HIGH-FREQUENCY/LOW AMPLITUDE EUSTATIC PARASEQUENCES IN NEOPROTEROZOIC ALTO PARAGUAI BASIN (MATO GROSSO, BRAZIL) *

AFONSO C. R. NOGUEIRA¹, CLAUDIO RICCOMINI²

¹Departamento de Geociências, FUA, Manaus, AM; Programa de Pós-Graduação em Geologia Sedimentar, Instituto de Geociências, USP, São Paulo, SP.
²Instituto de Geociências, USP, São Paulo, SP.

Presented by ANTONIO C. ROCHA-CAMPOS

Stratigraphic analysis of terrigenous and carbonate deposits of the Alto Paraguai basin revealed two third-order sequences (1-10 m.y.), consisting of glacial, platform, tidal-, wave- and storm-dominated shoreline, fluvial and deltaic depositional systems. Each sequence begins as a lowstand system tract followed by transgressive and highstand periods. Carbonate parasequences of Sequence 1, analyzed in outcrops in the Cáceres region, Mato Grosso, attributable to the Araras and, in part, the Raizama formations, were deposited in a warm peritidal setting made up of: association (1) subtidal deposits of dolomicrite, intradolomicrite, oosparrudite, low-angle to planar cross-stratified sandstone and siltstones; and association (2) inter- to supratidal facies consisting of dolomicrite, intradolomicrite and wavy- to megaripple-bedded intraclastic sandstone. Other features in the association (2) are hemispheroidal, planar and brain-like stromatolites, fenestral and birdseye laminations, desiccation cracks, rip-up clasts, curled mud flakes, pseudomorphs of nodular gypsum, and stromaclast/tepee breccia. The stacking patterns of meter-scale shallowing/brining-up parasequences form a thickening-upward signature defined by an increase in subtidal facies. This trend is attributed to the transition of transgressive to highstand system tracts related to third-order relative sea-level rise and reflects the increase of accommodation space for each successive parasequence. The parasequence sets in the Alto Paraguai basin record a post-Varanger carbonate platform subjected to high frequency (fourth/fifth-order)/low amplitude eustatic cycles in response to lower frequency (third order)/higher amplitude sea level change. — ( December 8, 2000 )

^* Supported by: FAPESP.
E-mail: acrnogue@usp.br