Carbonate systems

The know-how in carbonate systems requires digging into the basic concepts to increase interpretative accuracy and succeed in predictions. The more in-depth the knowledge about how fundamental processes work in the construction of the sedimentary record, the more efficient the resolution of problems.

However, there is a tremendous asymmetry in the knowledge of the processes operating in siliciclastic systems and the processes running in carbonate systems. Whereas siliciclastics mostly require understanding the physical laws, carbonate systems are derived from biological systems and need additional knowledge in the evolution of life first, second in the biotic responses to environmental changes and third in how environmental conditions have been changing on Earth. The implicit concatenation of these requirements, and the increased uncertainties when considering carbonates generated from older extinct biotas, has delayed the conceptual understanding of the development of carbonate systems. However, recent advances in ecology and palaeoecology, increase in palaeoenvironmental proxies and the progress in molecular evolution and the palaeobiological revolution are providing the basis to face the study of carbonate systems much more efficiently and diminishing the risk of unrealistic predictions.

In the first introductory section, the knowledge space in Sedimentary Geology is analyzed, placing the emphasis in the transfers of energy and matter existing in siliciclastic and carbonate systems, leading to frame the concept of carbonate factories: the sediment source.

Most carbonate rocks are of biological origin and photosynthesis is the primary step in organic production, at the base of the food web. Autotrophic processes in aquatic systems require inorganic carbon (IC), protons, nutrients and energy. When the proton donor is water, the subproduct is oxygen, but taking the proton from bicarbonate the subproduct is carbonate. ‘Food and feeding/follow the food’ section focuses on the analyses of the carbonate precipitation mechanisms and of the interrelated food web: the grazer chain and the microbial, picoplankton and sponge loops.

Light for energy and the hydrodynamic regime as the carrier for dissolved nutrients and organic carbon (food) are the most basic requirements for organic and hence carbonate production. ‘Boundary layers’ section provides insights into the impact of the boundary layers conditions: light and energy.

One sentence summarizes ‘Feed and food: feasting at the pycnoclines’ section. Feeding and feasting are behind the organic production and carbonate precipitation. Next, in ‘Carbonate production modes’ section, come the analyses of the different carbonate precipitation modes resulting from the complex interaction between ambient water chemistry and life. ‘Carbonate production systems through Earth’s history’ section examines the products of these complex interactions from the Archean to the Neogene.

‘Platform types’ section establishes the main typologies of carbonate platforms through the analyses of a series of case studies. The chapter ends with a corollary discussing (1) the interaction between factories (promotion vs suffocation), (2) the types of responses of carbonate platforms to external changes (linear vs nonlinear), (3) the uses and misuses of skeletal sediment associations and (4) the obstinate misuse of the sequence stratigraphic concepts in carbonate systems.