“U” is for “Unusual Variations of Trace Fossil Stones” and “V” is for “The Chevron Shape of Trace Fossils”

P is for Planet in a Pebble

Q is for Quartzite Stone from Kakanui

R is for Riverton Rocks Red Rock

S is for Slope Point Stone

T is for Timaru Today

The following are my Posts for “U” and “V” in the weekly alphabetical series of a Facebook Group I belong to, “New Zealand Lapidary, Rocks, Minerals, Fossils”. The first Posts in this Series can be found here. The Series Index is here.

“U” is for “Unusual Variations of Trace Fossil Stones” – These four trace fossil stones (also known as “fossil worm cast” stones) were all found on Gemstone Beach this morning [21 September 2021]. The waves were coming unusually high up the beach so my fossicking was restricted to just a couple of hundred metres in front of the car park. The first two stones:

“Unusual” because of the sheer number of small trace fossils in the stone.

“Unusual” because of the raised trace fossil. The trace is more resistant to eroding by the sea and sand, due to being of a harder material than the rest of the stone.

Stones three and four:

“Unusual” because of the large “blobby” light-coloured trace fossil.

“Unusual” because of the light colour of the stone and trace fossil – you might need to look carefully to see it.

The waves sweeping high up Gemstone Beach this morning, just before high tide.

“V” is for “<<<<<” – the chevron shape of some of the trace fossils (also known in the south as “fossil worm casts”) to be found in argillite. A chevron is an inverted V-shaped pattern (or a series of Vs in a line of any orientation). Its first use culturally can be traced back to Bronze Age pottery designs in Knossos, Crete. The word “chevron” is French and derives its meaning from the Latin word “caprio”, or rafter, due to its resemblance to building rafters. Chevron designs are often used on badges or insignia used by military or law enforcement to indicate rank or length of service. Chevron trace fossil shapes are often viewed in the international trace fossil literature to be indicative of the “protovirgularia” trace, and usually not attributed to the activity of worms. The diagram below is from a 2010 article on protovirgularia found in Patagonia, Argentina, published in the “Journal of Paleontology”. In this article, the authors state: “Chevronate structures assigned to Protovirgularia are best understood in terms of a push-and-pull mechanism of a split-foot mollusk, either a protobranch bivalve or a scaphopod: the penetration and the terminal anchors working sequentially. The separation between successive chevrons indicates the distance that the shell moved towards the foot during protraction of the pedal retractors. The open side of the chevrons indicates the direction of locomotion” (pages 732-733 in this academic article in the Journal of Paleontology.) Photos below are of trace fossil stones from Gemstone Beach (Southland) that I have collected over the past four to five years.

Source: http://www.researchgate.net/publication/240776411_Taphonomy_and_Paleoecology_of_the_Bivalve_Trace_Fossil_Protovirgularia_in_Deltaic_Heterolithic_Facies_of_the_Miocene_Chenque_Formation_Patagonia_Argentina?fbclid=IwAR0t5u3JbTRWA06ED9FooRfoIyLxgNJA0RShF9MGYKaXiKmzop4z4Cj8Vgg

The next Post in this Series can be found here.

Author: tumblestoneblog

Retired Academic, male, living in the New Zealand countryside near Whanganui with his wife as well as Jasper the dog, Fluffy the cat, Dancer and Penny, the horses, and a shed half-full of stones. Email john.tumblestone@gmail.com. View all posts by tumblestoneblog