Distribution of calcareous nannofossils in Upper Eoceno-Upper Miocene deposits from Northern Colombia and the Caribbean sea

Zusammenfassung

In this work, a detailed study based on the genus Sphenolithus was carried out in three sequences. Two were recovered onshore in Colombia �the Arroyo Alférez and Carmen de Bolívar, Estratigráfico 4 sequences� and one offshore, in the Caribbean Sea �ODP 999�. In all sequences the record is generally continuous and the preservation of the nannofossil assemblage is good. In this research, the standard biozonations of Martini (1971), Bukry (1973, 1975) and Okada & Bukry (1980) for the late Eocene to the late Miocene were used. Sphenolithus is consistently present in the sequences. Differences among the patterns of distribution, abundance and morphological aspects of Sphenolithus spp. were analyzed. The results of the study highlight certain taxonomic problems and the almost complete absence of paleoecological reconstruction, reflecting the fact that there have been relatively few studies undertaken on the Sphenolithus group in recent decades. Here, some of these limitations are overcome by combining the biostratigraphic Caribbean�Colombian pattern and morphometric analyses of selected taxa of Sphenolithus. Exceptional abundances in Sphenolithus heteromorphus were recorded in both the ODP 999 and Carmen de Bolívar, Estratigráfico 4 sections. Also, a very high abundance in Sphenolithus abies was identified in ODP 999. Both S. heteromorphus and S. abies become the dominant components of the nannofossil assemblage, constituting the SDI (Sphenolithus Dominance Interval) episodes. During the SDI, the dominance of smaller specimens of S. heteromorphus and S. abies was observed. Sphenolithus is considered to be a proxy for oligotrophic conditions that is adapted to an enhancement in ocean stratification, with a positive response to increases in superficial temperatures. In Northern Colombia and the Caribbean Sea, Sphenolithus had its SDI in both shallow�water (Carmen de Bolívar, Estratigráfico 4) and open marine (ODP 999) paleoenvironments.