A review and 3D model of the geology and hydrogeology within the Ruataniwha Basin.

Hawkes Bay

May 2018 HBRC Report No. RM19-241 Publication Number: 5393

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Environmental Science

A review and 3D model of the geology and hydrogeology within the Ruataniwha Basin

Hawkes Bay

May 2018 HBRC Report No. RM19-241 Publication Number: 5393

Prepared By: Simon Harper

HBRC Contact Name

Reviewed By:

John Begg – Geologist

Approved By:

Barry Lynch – Acting Manager – Environmental Science

Signed:

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Contents

1 Introduction ........................................................................................................................ 6

2 Project area ......................................................................................................................... 7

3 Purpose ............................................................................................................................... 9

4 Previous studies .................................................................................................................. 9

4.1 Early investigations ............................................................................................................. 9

4.2 Hydrocarbon exploration .................................................................................................. 10

4.3 Recent groundwater investigations .................................................................................. 11

4.4 Numerical groundwater models ....................................................................................... 12

5 Stratigraphy and hydrogeological units .............................................................................. 14

5.1 Overview of QMAP stratigraphy ....................................................................................... 14

5.1.1 Torlesse (composite) terrane ............................................................................ 14

5.1.2 Mangapurupuru Group rocks ............................................................................ 15

5.1.3 Tinui Group rocks............................................................................................... 16

5.1.4 Mangatu Group rocks ........................................................................................ 16

5.1.5 Tolaga Group rocks ............................................................................................ 17

5.1.6 Mangaheia Group rocks .................................................................................... 17

5.1.7 Quaternary deposits .......................................................................................... 20

5.2 Overview of Grant-Taylor (1978) stratigraphy .................................................................. 22

5.2.1 Ashley formation (informal name) .................................................................... 22

5.2.2 Pebbly Hill limestones (informal name) ............................................................ 22

5.2.3 Upokororo formation (informal name) ............................................................. 22

5.2.4 Blackburn formation (informal name) ............................................................... 22

5.2.5 Hugenden, Glen Appen, Ngaruru, Ongaonga, Tikokino formations.................. 23

5.2.6 Fairfield formation (informal name) .................................................................. 23

5.3 Overview of PDP (1999) hydrogeological units ................................................................ 24

5.3.1 Ancient Terrace Aquifer Group ......................................................................... 24

5.3.2 Older Terrace Aquifer Group ............................................................................. 24

5.3.3 Recent Terrace Aquifer Group ........................................................................... 25

5.4 Overview of Francis (2001) stratigraphy ........................................................................... 25

5.4.1 Miocene mudstone and sandstone ................................................................... 25

5.4.2 Mid to lower Pliocene Mudstone and siltstone ................................................ 26

5.4.3 Tukituki Sandstone ............................................................................................ 26

5.4.4 Upper Pliocene mudstone ................................................................................. 26

5.4.5 Upper Pliocene limestone ................................................................................. 26

5.4.6 Top Pliocene sandstone and siltstone ............................................................... 27

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5.4.7 Salisbury Gravel ................................................................................................. 27

5.4.8 Young gravels (informal name) ......................................................................... 27

6 Structure of the Ruataniwha Basin ..................................................................................... 29

6.1 Tectonic history ................................................................................................................. 29

6.2 Faults overview ................................................................................................................. 30

6.2.1 Ruahine Fault ..................................................................................................... 31

6.2.2 Mohaka Fault ..................................................................................................... 31

6.2.3 Wakarara and Rangefront faults ....................................................................... 32

6.2.4 Ruataniwha Fault ............................................................................................... 32

6.2.5 Oruawharo Fault ................................................................................................ 33

7 Development of three-dimensional models ........................................................................ 34

7.1 Summary of models built .................................................................................................. 34

7.2 General model development process ............................................................................... 34

7.3 Data used in the model development .............................................................................. 35

7.3.1 Topographic data ............................................................................................... 35

7.3.2 Geological and hydrogeological maps ............................................................... 35

7.3.3 Well log data ...................................................................................................... 35

7.3.4 Other data sources ............................................................................................ 35

7.4 Modelling limitations ........................................................................................................ 35

7.4.1 Model resolution ............................................................................................... 35

7.4.2 Mapping scale .................................................................................................... 36

7.4.3 Wells database .................................................................................................. 36

7.4.4 Interpretations................................................................................................... 36

7.4.5 Hydrogeological units ........................................................................................ 36

7.4.6 Noted discrepancies .......................................................................................... 36

8 PDP (1999) hydrogeological model ..................................................................................... 37

9 Francis (2001) geological model ......................................................................................... 38

10 Hybrid geological model .................................................................................................... 41

11 Lithological model construction ......................................................................................... 42

11.1 Spatial discretisation ......................................................................................................... 42

11.2 Block model Algorithm ...................................................................................................... 42

11.3 Spatial filtering and warping ............................................................................................. 43

11.4 Model results .................................................................................................................... 44

12 Summary ........................................................................................................................... 45

13 Conclusions ....................................................................................................................... 46

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14 References ........................................................................................................................ 48

Tables

Table 8-1: Summary of PDP (1999) model units and data sources for contact boundaries. 38

Table 9-1: Summary of Francis (2001) model units and data sources for contact boundaries. 39

Table 11-1: Project dimensions for lithological model. 42

Figures

Figure 2-1: Map of project area and boundary of the Ruataniwha Basin. 8

Figure 4-1: Hydraulic conductivity zonation in layer 1 (Phreatos Groundwater Research and Consulting, 2003). 12

Figure 4-2: Schematic cross section showing the layer configuration in Baalousha (from Baalousha Figure 5 (Baalousha, 2010)). Vertical exaggeration is 15x. 13

Figure 5-1: Photo of Torlesse (composite) terrane Rocks exposed in the Ruahine Ranges. 15

Figure 5-2: Photo of Sentry Box Formation outcrops at Sentry Box Hill. 19

Figure 5-3: A) Poutaki Pumiceous Formation, Duff Road, Kereru B) Close up of road cutting at Duff Road (Bland, Kamp, & Nelson, 2007) pg. 235. 20

Figure 5-4: Hydrogeological map of the Ruataniwha Plains (Pattle Delamore Partners, 1999). 24

Figure 6-1: Photo of Mohaka Fault Line (photo Dougal Townsend, GNS Science). 32

Figure 7-1: Leapfrog modelling procedure process. 34

Figure 7-2: Model discrepancy - capping of underlying layers within higher units. 37

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1 Introduction Groundwater underlying the Ruataniwha Plains is a major water resource for agriculture, drinking water and

maintaining surface water flows. Land use intensification and development of the aquifer for irrigation and

drinking water has resulted in a loss of groundwater head, reduction of base flows and a deterioration of

water quality (Baalousha & Waldron, 2013; White & Daughney, 2009). Groundwater and surface water

modelling has indicated the aquifer is at its environmental limit and further groundwater use will adversely

affect instream habitat and security of supply (Baalousha & Waldron, 2013).

To address low flows and water quality issues the Regional Council embarked on developing new policy aimed

at modifying existing rules governing water allocation and land use activities. This culminated in a combined

strategy to develop environmental limits for the Tukituki Catchment and advance water storage to assist with

meeting its environmental objectives. In 2013, the Tukituki Catchment Plan, known as Plan Change 6 (PC6)

was developed and referred to a Board of Inquiry for ruling over the proposed policies.

To assist in setting allocation limits the Regional Council developed a numerical groundwater model to

simulate the effects of groundwater pumping on water resources (Baalousha, 2009; Baalousha, 2010). The

effects from groundwater and surface water modelling were used to estimate security of supply and assess

habitat protection (Baalousha & Waldron, 2013). From this work, the Regional Council proposed an allocation

limit of 28.5 million m3/year to protect surface flows and instream habitat. This volume of allocation also

represented the estimated current groundwater used in 2010.

A separate numerical model, developed by Aqualinc Research Limited, indicated the basin could sustain a

greater volume of pumping, and proposed a limit of 45 million m3/year. However, the Board of Inquiry ruled

increased groundwater use would result in surface water effects, not in keeping with the purpose of the

Resource Management Act (1991), and go against the objectives and policies of the National Policy Statement

for Freshwater Management (Board of Inquiry, 2014). In 2014, the Board of Inquiry adopted the limits

proposed by the Regional Council. However, to provide a framework for additional groundwater use the

Board of Inquiry developed Tranche 2 allocation. This new block of allocation allows access to a further 15

million m3/year, provided a supplementary flow regime is in place to mitigate effects on surface water.

In 2017, the Hawke’s Bay Regional Council withdrew its support to develop water storage for the Tukituki

Catchment. A key benefit of this scheme was to help manage the impact of the new PC 6 minimum low flow

limits, without which there will be reduced irrigation security in 2018 for farmers with groundwater takes

connected to minimum flows, further exacerbated in 2023, when the restrictions on irrigation lift by 50%

(Hawkes Bay Regional Council, 2017). The annual farm earning (EBIT) impact of this reduced irrigation

security, without the Ruataniwha Water Storage Scheme, is an estimated reduction of $900,000 on average,

and over $4 million in the driest years (Hawkes Bay Regional Council, 2017).

Uptake of water rights during pre-feasibility of the storage scheme demonstrates demand for additional

water within the catchment is high. Without the scheme to meet these demands, further pressure is likely

to mount for access to groundwater under Tranche 2. Currently, there are nine applications seeking 27 million

m3/year of groundwater under Tranche 2 (Paul Barret, Principal Consent Officer, 2017, pers. comm.). To

assess the long-term and cumulative effects of increased allocation, and the effectiveness of proposed

mitigation schemes, groundwater and surface water modelling will be required. This will involve reviewing

the appropriateness of the existing Ruataniwha Plains groundwater model to assess these effects, and

potentially using new data to improve calibration and confidence of the model predictions. This report is the

first stage in this process and involves reviewing existing geological and hydrogeological data, and developing

a three dimensional framework to assist with evaluating the existing Ruataniwha Plains groundwater model,

or to build a new groundwater model.

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2 Project area The Ruataniwha Plains is located in Central Hawkes Bay on the East Coast of the North Island approximately

50 kilometres southwest of Hastings. The Ruataniwha Plains infills an elongate NNE–SSW trending basin

bounded by the Ruahine Range to the west, and by the Turiri and Raukawa Ranges, Pukeora Hills and Mount

Vernon to the east. The primary focus of this report is the geological, lithological and hydrogeological units

within the Ruataniwha Basin. The Tukituki Catchment boundary, from the Ruahine Ranges in the west to

Waipawa Township in the east, defines the extent of the project area. Herein, the project area is referred to

as the Ruataniwha Basin.

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Figure 2-1: Map of project area and boundary of the Ruataniwha Basin.The Tukituki River Catchment defines the project area boundary. This boundary has been clipped along State Highway two near Waipawa to exclude the Catchment area east of this demarcation.

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3 Purpose The purpose of this project are:

1. Review and summarise existing information about the geological, lithological and hydrogeological

structure of the Ruataniwha Basin for the following purposes:

a. An evaluation of the structure of recent numerical groundwater models

b. To assist with developing new conceptualisations for groundwater modelling

c. To update existing groundwater modelling conceptualisation

2. Build a three-dimensional framework for the Ruataniwha Basin to assist with comparing different

conceptualisations.

4 Previous studies

4.1 Early investigations

Early investigations mainly focused on describing the local and regional geology (McKay, 1877; McKay, 1879;

McKay, 1887). These early investigations were more interested in describing pre-Quaternary rocks rather

than younger alluvial deposits from which most of the groundwater beneath the Ruataniwha Plains is

abstracted. In 1926, Thompson (1926) stated no special project had been made of the “Notopleistocene”

beds of the district, besides the descriptions by Hill (Hill, 1893).

Hill (1893) first recognised the potential for the Ruataniwha Plains to contain a productive artesian system.

In 1892 on Hill’s advice, Mr Harding of Mount Vernon Station contracted Mr J.Gilberd of Taradale to drill a

well about 1.5 km northeast of Ongaonga township. The well was drilled to 96.3 metres and encountered

three separate groundwater layers, the deepest of which was free flowing and measured 5 metres above

land surface.

Between the late 19th century and mid-20th century, most groundwater exploration in Hawke’s Bay focused

on the Heretaunga Plains. In 1923, Hill wrote a paper on Hawke’s Bay artesian systems urging for regulation

of the groundwater resource to control the free flowing of artesian wells on the Heretaunga Plains and to

prevent overdrawing the groundwater supply (Hill, 1923). In his report, Hill summarised the drilling of

artesian wells around Ongaonga on the Ruataniwha Plains. Description of the wells in the Ruataniwha Basin

suggest development of the groundwater resource at that time was limited.

Kingma (1958) made some of the earliest descriptions of Quaternary deposits describing the Salisbury Gravel

on the eastern limb of the Wakarara Range (Kingma, 1958). Kingma undertook numerous geological studies

in Hawke’s Bay and produced a geological map covering the Ruahine Ranges (Kingma, 1970). Prior to Kingma

(1970), the best published geological map of the southern part of the Ruataniwha Plains (south of Takapau)

was that contained within Lillie 1953, NZGS Bulletin 46, The geology of the Dannevirke Subdivision

(Norsewood and Takapau District maps). However, there is also a draft geological map completed by Len

Brown for the Hawke’s Bay Regional Council.

In the late 1970s’ the Geological Survey undertook three investigations to explore the relationship between

erosion and geology in the Ruahine Ranges (Smale, et al., 1978). This resulted in the geology and structure of

the Ruataniwha Plains being investigated and mapped (Grant-Taylor, 1978). This map later assisted Pattle

Delamore Partners (PDP) in delineating hydrogeological units (Pattle Delamore Partners, 1999).

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4.2 Hydrocarbon exploration

Hydrocarbon exploration provides most of the knowledge on the deeper stratigraphy and structure beneath

the Ruataniwha Plains. In the early 1970’s Beaver Exploration New Zealand Ltd investigated the potential for

hydrocarbon reserves within limestone of the Te Aute Group. This resulted in the Tikokino seismic survey

with the objective of tracing the limestone from outcrop into the subsurface and establishing drilling sites

(Leslie & Hollingsworth, 1972).

The Tikokino seismic survey began in August 1970 and was completed in February 1971. Seismic lines were

spaced widely to give a broad geological picture of the structure in southern Hawke’s Bay and to delineate

possible structural traps in the Upper and Lower Tertiary sediments. The acquisition of data was poor in

northwestern hill area and fair to good in flatter areas (Hollingsworth, 1971). Complex faulting and paucity

of lines made interpretation difficult.

Two sets of maps were constructed from the Tikokino seismic survey. The first map, entitled “Horizon within

Pleistocene”, depicts an event recognisable over most of the survey area and much less affected by faulting

than a deeper horizon, and thus easier to correlate (Hollingsworth, 1971). From correlation with surface

outcrops, this event is thought to represent a carbonate horizon within the Pleistocene deposits

(Hollingsworth, 1971). The second map, entitled “Possible Carbonate Horizon within Pliocene”, depicts an

event affected by numerous faults, making correlation sometimes difficult, particularly in areas of poor data

(Hollingsworth, 1971).

A number of structural features identified from the seismic survey helped determine drilling sites for

exploration. Ongaonga-1 was the first of a three-well programme drilled under Beaver exploration (NZ) Ltd

(Leslie W. C., 1971a). The well was located on a closed subsurface seismic high, and the objective was to

encounter hydrocarbons in Pliocene carbonate rock (Leslie W. C., 1971a). The well penetrated 1468 metres

of Pleistocene and Pliocene sediments and 105 metres of Jurassic sediments before terminating at a depth

of 1573.4 metres. Tertiary rocks were a marine sequence of silty, fossiliferous mudstone and interbedded

coquina limestone that occurred 120 metres below surface gravel and boulder beds. The coquina limestone

contained freshwater and possessed excellent porosity and permeability but contained no significant

hydrocarbon reserves (Leslie W. C., 1971a).

Takapau-1 was the second well drilled. The well penetrated about 1000 metres of Pleistocene and Pliocene

sediments and 56 metres of Jurassic sediments before terminating at a depth of 1058.9 metres (Leslie W. ,

Takapau no. 1, Well completion Report, 1971b). The Tertiary sediments were overlain by 50 metres of gravels

and boulder beds composed entirely of rounded pebbles and cobbles of greywacke and dolerite, set in a fine-

grained reddish-brown and dark grey, silt, argillaceous groundmass (Leslie W. , Takapau no. 1, Well

completion Report, 1971b). As with Ongaonga-1, the targeted limestone contained freshwater and

possessed excellent porosity and permeability (Leslie W. , Takapau no. 1, Well completion Report, 1971b)

but no significant shows of hydrocarbons.

Indo-Pacific (NZ) Ltd undertook further seismic surveys in the late 1990’s (IP332 and IP328) and drilled a third

exploration well in southern Ruataniwha on Speedy Road. The Speedy-1 well drilled to a total depth of 876

metres but failed to reach the target horizon due to mechanical difficulties during drilling. Tertiary sediments,

including the Pukeora Oyster bed (Thompson, 1926) underlay 74 metres of alluvial gravels and clays.

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4.3 Recent groundwater investigations

In the 1990's, the Hawke’s Bay Regional Council carried out a review of studies in the Ruataniwha Plains

(Dravid P. N., 1993). This review identified the possibility of at least four aquifer groups including deep

Tertiary strata aquifers underlying the Ruataniwha Plains. In 1996, recommendations of the review were

incorporated in a 2-year joint project between HBRC and the Institute of Geological and Nuclear Sciences.

The programme was designed to monitor land use changes and the effects of increased water usage on the

groundwater environment. During the first year, groundwater and surface water information was collected

from monitor wells including groundwater levels and hydrochemistry. The programme also acquired

hydrology and hydrogeology information from river flow gaugings, and produced a piezometric survey and

geological map (Dravid, Cameron, & Brown, 1997).

In 1999, Pattle Delamore Partners Ltd undertook the development of a conceptual hydrogeological model.

In this project, ‘aquifer groups’ were defined on the basis of relative ages and compaction of deposits within

the alluvium sequences. This work relied on earlier investigations made by Grant-Taylor (1978). The Council

commissioned a further project of the geology beneath the Ruataniwha Plains in 2001 (Francis, 2001). Francis

(2001) produced subsurface contour maps and cross sections across parts of the plains. In 2001, Council

drilled six wells to improve the hydrogeological understanding of the basin and to assist with development

of a numerical model. The results from exploration drilling were summarised by Brown (Brown, 2002).

In 2009, the Hawke’s Bay Regional Council contracted GNS Science to complete an assessment of

groundwater-surface water interaction as part of a joint HBRC-GNS Science research project (Undereiner,

White, & Meilhac, 2009). As part of this assessment, a lithological model was developed to assist with

understanding the interaction between surface water and groundwater. Earthvision© software by Dynamic

Graphics Ltd was used to visualise gravel and clay layers and define aquifer and confining boundaries

respectively. Two aquifers were interpreted consisting of a shallow unconfined aquifer overlying a deeper

confined aquifer and separated by discontinuous clay layers.

In 2012, to assist with the general conceptual understanding of the aquifer system and to provide data for

calibration of the Ruataniwha Plains groundwater model, GNS Science investigated groundwater recharge

sources, recharge rates, ages and homogeneity of the groundwater within the Ruataniwha Basin

(Morgenstern, van der Raaji, & Baalousha, 2012). Results from hydrochemical and age tracer analysis

indicated most samples contained old water (MRT >25yrs) with samples from the southeastern part of the

basin containing the oldest water (MRT > 100yrs) and indicating less permeable material. There is a general

correlation between groundwater age and well depth, with increasing age in deeper wells. However, the

correlation is poor and indicates a highly heterogeneous aquifer. Hydrochemical data showed high variability

in space and time, consistent with the complicated hydrogeological setting of a multi-layered aquifer system

(Morgenstern, van der Raaji, & Baalousha, 2012).

Only groundwater near the Waipawa and Tukituki Rivers show river recharge signature, indicating gravel

deposits connecting the present riverbed to the deep groundwater system along these rivers. River-recharge

is only observed in the lower reaches of these rivers, downstream from losing stretches of the rivers. Oxic

groundwater is present only near the Waipawa River, indicating only this river has deposited relatively clean

gravel aquifers without organic matter that would otherwise deplete oxygen. All groundwater in the southern

part of the basin near small rivers and streams show a pure rain recharge signature. This indicates there is

little connection of rivers and stream there to the deep groundwater system.

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4.4 Numerical groundwater models

The first numerical model of the Ruataniwha Plains aquifer system was developed in 2002 (Murray, 2002a;

Murray, 2002b) as a simplified single-layer to estimate global water balance and provide a foundation for

subsequent investigation (Phreatos Groundwater Research and Consulting, 2003). The model represented

the groundwater resource as a single unconfined layer lumping together all alluvial sediments into one layer.

The base of the model was coincident with the predicted base of the Salisbury Gravel (Francis, 2001).

Concern the original model over-estimated the global balance for the basin, in particular rainfall recharge,

led to the development of a second model (Phreatos Groundwater Research and Consulting, 2003).

Calibration of the new model required the introduction of a second layer representing the Salisbury Gravel;

under the premise, this unit is geologically distinct, and therefore hydrogeologically distinct from the

overlying Late Quaternary gravels (Phreatos Groundwater Research and Consulting, 2003).

Layer 1 was set to simulate unconfined conditions. Higher conductivity properties were assigned over the

central plains area. Toward the west, the lower conductivity values were assigned identical properties with

layer 2, to represent the less permeable Salisbury Gravel. The thickness and depth of both layers used

information prepared by Francis (Francis, 2001).

Figure 4-1: Hydraulic conductivity zonation in layer 1 (Phreatos Groundwater Research and Consulting, 2003). The different colours represent different zones of hydraulic conductivity within the model. The value of hydraulic conductivity assigned to these zones is shown on the map.

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In 2009, a third numerical model (Baalousha, 2009) was built to assist in setting allocation limits and policy

for the Tukituki Catchment. This model was built using three layers and based mainly on delineations

provided by Francis (Francis, 2001). The top layer (layer 1) modelled by Baalousha (2009) represents the

informally named young gravel formation (Francis, 2001). Francis (2001) described these deposits as

unconsolidated gravel, clay, silt and volcanic ash of Late Quaternary age forming near-surface deposits over

much of the plains and on alluvial terraces to the north, west, and south of the plains. The bottom model

layer (layer 3) represents a sequence sediments which Francis (2001) referred to as the Salisbury Gravel.

Francis (2001) described these deposits as unconsolidated to slightly consolidated gravel, ignimbrite, clay and

minor peat or lignite comprising Salisbury Gravel (Erdman & Kelsey, 1992). A middle model layer (layer 2),

not delineated or described by Francis (2001) was included to represent an aquitard separating the upper

and lower model layers. The author assumes this middle layer is not representative of the physical system

but rather a modelling mechanism to help control leakage between layers 1 and 3.

Figure 4-2: Schematic cross section showing the layer configuration in Baalousha (from Baalousha Figure 5 (Baalousha, 2010)). Vertical exaggeration is 15x.

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5 Stratigraphy and hydrogeological units A number of group names, formally and informally describe the Ruataniwha Basin stratigraphic

nomenclature (Lee, Bland, Townsend, & Kamp, 2011; Grant-Taylor, 1978; Francis, 2001). This section

contains a summary of some of those stratigraphic and hydrogeologic units. In this report, the key studies

used to identify geological and hydrogeological units within the basin are:

1. Geology of the Hawke’s Bay (Lee, Bland, Townsend, & Kamp, 2011) – Stratigraphy identified in QMAP

are summarised in sections 5.1.

2. The geology and structure of the Ruataniwha Plains (Grant-Taylor, 1978) – Stratigraphy reported by

Grant-Taylor (1978) is summarised in section 5.2.

3. Ruataniwha Plains conceptual hydrogeological model (Pattle Delamore Partners, 1999) –

Hydrogeological units reported by PDP (1999) are summarised in sections 5.3.

4. Subsurface geology of the Ruataniwha Plains and relation to hydrology (Francis, 2001) – The

stratigraphy report by Francis (2001) is summarised in sections 5.4.

5.1 Overview of QMAP stratigraphy

5.1.1 Torlesse (composite) terrane

The oldest outcropping rocks in the Ruataniwha Basin are weakly metamorphosed sandstone and mudstone

of the Torlesse (composite) terrane. These greywacke basement rocks form the northeast trending axis of

the Ruahine Ranges. The Esk Head belt (Te), Kaweka terrane (Jtk), Pahau terrane (Ktp), Pohangina Melange

(Kep) and Waioeka petrofacies (Ktw) form the basement units within the mapped area.

Kaweka and Pahau terranes and Waioeka petrofacies form stratigraphically coherent belts and are

distinguished largely based on their petrographic compositions and detrital zircon population age

distributions (Spörli K. , 1978; Mortimer, 1995; Adams, Mortimer, Campbell, & Griffin, 2009). These deposits

are mainly composed of thin-bedded alternating sandstone and argillite with rare concretionary lenses and

conglomerate beds, and occasional thick sandstone beds (Grant-Taylor, 1978).

The units Esk Head belt and Pohangina Melange commonly bound the terranes and comprise largely of

tectonically mixed dismembered assemblages of these coherent basement terranes, and often include blocks

of other exotic lithologies such as limestone, chert and volcanics.

The Torlesse (composite) terrane is largely of deep marine origin and formed as submarine fans deposited at

the foot of submarine valleys and canyons at the eastern margin of Gondwana. Sparse macro and micro fossil

faunas from these rocks indicate Late Triassic to Late Jurassic ages (Stevens, 1963; Speden, 1976; Te Punga,

1978; Simes, 1985)There is little information on the depth of these rocks beneath the Plains other than the

logs from Ongaonga-1 and Takapau-1 (Leslie W. C., 1971a; Leslie W. , Takapau no. 1, Well completion Report,

1971b).

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Figure 5-1: Photo of Torlesse (composite) terrane Rocks exposed in the Ruahine Ranges.

Bedding has been tectonically disturbed, resulting in outcrop-scale folds and faults. Dark layers are argillite (lithified mudstone) while light-coloured layers are sandstone. The exposure is heavily veined by white minerals, probably quartz and zeolite. (http://juliansrockandiceblog.blogspot.co.nz/2012/11/a-dynamic-landscape-in-hawkes-bay.html)

5.1.2 Mangapurupuru Group rocks

Mangapurupuru Group rocks are not exposed at the surface in the Ruataniwha Basin. These rocks outcrop

to the southeast in the Whangai Range. Their presence beneath the Ruataniwha Plains is inferred based on

QMAP cross section A, however, there is no evidence the Group exists within the basin.

The Mangapurupuru Group includes the late Early Cretaceous Gentle Annie and Springhill formations, which

unconformably overlie Pahaoa Group in the Whangai Range (Crampton, 1989; Crampton, 1997). The Gentle

Annie Formation in the Whangai Range comprises of 400 metres of poorly sorted, pebbly, sandy mudstone

and muddy to sandy, matrix-supported sedimentary breccia-conglomerate, with minor alternating sandstone

and mudstone. Fossils from this formation in the Wairarapa area indicate a late Early Cretaceous age

(Crampton, 1997)

The Springhill Formation overlies the Gentle Annie Formation. The contact is poorly exposed in Hawke’s Bay

but conformable in the Wairarapa area. In Hawke’s Bay the Springhill Formation is about 750 metres thick

and consists of massive, fossiliferous, concretionary mudstone, alternating sandstone and mudstone and

minor pebble conglomerate, with sparse limestone beds and tuffs (Adams A. G., 1985; Crampton, 1997)

http://juliansrockandiceblog.blogspot.co.nz/2012/11/a-dynamic-landscape-in-hawkes-bay.htmlhttp://juliansrockandiceblog.blogspot.co.nz/2012/11/a-dynamic-landscape-in-hawkes-bay.html

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5.1.3 Tinui Group rocks

Tinui Group rocks unconformably overlies the Mangapurupuru Group in the Whangai Range and comprises

of the Tangaruhe, Tahora, Whangai and Waipawa formations. Rocks of the Tinui Group are exposed at the

surface at the eastern edge of the Ruataniwha Basin as part of a structurally complex faulted and folded zone

near Waipawa and Waipukurau within the core of the Raukawa Range and Ben Lomond hills. Here, the

mudstone-dominated upper parts of the Tinui Group are present mainly as the Whangai Formation and to a

lesser extent as the Waipawa Formation.

The presence of Tinui Group rocks (Whangai, Waipawa and Tangaruhe) are inferred at depth beneath the

Ruataniwha Plains. In cross-section, Francis (2001) inferred Whangai Formation at depth near the Waipawa

River and at the eastern edge of the Basin. QMAP cross sections also include Miocene rocks at depth overlying

Kaweka terrane rocks. However, the presence of Tinui Group rocks beneath the Ruataniwha Basin is

uncertain. Tinui Group rocks were not present within Takapau-1 and Ongagonga-1 (Leslie W. C., 1971a; Leslie

W. , 1971b), nor to the south at Rakaiatai-1 near Dannevirke (Darley, 1969). At Speedy-1 (Johnston &

Langdale, Speedy-1/1A Well Completion Report. Petroleum Report Series PR 2537., 2000), Mason Ridge-1

(Leslie W. , 1971) and Kereru-1 (Johnston & Francis, 1996) the stratigraphic level of Tinui Group was not

reached. Southeast of Takapau, Mangaheia Group rocks, overlie Pahau Terrane basement, indicating an

absence of Tinui Group there.

The Whangai Formation is up to 400 metres thick and the Waipawa Formation 35 metres. Dinoflagellates

and foraminifera indicate Late Cretaceous to Paleocene age (Moore P. R., 1988; Cutten, 1994). The

microfossil assemblages indicate strata deposited at shelf to bathyal depths (Wilson , Morgans, & Moore,

1989; Uruski, et al., 2006; Killops, et al., 2000). The contact with the underlying Whangai Formation is rarely

exposed but at several localities appears gradational. The Waipawa Formation is conformably overlain by

occasionally well-bedded to mainly massive mudstone of the late Paleocene- Eocene Wanstead Formation

(Rogers et al, 2001). Francis (2001) reports extensive fractures within the Whangai Formation at the surface,

which may act as a groundwater reservoir at depth if fractures persist and potentially provide a groundwater

resource in the hill country immediately outside of the catchment where unconsolidated alluvial aquifers are

non-existent.

5.1.4 Mangatu Group rocks

The Wanstead Formation of the Mangatu Group overlies Tinui Group rocks. These are the only Paleocene to

Oligocene rocks in the Ruataniwha Basin. Outside of the Ruataniwha Basin, Mangatu rocks are present

mainly between the Whangai Range and Waipawa area. Faulted slivers occur in the axis of the Elsthorpe

Anticline, along the coast from Waimarama to Porangahau, and at Te Hoe. The presence of Mangatu Group

rocks beneath the Ruataniwha Plains is uncertain and not included in Francis’s (2001) or QMAP’s (Lee, Bland,

Townsend, & Kamp, 2011) cross-sections.

The Wanstead Formation is typically a soft, green-grey or reddish mudstone, which shows some regional

variations (Lee, Bland, Townsend, & Kamp, 2011). The claystone of Wanstead Formation is usually highly

calcareous, but is characterised by a high proportion of bentonitic swelling clays (Francis, 2001). These clays

are likely to form impermeable boundaries to groundwater flow (Francis, 2001). Near the Tukituki River the

formation is at least 300 metres thick (Kingma, 1971) but outside the catchment thicknesses range between

75-300 metres (Lillie, 1953; Moore P. R., 1987). Microfossil assemblages indicate an age range of Paleocene

to Middle Eocene at shelf to bathyal depths (Lee, Bland, Townsend, & Kamp, 2011).

The Weber Formation consists of hard, sandy, brown and grey mudstone and alternating dark grey mudstone and sandstone (Lillie, 1953). In the core of the Elsthorpe Anticline, Weber Formation is finer grained than in the western exposures and consists of creamy or light brown, hard, calcareous mudstone with dark streaks,

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with minor glauconitic sandstone and mudstone (Lillie, 1953; Kingma, 1971; Pettinga J. R., 1980). Weber Formation was deposited in mid-bathyal water depths, in slightly shallower conditions than the Wanstead Formation (Field, et al., 1997)

5.1.5 Tolaga Group rocks

Tolaga Group Rocks unconformably overlie rocks of either the Mangatu or Tinui groups or rocks of the

Torlesse (composite) terrane (Lee, Bland, Townsend, & Kamp, 2011). Surface exposure of Tolaga Group rocks

is predominantly to the east of the Ruataniwha Basin, particularly between the Otane Ranges and the coast.

Their presence, however, immediately overlying faulted slivers of basement rocks along the Oruawharo Fault

south of the basin suggests it is present at depth beneath the basin, at least locally e.g. Well Speedy-1;

(Johnston & Langdale, Speedy-1/1A Well Completion Report. Petroleum Report Series PR 2537., 2000).

Tolaga Group rocks are marine and largely comprise massive mudstones and alternating sandstone and

mudstone, with local variations in lithofacies and thickness (Lee, Bland, Townsend, & Kamp, 2011).

5.1.6 Mangaheia Group rocks

Mangaheia Group rocks form a thick sequence of marine Pliocene sediments, which overlie the Cretaceous,

Paleocene and Miocene rocks (where present) and are faulted against basement rocks at the eastern flank

of the axial ranges. These deposits formed at the margins of an ancient seaway extending from Wairarapa

into Hawke’s Bay (Beu A. G., 1995; Pettinga J. R., 1980). Narrowing of the seaway combined with strong

oceanic currents provided optimal conditions for deposition of bioclastic limestone (Kamp & Nelson, 1987;

Kamp & Nelson, 1988; Nelson, et al., 2003; Caron, Nelson, & Kamp, 2004). At the base of the Ruahine Ranges,

Mangaheia Group sandstone and mudstone unconformably overlie the Torlesse (composite) terrane rocks

and dip eastward beneath the Ruataniwha Plains. These marine sediments are folded and faulted beneath

the plains, and resurface along the eastern margin of the basin forming the Raukawa Ranges, Pukeora Hills

and Mount Vernon, where they comprise mostly siltstone, limestone and sandstone.

Pliocene rocks in Hawke’s Bay are described under a number of group names e.g. (Harmsen, 1984b; Haywick,

Lowe, Beu, Henderson, & Carter, 1991; Kelsey, Erdman, & Cashman, 1993; Beu A. G., 1995; Bland, Kamp, &

Nelson, 2007). All Pliocene and some early Quaternary rocks are included in the Mangaheia Group.

Unconformities are widespread in the Late Pliocene succession, and dips become gentler in the younger rocks

towards the central parts of the Ruataniwha Strait (Lee, Bland, Townsend, & Kamp, 2011).

Whetukura and Te Onepu limestone

There are two prominent limestone horizons preserved in the Mangaheia Group sequence in the eastern

Ruataniwha Basin area, the Waipipian (early Late Pliocene) Whetukura Limestone (Beu A. G., 1995) and the

Mangapanian (Late Pliocene) Te Onepu limestone. The Mangaheia Group sequence, including the limestones

dips west and is uplifted to form the hills at the eastern margin of the Ruataniwha Plains. The limestones

crop out along an extensive west-dipping strike ridge between Hatuma, across the Tukituki and Waipawa

rivers towards Mason Ridge.

Whetukura limestone is coarse-grained, cross-bedded, yellow-grey limestone, which contains abundant

bryozoan and bivalve fragments in this area. It is up to 50 m thick and well exposed west of the Whangai

Range and at a limestone quarry west of Waipukurau (Lee, Bland, Townsend, & Kamp, 2011). Elsewhere, it is

mapped as a horizon that conformably overlie early Pliocene rocks (Lee, Bland, Townsend, & Kamp, 2011).

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The Te Onepu limestone is yellow-grey, coarse-grained limestone with well-developed cross-beds, which

crop out mainly in a northeast-trending belt from the Turiri Range in the south, northward to the Raukawa

Range. It forms a northwest-dipping cap on the entire Raukawa Range and much of the northern part of Turiri

Range (Harmsen, 1984b). Locally, it unconformably overlies rocks of the Whangai Formation and Tolaga

Group and outside of the Ruataniwha Basin is conformable on Late Pliocene Whetukura limestone or

Mangaheia Group mudstone near Hastings.

Te Onepu Limestone generally varies in thickness from 40 to 100 metres, although 140 metres is recorded at

Hatuma Quarry (Harmsen, 1985). The formation was targeted for petroleum exploration because of its

excellent reservoir qualities (Francis, 2001). Exploration drilling encountered the formation in Takapau-1 and

Speedy-1 exploration wells. In Takapau-1, the limestone is encountered between 839 and 938 metres and

described as a “very porous silt coquina limestone, medium to dark grey, poorly consolidated and very

friable” (Leslie & Hollingsworth, 1972).

Sentry Box Limestone & Mason Ridge Formation

Sentry Box Limestone was introduced and formally defined by Erdman and Kelsey in reference to a

fossiliferous pebbly grainstone cropping out on the western margin of the Ohara Depression at the foot of

the Ruahine Range (Erdman & Kelsey, 1992). Sentry Box Limestone is found in localised outcrops near the

Ruahine Ranges and consists of basal pebbly barnacle-rich limestone, sandstone, and siltstone

unconformably overlying basement or lower Late Pliocene rocks. This formation deposited in a high-energy

environment on or near a rock substrate (Beu A. G., 1995; Bland, Kamp, & Nelson, 2007). The presence of

many subantarctic species indicates deposition in very cold waters.

Mason Ridge Formation is uplifted on the eastern margins of the Ruataniwha Plains and is composed of 20-

50 metres of alternating shelf sandstone, limestone and mudstone. In western parts of Mason Ridge, the

formation is inferred to unconformably underlie both the Okauawa and Poutaki Formations. Although the

contacts with both formation are concealed, geological mapping suggests the contacts are unconformable

(Bland, Kamp, & Nelson, 2007).

The lower contact of the Mason Ridge Formation is poorly exposed, and has only been seen on Mason Ridge

Station and at its type section. The formation gradationally overlies the Makaretu mudstone through a

coarsening upward interval. No trace of the formation was found in the Taradale-1 drill hole, possibly because

water depths were too great or the clastic deposition was too rapid (Darley & Kirby, 1969). It is inferred to

be of Lower Nukumaruan age and deposited in inner to middle shelf environments.

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Figure 5-2: Photo of Sentry Box Formation outcrops at Sentry Box Hill. A) Stacked grainstone and packstone beds of the Sentry Box Formation on the western side of Sentry Box Hill. B) Close up view of the barnacle-dominated grainstone and packstone beds (Erdman & Kelsey, 1992) pg. 211.

Kereru and Kumeroa limestones

The Kereru and Kumeroa formations (Beu, Grant-Taylor, & Hornibrook, 1980) are composed of densely

packed shell beds and sandstone that dips gently eastwards off the Ruahine Ranges and southwest off the

Wakarara Range respectively. The Kereru Formation is located discontinuously on the eastern slopes of the

Ruahine Range. Kereru and Kumeroa formations are of Nukumaruan age and are considered to be correlative

representing the western and eastern facies of the same unit respectively. Kereru Formation is also age

equivalent to upper parts of the Esk Mudstone, which was deposited in a deeper marine environment in the

Tangoio-Esk areas.

Tourere Formation

The Tourere Formation is present east of the Oruawharo Fault zone, and unconformably overlies lower

Pliocene rocks. It comprises at least 100 metres of alternating sandy mudstone, coarse-grained sandstone

and barnacle-rich limestone.

Okauawa & Poutaki Pumiceous formations

The Okauawa Formation is widely distributed to the northeast of the Ruataniwha Basin. The formation

comprises of fossiliferous sandstone, shelly conglomerates, and siltstones that are also fossiliferous (Bland,

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Kamp, & Nelson, 2007). As mapped by Erdman and Kelsey (1992), the Okauawa Formation underlies the

Poutaki Pumiceous Formation beneath the Ruataniwha Plains.

Thick gravels near the base of the Okauawa Formation in the lower Ohara Stream (McKay, 1877) and on the

eastern front of the Wakarara Range probably deposited as the Ruahine and Wakarara Ranges began to

emerge (Erdman & Kelsey, 1992). The increasing abundance of coarse clastic sediments toward the south,

along the east front of the Wakarara Range may indicate the southern end of the Wakarara block emerged

first (Erdman & Kelsey, 1992). Okauawa Formation contains Late Nukumaruan fossils indicating deposition in

shallow marine conditions with interfingered non-marine to marginal-marine beds suggesting deposition

during sea level fluctuations.

Poutaki Pumiceous Formation represents the uppermost unit of the Mangaheia Group (Erdman & Kelsey,

1992) and lies unconformably on the Okauawa Formation. Above the unconformity, the Poutaki Pumiceous

Formation comprises a 1-1.5 m thick pumiceous sandstone bed containing rip-up mudstone and sandstone.

Above this, the formation consists of coarse pumiceous sandstone beds, pumiceous granule to cobble

conglomerates, dark green medium-grained sandstone beds, mudstone and massive mudstone with an

overall minimum thickness of 100 metres along the eastern front of the Wakarara Range (Erdman & Kelsey,

1992). Also present are lignite bands, tree trunks, and other carbonaceous matter. Marine fossils recovered

from the Poutaki Pumiceous Formation are Late Nukumaruan and comprise the youngest marine incursion

into the basin.

Figure 5-3: A) Poutaki Pumiceous Formation, Duff Road, Kereru B) Close up of road cutting at Duff Road (Bland, Kamp, & Nelson, 2007) pg. 235.

5.1.7 Quaternary deposits

Across the Ruataniwha Plains, most surficial early Quaternary deposits are mapped as part of the Kidnappers

Group (Flemming, 1959; Kingma, 1971). The group unconformably overlies Pliocene rocks of the Mangaheia

Group (Erdman and Kelsey 1992). The depositional environment of the Kidnappers Group during the early

Quaternary were initially intertidal and later non-marine (Kingma, 1971; Kamp P. J., 1990; Black, 1992). The

upper surface of the Kidnappers Group in the area is universally eroded and no contemporary landforms are

preserved; in contrast, alluvial landforms of the middle and late Quaternary are preserved as elevated terrace

remnants and Holocene alluvial flood plains.

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Kidnappers Group

Kingma (1971) named Kidnappers Group in reference to the well-exposed section between Clifton and Black

Reef at Cape Kidnappers at the southern end of Hawke’s Bay (Bland, Kamp, & Nelson, 2007). The definition

extends to incorporate the prominent thick Castlecliffian gravel beds (Salisbury Gravel) cropping out adjacent

to the northern Ruahine and Wakarara Ranges. These westerly beds are inferred to represent proximal non-

marine equivalents of marginal-marine strata exposed in the Clifton-Black Reef type section.

Salisbury Gravel and Mangatarata Formation

Salisbury Gravel gradationally overlies the Poutaki Pumiceous Formation. A prominent ignimbrite defines the

basal surface of the Salisbury Gravel (Erdman & Kelsey, 1992), but otherwise the lower part is difficult to

distinguish from the Poutaki Pumiceous Formation because they both comprise massive mudstone beds

interbedded with pumiceous sandstones and conglomerate beds (Erdman & Kelsey, 1992). Salisbury Gravel

within the Ruataniwha Basin is largely fluvial in origin but in places lacustrine (Francis, 2001). An age range in

Late Nukumaruan or Early Castlecliffian is inferred (Erdman & Kelsey, 1992).

Conglomerate beds throughout Salisbury Gravel are frequently trough cross-bedded, and sorting is generally

poor (Dyer, 2005). Pebble-to-cobble conglomerates become prevalent upsection, with interbeds of

pumiceous sandstone and more ignimbrites. Salisbury Gravel are differentiated from post-Castlecliffian

fluvial deposits by their more weathered gravels and distinct but irregular pumice interbeds (Kingma, 1971).

Towards the south, gravel or conglomerate beds are less dominant, and clay and peat beds indicate swamp

or lacustrine dispositional environments (Brown, 2002). These less gravel-rich deposits were named

Mangatarata Formation by Lillie (1953) and are correlative. In Francis (2001), Salisbury Gravel is

approximately equivalent to Upokororo formation described by Grant-Taylor (1978). Francis (2001) describes

the Salisbury Gravel as defining a reasonably clear NNE-trending syncline, parallel to and 1-2km east of

Highway 50 between Ongaonga and Tikokino. From Tikokino north, the syncline swings to a northerly trend.

Middle to late Quaternary deposits

Middle to late Quaternary deposits are characterised by underlying well defined terrace treads and separated

from younger terraces by risers and elevation. Most are moderately weathered undifferentiated poorly

sorted alluvial gravels and treads are capped by loess. Fan deposits and landslide materials are located close

to steeply incised channels or hillsides near the margin of the plains.

Holocene alluvium

Holocene alluvium underlies the active flood plains and represent the youngest deposits within the

Ruataniwha Basin. They contain unweathered, poorly consolidated alluvial gravels, sand and mud. The most

expansive deposit is located along the Waipawa River and north towards Butler Road. Other Holocene

deposits are localised to existing stream and river channels.

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5.2 Overview of Grant-Taylor (1978) stratigraphy

This section summarises the formations described by Grant-Taylor (1978). A summary of the Torlesse

(composite) terrane described by Grant-Taylor (1978) is covered previously in section 5.1.1

5.2.1 Ashley formation (informal name)

Grant-Taylor (1978) describes the Ashley formation as a clean even-grained sandstone that dip eastward off

the Ruahine Range at 8° and south-west off the Wakarara Range at about the same angle. This is the same

angle as the dip slope reported for the Kereru and Kumeroa deposits (Beu, Grant-Taylor, & Hornibrook, 1980).

The sandstone passes upward to sandy mudstone at about 150 m above the contact. Fossiliferous

concretionary horizons occur in the mudstone at about 300 m above the base. Limestone lenses occur at

several horizons within the Ashley Formation. The rocks unconformably overlie the Torlesse (composite)

terrane west of Ashley Clinton and Makaretu, and at the southern end of the Wakarara Range. East-west

seismic profiles indicate a thickening westward, and against the foot of the range the formation is reportedly

2000 metres thick (Hollingsworth, 1971). Macro fauna form the concretionary bed west of Ashley Clinton,

300 m above the base of the sequence, gave a Waipipian age (Late Pliocene) (Grant-Taylor, 1978). Age

determinations from the two drill holes similarly indicated a Nukumaruan age for the top and Waipipian age

for the base ( (Leslie W. C., 1971a; Leslie W. , Takapau no. 1, Well completion Report, 1971b).

5.2.2 Pebbly Hill limestones (informal name)

Pebbly Hill limestones are described by Grant-Taylor (1978) as pebbly coquina and shell limestone that occur

as serval horizons within the Ashley formation. In the western areas of the Ruataniwha Plains, outcropping

lenses contain variable, but generally considerable, proportions of small well-rounded greywacke pebbles.

Grant-Taylor (1978) reports Pebbly Hill limestones were intercepted during drilling of Ongaonga-1 at 274-

314m and 1461-1468m, and in Takapau-1 at 58-73 m and 838-942m.

5.2.3 Upokororo formation (informal name)

Grant-Taylor (1978) describe Upokororo formation as containing thick beds (up to 10 metres) of

conglomerate interbedded with sandstone, siltstone, mudstone, and fine-grained, slightly carbonaceous

pumiceous beds, which collectively exceed 100 metres thickness. The lower part is described as being

characterised by pumice flood deposits and interstitial sand composed of pumice (Grant-Taylor, 1978).

Higher in the sequence, the finer grained beds are less pumiceous and include mudstone derived from a

weathered regolith (Grant-Taylor, 1978). Grant-Taylor (1978) suggest shallow water deposition based on its

sedimentary features; however, Grant-Taylor (1978) noted there no indication whether the water was saline

or fresh.

5.2.4 Blackburn formation (informal name)

The oldest of the Late Quaternary deposits described by Grant-Taylor (1978) is the Blackburn formation. It

overlies the Upokororo formation and is composed of conglomerate, sandstone and mudstone without

conspicuous pumice beds. Its regular bedding suggests fluvial deposition in the lower section. The upper beds

are unsorted gravels suggesting a depositional environment of rivers overloaded with sediment, and the

terrace surface is therefore probably an alluvial fan surface. Grant-Taylor (1978) give it an Upper Okehuan or

Putikian age.

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5.2.5 Hugenden, Glen Appen, Ngaruru, Ongaonga, Tikokino formations

The Hugenden, Glen Appen, Ngaruru, Ongaonga and Tikokino formations form flights of raised terraces

composed of unsorted gravel over eastern parts of the Ruataniwha Plains. Although the younger deposits

have extensive areas of preserved surfaces, the older are much dissected. The lithology of these formations

is similar with few beds finer than conglomerate. No intrinsic characteristics for correlation have not been

found. A loess capping, usually less than 1 m thick, typically lies on the terrace remnants.

5.2.6 Fairfield formation (informal name)

The Fairfield formation described by Grant-Taylor (1978) are composed of sorted lenses of gravel and sand

with flood silt forming the surface away from the river channels. The deposits are confined to recent flood

channels in the deeply incised parts of river channels, but is more widespread in the further east near the

entrances of the Tukituki and Waipawa River gorges through the Raukawa Range. The formation is still

accumulating, forming the current riverbeds and flood plains in the Ruataniwha Plains. Grant-Taylor (1978)

gives an indicative age of less than 15,000 years.

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5.3 Overview of PDP (1999) hydrogeological units

This section summarises the hydrogeological units defined by PDP (1999). A summary of the Greywacke

(Torlesse (composite) terrane), Ashley formation, Pebbly Hill formation and Upokororo formation mapped

by PDP (1999) are described previously in sections 5.1 to 5.2. The names adopted by PDP (1999) to describe

the hydrogeological units within the Ruataniwha Basin, are used here for consistency. The extent of the units

mapped by PDP (1999) is illustrated in Figure 5-4.

Figure 5-4: Hydrogeological map of the Ruataniwha Plains (Pattle Delamore Partners, 1999).

5.3.1 Ancient Terrace Aquifer Group

The Ancient Terrace Aquifer Group crops out in the western upper plains and Ruahine foothills and is

identifiable topographically as the higher terrace flights. Very few boreholes are drilled within these older

sediments, which are considered significantly more compact and cemented than the younger terraces.

5.3.2 Older Terrace Aquifer Group

The Old Terrace Aquifer Group occurs beneath the Recent Terrace Aquifer Group in central and eastern plains

area, and outcrops to the west where the Old Terrace Aquifer Group has been uplifted. This aquifer occurs

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up to 120 metres below land surface, deepening to the east. The lithology described by PDP (1999) is similar

to the Recent Terrace Aquifer Group but more compact and cemented in places, containing a number of ash

and pumice horizons. The boundary between the Old and Recent Terrace Group is often indistinct (Pattle

Delamore Partners, 1999). Both semi-confined and confined aquifer conditions prevail in this aquifer group.

5.3.3 Recent Terrace Aquifer Group

The Recent Terrace Aquifer Group described in PDP (1999) occurs in the central part of the Ruataniwha Plains

at a depth between 25 and 80 metres. Aquifer conditions within the group range from semi-confined to

confined. The deposits reportedly consist of an interbedded sequence of gravels, silts and clay bound gravels

with individual layers varying from less than 1 metre to over 10 metres in thickness and are discontinuous

(Pattle Delamore Partners, 1999). PDP (1999) recognised two distinct hydrofacies within these materials, the

Central Plains Unconfined Aquifer and the Tukipo aquitard (also referred to as the shallow Tukipo aquitard).

Central Plains unconfined aquifer

The Central Plains unconfined aquifer is composed of clean gravels and sands with minor silt or silt-bound

layers. The aquifer is up to about 25 metres depth below land surface and most extensive within the Waipawa

Catchment. The loose gravels provide a conduit for surface water recharge and during summer when the

entire river flow maybe lost to groundwater.

Tukipo aquitard or Shallow Tukipo aquitard

The shallow Tukipo aquitard is a persistent dominantly clay-bound gravel lithology mapped between the

Makaretu and Tukituki rivers within the Recent Terrace Aquifer Group. The aquitard extends to a maximum

depth of 80 metres, thinning to the north. The eastern boundary interdigitates with more typical Recent

Terrace Aquifer Group and the western upstream boundary lies against an erosional surface on older terrace

deposits.

5.4 Overview of Francis (2001) stratigraphy

This section summarises the stratigraphy defined by Francis (2001). A summary of the Torlesse (composite)

terrane, Tinui and Mangatu Group rocks, and Te Onepu Limestone reported by Francis (2001) are covered

previously in section 5.1. The names adopted by Francis (2001) to describe the geology within the Ruataniwha

Basin are used are used here for consistency to describe these geologic units.

5.4.1 Miocene mudstone and sandstone

In the north of the Ruataniwha Plains, near the Waipawa River, Francis (2001) maps Miocene Mudstone

beneath the plains in basal contact with the Whangai Formation. To the south the deposits are the lower

most units mapped by Francis (2001). Their presence, however, immediately overlying faulted slivers of

basement rocks along the Oruawharo Fault south of the basin suggests it is present at depth beneath the

basin, at least locally e.g. Well Speedy-1; (Johnston & Langdale, Speedy-1/1A Well Completion Report.

Petroleum Report Series PR 2537., 2000).

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5.4.2 Mid to lower Pliocene Mudstone and siltstone

Mid to Lower Pliocene mudstone and siltstone mapped by Francis (2001) are basal Pliocene deposits in

eastern Ruataniwha and possibly represent the Raukawa Mudstone. The Raukawa Mudstone is widespread,

thick and consists predominantly of mudstone, and locally contains the Tukituki Sandstone (Thompson, 1926)

and its correlative, Argyll Sandstone member. It unconformably overlies Mesozoic to mid-Cenozoic strata or

Awapapa Limestone, and is overlain by Te Onepu Limestone. In Francis (2001), this layer overlies Whangai

Formation and Miocene rocks.

5.4.3 Tukituki Sandstone

The upper surface of the Tukituki Sandstone is in contact with the Te Onepu Limestone, and where present,

the Tukituki Sandstone always forms the uppermost part of the Raukawa Mudstone. Thompson estimated

these deposits to be 60 metres thick in an outcrop west of Waipukurau (Thompson, 1926). The Tukituki

Sandstone is considered highly porous and permeable and maybe recharged where it is exposed to the

Tukituki and Waipawa Rivers east of the Ruataniwha Plains (Francis, 2001). In the Speedy-1 (Johnston &

Langdale, 2000) well it was 65 metres thick, and to the north on Te Onepu Rd the equivalent Argyle Sandstone

member (Harmsen, 1984b) is 13 metres thick. In Ongaonga-1 it was 46 metres thick (Leslie W. C., 1971a).

5.4.4 Upper Pliocene mudstone

The Upper Pliocene Mudstone mapped by Francis (2001) most likely represents Makaretu Mudstone. The

mudstone is defined as the fine-grained interval overlying Te Onepu Limestone and gradationally underlying

the members of the Mason Ridge Formation (Dyer, 2005). The Makaretu Mudstone is a minimum of 20

metres thick in the region where described by Thompson (1926), at least 40 metres thick at the southern end

of the Raukawa Range, and increases to several hundred metres at the northern end of the range (Kelsey,

Erdman, & Cashman, 1993).

In Takapau-1 the Makaretu Mudstone is estimated at around 140 metres thick between 701-838 metres

below land surface (Leslie W. , Takapau no. 1, Well completion Report, 1971b) with a thickness of 5.1 m

between 778.5 and 783.6 m interpreted as Pukeora Oyster Bed. In Ongaonga-1 the Makaretu Mudstone is

33 metres thick and lies between Pukeora Oyster Bed at the upper surface, and Te Onepu Limestone at its

base. In Speedy-1, the Makaretu Mudstone was intercepted at shallower depths between 86-117 metres.

5.4.5 Upper Pliocene limestone

The Upper Pliocene limestone mapped by Francis (2001) most likely represents members within the Mason

Ridge Formation that gradationally overlies the Makaretu Mudstone. Mason Ridge Formation comprises a

coarsening upward unit with five members, three of which are limestone.

South of Station Road, these Nukumaruan limestones thicken and bed numbers increase to form three or

more thick beds separated by mudstone (Francis, 2001). The limestones define an extensive NNE plunging

syncline east of the Oruawharo Fault Zone (Francis, 2001). Limestone of Nukumaruan age also occur on the

western and northern flanks of the Takapau Hills, and dip northwest and north respectively off the north-

plunging anticline (Francis, 2001).

Relatively thin limestone beds of Nukumaruan age form outcrops dipping gently west at Ashcott Hill and in a

few other places to the west of Highway 50 (Francis, 2001). Far to the west of the Ruataniwha Plains,

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limestone of similar age crosses the upper reaches of the Waipawa and Tukituki rivers as well as upper

Tukituki Rd, Lookout Rd and Wakarara Rd. Here, the limestone crops out within a major fault zone and dips

almost vertically in places (Francis, 2001).

Pukeora Oyster Shell bed and equivalent limestone

The Pukeora Oyster Shell bed is equivalent to the Mahana limestone of the Mason Ridge Formation (Kelsey,

Erdman, & Cashman, 1993). The Pukeora Oyster Shell bed overlies the South Makaretu Mudstone, and is

exposed in a series of outcrops along the eastern margins of the Ruataniwha Plains from the Waipawa River

southwards to Maharakeke Rd (Francis, 2001). Although not mapped as an individual unit within Francis

(2001) it is presumed included within the Upper Pliocene limestone.

The shell bed consists of characteristically shelly limestone, packed with mostly whole oyster and brachiopod

shells in a medium to coarse highly calcareous sandy matrix. Several outcrops occur along Highway 2 near

the Ashcott Rd junction, and adjacent to Lindsay Rd to the north and Maharakeke Rd to the south (Francis,

2001). Although it is relatively thin in this area (10–15 m) and similar to the thickness in Speedy-1 well (13

m), it thickens to the north, south and west to become a series of limestone and mudstone beds with a total

thickness of up to 233 m (as seen in Ongaonga-1 (Leslie W. C., 1971a).

5.4.6 Top Pliocene sandstone and siltstone

The Top Pliocene sandstone and siltstone mapped by Francis (2001) may represent Maharakeke Mudstone

Member (Bland, Kamp, & Nelson, 2007) which is a mudstone member of the Mason Ridge Formation

between the lower Mahana Limestone and middle Torran Limestone members. However, the unit may also

include the Okauawa and Poutaki formations, which overlie the Mason Ridge Formation.

5.4.7 Salisbury Gravel

See section 5.1.7

5.4.8 Young gravels (informal name)

The young gravel deposits described by Francis (2001) are equivalent to the Holocene alluvium and some

Middle to Late Quaternary deposits described in Lee et al (2011). The young gravels overly the Salisbury

Gravel or marine Pliocene sediments at an angular unconformity. They are composed of sorted to poorly

sorted cobble to pebble gravels thinly interbedded with clay and silt. Poorly sorted gravels have a matrix of

sand, silt or clay. The young gravels were deposited in a dominantly alluvial environment, although it is

possible that some clays were deposited in a lacustrine environment, and peaty deposits accumulated in

temporary swamp settings.

The thickness of the young gravels is reportedly greater to east of Highway 50, mainly because of the

influence of several downthrown faults to the east which were most likely active during deposition. In many

drillers’ well logs, the distinction between Salisbury Gravel and young gravels is not especially clear (Francis,

2001). However, the thick ignimbrite some way below the top of Salisbury Gravel is characteristic, as is

relatively common lignite and thick lacustrine clay beds. In many places, the young gravels are typically red,

whereas Salisbury Gravel is blue-grey (Francis, 2001). Kingma (1971) describes the difference between post-

Castlecliffian deposits and Salisbury deposits based on weathering of their greywacke components; including

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the presence of pumice beds. In the Salisbury Gravel the greywacke deposits exhibit more advanced

weathering and irregular pumice interbeds.

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6 Structure of the Ruataniwha Basin The Ruataniwha Basin can by divided into three current structural and topographical domains. From west to

east, they include the main strike slip faults and contractional structures along the eastern margins of the

Ruahine Ranges, a region of low-lying plains and rolling hills, and the coastal ranges forming the eastern

boundary of the Ruataniwha Plains, which are characterised in parts by uplift and extensional faulting.

Anticlines and synclines within the basin are dominated by north-northeast striking reverse faults and

associated asymmetric folds. Faults are planar to depths of at least 1-2km and typically dip at 30-80° NW

(Beanland, Melhuish, Nicol, & Ravens, 1998). The structural map, derived mainly from interpretation of the

1970-71 seismic surveys, show various faults traversing the length of the basin (Hollingsworth, 1971). Most

faults disrupting strata within the basin do tend to die out northwards so that the associated folding becomes

more symmetrical and gentler. Alluvial terraces of Early Quaternary age are folded and warped by surface

and subsurface reverse faults.

In the Turiri and Raukawa Ranges bedding dips almost exclusively to the northwest, while bedding in the

west of the basin is dominantly (but not exclusively) to the southeast. A series of monoclines, anticlines and

synclines, with axes aligned northeast to southwest, have been recorded in Pliocene rocks to the south and

north of the basin (Lee et al. 2011). A number of faults with a similar orientation are mapped and show active

surface traces, particularly in the south (NZ Active Faults Database). These faults align well with those

mapped from seismic reflection data (e.g. Leslie 1971).

6.1 Tectonic history

Central Hawke’s Bay lies within the forearc region of the Hikurangi margin, which is a long (400-500km),

narrow region of subdued topography, bounded on the west by range-front contractional structures and to

the east by an accretionary wedge. Detailed mapping, both onshore and offshore, have shown the Pacific

Plate is being obliquely subducted beneath the edge of the Australian Plate since Miocene times (Pettinga J.

, 1982; Kamp & Nelson, 1988). This subduction process has strongly affected the landscape and evolution of

the Ruataniwha Basin.

Torlesse (composite) terrane rocks of the Ruataniwha Basin originally formed as part of a palaeofrontal

accretion at the edge of the Gondwana landmass, prior to the breakaway of New Zealand (Spörli & Ballance,

1989). Major uplift of the ranges began approximately 1 Ma ago. Consequently, many of the landform

features within the Ruataniwha Basin parallel the plate boundary.

During the late Cretaceous-early Tertiary a major marine basin, termed the “Eastern Basin” by Kingma (1960),

extended from North Canterbury, through Wairarapa and Hawke’s Bay, to the Ruakumara Peninsula. From

the early Miocene onwards, a period of renewed tectonic activity, episodic uplift, and subsidence formed

localised marine basins in different parts of the east coast of the North Island. This is attributed to the

development and propagation of a structurally complex accretionary wedge, in response to subduction at

the Hikurangi margin. By the late Miocene, Hawke’s Bay had been structurally divided into a western

basement high (axial ranges), a central depression (forearc basin), and an eastern high (coastal hills

associated with the accretionary wedge).

In the early Pleistocene a major seaway, the Ruataniwha Strait, extended more than 100 kilometres from

southeastern Wairarapa to Hawke’s Bay (Pettinga J. R., 1980; Beu, Grant-Taylor, & Hornibrook, 1980; Beu A.

G., 1995). Along its margins, limestone deposited on fault-controlled highs in the east, and on a coastal shelf

along the western side of the strait. Progressive uplift in the Ruataniwha Strait and sedimentation during the

Pliocene resulted in the formation of wide, shallow marine platforms, which were further uplifted through

the Late Pliocene (Browne, 1986).

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By the end of the Pliocene, uplift associated with the Mt Bruce fault block (Lee, Begg, & Forsyth, 2002) had

closed the southern end of the seaway and the resulting embayment began rapidly infilling with terrestrial

deposits eroded from the nearby ranges. Consequently, throughflow of currents ceased and two

independent basins developed - Hawke’s Bay to the north and Wairarapa to the south. Sea continued to

enter the Hawke’s Bay basin as far as Dannevirke c.700 ka (Krieger, 1992; Ballance, 1993).

The middle-late Pleistocene was characterised by accelerated uplift, especially along the Ruahine Ranges,

and by terrestrial infilling of the Ruataniwha Basin together with continued folding and faulting. The sea still

occupied eastern and southern parts of the basin and deposited estuarine and lagoonal sediments. To the

north, fluvial deposits of the river floodplains were accumulating and extending over the basin as uplift began

excluding the sea (Brown, 2002). Sediments derived mainly from the ranges, and the inland coastal hill

country indicate sea-level had withdrawn to about the present coastline by the 1.0-0.1 Ma (Kamp P. , 1992)

Large alluvial fans (Salisbury Terraces) deposited along the margin of the ranges, resulting from uplift during

the middle-late Pleistocene. Uplift also resulted in stream incision and erosion of material by mass movement

processes. Around the same time, intermittent volcanic activity in the central North Island resulted in

deposits of ignimbrites, ash, tuff and pumice across Hawkes Bay (Brown, 2002). Prevailing westerly winds

carried tephra into Hawke’s Bay, which was reworked by rivers and streams. During glacial and stadial times

intense physical weathering prevailed resulting in transportation of material through fluvial and aeolian

processes, including mantling much of the hill country and plains with loess. Interglacial times marked a

predominance of chemical weathering (paleosols) and river degradation.

The main accumulation of gravel occurred where river courses emerged from the mountain valleys onto

lower slopes. In temperate interglacial periods, vegetation re-established to higher altitudes and sediment

transportation was choked; despite abundant water. Rivers responded to the reduced sediment load by

entrenching into the glacial deposits at the western margin of the Ruataniwha Plains and redeposited gravel,

sand and silt further downstream across the plains. With continuing uplift, each successive glacial

aggradation - interglacial degradation cycle, produced another terrace bound by the previous terraces to

form flights of raised terraces. The oldest and highest of these raised terraces have an undulating sometimes-

tilted surface and are overlain with soils developed on loess and ash deposits. The younger lower terraces

are relatively flat with soils developed on stoney surfaces and overbank river deposits (Griffiths, 2001)

During the last 500,000 years, fluvial deposition has continued within the basin, and in places, recent alluvium

and/or tephras overlie rocks of Kidnappers Group (Bland, Kamp, & Nelson, 2007). In the northwest uplift

resulted in the Ngaruroro River entrenching into the Salisbury Gravel floodplain and ultimately forming a new

course directly east to the coast across the Heretaunga Plains. The Waipawa and Tukituki Rivers also

entrenched but maintained courses across the Ruataniwha Plains and through the ranges and hills of the

anticline. Late Quaternary landscape features over the coastal hill country indicate folding, faulting and uplift

continues to the present day (Bland & Kemp, 2014). Deposition, erosion and downstream reworking of fluvial

gravels are greatest where the major rivers enter the Ruataniwha Plains. This has resulted in extensive

deposits of gravel strata underlying the Waipawa and Tukituki Rivers.

6.2 Faults overview

Within Central Hawke’s Bay, four main belts of faulting can be identified:

(i) the Axial Ranges zone in the west, characterised by strike-slip faulting with lesser reverse

faulting;

(ii) the Ruataniwha Plains which is characterised by reverse faulting with lesser strike-slip faulting;

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(iii) the Central Belt which is characterised by reverse faulting, and

(iv) the Eastern or Coastal Ranges, which are dominated by normal faulting with a lesser component

of reverse faulting.

The active strike-slip faults, including the Mohaka and Ruahine faults, are oriented NNE-SSW and include

prominent active traces that are nearly linear and may extend for significant distances (Kingma, 1962;

Beanland S. , 1995). In Hawke’s Bay, the Mohaka and Ruahine faults have accommodated strike-slip

displacements during the Late Quaternary and are thus regarded as “active” (i.e. have ruptured to the surface

during the last 125 kyr, or multiple times in the last 500 kyr). These two faults form the western boundary of

the Ruataniwha Basin, between basement Torlesse (composite) terrane rocks and Neogene sediments. Faults

such as the Rangefront Fault and Wakarara Fault are active reverse-slip faults that account for shortening at

the front of the Ruahine Ranges.

The easternmost faults in the Ruataniwha Basin are the Oruawharo, Takapau and Ruataniwha faults; these

all include traces on the treads of last glacial gravel terraces in the south and almost certainly continue north

beneath Quaternary deposits. The Te Heka Fault zone, also comprising reverse faults, lies at the northern

end of the basin near Tikokino.

6.2.1 Ruahine Fault

The Ruahine Fault is located along the axial ranges in the Ruataniwha Basin. It is as an active strike-slip fault

that separates the Torlesse (composite) terrane rocks of the Ruahine Range from the softer marine Neogene

sediments to the east. Through much of the area of interest, the Ruahine Fault lies entirely within basement

Torlesse (composite) terrane rocks. Most uplift in the past was towards the west. However, recent uplift,

especially in the northern section of Ohara Depression is to the east, as confirmed by striations on the fault

surface is Tarapeke Stream and upthrown eastward scarps (Erdman & Kelsey, 1992). The Ruahine Fault has

a slip rate of 1-2 mm/yr, a single-event displacement of 2-5 m, and a recurrence interval of 1000-5000 yr

(Beanland & Berryman, 1987; Hanson, 1998). This produces a mean recurrence interval of c. 3000 yr.

6.2.2 Mohaka Fault

The Mohaka Fault is a NNE-striking active strike-slip fault that runs through the entire length of the Hawke’s

Bay region, and is a continuation of the Wellington Fault (Beanland S. , 1995). It is typically expressed at the

surface by a clear, straight to slightly sinuous fault trace between Alder Road, near the Hinerua Trust and

Mangleton Road with the Gwavas forest. The fault can be mapped crossing hillslopes and alluvial terraces.

Many of the larger hillslope streams show displacements of 30-40 m (Beanland S. , 1995) indicating repeated

movements along the fault during the Late Pleistocene to Holocene. The fault offsets bedrock units and some

large rivers by kilometres (Berryman, Van Dissen, & Mouslopoulou, 2002; Langridge, Berryman, & Van Dissen,

2005; Langridge & Villamor, 2011) and younger Late Quaternary features like spurs and streams by many

tens of metres. Data from trenches indicate that past earthquakes have ruptured the Mohaka Fault on

average every c. 1100 years (Langridge et al., 2013). Interpretation of a seismic reflection line which crosses

the Mohaka Fault indicates minimal (

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Figure 6-1: Photo of Mohaka Fault Line (photo Dougal Townsend, GNS Science).

6.2.3 Wakarara and Rangefront faults

The Wakarara and Rangefront faults are active NNE-striking reverse-slip faults characterised by a series of

discontinuous scarps along the front for the Wakarara Range (Langridge & Villamor, 2011), although at depth,

these traces are assumed to be part of a single fault. West of the faults, the Ruahine Ranges rise rapidly as a

fault block, this part of the Ruataniwha Basin has experienced uplift, but at a slower rate than the Ruahine

Range. The Wakarara fault trace is discontinuous and displays scarps up to 2 metres height in places

(Langridge & Villamor, 2011). The fault trace hugs the front the Wakarara Range and bends upvalley at

Poporangi Stream. This indicates the sense of movement is reverse, characterised by uplift of the Wakarara

Ranges. The dip of the fault has not been measured directly but is considered moderate to shallow (30-45°).

The Rangefront Fault is the south-western continuation of the Wakarara Fault (Langridge & Villamor, 2011).

It may be traced into the Manawatu region as a range-bounding structure. Vertical fault scarps are associated

with this fault between Makaroro River and the Tukituki River headwaters, including Tukipo Stream

(Langridge & Villamor, 2011). These fault scarps are preserved across likely Q2, Q1 and older terraces in these

areas (Lee, Bland, Townsend, & Kamp, 2011). The sinuous, multi-trace outcrop pattern of the fault as seen

across flat terraces suggest the Range Fault has a low to moderate dip (Langridge & Villamor, 2011).

6.2.4 Ruataniwha Fault

The Ruataniwha Fault is an oblique reverse fault identified in the southern part of the basin. High resolution

DEMs for the northern segment of the fault clearly show a well-defined fault scarp along the Ruataniwha

Fault trace as mapped by Lillie (1953; the Taniwha Fault) and Kingma (1962). An RTK GPS surveyed vertical

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and horizontal offsets up to 21 metres and possible single event horizontal offsets up to 2 metres (Klos, 2009).

Reinterpretation of seismic profiles collected within the Ruataniwha-Dannevirke Basin constrained the fault

dip to 56° ± 7° to the NW.

6.2.5 Oruawharo Fault

The Oruawharo Fault is the most obvious strike-slip fault in the southern part of the basin. Torlesse

(composite) terrane is found at the surface immediately west of the fault, and an associated anticline plunges

north under the plains a short distance east of Takapau (Francis, 2001). Seismic surveys show the fault and

the anticline decrease in displacement and amplitude northwards. Similar faul