The Neritic Carbonate Factory
Carbonate sediments in the vast cool-water, mid-latitude marine environment of southern Australia are fundamentally different from warm-water neritic, tropical carbonates. They are heterozoan and palimpsest, not photozoan and modern. Heterozoan particles (cf. James 1997) are biogenic, the only phototrophs are red calcareous algae, the only mixotrophs are large benthic foraminifers, and most of the benthic invertebrates from whence the particles came are filter feeders (Fig. 4.1). The sediments are palimpsest because they form relatively slowly and are mixed together with grains generated during earlier periods of deposition in this overall high-energy setting. Only recently has it been possible to recognize, separate, and interpret these particle types (Rivers et al. 2007). The different and progressively older particles formed at separate times are recognized herein as (1) relict (~70–25 ka), (2) stranded (18–10.4 ka), and (3) Holocene (<10.4 ka) grains. Today, the seafloor sediments are a mixture of particles of several ages, each of which reflect a different set of environmental controls (Fig. 4.2). The term recent is used herein to encompass all particles formed since the LGM and during MIS 1 and 2 and therefore includes both stranded and Holocene particles. This chapter is a description of the Holocene sediments, and by implication, stranded materials produced on the modern shelf. Relict particles have been documented in Chap. 3.