VOLUME CHANGE ACCOMPANYING CLEAVAGE DEVELOPMENT IN GRAPTOLITIC SHALESFROM GISBORNE, VICTORIA, AUSTRALIA

Studies on shape changes in deformed Oncograptus upsilon combined with strain analysis of pressure shadows around framboidal pyrite revealed that a small volume change of the order of 5 percent accompanied the cleavage development in the shales from Gisborne, Victoria. Starting f rom the proximal end, Oncograptus upsilon exhibits progressive increas e in the spacing between successive thecae along the stipes. A new tec hnique utilizing the distance between a specific number of thecae is u sed for computing the change in length along stipes of Oncograptus ups ilon. The low volume change, accompanying a more than 70 percent short ening deformation, indicates that there is a less significant mass los s during cleavage development than has been inferred from some studies on volume change from thecal spacing in deformed graptolites.