Some aspects of petrification of Miocene wood from Kaipara Harbour, New Zealand 

Sutherland, J. I. 

 

 

 

Chapter in book 

Silicified woods of probable Altonian (Lower Miocene) age occur in southeast Hukatere Peninsula, Kaipara Harbour, New Zealand. Pyroclastic flows, apparently flowing from a northerly direction, carried woods from a broadleaf - podocarp forest to mix with probable Avicennia (mangrove) growing in estuarine conditions close to the site of preservation. Many woods were partially or completely carbonized by the flow. Thin section petrography, scanning electron microscope micrographs, and X-ray diffractograms indicate the woods were silicified by silica in solution, formed by devitrification of volcanic glass. The sequence of silicification is likely to have been either opal - A -> opal - CT -> alpha - quartz and chalcedony, or directly to alpha - quartz and chalcedony. The degree of crystallinity of the quartz is not time dependent. The mode of occurrence of alpha - quartz, chalcedony, cristobalite, tridymite, lussatite and amorphous opal is described. Other minerals present in the woods include goethite and members of the saponite group, as well as organic compounds. (auth) 

 

saponite; nzms260q09; crystallinity; petrography; volcanic glass; opal; silica; devitrification; goethite; tridymite; fossil wood; chalcedony; miocene; x-ray diffraction; silica minerals; silicification; Kaipara harbour; minerals; nzms260q08; quartz; cristobalite; Biogeophysical