Seasonal Amazonian rainfall variation in the Miocene Climate Optimum

Abstract

Modern and fossil freshwater bivalves from north-eastern Peru are investigated to reconstruct seasonal rainfall patterns in Miocene Amazonia. Oxygen isotope variation in incremental growth bands of fossil bivalves reflects past hydrological conditions in the Miocene Climate Optimum (MCO), when the world was warmer than today. A calibration experiment was conducted on a modern bivalve. Modern river dwelling Triplodon corrugatus shows large amplitudinal changes in y 18 O, which mirror the seasonal variation in rainfall as a result of the annual migration cycle of the Inter Tropical Convergence Zone (ITCZ). Growth incremental oxygen isotope records of Miocene Amazonian Diplodon aff. longulus bivalves show strikingly similar patterns. This suggests that the seasonal migration of the ITCZ and the intensity of the hydrological cycle in the MCO were comparable to today. The implications are that humid climate conditions sufficient to sustain a rainforest ecosystem already existed~16 Ma ago. D

Amber from western Amazonia reveals Neotropical diversity during the middle Miocene

“…Unfortunately, the lignitic fragments are partly transformed into vitrinite, which precludes any infrafamiliar identification of the associated trees. The high diversity (13 different families for 14 specimens) and ecological disparity (presence of parasitoids, phytophagous, myxomycophagous, blood feeding, and detritivorous taxa) observed in even just this preliminary sample suggest a rich and complex entomofauna for the middle Miocene of western Amazonia (Table 2), consistent with broader continental and global conditions associated with the high Miocene floral diversity (30) and the Miocene Climate Optimum (12). In addition, the Iquitos amber yields some Hexapoda with aquatic affinities (Trichoptera, whose larvae are strictly aquatic) and a small ground soil fauna (Collembola), as also occurs in Baltic amber (28).…”

“…In fact, it appears to be relatively abundant and of large size within the locality. Even though the nature of the depositional environments of Pebas strata has been widely debated throughout the last decade (7,(10)(11)(12)(13)(14), with inferences ranging from fluvial, lacustrine, and brackish to tidal environments, most authors acknowledge the occurrence of episodic marine incursions, most likely of Caribbean origin (9-16).…”

“…For example, the diverse animals, plants, fungi, and cyanobacteria entrapped in this initial small amber sample substantiate that humid and densely forested environments in a tropical climate must have been present by the middle Miocene in western Amazonia. Future work on this assemblage should more widely elucidate the pattern of changes in biotic diversity, palaeoenvironment, and paleoecology of an area that experienced drastic environmental changes (7,8) throughout the Miocene (12,30).…”

Can shells of freshwater mussels (Unionidae) be used to estimate low summer discharge of rivers and associated droughts?

“…These records have been previously demonstrated to be a useful proxy for past rainfall patterns, water source, or river discharge (Gajurel et al 2006;Kaandorp et al 2005;Ricken et al 2003). In this study, the possibilities and limitations of using unionid aragonite oxygen isotope ratios (d 18 O ar values) as a proxy for past river discharge in the river Meuse are investigated.…”

Tectonic History of the Andes and Sub‐Andean Zones: Implications for the Development of the Amazon Drainage Basin

“…to Present prevailed in the Amazon foreland basin (Kaandorp et al 2005). Based on pollen analysis by Hoorn et al (1995), it was noted that at that time biodiversity in the Amazon wetland was similar to, or even greater than today (Hooghiemstra & Van der Hammen 1998;Van der Hammen & Hooghiemstra 2000).…”