system as a regional seal, where the hydrocarbons are mainly accumulated in the structural-stratigraphic lacustrine reservoirs formed in the rift stage. The middle segment developed salty rift-sag-type basins with rift and sag systems and with salt deposited in the transitional intercontinental rift stage, where the lacustrine shale in the lower part of the rifted lacustrine sequence and the marine shale in the lower part of the sag sequence formed in the marine post-rift stage are high-quality source rocks. This segment in the middle is mainly dominated by pre-salt lacustrine carbonate and post-salt marine turbidite plays. The northern segment is characterized by sag-type basins with a narrowly and locally distributed rifted lacustrine system and its overlying widely distributed thick marine sag systems. Gravity-flow (mostly turbidite) marine sandstones as good reservoirs were extensively developed in the sag stage due to the narrow shelf and steep slope. The post-rift marine shales in the lower part of the sag sequence are the main source rocks in the northern segment and the hydrocarbons generated from these source rocks directly migrated to and accumulated in the deep marine turbidite sandstones in the same sag sequence formed in the drift stage. From southern segment to northern segment, source rocks and hydrocarbon accumulations tend to occur in the stratigraphically higher formations. The hydrocarbon accumulations in the southern segment are mainly distributed in the rifted lacustrine sequence while that in the northern segment primarily occur in the post-rift marine sequence.

Modelling thermal lithospheric thickness along the conjugate South Atlantic passive margins implies asymmetric rift initiation

2021 ◽  
Author(s):  
Peter Haas ◽  
R. Dietmar Müller ◽  
Jörg Ebbing ◽  
Gregory A. Houseman ◽  
Nils-Peter Finger ◽  
...  
Keyword(s):  
South Atlantic ◽  
Heterogeneous Structure ◽  
South American ◽  
The South ◽  
Passive Margins ◽  
Margin Width ◽  
Lithospheric Thickness ◽  
Lithospheric Thinning ◽  
Tectonic Features ◽  
And Diffusion

<p>In this contribution, we examine the evolution of the South Atlantic passive margins, based on a new thermal lithosphere-asthenosphere-boundary (LAB) model. Our model is calculated by 1D advection and diffusion with rifting time, crustal thickness and stretching factors as input parameters. The initial lithospheric thickness is defined by isostatic equilibrium with laterally variable crustal and mantle density. We simulate the different rifting stages that caused the opening of the South Atlantic Ocean and pick the LAB as the T=1330° C isotherm. The modelled LAB shows a heterogeneous structure with deeper values at equatorial latitudes, as well as a more variable lithosphere along the southern part. This division reflects different stages of the South Atlantic opening: Initial opening of the southern South Atlantic caused substantial lithospheric thinning, followed by the rather oblique-oriented opening of the equatorial South Atlantic accompanied by severe thinning. Compared to global models, our LAB reflects a higher variability associated with tectonic features on a smaller scale. As an example, we identify anomalously high lithospheric thickness in the South American Santos Basin that is only poorly observed in global LAB models. Comparing the LAB of the conjugate South American and African passive margins in a Gondwana framework reveals a variable lithospheric architecture for the southern parts. Strong differences up to 80 km for selected margin segments correlate with strong gradients in margin width for conjugate pairs. This mutual asymmetry suggests highly asymmetric melting and lithospheric thinning prior to rifting.</p>

scholarly journals Conjugate volcanic passive margins in the austral segment of the South Atlantic – Architecture and development

2021 ◽  
Vol 212 ◽  
pp. 103461
Author(s):  
François Chauvet ◽  
François Sapin ◽  
Laurent Geoffroy ◽  
Jean-Claude Ringenbach ◽  
Jean-Noël Ferry
Keyword(s):  
South Atlantic ◽  
The South ◽  
Passive Margins

Hotspot origin for asymmetrical conjugate volcanic margins of the austral South Atlantic Ocean as imaged on deeply penetrating seismic reflection lines

2019 ◽  
Vol 7 (4) ◽  
pp. SH71-SH97 ◽  
Author(s):  
Kyle Reuber ◽  
Paul Mann ◽  
Jim Pindell
Keyword(s):  
Oceanic Crust ◽  
Seismic Reflection ◽  
Seismic Refraction ◽  
South Atlantic ◽  
Plate Motion ◽  
Basin Evolution ◽  
Spreading Ridge ◽  
The South ◽  
Volcanic Material ◽  
Conjugate Margins

We have interpreted 27,550 km of deep-penetrating, 2D-seismic reflection profiles across the South Atlantic conjugate margins of Uruguay/Southern Brazil and Namibia. These reflection profiles reveal in unprecedented detail the lateral and cross-sectional, asymmetrical distribution of voluminous, postrift volcanic material erupted during the Barremian-Aptian (129–125 Ma) period of early seafloor spreading in the southernmost South Atlantic. Using this seismic grid, we mapped the 10–200 km wide, continental margin-parallel limits of seaward-dipping reflector (SDR) complexes — that are coincident with interpretations from previous workers using seismic refraction data from the South American and West African conjugate margins. Subaerially emplaced and tabular SDRs have rotated downward 20° in the direction of the mid-Atlantic spreading ridge and are up to 22 km thick near the limit of continental crust. The SDR package is wedge shaped and thins abruptly basinward toward the limit of oceanic crust where it transitions to normal, 6–8 km thick oceanic crust. We have developed a model for the conjugate rifted margins that combine diverging tectonic plates and northwesterly plate motion relative to a fixed mantle position of the mantle plume. Our model explains an approximately 30% higher volume of SDRs/igneous crust on the trailing Namibian margin than on the leading Brazilian margin during the syn- and postrift phases. Our model for volcanic margin asymmetry in the South Atlantic does not require a simple shear mechanism to produce the asymmetrical volcanic material distribution observed from our data and from previously published seismic refraction studies. Determining the basinward extent of the extended continental basement is crucial for understanding basin evolution and for hydrocarbon exploration. Although these conjugate margins have evolved asymmetrically, their proximity during the early postrift stage suggests a near-equivalent, early basin evolution and similar hydrocarbon potential. Understanding the tectonic and magnetic processes that produce these observed asymmetries is critical for understanding volcanic passive margin evolution.

scholarly journals Passive margins evolved from a confined orogen: comparison of both sides of the South Atlantic (D.R. Congo - east Brazil)

2018 ◽  
Author(s):  
Gerben Van Ranst ◽  
Tiago A. Novo ◽  
Daniel Baudet ◽  
Antônio Carlos Pedrosa-Soares ◽  
Luc Tack ◽  
...  
Keyword(s):  
South Atlantic ◽  
The South ◽  
Passive Margins

Brazilian and African passive margins of the Central Segment of the South Atlantic Ocean: Kinematic constraints

2009 ◽  
Vol 468 (1-4) ◽  
pp. 98-112 ◽  
Author(s):  
Daniel Aslanian ◽  
Maryline Moulin ◽  
Jean-Louis Olivet ◽  
Patrick Unternehr ◽  
Luis Matias ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South ◽  
Kinematic Constraints ◽  
Passive Margins ◽  
Central Segment

Advancing Models of Facies Variability and Lacustrine Source Rock Accumulation in Rifts: Implications for Exploration

2016 ◽  
Author(s):  
Christopher A. Scholz
Keyword(s):  
East African Rift ◽  
Hydrothermal Systems ◽  
South Atlantic ◽  
Source Rocks ◽  
Reservoir Rock ◽  
The South ◽  
East African ◽  
Basin Scale ◽  
African Rift ◽  
Lake Basins

ABSTRACT Important syn-rift hydrocarbon discoveries in the Tertiary East African Rift and in the South Atlantic subsalt basins have in recent years promoted renewed interest in the variability of source and reservoir rock facies in continental rifts. This talk considers several important new observations and developments in our understanding of the sedimentary evolution of lacustrine rift basins. Offshore subsalt basins in the South Atlantic demonstrate the importance of lacustrine carbonates, and especially microbialites, as reservoir facies in extensional systems. The role of rift-related magmatism is significant in these basins, both as drivers of hydrothermal systems around and within rift lakes, and as a source of solutes that facilitate carbonate accumulations. In the Tertiary East African Rift, substantial new hydrocarbon resources have been identified, including onshore siliciclastic reservoirs in remarkably young and shallow parts of the sedimentary section in the Albertine Graben. Rollover anticlines and fault-related folds serve as important structures for several new fields in the East African Rift, but larger structures affiliated with accommodation zones, in many instances located far offshore in the modern lakes, remain untested. Lacustrine source rocks that accumulated in stratified lake basins are the source of the oil and gas in these systems, however there is still much to be learned about their spatial and temporal variability. There is observed considerable variation in the character of organic matter on the floors of modern African lake basins, even adjacent ones. A number of factors likely govern the amount of total organic carbon preserved within the basins. These include 1) primary productivity; 2) degree of siliciclastic dilution, which is controlled in part by offshore slopes and the extent of onshore catchments, and 3) physical limnology, controlled by climate and basin-scale physiography, and the fetch-depth ratio of the lakes, which determines the likelihood of water column stratification. Scientific drilling in the African Rift lake basins is providing considerable information on the high temporal hydroclimate variability of the region, especially in the later Tertiary and Quaternary, which substantially controls basin lithofacies.

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