From: Pedley, H. M. & Carannante, G. (eds) 2006. Cool-Water Carbonates: Depositional Systems and Palaeoenvironmental Controls. Geological Society, London, Special Publications, 255, 307–322. 0305-8719/06/$15.00 # The Geological Society of London 2006. Chemostratigraphy in Miocene heterozoan carbonate settings: applications, limitations and perspectives MARIA MUTTI 1 , CE ´ DRIC M. JOHN 1,2 & ANDREA C. KNOERICH 1 1 Institut fu ¨r Geowissenschaften, Universita ¨t Potsdam, PF 601553, D-14415 Potsdam, Germany (e-mail: mmutti@geo.uni-potsdam.de) 2 Present address: Department of Earth Sciences, University of California, Santa Cruz, USA Abstract: The temporal variability of geochemical proxies can be used in time intervals characterized by global changes in marine chemistry to achieve improved stratigraphic correlation. The application of this approach in rocks lithified by cementation requires particular attention, as the original isotopic signature may have been modified by diagenetic processes and, when bulk samples are used, could reflect facies-specific compositional changes as opposed to primary changes in the water column. This paper examines sedimentological and chemostratigraphic records from outcrops in the central Mediterranean and cores drilled on the Marion Plateau by the Ocean Drilling Program (ODP) Leg 194, where heterozoan carbonates accumulated during the Miocene. Specifically, the paper addresses how facies and preservation of original marine signatures differentially affect the quality of the dataset. The analysis indicates that, in general, heterozoan systems, relative to their tropical counterparts, show good preservation of marine signatures. Chemostratigraphy offers a viable low-resolution alternative for dating platform sediments considering the general lack of biostratigraphic markers in these settings. It is stressed, however, that care must be taken when interpreting these values, especially when the dataset is at a low resolution or when post-depositional dolomitization took place. Furthermore, chemostratigraphy in shallow-water environments cannot be done without detailed facies analysis, as facies changes may impact bulk-rock stable isotope values. Using the variability of geochemical proxies to achieve improved stratigraphic correlation (che- mostratigraphy) is a common method in palaeo- ceanographical studies of younger Neogene sediments, commonly unlithified and relatively unaltered (e.g. Keigwin 1979). The geochemical proxies used depend on the time interval targeted, but most commonly include carbon isotope ratios, oxygen isotope ratios and strontium isotope ratios of skeletal carbonate. The application of chemos- tratigraphy to lithified rocks requires additional considerations, as the original isotopic signature may have been modified by diagenetic processes. Chemostratigraphy in rock samples has been pioneered in Tethyan pelagic settings of Jurassic (Jenkyns & Clayton 1986; Jenkyns et al. 1994) and Cretaceous ages (Weissert 1989; Scholle & Arthur 1980; Weissert & Breheret 1991). Building on these successful applications, chemostratigra- phy in rock samples has been applied increasingly to a range of carbonate settings, spanning from pelagic to neritic (e.g. Vahrenkamp 1996; Drze- wiecki & Simo 1997; Gro ¨tsch et al. 1998; James et al. 2004). The degree of stratigraphical resolu- tion attained is highly variable, depending on (1) intrinsic limitations (such as isotopic homogeneity in the oceans, residence time of the specific geochemical parameter, rates of change through time), (2) the quality of the dataset (such as analysis of bulk rock vs. single component analy- sis) and (3) the preservation of original marine signatures and, therefore, the extent and nature of diagenetic processes. This paper explores the use of chemostratigra- phy in heterozoan carbonate environments depos- ited during the Miocene, and, using a selected number of case studies spanning different deposi- tional settings, discusses limitations and perspec- tives of this method. Specifically, how facies and preservation of original marine signatures differ- entially affect the quality of the dataset are addressed. Because the time-resolution of the studies discussed in this paper is lower than the residence time of all proxies considered here, homogeneity and residence time in the ocean are not discussed further. Miocene heterozoan carbonates Heterozoan carbonates (sensu James 1997) are widespread during the Miocene. A major compila- tion at the Mediterranean scale (Esteban 1996;