Geology of the Kaikoura Area - GNS Science

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predominant rock type but in the northwest, granite andultramafic clasts are locally present. Lenses of silt and sandare also present throughout the gravel deposits but arerarely significant.Except on present-day floodplains, the alluvial depositsform flights of aggradational terraces, with the older terracespreserved at progressively higher levels above the valleyfloors. Although stratigraphic or glacial episode nameshave been applied in local settings (Suggate 1965; Eden1989; Townsend 2001), the deposits are differentiated hereby age based on oxygen isotope stages (OIS). Mostdeposits are poorly dated and their ages are generally basedon the height of the capping terrace surface relative toothers in the valley. The extent of terrace dissection, degreeof clast weathering and the number and thickness of loessunits (see below) have also helped to constrain terracedeposit ages.The Plateau Gravel (eQl) occurs as isolated remnants thatoverlie the Dun Mountain Ultramafics Group on the crestof Red Hills Ridge (Fig. 17). The formation is up to 25 mthick and comprises poorly sorted and weakly stratifiedultramafic clasts, commonly less than 0.5 m across butwith large angular blocks near the base and sparse, wellroundedpebbles of Torlesse sandstone. The formationowes its preservation to the sandy matrix being cementedby magnesium compounds released from weathering ofthe ultramafic rocks. The age of the gravel is uncertain butis inferred to be no older than Middle Pleistocene (Johnston1990).Unmapped surficial depositsLoess deposits are not differentiated on the Kaikoura map,but they sometimes form significant sheets up to severalmetres thick on older terraces (Q4 to Q10) adjacent to majorrivers or in gullies in the lee of the prevailing westerlywinds. Identification of one or more loess-soil horizons(Fig. 51) may help to broadly distinguish the ages ofaggradation terraces. In the northeast of the map area, the26.5 ka Kawakawa tephra (Oruanui fall deposit; Wilson2001), sourced from the central North Island, commonlyoccurs as a layer in loess deposits on terraces older thanOIS 2 and locally in fan gravel deposits (Campbell 1986;Eden 1989; Benson & others 2001; Townsend 2001). Thec. 340 ka Rangitawa tephra (Kohn & others 1992; Berger &others 1994), also from the central North Island, occursrarely in loess older than OIS 10 in the northeast of themap area.Fill, of varying levels of compaction, is common underroads and railways, particularly in gullies and approachesto bridges. Small areas of uncompacted fill, the result ofthe dumping of domestic rubbish, are present adjacent tomany of the townships in the map area. All of these depositsare too small to show on the geological map.Alluvial fan and scree depositsAlluvial fan deposits (Q1a, Q2a, Q3a, Q4a, Q6a, Q8a,Q10a, eQa, uQa) are widespread throughout the map areaand many merge into the aggradation surfaces in the mainvalleys (Fig. 52). Many of the fans are too small to beshown on the map and are either omitted or incorporatedinto the corresponding alluvial terrace. Mappable screedeposits (Q1s) occur in the higher mountains and consistof locally derived, slightly weathered, angular clasts ofpebble to boulder size. Screes commonly merge with moregently sloping, water-borne alluvial fans towards the valleyfloors. Rock glacier deposits (Q1r) consisting of poorlysorted gravels up to boulder size occur on the InlandKaikoura Range (Fig. 53). Eight rock glaciers up to 1.2 kmlength and 500 m wide occur at elevations exceeding 2100m (Bacon & others 2001). These are probably activelyexpanding and moving, and result from permafrostconditions in an arid climate where there is a high ratio ofrock debris to snow supply.Figure 51 Loess on the south bank ofthe Clarence River near SH 1 showingtypical vertical fluting. The faint darkerbanding part way up the loess may bea paleosol, or buried soil. Thethickness of the loess and thepresence of the paleosol suggest thatthe age of the underlying gravel depositis at least OIS 4 (Q4a).44
Figure 52 Screes on the southern flanks of Dillon Cone merge into alluvial fans near a prominent gradient changemid-slope towards the Clarence River valley. The Elliott Fault crosses the range close to the change in slope. Q1a andremnant Q2a alluvial terraces occur close to the river.Photo CN8171/25: D.L Homer.Figure 53 Rock glaciers (left, lower right) and screes mantling the southern slopes of Mt Alarm on the Inland KaikouraRange.Photo CN25751/11: D.L. Homer.45
Page 1: 1 : 2 5 0 0 0 0 G e o l o g i c a l
Page 7: ABSTRACTThe Kaikoura 1:250 000 geol
Page 10 and 11: 27 10722181725814362333322621243128
Page 12 and 13: ProvinceSEDIMENTARY AND VOLCANIC RO
Page 14 and 15: Main Divide rangesGEOMORPHOLOGYThe
Page 16 and 17: Figure 9 Basin and range topography
Page 18 and 19: Figure 12 The active Alpine (Wairau
Page 20 and 21: 290PermianCarboniferous354Late Devo
Page 22 and 23: iotite granite, locally with megacr
Page 24: interlayered with the Rotoroa Compl
Page 28 and 29: Figure 19 Maitai Group sedimentary
Page 30 and 31: Torlesse composite terraneThe Torle
Page 32 and 33: Permian to Late Triassic semischist
Page 34: Zones of intra-Pahau mélange, char
Page 37 and 38: CRETACEOUS TO PLIOCENEFollowing ama
Page 39 and 40: Figure 31 Interbedded sandstone and
Page 41 and 42: Figure 34 The Seymour Group include
Page 43 and 44: of feldspar-clinopyroxene-biotite-a
Page 45 and 46: The Amuri Limestone (Pza, Eza) is w
Page 47 and 48: overlies older rocks (Carter & Land
Page 49 and 50: Late Miocene to earliest Late Plioc
Page 51: QUATERNARYThe tectonic regime initi
Page 55 and 56: Marine depositsMarine sand and grav
Page 57 and 58: and/or non-deposition (including th
Page 59 and 60: hydrous mica clay are widespread as
Page 61 and 62: Dunite boulders are sporadically co
Page 63 and 64: GEOLOGICAL HAZARDSParts of the Kaik
Page 65 and 66: The Modified Mercalli Intensity sca
Page 67 and 68: Table 2. Mean return periods for ea
Page 69 and 70: REFERENCESAdams, C.J. 2003: K-Ar ge
Page 71 and 72: Childerhouse, S.J.; Dawson, S.M.; S
Page 73 and 74: Holdaway, R.N.; Worthy, T.H. 1997:
Page 75 and 76: McPherson, R.I. 1988: Experimental
Page 77 and 78: Stewart, R.B. 1974: Geology of Mt M
Page 79: This map and text illustrate the ge

Geology of the Kaikoura Area - GNS Science

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