Age of the Hawks Crag Breccia

Transactions of the Royal Society of New Zealand : Earth Sciences, Volume 7, Issue 13, 27 August 1970, Page 241

Age of the Hawks Crag Breccia

Geoffrey Norris

J. B. Waterhouse

and

Department of Geology, University of Toronto, Canada

[Received by the Editor, 1 August 1969 ]

Abstract

The age of the Hawks Crag Breccia has long been in doubt. Age determinations for this formation have ranged from Triassic to Miocene using various methods — stratigraphy, structural relationships, paleontology, palynology, and radiometry. Recent palynologic studies of the Australian Mesozoic allow a more critical evaluation of the New Zealand rocks, suggesting that the Hawks Crag Breccia was deposited in the late Albian just prior to the arrival of angiosperms in New Zealand. This age supports the Cretaceous age assigned by radiometry (Aronson, 1965) to Westland granites.

Introduction

The Hawks Crag Breccia is a formation lying west of the Southern Alps and composed of sandstones and bouldery breccia up to 2,000 ft thick. It was probably deposited by torrential streams flowing from the front of a mountain range (Haast, 1861; Morgan and Bartrum, 1915; Henderson, 1917, 1929; Gage, 1948). Uranium has been found as coffinite layers and in granite boulders (Beck, Reed, and Willett, 1958; Wodzicki,' 1959).

Because the formatiori is terrestrial it has been difficult to fit in with the remainder of the largely marine sequences of New Zealand. These marine sequences have been gradually pieced together by Marshall (1912), Thomson (1917), Cotton (1955), and Lillie (1951) into a model of two sedimentary systems separated by an unconformity. Upper Paleozic and Triassic-Jurassic (= Hokonui) sediments were grouped into one great sedimentary system, and Middle Cretaceous and Tertiary beds were grouped into a second sedimentary system called the Notocene by Thomson (1917) and Notocenozoic by Cotton (1955). The Hokonui System and older rocks were deformed by an early Cretaceous orogeny, called the postHokonui Orogeny, and renamed the Rangitata Orogeny by Kingma (1959), following Park (1921). Speculations were of course offered on the Hawks Crag Breccia, and its possible significance in the overall scheme, but these were always hampered by the rather tenuous character of the evidence on which the age and correlations were based. Lamprophyre dykes were noted by Morgan and Bartrum (1915), supposedly suggestive of a Cretaceous age; whereas the syntectonic nature of the sediment suggested an early Tertiary age to Henderson (1917; 1929) . Ongley (1939) noted lithological similarity to the Henley and Taieri breccias of east Otago, but the age of these beds was equally enigmatic. A Hokonui (PTriassic) age was preferred by Hector (in McKay, 1877, 1878) for underlying beds on the

basis of obscure plant remains, whereas the same plants were later used to support a “ Notocenozoic ” correlation by McKay (1895) and Thomson (1913: 83). Whatever its age might be, some considered that the Hawks Crag Breccia did not really matter in broad stratigraphic-tectonic syntheses of the rest of New Zealand. It was regarded as a local, restricted, largely barren unit, an exception that could be ignored in the overall pattern. The indirect evidence for age ensured uncertainty of correlation, and this in turn prevented any significant understanding of its tectonic and stratigraphic relationship to the rest of New Zealand.

Two events rendered the Hawks Crag Formation important. First was the introduction of palynology as a tool for stratigraphic correlation. The discovery of spores in the Hawks Crag Breccia provided at last the promise of keying the formation into the rest of the succession and at least resolving the vexed question of whether its age was Hokonui or Notocenozoic. Secondly the entire scheme of the Notocenozoic and the post-Hokonui orogeny came under attack from Wellman (1950), who considered that the post-Hokonui orogeny was restricted in distribution and could be identified at only a few places, including Westland, where the Hawks Crag beds represented a syntectonic deposit of Lower Cretaceous age. This orogeny was followed by further Lower Cretaceous sedimentation, to form the Taitai beds, dated as Aptian by Marwick (1939) and Waterhouse (1959; 1965), and Clarentian beds dated as Albian-Turonian by Woods (1917) and Wright (1957), followed in turn by a further less extensive but nonetheless severe orogeny of Middle Cretaceous age.

The extent to which this constituted a radical reinterpretation is demonstrated by the reaction provoked. Cotton (1951; 1955), followed by Stevens (1965), reasserted the dogma that sedimentation throughout New Zealand ceased in the Upper Jurassic and was followed by wide Lower Cretaceous orogeny, planation, and deposition of the so-called Notocenozoic, commencing in the Middle Cretaceous, with no evidence of a second tectonic spasm. The Hawks Crag Breccia was assigned to the Hokonui System and doubt was cast on the Cretaceous age of the Taitai (or supposedly Aptian) sediments (Cotton, 1951).

As summarised in the following discussion on palynology, support for Cotton’s view on a Mesozoic age for the Hawks Crag Breccia was provided by the palynological work of Gouper (1953; 1960) and Norris (1968), with a demonstration that angiosperms were absent and the age supposedly Upper Jurassic and perhaps even slightly older than Middle Jurassic (Couper, 1960). Thus although some geologists, including Wellman (1959), disagreed with this age, most authorities regarded the formation as a terrestrial equivalent of the marine Hokonui sequences, including the four-mile Geological Survey maps (Bowen, 1964; Warren, 1967). The various views were summarised by Waterhouse (1965), one of the few recent writers to agree with Wellman’s view on a Cretaceous age for the Hawks Crag Breccia.

Age of Granite Boulders

The Hawks Crag Breccia is important to New Zealand geology for two other reasons. The presence of granitic and gneissose boulders in the breccia places an upper age limit on the rocks from which they were derived. Many of the boulders appear to have been derived from the “ Charleston ” Gneiss, now called the Constant Gneiss (Bowen, 1964; Laird, 1967), dated as Precambrian by Reed (1958), Grindley (1961) and Bowen (1964) on general geological evidence. This age, and consequently the general geological understanding of Westland, was challenged by Aronson (1965), who assigned a mid-Cretaceous age on the basis of rubidiumstrontium determinations to the Constant Gneiss. The rubidium-strontium method sometimes yields over-young ages, and geologists supporting Grindley’s reconstruction of Westland history were able to underline the incongruity of finding boulders of supposedly Cretaceous gneiss in a Jurassic sediment. However, the Cretaceous

age was supported by Waterhouse (1965; 1967; 1969), who noted that some of Grindley’s (1961) geological interpretations were erratic, so-called Cambrian proving to be Permian, and Precambrian conceivably being Cretaceous. Norris (1968: 341) also took note of this possible Cretaceous age, and cautioned against too ready a scepticism of the radiometric evidence.

Age of the Lamprophyre Dykes

The Hawks Crag Breccia is intruded by lamprophyric dykes which fail to penetrate the overlying Eocene coal-measures (Morgan and Bartrum, 1915), and are represented as boulders in the lower Paparoa Group (Gage, 1952), of TuronianSenonian age according to Wellman (1959: 109). Grindley (1963: 916) elaborated a proposal by Wellman (1957) that these lamprophyric dyke swarms provided evidence of transcurrent displacement along the Alpine Fault, for they could be matched across the fault with dyke swarms 110 miles away. Since the dykes penetrate the Hawks Crag beds, they have to be younger than that formation, with an upper limit enforced by the presence of lamprophyric boulders in the Paparoa beds and absence of dykes from the Tertiary coal measures. Grindley (1963: 916) proposed that the dykes had been intruded in the mid-Cretaceous and then separated by transcurrent movement along the Alpine Fault (for 110 miles) lasting over a period from mid-Cretaceous to recent times, with some 180 miles of transcurrent movement prior to the intrusion of the Hawks Crag Breccia. By contrast, Suggate (1963) had considered that most of the 280 miles transcurrent movement occurred in the Cretaceous, with some late Cenozoic movement, and Wellman (1964) and Waterhouse (1969) favoured 280 miles of shift since the mid-Tertiary. The age of the Hawks Crag Breccia thus has some relevance to the rate of shift along the Alpine Fault, if Grindley’s premises are accepted. Young (1969: 303) has noted that possibly lamprophyric dykes intrude the Fraser Formation, and has apparently supported Suggate’s suggestion that lateral movement along the Alpine Fault and Fraser Fault ceased in the Cretaceous,

Palynologig Evidence

Spore assemblages from the Hawks Crag Breccia are rare. Gouper (1953; 1960, in Wellman, 1959; in Suggate, 1957) described the microfloral characteristics of the Hawks Crag Breccia, chiefly from Garvey Creek. Norris (1968) has supplemented Couper’s observations with descriptions of a new assemblage from the Fox River area, about 30 miles west of Garvey Creek.

The age significance of the palynologic assemblages has been equivocal, owing to their apparently endemic character. Gouper (1953) originally designated the Hawks Crag Breccia Upper Jurassic because of the lack of angiosperm pollen in the assemblages and the stratigraphic relationship of the breccia beneath the Paparoa Beds, the latter at the time being classed as Lower Cretaceous. Later the Paparoa Beds were assigned to the Senonian as a result of more detailed paleobotanical studies by McQueen (1956) and Gouper (1960). Gouper {in Suggate, 1957: 37) noted that the Hawks Crag Breccia assemblage as a whole was similar to plant microfossil assemblages from the Upper Jurassic plant-bearing beds at Waikato Heads (Purser, 1961). Gouper gave no details of the Waikato assemblages other than noting that about 8,000 palynomorphs had been examined. On the basis of this comparison he suggested that the Hawks Crag Breccia was of Late Jurassic age. Norris (1968; 340) published partial species-lists of palynomorphs from the Puaroan B and Huriwai formation of Waikato Heads, south-western Auckland. He noted that, although there were some elements in common with palynomorphs from the Hawks Crag Breccia, several species were found in strata at Waikato Heads that were unknown in the Hawks Crag Breccia. These species occur in the Upper Jurassic and Lower Cretaceous of Australia and their presence in the Waikato Heads assemblages clearly distinguishes these from the Hawks Crag assemblages.

Couper (1960: 6) has reported that a study of Middle and Upper Jurassic marine and non-marine beds at Kawhia Harbour, Waikato Heads, and “ elsewhere in New Zealand ” had been made. Couper did not publish the results of his study but stated that comparison with these Middle and Upper Jurassic samples suggested that the Hawks Crag Breccia was “ Middle Jurassic or possibly slightly older As noted by Norris (1968: 337), records’of Couper’s Jurassic study were not available in the New Zealand Geological Survey files, and hence the results could not be re-evaluated.

The Hawks Crag Breccia rests with apparent conformity on the Ohika Beds. Palynomorph assemblages recovered from the Ohika Beds differ in composition only slightly from the Garvey Creek Hawks Crag assemblage (Couper, 1953; 1960). Couper (1960) suggested that both formations were probably of the same age. More intensive work on the palynology of the Ohika Beds is required to distinguish the spore-pollen assemblages from the Hawks Crag assemblages in the light of the richer Hawks Crag assemblage obtained from Fox River (Norris, 1968). In general, however, the Ohika assemblage does not appear to contain markedly older palynomorphs than the Hawks Crag Breccia assemblages.

Revised Age of Hawks Crag Breccia

Norris (1968) has suggested that the Hawks Crag Breccia, on palynologic evidence, may be either Upper Jurassic or Albian by comparison with Australian Jurassic-Cretaceous sequences. At the time his work was completed in late 1964, Dettmann’s (1963) work on Australian Neocomian-Middle Albian palynologic assemblages had been published, but no comprehensive studies on younger Cretaceous sequences were available. A Jurassic age assignment for the Hawks Crag Breccia was questioned by Waterhouse (1965) on the basis of lithological similarity to mid-Cretaceous sediments, the complexity of the putative floral migrations that are attendant on such an age, and Aronson’s (1965) geochronology of plutonic rocks on the west coast, which suggested a mid-Cretaceous age for the granites that apparently are represented as boulders in the Hawks Crag Breccia.

Recent publications by Dettmann and Playford (1968; 1969) on the stratigraphic palynology of the Australian Cretaceous allow a critical re-evaluation of the age of the Hawks Crag Breccia. Dettmann and Playford have demonstrated the presence of eight palynologic zones in eastern Australian Cretaceous sequences based on restricted ranges of certain spore—pollen taxa. They noted that in spite of the probable time-concordance of the zones recognised, coeval spore-pollen assemblages may be different both quantitatively and qualitatively in different areas. The zones are recognised on the basis of selected spore-pollen taxa of widespread distribution throughout eastern Australia.

The Hawks Crag assemblages described by Couper (1953) and Norris (1968) do not resemble the eastern Australian Cretaceous assemblages described by Dettmann (1963) and Dettmann and Playford (1968; 1969), though this is probably due to local environmental differences. Certain species are present in the Fox River assemblages, however, which in Australia have restricted age and are of considerable biostratigraphic importance.

Kraeuselisporites majus (Cookson and Dettmann) Dettmann; This species was described by Norris (1968) from the Hawks Crag Breccia at Fox River and was noted to occur in the Albian of Australia (Dettmann, 1963). Dettmann and Playford (1969) have provided additional data on this species and noted that it ranges from Lower Albian to approximately middle Cenomanian in eastern Australia. The evidence of a single species to indicate an Albian age for the Hawks Crag Breccia was considered by Norris (1968) to be outweighed by the overall floral composition, particularly in view of the lack of tricolpate angiosperm pollen in this formation.

Kraeuselisporites laceratus Norris: The presence of this species in the Hawks Crag Breccia lends additional support to the suggestion of Albian age for this formation. When first described by Norris (1968) the species was unknown beyond New Zealand. Three months later, however, Dettmann and Playford (1968) recorded the same species from Australia as a junior synonym, Kraeuselisporites jubatus Dettmann and Playford. This species ranges from Upper Albian to Lower Coniacian in Australia. The presence of Kraeuselisporites laceratus as well as Kraeuselisporites majus in the Hawks Crag Breccia reinforces strongly its Albian age. The remaining species in the Hawks Crag Breccia assemblages do not conflict with an Albian age, but most are long-ranging Upper Jurassic-Lower Cretaceous types as discussed by Norris (1968). A re-examination of material from the Ohika Beds by Evans (in press) has indicated that Kraeuselisporites laceratus may be present. This would suggest that the Ohika Beds are not greatly older than the Hawks Crag Breccia, possibly also being of late Albian age. According to Evans’ interpretation of the morphology of Perotriletes, the species laceratus should be recombined with this genus.

None of the assemblages from the Hawks Crag Breccia or superjacent rocks contains angiosperm pollen (Norris, 1968). In Australia Kraeuselisporites laceratus appears in the higher part of its range in conjunction with tricolpate angiosperm pollen. In the lower part of its range, however, in the uppermost horizons of the Coptospora paradoxa Zone, K. laceratus appears just prior to the first appearance of angiosperms in the late Albian (Dettmann and Playford, 1968; 82). Presumably the Hawks Crag Breccia was deposited in the late Albian just prior to the arrival of angiosperms in New Zealand. Dettmann and Playford (1969) have noted that angiosperms appeared in eastern Australia in the late Albian as dated by Foraminifera. The earlier record of angiosperm pollen in New Zealand according to Couper (1960, in Wellman, 1955), is in the Upper Albian type Coverian stage which is equivalent to the younger Ngaterian stage according to Hall, 1963 (but possibly still pre-Ngaterian, as in Wellman, 1959, according to pers. comms. from Dr R. G. Henderson, Department of Geology, University of Queensland, Townsville, Australia). This record is based on the presence of a single unfigured specimen of a tricolpate grain tentatively identified as a species of Tricolpites by Couper {in Wellman, 1955: 108; in Wellmann, 1959: 147). Couper (1964) has suggested that simple tricolpate pollen evolved in the early Albian at the latest in many parts of the world. A late Albian date for the advent of tricolpate pollen, however, is suggested by recent work in Australia, North America, Europe, USSR, and equatorial Africa (Dettmann and Playford, 1969; Brenner, 1963; Norris, 1967; Groot and Groot, 1962; Zaklinskaya, 1962; Jardine and Magloire, 1965). Hedlund and Norris (1968) have recently reported a Middle Albian tricolpate angiosperm pollen assemblage from the central United States, but the Lower Albian entirely lacks tricolpate pollen in North America and elsewhere, to judge from available data. There is no evidence to suggest that tricolpate pollen evolved in the New Zealand region prior to the latest Albian or earliest Cenomanian. Consequently the absence of these morphologic types in the Hawks Crag Breccia does not conflict with a late Albian age for this formation.

Conclusions

The Albian age for the spores of the Hawks Crag Breccia changes our understanding of New Zealand geology in several ways. It suggests that the formation cannot be classed with the Hokonui System. Wellman (1950) was nearer the truth in preferring a Cretaceous age, but even he would not appear to have anticipated such a young age as is here indicated. It seems difficult to regard the formation as a syntectonic breccia contemporaneous with the Rangitata Orogeny; yet the formation appears to be older than the Upper Cretaceous orogeny also favoured by Wellman (1950: 1959). We are unable to find any convincing reflection of this

deposit in the marine sequences to the east, though it could be tentatively matched with the widespread ?Albian basal conglomerate found at the base of dark compacted mudstone with Myloceras in south-eastern Wairarapa (Waterhouse, in Wellman, 1959: 116; McLean, 1953; Waterhouse, 1954), and perhaps with the apparent hiatus between Korangan (?Aptian) and somewhat younger sediment throughout the northern Wairarapa and the Raukumara Peninsula (Wellman, 1959, Table I). This is very speculative, and the Breccia may prove to be a reflection of a severe and localised upheaval restricted to Westland. We fully agree with Wellman (1950) that the formation is of considerable tectonic significance and suggest that it will ultimately prove to be relevant to the structural evolution of New Zealand.

The mid-Cretaceous age for the Hawks Crag Breccia provides a very satisfactory independent support for the radiometric ages obtained by Aronson (1965). There is overall agreement, or at least lack of disagreement, between radiometry and spore analysis that the Constant Gneiss and Hawks Crag are Cretaceous. This conflicts with Grindley’s (1961) reconstruction of Westland geology and is in harmony with (but not proof of) the transcurrent and continental displacements suggested for New Zealand by Waterhouse (1969).

The contribution to estimating the time and rate of movement along the Alpine Fault is less significant, because Grindley (1963) had postulated a Lower Cretaceous age for the Hawks Crag Breccia, and an Albian age would simply involve a change of some 20 to 30 million years at the most. If we accept Grindley’s hypothesis, we could suggest a slightly faster rate of strike-slip movement along the fault since the intrusion of the dykes, but no fundamental change is required. Our view is that his suppositions are poorly based, and much inferior to the criteria of modern displacement rates and displacement of early Tertiary marine and coal beds and structures, which favour nearly 300 miles displacement along the Alpine Fault since the Miocene (Wellman, 1964; Waterhouse, 1969).

Future Work

The Jurassic and Cretaceous ages assigned to terrestrial deposits on palynological evidence in Couper (1953, 1960) and various four-mile map sheets appear to require considerable revision. This is related to the lack of a detailed palynological sequence for pre-Tertiary rocks in New Zealand. However, the excellent work by palynologists on Cretaceous sequences of Australia is full of promise for dating the New Zealand succession, and it should be keyed into macro-faunal examinations of the Lower and Middle Cretaceous.

Acknowledgments

We wish to thank Dr M. E. Dettmann and Dr G. Playford (University of Alberta) for giving access to their data prior to publication and for pointing out the synonymy of the species of Kraeuselisporites noted here. Mr P. R. Evans (Esso Standard Oil, Australia) has kindly summarised for us his conclusions regarding New Zealand type material, also prior to publication.

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G. Norris and J. B. Waterhouse, Department of Geology, University of Toronto, Canada.

Printed by Otago Daily Times Ltd., Dunedin, New Zealand.

and Periods Wellman, 1950, 1951, 1953, 1961 1960 Aronson, 1965 Waterhouse, 1965, 1969 Norris, 1968 This Paper Grindley, 1961 Aronson, 1965 Waterhouse, 1965, 1969 Norris, 1968 This Paper Tertiary Senonian Cretaceous Turonian Cenomanian Albian Constant Gneiss Crag ?? Hawks Aptian Neocomian Hawks Crag Hawks Crag Constant Gneiss Constant Gneiss Jurassic Crag Triassic Paleozoic Pre-cambrian Constant Gneiss

Table I.—Summary of ages assigned to Hawks Crag and Constant Gneiss by various authors.