New Zealand Journal of Geology and Geophysics abstracts

---

Sulphur mobility and sulphur-mineral precipitation during early Miocene-Recent uplift and sedimentation in Central Otago, New Zealand

J. H. YOUNGSON

Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand

Abstract  Since the late Oligocene - early Miocene, three distinct uplift events have resulted in widespread sediment deposition in Central Otago, South Island, New Zealand. These events are marked in the sedimentary record by the early-middle Miocene Manuherikia Group, late Miocene-Pliocene Wedderburn and Maori Bottom Formations, and Quaternary schistose fan gravels. Each event was accompanied by some basement erosion and extensive recycling of older sediments. Early-middle Miocene Manuherikia Group quartzose sands and conglomerates (Dunstan Formation) lying on the schist probably represent recycled early Tertiary freshwater +/- marine sediments, still preserved in east and west Otago.

Dunstan Formation sediments are cemented with framboidal marcasite and subordinate crystalline pyrite (both FeS2) to within a few metres of the surface at many localities. Heavy- mineral concentrates from Quaternary alluvial fan sediments commonly contain small cubes and/or dodecahedra of authigenic pyrite. Sand and conglomerate outcrops of Hogburn, Wedderburn, and Dunstan Formations and, to a lesser extent, of other sedimentary units, commonly display efflorescences of sulphate minerals. At the time of sampling, these included ferricopiapite [Fe4.67(SO4)6(OH)2.20H2O], gypsum [CaSO4.2H2O], anhydrite [CaSO4], jarosite [(K,Na,NH4)Fe3(SO4)2(OH)6], alum [Al2(SO4)3], and a yellow, unidentified, amorphous sulphur mineral precipitate.

The widespread occurrence of authigenic sulphur minerals in basin sediments attests to substantial sulphur mobility in groundwater during coupled uplift and sediment deposition events. Sulphur in the authigenic minerals is suggested to have been derived primarily from pre-existing sulphur minerals in older sediments oxidised during uplift, and from erosion and leaching of basement rock. The chemistry of groundwater and surface water suggests that this recycled sulphur component has been augmented by inputs derived from a marine source, probably by wet deposition of marine sulphate aerosols from the atmosphere. Aerosols may be the dominant sulphur source in the periods between significant pulses of sediment recycling.

Keywords  Central Otago; uplift; groundwater; sedimentary recycling; Miocene; Pliocene; Quaternary; sulphur mobility; authigenic sulphur minerals; marine aerosols

New Zealand Journal of Geology and Geophysics, 1995, Vol. 38: 407-417

0028-8306/95/3804-0407 $2.50/0 (c) The Royal Society of New Zealand 1995

PDF file of entire paper: medium quality (1937K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page