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Palaeoenvironments during a terminal Oligocene or early Miocene transgression in a fluvial system at the southwestern tip of Africa
Abstract
A multi-proxy study of an offshore core in Saldanha Bay (South Africa) provides new insights into fluvial deposition,
ecosystems, phytogeography and sea-level history during the late Paleogene-early Neogene. Offshore seismic data
reveal bedrock topography, and provide evidence of relative sea levels as low as -100 m during the Oligocene. 3D
landscape reconstruction reveals hills, plains and an anastomosing river system. A Chattian or early Miocene age for
the sediments is inferred from dinoflagellate taxa Distatodinium craterum, Chiropteridium lobospinosum, Homotryblium
plectilum and Impagidinium paradoxum. The subtropical forest revealed by palynology includes lianas and vines,
evergreen trees, palms and ferns, implying higher water availability than today, probably reduced seasonal drought
and stronger summer rainfall. From topography, sedimentology and palynology we reconstruct Podocarpaceaedominated
forests, Proto-Fynbos, and swamp/riparian forests with palms and other angiosperms. Rhizophoraceae
present the first South African evidence of Palaeogene/Neogene mangroves. Subtropical woodland-thicket with
Combretaceae and Brachystegia (Peregrinipollis nigericus) probably developed on coastal plains. Some of the last
remaining Gondwana elements on the sub-continent, e.g., Araucariaceae, are recorded. Charred particles signal fires
prior to the onset of summer dry climate at the Cape. Marine and terrestrial palynomorphs, together with organic and
inorganic geochemical proxy data, suggest a gradual glacio-eustatic transgression. The data shed light on Southern
Hemisphere biogeography and regional climatic conditions at the Palaeogene-Neogene transition. The proliferation of
the vegetation is partly ascribed to changes in South Atlantic oceanographic circulation, linked to the closure of the
Central American Seaway and the onset of the Benguela Current ~14 Ma.
... The sediments are believed to be of earliest Miocene age. A Chattian to early Miocene age for the Saldanha Bay deposits is suggested on the base of the dinoflagellate indicator taxa Distatodinium craterumEaton, Chiropteridium lobospinosum GochtHomotryblium plectilum, Drugg and Loeblich Jr. as well asImpagidinium paradoxum (Wall 1967) Stover et Evitt 1978 (see details in Roberts et al. [2017] including supplements). For a full geological, stratigraphic, palaeontological and palaeoenvironmental background of this locality/core see Roberts et al. (2017). ...
... A Chattian to early Miocene age for the Saldanha Bay deposits is suggested on the base of the dinoflagellate indicator taxa Distatodinium craterumEaton, Chiropteridium lobospinosum GochtHomotryblium plectilum, Drugg and Loeblich Jr. as well asImpagidinium paradoxum (Wall 1967) Stover et Evitt 1978 (see details in Roberts et al. [2017] including supplements). For a full geological, stratigraphic, palaeontological and palaeoenvironmental background of this locality/core see Roberts et al. (2017). The sedimentary rock sample was processed and fossil pollen grains ...
... Based on the available host ranges of recent African Loranthaceae (Table II; Tables S1-S21 in Supplemental data) it seems that most of the genera are generalists and parasitising many species/genera/families. The fossil palynoassemblage containing the Saldanha MT is extremely taxon rich (Roberts et al. 2017) and composing pollen from at least 150 different angiosperms verified using SEM (Grímsson et al. unpublished ...
An ongoing re-investigation of the early Miocene Saldanha Bay (South Africa) palynoflora, using combined light and scanning electron microscopy (single grain method), is revealing several pollen types new to the African fossil record. One of the elements identified is Loranthaceae pollen. These grains represent the first and only fossil record of Loranthaceae in Africa. The fossil pollen grains resemble those produced by the core Lorantheae and are comparable to recent Asian as well as some African taxa/lineages. Molecular and fossil signals indicate that Loranthaceae dispersed into Africa via Asia sometime during the Eocene. The present host range of African Loranthaceae and the composition of the palynoflora suggest that the fossil had a range of potential host taxa to parasitise during the early Miocene in the Saldanha Bay region.
... The Namib Desert is one of the world's oldest deserts, existing continuously since the Middle Miocene (Senut and Ségalen, 2014). Its formation is traced back to the onsets of the Benguela current and the Benguela upwelling system, which took place between 14 and 10 Ma (Rommerskirchen et al., 2011;Roberts et al., 2017;Chase et al., 2019). Paleoclimate information from the Namib Desert still is very scarce and discontinuous, since the long-lasting aridity and strongly seasonal rainfall regimes have excluded the formation of long lake, wetland or cave records (e.g., Chase et al., 2019). ...
... As the Namib Desert, the Atacama Desert in Chile is a very old westcoast desert that is located in the subtropical high-pressure belt of the Southern Hemisphere. Both deserts additionally have in common that they owe their aridity in part to cold coastal upwelling latest since the Miocene (Hartley et al., 2005;Roberts et al., 2017). The aridity in the core of the Atacama is, however, enhanced by the subduction of the Nazca Plate beneath the South American continent, leading to an 800-2000 m high coastal cliff that hampers moisture (Rutllant et al., 2013), whereas the Namib is tectonically stable (van der Wateren and Dunai, 2001). ...
... This kind of temperate woodland is missing in the Cape. Palaeobotanists (see Roberts et al. 2017 and literature cited therein) concur in the opinion that the Cape was home to subtropical woodlands/forests at the Eocene-Miocene boundary and that these may well have been surviving the entire Early Miocene, perhaps until Mid-Miocene, when global aridification set in (Zachos et al. 2001). Cowling et al. (1996) suggested a link between the origins of the Cape MTE and the global cooling and aridification events in Pliocene. ...
... However, it may well be that fullyfledged fynbos is of Pliocene origin (Dupont et al. 2011), replacing the fire-prone shrublands called Proto-Fynbos (e.g. Roberts et al. 2017). Proto-Fynbos here refers to scrub formation reminiscent (by the composition of participating plant families) of today's fynbos shrublands, as defined, for instance, by Rebelo et al. (2006). ...
Mediterranean-type ecosystems (MTEs) are members of the zonobiome S1 (Ethesial Zone). Five regions support MTEs—two in the Northern Hemisphere and three in the Southern Hemisphere. The latter, including the Chilean, Cape (South Africa), and Australian MTE, are the subject of this chapter. MTEs have attracted much attention from biogeographers mainly because of a disproportionally high species diversity and endemism and ecologists because of remarkable physiognomic similarity, often explained by convergent evolutionary processes. This chapter focuses on four intriguing issues associated with the Southern-Hemisphere MTEs, namely (1) one-clade domination of Australian MTE woodlands by eucalypts, (2) very low tolerance against the fire of the Chilean MTE, (3) lack of flammable woodlands in the Cape region, and (4) low-key presence of annuals in the MTEs of the Cape and Australia.KeywordsAustralian eucalypt woodlandsCaliforniaCape fynbosChilean MatorralEvolutionary biome assemblyMediterranean BasinSouthwest Australian Floristic RegionOld stable landscapes
... palms, Winteraceae, Sarcolaenaceae, Podocarpaceae). Deposits from Saldanha bay from the late Palaeogene indicate a variety of biomes including evidence for a Cape floristic element (Roberts et al., 2017). The Noordhoek deposit shows a transition in dominant vegetation type, containing an older pollen assemblage with, inter alia, Podocarpaceae, Widdringtonia (Cupressaceae), Arecaceae, Croton (Euphorbiaceae), indicating temperate to subtropical evergreen forest and a younger pollen assemblage in which fynbos vegetation is dominant (e.g. ...
... Alternatively, it could result from a summer dry, winter rainfall regime limiting growth rates (Keeley et al., 2011). It is possible that the establishment of the current fire regime pre-dates the onset of the summer dry climate in the Cape (He et al., 2016;Roberts et al., 2017) and thus could be consistent with both filters. ...
The Cape flora is compositionally biased, being dominated by a few fynbos clades (such as Iridaceae, Ericaceae, Proteaceae and Restionaceae) that make up major part of the distinct heathland vegetation in the Cape Floristic Region. Uncertainty exists concerning what excluded the subtropical to tropical palm-dominated woodland/forest vegetation that was the dominant component in the CFR in the Paleocene and allowed the fynbos clades, which are largely derived from outside Africa, to establish and radiate. Two filters have been proposed. The first postulates that the establishment of the Mediterranean climate driven by the late Miocene initiation of the cold-water Benguela Upwelling System (BUS) eliminated the African lineages and allowed the establishment and radiation of sclerophyllous plant clades ("the Mediterranean climate model", MCM). Alternatively, the "oligotrophic soils model" (OSM) postulates that the oligotrophic soils, gradually exhumed by post-Gondwanan Late Cretaceous - early Cenozoic erosion, acted as a filter excluding the African lineages. In this study, we re-calibrate the fynbos clade Phylica (Rhamnaceae), the genus initially used to test the MCM, using new fossil data to test if the crown age precedes the Late Miocene. Our results indicate that we cannot significantly reject a crown age of Phylica consistent with the MCM. We compare the MCM and OSM model for the Cape fynbos flora by compiling the crown ages of 22 fynbos clades. We show that crown ages are not clustered in time around the initiation of the BUS but, are dispersed throughout the Cenozoic. This suggests that oligotrophic soils, rather than summer drought, acted as a filter. Consequently, we argue that the fynbos clades radiated separately in expanding edaphically controlled heathland patches in the Cape mountains as sandstone exhumation after the Gondwanan break-up progressed.
... They are very rare to abundant (0.6%-58%) in C-B1 and absent to common in O-A1 (up to 34.6%) and include small wind-pollinated taxa, which due their high buoyancy, are widely distributed (Oboh, 1992) and mixed with fluvial transported taxa in the deposits. Large, heavy ornamented sporomorphs might signal short transport distances in a low energy environment (Roberts et al., 2017). Sporomorphs can give an indication of transport and oxidation levels when they are, for instance, reworked, or show degradation and corrosion (Oboh, 1992). ...
... As this is potentially the oldest record of the family on the continent, more thorough examination is needed to determine whether this record can be used in phylogenetic and biogeographic analyses. Other reports of Araliaceae from Africa include pollen of Araliaceoipollenites from the latest Oligocene-early Miocene Elandsfontyn Formation, Saldanha Bay, South Africa (Roberts et al. 2017) and Cussonia-type and Polyscias-type araliaceous-a nity pollen from the Oligocene of Ethiopia (Yemane et al. 1987, Kappelman et al. 2003. Again, these pollen records may represent Araliaceae, but a more in-depth review of the material with light and SEM microscopy may be required. ...
Astropanax is a monophyletic genus found in the Africa–Madagascar–Seychelles region whose evolutionary and biogeographic history, and that of related Araliaceae genera, are poorly known. In this paper, we report the presence of Astropanax leaves and pollen in Ethiopia 21.73 million years ago from the Mush Valley locality, which preserves leaf material with cuticles, fruits, seeds, woods, and less common biota including insects. Astropanax was part of a moist tropical forest community surrounding a volcanic crater lake and dominated by a single legume taxon (Englerodendron mulugetanum). Forty-nine leaf morphotypes have been documented at Mush and, along with Astropanax, identified taxa all have living relatives mainly confined to west, central, and east African forests. The plant genera found together at Mush include groups limited today to both lowlands (e.g. the swamp palm, Sclerosperma), and uplands (e.g. Hagenia). Astropanax species are most often found today in the uplands. Subsequent to the early Miocene, some genera present at Mush may have diverged into lineages that comprise the highland and lowland forest species known today. Araliaceae fossils are known from Paleogene localities primarily across the northern continents; the occurrence of Astropanax in the early Miocene of Ethiopia appears to represent the earliest definitive occurrence of Araliaceae on the African continent.
... The rivers, lakes and wetlands of Africa have been vibrant and biologically diverse ecosystems from before the time, more than 100 million years ago, when Africa split from South America to become a continent. Over the geological ages, freshwater ecosystems and the organisms inhabiting them evolved and shifted in response to biotic interactions and a physical landscape continually reshaped by tectonic and climatic processes (Stewart, 2001;Otero et al., 2009Otero et al., , 2017Roberts et al., 2017;Masese and Dalu, 2024, Chapter 1;Dube et al., 2024, Chapter 2;O'Brien et al., 2024, Chapter 3;Mwaijengo et al., 2024, Chapter 4;Muvundja et al., 2024, Chapter 5;Dalu et al., 2024b,c, Chapters 6 and 7). Homo sapiens appeared on the continent approximately 0.2 million years ago, likely in an area of palaeo-wetlands in southern Africa (Chan et al., 2019). ...
... It was caused by margin uplift resulting in a relative sea-level fall (possibly beyond the shelf break which is a topic of controversy in literature) and is evidenced by; tilting topsets in the Walvis Basin, and a 350 m difference in elevation between the late Eocene and Oligocene shorelines of the northern Orange Basin at ∼ 30 Ma, as observed in the shallower reaches of the SW African margin (Hirsch et al., 2010;Baby et al., 2018). Along the coast, well data from Saldanha Bay record sea levels as low as −100 m during the Oligocene (Roberts et al., 2017). The early Miocene corresponds to a sea-level lowstand caused by tectonic uplift attributed to the African superswell ( Fig. 3; Séranne and Anka, 2005;Wigley and Compton, 2006;Hirsch et al., 2010). ...
Deep-water fold-and-thrust belt (DWFTB) systems are gravity-driven collapse structures often found in passive margin settings and are comprised of a linked up-dip extensional domain, central transitional/translational domain, and down-dip compressional domain. Many Late Cretaceous DWFTB systems occur along the SW African passive margin with multiple, over-pressurized, seaward-dipping shale detachment surfaces accommodating gravitational slip. In this study we use 3D reflection seismic data to constrain the strato-structural evolution of the translational and compressional domains of a Late Cretaceous DWFTB system and the overlying Cenozoic deposits in the Orange Basin, South Africa. The stratigraphy and structure of the Late Cretaceous DWFTB system is shown to have controlled fundamental sedimentary processes and the stability of the evolving margin. The compressional domain exhibits large-scale landward-dipping DWFTBs with thrust faults detaching the main Turonian shale detachment surface at depth and terminating at the early Campanian surface. A major ∼ 7 km wide seafloor slump scar reflecting margin instability occurs directly above a syncline of the same width from the buried DWFTB system's compressional domain. The translational domain is imaged as a complex region displaying overprinted features of both extensional and compressional tectonics with the downslope translation of sediment comprising listric normal and then thrust and oblique-slip faults distally. Thrust sheets are segmented along strike by extensive oblique-slip faults which extend from the translational domain into the down-dip compressional domain. Smaller, localized fold-and-thrust belts are found directly below the kilometre-scale DWFTB system in the down-dip compressional domain detaching a lower, Albian shale detachment surface which corresponds to an older gravitational collapse. The upward propagation of normal and oblique-slip faults with progressive sedimentation is hindered by the Oligocene or Miocene stratigraphic markers corresponding to mass erosional processes in the Cenozoic. A large (∼ 2.3 km wide), roughly slope-perpendicular Oligocene submarine canyon formed by turbidity currents is attributed to a major sea-level fall at ∼ 30 Ma. Oceanographic circulation is shown to have held a significant control on the deposition of mid-Miocene to present-day sedimentary sequences. Between 1200 to 1500 m water depths along the upper continental slope well-preserved extensive slope-parallel, sinusoidal channel-like features occur on the Miocene stratigraphic marker. The channels are confined within a ∼ 14 km wide zone at the interface of the upper northward-flowing Antarctic Intermediate Water (AAIW) and deeper southward-flowing North Atlantic Deep Water (NADW) currents. The erosive interaction of these oppositely flowing bottom currents combined with the effects of the Benguela Upwelling System (BUS), all of which formed or intensified at ∼ 11 Ma, are responsible for the creation and preservation of the extensive slope-parallel channels. This study shows the difference in structural styles of the translational and compressional domains of a Late Cretaceous DWFTB system and the processes responsible for mass-scale erosion in the Cenozoic.
... Inland records from kimberlite pipes show a mixed flora with some fynbos elements (Proteaceae, Ericaceae and Restionaceae) in the Palaeogene in a tropical to warm temperate environment 95 . From the southwestern Cape coast (where fynbos occurs today), fynbos elements were present (restios, ericas, proteas) during the Oligo-Miocene, mixed with palm and miombo floras, and interpreted as tropical to subtropical forest with lianas, vines, evergreen trees, palms and ferns [96][97][98] . Taken together, these lines of evidence point towards a much more complex history of the fynbos biome than previously thought. ...
The rapid Cretaceous diversification of flowering plants remains Darwin’s ‘abominable mystery’ despite numerous fossil flowers discovered in recent years. Wildfires were frequent in the Cretaceous and many such early flower fossils are represented by charcoalified fragments, lacking complete delicate structures and surface textures, making their similarity to living forms difficult to discern. Furthermore, scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification, including the role of fire in shaping flowering plant evolution. We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown-eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions together with burned plant remains in Cretaceous amber from northern Myanmar (~99 million years ago). These specialized flower species, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., exhibit traits identical to those of modern taxa in fire-prone ecosystems such as the fynbos of South Africa, and provide evidence of fire adaptation in angiosperms.
... Furthermore, reconstructions of floristic and vegetation patterns of the Paleogene of large parts of the Northern Hemisphere, especially Eurasia, based on palaeobotanical evidence, i.e. leaves, fruits, seeds, wood, palynomorphs were intensively carried out (e.g., Utescher and Mosbrugger 2007;Herman et al. 2017; Casas-Gallego and Barr on 2020; Utescher et al. 2021). Although this time window was a crucial period for the development of modern ecosystems, following the global climatic cooling at the Eocene-Oligocene boundary (e.g., Prothero 1994;Mai 1995), vegetation reconstructions especially palynoflora-based reconstructions are still very few, in particular for Africa, except for a little number of contributions such as Roberts et al. (2017) for southern Africa. ...
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Abstract
A palynological investigation was carried out on 24 samples from the Oligocene Dabaa Formation, which cuts across the Amana-1X well, located in the Abu El Gharadig Basin, north Western Desert, Egypt. Palynological evidence presented here suggests an early Oligocene age for the studied Dabaa Formation. In addition, the palynological assemblages provide supplementary evidence for depositional environments. They are generally indicative of outer-shelf to upper slope environment under oxic to anoxic conditions for the lower part of the studied Dabaa Formation, but infrequent occurrences of more diverse assemblages suggest an inner neritic marine environment for strata at some levels in the upper part of the studied section. It was during the Oligocene that marked floral changes leading to the development of modern plant associations began such as temperate deciduous forests (with e.g., Acer and Betulaceae) which expanded greatly in the mid latitudes. A distinctive vegetational pattern could be outlined within the deposition of the Dabaa Formation. This pattern includes mangroves represented by taxa such as Zonocostites ramonae, Psilatricolporites crassus and Verrucatosporites usmensis. Another considerably different association with plenty of the freshwater algae Botryococcus and Pediastrum spp. at this level or tropical forests at slightly elevated altitudes (ever wet climate) are dominated by a variety of tropical forest taxa including Malvaceae and Striatricolpites, together with Retitricolporites irregularis, Psilatricolporites operculatus, Retibrevitricolporites ibadanensis, Retitricolporites spp. and Psilamonocolpites spp. in addition to ferns and tree ferns where tropical floras dominate. Also recognized are elements of savanna or open woodland (less humid climate) taxa like Poaceae pollen (grass) such as Monoporopollenites annulatus associated with Amaranthaceae (e.g., Chenopodipollis multiplex), Cyperaceae spp., Echiperiporites estelae, Proteacidites cooksonii, Cicatricosisporites dorogensis and Pteris. Finally, the montane ecosystems may have occurred at the slopes of mountains including rare pollen assigned to Sapotaceae (Psilastephanocolporites spp.) and Anacardiaceae (Retitricolpites simplex) which are probably part of the palynoflora due to long-distance transport.
... The use of mangrove sediments for RSL reconstructions has generally focussed on records extending from the Mid-Holocene to recent because of the accessibility of fossil sediments in the present day intertidal and nearshore marine environment, although studies investigating sediments back to Pleistocene times and older do exist (e.g. Caratini and Fontugne 1992;Roberts et al. 2017). ...
Deciphering the timing, magnitude, and geographic variability of relative sea-level changes from geological records is critical for projecting future sea-level changes. Mangrove sediments provide an archive of past sea-level changes because they occupy intertidal zones along coastlines in low latitude locations. Such locations are important because they are far from present and former polar ice sheets that influence relative sea levels via glacio-isostatic adjustment. However using mangrove sediments for quantitative relative sea-level reconstructions is challenging due to variable fossil preservation and issues with radiocarbon dating. To evaluate the utility of mangrove sediments for high-resolution relative sea-level reconstructions, I studied two mangroves on Mahé, Seychelles.
To determine what materials are best suited for radiocarbon analysis, I compared radiocarbon ages from bulk sediments, organic concentrates, and macrofossils. I find that radiocarbon ages from bulk sediment and organic concentrate are indistinguishable and therefore both methods likely sample younger carbon. These results demonstrate that macrofossils sourced from above-ground (e.g. leaves) are the most reliable materials for constructing radiocarbon chronologies in mangrove sediments.
I examined the utility of mangrove pollen as a sea-level indicator through vegetation mapping and pollen trapping in two Seychelles mangroves. Mangrove species are broadly zoned according to elevation, but the results from annual pollen traps demonstrate pollen rain is poorly associated with vegetation. Additionally, low pollen concentrations in surface sediments suggest that it is unlikely pollen-based proxies will improve existing uncertainties on relative sea-level reconstructions in Seychelles.
To test the utility of geochemical properties for relative sea-level reconstructions in Seychelles mangroves I characterised the TOC, TIC and lipid biomarker compositions in surface sediments at two mangroves sites. Sedimentation is controlled by hydrogeomorphological factors, and therefore TOC and TIC do not provide sufficient information alone to reconstruct past elevation changes. However, biomarker distributions may be indicative of different vegetation and elevation zones.
... The high frequency of coastal fog as a result of upwelling of the cold Benguela Current is a supplementary source of moisture (Kruger, 2004b). The west coast is bounded on the landward margin by the Cape Fold Belt and is sporadically blanketed by Miocene-Holocene marginal marine, fluvial and aeolian deposits of the Sandveld Group (Roberts et al., 2006(Roberts et al., , 2017, with thicker deposits occupying depressions. ...
We present a diatom record from a well‐dated 15.25 m composite sedimentary core from Verlorenvlei, a shallow coastal lake on the west coast of South Africa. We show that fluctuations in the diatom record occur in response to changes in sea level, ocean–atmosphere interactions and latitudinal shifts in the wind belts. During the early to mid‐Holocene, the system primarily responds to sea level changes. A marine community that favours high nutrients is evident, particularly during 9200–8000, 7420–7000 and 6200–5600 cal a bp, corroborating periods of Benguela upwelling linked to fluctuations in the southeast trade winds. Increases in bioproductivity (%TOC, C/N) and fresher‐water diatoms are associated with wetter conditions over the region and the northward migration of the southern westerly wind belt, most notably between 8000 and 7500 cal a bp and over the last 700 years. The latter trends are concomitant with changes in the extent of Antarctic sea ice and availability of moisture in southern South America. During the late Holocene, as sea levels stabilised to modern levels, climate variability is more strongly evident. The body of evidence further reveals the sensitivity of the region to high‐latitude atmospheric mechanisms, but also showcases the significance of the southeast trade winds.
... Fire is considered to have been a key selective force in the evolution of the megadiverse fynbos shrublands of the Cape Floristic Region (CFR) (Allsopp et al., 2014;Cowling, 1987). Based on molecular phylogenies of obligate post-fire flowering orchids (genus Disa), summer drought and its associated fire regime in the CFR have been estimated to date back to the Early Miocene (19.5 Ma BP) (Bytebier et al., 2011), while the oldest direct evidence for fire, in the form of fossil charcoal, in the region is in the Late Oligocene or Early Miocene (Roberts et al., 2017). A period of global cooling and drying, which followed the mid-Miocene climatic optimum (ca. ...
Landscape-level fire governs vegetation structure and composition in the contemporary Cape Floristic Region (CFR) and was key to the existence of Middle Stone-Age hunter gatherers on the Palaeo-Agulhas Plain (PAP). However, virtually nothing is known about Pleistocene fire regimes of the CFR. We characterized the fire danger climate of the PAP during the Last Glacial Maximum (LGM; 19–26 ka BP) based on palaeo-climate simulations and explored the severity and seasonality of fire danger weather along west-east and coastal-inland gradients across the PAP. We used knowledge of relationships between contemporary fire climate and contemporary CFR fire regimes to propose LGM fire regimes in relation to simulated LGM fire climate. We found that the severity of fire weather during the LGM across the PAP was significantly higher than present; mean fire danger index scores and the incidence of high fire danger days were greater, while the seasonality of fire weather was more pronounced, exhibiting summer-autumn fire regimes across the PAP. Although a more severe fire climate suggests potentially more frequent fires than present, slower fuel accumulation due to colder temperatures, reduced solar radiation and lower atmospheric CO2 may have partly countered this effect. Our proposed LGM fire regimes predict the vegetation of the PAP to have been dominated by fire tolerant, largely Mediterranean-climate formations such as fynbos, renosterveld and grassland, but is unlikely to have provided a driver for mass seasonal east-west migration of large grazers on the PAP.
... Strömberg [ [92,93] . 此外, 沉积学、微化石及地震剖面研 究发现, 南非海岸线在OMT时下降了近500 m [94] , 类 似的海平面下降过程也在非洲西南部的萨尔达尼亚湾 找到了证据 [95] . El Atfy等人 [96] 对来自埃及苏伊士湾努 克胡尔组 [100] . ...
... Considering the relationship between the Pakhuis and 2017) rock hyrax middens, as well as the afrotemperate forest pollen record from Eilandvlei (Quick et al., 2018), and proxies records relating to the position of the southern westerlies, including reconstructions of Southern Ocean summer sea-surface temperatures and sea ice presence (Nielsen et al., 2004) and the sea-salt sodium flux data from the EPICA Dronning Maud Land ice core from Antarctica, a proxy for sea-ice extent (Fischer et al., 2007;Roberts et al., 2017). ...
The Cape Floristic Region (CFR) is one of the world's major biodiversity hotspots, and much work has gone into identifying the drivers of this diversity. Considered regionally in the context of Quaternary climate change, climate stability is generally accepted as being one of the major factors promoting the abundance of species now present in the CFR. However, little direct evidence is available from the region, and responses to changes in global boundary conditions have been difficult to assess. In this paper, we present new high-resolution stable isotope data from Pakhuis Pass, in the species-rich western CFR, and contextualise our findings through comparison with other records from the region. Combined, they indicate clear, coherent changes in regional hydroclimate, which we relate to broader forcing mechanisms. However, while these climate change events share similar timings (indicating shared macro-scale drivers), the responses are distinct between sites, in some cases expressing opposing trends over very short spatial gradients (<50 km). We describe the evolution of these trends, and propose that while long-term (10 5 yr) general climatic stability may have fostered high diversity in the region through low extinction rates, the strong, abrupt changes in hydroclimate gradients observed in our records may have driven a form of allopatric speciation pump, promoting the diversification of plant lineages through the periodic isolation and recombination of plant populations.
... Strömberg [ [92,93] . 此外, 沉积学、微化石及地震剖面研 究发现, 南非海岸线在OMT时下降了近500 m [94] , 类 似的海平面下降过程也在非洲西南部的萨尔达尼亚湾 找到了证据 [95] . El Atfy等人 [96] 对来自埃及苏伊士湾努 克胡尔组 [100] . ...
Although the Oligocene-Miocene transition (OMT) is a well-known key stage in moving from the Oligocene to the Miocene, and many studies have considered the environmental changes and biological evolution during this period, the results of this research are currently poorly summarized. Here, we gather information from previous OMT-related work in geology, geography, astronomy, paleontology, evolutionary biology, biogeography, and other disciplines. When we systematically collated these documents and data, we found the following. First, the OMT should be constrained to the period from around 25–22 Ma (million years ago) based on the climate fluctuations between the late Oligocene and the early Miocene. Second, compared with the Oligocene–Miocene boundary (OMB, 23.03 Ma), the OMT has particular significance for the study of biological evolution. In addition, we speculate that the environmental changes occurring around the world during the OMT were not isolated accidents, and instead were likely related events induced by orbital forcing. Global climatic changes could have shaped regional environments by adding to local shifts, and such effects may have had a profound impact on species evolution and adaptation at a regional scale. Thus, the OMT is a key period of global environmental change and biological evolution, and a thorough study of organisms’ evolutionary adaptation histories during this era will be of great significance for understanding the biological strategies that will arise in response to future climate changes.
... Palynologists working in Africa may not yet be fully aware of the presence of this pollen group or of its affiliation. This is supported by the current identification of the Miocene Mush MT pollen in the Mush Valley palynoflora (Ethiopia), where this pollen type was most likely previously referred to Myristicaceae (Danehy 2010), and the Saldanha MT (Hyaenanche lineage) pollen in the Saldanha Bay palynoflora (South Africa), a well-studied Miocene flora, where this type of pollen was previously referred to Baumannipollis with affiliation to Malvaceae (Roberts et al. 2017). ...
The pantropical Picrodendraceae produce mostly spheroidal to slightly oblate, echinate pollen grains equipped with narrow circular to elliptic pori that can be hard to identify to family level in both extant and fossil material using light microscopy only. Fossil pollen of the family have been described from the Paleogene of America, Antarctica, Australia, New Zealand, and Europe, but until now none have been reported from Afro-India. Extant pollen described here include representatives from all recent Picrodendraceae genera naturally occurring in Africa and/or Madagascar and south India and selected closely related tropical American taxa. Our analyses, using combined light microscopy and scanning electron microscopy, show that pollen of the Afro-Indian genera encompass three morphological types: Type 1, comprising only Hyaenanche; Type 2, including Aristogeitonia, Mischodon, Oldfieldia and Voatamalo; Type 3, comprising the remaining two genera, Androstachys and Stachyandra. Based on the pollen morphology presented here it is evident that some previous light microscopic accounts of spherical and echinate fossil pollen affiliated with Arecaceae, Asteraceae, Malvaceae, and Myristicaceae from the African continent could belong to Picrodendraceae. The pollen morphology of Picrodendraceae, fossil pollen records, a dated intra-familial phylogeny, seed dispersal modes, and the regional Late Cretaceous to early Cenozoic paleogeography, together suggest the family originated in the Americas and dispersed from southern America across Antarctica and into Australasia. A second dispersal route is believed to have occurred from the Americas into continental Africa via the North Atlantic Land Bridge and Europe.
... Until the late Miocene (5.3 -11.6 Ma) the area now incorporating the CFR was largely covered in mesic forest, with fynbos restricted to mountain tops, according to paleo records (Coetzee, 1983;Scott 1995;Dupont et al., 2013;Roberts et al., 2017). From the late Miocene with the onset of increasing summer aridity particularly in the western CFR, however, it has been hypothesized that forest distribution contracted and became restricted to mesic habitats (Verboom et al., 2014;Linder & Verboom, 2015). ...
Open- (e.g. grassland, savanna, shrubland) and closed-canopy (e.g. forest) biomes frequently coexist in the same landscape, where open environments tend to be fire-prone with higher light, but lower nutrient and water availability than closed environments. Environmental heterogeneity could select for divergent floristic assemblages and adaptive traits, from which emergent differences in resource availability and fire incidence contribute to excluding species from the alternate habitat. In this thesis, I investigated whether the coexistence of open–closed canopy biomes, such as forest and fynbos in the Cape Floristic Region, is contingent on environmental heterogeneity coupled with contrasting species traits. Given the heterogeneity in multiple environmental properties between open- and closed-canopy biomes, I hypothesized that boundaries between open- and closed-canopy biomes will display greater floristic turnover compared to boundaries between structurally similar biomes (e.g. open- and open-canopy biomes). To explore this, genus- and family-level turnover were correlated with climate, fire, leaf area index (LAI: proxy for understorey light) and soil properties across biome boundaries in South Africa. Both genus- and family-level turnovers were highest across open–closed boundaries and most strongly predicted by increased differences in LAI, suggesting that contrasting light regimes provide significant adaptive challenges for plants. The potential effect of contrasting light regimes is highlighted by the absence of open-canopy species from forest understoreys, where low, dynamic light could limit the ability of plants to acquire sufficient carbon. This apparent shade intolerance led to the hypothesis that open-canopy species lack the traits to maintain a positive carbon balance under low and dynamic light. To test this, leaf traits and photosynthetic response to continuous or dynamic light were compared between forest and fynbos species grown under three light treatments. Fynbos species experienced high mortality under shade treatments, produced leaves that were thicker, up to 1000 times smaller, had lower photosynthetic rates (0.8 versus 3.4mol m-2 s-1) under continuous low light (400 mol m-2 s-1) and lower light-use efficiency during dynamic light sequences than forest species. These differences imply that shade intolerance in fynbos species is associated with traits that are inefficient at harvesting light and require relatively continuous high intensity light for carbon assimilation. Moreover, these inefficiencies would make it difficult to support the carbon intensive traits (e.g. cluster roots, lignotubers, sclerophyllous leaves) that facilitate fire survival and nutrient acquisition/conservation in open habitats. In contrast, forest species are able to colonize open habitats during the long-term absence of fire, implying that they are able to tolerate high light and low nutrient conditions. Given that plants frequently cope with contrasting conditions through the expression of phenotypic plasticity, it was hypothesized that closed-canopy species possess greater plasticity than open-canopy species. To assess this, the response of leaf traits and foliar nutrition to changes in LAI and soil nutrition were compared between forest and fynbos species in the field. Leaf size and specific leaf area in forest species correlated positively with LAI and soil nutrition, whereas fynbos species response was weak, suggesting that forest species are more plastic. This plasticity may be realised by the variable light conditions forest species experience through their canopy and the occupation of higher nutrient soils, which alleviate belowground constraints. By comparison, the occupation of low nutrient soils by fynbos may inhibit plasticity given the selection of inflexible, conservative leaves. Consequently, I propose that the coexistence of open- and closed-canopy biomes arises from the steep turnover in selective regimes, which together with the contrasting adaptive traits and degrees of phenotypic plasticity they require, act together to competitively exclude species from the alternate habitat.
... Complex climate and cultural changes place the Holocene beyond the scope of this review and it is discussed in separate studies Ecker et al., 2018). Earlier time periods such as the Neogene are also excluded from this study because the evidence of marked changes that have been found in the south-western Cape from these periods cannot be associated with the peopling of South Africa (Coetzee and Rogers, 1982;Roberts et al., 2017). Also excluded is the interval from the beginning of the Pleistocene to the Middle Pleistocene, which included important but limited palynological evidence, e.g. at Sterkfontein, Malapa and Kromdraai Bamford et al., 2010;Scott, 1995;Scott and Bonneville, 1986;Scott et al., 1997;Carri on and Scott, 1999). ...
An investigation of the vegetation and climate from the Middle Pleistocene until the end of the Late Pleistocene reveals a plethora of terrestrial and marine biological, geological and archaeological evidence for marked and complex climate cycles of change, which reflect on past circulation patterns. While acknowledging the usefulness of diverse proxies for detecting these changes, an efficient way to summarize past events is to focus on one of them, viz. fossil pollen, which, although providing scattered and incomplete records, gives fairly direct reflections of past climates and vegetation growth. The findings are structured according to six subregions and reveal distinct changes in temperature and moisture patterns, e.g. during the Last Glacial Maximum (LGM) and the Younger Dryas. The data suggest an environmental background against which cultural evolution took place, e.g., the appearance of Fauresmith, Still Bay, Howiesons Poort and Later Stone Age lithic industries. The pollen archives can be associated with global climate changes, as recorded in isotopes in marine sequences (Marine Isotope Stages or MISs). The observations show differences between regions, which can serve as a base for improving palaeo-data to eventually simulate past and future climates and to better understand the role of past global climates in relation to human and animal occupation in Southern Africa.
... Peninsula (Coetzee & Praglowski, 1988;Neumann et al., 2017;Roberts et al., 2017), Qatanipollis species from the Albian of Israel (Schrank, 2013;Walker, Brenner, & Walker, 1983); and Walkeripollis gabonensis J.A.Doyle, Hotton & J.V.Ward from the late Barremian to early Aptian of Gabon, equatorial western Africa (Doyle et al., 1990). Of these, P. agatdalensis shares the most (overlapping) features with the~40 Myr younger tetrads from South Africa, whereas the~50 or 65 Myr older African and Near Eastern fossils differ by a least half of the major traits (Table 1; Appendix S3). ...
Aim
Winteraceae comprise c . 130 species in seven genera, with the greatest species diversity in the Pacific ( Pseudowintera , Zygogynum ), Australia ( Bubbia, Tasmannia ), New Guinea ( Belliolum , Bubbia, Zygogynum , Tasmannia ) and Madagascar ( Takhtajania ). Only Drimys occurs in South America. Because of their Cretaceous leaves, wood and pollen fossils, and their lack of xylem vessels, Winteraceae throw light on early angiosperm evolution. We describe a Winteraceae pollen tetrad from the Paleocene of Greenland, review the family's fossil record and palaeogeography and document its current climate preferences.
Location
Worldwide.
Methods
Extant and fossil pollen were studied with light and scanning electron microscopy. Molecular phylogenetic and character mapping approaches were used to infer the evolution of pollen characters, and 37,842 collections from the Global Biodiversity Information Facility were used to infer the climate and vegetation types occupied by today's Winteraceae and to compare them to the Paleocene climate and vegetation of Greenland as inferred from the fossil record of other families.
Results
Winteraceae are the only flowering plants with persistent, acalymmate tetrads composed of ulcerate grains with a distinct reticulate sculpturing. The tetrad described here as Pseudowinterapollis agatdalensis Grímsson & Zetter spec. nov. comes from Agatdalen valley in western Greenland and dates to the Early Paleocene, Danian, 64–62 Ma. It shows the complete character suite of modern Winteraceae and overlaps the LM characters of the three previously known Pseudowinterapollis species from Australia, New Zealand and South Africa. The palaeoflora of the Agatdal Formation consisted of a mixed deciduous–evergreen forest resembling habitats where Winteraceae occur today.
Main conclusions
Macro‐ and microfossil records of Winteraceae extend back to the Upper Cretaceous in both Laurasia and Gondwana, and the family's biogeography, like that of its sister family, Canellaceae, cannot be understood by focusing only on southern Gondwana. Winteraceae instead were part of broadleaved forests in Paleocene and Eocene North American and Greenland and may have reached Europe via the North Atlantic Land Bridge, explaining Eocene Winteraceae wood in northern Germany.
... The early Miocene South African Winteraceae pollen tetrads were previously figured and discussed by Coetzee (1981Coetzee ( , 1983; single type, as Pseudowinterapollis sp. based on LM), Coetzee & Muller (1984;two types, considered to resemble recent Drimys piperita and Bubbia isoneura based on LM), Coetzee & Praglowski (1988; two types, "Drimys piperita-type" based on LM and SEM, and "Zygogynum queenslandianum-type" based on LM) and Roberts et al. (2017; single type, identified as Pseudowinterapollis couperi Krutzsch based on LM). None of those papers provided a detailed description of the fossils; the only measurements and descriptions given by Coetzee & Praglowski (1988) do not refer to the fossils but to recent tetrads which they considered the closest morphological analogue. ...
When applying high-resolution microscopy, the pollen morphology of extant taxa can be used to classify fossil pollen, that is, to address the latter in the established systematic-phylogenetic framework. Here we investigate tetrads and pollen features of 20 different Winteraceae species, most of them belonging to the early-diverging generic lineages Tasmannia, Drimys and Pseudowintera. The tetrads and pollen are grouped into eleven pollen types based on diagnostic features observed by both light and scanning electron microscopy. The high-resolution scanning electron micrographs of recent material allow detailed comparison with fossil material, resulting in a more accurate affiliation of fossil tetrads/pollen to extant lineages. As a case study, early Miocene Winteraceae tetrads from South Africa are re-examined and formally described. The systematic placement of the African fossils is discussed in light of the pollen types presented here.
... An early Miocene marine core from Saldanha Bay to the north of Cape Town reveals a diverse palynoflora with mangrove elements (Rhizophoraceae), subtropical forest dominated by Podocarpaceae, palms and dicotyledons including basal angiosperms like Winteraceae, proto-fynbos with Proteaceae, Ericaceae and Restionaceae, riparian/swamp forest and wetland taxa. The assemblage reflects a diverse flora during a major transgression most probably during the early Miocene as dated by dinoflagellates (Roberts et al. 2017, fig. 1). ...
Two case studies were conducted in order to evaluate non-HF processing of clastic sediments with
consecutive heavy-liquid separation (sodium polytungstate) for both terrestrial and marine archives.
Case study 1: Three palynological processing methods (H2O2, HF, (NaPO3)6) (Riding & Kyffin-Hughes
2006, 2011) where applied to Miocene clays of the clay pit Adendorf near Bonn, which were known to
contain numerous, well-preserved palynomorphs (Nitz 2014). All three methods were followed by
heavy-liquid separation (sodium polytungstate), sieving with 10 µm respectively 250 µm grids and slide
preparation in glycerine jelly (see Fig. 1). The reason for carrying out this test series is the fact that the most
common method (HF) presents considerable health risks. A detailed cost and time calculation was compiled in order to identify the most efficient method. The HF method was most time intensive, both HF and
H
2O2have to be handled with special care, whereas (NaPO3)6 is considered a harmless substance. All three
methods are roughly comparable under palynological aspects (number of pollutants, pollen percentages),
although for a verification more tests would be necessary to assure statistical significance. In terms of costs
the H
2O2 method is much more expensive than the other two methods, whereas the (NaPO3)6) method is
the cheapest. Consequently, the (NaPO3)6) method proved to have a number of advantages in comparison
to the other tested methods (Franke 2014). Case study 2: Clayey (fine) sandy sediments from a Holocene marine core taken during a METEOR
cruise offshore eastern South Africa in the frame of the RaiN2 project (Regional Archives for Integrated
iNvestigations) (Zabel et al. 2016) were processed applying the (NaPO3)6) method followed by
heavy-liquid separation with a density of 2 g/ml and sieving with 10 µm and 250 µm grids respectively and
slide preparation. A moderate to low pollen concentration was obvious, but the number of Lycopodiumspores was also suspiciously low. After heavy-liquid separation (density 2 mg/l), probably due to gravity
effects and trapped palynomorphs under abundant clastics, many palynomorphs and Lycopodium spores
(added to calculate the pollen concentration) were found in the heavy fraction and caused the loss in the
light fraction. In order to concentrate especially the pollen and spores, the residue was subject to a 2nd
heavy-liquid separation with a density of 2.1 g/ml. Two consequences were observed: firstly, the concentration of palynomorphs and Lycopodium spores increased strongly and secondly, beautifully preserved
silicate microfossils, including sponge spicules, silicoflagellates and diatoms were available for analysis.
Although the 2nd heavy-liquid separation was more time consuming, the obvious advantages in the current case justify additional work and expense.
We tested and improved the (NaPO3)6) method for our lab in case study 1, and add valuable information,
e.g. about time and cost expenses to earlier studies, e.g. by Riding & Kyffin-Hughes (2006, 2011). We also
show how effective heavy-liquid separation with sodium polytungstate can be for concentrating
palynomorphs in case study 2, with the secondary effect of making silicate microfossils available for study.
... An early Miocene marine core from Saldanha Bay to the north of Cape Town reveals a diverse palynoflora with mangrove elements (Rhizophoraceae), subtropical forest dominated by Podocarpaceae, palms and dicotyledons including basal angiosperms like Winteraceae, proto-fynbos with Proteaceae, Ericaceae and Restionaceae, riparian/swamp forest and wetland taxa. The assemblage reflects a diverse flora during a major transgression most probably during the early Miocene as dated by dinoflagellates (Roberts et al. 2017, fig. 1). ...
Our aim is to compare Quaternary palynological records from southern Africa to Neogene records in
order to understand the evolution of the remarkably diverse vegetation on the subcontinent and the evolution of its distinctive biomes. An early Miocene marine core from Saldanha Bay to the north of Cape
Town reveals a diverse palynoflora with mangrove elements (Rhizophoraceae), subtropical forest dominated by Podocarpaceae, palms and dicotyledons including basal angiosperms like Winteraceae,
proto-fynbos with Proteaceae, Ericaceae and Restionaceae, riparian/swamp forest and wetland taxa. The
assemblage reflects a diverse flora during a major transgression most probably during the early Miocene
as dated by dinoflagellates (Roberts et al. 2017, fig. 1). However, one of the most peculiar findings is
evidence of a subtropical woodland with Combretaceae, Burseraceae (Commiphora-type) and even
Brachystegia (Peregrinipollis nigericus) at Saldanha Bay. Woodland, albeit with often different taxa, is
known already from the interior of the subcontinent during the early Palaeogene (Scholtz 1985) but was hitherto unknown from the Miocene of the Cape region. In order to track down botanical affinities of the
Saldanha Bay taxa we apply a method combining SEM and LM images and compare fossil pollen to recent
pollen taxa. A comparison of the woodland taxa to modern pollen types revealed similarities to pollen
spectra known from Quaternary deposits, e.g. from the Zambezi catchment (Dupont & Kaufmann 2017),
or southern central Mozambique (McWethy et al. 2016). In southern Mozambique a mosaic of Ericaceae
heathlands and montane podocarp forest exists, whereas the coastal area is characterized by coastal forest
and Rhizophora-dominated mangroves under the influence of a monsoonal climate influenced by the
warm Agulhas current. Another distinct modern vegetation unit in that region is Miombo woodland
where its main constituent, insect-pollinated Brachystegia sp., is notably under-represented in pollen
profiles due to low pollen productivity. Apparently, the Saldanha Bay taxa often share the same families
with the vegetation in southeastern Africa and might have their most recent counterpart in that region –
although we are aware that such comparisons are highly tentative for many reasons (uncertain botanical
affinities of fossil pollen, broader ecological range of taxa during the Neogene). This underlines our
hypothesis that the Saldanha Bay vegetation during the early Neogene developed under completely
different climatological conditions than the current regional vegetation. Probably a monsoonal climate,
which was quite similar to the climate experienced along the Indian Ocean coastal belt nowadays with
high precipitation and pronounced summer rainfall, supported a lush growth of ferns. We suggest that
Miombo woodland might have developed during the Palaeogene in the Cape during the early Miocene
but disappeared later in this epoch, coincident with the development of a more arid, winter rainfall
climate under the influence of a strengthening cool Benguela current. During the Quaternary, Miombo
woodland occupied an extensive region in south-central Africa with a centre in the Zambezi region, with
only a tiny representation in the extreme northeast of South Africa. Miombo woodland retracted during
the glacials in a regionally varying pattern and spread during warmer interglacials (McWethy et al. 2016,
Dupont & Kuhlmann 2017).
... Mangrove forest has been noted in stratigraphic records at least since the Paleogene/Neogene (Willumsen et al., 2014;Roberts et al., 2017). They are important habitats, today occurring between the latitudes 25°S and 25°N (Giri et al., 2011), providing plentiful natural resources to coastal dwelling communities and shelter from floods and storms (Massuanganhe et al., 2015). ...
Many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation from river inflows. In this paper we use the example of the Save River delta to assess the palaeogeographic distribution of mangrove wetlands and to analyze their dynamics. To track past occurrences of mangrove wetlands in the study area we have integrated sedimentological data with siliceous microfossil analysis combined with AMS radiocarbon and OSL dating. The results show a fine-grained deposit with an approximate thickness of 2. m, present at different sampling sites. In the upper deltaic plain, the deposit is interbedded between sand layers, while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position. In most of the sampling sites the deposit shows a succession with brackish-marine diatoms at the bottom of the sequence while the upper part shows only scattered occurrences. Based on sedimentological and microfossil characteristics we have interpreted the layer to represent a mangrove wetland deposit. The development of the deposit in the study area is suggested to have been initiated around 3100. cal. yr BP, induced by sea-level rise. Thereafter, the development followed the combined effect of a sea-level fall and delta progradation processes. In some areas, particularly in the proximal part of the delta, the mangrove deposit has developed progressively on top of the delta-front. From around 1300. years ago (OSL) onwards, massive alluvial sedimentation impacted the mangrove ecosystem. However, the retreat of mangrove wetland coincided with a regional fall of sea level. At the edges of the alluvial deposit, the current mangrove ecosystem has reclaimed the habitat in some sectors where gully erosion has exposed the once extinct mangrove habitat.
... Speciation of Restionaceae at the generic level, whose soil-stored diaspores are stimulated to germinate by fire (essentially smoke), peaked in the period 35-5 Ma ). Confirmation of fire-proneness at these times comes from charcoal records in the highly mixed vegetation (with 6 Proteaceae pollen types) of Saldanha Bay, 100 km N of Cape Town, 25-20 Ma (Roberts et al. 2017) and the Namibian grasslands, 1600 km north of Cape Town, 9-3 Ma (Hoetzel et al. 2013). The association of fire with C4 grasslands is well-established (Scheiter et al. 2012) and these can be traced from 18 Ma in Africa, especially from 10 Ma (Edwards et al. 2010). ...
It has been proposed in separate studies that fire or frost were the critical selective agents in the evolution of subshrub geoxyles (SGs) in African subtropical grasslands. We attempt to resolve this controversy by examining the evolution of SGs among the entire genus Protea that is widespread throughout southern/central Africa. We show that SGs are not confined to grasslands but occur in a wide range of non-forest types, including mediterranean shrublands. SG proteas arose 1−11 million years ago but their multiple origins among other geoxyles, confounded by strong intraspecific variability among grassland species, makes it impossible to identify the ancestral growth form. We conclude that the evolutionary history of SG proteas has occurred under lightning-prone conditions that promoted fire and were essentially frost-free; exposure to frost has been limited to certain elevated locations in more recent times. This is supported by many SGs having pyrogenic flowering and lack of seed storage among grassland species.
Background and aims:
The prevailing view from the areocladogenesis of molecular phylogenies is that the iconic South African Cape Proteaceae (subfamily Proteoideae) arrived from Australia across the Indian Ocean in the Upper Cretaceous (100‒65 million years ago, Ma). Since fossil pollen indicates that the family probably arose in North-West Africa during the early Cretaceous, an alternative view is that it migrated to the Cape from North-Central Africa. The plan therefore was to collate fossil pollen records throughout Africa to determine if they are consistent with an African (para-autochthonous) origin for the Cape Proteaceae, and to seek further support from other paleo-disciplines.
Methods:
Palynology (identity, date and location of records), molecular phylogeny and chronogram preparation, biogeography of plate tectonics, and paleo-atmospheric and ocean circulation models.
Key results:
Our collation of the rich assemblage of Proteaceae palynomorphs stretching back to 107 Ma (Triorites africaensis) in North-West Africa showed its progressive overland migration to the Cape by 75‒65 Ma. No key palynomorphs recorded in Australia-Antarctica have morphological affinities with African fossils but specific clade assignment of the preMiocene records is not currently possible. The Cape Proteaceae encompass three molecular-based clades (tribes) whose most-recent apparent ancestors are sisters to those in Australia. However, our chronogram shows that the major Adenanthos/Leucadendron-related clade, originating 54‒34 Ma, would have 'arrived' too late as species with Proteaceae affinities were already present ~20 My earlier. The Franklandia/Protea-related clade arose 118‒81 Ma so its distinctive pollen should have been the foundation for the scores of palynomorphs recorded at 100‒80 Ma but it was not. Also, the prevailing winds and ocean currents trended away from South Africa rather than towards, as the 'out-of-Australia' hypothesis requires. Based on the evidence assembled here, we list three points favouring an Australian origin and nine against; four points favouring an Antarctic origin and seven against; and nine points favouring a North-Central African origin and three against.
Conclusions:
We conclude that a gradual migration of the Proteaceae from North-Central Africa southeast→south→southwest to the Cape and surrounds occurred via adaptation and speciation during the period 90‒70 Ma. We caution that incorrect conclusions may be drawn from literal interpretations of molecular phylogenies that neglect the fossil record and do not recognize the possible confounding effects of selection under matched environments leading to parallel evolution and extinction of bona fide sister clades.
The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum (HCO), using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources: mangrove-derived, terrigenous, and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope (δ
13Corg) and the molar ratio of total organic carbon to total nitrogen (C/N). The percentage of mangrove-derived organic matter (MOM) contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.
No account of the effects of fire in mountain fynbos would be complete without considering invasive alien plants. Introduced plants are a striking feature of fynbos landscapes, and they have a marked effect on the functioning of natural ecosystems (Richardson et al. 1991).
Fossil pollen sequences from the Cape Peninsula and the Saldanha region indicate that sub tropical vegetation and climates existed in these regions during the Miocene. The pollen record from the Cape Peninsula may point to the extinction of some taxa by the terminal Miocene/Early Pliocene with the subsequent strong development of macchia. This major change can probably be related to the maximum build-up of the Antarctic ice-cap in the latest Miocene and the accompanying profound palaeoceanographic changes such as the major cooling of the Benguela current with its effect on the aridification of the Namib desert, and the global glacio-eustatic sea level drop.Parallel palynological and lithological studies in the Saldanha region show that prominent Miocene vegetation shifts were linked to profound local changes in the palaeoenvironment associated with the northward migration of the Miocene Berg River. Such studies are of paramount importance for the possible assessment of the causes of changes in the palaeoenvironment and should first be carried out at many more sites over a wide region. It is to some extent premature to draw firm conclusions as to the origin and migration of some taxa in southern Africa. The record of very primitive angiosperms such as the ClavatipolleniteslAscarina complex and Winteraceae is of considerable phytogeographic interest.
Rhoicissus sekhukhuniensis Retief, Siebert & A.E.van Wyk, a rare new species from South Africa, is described, illustrated and compared with other members of the genus. It is a scandent shrub, rarely a robust climber, the young growth with a dense indumentum of reddish brown hairs. The species is closely related to the simple-leaved R. tomentosa (Lam.) Wild & R.B.Drumm., from which it can be distinguished by trifoliolate leaves with coarsely toothed margins. Pollen grains are tricolporate with a reticulate tectum. R. sekhukhuniensis is endemic to the Sekhukhuneland region, a centre of plant endemism associated with ultramafic rocks (mainly norite, anorthosite and pyroxenite) of the Eastern Bushveid Igneous Complex.
Wild fire is an important disturbance that shapes global biome distributions and maintains the structure, function and biological diversity of plant communities in fire-prone environments. Physical, chemical and architectural properties of plants are known to affect flammability. We wished to explore how these traits contribute to fire properties at the individual species level and how flammability varies with other plant traits, including recruitment strategy. We studied flammability and traits that contribute to it in 29 woody species occurring in fynbos and renosterveld shrublands in the Cape region of South Africa. Fifteen of the species had fire-stimulated recruitment and 14 recruit in unburnt, older vegetation. Flammability was measured on whole plants or large shoots with intact architecture. Results across all species were consistent with other studies in finding that the proportions of dead and fine fuel are good predictors of flammability. Significantly higher flame temperatures and proportions of sample units burnt were recorded for fire-stimulated vs. non-fire-stimulated recruiters. These differences were associated with significant differences in the dead fuel proportion and fuel bed porosity between recruitment strategies. This is consistent with the hypothesis that flammability is most likely to be selected for in species that are the first to occupy post-burn gaps, where a combination of increased flammability and recruitment success enhances their fitness in the fire-prone environment.
Long-term trends in climate, hydrology and geomorphology contributed to the formation of the current
biomes of southern Africa. The Neogene terrestrial fossil record is patchy, due to the geomorphological
evolution of the subcontinent and the restricted distribution of suitable sediment deposits. Here we
review the hypotheses on the evolution of the topography and environment and concentrate on the
fossil record, especially pollen, wood, charcoal, leaves and biomarkers. Tectonic studies suggest a lower
relief landscape than at present at the onset of the Neogene. Southern Africa was drained by two river
systems – the Kalahari and the Karoo Rivers – and was affected by an initially weak, cool Benguela
current along the western coastline, gradually promoting an aridity trend along the southwestern coast.
The Cape region during the Miocene, when the Great Escarpment began to evolve, was characterised
by humid, subtropical forests not unlike those still occurring on the much wetter subtropical eastern
shore of southern Africa. Southern Namibia (Sperrgebiet) was probably covered by a “proto-savanna”;
hyper-aridity developed further north along the Namibian coast. Probably with more uplift, the
hydrological regime changed c. 15 Ma when the palaeo Karoo and Koa Rivers were captured by the
Kalahari/Orange River and drained western South Africa. Miocene fossil sites are missing in
southeastern Africa. In southwestern Africa an enhanced aridity trend and the shift to a winter rainfall
regime during the late Miocene-Pliocene was triggered by the development of the Westerly wind
system and further strengthening of the cold Benguela current enhanced by the development of the
Antarctic sheet and opening of the Drake passage. Eastern southern Africa was dominated by the Great
Escarpment and relatively shorter deeply incised rivers and higher rainfall than the west. The Pliocene
saw the evolution of the Fynbos and Succulent Karoo biomes including the further radiation of several
drought adapted plant families encompassing the Asteraceae and Aizoaceae. At the transition towards
the Pleistocene, the region around Sterkfontein in eastern central southern Africa, important for
hominid evolution, experienced a shift from a woody environment towards more xeric, open conditions.
The Savanna biome today stretches from northeastern South Africa as far north as East Africa; the
Grassland and Fynbos biomes are unique and the more arid biomes are dominant in the western half of
southern Africa.
Significance
The flowering plant family Asteraceae (e.g. sunflowers, daisies, chrysanthemums), with about 23,000 species, is found almost everywhere in the world except in Antarctica. Asteraceae (or Compositae) are regarded as one of the most influential families in the diversification and evolution of a large number of animals that heavily depends on their inflorescences to survive (e.g. bees, hummingbirds, wasps). Here we report the discovery of pollen grains unambiguously assigned to Asteraceae that remained buried in Antarctic deposits for more than 65 million years along with other extinct groups (e.g. Dinosaurs, Ammonites). Our discovery drastically pushes back the assumed origin of Asteraceae, because these pollen grains are the oldest fossils ever found for the family.
The Cretaceous oceanic circulation has been quite different from the modern with a different distribution of the continents on the globe. This has resulted in a much lower temperature gradient between poles and equator. We have studied seismic reflection data and used numerical simulations of atmosphere and ocean dynamics to identify important steps in modifications of the oceanic circulation in the South Atlantic from the Cretaceous to the Cenozoic and the major factors controlling them. Starting in the Albian we could not identify any traces of an overturning circulation for the South Atlantic although a weak proto-Antarctic Circumpolar Current (ACC) was simulated. No change in circulation was observed for the Paleocene/early Eocene South Atlantic, which indicated that this period has witnessed a circulation similar to the Albian and Cenomanian/Turonian circulation. The most drastic modifications were observed for the Eocene/Oligocene boundary and the Oligocene/early Miocene with the onset of an ACC and Atlantic meridional overturning circulation (AMOC) and hence southern sourced deep and bottom water masses in the western South Atlantic. A modern AMOC, which intensified in strength after closure of the Central American Seaway (CAS), and a strong ACC have resulted in current controlled sedimentary features and wide spread hiatusses in the South Atlantic since the middle Miocene. The opening of Drake Passage in early Oligocene times and the closure of the CAS at ~ 6 Ma, i.e., tectonic processes, have been identified as the key triggers for the observed most severe changes in oceanic circulation in the South Atlantic.
This article deals with the most important aspects of nearly twenty years of intensive study of the pollen-and-spore content of Tertiary sediments in some parts of tropical South America, Africa and Asia. For a proper evaluation, the character of the data, including the selection and preparation of the samples, the diversity of previous recording and the statistically achieved uniformity in presentation of these basic data needs a full exposition, given in the introduction. This is directly followed by an explanation of the process of elimination of all stratigraphically unimportant species. The resulting interpretation of climatic and topographical influences on the dispersal of pollen and spores is illustrated with examples from the fossil record. The disturbing effect of redeposition forms a problem, which in some cases can be solved. Now that the main ways of dispersal of pollen and spores are understood, the characteristics of the three major depositional environments can be distinguished by purely statistical analysis, without necessarily having any botanical information from probably related Recent plant species. Additionally botany and palaeontology may bring supporting evidence. This many-sided approach leads to the discrimination between local and regional features of environmental or time-stratigraphical significance which is needed for the evaluation of long-distance correlation. As a result the marker species can be classified into: (1) a restricted number of pantropical marker species; (2) a larger number of marker species which occurred in both the South American and west African regions, tropical today (transatlantic distribution); and (3) a still greater quantity of species which are of significance only within a single botanical province (intracontinental distribution). Thus a broad stratigraphical framework on a pantropical scale is established, which may be further subdivided regionally. These three systems of subzonation are compared with independent zoopalaeontological time-stratigraphical correlation and discussed in great detail, with special emphasis on the Carribean data. The major palynological changes marking the boundaries of the pantropical subzonation are thought to reflect the evolution of new groups of plants. They are mostly marked by a gradual incoming of pollen types. Extinction of plants is stratigraphically of less value, since they may have survived longer in one area than in another. Climatic boundaries are next in importance, but in general they are more restricted to specific regions. Similarly the immigration of plants, although producing sharp and useful boundaries, is only of regional value. Of least significance for regional correlation are the locally restricted boundaries which are caused by changes in habitat or dispersal. They may still be valuable for studies within one basin. An intriguing aspect of the palynological studies is formed by the possible affinity of the fossil type with Recent botanical species. Such affinities are obviously present in many fossil types. Whereas most are restricted to the level of family relationship, some interesting cases of much closer affinity are recorded here. In exceptional cases the morphogenetic development and migration of a restricted group of related pollen types can be traced. In the final section of this paper the species selected for this study have been formally described and illustrated; they include several new ones. The study is further documented by distribution charts and sections showing the stratigraphical significance of the marker types, as discussed in detail in the stratigraphical section.
New borehole data have been utilized to adapt and extend the lithostratigraphy of Cenozoic sediments between Cape Town and Eland's Bay. Bedrock is composed of deeply weathered rocks of the Malmesbury Group and the Cape Granite Suite. A Miocene to Early Pliocene stratigraphy and its relationship to climatic variations and transgressive events is discussed. -Author
Detailed palynological investigations have been carried out on the Oligocene/Miocene (O/M) transition of the Contessa and Santa Croce di Arcevia sections (Umbria-Marche Basin, central Italy), emphasizing dinoflagellate cysts (dinocysts). Results are compared and combined with recently established information from the O/M GSSP section (Lemme section, Tertiary Piedmont Basin, NW Italy). The combined qualitative and quantitative dinocyst distribution patterns allow detailed correlations between the sections. In addition, the quantitative dinocyst record enables the recognition of sea-level and sea surface temperature fluctuations. These are used to further strengthen correlations made on the basis of the qualitative dinocyst information. -from Authors
Important palynological studies were completed by Scholtz (1985) on material from the Arnot Pipe on the farm Banke in Namaqualand, Northern Cape Province. The results comprised a rare record of early Tertiary vegetation in southern Africa. The body of Scholtz's research consisted of systematic, descriptive palynology including the description of one new genus and fifteen new species. Ongoing research into South Africa's Tertiary palynology requires that the type specimens from Arnot be used for comparative purposes. However, the microscope slides on which they were founded were not available for examination. Another set of slides, representing two of the seven samples taken at Arnot, was used to search for neotype specimens to replace the missing holotypes. Specimens representing all fifteen new species were found, but were often badly preserved, obscured by debris or trapped between air bubbles as the condition of the decade-old microscope slides had deteriorated. Only specimens in good condition were selected as neotypes, and comprehensively illustrated. Four of Scholtz's new species were transferred to alternative, more applicable, genera.
A site in Namaqualand, Western Cape Province, has yielded a diverse and well-preserved palynoflora. The site consists of a quarry, exposing a palaeochannel containing fluviatile sands, silts and clays with accompanying peat horizons. This paper presents a qualitative account of the pollen and spore assemblages extracted from the peats. Angiosperms were dominant both in terms of the number of individuals and the recognised types. Identifications were made where possible with reference to published illustrations and descriptions. There was a total of 69 palynomorph types, including spores, gymnosperm and angiosperm pollen.
Soils of South Africa is the first book in seventy years that provides a comprehensive account of South African soils. The book arranges more than seventy soil forms into fourteen groups and then provides, for each group: • maps showing their distribution and abundance throughout South Africa • descriptions of morphological, chemical and physical properties • a detailed account of classification and its correlation with international systems • a discussion of soil genesis which includes a review of relevant research papers • appraisal of soil quality from a land use perspective as well as for its ecological significance • illustrative examples of soil profiles with analytical data and accompanying interpretations. There is also a fascinating account of the special relationship that exists between South African animals and soil environments. Soils of South Africa should interest students and researchers in the earth, environmental and biological sciences, as well as environmental practitioners, farmers, foresters and civil engineers.
A review of climatic change in southern Africa over the last half million years is presented. The foundation for the synthesis is the use of continuous and near-continuous data series derived from deep-sea ocean sediment cores, terrestrial sediment cores, and stalagmites in South African caves. These are supplemented by non-continuous data from a variety of sites over southern Africa wherever possible. The climatic consequences of changes in the eccentricity of the earth's orbit and in the precession of the equinoxes are examined and it is shown that changes at the Milankovitch frequencies of around 100 000 and 23 000 years are apparent in the record. The extent to which changes since the last interglacial at around 125 000 BP in southern Africa corresponded to those occurring elsewhere and the degree to which atmospheric-ocean general circulation modelling replicates past conditions are examined. Particular attention is paid to the climate of the last three millennia and the nature of local teleconnections within South Africa and those occurring between the country and major sites elsewhere on the globe. The patterns of change that have occurred over southern Africa are shown to fit coherently into a model of expanding and contracting circumpolar and tropically-induced atmospheric circulation adjustments. These have taken place both systematically over long time scales and abruptly from time to time to produce a high degree of variability and frequent abrupt change superimposed on longer-termed oscillations. As the resolution of the record has been improved, so the variability of the southern African climate has been demonstrated to increase and abrupt, extreme changes have been shown to be increasingly common.
The flora of southern Africa is, for its latitude and area, very species-rich. Although the hyperdiverse Cape flora contributes almost half of this richness, three other radiations (desert, grassland, and woodland) contribute significantly to the botanical wealth of southern Africa. Each radiation occurs in a different ecological setting and has a different diversification history. Such parallel radiations can develop in suitably complex environments, given gradual change through time and no region-wide catastrophes. These four radiations cross-seeded each other, with clades spawning subclades in other radiations, thus linking all four into one complex radiation. This led to an increase in the number of diversifying clades in each radiation. Such complex radiations accumulate diversifying lineages over a long time, spawn daughter radiations on other continents, and become powerhouses of global-biodiversity generation. We suggest that several of the most species-rich regions may harbor such complex radiations.
The causes and consequences of plant flammability are a contested issue. In fire-prone ecosystems, high flammability is invoked as a trait (in combination with fire-survival traits) that enhances reproductive success and reduces competition in the post-fire environment. On the other hand, flammability may be a consequence of other selective forces, for example, deterring herbivores. Here, we use a standardised method for estimating the flammabilities of 99 species distributed across five biomes in a small area of the southwestern Cape Floristic Region, South Africa. The fire-prone Fynbos and Grassland biomes included many highly flammable species, notably among graminoids and small-leaved shrubs with densely packed, fine twigs. However, Fynbos included many weakly flammable species. In the fire-free biomes (Forest, Nama-Karoo and Thicket), most species had low flammability, especially succulents. However, flammable species also occurred in all three biomes, including species with traits normally attributed to non-flammable species (e.g. large leaves sparsely arranged on coarse twigs). Since these biomes are fire-free, flammability in these species cannot be attributed to a fire-related selective regime.
We measured dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and their corresponding Δ14C and δ13C values in order to study the sources and fates of DOC in the York River Estuary (Virginia, U.S.A.). The Δ14C and δ13C values of DOC and DIC at the freshwater end-member indicate that during periods of moderate to high flow, riverine DOC entering the York was composed of decadal-aged terrestrially organic matter. In nearly all cases, DOC concentrations exceeded conservative mixing lines and were therefore indicative of a net DOC input flux from within the estuary that averaged 1.2 μM L-1 d-1. The nonconservative behavior of DOC in the York River Estuary was also apparent in carbon isotopic mixing curves and the application of an isotopic mixing model. The model predicted that 20-38% of the DOC at the mouth of the estuary was of riverine (terrestrial + freshwater) origin, while 38-56% was added internally, depending on the isotopic values assigned to the internally added DOC. Measurements of Δ14C and δ13C of DOC and DIC and marsh organic matter suggest that the internal sources originated from estuarine phytoplankton and marshes. The isotopic mixing model also indicates a significant concomitant loss (27-45%) of riverine DOC within the estuary. Changes in DOC concentration, Δ14C-DOC, and δ13C-DOC were also measured during incubation experiments designed to quantify the amounts, sources, and ages of DOC Supporting the carbon demands of estuarine bacteria. Results of these experiments were consistent with an estuarine source of phytoplankton and marsh DOC and the preferential utilization of young (14C-enriched) DOC in the low-salinity reaches of the York. However, the average removal of riverine DOC by bacteria accounts for only ∼4-19% of the riverine pool; therefore, other significant sinks for DOC exist within the estuary.
Food webs in conventional (high-input) and integrated (reduced-input) farming systems were simulated to estimate the contribution of soil microorganisms and soil fauna to nitrogen mineralization during the growing season. Microbes accounted for approximately 95% of the biomass and 70% of total nitrogen mineralization in both management practices. Among the soil fauna, amoebae and bacterivorous nematodes were the most important contributors to nitrogen mineralization. The model calculated nitrogen mineralization rates close to the observed rates for both fields and depth layers. In the integrated plot there were relatively high rates of mineralization in the 0-10 cm layer compared with the 10-25 cm layer, whereas in the conventional plot no differences were observed between depth layers. According to the present model, the impact of functional groups on nitrogen mineralization could exceed the simulated direct contribution to nitrogen mineralization. -from Authors