Late Holocene paleoenvironments of the floodplain of the Solimões River, Central Amazonia, based on the palynological record of Lake Cabaliana

Abstract

Th e core PD-67 of 160 cm depth was collected from the delta of Lake Cabaliana situated on the Solimões River. Seventeen samples were removed for palynological and sedimentological analysis and three for radiocarbon analysis. Two dry periods, both in the Late Holocene, were observed (2800-2550 cal yr BP, 1450-550 cal yr BP) separated by a wetter phase (2550-1450 cal yr BP). In 2800-2550 cal yr BP, varzea forests of Alchornea, Symmeria, Cecropia, Alternanthera and Asteraceae were predominant. Beginning in 2,550-1450 cal yr BP, the varzea was characterized by pioneer elements, such as Cassia, Laetia, Mabea, Symmeria and Cecropia, and by the expansion of Poaceae, Cyperaceae, Sagittaria, Montrichardia and Asteraceae. In 1450-550 cal yr BP the succession of varzea continued with Pseudobombax, Laetia, Luehea/Lueheopsis and Ryanaea increasing simultaneously with the terra fi rme vegetation of Rutaceae, Sapotaceae, Styrax, Scleronema, Anthurium, Araceae, pteridophytes and Pariana. Th e successional dynamics at Lake Cabaliana indicated that the local varzea had become established recently, and is composed of a mosaic of diff erent successional stages of vegetation infl uenced mainly by fl ood pulse and variation in rainfall. It is therefore possible to propose that the recent climate history of Central Amazonia refl ects changes in rainfall patterns in the basin.

Miocene Palynology of the Solimões Formation (Well 1-AS-105-AM), Western Brazilian Amazonia

“…Throughout core 105-AM, spore counts were quite high (Figure 10C), which was similar to other palynological analysis in the Solimões Formation (e.g., Silva-Caminha et al, 2010;Kern et al, 2020). This abundance contrasted with much less fern spores in the Holocene localities compared herein (Absy, 1979;Behling et al, 1999) and elsewhere in Amazonia (e.g., Irion et al, 2006;Sá et al, 2016;Rodríguez-Zorro et al, 2018). However, a pollen study in western Amazonia near the 105-AM site by Roucoux et al (2013) found high fern spore abundances during the formation of a peat deposit in the Late Holocene.…”

“…These differences support our interpretations of swamps in the early to early middle Miocene and a more dynamic fluvial system in the middle to late Miocene part of the 105-AM record. Scanty Mauritia and high Poaceae pollen were common features in surface river sediments (Gomes et al, 2021;Akabane et al, 2020) and Holocene records from fluvial lakes in Amazonia (Absy, 1979;Irion et al, 2006;Sá et al, 2016). Furthermore, high Poaceae counts in these settings can be an indicative of várezas (Akabane et al, 2020); in the 105-AM samples, Poaceae abundance correlated reasonably with abundance of floodable elements (r 2 = 0.31, P < 0.001).…”

Going north and south: The biogeographic history of two Malvaceae in the wake of Neogene Andean uplift and connectivity between the Americas

“…Based on this analysis we conclude that R. guianensis associated taxa (NLR: Alchornea, Araliaceae, Fabaceae, Malpighiaceae, Polygonaceae, and Sagittaria) are typical in floodplain forests such as described in modern fluvial settings in the Amazon region (Wittmann et al, 2010;Sá et al, 2016;Salamanca et al, 2016). We also observe that they rarely co-occur with taxa from Mauritiidites or Grimsdalea palm swamps, nor with taxa from the mangrove vegetation formed by Zonocostites-type pollen.…”

The onset of grasses in the Amazon drainage basin, evidence from the fossil record

“…Very high (50 -90%) amounts of Poaceae pollen in palynological records give strong evidence for the existence of savanna habitats (Salgado-Labouriau 1979, Bush 2002. However, aquatic environments can also feature large amounts of grass pollen (e.g., Behling et al 2001, Sá et al 2016. And to complicate matters further, savannas and aquatic environments are both characterized by different species of the subfamily of the Panicoideae.…”