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

Abstract

This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion byand building ofthe formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E-W plateau border and the start of Violão Lake formation during the Pliocene-Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36000calyear BP. At about 31000calyear BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation.

Pollen Morphology of Convolvulaceae from Southeastern Amazonian Cangas and Its Relevance for Interaction Networks and Paleoenvironmental Studies

“…There are two vegetation types in Serra dos Carajás, humid evergreen tropical forests (HETF), which occur on the slopes of the plateau, interrupted by canga vegetation on the plateau at 600–800 m altitude ( Figure 1 B), which colonizes the lateritic crusts under edaphic conditions [ 15 , 30 ]. Several geoenvironments are described for canga areas, such as rupestrian and swampy fields, flat grasslands associated with sinkholes, active lakes, dry forests over degraded cangas, and open forests over aluminous-rich lateritic covers [ 31 , 32 , 33 , 34 ].…”

Pollen Morphology of Convolvulaceae From Serra Dos Carajás, Southeastern Amazonia

“…There are two vegetation types in Serra dos Carajás, humid evergreen tropical forests (HETF), which occur on the slopes of the plateau, interrupted by canga vegetation on the plateau at 600-800 m altitude (Figure 1B), which colonizes the lateritic crusts under edaphic conditions [15,30]. Several geoenvironments are described for canga areas, such as rupestrian and swampy fields, flat grasslands associated with sinkholes, active lakes, dry forests over degraded cangas, and open forests over aluminous-rich lateritic covers [31][32][33][34].…”

Desafios e Perspectivas na Conservação da Isoëtes cangae

“…As crostas lateríticas da Serra dos Carajás foram formadas a partir do intemperismo de formações ferríferas bandadas e rochas metavulcanossedimentares há cerca de 65 milhões de anos, resultante do estabelecimento de um clima tropical úmido na região (Vasconcelos et al 1994, Maurity e Kotschoubey 1995. Ciclos sucessivos de intemperismo, reativação de falhas tectônicas preexistentes e colapso dessas crostas lateríticas, durante os últimos 5 milhões de anos, produziram depressões as quais, em alguns casos, evoluíram para lagos de altitude (Souza-Filho et al 2020).…”

“…Por outro lado, a variação de volume foi substancialmente maior, compreendendo cerca de cinco ordens de magnitude, de 56 m 3 a 1 944 460 m 3 . Ainda com base nos dados morfológicos, frutos dos estudos geofísicos realizados na área, os lagos da região podem ser classifi cados como circulares a subcirculares e côncavos, formados principalmente por processos de dissolução (Souza-Filho et al 2020).…”