171,330 research outputs found
Cyclic sediment deposition by orbital forcing in the Miocene wetland of western Amazonia? New insights from a multidisciplinary approach
No full textAuthors: Carina Hoorn*, Tyler Kukla, Giovanni Bogotá-Angel, Els van Soelen, Catalina González-Arango, Frank P. Wesselingh, Hubert Vonhof, Pedro Val, Gaspar Morcote-Rios, Martin Roddaz, Elton Luiz Dantas, Roberto Ventura Santos, Jaap S. Sinninghe Damsté, Jung-Hyun Kim, Robert J. Morley*Supplementary data In the Miocene, a large wetland system extended from the Andean foothills into western Amazonia. This system has no modern analogue and the driving mechanisms are not yet fully understood. In this study we investigate the presumed orbital cyclicity that controlled sediment deposition, while also assessing sediment source and biomes in the Miocene wetland. We do this by integrating lithological, palynological, malacological and geochemical data from the Los Chorros site (Amazon River, Colombia), and by placing our data in a sequence stratigraphic framework. In this sequence biostratigraphic evaluation, the Los Chorros succession is visualised to be composed of a series of flood-fill packages, with a rapid initial flood, marine-influenced conditions at the time of maximum flood, followed by a longer regressive infill phase. Marine, mangrove, and lacustrine indicators suggest that the outcrops at Los Chorros represent predominant marine-influenced lacustrine conditions during periods of sea level highstand. The sequence biostratigraphic evaluation further points to eight 41 kyr obliquity-driven depositional cycles, with rapid phases of transgression. Mangrove elements would have colonised within the timeframe of each sea level rise. Based on this relative age constraint and comparison to regional records, deposition likely took place prior to the 13.8 Myr global sea level fall, and most likely during the period just after 14.5 Ma, towards the end of the Middle Miocene Climatic Optimum (MMCO). Palynological evidence further suggests that to the west, surface elevation ranged from ~1000 up to ~3500 m and hosted protoparamo vegetation, the oldest yet reported and in agreement with predictions from molecular studies. In contrast, contemporaneous sites to the northeast of the wetland consisted of fluvial and cratonic formations, as shown by their Nd and Sr isotopic sediment signature. In summary, our data lead to an improved understanding of how geological and astronomical mechanisms controlled the floral and faunal distribution and controlled sediment deposition in western Amazonia during the middle Miocene. As Miocene conditions strongly contrast with modern western Amazonia, our data provide an important context for the deep time history and evolution of the modern western Amazon rainforest
Late Holocene palaeoenvironmental history of Khawr Rawri and Khawr Al Balid (Dhofar, Sultanate of Oman)
No full textThe coastal wetlands in Dhofar (Sultanate of Oman) provide a record of Late Holocene palaeoenvironmental history. The age of the surface sediments at some selected sites in the estuaries, locally known as khawrs and qurms, ranges from 750 to 390 calendar years (cal y) BC to Present. Geomorphological data suggest that prior to 270–420 cal y AD these estuaries were open to the sea and received a high input of fresh water from the mountains. At least from 270-420 cal y AD onwards, the physiography of the estuaries changed as a consequence of dwindling fresh water input from the mountains. As a result, the open estuaries changed into barrier dominated estuaries with periodical input of saline and fresh water. Palynological data indicate that the estuaries are mainly filled with (i) pollen and spores from the surrounding vegetation; (ii) a regional input of pollen and spores through surface and subsurface runoff from mountains, coastal plain and, wadis; (iii) pollen and spores from East Africa and the Indian subcontinent brought in by the monsoon. Between 750–390 cal y AD and 270–420 cal y AD the local input of khawr taxa prevailed whereas from 270–420 cal y AD to Present coastal plain and wadi taxa prevail. Both geomorphological and palynological data suggest the ancient centers of trade such as Samhuram at Khawr Rawri (ca. 100 BC–100 AD) and Zafar at Khawr Al Balid (12th–15th centuries AD) were affected by important hydrological changes related to desertification of the region as a consequence of a weakening SW (summer) monsoon
Climate and geological change as drivers of Mauritiinae palm biogeography
No full textSYNTHESIS - Journal of Biogeography - DOI: 10.1111/jbi.14098ABSTRACT Aim. Forest composition and distribution are determined by a myriad of factors, including climate. As models of tropical rain forest, palms are often used as indicator taxa, particularly the Mauritiinae. We question, what characterises the Mauritiinae pollen in the global fossil record? And when did the Mauritiinae become endemic to South America?Location. Global tropics.Taxon. Mauritiinae palms (Arecaceae: Lepidocaryeae).Methods. Pollen trait data from extinct and extant Mauritiinae pollen was generated from light-, scanning- and transmission electron microscopy. Statistical morphometric analysis was used to define species and their relationships to other Mauritiinae. We also compiled a comprehensive pollen database for extinct and extant Mauritiinae and mapped their global geographical distribution from Late Cretaceous to present, using GBIF and fossil data.Results. Our morphometric analysis identified 18 species (11 extinct and seven extant), all exhibiting exine indentations, a synapomorphy of the subtribe. The fossil taxa and early divergent extant Lepidocaryum are all monosulcate, whereas the extant Mauritia and Mauritiella species are all monoulcerate. Palaeobiogeographical maps of fossil Mauritiinae pollen occurrences suggest the taxon originated in equatorial Africa during the Cretaceous, and expanded their range to South America, and to India in the Paleocene. Range retraction started in the early Eocene with extirpation from India, and reduction in diversity in Africa culminating at the Eocene–Oligocene Transition (EOT). In contrast, in South America the distribution is maintained, and since the Neogene Mauritiinae palms are mostly restricted to swampy, lowland habitats. Main conclusions. Morphometric analysis shows that since their origin Mauritiinae pollen are relatively species poor, and Mauritiidites resembles Lepidocaryum. We also conclude that the biogeographical history of the Mauriitinae and, by extension, tropical forests was strongly affected by global climatic cooling events. In particular the climate change at the EOT was a fundamental determinant of current tropical forest distribution.KEYWORDSArecaceae, Eocene–Oligocene Transition (EOT), fossil record, global cooling, interplate dispersal, Lepidocaryum, Mauritia, Mauritiella, Neotropics, palynolog
Northward expansion of the southern-temperate podocarp forest during the Early Eocene Climatic Optimum: Palynological evidence from the NE Tibetan Plateau (China)
No full textThe early Eocene (53.3 to 41.2 million years ago (Ma)) is often referred to as a model for a greenhouse Earth. In the Xining Basin, situated on the North-eastern Tibetan Plateau (NETP), this time interval is represented by an extensive and well-dated sedimentary sequence of evaporites and red mudstones. Here we focus on the palynological record of the Early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma) and study the fossil gymnosperm pollen composition in these sediments. In addition, we also investigate the nearest living relatives (NLR) or botanical affinity of these genera and the paleobiogeographic implications of their occurrence in the Eocene of the NETP. To reach our objective, we complemented transmitted light microscopy with laser scanning- and electron microscopy techniques, to produce high-resolution images, and illustrate the morphological variation within fossil and extant gymnosperm pollen. Furthermore, a morphometric analysis was carried out to investigate the infra- and intrageneric variation of these and related taxa. To place the data in context we produced paleobiogeographic maps for Phyllocladidites and for other Podocarpaceae, based on data from a global fossil pollen data base, and compare these with modern records from GBIF. We also assessed the climatic envelope of the NLR. Our analyses confirm the presence of Phyllocladidites (NLR Phyllocladus, Podocarpaceae) and Podocarpidites (NLR Podocarpus, Podocarpaceae) in the EECO deposits in the Xining Basin. In addition, a comparative study based on literature suggests that Parcisporites is likely a younger synonym of Phyllocladidites. Our findings further suggest that the Phyllocladidites specimens are derived from a lineage that was much more diverse than previously thought, and which had a much larger biogeographical distribution during the EECO than at present. Based on the climatic envelope of the NLR, we suggest that the paleoclimatic conditions in the Xining Basin were warmer and more humid during the EECO. We conclude that phylloclade-type conifers typical of the southern-temperate podocarp forests, had a northward geographical expansion during the EECO, followed by extirpation.Supporting data for figures in the main text [See: https://doi.org/10.1016/j.revpalbo.2023.104914]Table S1. Cleaned GBIF occurrence data of Podocarpus and Phyllocladus (Fig. 2).Table S2. Sporomorph counts for the PEX samples, ranging in age from 53.02 (52.81-53.52) to 52.36 (52.11-52.57) Ma (Meyer et al., 2022) (Fig. 4). Table S3. Measurements of all modern and fossil gymnosperm pollen that were used in this study (Fig. 5). Table S4. Fossil Pollen Dataset of Phyllocladidites and Parcisporites for constructing paleomaps (Fig. 6).Table S5. Fossil Pollen Dataset of Phyllocladidites and Parcisporites according to biogeographical realms for making stratigraphical range chart (Fig. 7).Table S6. Climate data for grid-based cleaned-GBIF occurrence data of Podocarpus and Phyllocladus (Fig. 8)
On the origin of Amazonian landscapes and biodiversity: a synthesis
No full textIn northern South America the Cenozoic was a period of intense tectonic and climatic interaction that resulted in a dynamic Amazonian landscape dominated by lowlands with local and shield-derived rivers. These drainage systems constantly changed shape and size. During the entire Cenozoic, the Brazilian and Guiana Shields were stable mountainous areas. Andean-derived river systems increased in importance especially in the Neogene. A remarkable feature in western Amazonian history is the waxing and waning of large lake systems and embayments. By the Late Miocene (about 11 Ma), the Andes were connected with the Atlantic through an incipient Amazon River, and from c. 7 Ma Andean-derived river systems became fully established in central and eastern Amazonia and the modern landscape configuration had developed. Rainforests already existed in northern South America during the Paleogene, but the modern rainforests - with resemblance to the Present forest - only developed during the Miocene. The western Amazonian Miocene record contains very diverse aquatic faunas (molluscs, ostracods, turtles, crocodiles, fishes) as well as terrestrial mammals. Remarkable gigantic forms thrived in Amazonian ecosystems at the time. Since the Late Miocene, edaphically heterogeneous lands emerged in western Amazonia in areas previously occupied by lake systems. At the same time nutrient-rich deposits spread over central and eastern Amazonia, an event that, based on molecular phylogenetic studies on extant taxa, coincided with diversification of terrestrial taxa. Molecular-based time estimates confirm the steady diversification and mostly pre-Quaternary origin of extant Amazonian taxa. A significant portion of the current species richness is attributed to a combination of relatively constant wet and warm climates and a heterogeneous edaphic substrate. The Quaternary was a time of distribution shifts, but can no longer be considered a time of diversification in Amazonia
The Development of the Amazonian Mega-Wetland (Miocene; Brazil, Colombia, Peru, Bolivia)
No full textThe scenery of Western Amazonia once consisted of fluvial systems that originated on the Amazonian Craton and were directed towards the sub-Andean zone and the Caribbean. In the course of the Early Miocene these fluvial systems were largely replaced by lakes, swamps, tidal channels and marginal marine embayments, forming a mega-wetland. In this chapter we will review the characteristics of this mega-wetland and its different phases of development. These aquatic environments hosted a diverse fauna whereas the shores of these systems were fringed by palm swamps, and a diverse rainforest occurred in the peripheral dry lands. The genesis of this wetland was primarily driven by geological mechanisms such as the Andean uplift, and an increase in accommodation space in the sub-Andean and intracratonic basins. Additionally, high precipitation rates also played an important role in wetland formation. The earliest phase of wetland development is recorded in boreholes drilled in the sub-Andean foreland basins of Peru and Colombia, and in the intracratonic Solimões Basin of western Brazil. During the latest Oligocene to Early Miocene (~24 to 16 Ma) lacustrine conditions alternated with episodes of Andean and cratonic fluvial drainage as well as marginal marine influence. In Amazonia, marine incursions are intercalated as thin beds in the Middle to Upper Miocene fluvial strata and contain marine and coastal taxa (foraminifera, mangrove pollen). Lacustrine conditions expanded further during the Middle Miocene to early Late Miocene (~16 to 11.3 Ma; Pebas phase). During this period the lake-embayment and swamp systems - fringed by forested lowland - reached their maximum extension. This wetland was subject to marginal marine influence and sustained a large radiation of endemic aquatic invertebrate faunas. During its maximum extent the wetland covered an area of more than 1.5 × 106 km2 - comprising much of the Present western Amazonian lowlands. From the Late Miocene onwards uplift rates in the Eastern Cordillera, Cordillera Real and Cordillera de Merida substantially increased and the Andes became a continuous barrier. This barrier effectively separated lowland Amazonia from Orinoquia and the Magdalena Valley and closed off all lowland connections with the Pacific and the Caribbean. The wetland system became a complex environment where deltaic, estuarine and fluvial environments coexisted. This Late Miocene fluvial-tidal-dominated wetland (~11.3 to 7 Ma, Acre phase) hosted a species-rich vertebrate fauna, but (in contrast to the Pebas phase), the molluscan fauna was species poor and already strongly resembled the modern Amazonian fluvial fauna. This system represents the onset of the transcontinental Amazon River. From 11.3 Ma onwards, sediments of Andean origin reached the Atlantic continental shelf and initiated the build-up of the Amazon Fan
Historische Erzehlung Der Frantzösischen Tyranney/ Verübet in den Dörfern Lunen/ Loosdrecht/ Waverveen/ Bootshol/ Abkonde/ Nichtevecht/ [et]c.
No full text- …
