IAG 1999 Regional Conference on Geomorphology
Gloria Hotel of Rio de Janerio, Brasil, July 17-22, 1999
Abstracts - Sandra Baptista da Cunha and Antonio Jose Teixeira Guerra (Eds.)

RECENT AND ANCIENT SEDIMENTS IN THE JAGUARIBE RIVER MOUTH AND ADJACENT AREAS: RE-DIMENSIONING THE ROLE OF THE AEOLIAN ACTION IN THE GEOMORPHOLOGICAL EVOLUTION OF THE EASTERN COAST OF THE CEARÁ STATE, NORTHEAST OF BRAZIL

Sales, V.C.1,2 and Peulvast, J.P.2

1Universidade Federal do Ceará, Fortaleza, CE, Brasil, vcs@ufc.br
2Université Paris-Sorbonne and Université Paris-Sud, France, peulvast@planeto.geol.u-psud.fr


The eastern coast of the Ceará State, Northeast of Brazil, lies east of the Jaguaribe River, which drains the eastern and southern Ceará. The downstream segment of this river is a SW-NE orthoclinal valley inset in a wide <<inner lowland>> between the Precambrian basement to the west and the Middle-Upper Cretaceous 'Potiguar Basin' to the east. Its lower course turns westwards 40 km before reach the shoreline, where the oldest beds of the basin outcrop as non-continuos active seacliffs 20/30m high. The Cainozoic sediments have been mapped as 'Barreiras Group', a (Later Tertiary? Pleistocene?) deposit of torrential or fluvial continental clastics, locally represented by the 'Faceira Formation', a fluvial terrace that occurs along the west side of the river , and by the 'Barreiras Formation', which conceals the northeastern continuation of the basin, outcropping as lower seacliffs at the shoreline. Some publications stress the role of neotectonics in the orientation of the lower course of the river and in the contact Cretaceous and Tertiary sediments at the seacliffs. The identification of old dune deposits possibly interfingered with fluvial and lacustrine deposits, (Late Pleistocene or even older?) on the coast and inland, in the area mapped as 'Barreiras Formation', lead us to suggest that after have been excavated (Pleistocene lower sea-levels?) along strike the Cretaceous sandstone to the present coast or beyond, the lower course of the river migrated to the west as a result of dune damming, laterally eroding the north-east continuation of the Tertiary terrace. In the sequence, and in relation with last Pleistocene and Holocene high sea-levels, the valley has been filled by aeolian deposits and the shoreline exposed to coastal retreat, resulting in seacliffs cut into the dunes. This interpretation stresses the influence of Upper Pleistocene-Holocene dynamic related to coastal processes in the geomorphological evolution of the area.


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