The Application of SEM-EDS for the Surface Texture of Foraminifera: Identification of Early Diagenesis of Reworked L. dimidiatus within Modern Coastal Deposits
Sediment recycling has been known to occur within Quaternary coastal barriers of the greater
Coorong Coastal Plain, southern Australia. A high degree of reworking of skeletal carbonates from Late
Pleistocene deposits (Robe Range) is evident based on the novel application of amino acid dating of the
single-foraminifera species Lamellodiscorbis dimidiatus. More importantly, some apparently transparent,
well-preserved tests indicate anomalously high extents of amino acid racemization, implying that reworked
fossils could not be easily distinguished based on taphonomic signatures such as corrosion. Here, we
examine the surface microtexture of this species, constrained with well-preserved specimens, on a modern
beach of Canunda, southern Australia, using scanning electron microscopy coupled with energy dispersive
spectroscopy (SEM-EDS). The aim is to identify surface features of foraminifera in more detail, capturing
signs of early diagenesis associated with weakly consolidated Late Pleistocene coastal barriers. The results
reveal that some well-preserved tests show localized blocky calcite cementation, most notably within
intraseptal spaces or impact sites. The EDS spectra of cement indicate lower Mg content than unaltered
foraminifera surface. This suggests low-Mg calcite precipitation due to meteoric diagenesis experienced by
the onshore Late Pleistocene coastal barrier. It implies that these foraminifera shells are reworked fossils
originated from older successions and were subsequently redeposited within the present-day beach. SEMEDS
used in this study demonstrates its capability in examining small-scale carbonate diagenesis products
beyond the traditional binocular microscope. Thus, this tool is recommended to aid amino acid dating in
detecting reworked fossils.
