Cambrian and Ordovician faunas and stratigraphy, Mt Patriarch, New Zealand

Abstract

Forty‐one species of trilobites and two of graptolites are described from the Patriarch Formation and the overlying Summit Limestone of the northwest Nelson area, New Zealand. Most of the trilobites are recorded for the first time from Australasia. The stratigraphy of both formations is revised and stratigraphic columns presented. Five successive faunules, shown to span the Cambrian‐Ordovician boundary, are recognised in the sequence, and are correlated internationally. Stratigraphically important conodonts from the area are figured and briefly discussed. Faunule 1, in the lower 220 m of the Patriarch Formation, contains the Lotagnostus‐Hedinaspis‐Hysterolenus trilobite fauna, which is found around the world in Late Cambrian strata. Twenty‐three trilobite species occur, including three new species: the aulacopleurid Proteuloma ahu, the shumardiid Shumardia (Conophrys) tauwhena, and the nepeid Amzasskiella kupenga. Faunule 2, from the upper 250 m of the Patriarch Formation, contains the graptolites Rhabdinopora ex gr. scitulum and Anisograptus cf. dclicatulus, and the conodonts Cordylodus angulatus, Oistodus lanceolatus, TAcanthodus costatus, and Hirsutodontus simplex, together with five species of trilobites. The conodonts and graptolites indicate an early Tremadoc age. Faunule 3, from the lower 64 m of the Summit Limestone, contains 18 species of trilobites, including one new species, Leptoplastides grindleyi, as well as the South American taxa Kainella meridionalis Kobayashi, 1935, Apatokephalus sp. aff. A. tibicen Pribyl & Vaněk, 1980, and Onychopyge sp. aff. O. riojana Harrington, 1938 indicating a late Tremadoc age. The lower of the two conodont faunules described by Cooper and Druce from Unit 1 of the Summit Limestone, constitutes Faunule 4, and is here assigned a late Tremadoc age; their upper conodont faunule, from Unit 3 of the Summit Limestone, constitutes Faunule 5 (early Arenig).

Faunule 3 has generic links with South America but, overall, cosmopolitan genera dominate the trilobite assemblages and, especially in Faunule 1, faunal composition reflects biofacies rather than paleogeography. The environments inferred for the Anatoki Formation and lower Patriarch Formation are a turbidite fan or basin in an off‐shelf setting; subsequent “shallowing is indicated by carbonate development near the top of the Patriarch Formation, and further shallowing, to shelf depths, is indicated by the Summit Limestone and its trilobite fauna.

Keywords:

• Cambrian
• Ordovician
• biostratigraphy
• trilobites
• graptolites
• conodonts
• Mt Patriarch
• Anatoki Formation
• Patriarch Formation
• Summit Limestone
• Takaka Terrane
• international correlation