Contribution to Early Holocene vegetation and climate history of Eastern Orinoco Llanos, Venezuela, from a paleoecological record of a Mauritia L.f. swamp

Abstract

A palynological analysis of an organic paleosol found at 150-125 cm depth in a Mauritia swamp from the Eastern Orinoco Llanos is presented. The 25 cm pollen record summarizes the vegetation history during the Early Holocene, from 10,225 to 7,800 calendar yr BP. The vegetation was characterized by a Poaceae marsh, where Asteraceae, Melastomataceae, Schefflera-type and Phyllanthus were the most abundant shrubs and trees. Pollen-types richness was lower than that recorded today in similar environments, and Mauritia pollen was absent. Results suggest that climate was as humid as present during the beginning of the Holocene, with a decreasing trend in humidity from around 8,000-7,000 yr BP, in coincidence with the beginning of the "Early-Mid-Holocene Dryness" that affected deeply the Amazon Basin and neighboring areas. Dry climatic conditions could have existed in the study site until the Mid-Late Holocene when a Mauritia swamp developed, and humid conditions similar to present established. Main climate phases inferred in our study site fit well with regional trends recorded in other places located north Amazon Basin. However, conclusions are still limited by the lack of additional Quaternary records in the Orinoco Llanos area, avoiding regional correlations. KEYWORDS: Orinoco Llanos, Mauritia swamp, Early Holocene, paleoclimate, Early-Mid Holocene Dryness.Contribuição para a história da vegetação e clima durante o Holoceno Temprano do Llanos Orientais do Orinoco, Venezuela, a partir de um registro paleoecológico de um pântano Mauritia L.f. RESUMORealizou-se uma análise de pólen amostrada em paleossolos orgânicos, entre 150-125 cm de profundidade, em um pântano Mauritia os lhanos do Orinoco. O registro de pólen dessa amostra resumiu a história da vegetação durante o Holoceno Temprano, entre 10,225-7,800 cal. anos AP. A vegetação durante esse período foi caracterizada por um pântano de Poaceae, com maior abundância de arbustos e árvores de Asteraceae, Melastomataceae, tipo-Schefflera e Phyllanthus. Encontrou-se que a riqueza de tipos polínicos no Holoceno Temprano foi menor do que a riqueza atualmente encontrada em ambientes similares; o pólen de Mauritia esteve ausente de todas as amostras. Os resultados deste estudo sugerem que o clima durante o início do Holoceno foi úmido, semelhante ao clima atual. Houve também uma tendência de diminuição de umidade entre 8,000-7,000 anos AP, o que coincidiu com o início da "seca do Holoceno Temprano-Médio". Esta seca afetou profundamente a Bacia Amazônica e áreas adjacentes, persistindo no local de estudo até o Holoceno Médio-Final, período em que surgiram o pântano Mauritia e as condições climáticas atuais. Fases climáticas principais deduzidas se encaixam bem com as tendências regionais registradas em outros lugares localizados ao norte da Bacia Amazônica. No entanto, as conclusões ainda são limitadas pela falta de novos registros quaternários na área lhanos do Orinoco, evitando correlações regionais. PALAVRAS-CHAVE: lhanos do Orinoco, Mauritia pântano, Holoceno Tempra...

Amazon forest dynamics under changing abiotic conditions in the early Miocene (Colombian Amazonia)

“…The predominance of Mauritiidites franciscoi and its associated taxa in zones II to III of the Miocene record do resemble the palynological composition of the Quaternary Mauritia swamp successions in north‐western Amazonia (Urrego, ; Behling et al ., ; Giraldo et al ., ) and in Venezuela (e.g. Leal et al ., ). This assemblage also is reminiscent of the modern morichales ( Mauritia stands in Orinoquia), canaguchales (Mauritia stands in Amazonia), and the Venezuelan highlands (see Lasso et al ., ).…”

Climate variability and human impact in South America during the last 2000 years: synthesis and perspectives from pollen records

“…Another limitation is that most palaeoecological records available for the GS uplands are from their southern sector, which is the lowermost part of the peneplains and has a different climate and vegetation regime as compared to the northern sector. Some records from the northern sector are available that fit with the chronological PAGES-2k requirements (Leal et al, 2011), but only summary diagrams are provided in peer-review publications and therefore they cannot be used in this reconstruction. The decadal to multidecadal analysis of a new core obtained in Kamoirán (PATAM10-A07), in the northern GS uplands, is in progress.…”