Late quaternary geomorphological evolutionary dynamics of the Araripe sedimentary plateau, northeast of Brazil

Abstract

The stratigraphic and geochronological data, compared to the set of ages already known for the semi-arid Northeast of Brazil, allowed us to understand part of the geomorphological dynamics of the sub-humid sector of the Araripe Plateau, in the south of the State of Ceará. Paleoenvironmental records were recovered through the study of Quaternary deposits generated by climatic inputs, in the range of 72.0 ka BP to the Early Holocene. Except for section CSM-C, it was observed that all other debris flows found do not exceed the MIS 3/LMG in age, and that morphogenetic events linked to gravitational flows are constrained until the Lower Holocene, coinciding with the findings in other sectors of the Northeast of Brazil such as the Borborema Highlands. Thus, as in other locations, it appears that the depositional processes and the formation of successive colluvial ramps in the Araripe Plateau occurred at times of strong climatic instability, as periods of intense rainfall disrupted the pedo-geomorphic equilibirum of the landscape. Despite the undeniable predominance of semi-arid conditions for the Brazilian Northeast during the Quaternary, the results obtained suggest that such conditions were neither homogeneous nor constant, and that in the last 40.0 ka. BP the Northeast experienced climatic fluctuations with abrupt oscillations, on millennial scales, from dry to wetter conditions and vice versa, which apparently coincide with the displacement of the ITCZ to more southern positions in line with the Heinrich events in the Northern Hemisphere. From the end of the Lower Holocene towards the Present, drainage began to actively dissect colluvial sediments, in response to continued changes in the base level around the Plateau. This scenario led to a longitudinal reworking of the sediments along valley bottoms and channels, forming fluvial plains. This aspect points to the fact that the surface dynamics of the landscape, at least from the Middle Holocene onwards, was rather defined by changes in the base level (and ultimately in land use), and erosion of colluvial deposits, than by the entry of new episodes of climatically conditioned sedimentation of great magnitude.