Lithostratigraphy and Biostratigraphy of Swinburn; Proxies for Paleogeography from Central Otago Marine Strata

Author:

Richards, Marcus

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Abstract:

The Maniototo Basin preserves localised Cenozoic marine strata that can be correlated into Waitaki Valley, with formation names as used in the southern Canterbury Basin. The clastic-dominated strata were derived from an Otago Schist source on Zealandia during maximum submergence. Long-recognised marine strata from the Maniototo are the Naseby Greensand and Green Valley Limestone. This study recognises formations including: Kauru, Wharekuri (truncated by the Marshall Unconformity), Kokoamu, and Otekaike. The basin-wide greensand resting on the Marshall Unconformity is Kokoamu Formation with an age of Whaingaroan- Duntroonian. The Naseby Greensand of Kyeburn is now identified as a composite of units including Whaingaroan to Waitakian-aged fossils and is equivalent to Wharekuri, Kokoamu and Otekaike Formation. The use of Naseby Formation should be discontinued. Kokonga - Green Valley Limestone is Otekaike equivalent. We now detail a 200 m section at Swinburn, comprising massive fossiliferous marine rocks with a pervasive micaceous, very fine quartz sand to silt component. The sequence is variably (in places richly) glauconitic, grading up through calcareous sandstones to a packstone unconformably overlain by Wedderburn Formation and capped by basaltic volcanics. Foraminifera and ostracods date these units as upper Runangan - lower Whaingaroan to mid-Waitakian; low planktic foraminiferal percentages are consistent with limited oceanic influence. Uncommon fossil scallops (Pectinidae) in the Janupecten - Lentipecten lineage are consistent with microfossil ages. This sequence is thicker, more clastic - dominated, and nearer to sediment source (probably Otago Schist) than in the Waitaki. The background sedimentation of subangular very fine sand and silt found iii throughout the Oligocene indicates a continuous supply from the terrestrial source. A nearby stratigraphically lower sequence includes quartzose coal measures, inferred estuarine mudstones with rare molluscs, and intertidal shales, consistent with a paralic to estuarine setting, and is a correlative of Kauru Formation. The beds show a pattern of marine transgressions and regressions peculiar to this site. Hedecardium indicates a Bortonian to Kaiatan age. In summary, the Swinburn sequence formed in a shallow, possibly early- to mid-Cenozoic epicontinental sea with a productive source of terrigenous clastics. There is no firm evidence of outer shelf settings.

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xv, 127 pages A4

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2014Richards

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http://download.otagogeology.org.nz/temp/Abstracts/2014Richards.pdf

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Citation

Richards, Marcus, “Lithostratigraphy and Biostratigraphy of Swinburn; Proxies for Paleogeography from Central Otago Marine Strata,” Otago Geology Theses, accessed November 29, 2021, http://theses.otagogeology.org.nz/items/show/585.

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