GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 327-5
Presentation Time: 9:00 AM-6:30 PM


HIRUMA, Silvio Takashi1, FURQUIM, Sheila Aparecida Correia2 and TEIXEIRA, Antonio Luiz1, (1)Instituto Geológico, Secretaria do Meio Ambiente/SP, Rua Joaquim Távora, 822, Vila Mariana, São Paulo, 04015-011, Brazil, (2)Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo (UNIFESP), Rua São Nicolau, 210, 4° andar, Centro, Diadema, 09913-030, Brazil,

Colluvial deposits occur widespread in the tropics and have a potential paleoenvironmental significance. The chronology of these deposits in the summit areas on the flanks of the continental rift of southeastern Brazil (Serra do Mar and Serra da Mantiqueira) has been established by radiocarbon dating of buried dark humic horizons (paleosols). This work focuses on two complex successions of colluvial deposits intercalated with up to three buried dark humic horizons located in the Senador Amaral and Cambuí/Monte Verde plateaus, both in the Serra da Mantiqueira, at altitudes of 1,510 and 1,568 m, respectively. Both successions occur in lower and concave hillslope morphological units and are characterized by dark brown (7.5YR 3/3)/dark reddish brown (5YR 3/3) (colluvial deposits) to black (10YR 2/1) (paleosols) colors and sandy loam to clay texture. Most of the horizons have no structure (massive), but some of them have a granular structure or show subangular blocks. Granules and angular pebbles of quartz, feldspar and weathered bedrock are dispersed in the matrix. Two generations of paleosols were identified in Senador Amaral plateau, with radiocarbon ages of 2,370±30 BP and 8,220±30BP, whereas, in the Cambuí/Monte Verde plateau, three generations of paleosols were identified with older ages: 14,180±50 BP, 25,410±110 BP, and 28,990±170 BP. The ages of these paleosols are similar to those obtained in previous studies at the Campos do Jordão, Itatiaia and Bocaina plateaus, on both flanks of the continental rift of southeastern Brazil, probably indicating a similar hillslope evolution in the Late Quaternary. Chronological data show a recurrence of the processes of colluviation (slope degradation) and pedogenesis (relative stability/lesser morphodynamic activity), which is probably associated with changes in environmental conditions. This research was supported by the FAPESP (Process 2014/01648-7).