Speleothem architectural analysis: integrated approach for stalagmite-based paleoclimate research

Abstract

Carbonate stalagmites have become increasingly attractive to Quaternary paleoclimate research, as they can be accurately dated by radiometric methods and concurrently yield high-resolution multi-proxy records of past climate conditions. Reliable series however require the precise characterization of stalagmite internal micro-stratigraphy, a task too often poorly accomplished despite the recent advances in speleothem research. This weakness is due to the lack of a robust integrative methodological framework capable of integrating the wide range of petrographical and micro-stratigrafical methods currently used in speleothem characterization. For covering this need, this review introduces the Speleothem Architectural Analysis (SAA), a holistic approach inspired in well-established stratigraphic procedures such as the architectural element analysis and the sequence stratigraphy, commonly used by geoscientists for categorizing internal stratigraphic heterogeneities in sedimentary deposits. The new approach establishes a six-fold hierarchy of speleothem architectural elements and their bounding surfaces: individual crystallites (1st order), single growth layers (2nd order), speleothem fabrics (3rd order), stacking patterns sets (4th order), morphostratigraphic units (5th order), unconformity-bounded units and major unconformities (6th order). Each category of architectural element is formed in a different range of time, from intervals as short as a year/season to others of centuries or millennia. The SAA, which has the capability of incorporating any petrographic or stratigraphic classification, provides a useful, systematic, and versatile tool for unraveling the complexities of speleothem growth, and thus for genetically interpreting stalagmites in a multi-temporal scale. A detailed speleothem stratigraphy must be the basis for performing robust reconstruction of paleoclimate series. They should precede and accompany any work focused in absolute age dating or in reconstructing paleoclimate by means of any geochemical proxy.