Geology of the Kaikoura Area - GNS Science

30 km along the Awatere valley to the northeast (Allen1962). Extrusive trachybasalt and trachyandesite areinterbedded with volcanic conglomerates, sandstone andlimestone lenses (Weaver & Pankhurst 1991). In the lowerpart of the formation, the flows are terrestrial, but near thetop pillow basalts are interbedded with marine tuffs (Challis1966). The flows are petrologically similar to theTapuaenuku Intrusive Complex (see below). The LookoutFormation and Gridiron Formation volcanics are inferredto have been fed by numerous basanitic dikes emanatingfrom the Mt Tapuae-o-Uenuku intrusion during the earliestLate Cretaceous.The Hapuku Group (Kh; Laird & others 1994) crops outbetween the Hapuku and Kekerengu rivers and in thenortheast Clarence valley. Near Ouse Stream, the HapukuGroup is structurally subdivided by the synsedimentaryOuse Fault. West of the fault the group consists of theNidd and Willows formations and other unnamedsedimentary rocks. The Willows Formation comprisespurplish-brown, epiclastic conglomerate of basalticcomposition (Reay 1993). The Nidd Formation (Lensen1978) is preserved as fault-bounded slivers southeast ofthe Clarence Fault and comprises richly fossiliferous,weakly bedded, purple-brown siltstone to very fine-grainedsandstone, commonly glauconitic and burrowed. West ofthe Ouse Fault the Hapuku Group rests with erosionalcontact on the Wallow Group.East of the Ouse Fault, Hapuku Group consists of the BurntCreek Formation (Lensen 1978). The formation has basalpoorly sorted, clast-supported conglomerates containingclasts of sandstone, mudstone, quartzite, chert, and felsicvolcanic and plutonic rocks. These conglomerates gradeupwards into pebbly mudstone, sandstone and siltstone(Fig. 33). The Burnt Creek Formation lies with sharp angularunconformity on Pahau terrane and it is inferred to havebeen deposited in a tectonically controlled basin in themiddle Late Cretaceous (Crampton and Laird 1997).The Seymour Group occurs in the northern part of theKaikoura map area between Cape Campbell and WhalesBack, north of Waiau. The middle Late Cretaceous(Piripauan) Paton Formation (Kyp; Webb 1971) consistsof glauconitic, fine- to medium-grained sandstone andgraded sandstone and siltstone. The formation iscommonly bioturbated and locally contains abundantinoceramid fossils, as fragments or as whole valves. ThePaton Formation unconformably overlies Bluff Sandstone(Reay 1993), is locally scoured into the Hapuku Group(Crampton and Laird 1997), or conformably andgradationally overlies the Burnt Creek Formation (Field,Uruski & others 1997). The formation is inferred to haveformed in an inner to mid-shelf environment, based onsedimentary structures and dinoflagellates (Laird 1992;Schiøler & others 2002).Undifferentiated rocks of the Seymour Group (Ky) includelatest Cretaceous (Haumurian) Herring and Woolshedformations, and to the east of the London Hill Fault, theButt and Mirza formations (Suggate & others 1978; seebelow). Collectively, these rocks are time-equivalents ofthe Whangai Formation of the North Island’s East Coast(Lee & Begg 2002). In the Clarence valley-Kekerengu area,Herring Formation overlies Paton Formation with a sharpcontact. It is predominantly a light grey, sulphurous muddysiltstone interbedded with pale, well-sorted fine sandstone.The formation has a characteristic rusty brown appearancewhen weathered, due to iron staining leaching from jointplanes. Jarosite staining and pyrite nodules are common.The formation commonly contains spectacular ovoidconcretions, up to 3 m diameter (Reay 1993), and locallyabundant sandstone dikes. Microfossils indicate a mid- toouter shelf environment of deposition (Schiøler & others2002; Crampton & others 2003). The Woolshed Formation(Fig. 34a) is a local facies variant exposed north ofKekerengu and consists of muddy siltstone containingabundant concretions (Suggate & others 1978).In the Ward coastal area, east of the London Hill Fault, theupper Seymour Group includes conglomerates, slumpedhorizons and channelled sandstone bodies of the MirzaFormation (Suggate & others 1978), white micritic limestone(Flaxbourne Limestone) and turbidites deposited bysediment gravity flow processes (the Butt Formation (Fig.34b); Laird & Schiøler 2005; Hollis & others 2005b). Thestratigraphy east of the London Hill Fault more closelyresembles that of Late Cretaceous rocks of the Wairarapaarea, rather than Marlborough (Laird & Schiøler 2005).From the Clarence valley to the coast, the uppermostSeymour Group includes latest Cretaceous BranchSandstone, which overlies the Herring Formation withsharp but conformable contact. The formation consists ofmassive, well-sorted, muddy fine sandstone, typicallyabout 10 m thick, but locally up to 40 m, and is interpretedas an offshore sand bar (Reay 1993).Figure 33 The Burnt Creek Formation siltstone andsandstone in Ouse Stream are typical of the upperHapuku Group.Photo: J.S. Crampton.32South of Kaikoura, Late Cretaceous rocks equivalent inage to the Seymour Group are mapped as the lower part ofthe Eyre Group (lKe; Warren & Speden 1978; Browne &Field 1985; Andrews & others 1987; Warren 1995; Fig. 28).Undifferentiated Eyre Group (KEe) may also includeCretaceous sedimentary rock, where it is too thin to