Geology of Wharekuri Creek

McDermid, Isabella (Isabella Rose Cross), 1975-

Oligocene and Neogene strata at Wharekuri Creek, Waitaki Valley, North Otago record a transgressive-regressive marine sequence, lacustrine and braided river deposits. Marine strata include three calcareous, glauconitic, fossiliferous marine units: Wharekuri Greensand (Lower Whaingaroan); Kokoamu Greensand/Kekenodon Beds (Upper WhaingaroanDuntroonian); and Otekaike Limestone (Duntroonian-?Waitakian). The Kokoamu Greensand is separated from Wharekuri Greensand by a bored surface, Fordyce and Watson (1998) interpreted this as the mid-Oligocene unconformity, which Fulthorpe et al. (1996) correlated with a global eustatic sea level fall. The Wharekuri Creek marine rocks contain members of the stratigraphically important pectinid bivalve lineage Janupecten-Lentipecten. Here,Janupecten show progressive reduction in sculpture leading to evolution of smooth-shelled Lentipecten. The evolution to smooth valves indicates enhanced level-swimming ability. Deposition of the coarsening upward Southburn Sand {Early? Miocene), following the Otekaike Limestone, represents a transition to a near shore environment. The Waitangi Coal Measures (Middle?-Late? Miocene), which may overlie the Southburn Sand unconformably, are tentatively placed within the Manuherikia Group of Central Otago, because they also represent a deltaiclacustrine succession of peat, laminated muds, clays, and sands. Following accumulation of the coal measures at Wharekuri Creek, the Kurow Gravels were deposited as longitudinal bars in a braided river system. The name Kurow Group is not used here, because the name Kurow Gravels takes priority. Late Cenozoic faulting, presumably associated with development of the Southern Alps, has deformed the sedimentary sequence at Wharekuri Creek. The Kokoamu Greensand is juxtaposed against the Southburn Sand by the Waitangi Fault and the Southburn Sand is faulted against the Waitangi Coal Measures. The Wharekuri Fault has uplifted semi-schist basement of the Haast Schist Group against the Waitangi Coal Measures and the Kurow Gravels. Gravels and angular debris from the St Marys Range cover much of the area so that it is not possible to see crosscutting relationships which may indicate the sequence of faulting.

131 p. : ill. (some col., one folded), maps ; 30 cm.

1998McDermid

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