HIGH-RESOLUTION STRATIGRAPHY AND SEDIMENTARY EVOLUTION OF COARSE-GRAINED CANYON-FILLING TURBIDITES FROM THE UPPER CRETACEOUS TRANSGRESSIVE MEGASEQUENCE, CAMPOS BASIN, OFFSHORE BRAZIL

Coniacian to Lower Maastrichtian coarse-grained turbidites fill intra- slope, fault-controlled canyons in the Campos Basin, off-shore Brazil. They form part of an Upper Albian to Lower Paleocene transgressive su ccession characterized by onlapping, deepening upward sedimentation th roughout the eastern Brazilian margin. In the Carapeba and Pargo (CRP PG) oil fields the turbidites consist mainly (> 95%) of graded beds wi thout any other sedimentary structures, Individual beds are up to 12 m thick and are composed of small pebble (< 2 cm) to granule-rich sands tones, and medium to very coarse sandstones, The finer-grained portion s of these graded beds show better sorting and higher porosity, and th ese characteristics can be recognized in density logs, Use of 92 densi ty logs calibrated with 13 cores permitted the mapping of 198 coarse-g rained turbidites in the CRP-PG turbidite system. The turbidites form eight thinning- and fining-upward facies successions, some bounded by regional unconformities or local erosion surfaces, The successions are 27-140 m thick and contain 7-58 turbidites. Their durations are estim ated to be between 0.4-0.9 m.y. They form 1-12 km wide, tabular or lin guoid sandstone bodies in which the younger or more distal turbidites become finer-grained, thinner bedded, and more discontinuous upsection and downcanyon. The successions are stacked in an overall retrogradat ional pattern for at least 20 km, recording the backfilling of the CRP -PG canyon. Turbidites in the CRP-PG area were probably deposited duri ng falls of relative sea level that punctuated the overall transgressi ve setting of the late Cretaceous and early Tertiary, There is a misma tch between the number of successions (eight) and the number of time-e quivalent third-order fluctuations of relative sea level (four and par t of a fifth; Haq et al 1988), suggesting that eustatic sea level fluc tuation was not the dominant control on most of the successions, Cross sections and isopach maps of the successions do not suggest internal channeling, and a channel-fill origin for the fining- and thinning-upw ard successions seems unlikely, We therefore suggest that episodic tec tonic re activation in the uplifted Precambrian source area, and fault ed basin margin, led to relatively abrupt increases in the volume of s ediment supplied to the head of the canyon across a narrow shelf, Stea dy denudation and decreasing supply of sediment led to formation of th e fining- and thinning upward successions.