Lacustrine carbonates in rift settings: the interaction of volcanic and microbial processes on carbonate deposition

Abstract

Abstract The relatively simplistic facies models for lacustrine carbonates do not currently incorporate either the diversity of microbialite carbonate development or the influence of volcanic-related processes found in rift settings. The basic nature of the carbonate factories in these systems, whether microbial, macrophytic, skeletal or abiogenic, is not resolved. Lacustrine microbialites can develop in shallow lakes as concentrations of microbialite mounds covering many hundreds of square kilometres, or as bathymetrically controlled facies belts, but in many rift settings vent-related thermal and non-thermal carbonates (travertines and tufas) are a major component. Subaqueous vent-related carbonates, with evidence of microbial activity, can produce seismic-scale carbonate build-ups in deeper lakes or apparently more stratiform accumulations in shallow lakes. In lakes with only volcanic catchments, Mg and silica activity, coupled with high carbonate alkalinity and microbial influences, can potentially generate a complex set of mineral–microbe interactions and products, creating a unique set of challenges for predicting and understanding reservoirs in such settings.