Evolution of the Giant Foresets Formation, northern Taranaki Basin, New Zealand


Hansen, R.J.; Kamp, P.J.J.

Proceedings of New Zealand Petroleum Conference 2002, 24 – 27 February: 419-435

2002


Plio-Pleistocene aggradation and progradation has resulted in the rapid outbuilding of the continental shelf margin, northern Taranaki Basin. Seismic reflection profiles reveal that this outbuilding is characterised by bold clinoforms which offlap in a basinward direction. This stacked succession of clinoforms, collectively termed the Giant Forests Formation, obtains thicknesses of over 2 km in places, and has had a significant effect on the thermal regime of the region. This integrated study was initiated to document the Late Neogene evolution of this formation, and thereby gain insights on sedimentary distribution patterns, timing of sedimentation, and controls on progradation and aggradation. Latest Miocene extension in the northern Taranaki Basin, related to rotation of the Hikurangi subduction zone, greatly influenced sedimentation patterns in the Pliocene. Palinspastic reconstruction shows that initial extension of the Northern Graben occurred before Giant Foresets Formation sedimentation began. Sediment, sourced from erosion to the east, was preferentially funneled into the newly created Northern Graben during the late Miocene and Early Pliocene, while areas to the north and west underwent a period of sediment starvation. During the late Pliocene, and into the Pleistocene, sediment accumulation outpaced graben extension, and by the end of the Mangapanian, the graben was overtopped. During this period, the progradational front associated with the outbuilding of the continental shelf-slope margin advanced northwards. Throughout the Nukumaruan, continuing to the present day, shelf migration was extremely rapid. While at least seven cyclical sea-level changes, with an approximate periodicity of 400 ka (fourth-order) have been identified, overall, depths shallowed from dominantly bathyal, to dominantly shelfal.

Evolution
of
the
Giant
Foresets
Formation,
northern
Taranaki
Basin,
New
Zealand
Rochelle
J
Hansen,
Peter
JJ
Kamp
Department
of
Earth
Sciences,
The
University
of
Waikato,
Private
Bag
3105,
Hamilton
2001,
New
Zealand
Abstract
Plio-Pleistocene
aggradation
and
progradation
has
resulted
in
the
rapid
outbuilding
of
the
continental
shelf
margin,
northern
Taranaki
Basin.
Seismic
reflection
profiles
reveal
that
this
outbuilding
is
characterised
by
bold
clinoforms
which
offlap
in
a
basinward
direction.
This
stacked
succession
of
clinoforms,
collectively
termed
the
Giant
Foresets
Formation,
obtains
thicknesses
of
over
2
km
in
places,
and
has
had
a
significant
effect
on
the
thermal
regime
of
the
region.
This
integrated
study
was
initiated
to
document
the
Late
Neo-
gene
evolution
of
this
formation,
and
thereby
gain
insights
on
sedimentary
distribution
patterns,
timing
of
sedimentation,
and
controls
on
progradation
and
aggradation.
Latest
Miocene
extension
in
the
northern
Taranaki
Basin,
related
to
rotation
of
the
Hikurangi
subduction
zone,
greatly
influenced
sedimentation
patterns
in
the
Pliocene.
Palinspastic
reconstruction
shows
that
initial
extension
of
the
Northern
Graben
occurred
before
Giant
Foresets
Formation sedimentation
began.
Sediment,
sourced
from
erosion
to
the
east,
was
preferentially
funneled
into
the
newly
created
Northern
Graben
during
the
late
Miocene
and
early
Pliocene,
while
areas
to
the
north
and
west
underwent
a
period
of
sediment
starvation.
During
the
late
Pliocene,
and
into
the
Pleistocene,
sediment
accumulation
outpaced
graben
extension,
and
by
the
end
of
the
Mangapanian,
the
graben
was
overtopped.
During
this
period,
the
progradational
front
associated
with
the
outbuilding
of
the
continental
shelf-slope
margin
advanced
north-
wards.
Throughout
the
Nukumaruan,
continuing
to
the
present
day,
shelf
migration
was
extremely
rapid.
While
at
least
seven
cyclical
sea
level
changes,
with
an
approximate
periodicity
of
400
ka
(fourth-order)
have
been
identified,
overall,
depths
shallowed
from
dominantly
bathyal,
to
dominantly
shelfal.
Introduction
The
depositional
history
of
the
northern
part
of
Taranaki
Basin
(Fig.1)
is
characterised
by
rapid
progradation
and
aggradation
of
a
late-early
Pliocene
to
Recent
continental
margin
succession
that
underlies
the
modern
shelf
and
slope.
It
is
characterised
by
clinoform
development,
and
the
stratigraphic
name
ascribed
to
the
whole
succession
is
the
Giant
Foresets
Formation
(Shell
BP
Todd
1976).
This
formation
reaches
a
thickness
of
2200
m
and
comprising
a
substantial
part
of
the
total
basin
fill.
It
represents
a
major
part
of
the
regressional
phase
of
Taranaki
Basin
and
we
associate
it
with
the
2nd
order
Rangitikei
megasequence
(Kamp
et.al
.,
this
volume),
which
is
also
represented
in
Wanganui
Basin.
The
thickness
and
rapid
accumulation
of
the
Giant
Foresets
Formation
will
have
had
a
significant
impact
on
the
petroleum
systems
of
Taranaki
Basin,
particularly
in
terms
of
driving
the
maturation
of
hydrocarbons
and
their
migration
(Beggs
1990;
McAlpine
2000).
Surprisingly,
few
detailed
studies
have
been
undertaken
on
the
Giant
Foresets
Formation.
The
primary
objective
of
this
study
has
been
to
develop
a
better
understanding
of
the
evolution
of
the
Giant
Foresets
Formation.
This
has
involved
integration
of
data
derived
by
several
techniques,
including
mapping
and
interpretation
of
seismic
reflection
profiles,
analysis
of
geophysical
(wireline)
logs,
acquisition
and
analysis
of
planktic
and
benthic
foraminiferal
data
for
key
well
sections,
as
well
as
decompaction
and
backstripping
of
reflection
lines
for
palinspastic
reconstructions.
This
paper
provides
a
broad
overview
of
these
techniques
as
applied,
and
presents
some
preliminary
results
obtained
to
date.
The
investigation
is
ongoing.
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
419
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Fig.1:
(A)
Location
of
study
area
including
structural
features
of
the
region.
(B)
inset
shows
location
of
detailed
study
area.
Top
Miocene
features
after
Thrasher
and
Cahill
(1990).
Geological
setting
The
parts
of
Taranaki
Basin
investigated
in
this
study
include
the
Northern
Graben
and
the
northwestern
part
of
the
Western
Stable
Platform
(Fig.1).
The
Northern
Graben
is
delineated
to
the
west
by
the
Cape
Egmont
Fault
Zone
and
to
the
east
by
the
Turi
Fault
Zone.
The
Western
Stable
Platform
has
been
influenced
by
crustal
flexure
(Holt
and
Stern
1994)
but
has
not
been
internally
disrupted
by
faulting
(King
and
Thrasher
1996).
A
synthesis
of
the
geological
character
and
development
of
Taranaki
Basin
has
been
written
by
King
and Thrasher
(1996).
The
basin
formed
during
the
late
Cretaceous,
and
initially
underwent
extension
associated
with
Tasman
Sea
spreading.
During
the
latest
Cretaceous
to
early
Oligocene
the
basin
accumulated
sediments
in
a
type
of
passive
margin
under
a
regional
transgression
where
subsidence
exceeded
sedimentation.
From
the
middle
to
late
Oligocene
the
eastern
margin
of
the
basin
started
to
subside
more
rapidly,
and
this
has
been
attributed
to
lithospheric
loading
associated
with
the
initial
phase
of
development
of
the
Australia-Pacific
plate
boundary
zone
through
the
New
Zealand
platform.
During
the
Miocene
the
basin
registered
in
its
structures
and
sediment
types
the
influence
of
the
evolving
plate
boundary
much
more
clearly.
This
involved
earliest
Miocene
basement
overthrusting
on
the
Taranaki
Fault,
and
late-early
Miocene
formation
of
the
Tarata
Thrust
Zone.
By
the
middle
Miocene
the
direct
effects
of
compression
within
the
northern
part
of
the
basin
and
along
its
eastern
margin
had
ceased.
This
coincided
with
the
onset
of
submarine
arc
volcanism
within
northern
part
of
the
basin
(Mohakatino
Volcanic
Centre;
Fig.
1).
The
volcanic
arc
paralleled
the
trend
of
the
contemporaneous
subduction
zone.
Eruptions
continued
until
about
7-8
Ma
(King
and
Thrasher
1996).
The
volcanic
massifs
remained
as
topographic
highs
influencing
sediment
distribution
patterns
until
the
late
Pliocene.
During
the
Pliocene
the
volcanic
arc
migrated
southeastward
onshore
into
the
Taupo
Volcanic
Zone,
where
it
has
been
active
since
the
latest
Pliocene
or
early
Pleistocene.
Following
the
migration
of
volcanism
onshore,
the
northern
parts
of
Taranaki
Basin
became
extensional,
with
formation
of
the
Northern
and
Central
Grabens.
These
depocentres
were
rapidly
in
filled
by
progradation
of
the
Giant
Foresets
Formation.
The
Giant
Foresets
Formation
comprises
a
shelf
to
slope
to
basin
floor
succession
of
fine
muds,
through
to
silts
and
sands
(ARCO
Pet.
Ltd.
(NZ)
Inc.1992;
Shell
BP
Todd
1981;
Hematite
Petroleum
1970).
The
top-sets
often
contain
shelly
or
pebbly
intervals,
and
the
succession
is
sporadically
volcaniclastic.
Correlative
units
of
the
Giant
Foresets
Formation
onshore
include
the
Tangahoe
Mudstone
and
Whenuakura
Subgroup
and
younger
Nukumaruan
and
Castlecliffian
strata
in
Wanganui
Basin
(Fig.2)
(Kamp
et.al
.,
this
volume).
The
Giant
Foresets
Formation
is
underlain
by
AGE
(Not
to
absolute
time
sea
e)
N
-
NW
S
-
SE
FORMATIONS
!Taranaki
Peninsula
!
2
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Facies
and
Relative
Level
Fall
Sea
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Shelf
2.
la
and
n.
G
slope
C
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muds
N
te.
6
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E
.o
Shelf
1
sands
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OCENE
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:
Slope
slits
Shelf
a
Turbidite
muds
msands
1
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sediments
1
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URENUI
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TAIMANA
FM
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Fig.2:
Miocene
to
Recent
stratigraphic
framework
for
Taranaki
Basin.
This
figure
illustrates
the
general
age
and
progradational
nature
of
the
Giant
Foresets
Formation.
Modified
from
King
and
Thrasher
(1996).
420
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
i i
i
2
A
l2
4
A
A A
A
A
Ma
Arlkl
Fm
Ariu
Fin
lionaketind
Form•tlon
gas
Fm
Ariki
Fm
0
Manganui
Formation
Mohakatino
Formation
Giant
Foresails
Formation
863
2
c
5calcareaus
Giant
Foresets
Formation
or.
Mohakatino
Formation
k
SW
Westem
Stable
Platform
Northern
Graben
NW
NE
AliId-1
n
gaa-1
Kahawai-1
Turi-1
X
Arawa-1
s
+
-
Taimana-1
50
Km
Fig.3:
Seismic
grid
and
well
location
map.
Line
P95-158
(highlighted)
is
used
in
the
palinspastic
reconstruction.
Dashed
line
shows
transect
for
Fig.4
(chronostratigraphic
panel).
the
Manganui,
Mangaa,
or
Ariki
formations
and
in
places
by
Miocene
volcanic
massifs
(e.g.
Kora-1
well
site)
(Fig.2).
Data
sets
Thirty
two
seismic
lines,
including
25
from
the
P95-series
(Petrocorp
Exploration,
PR
2261,
1995)
and
seven
from
various
earlier
data
sets,
have
been
interpreted
as
part
of
this
investigation
(Fig.3).
The
reflection
lines
have
been
interpreted
using
methods
outlined
in
Mitchum
et.al
.
(1977)
and
Vail
(1987).
More
than
60
discrete
seismic
units
have
been
identified
and
mapped.
Many
of
these
units
have
been
able
to
be
mapped
over
a
wide
area,
and
have
provided
the
basis
to
construct
structure
contour
and
isopach
maps.
This
has
allowed
the
development
of
the
shelf-slope margin
to
be
tracked
through
time.
General
lithologic
trends
in
the
Giant
Foresets
Formation
have
been
established
from
geophysical
wireline
logs
for
each
of
the
wells
in
the
study
area
(see
Fig.3
for
well
locations),
well
completion
reports
and
composite
well
logs.
The
foraminiferal
content
of
numerous
unwashed
well
cutting
samples
from
each
of
four
wells
(Arawa-1,
Ariki-1,
Kora-1
and
Wainui-1)
have
been
analysed,
revealing
paleoenvironmental
information,
including
water
depth
and
changes
in
benthic
species
and
abundance
levels.
These
data
are
useful
in
better
understanding
the
depositional
history
of
the
Giant
Foresets
Formation.
They
are
also
being
explored
to
establish
whether
or
not
they
can
identify
cyclicity
in
environmental
parameters
at
the
level
observed
in
the
seismic
reflection
lines.
Backstripping
and
decompaction
modelling,
using
age,
paleobathymetric,
and
lithologic
data
obtained
from
the
methods
outlined
above,
have
enabled
palinspastic
reconstruction
of
several
seismic
lines.
These
reconstructions,
coupled
with
paleogeographic
maps,
effectively
summarise
the
geological
history
and
evolution
of
the
Giant
Foresets
Formation.
Chronology
The
Giant
Foresets
Formation
is
the
uppermost
stratigraphic
unit
in
the
northern
part
of
Taranaki
Basin.
The
youngest
parts
of
the
formation
are
therefore
of
Recent
age
and
include
the
surficial
sea-floor
sediments.
The
base
of
the
unit
is
however
strongly
progradational
in
a
north
to
northwest
direction
(Fig.2)
and
therefore
will
be
diachronous.
The
age
of
the
base
of
the
formation
is
also
complicated
by
the
widespread
occurrence
of
a
condensed
section
and
paraconformity,
and
the
practical
difficulty
of
identifying
10
10
20
Kilometres
,...mg...preeentedbyArda
Format=
Fig.4:
Chmnost
atigraphic
panel,
northern
Taranaki
Basin.
Timescale
and
stage
boundaries
after
Morgans
etaL
(1997).
Stage
abbreviations;
Wq—Haweran,
Wn—Nukumaruan,
Wm
—Mangapanian,
Wp
—Waipipian.
Note
that
the
greatest
thickness
obtained
by
the
Avid
Formation
at
any
site
is
about
110
m
(Mid-
1).
Much
ofthe
time
repnzsentedby
the
appanznt
unconfoimity
may
actuallybe
represented
by,
but not
identified
in,
theArild
Foimation.
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
421
(c)
(d)
(a)
Topsets
-
sub-parallel,
sub-horizontal,
moderately
continuous
reflectors;
(b)
Progradational
foresets
-
offlapping
and
dipping
basinward,
moderately
continuous
reflectors;
(c)
Degradational
foresets
-
lower
amplitude,
more
steeply
dipping
and
chaotic
reflectors;
(d)
rttomsets
-
sub-horizontal,
slightly
inclined
reflectors,
with
variable
continuity.
Fig.5:
Schematic
illustration
of
foreset
divisions
(after
Beggs
1990),
showing
relative
position
in
a
shelf-
slope-
basin
setting.
(a)
(b)
the
New
Zealand
Pliocene
Stages
within
the
condensed
section
given
the
spacing
of
cutting
samples.
The
Ariki
Formation
was
named
for
a
marl
encountered
in
Ariki-1,
which
has
a
Kapitean
(latest
Miocene)
age
(Fig.4)
and
110
m
thickness.
The
Ariki
Formation
underlies
the
Giant
Foresets
Formation.
The
Ariki
Formation
has
also
been
identified
in
this
study
in
several
other
well
sections.
It
occurs
in
Wainui-1,
Tangaroa-1,
and
Te
Kumi-1.
A
thin
(c.21
m-thick),
marl
is
noted
at
Kahawai-1,
and
may
be
an
equivalent
of
the
Ariki
Formation
based
on
age
and
stratigraphic
position.
At
all
sites
where
it
is
present,
this
marl
is
associated
with
a
sharp
increase
in
planktic
foraminiferal
percentage
compared
with
the
overlying
Giant
Foresets
Formation.
This
increase
in
planktic
foraminiferal
content
is
a
feature
that
can
be
used
to
help
locate
the
base
of
the
Giant
Foresets
Formation,
or
time
equivalent
horizons,
even
in
more
terrigenous
rich
sediments
(Manganui
Formation),
for
example
in
Arawa-1
and
Taimana-1,
and
at
the
base
of
the
Mangaa
Formation
in
Awatea-1
and
Mangaa-
1.
At
many
of
these
sites,
with
the
exception
of
the
more
southerly
wells
(Taimana-1,
Arawa-1)
late
Tongaporutuan
to
late
Kapitean
and
sometimes
Opoitian
sediments
are
very
condensed
(Fig.4).
In
Fig.4
the
extent
of
the
Ariki
Formation
in
space
and
time
and
the
extent
of
the
associated
paraconformity,
as
we
have
established
it
to
date,
are
mapped
in
a
southwest
to
northeast
transect
that
takes
in
many
of
the
hydrocarbon
wells.
The
origin
of
this
condensed
section
is
related
to
a
period
of
terrigenous
sediment
starvation
across
much
of
the
northern
part
of
Taranaki
Basin.
It
corresponds
to
the
accumulation
of
the
thick
Kiore
and
Matemateaonga
Formations
in
the
King
Country
and
Wanganui
basins
as
a
prograding
continental
margin,
and
the
limited
extent
of
this
progradation
in
Taranaki
basin
(Kamp
et.al
.,
this
volume).
Later
parts
of
the
paraconformity
development
are
related
to
a
marked
early
Opoitian
(earliest
Pliocene)
tectonic
pulldown
of
Wanganui
Basin
and
Toru
Trough
(earliest
Pliocene),
which
caused
a
dramatic
flooding
and
southward
onlap
across
Wanganui
Basin
and
southeastern
parts
of
Taranaki
Basin.
This
caused
the
accumulation
of
the
Matemateaonga
Formation
to
cease,
and
the
water
depths
to
increase
from
shoreface
to
bathyal,
allowing
the
Tangahoe
Formation
to
accumulate
at
slope
depths;
contemporary
shelf
sedimentation
was
focused
to
the
south
in
Wanganui
Basin.
The
deposition
of
the
Giant
Foresets
Formation
represents
the
progradation
of
a
second
continental
margin
(Rangitikei
megasequence)
northward
into
Wanganui
and
Taranaki
basins
(Kamp
et.al
.,
this
volume).
The
Giant
Foresets
Formation
in
northern
parts
of
Taranaki
Basin
are
younger
than
4
Ma
(Fig.4).
Note
in
Fig.4
the
occurrence
of
the
Mangaa
Formation
in
the
Northern
Graben,
and
that
its
accumulation
reflects
deposition
during
the
early
Pliocene
(Opoitian
Stage).
Geophysical
characteristics
Seismic
reflection
characteristics
of
the
Giant
Foresets
Formation
The
Giant
Foresets
Formation
is
well
known
for,
and
indeed
was
named,
for
its
spectacular
stacked
succession
of
bold
off-lapping
clinoforms
that
prograde
towards
the
modern
continental
slope
(Shell
BP
Todd
1976).
The
formation
typically
has
four
parts
based
on
its
seismic
character
(Beggs
1990)(Fig.5).
1.
Top-sets.
These
comprise
sub-parallel,
sub-horizontal,
moderately
continuous
reflectors.
Lithologies
include
sandstone,
muddy
siltstone,
and
shellbeds
or
disseminated
shell
hash,
consistent
with
accumulation
on
a
continental
shelf.
2.
Progradational
foresets.
These
display
moderately
continuous
reflectors,
off-lapping
in
a
basinward
direction.
The
depositional
setting
is
a
continental
422
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
slope
with
accumulation
of
fine-grained
mudstone
and
muddy
siltstone.
3.
Degradational
foresets.
These
reflectors
represent
structure
on
a
continental
slope,
but
the
reflectors
dip
at
steeper
angles
than
the
depositional
surface,
and
are
more
chaotic
reflecting
mass
movement
downslope.
The
units
are
lithologically
variable.
Units
can
incise
deeply
into
underlying
strata.
4.
Bottom-sets.
These
sub-horizontal
to
slightly
inclined
reflectors
represent
deposition
on
a
basin
floor.
They
may
have
variable
continuity.
Lithologies
making
up
these
units
can
be
sandstone
or
mudstone.
Figure
6
illustrates
an
uninterpreted
and
an
interpreted
version
of
line
P95-158
(Fig.3).
The
grid
of
seismic
has
been
used
to
map
multiple
seismic
units
throughout
the
study
area. This
has
involved
60
seismically
distinct
units,
or
packages.
Most
of
these
seismic
units
have
(or
have
had)
top-set,
foreset
(either
progradational
or
degradational)
and
bottom-set
components.
However,
along
the
eastern
margin
of
the
basin
there
has
been
substantial
post-depositional
uplift
and
parts
of
the
seismic
units
have
been
truncated
by
erosion.
Interpretation
of
the
seismic
grid
enables
construction
of
structure
contour
and
isopach
maps
(in
TWT
and
depth/
thickness).
These
can
then
be
used
to
interpret
several
features,
including
depositional
style
(e.g.
whether
or
not
the
shelf
margin
advanced
as
a
series
of
depositional
lobes,
or
a
more
linear
foreset
front),
changing
location
of
depocentres,
migration
direction
of
the
shelf
margin,
and
overall
geometry
of
the
formation.
Of
particular
importance
is
the
base
Giant
Foresets
Formation
structure
contour
map,
shown
in
Fig.7
in
TWT.
This
map
shows
that
most
accommodation
was
generated
within
the
Northern
Graben,
and
to
the
north
and
west
of
the
study
area,
with
a
smaller
fault-bound
depocentre
immediately
to
the
northeast
of
Arawa-1.
A
series
of
isopach
maps
(Fig.8)
show
how
the
Northern
Graben
was
infilled
during
the
middle
to
late
Pliocene
(Waipipian-Mangapanian
Stages;
Figs
8a&b).
The
Opoitian
isopach
map
includes
Mangaa
and
Manganui
W
Western
Stable
Platform
Formations.
By
the
Nukumaruan
Stage,
the
foreset
front
was
clearly
made
up
of
a
linear
sedimentary
body.
Individual
seismic
units
occur
as
a
series
of
migrating
lobes
within
these
fronts.
Sediments
were
thickest
during
the
Opoitian-
Mangapanian
Stages
over
the
Western
Stable
Platform,
while
in
the
Northern
Graben,
the
majority
of
sediment
was
deposited
during
the
Opoitian
(in
the
central
part
of
the
graben)
and
from
the
Nukumaruan
onwards.
Wireline
log
motifs
The
characteristics
of
wireline
logs
were
examined
for
each
of
the
11
wells
used
in
the
study
area
(e.g.
Fig.9).
Log
types
include
gamma
ray
(GR),
spontaneous
potential
(SP),
sonic,
resistivity,
and
density
logs.
Lithology
was
interpreted
from
a
combination
of
available
wireline
logs,
composite
well
logs,
and
well
completion
reports.
This
in
turn
enabled
lithologies
to
be
attributed
to
specific
log
motifs
or
combinations
of
log
motifs.
These
reveal
that,
in
comparison
with
underlying
formations,
the
Giant
Foresets
Formation
has
few
distinctive
characteristics.
The
overall
muddy/silty
nature
of
this
formation
is
reflected
in
the
quiet
log
signatures,
although
an
overall
coarsening
upwards
nature
is
noted
in
some
wells.
The
base
of
the
formation
is
nearly
always
delineated
by
a
sharp
kick
to
the
left
on
GR,
independent
of
the
lithology
of
the
underlying
formation.
Given
the
clarity
of
clinoform
development
in
many
of
the
seismic
reflection
lines
it
is
surprising
that
the
wireline
logs
are
apparently
so
bland.
However,
when
enlarged,
and
compared
against
the
seismic
section
for
each
well
(Fig.10),
a
distinct
relationship
between
prominent
reflectors
(clinoforms)
and
the
base
of
upward-fining
or
upward-coarsening
units
or
packages
of
units
is
evident,
even
though
these
units
may
only
display
variation
within
fine-grained
lithologies.
Paleoenvironmental
interpretation
Detailed
analysis
of
foraminifera
from
suites
of
cutting
samples
from
each
of
four
wells
(Ariki-1,
Arawa-1,
Kora-1
and
Wainui-1)
has
enabled
paleobathymetry
and
depositional
environments
to
be
established
for
sections
Northern
Graben
(a)
Seismic
reflection
profile
P95-158,
uninterpreted.
.
Giant
Foreseti
Formation
-
kl
Formation
(b)
Seismic
reflection
profile
P95-158,
interpreted.
Fig.6:
Example
of
one
of
the
seismic
reflection
profiles
used
in
this
study
(P95-158;
refer
to
Fig.3
for
location).
Note
the
highly
incised
nature
of
the
degradational
foresets
compared
with
the
smoother
profile
of
the
progradational
foresets.
See
also
Fig.14
for
palinspastic
reconstruction
of
line.
Depth
is
in
two-way-travel
time
(seconds).
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
423
Legend
50-100
msecs
1850-1900
msecs
2600-2650
msecs
Subaerlal
Faults
\\
Top
Miocene
channels
\
order
of
100
m
would
be
significant
at
shelf
depths,
such
changes
would
not
cause
the
same
sedimentary
response
at
bathyal
depths,
at
which
all
sites
resided
during
this
period.
Changes
in
relative
sea
level
do
become
more
obvious
in
the
top-sets.
2.
Two
bathymetric
deepening
events
occurred
during
the
interval
studied.
The
first
occurred
during
the
mid
Pliocene
(Waipipian),
and
in
all
cases
shows
a
deepening
from
upper
bathyal
to
mid
bathyal.
This
event
appears
to
have
been
longest
at
one
of
the
deeper
sites
(Wainui-1).
The
second
occurred
during
the
late
Nukumaruan
to
Castlecliffian,
with
a
deepening
from
mid/outer
shelf
to
outer
shelf/upper
bathyal
depths
(depending
on
site)
recorded.
Cyclicity
A
Ari
Mul-1
/
O
sva-1
Taima
j
10
0
10
20
Kilometres
through
the
Giant
Foresets
Formation.
The
analyses
included
the
calculation
of
foraminiferal
planktic:benthic
ratios
to
show
changing
surface
water
mass
with
time,
and
statistical
analysis
of
benthic
species
and
diversity,
as
well
as
cluster
analysis,
to
highlight
depth
trends.
Figure
11
illustrates
the
results
of
cluster
analysis
for
Ariki-1,
using
the
Multivariate
Statistical
Package
developed
by
Kovach
(1999).
Species
associations
were
clustered
using
modified
Morista
Similarity,
and
faunal
sample
associations
clustered
using
Bray-Curtis
Distance
Matrix.
Depth
ranges
were
estimated
using
the
resultant
dendrograms,
and
a
paleobathymetric
curve
generated
for
each
well
(Fig.12).
These
show
several
features.
1.
During
the
Pliocene,
cyclical
changes
in
sea
level
at
41
ka
periodicity,
as
evident
form
the
oxygen
isotope
records
of
deep
sea
cores,
were
not
readily
observable
in
terms
of
changing
water
depth.
While
changes
in
sea
level
of
the
Unlike
Wanganui
Basin,
where
shelf
cyclothems
can
be
clearly
observed
and
correlated
on
the
basis
of
the
regular
occurrence
of
shellbeds
(both
in
outcrop
and
well-log;
e.g.,
Kamp
et
al.
in
prep.,
this
volume;
McIntyre,
2001),
sediments
of
the
Giant
Foresets
Formation
display
few
characteristics
that
lend
themselves
to
delineation
of
cyclothems.
This
is
in
part
due
to
the
dominantly
muddy
nature
of
the
sediment,
and
in
part
to
the
generally
deep-water
depositional
setting,
but
may
also
be
due
to
the
fact
that
the
majority
of
sediment
is
inferred
to
have
been
deposited
during
periods
of
low
relative
sea
level.
While
the
Giant
Foresets
Formation
contains
successive
clinoforms,
it
is
not
immediately
apparent
that
the
sediments
between
successive
clinoforms
represent
individual
eustatic
sea
level
cycles.
It
is
therefore
necessary
to
have
another
means
of
assessing
sea
level
change.
To
help
define
cyclicity,
both
in
terms
of
which
seismic
units
represent
actual
relative
sea
level
change,
and
which
ones
represent
'event'
deposition,
wireline
interpretation
and
foraminiferal
information
from
Ariki-1,
Arawa-1,
Kora-1
and
Wainui-1
were
integrated
with
seismic
reflection
profiles
(e.g.
Fig.13).
Textural
trends
(obtained
from
sieve
and/or
laser-
sizer
analyses) were
also
incorporated
in
the
data
integration.
This
work
is
still
on
going,
however,
some
trends
have
been
identified.
1.
Peaks
in
the
abundance
of
benthic
foraminifers
are
often
coincident
with
spikes
in
sediment
texture
(indicated
either
by
textural
logs
and/or
wireline
characteristics).
These
also
Fig.7:
Base
Giant
Foresets
Formation
structure
contour
map,
in
two-way-travel
time
(msecs).
Compiled
from
Hansen
(in
prep.)
and
Thrasher
and
Cahill
(1990).
424
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
Waipipian-Mangapanian
4
4
O
late
Nukumaruan-Recent
O
GJ
Bs
o
/
0-50
m
600-650
m
1700-1750
m
Opoitian
4.
€)
O
\
_
_
Po
o
+."
`s
0
o
C7
rf
Nukumaruan
Q
i
0
+
0
0'
m
line
Fault
Paleo-high
Well
site
contour
intervals
are
in
50
m
incremetns
Fig.8:
Isopachs
showing
depositional
pattern
for
the
Giant
Foresets
Formation
through
time.
Thickness
is
in
metres.
'0'
m
line
is
point
at
which
sediment
is
no
longer
represented
as
a
result
of
erosion
and/or
non-deposition.
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
425
Ariki-1
1=1.111
Sea
bed
Resistivity
Bulk
Density
Gamma
Ray
SP
Sonic
(MSFL)
(ILD/SFL)
(Neutron
porosity
%)
800
90
100
Co
E
I
t5
LL
co
O
LL
C0
LL
LL
0
Casing
change
Ariki
Formation
Lithology
clay
silt
silty
sand/sandy
silt
sand
marl
volcaniclastic
Mohakatino
(Upper)
Manganui
Formation
E
LL
O
C
0
2
2600
Moki
Formation
Equivalent
Fig.9:
Wireline
log
signals
for
the
Giant
Foresets
Formation.
Note
that
all
logs
display
a
characteristically
quieter
signature
than
underlying
formations.
Base
of
the
formation
is
often
delineated
by
a
kick
to
the
left
on
GR
and
SP,
and
to
the
right
on
resistivity
and
bulk
density.
426
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
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,
:111'd1
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GR
100
220
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Sonic
Texture
(%
sand)
0
100
1.2
1.3
1.5
FFI•••••••e•••nomemn-r.,..,....
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ebb
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1
27,i
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40.:
ikneb
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r
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_
f
7,
1
J
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Fig.10:
Correlation
of
wireline
log
and
seismic
reflection
profile
for
Ariki-1.
Bold
reflector
horizons
correlate
well
with
bases
of
upward-
fining
or
upward-coarsening
units,
or
packages
of
units.
Textural
trends
have
been
added
for
comparison.
coincide
with
increases
in
the
abundance
of
shallow
water
benthic
faunas
in
deep
water
sediments.
This
may
indicate
the
influx
of
shelf
sediments
to
deeper
water
conditions
possibly
associated
with
periods
of
falling
sea
level
(e.g.
Pickering
et
al.
1989).
2.
Opportunistic
benthic
species,
such
as
Uvigerina
perigrina,
Bulimina
marginata,
f.
aculeata,
and
Evolvocassidulina
orientalis,
are
able
to
colonise
and
multiply
rapidly
in
environments
that
are
stressful
to
other
species
(e.g.,
an
environment
of
high
organic
carbon
influx
(van
der
Zwann
et
al.
1999;
sen
Gupta
and
Machain-Castillo
1993)).
High
numbers
of
these
species,
coupled
with
low
overall
species
diversity,
suggests
periods
during
which
the
sea
floor
environment
has
undergone
a
dramatic
change,
and
has
been
subsequently
re-colonised
by
species
that
are
able
to
proliferate
under
the
stressful
conditions.
Such
a
dramatic
change
may
occur
as
a
result
of
a
catastrophic
sedimentary
event
(e.g.,
debris
flow,
slump).
Some
of
these
events
may
be
related
to
sea
level
changes.
3.
There
is
a
positive
correlation
between
lower
planktic
foraminiferal
abundance
(indicating
less
oceanic
conditions),
and
peaks
in
benthic
abundance
(Fig.13).
In
deeper
water
situations,
eustatic
sea
level
change
is
not
of
sufficient
magnitude
to
change
bathyal-restricted
habitats,
whereas
on
the
shelf,
a
fall
or
rise
in
sea
level
of
c.60-100
m
will
severely
alter
the
dynamics
of
shallow
water
environments.
However,
lowering
sea
level
may
change
surface
water
mass
conditions,
changing
(decreasing)
surface
productivity,
and
theoretically
resulting
in
fewer
planktic
faunas.
The
integration
of
these
various
types
of
data
are
still
in
the
early
stages.
We
are
attempting
to
test
the
hypothesis
that
mixed
shallow
and
deep-water
faunal
assemblages,
when
correlated
to
peaks
in
the
textural
curve,
and
dips
in
planktic
ratios,
can
be
used
as
proxies
for
sea
level
change.
As
sea
level
lowers
and
shorelines
move
seaward,
coarser-grained
lithologies,
sourced
from
more
energetic
shallower
water
environments,
are
more
likely
to
be
transported
to
deeper,
less
turbid
environments.
At
such
times,
postmortem
transportation
of
shallow
water
faunas
escalates,
and
the
associated
influx
of
organic
carbon
allows
the
proliferation
of
opportunistic
species.
Falling
sea
level
conditions
may
be
indicated
by
the
inclusion
of
shallow
water
taxa
in
deeper
water
faunas,
and
a
corresponding
decrease
in
planktic
abundance.
Sedimentation
related
to
event
deposition,
on
the
other
hand,
may
instead
be
registered
by
either
an
isolated
textural
peak,
or
a
sudden
increase
in
numbers
of
opportunistic
species.
Bold
reflectors
on
seismic
reflection
profiles,
such
as
those
that
bound
clinoform
sets,
are
inferred
to
arise
from
partial
lithification
during
sea
level
highstands
(Beggs,
1990).
By
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
427
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Paleobathymetry
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ff
5
Paleobathymetry
Paleobathymetry
LLZ
Western
Stable
Platform
Northern
Graben-e.
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LL
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Arawa-1
/
1
wo..
Kora-1
Wainui-1
Ariki-1
a
Mangaa-1
Fig.12:
Paleobathymetric
curves
estimated
for
Arawa-1,
Ariki-1,
Kora-1,
and
Wainui-1.
Mangaa-1
is
also
included
as
the
biostratigraphy
for
this
well
has
recently
been
re-evaluated.
(Waghorn
et
al.,
1996).
Thick
arrows
highlight
general
bathymetry
trends.
Circled
numbers
indicate
possible
correlatable
events.
See
Fig.9
for
lithologic
key.
integrating
environmental
and
textural
data
with
seismic
reflection
profiles,
it
is
possible
to
identify
an
order
of
cyclicity
previously
not
identified.
For
example,
in
Fig.
13
(Ariki-1),
seven
cycles
with
an
approximate
periodicity
of
400
ka
(fourth-order
eustatic),
have
tentatively
been
identified.
Each
of
these
correlate
to
one
or
more
discrete
seismic
packages.
Palinspastic
reconstruction
Backstripping
and
decompaction
of
sedimentary
units
is
an
effective
way
of
summarising
the
geological
evolution
and
burial
history
of
an
exploration
well or
section.
This
is
achieved
by
sequentially
removing
layers
of
sediment,
thereby
allowing
underlying
units
to
rebound
back
to
their
original
surface
position.
Normally,
this
is
performed
on
a
single
well
or
on
a
series
of
wells.
For
this
study,
a
backstripping
program
written
by
K.
Sircombe
was
run
on
a
seismic
reflection
profile
(line
P95-158).
All
depths
in
TWT
were
converted
to
depths
in
metres
using
a
binomial
supplied
by
Geosphere
Exploration
Services
Ltd.
Porosity
and
paleobathymetry
were
established
from
wireline
and
lithological
data
and
foraminiferal
paleobathymetry.
Compaction
coefficients
were
determined
by
estimating
the
relative
proportions
of
sand,
silt, mud,
and
limestone/marl
of
each
individual
seismic
unit
through
which
a
borehole
was
drilled.
Using
initial
(surface)
porosity
values
(after
Funnell
et
al.,
1998),
porosity
with
depth
was
calculated
using
Equation
1.
porosity
=
po
exp(-z/d)
Equation
1
where
po
=
initial
porosity
at
the
surface,
z
=
depth,
and
d
=
compaction
co-efficient
The
values
obtained
for
each
seismic
unit
were
then
combined
using
a
mixing
law
(Equation
2)
to
provide
porosity
variation
with
depth.
combined
porosity
(l/p)
=
summation
(vi/pi)
Equation
2
where
p
=
porosity,
vi
=
proportion
of
a
particular
lithology,
and
pi
=
porosity
determined
from
Equation
1.
Similarly,
decompaction
co-efficients
(after
Funnell
et
al.,
1998)
were
mixed
according
to
the
proportion
of
each
lithology,
to
obtain
a
value
representative
of
the
mixed
porosity.
Line
P95-158
(Fig.14;
refer
also
to
Fig.6
for
un-interpreted
and
interpreted
line)
was
chosen
for
decompaction
as
it
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
429
gi
g
18
x
saws
8HE4F
BATHYAL
M
O
U
M
L
u
J3
V
d
e
event
'elated
to
slumping
of
the
shelf
margin
disc,nfonnity
sediment
starvation
Obser
va
t
ions
Watermass
Species
spikes:
Opportunistic
species
shallow
water
faunas
0.1
GR
Sonic
Texture
Benthic
(%
sand)
abundance
1111
0.2
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.
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•••-
°
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co
C
0.9
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.
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Tt-
Mohakatino
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-
Formation
-
'-
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r"="7
0.6
0.7
0.8
L
.
Ariki-1
oe
I
2.4
by
72.3„,
J.
.
mi.
.1
,
ONN•i.
Fig.13:
Integrated
seismic
reflection,
wireline
logs,
textural,
and
foraminiferal
data,
to
highlight
cyclical
trend
in
the
Giant
Foresets
Forma-
tion.
Fourth-order
eustatic(400
ka)
cycles
are
tentatively
identified.
Note
the
dramatic
decrease
in
planktic
percentage
between
the
Ariki
and
Giant
Foresets
Formations.
intersects
two
wells
(Tangaroa-1
and
Kahawai-1),
which
could
be
used
to
obtain
lithologic
data.
It
also
contains
many
of
the
seismic
units
mapped
across
the
study
area,
and
extends
from
the
Turi
Fault
Zone
in
the
east
to
the
modern
shelf
margin
and
slope.
Because
of
the
large
fault
at
the
eastern
end
of
the
line,
and
the
rapidly
increasing
water
depth
at
the
western
end
of
the
line,
P95-158
was
broken
into
6
parts,
depths
to
seismic
units
adjusted
using
relative
shelf-
slope-basin
position
as
indicated
on
the
reflection
profile
(where
the
shelf
break
is
estimated
to
be
—250
m),
and
porosity
and
decompaction
values
extrapolated
from
the
nearest
well.
Inherently,
errors
will
arise
due
to
changes
in
lithology
along
the
length
of
the
line
that
cannot
be
accounted
for.
The
resulting
palinspastic
reconstruction
clearly
illustrates
the
development
of
the
asymmetrical
Northern
Graben.
Initially,
basin
floor
and
basin
floor
fan
sediments
(variously
sandy
to
muddy
bottom-sets)
began
to
infill
a
graben
that
had
already
begun
developing
by
4
Ma
(Fig.
14d;
Mangaa
Formation).
Bottom-sets
sedimentation,
followed
by
the
appearance
of
foresets
marking
the
progradation
of
the
continental
margin,
continued
to
infill
the
graben
concurrently
with
graben
development,
as
illustrated
by
Figs.
14b
and
14c.
This
series
of
figures
also
illustrates
that
the
Western
Stable
Platform
(west
of
Tangaroa-1)
has,
in
sharp
contrast,
remained
relatively
quiescent
during
the
Plio-
Pleistocene.
This
has
previously
been
described
in
King
and
Thrasher
(1996).
Major
uplift
on
the
large
fault
to
the
west
of
Kahawai-1
(part
of
the
Turi
Fault
Zone)
occurred
during
the
Mangapanian-Waipipian
Stages,
with
continual
uplift
noted
through
to
the
Nukumaruan
(note
tectonic
curve).
Conversely,
the
western
margin
of
the
graben
was
affected
to
a
much
lesser
degree,
as
indicated
by
a
much
smoother
profile
to
the
tectonic
curve.
Late
Miocene
to
Late
Pleistocene
paleogeography
One
of
the
main
objectives
of
this
study
is
to
better
constrain
the
paleogeographic
development
of
the
northern
part
of
Taranaki
Basin.
This
is
being
achieved
by
the
integration
of
seismic
reflection
data
(for
geometry,
sediment
distribution,
location
of
channels
and
other
sediment
pathways
and
barriers,
and
migration
of
the
shelf-slope
break),
wireline
log
data
(primarily
for
lithologic
information),
and
foraminiferal
paleoecologic
data
(paleobathymetry,
influx
of
shallow
water
taxa).
Figure
15
displays
a
series
of
paleogeographic
maps
that
illustrate
and
document
the
evolutionary
development
of
the
Giant
Foresets
Formation
within
the
northern
part
of
Taranaki
Basin.
430
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
0
x
I'I
LL
C
WLL
w
F
y
i
y
O
1
.
"
j
y
ny
spuoaas
ul
aW!
uoipagau
5
I
I
I
0
(a)
Se
ism
ic
line
P95-
15
8,
in
terp
re
te
d
i
t
0
S'E
a
I
a
(w)
lanai
sas
mopq
sidaa
2
t
I
(w)
lanai
ses
Molaq
Lacloa
a
(c)
Ea
r
ly
Nu
ku
ma
ru
a
n
(c.
2
Ma)
DI
BY
4
mc%
(la)
la
,
Moles
Fig.14:
Palinspastic
reconstruction
of
seismic
reflection
profile
P95-158.
Seismic
units
have
been
progressively
decompacted
and
backstripped.
Dashed
line
is
tectonic
curve.
Late
Opoitian
(late-early
Pliocene)
marks
the
age
at
the
base
of
the
Giant
Foresets
Formation
along
this
profile.
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
431
-
_
L
-
\
I
L
"'
-
-/
lower
bathyal
-
tnitHowof
both
sub
-
serial
gap
and
upper
bath
yal
Urenul
Fonnation
outcrop
-
.
/
e-a--------7and
"""'
t
u
ll
n
erosion
-
d)
Manganian
(c.2.6
Ma)
uplift
and
erosion
—dew
s
,,
nom
aplin
.
.r
p
n
.
r
/
moslon
Legend
shelf
(depths
not
defined)
E
sandy
inner
shelf
silty
Inner-mld
shelf
volaanialastic
mid-outer
shelf
upper
bathyal
middle
bathyal
lower
bathyal
faults
volcanic
centers
l a
volcanialestic
fans
Al
paleohlghs
submarine
fans
shelf
breaks
channels
shells
rid
conglomerate
e
sediment
pathways
t
subsidence/uplift
p,
01;01.
(e)
Early
Nukumaruan
(c.2
Ma)
(f)
Late
Nukumaruan
to
Castlecliffian
(c.1
Ma)
(a)
Late
Tongaporutuan
to
early
Kapitean
(c.8
Ma)
7
_
lower
bathyal
=
IFICI•1
:
,
/
Sedimont
-7"
(-/
-
Shelf
Km
(b)
Late
Opoitian
(c.4
Ma)
d
or
)
(c)
Waipipian
(c.3
Ma)
Legend
shelf
(depths
not
defined)
inner
shelf
inner-mid
shelf
mld-outer
shelf
upper
bathyal
middle
bathyal
lower
bathyal
sandy
faults
7
silty
volcanic
centers
7
volcanidastic
volcanidastic
fens
E
shells
do
,
peleohighs
E
conglomerate
e•
:
submarine
fans
E
sediment
pathways
t
shelf
breaks
E
subsidence/uplift
1.1
.1.
channels
Hansen
and
Kamp,
Fig.15
Hansen
and
Kamp,
Fig.15
Fig.15:
Paleogeographic
reconstructions.
Maps
compiled
using
data
from
Hansen
(in
prep.),
Kamp
et
al.,
(in
prep),
Stagpoole
(1997),
and
King
and
Thrasher
(1996).
Figures
15(d)
to
15(f)
continued
over
page.
432
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
During
the
late
Tongaporutuan
to
early
Kapitean
(c.8
Ma;
Fig.15a),
before
the
shelf-slope
break
migrated
northward
from
the
southern
part
of
the
Taranaki
Basin,
the
study
area
experienced
under
bathyal
conditions.
Volcanism,
which
had
begun
in
the
region
at
c.14
Ma,
was
beginning
to
wane,
though
surrounding
sediments
(Mohakatino
and
Manganui
Formations)
were
still
variously
volcaniclastic
as
a
result
of
sporadic
eruptions
and/or
the
emplacement
of
volcaniclastic
turbidites.
Large
fans
were
forming
to
the
south
and
east
(Mount
Messenger
Formation).
Initial
opening
of
the
Northern
Graben
in
the
latest
Miocene
is
possibly
indicated
by
slightly
deeper
water
depths
recorded
at
Awatea-1
and
Mangaa-1.
Many
wells
centered
on
the
Northern
Graben
record
only
a
very
thin
Kapitean
to
Opoitian
succession
(Fig.15b).
In
more
westerly
located
wells
(Wainui-1,
Ariki-1,
Te
Kumi-1,
and
Tangaroa-1),
much
of
this
missing
time
is
represented
by
the
Ariki
Formation,
a
condensed
marly
unit.
To
the
south,
in
the
vicinity
of
Arawa-1
and
Taimana-1,
sediment
was
accumulating
as
a
series
of
large
lobate
fans
evident
on
seismic
reflection
profiles.
These
fans
are
interesting
because,
although
analysis
of
benthic
foraminifera
suggests
shallow-
water
(mid
shelf)
depths,
their
position
on
seismic
reflection
profiles
indicate
that
deposition
occurred
seaward
of
the
shelf-
slope
break.
This
suggests
that
an
efficient
mechanism
was
in
place
to
transfer
sediment
containing
high
concentrations
of
shallow-water
faunas
from
the
shelf
to
slope.
Indeed,
a
little
further
to
the
southeast,
channelised
conglomerates
have
been
identified
within
the
Kapitean
stratigraphy
of
New
Plymouth-2
(Shell
BP
Todd,
1965).
Deeply
incised
channel
complexes
are
also
common
in
the
Urenui
Formation,
a
late
Miocene
succession
that
crops
out
in
cliffs
on
the
northern
Taranaki
coastline.
During
the
late
Kapitean
to
Opoitian,
sandy
sediments
were
also
being
deposited
in
the
Northern
Graben.
These
sediments
form
the
Mangaa
Formation.
The
sediment
was
most
likely
sourced
from
uplift
and
erosion
of
the
landmass
to
the
east
in
the
King
Country.
Sediments
could
not
reach
areas
west
of
the
graben
because
of
the
differential
subsidence
in
the
graben
and
because
volcanic
massifs,
which
were
for
the
most
part
extinct,
formed
a
series
of
paleohighs
that
directed
sediments
to
the
north.
Sedimentation
during
the
Waipipian
(c.3
Ma;
Fig.15c)
began
to
outpace
accommodation
created
by
the
graben
extension.
The
central
part
of
the
graben
was
still
a
focus
of
deposition,
but
by
now
thicker,
silty
and/or
muddy
sequences
were
being
deposited
over
much
of
the
Western
Stable
Platform,
and
particularly
within
a
fault-bound
depositional
low
to
the
east
of
Arawa-1.
Water
depths
had
begun
to
shallow
during
this
period,
although
bathyal
conditions
persisted.
Few
distinct
channels
have
been
mapped,
however,
channelisation
is
indicated
by
the
hummocky
profiles
of
some
horizons
(along
strike)
on
seismic
reflection
profiles.
While
volcanic
massifs had
been
buried
by
accumulating
sediment
by
the
end
of
this
period,
they
still
formed
positive
relief
on
the
sea
floor,
and
probably
influenced
the
direction
of
sediment
flow.
This
pattern
continued
during
the
Mangapanian
Stage
(Fig.15d)
with
dominantly
muddy
sedimentation,
and
progressive
shallowing.
Mangapanian
aged
sediments
appear
to
be
thin,
though
this
may
be
a
manifestation
of
the
difficulty
of
constraining
this
stage
from
microfaunal
data.
The
Waipipian-Mangapanian
isopach
map
(Fig.8)
illustrates
that
by
the
end
of
the
Mangapanian
Stage,
the
prograding
front
of
the
Giant
Foresets
Formation
was
encroaching
into
the
study
area.
It
was
not
until
the
Nukumaruan
Stage
that
the
foreset
front
began
to
rapidly
advance
across
the
study
region.
Figures
15e
and
15f
illustrate
how
progressive
shelf
margins,
mapped
from
seismic
reflection
profiles
migrate
northwards
and
westwards.
Sediment
was
now
being
dominantly
sourced
from
the
south,
in
part
because
uplift
on
the
Turi
Fault
Zone
provided
a
barrier
for
sediment
from
the
east,
but
mainly
because
of
substantial
uplift
and
erosion
of
the
Southern
Alps.
Throughout
the
Nukumaruan
Stage
the
study
region
shallowed
from
bathyal
depths
(end
of
Mangapanian)
to
shelf
depths,
with
marginal
neritic
watermass
conditions
prevailing.
Much
of
the
sediment
represented
by
the
Nukumaruan
is
variously
sandy,
silty,
shelly,
and
occasionally
pebbly,
even
at
the
deepest
water
sites,
indicating
a
near-shore
component.
Several
mapped
channels
and
channel
complexes
are
inferred
to
have
been
involved
in
the
remobilisation
and
transport
of
this
sediment
to
deeper
water.
Isopachs
maps
of
the
Nukumaruan/late
Nukumaruan
to
Castlecliffian
starta
(Fig.8)
show
migration
of
the
foreset
front.
Foresets
are
particularly
thick
in
the
late
Nukumaruan
(to
Recent),
associated
with
the
development
of
degradational
foresets.
These
are
inferred
to
have
resulted
from
slumping
of
the
continental
margin
during
periods
of
low
sea
level
(Beggs
1990),
although
the
large
thickness,
and
seismically
distinct
character
of
these
upper
units,
suggests
that
there
was
a
significant
contribution
from
sediment
sourced
across
the
contemporary
shelf.
Discussion
Interpretation
of
geophysical
datasets,
including
seismic
reflection
profiles
and
wireline
logs,
integrated
with
foraminiferal
paleoecology
and
palinspastic
reconstruction,
has
enabled
documentation
of
the
Plio-Pleistocene
evolution
of
the
Giant
Foresets
Formation
in
the
northern
part
of
Taranaki
Basin.
While
overall
migration
of
the
foreset
front
(continental
margin)
has
progressed
in
an
uncomplicated
southeast
to
northwest
direction,
depositional
patterns
have
been
influenced
by
several
factors.
These
include
barriers
such
as
topographic
relief
provided
by
extinct
Miocene
volcanoes,
accommodation
space
provided
by
contemporaneous
extension
of
the
Northern
Graben
and
other
depositional
sinks
(e.g.,
the
depression
near
Arawa-1),
and
interruptions
to
the
supply
of
sediment
flux
as
well
as
accelerations
in
this
flux.
The
Giant
Foresets
Formation
is
clearly
cyclothemic
in
nature,
and
has
long
been
recognised
as
representing
a
second-order
tectonic
cycle
(King
and
Thrasher
1996).
This
study
suggests
that
at
least
fourth
order
(400
ka)
eustatic
cycles
can
be
identified
in
the
formation
through
integration
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
433
of
geophysical
and
paleoenvironmental
data.
Deposition
of
the
formation
has
also
been
influenced
by
accommodation
space
formed
by
contemporary
extension
of
the
Northern
Graben.
Progradation
occurred
in
a
southeast
to
northwest
direction,
but
was
initially
directed
into
the
depositional
sink
created
by
the
Northern
Graben,
and
then
by
the
depositional
low
to
the
east
of
Arawa-1.
Topographic
relief
provided
by
extinct
Miocene
volcanic
massifs,
and
the
asymmetrical development
of
the
Northern
Graben,
provided
bathers
to
effective
sediment
transport
to
western
areas
during
the
early
to
mid
Pliocene.
By
the
Waipipian
to
Mangapanian,
these
factors
were
no
longer
quite
so
influential,
and
sediment
deposition
across
the
study
area
was
expressed
as
a
migrating
series
of
sedimentary
(fan?)
lobes.
Compounded,
these
lobes
are
displayed
as
a
linear
body
that
illustrates
the
relative
position
of
the
prograding
continental
wedge
through
time.
Acknowledgements
We
wish
to
acknowledge
the
assistance
given
to
us
by
Bruce
Hayward,
Glen
Thrasher,
Peter
King
and
Rob
Funnell
in
various
parts
of
this
investigation.
Reasearch
funding
was
provided
by
the
NZ
Foundation
for
Reasearch,
Science
and
Technology.
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Authors
ROCHELLE
HANSEN
has
an
MSc
degree
from
the
University
of
Waikato
and
is
currently
undertaking
a
PhD
degree
on
the
character
and
development
of
the
Giant
Foresets
Formation
in
northern
Taranaki
Basin.
PETER
KAMP
is
professor
of
Earth
Sciences
at
the
University
of
Waikato
(Hamilton)
and
holds
MSc
and PhD
degrees.
He
has
published
widely
on
the
tectonic
development
of
New
Zealand
and
its
impact
on
the
development
of
sedimentary
basins.
A
particular
interest
is
the
thermochronology
(thermal
history)
of
basement
and
sedimentary
basins,
assessed
by
fission
track
analyis
and
(U-Th)/He
thermochronometry.
He
is
leader
of
a
basin
analysis
programme
involving
Wanganui
Basin
and
its
relationship
to
Taranaki
Basin
and
the
King
Country
Basin.
2002
New
Zealand
Petroleum
Conference
Proceedings
24-27
February
2002
435