摘要
Based on palynological and geochemical data(Organic Carbon-C_(org)and Sulphur-S)of sedimentary samples from a vibrocore,considerations about the palaeoenvironmental evolution of Itapeva Lake region during the Holocene are made.The analysed core(BOXVI)consists in its lowermost part of a fine to medium sand packet,rich in glauconitic minerals,whose upper limit is considered to be the Holocene-Pleistocene contact.Using Cluster analysis on palynomorphs combined with C_(org)and S data,it was possible to distinguish four zones related to the Holocene transgression-regression cycle.Variations in C_(org)and S data permitted the recognition of changes in palaeosalinity.Zone 1 represents the beginning of the Holocene sedimentation;palynomorphs composition reveals a marsh environment under predominating freshwater conditions.In Zone 2,the occurrence of dinoflagellate cysts and high S values,indicating brackish water,reflects Holocene sea level highstand around 5100yrs.B.P.High concentration of Cyperaceae associated with a significant increase in C_(org)in Zone 3 indicates a typical marsh environment influenced at least sometimes by higher saline water,reflecting a regression phase.Salvinia natans(L)All.and Cyperaceae grains are considered to be the most significant palynomorpha in Zone 4,characterising a freshwater marsh.Based on the occurrence of dinoflagellates sample 2,Operculodinium sp.,related to marine to estuarine environments,a question arises regarding about the time at which BarrierⅣbecame completely closed.
基金
This research was carried out as a part of a joint Brazilian-German project between Universidade Federal do Rio Grande do Sul,Brazil and University of Tubingen,Germany,with the support of CAPES/DAAD/PROBRAL project
The first author thanks the Brazilian Council for Sciences and Technolog BY(CNPq)for the scholarship support.
