Late paleozoic glacial sedimentation in Northeastern Brazil: new results

LATE PALEOZOIC GLACIAL SEDIMENTATION IN NORTHEASTERN BRAZIL: NEW RESULTS

J

^*1

and MARCIA ERNESTO ²

¹

²Instituto Astronômico e Geofísico, USP, São Paulo, SP.

A glacial origin for late Paleozoic rocks of the Batinga Formation (Sergipe-Alagoas Basin) and Curituba Formation (Santa Brígida graben) are now well established on the basis of occurence of diamictites bearing faceted and striated clasts in places resting on glacially striated Precambrian pavement, intraformational soft-sediment, glacially and floating ice striated surfaces, and rhythmites containing dropstones. Additional studies have been performed on these rocks including facies analysis and regional compilation of orientation of glacial striae and paleocurrent, and of subsurface data. This allowed the delineation of a broad paleoenvironmental and paleogeographic picture of the glacial deposits. Facies distribution suggests a SE-NW change from more proximal glacial conditions in the Batinga Formation to distal (probably glacial marine) conditions in the Curituba Formation. Striae on pavements and surfaces are consistently oriented from SE-NW. Sense of movement of glacier cannot be clearly established. Local evidence, however, may indicate flow toward SE. Lithofacies and isopach maps depict a major depocenter of the Batinga Formation situated to the SE of the Igreja Nova dome, suggesting that this structure may have behaved as an elevated area in the late Paleozoic.

Preliminary paleomagnetic results indicate a mean magnetization direction of declination of approximately 185^o and inclination of 43^o, similar to the magnetization of other South American late Paleozoic formations. The magnetization of the Batinga sediments was acquired in a geomagnetic field of reversal polarity that was dominant during the Permo-Carboniferous ( Kiaman superchron). The shallow inclination (about 43^o) indicates that the studied area was located at a low latitude (about 25^oS) during the acquisition of the magnetic remanence. (December 10, 1999)

^*Scholarship holder PIBIC-CNPq.

Scholarship holder PIBIC-CNPq.

Publication Dates

• Publication in this collection
  05 Jan 2001
• Date of issue
  Dec 2000