Sediments under the Microscope

In this video, geoarchaeologist Dr Mike Morley explains particular features of sediments from Liang Bua as we view them under a microscope.

Taking a close look at the slides helps to diagnose particular depositional environments and the ways in which sediments were deposited in the cave. We can then begin to answer the following questions:

• Was it wet or dry?
• Was it cold or warm?
• What happened to the sediments after they were deposited?
• Have they been eroded?
• Have they been heated?
• Have they been chemically modified?

Sediment Observations

The following summaries highlight key features of sediments from Liang Bua (as observed in the video above)

MM7

Cracks and voids indicate burrowing by insects or worms, or the penetration of roots by vegetation. The grey layer consists of volcanic ash blown into the cave during and/or after a volcanic eruption.

MM6

Distinctive burnt layer (consisting of fine-grained brown silts, coarse particles, limestone gravel, baked pieces of clay and charcoal) indicates evidence of fire use. The calcium carbonate layer consists of wood ash.

MM4

Presence of black material (manganese oxide) produced by water percolating through bat droppings (which are highly acidic) on to flowstones (calcium carbonate).

Conversation starter

Mike explains that bat droppings create a highly acid-loaded environment that causes chemical changes to the sediments (a process called diagenesis).

• How might these changes affect the nature of information that can be gathered about the sediments, and the fossils and artefacts contained within them?