Quaternary stratigraphy, structure, and deformation of the Upper Hutt Basin, Wellington, New Zealand

Abstract

hence drainage restriction at Taita Gorge. Elevated Last Glacial terraces at the northeast and southwest ends of the basin dip below Holocene gravels towards the middle of the basin, indicating relative longitudinal basin subsidence.Keywords NZMS 260 R27; Wellington; Upper Hutt Basin; Quaternary; sediments; seismic reflection; gravity; deformation; Wellington Fault; active basin development Abstract The Upper Hutt Basin is one of three onshore Quaternary basins in the Wellington region, New Zealand. This northeast-trending basin is bounded along its northwest margin by the predominantly strike-slip Wellington Fault, northwest of which upthrown Torlesse Terrane basement rocks crop out. Quaternary sediment filling the basin rests unconformably on the basement rocks, onlapping the sloping basement surface at the east side of the basin. Interpretation of the seismic and gravity data indicates a total sediment thickness of c. 360-480 m in the main Upper Hutt Basin and 225 m in the Witako Basin. Gravity modelling indicates a dip of c. 60° to the northwest for the Wellington Fault, and has defined a basement high within the basin, which is the subsurface continuation of a NNE-trending topographic spur. The basement high separates a sub-basin, the Witako Basin, from the main Upper Hutt Basin. A drillhole near the basement high penetrated interbedded 10-50 m thick gravel and silt/peat units and reached basement at 204 m. Other drillholes indicate that this stratigraphy, at least in the upper 80 m, is consistent in the southwest area of the basin. There are few constraints on the chronology of the sequence in the basin, but a unit of silt and peat between 51.5 and 68 m depth in one drillhole yielded cool climate pollen assemblages and is of early Last Glacial age (50-80 ka).

Late Quaternary activity of the Scorciabuoi Fault (southern Italy) as inferred from morphotectonic investigations and numerical modeling

“…A rough estimate of the time necessary to entrench the Sauro Valley is 180–370 ka (i.e., ∼550 m divided by 1.5–3.0 mm/a), and therefore the beginning of the aggradation process associated with the oldest preserved terraced deposits (F 4 ) could not occur before 80–270 ka (i.e., ∼450 minus 180–370 ka, Figure 6b). We should also consider that F 4 has a minimum thickness of 30–35 m and that accretion rates in similar incised valleys could range between 0.1 and 10 mm/a [e.g., Melhuish et al , 1997; Foyle and Oertel , 1997; Boski et al , 2002; BDP‐99 Baikal Drilling Project Members , 2005; Ward et al , 2005; Frouin et al , 2007]. Assuming a conservative value of 1 mm/a, the age of the top surface of F 4 (namely, T 4 ) possibly ranges between 50 and less than 240 ka (i.e., 80–270 minus 30–35 ka, Figure 6c).…”

Wrench tectonics flip at oblique subduction. A model from New Zealand

“…The western splays of the "horse tail" structure (WeF & WaF) became most-active since Latest Pliocene times [22] which therefore substantiate the "horse tail" structure of North Island does not correspond to some kind of northward dying out of the dextral movement. Rather it supports a westward progressive transfer of tectonic activity from the ATF and AF to the WeF & WaF that commenced during Pliocene times.…”

“…Cependant, dans cette " queue de cheval ", les branches orientales du dispositif ne sont plus le lieu d'une intense activité tectonique, alors que les branches occidentales sont extrêmement actives depuis le Pliocène terminal[22]. La déformation décrochante n'a donc pas cessé dans le butoir du prisme d'accrétionde Hikurangi, mais elle a migré vers l'ouest au cours du Pliocène.…”

Whitemans Valley Fault: A newly discovered active second order fault near Wellington, New Zealand—implications for regional seismic hazard

“…The fault dips beneath the hills on the western side of Whitemans Valley, and presumably occurs at depth beneath Eastbourne, Wainuiomata, Taita, and the Trentham-Heretaunga area. A seismic profile across the Upper Hutt Basin (Melhuish et al 1997) is orientated subparallel to the extrapolated position of the fault and therefore does not image a fault. It does, however, indicate that a significant subsurface topographic feature extends across the basin, elevated on the south side of the Witako sub-basin.…”