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The GSSP assigned to each stage is that stage's lower boundary and oldest point. Ages are given in "million year ago" (mya). They are obtained with different radiometric dating methods depending on the type of rock and its age. Ages that have a tilde (~) prefix are approximate ages for GSSPs that have not been defined or not been accurately dated.
A geologic section has to fulfill a set of criteria to be adapted as a GSSP by the ICS. The following list summarizes the criteria: [2] [3] 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).
Dob's Linn is important in geology as the location of the Global Boundary Stratotype Section and Point (GSSP) [3] which marks the boundary between the Ordovician and Silurian periods, and marks the base of the Llandovery epoch, on the geologic time scale. Dob's Linn was ratified as the GSSP by the International Union of Geological Sciences in ...
The Precambrian-Cambrian boundary lies 2.4 m above the base of the second member, which is the lowest occurrence of Treptichnus pedum. The traces can be seen on the lower surface of the sandstone layers. The first calcareous shelled skeletal fossils (Ladatheca cylindrica) are 400 m above the boundary.
The Wenlock's beginning is defined by the lower boundary (or GSSP) of the Sheinwoodian.The end is defined as the base (or GSSP) of the Gorstian. [9]The Wenlock is divided into the older Sheinwoodian and the younger Homerian stage.
Fortune Head is a headland located about 1.6 km (0.99 mi) from the town of Fortune on the Burin Peninsula, southeastern Newfoundland.. A 140 m (460 ft) thick section of rock along its cliffs is designated the Global Boundary Stratotype Section and Point (or GSSP) representing the boundary between the Precambrian era and the Cambrian period, 538.8 million years ago.
The first appearance of the graptolite Nemagraptus gracilis defines the boundary. The rock section consists primarily of dark-gray shale and mudstone, except for a phosphorite marker bed 1.4 m above the GSSP, and was probably deposited at a water depth exceeding 100 m. Drill cores have revealed almost identical stratigraphy across an area ...
Defining the boundary based on the extinction of Epigondolella bidentata placed it at magnetozone G+, the first of several major normal-polarity sections. [ 15 ] The early reverse-polarity zones (B− to D−) were correlated with PM11r, a reverse-polarity section at the top of Pizzo Mondello , a similar Carnian-Norian sequence in Sicily .