Micrograph of the Month: Calcareous cave sediments from Fiji

This month we have a beautiful set of micrographs from a limestone cave on the Rove Penninsula of Fiji. These samples were collected as part of a pilot study with the University of the South Pacific way back in 2007, when I was avoiding finishing PhD write up and decided to go do some field work in the South Pacific, as you do. The samples come from a test pit that was excavated to identify the sequence of sediments within the cave, and to assess whether there was any Lapita occupation. The micromorphology samples were collected to identify activity traces that may be associated with the occupation. In the end the samples were not prioritised as the dates suggested that the occupations were much more recent, within the past 1000 years. However I do like to go back to them time to time, and will hopefully write something properly on them when I have time. For now I will share these beautiful images, maybe some of the most beautiful I have seen! The cave was incredibly humid, in fact there was a trowel from the previous seasons' survey with a wooden handle that had completely decomposed! This has also led to a fairly rapid decay of the roof collapse material. Despite being composed of limestone, cutting through these samples blocks was like slicing through fudge - the sediments are remarkably soft. The upper left image shows how the soft sediments have become mixed with bits of bone, the upper right shows the incorporation of charcoal. All of the images show skeletal material of various marine organisms. I am not an expert on these creatures, but my guesses are that we have various types of forams, along with coral. If any geologists would like to help me identify these beasties I'm very open to working with you to write up these slides!


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