Since 2000, Green Point has been the Global Stratotype Section and Point (GSSP) for the sedimentation line between the Ordovician and Cambrian periods. That is an official reference point used by the global scientific community when studying geology and fossils for this time period. There are high-quality formations that also cover this geological layers period in Kazakhstan, China, Australia, and Great Britain.
Logging Requirements:
1. In your opinion, is the fissal shale or the limestone HARDER? Using one to scratch the other, which one leaves part of itself on the other, thus proving that it is the softer?
2. Contrast the ribbon limestone with the conglomerate limestone. What are TWO ways they are different?
3. What is ONE difference you see between the Ordovician layers to your left with the Cambrian layer to your right.
4. Which layers, the Ordovician or Cambrian are “earlier” in the rock record? (see description); What is the approximate angle of tilt? A. 20 deg B. 50 deg C. 80 deg D. 90 deg +
Description:
This site is TRULY best viewed at low tide (INACESSIBLE “Point” between C & O at high tide!).
As you walk the beach (after going through the little fishing village just below parking cords), you should first stop at the official GSSP Marker, simply to remind yourself of the importance geologically of this spot.
As you walk towards GZ, you should notice two very different “columns” of rock, a very dark and a very light.
Shale:
The dark layers are fissal shale, and it is dark because it has its origins as a lot of organic material. Some of the shale is greenish, meaning it turned to rock at deep, oxygen poor depths of ocean.
Limestone:
The other rock is limestone, of two very different types. The first and most predominate is the ribbon limestone. (logging req #1). The other is a limestone conglomerate (jumble of rocks of differing sizes “cemented” together). About 100 feet / 30 meters prior to reaching GZ you will see a single wide layer of this conglomerate (logging requirement #2). This single conglomerate layer was formed by an underwater landslide which brought the undersea rocks and sediment down the sloping sea floor in a jumble that later “cemented” together. The thin limestone layers are sometimes “rippled” because of either tectonic compression or sediment compression.
The formation:
The formation at Green Point formed offshore to the east and was pushed onto the Humber zone as part of the Humber Arm allochthon. It provides an incredible range of years of deep water sediment accumulation in the Iapetus ocean near the continental slope. Over 10,000 fossils (mostly microscopic) have been found at Green Point, and have been used to date the sediment layers and determine that Bed 23 (GZ) is the dividing line between the two time periods because of the discovery of a specific conodont, Iapetognathus fluctivagus.
Normally younger sedimentary rock layers lie above older rock layers. However, as you can see at GZ, the layers are dramatically tilted. When you arrive at GZ, you are standing at the official O-C boundary. Logging requirements ask for you to assess what you see.
Terms:
Stratotype -- an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale.
According to Wikipedia, there are several GSSP criteria including:
• A GSSP has to define the lower boundary of a geologic stage. • The lower boundary has to be defined using a primary marker (usually first appearance datum of a fossil species).
• There should also be secondary markers (other fossils, chemical, geomagnetic reversal).
• The horizon in which the marker appears should have minerals that can be radiometrically dated.
• The marker has to have regional and global correlation in outcrops of the same age
• The marker should be independent of facies.
• The outcrop has to have an adequate thickness
• Sedimentation has to be continuous without any changes in facies
• The outcrop should be unaffected by tectonic and sedimentary movements, and metamorphism
• The outcrop has to be accessible to research and free to access. Conodont – jaw like fossil remains of a prehistoric extinct marine animal likely related to the lamprey
Iapetognathus fluctivagus -- This is the Conodont fossil that is the “index datum” that helps define the line “fossil-wise” between the Ordovician and Cambrian periods.
Conglomerate – sedimentary rock that has a lot of rounded rocks (larger than grains of sand) cemented together in a matrix. Conglomerate is formed from pebble sized and larger clasts. Non-geologists often think of it as "concrete." in contrast, limestone is composed of finer grain material, sand sized or smaller.
Resources:
Hild, Martha Hickman., and Stephanie Porter. Geology of Newfoundland: Touring through Time at 48 Scenic Sites. Portugal Cove-St. Philip's, N.L.: Boulder Publications, 2012. Print.
International Commission on Stratigraphy www.stratigraphy.org "Global Boundary Stratotype Section and Point." Wikipedia. Wikimedia Foundation, 07 Nov. 2013. Web. 15 July 2013.
"Iapetognathus Fluctivagus." Wikipedia. Wikimedia Foundation, 30 June 2013. Web. 15 July 2013.