Upland Lakes of the Carajás Region: Origin and Development through Time

Abstract

Upland lakes (ULs) of the Carajás, southeastern Amazonia, have been intensively studied to their evolution during the Quaternary, as well as the development of the associated biota. In this review, several classical and modern approaches from structural geology to the pollen rain and sedimentary data which cover an area of around 41,300 km2 were compiled. Multi-elemental geochemistry indicates that the detrital sediments derived from weathered crusts and soils, while the sedimentary organic matter represent autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3 plants and freshwater DOC) sources. Modern pollen rain suggests that even small lakes and canga areas can reflect forest signal, which depends on the topographic control and prevailing wind direction on pollen deposition. Integrated data of the sedimentary cores indicate that the active lakes never dried up during the last 50 ka cal BP. However, subaerial exposure occurs on filled lakes such as ST02 Lake during the LGM, LB3 and R2 lakes at the mid-Holocene due to drier paleoclimate conditions. Considering the organic proxies, only LB3 Lake presents expansion of C4 canga (montane savanna) plants since ULs of the Serra da Bocaína does not present siderites. Siderite formation on ULs deposits also points to drier paleoenviromental conditions, interrupting predominantly wet conditions. However, there is no evidence for widespread expansion of savanna into Southeastern Amazonia during the late Pleistocene and Holocene.

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south‐eastern Amazonia

“…These findings are highly similar to those for the massive siderite bed that formed in Carajás lakes (Guimarães et al, 2016(Guimarães et al, , 2019bReis et al, 2017). Consequently, the presence of siderite beds, which is associated with redox conditions, affects pollen preservation and results in a very low pollen concentration (Guimarães et al, 2019b). Thus, we posit that siderite beds were a product of large-scale dry events that synchronously affected the eastern and western parts of the Amazon region.…”

“…High Fe/Al ratios in these beds were also identified from~34k to 20 cal a BP (Cordeiro et al, 2011). These findings are highly similar to those for the massive siderite bed that formed in Carajás lakes (Guimarães et al, 2016(Guimarães et al, , 2019bReis et al, 2017). Consequently, the presence of siderite beds, which is associated with redox conditions, affects pollen preservation and results in a very low pollen concentration (Guimarães et al, 2019b).…”

“…This general wet phase was interrupted by episodic dry events, which were observed by the formation of scattered siderite nodules. This could cause a relatively mixed environment, as supported by the high values of redox-sensitive elements such as Mo and P with a lower peak of Ba/Al (Guimarães et al, 2019b).…”

“…Previous studies on Carajás were conducted on swampy grasslands (filled lakes); therefore, most of these records may reflect hydrarch succession and basin-filling rather than a paleoclimate signal (Guimarães et al, 2018(Guimarães et al, , 2019b. In addition, each upland lake (UL) of the Carajás has a unique geomorphological setting (Silva et al, 2018) that influences the sediment yield and geochemical characteristics due to complex basin processes (Sahoo et al, 2015(Sahoo et al, , 2016a(Sahoo et al, , 2017a(Sahoo et al, , 2019.…”

The role of fault reactivation in the development of tropical montane lakes

“…(A) Geological map of the Carajás region in the Brazilian Amazon showing the main lithological units and geological structures (modified from Vasquez et al , 2008 and Guimarães et al ., 2019). The studied lake is located in the lateritic crusts of the Serra Sul (S11D, yellow box).…”