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ISSN 2538-1016; 28 NEW ZEALAND DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH BULLETIN 171 SEDIMENT A TI ON IN HAWKE BAY by H. M .. PANTIN I New -Zealand Oceanographic Institute Memoir No. 28 1966 SEDIMENTATION IN HAWKE BAY This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ Photograp/1: Rayo/ N.Z. Navy RNZFA Isa Lei from which some of the Hawke Bay sampling was carried out. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ NEW ZEALAND DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH BULLETIN 171 SEDIMENTATION IN HAWKE BAY by H. M. FANTIN New Zealand Oceanographic Institute Memoir No. 28 1966 Price 15s. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ This publication should be referred to as N.Z. Dep. sci. industr. Res. Bull. 171. © Crown Copyright Printed by Wright and Carman Ltd., under the Authority of R. E. Owen, Government Printer, Wellington, New Zealand, 1966. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ FOREWORD Until recently, no substantial studies of the distribution of sediments on the New Zealand shelf have been carried out. This memoir presents the results of the first such investigation carried out by the Institute, and considers the nature and origin of the superficial sediment over an area of 1 OOO square miles of the eastern shelf. The material has been prepared for publication and received preliminary editing by Mrs P. M. Cullen. J. W. BRODIE, Director, New Zealand Oceanographic Institute, Wellington. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ CONTENTS Page Page FOREWORD 5 Discussion of Sedimentary Regime-Continued Off-shore Gravel Zones 44 ABSTRACT 9 Central Zone 44 Lachlan Ridge 46 TOPOGRAPHICAL AND GEOLOGICAL Age of Central-zone Layer and Rates of Sedi- SETTING 9 mentation in the Mud Belt ____ 46 BATHYMETRY 14 PROVENANCE 48 Sources of Data 14 Description of Bathymetry 17 AUTHIGENIC MINERALS 50 Sediment Sampling 18 Glauconite 50 Limonite 52 DISTRIBUTION AND NATURE OF SEDI- Summary of Factors Controlling Formation of MENTS 24 Glauconite and Primary Authigenic Limonite 53 24 ( 1) Off-shore Gravel Zones (2) Off-shore Sand Belt 24 INTERNAL STRUCTURES IN THE SEDI- MENTS 56 Mud Belt 28 (3) Lamination 56 Central Zone 37 ( 4) Banding 57 ( 5) Sediments Associated with the Lachlan Ridge 39 Organic Structures 58 Lachlan Ridge Gravels 39 Aggregates 58 Finer Sediments of the Lachlan Ridge 40 Organic Burrows 59 Mottling 59 DISCUSSION OF SEDIMENTARY REGIME 42 ACKNOWLEDGEMENTS 61 Factors Controlling the Deposition of Sediment 42 Off-shore Sand Belt (main part) and Mud REFERENCES 62 Belt 42 Sand-belt Salient 43 INDEX 63 FIGURES Page Page l. Locality map 10 9. Weight percentage of sediment with diameter 2. Topographic map of the Hawke's Bay more than 66µ, uncorrected for the pre- coastal area 11 sence of aggregates 25 3. Geology of the coastal areas of Hawke's 10. Grain-size distributions with selected sedi- Bay 12 ment samples 26 4. Outline of bathymetry with position of shelf, 11. Weight percentage of sediment with diameter slope, and shelf edge in Hawke Bay 14 more than 66µ, corrected for the presence of aggregates 27 5. Detailed bathymetry and station positions ____ 15 6. Isopachs on main subsurface reflector within 12. Weight percentage of sediment with diameter the sediments 16 more than 2 mm 29 7. Distribution of sounding lines that show sub- 13. Surface current directions in Hawke Bay ___ _ 43 surface reflecting horizons ____ 17 14. Conditions for the formation of glauconite 8. Stratigraphy of Hawke Bay cores ____ _ ___ 20, 2 l and primary authigenic Iimonite ___ _ 54 7 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ CONTENTS-Continued TABLES J. Rates of Discharge of Hawke's Bay Rivers 12 8. Characteristics of Sand and Mud Fractions 2. Station List 19 in Sediments Associated with Lacblan Ridge 39 3. Counts of Grain Types in Surface Samples 3 l, 32 9. Characteristics of Pumice and Foraminiferal 4. Counts of Grain Types in 250-500µ Fractions Infillings in Sediments Associated with from Cores 33 Lachlan Ridge 39 5. Counts of Grain Types in 66-125µ Fractions 10. Sources of Hawke Bay Sediments ____ 48 from Cores 34 11. Distribution of Micro-environments Contain­ 6. Fraction Containing Median Diameter of ing Autbigenic Glauconite and Primary Sand Component in Samples from Cores 35 Authigenic Limonite 50 7. Characteristics of Pebbles in Sediments Asso- ciated with Lachlan Ridge 38 PLATES Frontispiece. RNZFA Isa Lei 3. Typical structures in Hawke Bay cores 69 l. Nukumaruan (Lower Pleistocene) beds at 4. Echo soundings obtained by HMNZS Lach/an Matangimomoe 67 in Hawke Bay 70 2. Typical structures in Hawke Bay cores 68 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ SEDIMENTATION IN HAWKE BAY Abstract The surface sediments in Hawke Bay are divided into five groups: offshore gravel zones, sand belt, mud belt, central zone, and sediments associated with the Lachlan Ridge. These distinctions are made primarily on grain size. Over much of the Bay a relatively coarse sediment layer, sampled by coring, appears as a subsurface reflector on echo-sounding records. This layer underlies the relatively fine sedi­ ments of the mud belt and outcrops in the central zone. Shell material from the central zone has been 14C-dated as approximately 10,000 years B.P. The subsurface reflector shows the effect of faulting. The sand belt separates the mud belt from the shoreline and the distribution of these two zones appears to be governed by present-day sedimentation. The central zone and parts of the Lachlan Ridge are at present non-sedimentation areas. Other parts of the Lachlan Ridge are areas. of slow sedimentation. Clastic minerals in the sediments of the Bay are mainly derived from the Mesozoic grey­ wacke suite of the North Island or from the Taupo volcanic sequence, Quaternary in age, which covers a wide area in the region of Lake Taupo and includes ash layers extending as far as the coast of Hawke Bay. Tertiary sedimentary rock fragments are common only on the Lachlan Ridge. Authigenic glauconite is present on the Lachlan Ridge and in part of the sand belt. The mineral occurs as ovoids, subangular grains, pumice vesicle infillings, and foraminiferal infillings. Yellowish pumice infillings, which occur in the central zone and on parts of the Lachlan Ridge, apparently owe their colour to primary authigenic limonite. Secondary authigenic limonite, formed by the oxidation of glauconite, is found in the same areas as the latter mineral. TOPOGRAPHICAL AND GEOLOGICAL SETTING Hawke Bay is a conspicuous re-entrant on the Tangoio Bluff and Matangimomoe a long line of =.ast coast of the North Island, New Zealand, cliffs rises from 200 ft in the south to nearly measuring some 50 miles from north-east to 1300 ft in the north. The height of the cliffs then south-west and extending about 25 miles inwards decreases rapidly, falling to 400-500 ft about 2½ from the general line of the coast (Fig. 1). The miles north-east of Matangimomoe. Cliffs up to landscape is mostly rugged and hilly with a deeply 600 ft in height are present along much of the incised fluvial topography, the principal excep­ coast between Matangimomoe and Tuhara, al­ tion being the wide, low-lying Heretaunga Plains. though the cliff-line is more broken by stream and The high relief is largely due to rapid uplift dur­ river valleys than is the case between Tangoio ing the late Quaternary; the numerous marine Bluff and Matangimomoe. Cliffs up to 200 ft in benches and river terraces, together with the up­ height occur locally around Waikokopu. Cliffs are lift of the coast in the Napier-Wairoa district at again present along many parts of Mahia Penin­ the time of the 1931 earthquake,* show that tec­ sula, and range up to 600 ft in height, although tonic activity has continued up to the present day. they are usually only 200-400 ft high. Portland Morphologically the coast varies from sectors Island is ringed by steep bluffs and cliffs 200- '.'ith high undulating sea cliffs to low-lying sectors 300 ft high. (Fig. 2.) "'ith gravel bars and sandhills. The sea cliffs have The low-lying parts of the coast are late been cut by marine erosion across spurs and Quaternary aggradation surfaces, the deposits ridges of soft Tertiary or Lower Quaternary rocks. consisting of sands and gravels in various pro­ Oills ranging from 200 ft to 500 ft in height run portions. The most extensive of these low-lying from Cape Kidnappers to Clifton. Between sectors runs from Clifton to Tangoio Bluff, with • The maximum coastal uplift associated with the 1931 Napier in the centre.

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