The Araçatuba paleoswamp and the Bauru Basin initial sedimentation

THE ARAÇATUBA PALEOSWAMP AND THE BAURU BASIN INITIAL SEDIMENTATION^*

LUIZ A. FERNANDES¹, PAULO C. F. GIANNINI²AND ANA M. GÓES³

¹Departamento de Geologia, Universidade Federal do Paraná, Curitiba, PR.

²Instituto de Geociências, Universidade de São Paulo, São Paulo, SP.

³Centro de Geociências, Universidade Federal do Pará, Belém, PA.

Presented by ANTONIO C. ROCHA-CAMPOS

The Bauru Basin (lower Cretaceous) corresponds to a continental sandy succession, on a basaltic substratum (Serra Geral Formation, Early Cretaceous). Its first depositional phase, essentially desertic, corresponds to a progressive burial of the basaltic surface by a widespread and homogeneous sandy blanket, formed mainly by eolian sheets, with small dunes and minor interbedded loess deposits. The rare fluvial deposits of this phase refer to desert flash floods wadis. The original relief of the substratum favored the formation of an endorrheic drainage system in the interior of the basin, causing the appearance of a large swampy area under semi-arid climate, the Araçatuba paleoswamp.

The swamp deposits (Araçatuba Fm.) comprise siltstone and tabular strata of very fine, massive sandstone, up to decimeters thick, with typical greenish-gray color. Carbonatic cement may form tabular crusts parallel to the stratification. Sometimes, fining upward beds show incipient planar lamination in their upper part, where desiccation cracks and root marks are common. Dolomite pseudomorphs and moulds and pseudomorphs of gypsum radial fibrous aggregates were identified. The crystal moulds may be associated with root marks, indicating subaerial exposition cycles. Mudstones with crystal moulds occur sporadically interbedded with climbing-ripple cross-laminated siltstones, that characterize deposition in calm shallow saline waters undergoing phases of subaerial exposition. In the Araçatuba Formation occurrence area, sigmoidal sandy bodies, sometimes with convolute bedding, suggest deposition, sliding and fluidization of marginal aqueous deposits. The constant arrival of wind-blown sand, that initially formed dunes and sand sheets marginally to the swamp, buried the original depression. The Araçatuba Formation is enclosed and overlain by eolian deposits of the Vale do Rio do Peixe Formation. — ( December 8, 2000 )

Publication Dates

• Publication in this collection
  05 Oct 2001
• Date of issue
  Sept 2001