Geochemical and petrographical characterization of fine-grained carbonate particles along proximal to distal transects

The origin of carbonate ooze particles is often poorly understood. This is due to their polygenic origin and potential post-depositional alteration. Here, the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown. The focus is on grain size and morphology, mineralogy and isotope signatures. Two contrasting proximal-to-distal transects were investigated: (1) the Miocene leeward margin of Great Bahama Bank (ODP Leg 166) and (2) the transition between the Maiella platform and the Umbria-Marche basin in central Italy near the Cenomanian-Turonian boundary. In both case settings, carbonate partides of biogenic origin include at least three groups of organisms: (i) planktonic foraminifera, (ii) calcareous nannofossils and (iii) fragments of unspecified neritic skeletal material. Two further particle types lack diagnostic structures, and based on particle size and mineralogy, are here referred to as (iv) macroparticles (5-20 mu m, mainly xenomorphic) and (v) rnicroparticles (< 12 mu m, mainly automorphic to sub-automorphic). Macro- and microparticles represent 50 to 80% of the carbonate phase in slope and toe-of-slope domains and share characteristic carbon and oxygen isotope signatures. Macro- and microparticles are considered shallow-water precipitation products subsequently exported into the slope and toe-of-slope domains. Macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and/or bioinduced precipitation in the water column. In some cases, macro- and micropartides may have an early diagenetic origin. The identification of the origin of fine-grained particles allows for a quantitative assessment of exported, in situ and diagenetic carbonate materials in periplatform environments. The data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite. (c) 2012 Elsevier B.V. All rights reserved.