Sequence stratigraphy of the Nukumaruan Stratotype (Pliocene‐Pleistocene, c. 2.08–1.63 Ma), Wanganui Basin, New Zealand

Abstract

Late Pliocene to Early Pleistocene (c. 2.08—1.63 Ma) strata exposed in coastal cliffs along Nukumaru and Ototoka beaches near Wanganui, between the top of the Nukumaru Limestone and the base of the Butlers Shell Conglomerate, comprise 11 depositional sequences of a total thickness of c. 86 m. The sequences consist predominantly of silicilclastic shoreline facies. Non‐marine facies (including palaeosols), and a variety of shallow‐marine shellbed facies, are also represented. Patterns in facies composition and sequence architecture reveal three sequence motifs (Maxwell, Nukumaru, and Birdgrove) that represent progressively increasing maximum palaeowater depths within a broadly basin‐margin palaeogeographic setting. The sequence motif changes systematically up section and records a lower order tectonic influence on accommodation that has modulated the stacking patterns of individual sequences. Correlation of the sequences with oxygen isotope stages 77–57 is achieved using the basin‐wide Ototoka tephra, and indicates that the sequences accumulated in response to obliquity driven (41 k.y. duration) glacio‐eustatic sea‐level oscillations. Correlation of the Nukumaru coast sequences with other sections along basin strike, and the global oxygen isotope record indicates that (i) 500 k.y. (δ¹⁸O stages MIS 56–34) is missing at the unconformity between the Nukumaruan and overlying Castlecliffian stratotypes on the Wanganui coast, and (ii) the Pliocene‐Pleistocene boundary lies within sequence NC7 at the base of the Lower Maxwell Formation.

Keywords:

• cyclothem
• sequence
• motif
• systems tract
• tephra
• cyclostratigraphy
• obliquity
• glacio‐eustasy
• sea level
• Pliocene
• Pleistocene
• Nukumaruan
• Wanganui Basin
• New Zealand

Notes

School of Earth Sciences, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia.

Present address: School of Environmental Science and Management, Southern Cross University, P.O. Box 157, East Lismore, NSW 2480, Australia. Email: [email protected]

Institute of Geological and Nuclear Sciences, P.O. Box 30 368, Lower Hutt, New Zealand.

Marine Geophysical Laboratory, James Cook University, Townsville, QLD 4811, Australia.

Research School of Earth Sciences, Australian National University, Canberra, ACT 2000, Australia.