WATER STRATIFICATION IN COASTAL LAGOONS - ITS INFLUENCE ON FORAMINIFERAL ASSEMBLAGES IN 2 BRAZILIAN LAGOONS

Foraminiferal assemblages were studied in two Brazilian stratified lag oons: the restricted Cananeia-Iguape lagoon which exhibits inclined wa ter stratification and the choked Lagoa da Conceicao, where strong hor izontal stratification occurs during the rainy season. Water stratific ation has been shown to influence the distribution of foraminiferal as semblages. In the restricted lagoon, the transition from marine to con tinental water conditions induces a progressive change in foraminifera l assemblage, both horizontally and vertically. In the choked lagoon, the presence of two different water masses separated by a halocline le ads to the presence of two distinct assemblages. The first, located in the depressions, characterized by the dominance of rotaliids indicate s a stronger marine influence. The second, present in the shallow wate r, characterized by textulariids, indicates more restricted conditions . The dominance of calcareous species in the depressions, where organi c rich sediments are potentially liable to dissolve calcareous tests s hows that, even if it may greatly modify the thanatocoenoses, the diss olution does not destroy all the information. The differential impact of stratification on foraminiferal assemblages from these two sites cl early demonstrate: (1) that it is impossible to propose a universal mo del for foraminiferal distribution in lagoons; but (2) that the forami niferal assemblages can provide valuable information for modem hydrody namics and, with some caution, also for fossil lagoonal environments. (C) 1998 Elsevier Science B.V. All rights reserved.