Middle Eocene mixed carbonate-siliciclastic systems in the southern Caribbean (NW colombian margin)

Abstract

Middle Eocene carbonates and mixed carbonate-siliciclastic deposits occur in disconnected outcrops in the San Jacinto Fold Belt in northern Colombia. Three lithofacies were distinguished: A) claystones and siltstones with planktonic components; B) packstones/rudstones with red algae and claystone-siltstone rip-up clasts in medium to thick plane-parallel, plane-convex, and channel-shaped beds; and C) poorly-bedded rhodolith rudstones with minor larger benthic foraminifers. The latter are interpreted as rhodolith beds accumulated in middle-ramp settings. Lithofacies B consists of bioclasts from the middle ramp redeposited as sediment gravity flows in individual beds and in small channel-lobe systems in the outer ramp and slope. The autochthonous sedimentation basinward from the middle ramp was dominated by hemipelagic claystones and siltstones (Lithofacies A). In outcrops with exposure of vertical successions, these facies are arranged in a transgressive pattern. The limited continuity of outcrops prevents any assessment of the original extension of ramps and lateral dimensions of channel-lobe systems. Comparison with modern tropical rhodolith beds suggests that the middle Eocene carbonate factories in the southern Caribbean developed on ramps under mesotrophic conditions.