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Why was the Dob’s Linn site suitable for defining the beginning of the Silurian Period?

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Silurian paleogeography — Silurian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the middle part of the Silurian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The Dob’s Linn site in Scotland was selected as the Global Stratotype Section and Point (GSSP) for the base of the Silurian Period primarily because of its environmental stability during a time of global transition.12

While many other locations worldwide experienced stratigraphic unconformities—gaps in the rock record caused by sea-level fluctuations related to Late Ordovician glaciation and subsequent deglaciation—the Dob’s Linn locality was situated in deep marine waters. This depth allowed the site to remain unaffected by these physical phenomena, preserving a continuous sedimentary record that includes the critical Parakidograptus acuminatus graptolite biozone.12

By formally defining the boundary 1.6 meters above the base of the Birkhill Shale Formation, geologists established a reliable "golden spike" that marks the first occurrence of P. acuminatus alongside Akidograptus ascensus, providing a clear, globally recognized marker for the beginning of the Llandovery Series.2