BARBOSA, CATIA F.
Dept. Geologia/UFF, Av. Litoranea s/n., 24210-340. Niteroi, R.J., Brazil

Abstract: Foraminifera and Arcellacea Zonation as Sea Level Indicators in Brazilian Mangroves and Freshwater Marsh

The zonation of mangrove foraminiferal associations expressed by small vertical variations in biofacies is applicable to sea level fluctuation studies. For that purpose, foraminiferal and thecamoebian zonations were carried out in the mangrove around Guaratuba estuary (Parana, southern Brazil), and around the incipient brackish mangrove of Saquarema, and the freshwater marsh of Jacarepia lagoons, (Rio de Janeiro, southeastern Brazil). Each coastal sedimentary environment differs in latitude, climate, physico-chemical conditions, botanical zonation and lithofacies. Standard 10 cc samples were collected at stations and detailed topography of transects was carried out from low tide, up to high higher water, with the lower limit of vegetation taken as mean tide level. Topography and salinity influence the distribution of three biofacies zonation. The higher supratidal topographic biomarker Haplophragmoides spp. is dominant in both regions, under different environments and salinity. In this zone Trochammina inflata occurs in Parana, and Trochammina macrescens in Rio as salinity sensitive. This zone is the best sea level indicator as it has a small vertical range (12 cm) and marks the spring tides, being also the most consistent. However, as far as presently known, the preservation potential of Haplophragmoides in cores is poor. In intertidal zone, salinity biomarkers of Parana are Trochammina inflata, Polysaccammina hiperalina, and Miliammina fusca. Trochammina macrescens occurs in Saquarema and Centropyx aculeata predominates in Jacarepia. Infratidal zone in Parana presents Arenoparella mexicana, Tiphotrocha comprimata, T macrescens f. macrescens and Difflugia oblonga; T macrescens f. polystoma predominates in Rio.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas