THE APPLICATION OF SEM-EDS FOR THE SURFACE TEXTURE OF FORAMINIFERA: IDENTIFICATION OF EARLY DIAGENESIS OF REWORKED L. DIMIDIATUS WITHIN MODERN COASTAL DEPOSITS

Rahmadi Hidayat, Sarju Winardi, Akmaluddin Akmaluddin

Abstract


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. SEM-EDS 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.


Keywords


scanning electron microscope, sediment reworking, foraminifera, L. dimidiatus

Full Text:

PDF

References


Chakroun, A., Miskovsky, J.-C., and Zaghbib-Turki, D., 2009. Quartz grain surface features in environmental determination of aeolian Quaternary deposits in northeastern Tunisia. Mineralogical Magazine, 73(4): 607–614.

Chave, K.E., 1954. Aspects of the Biogeochemistry of Magnesium 1: Calcareous marine organisms. Journal of Geology, 62(3): 266–283.

Chen, L., Xu, J., and Chen, J., 2015. Applications of scanning electron microscopy in earth sciences. Science China Earth Sciences, 58(10): 1768–1778.

Dewi, K.T., Priohandono, Y.A., and Masduki, A., 2016. Abnormal microfaunal shells as early warning indicator of environmental changes surrounding Berau Delta, East Kalimantan. Bulletin of the Marine Geology, 26: 31–40.

Dewi, K.T., Nurdin, N., Priohandono, Y.A., and Sinaga, A., 2015. Benthic foraminifera in marine sediment related to environmental changes off Bangka Island, Indonesia. Berita Sedimentologi, 33: 47–54.

Hidayat, R., 2022. Late Quaternary evolution of Robe Range, southeast South Australia: An archive of deposition and destruction of a coastal barrier complex. Unpublished Ph.D Thesis, University of Wollongong.

Hidayat, R., Murray-Wallace, C. V., and Jacobs, Z., 2023. Late Pleistocene evolution of Robe Range , southern Australia – The timing and carbonate source dynamics of coastal dune development. Marine Geology, 456: 106987.

James, N.P., and Bone, Y., 2011. Neritic carbonate sediments in a temperate realm: Southern Australia. Springer Netherlands, 254p.

James, N.P., Bone, Y., Joury, M., Malcolm, I., and Kyser, T.K., 2018. Diagenesis and compositional partitioning of Quaternary cool-water carbonate aeolianites: southeastern Australia. Journal of Sedimentary Research, 88(4): 431–448.

Joury, M.R.F., James, N.P., and James, C., 2018. Nearshore cool-water carbonate sedimentation and provenance of Holocene calcareous strandline dunes, southeastern Australia. Australian Journal of Earth Sciences, 65(2): 221–242.

Khadkikar, A.S., and Basavaiah, N., 2004. Morphology, mineralogy and magnetic susceptibility of epikarst-Terra Rossa developed in late Quaternary aeolianite deposits of southeastern Saurashtra, India. Geomorphology 58(1-4): 339–355.

Krinsley, D.H., and Doornkamp, J.C., 1973. Atlas of quartz sand surface textures. Cambridge University Press, 102p.

Loucks, R.G., and Patty, K., 2017. Vadose diagenetic dissolution textures, cementation patterns, and aragonite and Mg-calcite alteration in the Holocene Isla Cancun eolianite aragonitic ooids: modern analog for ancient ooid-grainstone pore networks. Gulf Coast Association of Geological Societies, 6: 1–20.

Miller, D., Westphalen, G., Jolley, A.M., Rutherford, H., Colella, D., and Holland, S., 2009. Marine habitat within selected areas of the South East NRM Region. Department for Environment and Heritage, Government of South Australia.

Murray-Wallace, C.V., 2018. Quaternary history of the Coorong Coastal Plain, Southern Australia: An archive of environmental and global sea-level changes. Springer International Publishing, Switzerland, 229p.

Murray-Wallace, C.V., Brooke, B.P., Cann, J.H., Belperio, A.P., and Bourman, R.P., 2001. Whole-rock aminostratigraphy of the Coorong Coastal Plain, South Australia: Towards a 1 million year record of sea-level highstands. Journal of Geological Society London, 158: 111–124.

Ohmori, H., Endo, K., Uesugi, Y., and Horikoshi, M., 1987. Stratigraphy and geomorphologic history of Holocene dunefield near Millicent along the southeastern coast of South Australia. Journal of Geography (Chigaku Zasshi), 96(1): 1–22.

Oliver, T.S.N., Murray-Wallace, C. V., and Woodroffe, C.D., 2019. Holocene shoreline progradation and coastal evolution at Guichen and Rivoli Bays, southern Australia. Holocene, 30: 106–124.

Oliver, T.S.N., Tamura, T., and Murray-Wallace, C.V., 2020. Identification of reworked foraminifera in temperate carbonate sediments – A pilot study from the Coorong Coastal Plain, southern Australia. Marine Geology, 421: 106096.

Reeckman, S.A., and Gill, E.D., 1981. Rates of vadose diagenesis in Quaternary dune and shallow marine calcarenites, Warrnambool, Victoria, Australia. Sedimentary Geology, 30(3): 157–172.

Rivers, J.M., James, N.P., Kyser, T.K., and Bone, Y., 2007. Genesis of palimpsest cool-water carbonate sediment on the continental margin of southern Australia. Journal of Sedimentary Research, 77: 480–494

Short, A.D., 2020. Australian Coastal Systems. Springer International Publishing, 1256p.

Vos, K., Vandenberghe, N., and Elsen, J., 2014. Surface textural analysis of quartz grains by scanning electron microscopy (SEM): From sample preparation to environmental interpretation. Earth-Science Reviews, 128: 93–104.




DOI: http://dx.doi.org/10.32693/bomg.38.2.2023.831