The Geology of the Southern Mamaku Plateau.

Author:

Keiller, IG

Year:

Project type:

Advisers:

Abstract:

THE AREA MAPPED COVERS A 64 SQUARE KILOMETRE AREA BETWEEN TOKOROA AND THE SOUTHERN EDGE OF THE MAMAKU PLATEAU. SIX RHYOLITIC PYROCLASTIC UNITS ARE MAPPED AND DESCRIBED.
THE OLDEST EXPOSED FORMATION IS THE WHAKAMARU IGNIMBRITE. STRATIGRAPHICALLY ABOVE ARE THREE NEW PYROCLASTIC DEPOSITS, ONE OF WHICH IS BEING PROPOSED FOR FORMATIONAL STATUS.
THE OLDEST OF THESE THREE DEPOSITS IS A THIN PLINIAN FALL WITH AN OVERLYING TWENTY FIVE METRE, NON-WELDED* CRYSTAL POOR, PUMICE RICH, FINES CONCENTRATED, IGNIMBRITE THAT SITS UNCONFORMABLY ON A THICK PALEOSOL ABOVE THE WHAKAMARU IGNIMBRITE. THIS DEPOSIT IS HERE INFORMALLY NAMED THE CHIMP FORMATION. THE NEXT DEPOSITS ARE A SIX METRE THICK GROUP OF PUMICE AIRFALL UNITS, EACH SEPARATED FROM THE OTHER BY A PALEOSOL, WHICH SITS UNCONFORMABLY ON THE CHIMP IGNIMBRITE, AND HERE ARE INFORMALLY NAMED THE GALAXY TEPHRAS.
THE POKAI IGNIMBRITE IS THE NAME FORMALLY PROPOSED FOR THE NEXT DEPOSIT, WHICH COMPRISES A PLINIAN FALL AND IGNIMBRITE UNIT. A TYPE SECTION IS SET UP FROM A 30 METRE SECTION IN POKAI ROAD. THE PLINIAN FALL CONSISTS OF MEDIUM TO COARSE LAPILLI SIZE PUMICE INTERBEDDED WITH FINE RAINFLUSHED ASH BEDS. THE PLINIAN FALL IS SHARPLY OVERLAIN BY THE IGNIMBRITE WITHIN WHICH CREAMY WHITE TO YELLOW PUMICE, IN A PALE BROWN MATRIX AT THE BASE PASS PROGRESSIVELY TO ORANGE-BROWN PUMICE IN A DARK GREY MATRIX AT THE TOP. THIS PUMICE RICH, CRYSTAL POOR IGNIMBRITE FORMS A THICK SINGLE COOLING UNIT1 WITHIN WHICH THREE FLOW UNITS ARE RECOGNISED.AND NORMAL THERMAL ZONATION IS DISPLAYED. A NORTH EASTERLY SOURCE IS POSTULATED FOR THIS DEPOSIT.
SIX METRES OF MAMAKU IGNIMBRITE LIES UNCONFORMABLY ABOVE THE POKAI FORMATION. THE LAST ERUPTIVE DEPOSIT EMPLACED IN THE STUDY AREA WAS THE AD186 TAUPO IGNIMBRITE WHICH FORMS DISTINCTIVE VALLEY PONDED DEPOSITS OF VARYING THICKNESS WITHIN THE AREA.
*TO MODERATELY WELDED

Named Localities:

Thesis description:

vi. 177 p. ill, diagms, photos. Map (folded in pocket); 30 cm.

Department:

OU geology Identifier:

1987Keiller

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Location (WKT, WGS84):

POLYGON ((175.90120369300007 -38.259195235999982,175.885621234000041 -38.259586481999975,175.878423829000099 -38.259766491999983,175.877145850000034 -38.233158713999956,175.876261570000111 -38.214735944999973,175.883953707000046 -38.211589601999947,175.898898053000039 -38.205474634999973,175.86755027300012 -38.190192482999976,175.863798032000091 -38.188362255999948,175.869880604000059 -38.188211896999974,175.910997663000103 -38.18718716199993,175.935130269000069 -38.186578942999972,175.966638615000079 -38.185777316999975,175.968670892000091 -38.230842732999974,175.968742046000102 -38.23241948499998,175.969012901000042 -38.238420963999943,175.969405461000065 -38.247117253999932,175.969815809000124 -38.256205247999958,175.969871850000118 -38.257446193999954,175.96984293200012 -38.257446938999976,175.968004628000017 -38.257494287999975,175.90120369300007 -38.259195235999982))

Files

http://download.otagogeology.org.nz/temp/Abstracts/1987Keiller.pdf

Collection

Citation

Keiller, IG, “The Geology of the Southern Mamaku Plateau.,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/214.

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