Progradation rates of coastal barriers estimated from the 14 C age of soil organic matter

Abstract

The antecedent geomorphological and structural framework combined with nearshore dynamics and sediment budget provided the conditions necessary for the formation of coastal plains along the southern Brazilian littoral during the Holocene. To establish a temporal framework for littoral accretion, we applied 14 C dating of humic organic material from the B‐horizon of spodosols. The dated soils developed under Atlantic tropical forest, which covers the coastal barriers along the Santa Catarina shoreline of south‐east Brazil. The obtained ages point to a highly coherent trend in barrier accretion and indicate that the transfer of organic matter from the surface to the B‐horizon has largely been occurring vertically at the same time as the sediment surface was colonized by Atlantic forest. Accretion of the strandplain in the coastal cell of Volta Velha began ca. 6800 cal a BP, initially at a rate of ca. 22 cm a −1 and reaching 58 cm a −1 during the last 3 ka. Structural analysis of the dated humic material was by analytical pyrolysis and solid‐state 13 C nuclear magnetic resonance spectroscopy. Both techniques revealed marked compositional differences between the organic matter of different ages, which are discussed in terms of time‐dependent degradation processes.

Bibliographic Information