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Exotic thrust sheets with rafts of locally derived strata: Northland Allochthon in Waihou Valley, Northland, New Zealand
| Content Provider | Scilit |
|---|---|
| Author | Evans, R. B. Hayward, B. W. |
| Copyright Year | 1990 |
| Abstract | In the Waihou Valley, Northland, the Pirau Fault juxtaposes Waipapa Group basement to the north against Cretaceous-Oligocene strata to the south. On the downthrown side, one isolated outcrop of basal Akarana Supergroup flysch (Late Oligocene) rests unconformably upon basement, and is correlated with identical autochthonous beds 2 km and 5 km to the west. South and east of this outcrop, the lowest exposed unit (base unseen) comprises intensely deformed red and grey claystone (Late Cretaceous-Paleocene) with less common, fragmented masses of blue-grey quartzose sandstone and argillaceous limestone. Enclosed within this unit is a several-cubic-kilometre raft of Te Kuiti Group and Akarana Supergroup strata (Late Eocene-Late Oligocene), comprising a conformable sequence from Ruatangata Sandstone (Kaiatan-Runangan, 10+ m) through Mangapa Mudstone (Runanganearly Whaingaroan, 0–50 m) and Whangarei Limestone (Whaingaroan — earliest Waitakian, 0–60 m) into Pukepoto Formation (new, early Waitakian, 120+ m). This rafted sequence is of considerable regional geological significance. The multicoloured claystones and enclosed rafted units are overthrust by a sequence of Late Cretaceous?-Paleocene rocks, comprising 160+ m of Punakitere Sandstone overlain by 300 m of Ngatuturi Claystone and a further unit of Punakitere Sandstone, which tectonically adjoins a large mass of Waikaraka Siltstone (early Late Cretaceous, 200+ m). Pleistocene Horeke Basalt overlies all these units and oversteps. the Pirau Fault. Whereas the autochthonous basal Akarana Supergroup unit is little deformed, structure within the displaced units of Cretaceous-Oligocene age is complex. Within the lower overthrust sheet, the multicoloured claystones have been completely dismembered and transposed by shearing to form a melange-like fabric, although the enclosed raft of Te Kuiti and Akarana lithologies is sheared only at the margins and intemally is cut only by high-angle faults. Within the upper overthrust sheet, the Punakitere Sandstone and rafted Waikaraka Siltstone have been offset and tilted by widely spaced shears, whereas the thinly bedded, siliceous Ngatuturi Claystone has been transposed by shearing to a broken formation. Although the displaced units are locally intemally complex, the broad lithologic patterns are simple. All of the displaced strata form part of the Northland Allochthon, which in this area was emplaced in the Waitakian and early Otaian (latest Oligocene — earliest Miocene). |
| Related Links | http://www.tandfonline.com/doi/pdf/10.1080/00288306.1990.10425701?needAccess=true |
| Ending Page | 464 |
| Page Count | 10 |
| Starting Page | 455 |
| ISSN | 00288306 |
| e-ISSN | 11758791 |
| DOI | 10.1080/00288306.1990.10425701 |
| Journal | New Zealand Journal of Geology and Geophysics |
| Issue Number | 3 |
| Volume Number | 33 |
| Language | English |
| Publisher | Informa UK Limited |
| Publisher Date | 1990-07-01 |
| Access Restriction | Open |
| Subject Keyword | Journal: New Zealand Journal of Geology and Geophysics Geology Northland Allochthon Akarana Supergroup Pukepoto Formation (new) Ruatangata Sandstone Mangapa Mudstone Whangarei Limestone Ngatuturi Claystone Punakitere Sandstone Waikaraka Siltstone Overthrust Geology Foraminifera New Stratigraphic Names |
| Content Type | Text |
| Resource Type | Article |
| Subject | Geology Geophysics |
