There i s not enough data for i sopach ma ps to The u n i t E 2 i s proba b l y the res u l t of ei ther s evera l 1 S howers 1 or a cl o sel y spaced seri es of i ntermi ttent erupti o n s .
E l
E l occurs bel ow E 2 i n deep road c u tti ngs . The l a p i l l i a re heav i l y i ron s ta i ned a nd th ere i s a prom i nent ba sal band composed o f l oo s e , yet c l osel y pac ked pumi ceous l a p i l l i , wh i c h ha s been correl a ted wi th Nea l l 1 S Ahuahu Lap i l l i . The l ower boundary i s d i sti nct a nd wavy .
C R I TER I A : A d i sti nct band of coa rse pumi ceous l a p i l l i , l oose wi th a
l i ttl e coarse a s h , occurs bel ow a bu ri ed so i l . I n the u pper part a
coarse sandy l oam a s h , wi th a few l i thi c l a pi l l i , l Omm i n d i amete r , g rades t o a ba sal band of pumi ceou s bl ocks and l a p i l l i a n d fi ne l i th i c l a pi l l i , 5mm and l es s i n d i amter , wi th ma ny ma f i c c rysta l s ( F i gure 3 . 1 3 ) .
TYPE SECT I ON : The type sec t i on i s des i g nated 0 . 6 km from Card i ff , on
the s outh s i de of Opu na ke Road , above the Wa i ngongoro Stream , at N l l9/ 797550 .
D I STRIBUT I ON AND SOURC E : T here i s not enough d a ta for i sopach ma ps
to be drawn . El i s of a i rfal l ori g i n from Mt . Egmont .
REFERENCE LOCAL I T I ES : Two reference l ocal i t i e s a re des i g nated . The f i rst i s on Opunake Road , adjacent to Mangato k i S tream a t N l l 9/ 7 57532
( s ee Sect i o n 1 , Appendi x I I I) . The u n i t averag es 400mm i n th i c knes s , o n the south ex posure , a t the s ec t i on furthest away from the br i dg e .
The s econd cutt i ng i s on Fi nnerty Road a t the j u nc t i on wi th Ro na l d Road at N l l 9/81051 6 .
VAR I AT I ON : Away from sourc e the pumi ceous and l i th i c l a pi l l i are
prog res s i ve l y redu ced to sca ttered bl ocks and coarse ash wh i c h become obscure .
Al o ng the E l tham Road , between Ka ponga and Pa l mer Road , E 2 and E l have a doub l e-ba nded a ppearance caused by the two promi nent pumi ceous and l i th i c l a pi l l i bands .
. · . ·. : • o . . : . · . . · · : · •(:7. . . · . .. . C) ()
6 C) <
. a 4 · · . • D o • . A ·. (). �· oo . . · · . · ·a· E2 bas a l l a pi l l i D i s t i nct wavy bounda ry E l B u ri ed soi lDi s ti nct band o f coarse p umi ceo u s l api l l i , l oose wi th a l i ttl e coarse ash
. . . ' · ·.· . "'.· ·.·• . . : •. ... · . ·• . . · • .< ·• · · · · • � · · . Fi g ure 3 . 1 3
�
�
[QJ
wi th a few l i th i c l a pi l l iBasal band o f p umi ceous b l ocks a nd l ap i l l i , fi ne l i th i c l api l l i and mafi c c rysta l s Di sti nct wavy bo undary
B uri e d s o i l
o f un i t E l
Buri e d s o i l
P umi ceous l a pi l l i a n d bl ocks
L i th i c l a pi l l i
Ma fi c c rys ta l s
Coa rs e a s h
Ma hoe
T he u n i t i s a prom i nent tep h ra at approx imately 3m depth i n mo s t expo sures . T h e name o f t h i s teph ra fo rma t i on comes from t h e a rea known as Mahoe , l Okm south- wes t of Stra tford , where the tephra i s wel l exposed . C R I TER IA : The c l osel y pac ked pumi ceous l a pi l l i , 7 . 5YR 5/8- 5/ 6 ( s trong brown ) a re fi rm and have a d i s t i n c t i v e lOYR 4 / 1 ( dark grey ) i nterna l col o u r , w i t h a
averag i ng 20mm 2 - 5mm
1
i t h i cho ney-comb a ppea rance . Numerou s l i th i c l a p i l l i ,
or g reater i n d i ameter , g rade downwa rds to very fi ne l a pi l l i , wh i ch form a d i s t i nc t u nd u l ati ng l ower bou nda ry .
The hori zon i s c ha ra cteri sti cal l y l oose and s trong l y i ron s ta i ned , wi th 5YR 4 / 6 ( yel l owi s h - red ) coat i ng s ( F i gu re 3 . 14 and P l a te 3 . 9 ) .
TYPE SECT I ON : The type sect i on i s des i g nated on Opunake Road , 0 . 8km
from Mahoe , i n the south road ba n k , at N l l9/ 738528 . The u n i t averages
3 50mm thi ckness at th i s c u tti ng .
REFERENCE LOCAL I T I ES : Four reference l oca l i ti es a re de s i g na ted .
The fi rst c u tti ng i s on F i n nerty Road , a t the j u nc t i on wi th Rona l d Road ,
i n the no rth ba n k , at N 1 1 9/81051 6 . The second cu tti ng i s 0 . 6 km from
Card i ff , on the south s i de of Opuna ke Road , above the Wa i ngongoro S tream at N 1 19/797 550 .
The t h i rd cutti ng i s on the south s i de of Monmouth Road , l km from Pembroke cro s s roads a t N 1 19/ 8 1 3 603 .
The fourth cutt i ng i s des i g nated bes i de S tate H i g hway 3 , near Ta ri k i , i n a sect i on by the ra i l way l i ne at N 1 09/81 5703 , where the u n i t averages 200mm i n t h i c knes s .
VAR I AT I ON : The uni t c a n conta i n sca ttered " cream ca kes " for examp l e , a t the type section expo s u re , and the fi ne l i t h i c s a t the ba s e often poc ket , a s for exampl e on Opu na ke Road , adj a cent to Ma ngato ki Stream at N l 1 9/ 7 5 7 53 2 .
The l i th i c studded a s h , between E l and Ma hoe someti mes conta i ns a m i nor ba nd of med i um pum i ceous l a p i l l i , wh i c h rema i n s unnamed .
Pl ate 3 . 9
Reference l oc a l i ty for the Mahoe tephra . The cutti ng i s on Opunake Road , 0 . 6 km from Card i ff , above th e Wa i n gon goro Stream at N l l 9/ 797550
El bas al band of pumi ceous bl ocks and l ap i l l i , fi ne l i th i c l a pi l l i and ma f i c crysta l s
'
. ..
'Di sti nct , wavy boundary
Buri ed s o i l i n unnamed a s h
Ma hoe tephra
Di s t i nct , undul ati ng boundary Un named ash o •
:
' • o , f • o, � 11 : :·:�· �·.� �4 �. : �:-::�', �/, · •• �·.!A�': ·.. �.::: �<·;': ·.:: :.�: �:.:::;
Fi gure 3 . 14 of the Ma hoe 00 �Oma h i na
T he Oma h i na Tephra i s an i mportant s trati g ra p h i c marker , i n the south-east of the s tudy a rea , wh ere i t has been i d enti f i ed a t two
l ocal i ti es . I t i s a d i sti ncti ve wh i te , rhyo l i ti c c l ay and i s proba b l y
the a i rfa l l equ i va l ent of o n e of t h e centra l North I s l and i g n imbr i te sheets .
T he Tephra has been fi s s i on tra c k da ted at �· 370 Ka B . P . ( P i l l an s ,
1 98 1 ) . P i l l a n ' s work has s hown that the Tephra overl i es wave-cut
surfaces wi th i n p re-Ka i atea I l l a nd Ka i a tea I l l terraces but i s absent
from wi thi n the younger Bru n swi c k cover beds . T h i s i nd i cates that the
cutti ng of pre-Ka i atea I l l and Ka i a tea I l l surfaces predates the ex i s tence of the Oma h i na Tephra .
The Tephra has been found i n the south -eastern hi l l coun try of El tham County , on Rotokare Road a t N 1 19/9044 23 and on Ti r imoana Road at N 1 1 9/ 9 2241 5 . The Tephra i s we l l exposed at the l atter l ocati on
( Pl ate 3 . 1 0 ) where i t i s 80 to 1 0 0mm t h i c k , occurri ng above vol can i c brecc i a s tha t probabl y were der i v ed from the Ka i ta ke centre .
i i . THE WESTERNMOST OCCURRENCES OF AOKAUTERE ASH AND I M P L I CAT I ONS FOR THE LATE QUATERNARY IN TARANAKI
T h e Aokautere Ash ( Cowi e , 1 9 64 ) i s a rhyo l i t i c ash now recog n i sed a s the l ower member of the Kawa kawa Tephra Forma ti on ( Vucet i c h and
Howa rth , 1 9 76 ) . The name Kawa kawa Tep hra i s appl i ed where the presence of two o r more memb ers of th i s format i on can be demo n s tra ted
strati g rap h i ca l l y .
T h e u pper Orua n u i Brec c i a Member , m i dd l e Sci nde I s l and Ash Member and Ao kau tere Ash a l l ori g i na ted from the same vol ca n i c epi sode , centred i n the L a k e Taupo a rea , approx i mate l y 2 0 , 000 years ago .
A t the type s ec t i o n on Whangamata Road ( N93/ 373458 ) the Aokau tere Ash Member compri ses mu l t i pl e bedded med i um to coarse ash of a i rfa l l
ori g i n . T here i s a rad i ocarbon age ( NZ 1 056A ) of 1 9850 ± 3 1 0 yea rs B . P .
for wood bel ow the a s h ( Na i rn , 1 9 7 1 ) .
A t l ea s t 1 00mm of the a s h wa s depo s i ted over much of the central and ea s tern North I s l a nd . P u l l ar a nd B i rrel l ( 1 9 7 3 ) i nd i ca ted that the
8 6
P l a te 3 . 10
Secti o n e xposed on Ti ri moana Road at N l l9/9224 1 5
s how i ng the Oma h i na Teph ra i n terbedded i n a n des i ti c a s hes .
mos t we s terly occurrences o f 100mm th i ckness to be i n the Wanganui and
Otorohanga d i s tri cts . Prev i o u s l y a 900mm depos i t of the ash was
recogni sed by J . F . Ai tken near Turutu rumokai Pa , H awera , wh i ch l ed to
the d i s covery of further s i tes , ea s t of H awera . Recently a mo re wi de
s prea d di stri buti on to th e wes t of the so urce area has been es tabl i sh ed
i n the E l tham-Mahoe-Awa tuna di s tri ct ( Appendi x I I ) . Th es e a re th e
westernmo s t l oca l i ti es ye t k nown for the Ao ka utere Ash and occur between
200-4 50m el evati on and i n c l o se p ro x i mi ty to Mt. Egmo nt ( Fi gure 3 . 1 5).
I t i s s i g ni fi cant that i n the Hawera area the Ash i s overl a i n by tep h ra and teph ri c l oess and occ urs a t depths of 1 . 5 - 2m , wh i l e to the wes t , i n E l th am Cou nty the Ao kautere Ash has been l ocated u p to 7 . 5m
from the s u rfa ce beneath a deep teph ra sequence wi th some teph ri c l oess . The a ppeara n ce of th e Aok a u tere Ash a t Opunake Road near Ro na l d Road at N 1 19/ 795550 i s : -
80mm t h i c kness th i n ni ng to 60mm of 7 . 5Y R 6/4 ( l i ght b rown)
p umi ceous s a n d wi th a di ffus e upper bo unda ry and s harp undul ati ng l ower boundary ( Pl ate 3 . 1 1) .
The di sti ncti ve and often cons pi cuo us appeara nce of th e Ao kautere As h a s a t i me pl ane faci l i tates the dati ng of l ah a ri c depos i ts . The Ash occurs l es s than 1m above vo l cani c brecci as to th e s o uth -east of Mt .
Egmont and the se b recc i as can be correl ated w i th the Pungarehu Formati o n ,
dated ( N Z 1623A) a t 22 , 100 ± 6 00 yea rs B . P . These s u rfaces we re fo rmerly
ma pped as Lepperton Lahars (Hay , 1967) a nd as cri bed to a fri g i d cl i mati c
peri od pri or to the Stratfo rd Lah a rs , w h i c h were k nown to be o l de r tha n
4 5 , 000 years ( Grant- Tayl o r , 1970) . These da tes a re no l o nger tenabl e .
The fo rmer col l a pse of Mt . Egmont abo ut 2 2 , 000 yea rs ago mus t now be rega rded as havi n g been a much l a rger event than was previ o u s l y
apprec i a ted , probab l y repres enti ng a Bezymi anny-type explos i on a n d e o l l aps e .
The th i c knes s of teph ri c and associ ated ma teri a l s exc l udi ng l ah a ri c and a l l uvi a l depos i ts , tha t have acc umul a ted above the Aokautere As h , i n
Taranak i , h ave been pl otted (Fi g ure 3 . 1 6) . Where the Aokautere As h has
not been pos i ti vel y i denti fi ed data on the thi ckness of materi a l s above
the Pungareh u Fo rma ti on (�. 2 2 , 000 years o l d) and the Sa unde rs Ash
(�. 1 7 , 000 yea rs o l d) have been i nc l uded . Th e i sopachs for these ma teri a l s
i nd i cate tha t duri ng the l a s t 20 , 000 yea rs there has been mo re than 7m a cc umul a t i on of tephra i n the vi ci ni ty of Mt . Egmo n t .
F i g ure 3 . 1 5 N E W
PlYMOUTH
' ' I �-' I \ \ \ I I ., I "" \ ., \ ' ' •Mt.
Egmont
40 • • 50 • 10mm
Thi c kness ( i n
mm)
and forAokautere Ash i n cen tra l and s o uthern Ta ran a k i
8 8
P l a te 3 . 1 1
Secti on exposed i n paddock adj acent to Opunake Roa d , n ea r Rona l d Road a t N l l 9 / 7 9 5 5 50 .
The Aoka utere Ash i s 80 mm th i ckness
thi n n i ng to 60 mm , w i th a s h a rp base