The Middle Ordovician Pseudoclimacograptus decoratus Zone (Llanvirn) and Climacograptus bicornis Zone (early Caradoc) of the Pacific Faunal Province are documented from the Tatshenshini River map area in the northern Alexander Terrane. Graptolites were collected from three separate localities of uncertain stratigraphic position within the informal unit 1Pza. The ages of the collections are critical to dating the stratigraphic succession of the Lower Paleozoic rocks within the highly deformed terrane.Regionally, unit 1Pza can be correlated with the Descon Formation of Prince of Wales Island, southeastern Alaska, which also forms part of the Alexander Terrane. The original position of the Alexander Terrane is uncertain, but there are broad similarities between the Paleozoic stratigraphic package of the terrane and those of the Sierra Nevada of the western United States, southeastern Australia, and eastern Siberia.

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