Stratigraphy and Holocene evolution of a regressive barrier in south Brazil

• Published in: Marine geology Vol. 165; no. 1; pp. 87 - 108
• Main Authors: Lessa, G.C., Angulo, R.J., Giannini, P.C., Araújo, A.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2000
• Subjects: Barrier; Brackish; Holocene; Marine; Sea level; Stratigraphy; ASW, Brazil, Parana, Paranagua; Barrier; Stratigraphy; Sea level; Holocene
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/S0025-3227(99)00130-9

The Paranaguá coastal plain is a 600 km 2 barrier system located in south Brazil (25° 30′ S) and is largely made up of Pleistocene and Holocene beach ridges. Sea level history in the area is characterized by a gradual, 3.5 m sea level fall in the last 5000 years. Several reverse-circulation drill logs from the Pleistocene and Holocene sectors allowed for the definition of a general morphostratigraphic model of the coastal plain, which proposes the staking of at least two generations of marine deposits upon continental and paleo-estuarine sediments. Analysis of shallow vibro-cores and exposures along back-barrier creeks indicates the existence of four transgressive (estuarine, estuarine channel, overwash and flood-tidal delta) and three regressive (beachface, nearshore and upper shoreface) sedimentary facies in the Holocene section of the coastal plain. The morphostratigraphy suggests that barrier emplacement took place at the last stages of the post-glacial marine transgression, when the back-barrier estuary was squeezed in between the Pleistocene and Holocene barriers. Holocene barrier progradation was significant in both the shore-normal and longshore direction, and was apparently very swift in the last thousand years corresponding to a period when sea level fell by 1.5 m, and when about half of the present barrier volume was accumulated. Higher progradation rates are ascribed to the arrival of sediment yielded by an active littoral drift system, which appears to have eroded large extents of several Holocene barriers along 100 km of coastline.