This is a slight expansion and rearrangement of my letter “U” contribution to the current weekly Alphabetical Series in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. In the 2021 version of this Series I posted “U is for Unusual Variations of Trace Fossil Stones”.
U is for U-Shaped Trace Fossil Found Near Ure (Waima) River Mouth
I have struggled to find a stone starting with “U” so I’ve decided to go with one I found about four years ago just south of the Ure (Waima) River mouth (see Day 24 in this Post). With a little imagination, this stone has a U-shaped trace fossil in it.
Between Kaikoura and Ward on State Highway One, not long after crossing from Canterbury into Marlborough, you come to a bridge over a river marked as “Waima (Ure) River”. Marlborough Online states: “The Waima (literally meaning white water, due to the limestone in the river bed) or Ure River has its mouth a few kilometres south of Ward, and is the southernmost river fully within the current Marlborough District… For much of its length of about 30 kms, it flows through rugged limestone gorges… The European name Ure presumably derives from the Ure River in Yorkshire which also runs through limestone country.”
Along this coast, you can find many limestone pebbles that contain trace fossils – lines of dark-coloured burrows or trails through sediment that have been preserved in the light-coloured stones. I have collected a number of them with a wide range of trace shapes and sizes. Here are four more from the same beach:
On page 64 of “A Photographic Guide to Fossils in NZ” by H. Campbell et al. (2013), it is noted that these trace fossils can be found in Muzzle Group geological strata in Marlborough, in fine-grained limestone, marl, mudstone and siltstone, laid down in deep water (over 150 metres), the traces due to burrowing activity by something like an echinoderm. An echinoderm is a marine invertebrate, like a starfish, sea urchin, or sea cucumber, that has a spiny skin and a five-part (or more) radial symmetry. Other marine animals leave traces as well.
These stones are too soft to tumble polish successfully but a short tumble in fine grit removes a thin outer layer, smooths the stone and clarifies the traces. It also often leaves a nice smooth waxy-feeling stone.
For more on this type of stone see “Selection of Tumbled Ward Beach Stones: Part 1 – Trace Fossils in Limestone”.
The next Post in this Series is “V is for Veined Vein?”. An Index for this Alphabetical Series is here.
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