Holocene coastal tectonics in NE Brazil

Abstract

Abstract We have identified two beachrock facies in NE Brazil which can be used as reliable sea-level indicators. Facies (a) represents the lower foreshore and the upper shoreface, being mainly characterized by coarse unsorted sandstones with trough cross-stratification, whereas facies (b) corresponds to sediments deposited on the middle to lower foreshore and is usually characterized by medium to coarse, better sorted sandstones which form seaward-dipping, swash cross beds. The age of the beachrock bodies ranges from c. 7000 to 1150 cal. a bp . Although the relative sea-level record is complicated by oscillations which are probably due to minor climatic changes, it was possible to identify a general rise at c. 7000 cal. a bp which reached its maximum of +2 m c. 5000 cal. a bp and then started to fall to its present level some 300 years later. Our sea-level data are consistent with glacio-hydroisostatic models for the region but dates of 4080 cal. a bp on shells in growth position at +5 m above sea level and 2780 cal. a bp on a beachrock at sea level east of the Carnaubais fault point to rapid, possibly coseismic, late Holocene emergence.