Stratigraphy and depositional environment of the Kyeburn Formation (Cretaceous), a wedge of coarse terrestrial sediments in Central Otago

Open-file seismic reflection data, from the offshore area west of Greymouth, show a large segmented half-graben structure, over 40 km long, up to 15 km wide, and trending WNW-ESE. Although the structure is not drilled, regional seismic interpretation suggests it is of Cretaceous age. The geometry of the structure indicates extension of about 20%. Strata of similar age onshore are thought to have been deposited in half-grabens with a similar orientation. In contrast, structures containing Late Cretaceous to Paleocene deposits onshore, trend NNE-SSW, almost at right angles to the earlier trend. Cretaceous dike orientation data show a bimodal distribution, with the main trends being WNW-ESE and NNE-SSW. Together with published radiometric and fission-track ages from basement and Cretaceous igneous rocks, these data show that there were at least three distinct periods of tectonic/magmatic activity: (1) NNE-SSW directed extension, uplift, plutonism, and minor volcanism in the interval 125-90 Ma; (2) multiple dike intrusion and decreased NNE-SSW directed extension and uplift in the interval 90-80 Ma; and (3) breakup unconformity, volcanism, dike intrusion, waning subsidence in WNW-ESE trending basins, initiation of NNE-SSW transtensional basins, and uplift in the interval 80-60 Ma.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Extensional tectonism and magmatism during the middle Cretaceous to Paleocene, North Westland, New Zealand

Bishop

1992

“…However, Macraes deformation and mineralisation occurred in Late Jurassic to arly Cretaceous, distinctly earlier than the Rise & Shine Shear Zone (Cox et al 2006). xtensional deformation began in the Otago Schist in the middle Cretaceous and continued to the middle Tertiary (Bishop & Laird 1976;adams & Raine 1988;Carter 1988;Gray & Foster 2004). extension-related subsidence in the Late Cretaceous to middle Tertiary (late Paleogene) was accompanied by marine transgression and cutting of a widespread low-relief erosion surface, the waipounamu erosion Surface (Landis et al 2008).…”

Section: Post-metamorphic Deformationmentioning

confidence: 99%

“…1, 2, 10a) (Bishop & Laird 1976). The middle Cretaceous normal fault system resulted in juxtaposition of rocks of different metamorphic grade along the northeast margin of the schist belt (Deckert et al 2002;Mackenzie & Craw 2005), so these faults have had a major influence on the structural evolution of North Rough Ridge (above).…”

Section: Mineralised Faults Kink Foldsmentioning

confidence: 99%

Structural and lithological controls on gold mineralisation at Oturehua on the northeastern margin of the Otago Schist, New Zealand

Mackie

MacKenzie

Craw³

2009

A set of more than 50 mineralised normal faults cuts lower greenschist facies rocks at the northeastern margin of the Otago Schist belt near Oturehua, central Otago. The faults strike northwest and dip steeply (>60°) northeast, and individual mineralised zones are traceable for up to 700 m along strike. The mineralised faults are closely associated with, and are generally parallel to, a swarm of northwest striking, steeply dipping extensional quartz ± ankerite veins (centimetre scale) that occur over an area of at least 25 km 2 in the host schist. Mineralised faults contain 10-100 cm thick quartz veins that are traceable as interlinked structures for tens of metres along strike. where faults cut massive quartz-feldspar-rich schist, the veins are planar, contain scattered sulfide minerals and visible gold, and there has been little alteration of essentially undeformed adjacent wall rock (centimetre scale). in contrast, muscovite-rich laminated schist host rock is extensively deformed and altered adjacent to mineralised faults (metre scale), with addition of quartz (silicification) and ankeritic replacement of metamorphic chlorite by kaolinite and/or sericitic muscovite. Veins adjacent to laminated (micaceous) schist contain abundant breccias with variably altered clasts. widespread addition of auriferous sulfide minerals, mainly arsenopyrite, has occurred in the laminated schist alteration zones and breccias. The mineralised faults formed in the hinge of a northwest-trending post-metamorphic antiform, and the faults may have been localised by zones of weakness associated with kink folding in the hinge of the antiform. Hydrothermal fluids responsible for mineralisation were channelled by the normal faults. These faults developed by coalescence of extensional fractures in the schist rock mass during middle Cretaceous regional extensional unroofing of the Otago Schist belt. The location of these mineralised faults near the margin of the Otago Schist belt suggests a genetic relationship between mineralisation and the regional northwest-striking normal fault systems that cut and define the schist margin.

“…These sediments are typically breccia fans, fluvial conglomerates, and finegrained lacustrine sandy/silty coal measure facies (Harrington 1958;Bishop & Laird 1976). They comprise the Matakea Group of Carter (1988a) and Hoiho Sequence of Beggs (1993) and are the earliest phase of sedimentation culminating in the Cretaceous-Tertiary transgressiveregressive cycle (Carter & Norris 1976;Carter 1988a, b).…”

Section: Mid-late Cretaceous Unconformitiesmentioning

confidence: 99%

Allostratigraphy of coastal south and east Otago: A stratigraphic framework for interpretation of the Great South Basin, New Zealand

McMillan

Wilson

1997

Sixteen unconformities, some with correlative conformities, are recognised within the Late CretaceousTertiary transgressive-regressive sediments of coastal Otago. These provide the basis for stratigraphic division and correlation with seismic reflectors in the offshore ageequivalent sediments of the Great South Basin. The ages of the unconformities/conformities are constrained mainly by dinoflagellate biostratigraphy, but foraminiferal biostratigraphy is important for the Oligocene-Miocene. In terms of current biozone-stage correlation, the 16 unconformities comprise the following: two intra-Haumurian (Late Cretaceous) unconformities, one at the K/T boundary, three intra-Teurian (Paleocene) unconformities, two of early Waipawan age, two of late Mangaorapan -early Heretaungan age, a late Heretaungan unconformity, a late Porangan -early Bortonian unconformity, a late Bortonian unconformity (a total of seven Eocene unconformities), a late Runangan -early Whaingaroan unconformity, a late Whaingaroan unconformity (both Oligocene), and a midWaitakian (Miocene) unconformity. Other, early-midCretaceous unconformities are inferred from offshore seismic profiles. Six unconformities/correlative conformities in onland Otago provide the basis for recognising four informal alloformations.