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Título

STRUCTURAL AND STRATIGRAPHIC INSIGHTS OF THE NAMIBE BASIN: IMPLICATIONS FOR HYDROCARBON EXPLORATION IN THE SOUTH ATLANTIC

Texto do resumo

The Namibe Basin in southern Angola is significant as it marks the southernmost boundary of the South Atlantic saline basins. The basin was developed during the Cretaceous period as part of the rift-to-drift evolution during the breakup of the South Atlantic. It is part of the same geological system as the hydrocarbon-rich Kwanza, Santos, and Campos offshore basins. The onshore portion of the Namibe Basin provides a unique detailed view of the lateral and vertical relationships within the Pre-Salt, Salt, and Post-Salt South Atlantic petroleum systems. To understand its structural and stratigraphic elements, volcanic development, and basin evolution mechanisms, we conducted detailed fieldwork, including rock description and analysis and 3D outcrop modeling using drone aerial surveys. This study demonstrated the Bero Volcanic Complex (BVC) relation with the rift-related Paraná-Etendeka Large Igneous Province (LIP). Overlying the BVC and basement rocks, a series of carbonates and clastic rocks from the Cangulo and Tumbalunda Formation. These rocks are attributed to the "Late Sag" pre-salt sequence of the South Atlantic. The Aptian-aged Loeme Formation evaporites overlie these units, and the contact with the overlying Loeme Evaporite Formation is conformable. The Loeme Formation evaporites consist of a 40-70m thick package of gypsum-anhydrite, and the top of these evaporites shows clear evidence of karstification/dissolution. Subsequently, a large-scale transgression is recorded over the evaporitic basin, evidenced by Albian marine clastic and carbonatic deposits. The carbonates are predominantly algal (rhodolites, thrombolites) or contain a relatively restricted marine fauna (nerineid gastropods, oysters). This sequence is abruptly overlain by a thick Albian to early Cenomanian succession of fluvial to alluvial clastics (Giraul Formation). This contact may include significant erosion, placing red bed conglomerates, aeolian sands, and palaeosols over the underlying stratigraphy. In the Piambo area, these sediments are intruded and overlain by the Bentiaba Basanite Formation volcanic rocks. Structurally, the Namibe Basin exhibits fault segmentation and fault block compartmentalization. NW-SE trending faults dominate the southern region, while NE-SW and NNE-SSW faults become progressively more prominent in the northern region. The structural style and segmentation pattern evident in the Namibe Basin reveal an oblique rifted margin. Therefore, our study suggests that the onshore Namibe Basin shed critical assessment and constraints on the depositional evolution of the complex Pre-Salt, Salt, and Post-Salt South Atlantic petroleum systems.

Palavras Chave

3D modeling; Sedimentology; Oblique Rifted Margin; Onshore Angola