Angola Continental Margin—Sites 364 and 365 (2025)

Evolution of the Southwestern Angolan Margin: episodic burial and exhumation is more realistic than long-term denudation

International Journal of Earth Sciences, 2018

There are two main points of view regarding how continental margins evolve. The first one argues that the present-day margins have been developed by long-term denudation since a major exhumation episode, probably driven by rifting or another relevant tectonic event. The second one argues that continental margins underwent alternating burial and exhumation episodes related to crustal tectonic and surface uplift and subsidence. To demonstrate that the proximal domain of the southwestern Angolan margin has evolved in a polycyclic pattern, we present a review of geological and thermochronological information and integrate it with new combined apatite fission-track and (U-Th)/He data from Early Cretaceous volcanic and Precambrian basement samples. We also provide hypotheses on the possible mechanisms able to support the vertical crustal movements of this margin segment, which are also discussed based on some modern rifting models proposed for Central South Atlantic. The central apatite fission-track ages range from 120.6 ± 8.9 to 272.9 ± 21.6 Ma, with the mean track lengths of approximately 12 µm. The single-grain apatite (U-Th)/He ages vary between 52.2 ± 1 and 177.2 ± 2.6 Ma. The integration of the thermochronological data set with published geological constraints supports the following time-temperature evolution: (1) heating since the Carboniferous-Permian, (2) cooling onset in the Early Jurassic, (3) heating onset in the Early Cretaceous, (4) cooling onset in the Mid-to Late Cretaceous, (5) heating onset in the Late Cretaceous, and (6) cooling onset in the Oligocene-Miocene. The thermochronological data and the geological constraints, support that the proximal domain of the southwestern Angolan margin was covered in the past by pre-, syn-, and post-rift sediments, which were eroded during succeeding exhumation events. For this margin segment, we show that a development based on long-term denudation is less realistic than one based on burial and exhumation episodes during the last 130 Myr.

Palynostratigraphy and palaeoenvironmental shifts in Oligocene and Miocene strata from offshore Angola, west-central Africa Palynostratigraphy and palaeoenvironmental shifts in Oligocene and Miocene strata from offshore Angola, west-central Africa

Palynology Publication details, including instructions for authors and subscription information: A palynological investigation of 15 ditch cutting samples from Borehole 8, located off the Angolan coast, west-central Africa, revealed Late Oligocene (Chattian) to latest Middle to earliest Early Miocene (Serravallian/earliest Tortonian?) marine dinoflagellate cysts, freshwater colonial algae and terrestrial palynomorphs. Various early Miocene pollen characterising the Verrutricolporites rotundiporus Zone of Legoux (1978) confirm the location of the Oligocene–Miocene boundary in relation to a new short-ranging early Miocene dinoflagellate cyst taxon Cristadinium headii sp. nov. The Oligocene to Miocene dinoflagellate cyst assemblages reflect three periods, A–C, with high palaeoproductivity, corresponding to periods in the latest Oligocene (late Chattian), Early Miocene (late Aquitanian–early Burdigalian?) and the base of the Middle Miocene (Langhian). Early to middle Miocene acme intervals of Cleistosphaeridium placacanthum and Cribroperidinium tenuitabulatum are considered to reflect two regional oceanographic events due to intense upwelling along the West African coast. A distinct Early Miocene episode of brackish-water outflow from the nearby Angolan mainland is also reflected by the palynological assemblages, perhaps linked to the global Mi-1 event. Changes in relative abundance of grass pollen indicate a gradual change towards a drier and perhaps also warmer Burdigalian–Langhian climate during which the Angolan savanna developed, followed by cooler and perhaps more humid conditions following the Miocene Climatic Optimum.

Palynostratigraphy and paleoenvironmental shifts in upper Oligocene to Miocene strata off Angola, west-central Africa

Palynology, 2014

Palynostratigraphy and palaeoenvironmental shifts in Oligocene and Miocene strata from offshore Angola, west-central Africa

A palynological investigation of 15 ditch cutting samples from Borehole 8, located off the Angolan coast, westcentral Africa, revealed Late Oligocene (Chattian) to latest Middle to earliest Early Miocene (Serravallian/earliest Tortonian?) marine dinoflagellate cysts, freshwater colonial algae and terrestrial palynomorphs. Various early Miocene pollen characterising the Verrutricolporites rotundiporus Zone of Legoux (1978) confirm the location of the Oligocene–Miocene boundary in relation to a new short-ranging early Miocene dinoflagellate cyst taxon Cristadinium headii sp. nov. The Oligocene to Miocene dinoflagellate cyst assemblages reflect three periods, A–C, with high palaeoproductivity, corresponding to periods in the latest Oligocene (late Chattian), Early Miocene (late Aquitanian–early Burdigalian?) and the base of the Middle Miocene (Langhian). Early to middle Miocene acme intervals of Cleistosphaeridium placacanthum and Cribroperidinium tenuitabulatum are considered to reflect two regional oceanographic events due to intense upwelling along the West African coast. A distinct Early Miocene episode of brackish-water outflow from the nearby Angolan mainland is also reflected by the palynological assemblages, perhaps linked to the global Mi-1 event. Changes in relative abundance of grass pollen indicate a gradual change towards a drier and perhaps also warmer Burdigalian–Langhian climate during which the Angolan savanna developed, followed by cooler and perhaps more humid conditions following the Miocene Climatic Optimum.

Geologic Evolution, Sedimentation, and Paleoenvironments of the Angola Basin and Adjacent Walvis Ridge: Synthesis of Results of Deep Sea Drilling Project Leg 75

Initial Reports of the Deep Sea Drilling Project, 1984

The section recovered at Site 530 (Holes 53OA and 530B) consists of eight sedimentary units and one basalt unit. The composition of the basalt recovered in Hole 53OA is distinct from typical mid-ocean ridge basalts (MORBs) but is similar to that of Hawaiian tholeiites and basalt from the central part of Walvis Ridge. Throughout most of its history, the southern Angola Basin received large volumes of redeposited material in the form of turbidites and, most recently, debris-flow deposits. Most of this material was derived from Walvis Ridge to the south, but thickness trends of acoustic units suggest that some of the sediment was derived from the African continental margin to the east. The basal sedimentary unit (Albian to Santonian) at Site 530 contains 262 beds of black shale that are interbedded with green and red claystone. Black shale makes up less than 10% of the total section, but in two cores of early Turonian age, black shale beds compose about 50% of the section. The black shales contain up to 19% organic carbon (average of about 5%) that is mainly of autochthonous marine origin but with significant contributions from terrigenous organic matter. The origin of these more-and less-reduced interbedded lithologies with varying amounts and types of organic matter, and variable amounts of pelagic, hemipelagic, and turbiditic sediment is complex and cannot be explained by any one simple process. Many factors affecting the concentration of dissolved oxygen in the bottom waters of the Angola Basin varied throughout the middle Cretaceous to produce bottom-water conditions that fluctuated between mildly oxic and oxygen-deficient, but most of the time bottom-waters and sediment-interstitial waters were sufficiently oxic to permit the accumulation of red oxidized sediment. A relatively complete sedimentary record of the Cretaceous/Tertiary boundary was recovered within a sequence of mudstone and marlstone turbidites in Hole 530A. There is a significant increase in the concentration of iridium above background levels at the boundary. High concentrations of many other elements also occur within the same stratigraphic interval as the iridium anomaly. Furthermore, there is a marked decrease in CaCO 3 in the Tertiary strata above the iridium anomaly which suggests that the production of shallow-water carbonate also may have been affected by whatever caused elevated concentrations of iridium and other elements. These observations are consistent with the asteroid-impact theory proposed to explain the worldwide occurrence of an iridium anomaly at the Cretaceous/Tertiary boundary. The Cenozoic history of the Angola Basin was controlled mainly by (1) restriction of bottom-water flow from the south by Walvis Ridge; (2) development of glaciation on Antarctica; (3) opening of circulation passages in the southern oceans; (4) rapid turnover of cold, nutrient-rich waters that resulted in high productivity of diatoms; (5) influx of terrigenous sediment mainly by turbidity currents; and (6) production and preservation of carbonate sediment. The most distinctive Cenozoic event recorded in the section at Site 530 is the beginning of extensive glaciation on Anarctica and concomitant initiation of modern thermohaline bottom-water circulation that is manifested as a middle Eocene to middle Oligocene unconformity or compressed section accompanied by a drastic decrease in accumulation of CaCO 3. Diatom abundances in HPC cores from Walvis Ridge (Site 532) and Angola Basin (Hole 53OB) indicate that Benguela upwelling in these areas began in the late Miocene, reached a peak in the late Pliocene to early Pleistocene, and declined thereafter. Short-term variations in sediment composition at Site 532 are manifested as cyclic variations in concentrations of clay, CaCO 3 , and organic carbon with average periodicities of about 30-60 k.y. The main variability that produced the cycles probably was the influx of terrigenous clastic material which diluted the CaCO 3. The sediment at Site 532 also contains several percent organic carbon that is dominantly of marine origin, but with significant terrigenous components. Data from multichannel seismic, gravity, and magnetic surveys were used to define the regional stratigraphic and structural evolution of Walvis Ridge and adjacent Cape and Angola basins. Six structural provinces are recognized, four on Walvis Ridge and two additional provinces that correspond to the Cape and Angola basins. The two eastern structural provinces on Walvis Ridge are underlain by continental crust. The two western structural provinces are underlain by oceanic basement. Two main directions of faults are evident in seismic profiles, one trending N 10° and one trending N 60°. The N 60° trend corresponds to the general orientation of the northern and southern flanks of Walvis Ridge as well as to the dominant direction of fracture zones. During the first phase of separation of Africa from South America (ca. 120-130 m.y. ago), a voluminous mass of volcanics was emplaced simultaneous with the emplacement of basalt in the Parana Basin of Brazil and the Kaokoveld Region of South Africa. This period of volcanism also formed the series of seaward-dipping internal basement reflectors that are characteristic of the two structural provinces of Walvis Ridge. A system of fault blocks developed in the brittle upper part of the newly formed crust. During the second phase of rifting, which ended before late Aptian, more tilted fault blocks were created in the upper brittle stratified continental crust. Magnetic lineations in basement rocks in the Angola and Cape basins in the vicinity of Walvis Ridge are not distinct but suggest that oceanic crust began to be emplaced between 120 and 112 m.y. ago (Barremian to early Aptian). At least part of the oceanic crust of the central plateau of eastern Walvis Ridge (structural province 3) may have been emplaced before any oceanic crust formed in the adjacent basins. A ridge jump occurred during the late Aptian to early Albian in the southern part of the Angola Basin which translated the previously formed oceanic crust and its overlying evaporite deposits on the South American side. Several ridge jumps occurred on both sides of Walvis Ridge during the Late Cretaceous and early Tertiary to produce a 500-km-long segment of mid-ocean ridge.

The Fossil Record of Biodiversity in Angola Through Time: A Paleontological Perspective

Biodiversity of Angola, 2019

This chapter provides an overview of the alpha paleobiodiversity of Angola based on the available fossil record that is limited to the sedimentary rocks, ranging in age from Precambrian to the present. The geological period with the highest paleobiodiversity in the Angolan fossil record is the Cretaceous, with more than 80% of the total known fossil taxa, especially marine molluscs, including ammonites as a majority among them. The vertebrates represent about 15% of the known fauna and about one tenth of them are species firstly described based on specimens from Angola.

Tectonic Drift, Climate, and Paleoenvironment of Angola Since the Cretaceous

2010

Africa is the only continent that now straddles arid zones located beneath the descending limbs of both the northern and southern Hadley cells, and it has done so since it became a distinct continent in the Early Cretaceous. Since that time, Africa has drifted tectonically some 12 degrees north and rotated approximately 45 degrees counterclockwise. This changing latitudinal setting and position of the landmass under the relatively stable Hadley Cells is manifested as southward migration of climatic zones over the past 132 million years. Data from kerogen, X-ray diffraction analysis of sedimentary matrix, carbon isotopes from shell samples and tooth enamel,new 40Ar/39Ar radiometric dates, pollen and plant macrofossils, and fossil vertebrates indicate a productive upwelling system adjacent to a coastal desert since the opening of the South Atlantic Ocean; however, the position of the coastal desert has migrated southward as Africa drifted north, resulting in today's Skeleton Coast and Benguela Current. This migration has had a profound effect on the placement of the West African coast relative to areas of high marine productivity and resulting extensive hydrocarbon deposits, on the placement of arid zones relative to the continent especially the Skeleton Coast desert, on the climatic history of the Congo Basin (which shows a Late Cretaceous decrease in aridity based on the relative abundance of analcime in the Samba core), and in reducing the southern temperate region of Africa from 17% of continental area during the Cretaceous to 2% today. We show here that these related geographic and environmental changes drove ecological and evolutionary adjustments in southern African floras and faunas, specifically with respect to the distribution of anthropoid primates, the occurrence of modern relicts such as the gnetalean Welwitschia mirabilis, endemism as in the case of ice plants, and mammalian adaption to an open environment as in springhares. Africa's tectonic drift through climate zones has been a first-order environmental determinant since the Early Cretaceous.

Carbon isotope stratigraphy and 40Ar/39Ar age of the Cretaceous South Atlantic coast, Namibe Basin, Angola

Journal of African Earth Sciences, 2014

We present the d 13 C and paleomagnetic stratigraphy for marine strata at the coast of southern Angola, anchored by an intercalated basalt with a whole rock 40 Ar/ 39 Ar radiometric age of 84.6 ± 1.5 Ma, being consistent with both invertebrate and vertebrate biostratigraphy. This is the first African stable carbon isotope record correlated to significant events in the global carbon record spanning the Late Cenomanian to Early Maastrichtian. A positive $3‰ excursion seen in bivalve shells below the basalt indicates the Cenomanian-Turonian Boundary Event at 93.9 Ma, during Oceanic Anoxic Event 2. Additional excursions above the basalt are correlated to patterns globally, including a negative $3‰ excursion near the top of the section interpreted as part of the Campanian-Maastrichtian Boundary Events. The age of the basalt ties the studied Bentiaba section to a pulse of Late Cretaceous magmatic activity around the South Atlantic and significant tectonic activity, including rotation, of the African continent.

Origin and diagenetic evolution of gypsum and microbialitic carbonates in the Late Sag of the Namibe Basin (SW Angola)

Sedimentary Geology, 2016

Ephemeral evaporitic conditions developed within the uppermost part of the transgressive Late Sag sequence in the Namibe Basin (SW Angola), leading to the formation of extensive centimetre-to metre-thick sulphate-bearing deposits and correlative microbialitic carbonates rich in pseudomorphs after evaporite crystals. The onshore Pre-Salt beds examined in this study are located up to 25 m underneath the major mid-Aptian evaporitic succession, which is typified at outcrop by the gypsiferous Bambata Formation and in the subsurface by the halite-dominated Loeme Formation. Carbonate-evaporite cycles mostly occur at the top of metre-thick regressive parasequences, which progressively onlap and overstep landward the former faulted (rift) topography, or fill major Pre-Salt palaeo-valleys. The sulphate beds are made up of alabastrine gypsum associated with embedded botryoidal nodules, dissolution-related gypsum breccia, and are cross-cut by thin satin-spar gypsum veins. Nodular and fine-grained fabrics are interpreted as being diagenetic gypsum deposits resulting from the dissolution and re-crystallisation of former depositional subaqueous sulphates, whereas gypsum veins and breccia result from telogenetic processes.

Aptian-Albian planktic foraminifera from DSDP Site 364 (offshore Angola): Biostratigraphy, paleoecology, and paleoceanographic significance

Journal of Foraminiferal Research, v. 43, no. 4, p. 442-462, 2013

This work presents a taxonomic, biostratigraphic and paleoecological study of planktic foraminifera recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Twenty-nine planktic foraminiferal species were identified, enabling the identification of late Aptian–late Albian biozones, from the Hedbergella trocoidea Zone to the Pseudothalmanninella ticinensis Zone. A major unconformity from the latest early–earliest late Albian was identified in core 31, with the Microhedbergella rischi Zone in direct contact with the Pseudothalmanninella ticinensis Zone. The recovered assemblages are characterized by open marine epipelagic dwellers and indicate predominant mesotrophic environmental conditions throughout the studied stratigraphic succession. Aptian planktic foraminiferal assemblages have a tropical/subtropical paleobiogeographic affinity, supporting a surface-water connection between the central proto-Atlantic Ocean and the northern South Atlantic Ocean (north of the Walvis Ridge-Rio Grande Rise) by the late Aptian. Trends in isotopic values for d13C suggest a late Aptian age (Globigerinelloides algerianus Zone) for the stratigraphic interval from core 42 to ,core 37, where age-diagnostic foraminiferal species are missing. Black shale levels in cores 42–39 are probably the local expression of the ‘‘late Aptian anoxic event’’.