Geology of Fox River Headwaters. Brighton Survey District, South-West Nelson.
[Read before Wellington Branch, October, 1945; received by Editor, November 13, 1945.]
A Map is presented showing the geology of the Fox River headwaters. Eleven formations are described, of which eight are marine and three terrestrial. The marine formations include Eocene. Oligocene, and Miocene beds. The oldest fossiliferous stage represented is Kaiatan and the youngest is a new stage as yet unnamed, post-Awamoan and pre-Taranakian in age. Two of the three teriestrial formations contain thick seams of coal. Near the coast this coal is sub-bituminous in rank, but in the mapped area inland it is a semi-anthracite. The anthracite outerops are described in detail, and it is shown that although some seams are thick, the beds are, on the whole, far too disturbed to permit economic mining.
Location. — The basin drained by the headwaters of the Fox River has an area of five square miles and lies entirely within Brighton Survey District, near the southern boundary of Nelson Land District. The district is uninhabited and almost all is covered with thick forest. No part is easily accessible, and the eastern part, which includes the foothills of the Paparoa Range, is much rougher and higher than the western part nearer the coast.
Topography.—The surface relief can be considered as part of five zones, each of which extends north and south beyond the mapped area: (a) a lower-limestone escarpment, (b) a mudstone-erosional depression, (c) an upper-limestone escarpment, (d) a fault-angle depression with soft sediments, (e) foothills of the Paparoa Range.
The western part is controlled by the two beds of limestone, both of which dip gently east to the fault-angle depression formed by the Lower Buller Fault. East of the fault the ground rises steeply towards the crest of the Paparoa Range, which is just outside the mapped area and over 4,000 ft in height.
Streams from the Paparoa Range flow across the fault-angle depression towards the coast, and have cut gorges through the two limestone escarpments. The lower-limestone escarpment extends nearly to the coast, and is trenched by profound gorges. The upper and more easterly band of limestone is less pure and less hard than the lower one; and, although it forms gorges, these are neither so high nor so sheer as those formed by the lower limestone. The two bands of limestone are separated by a thin band of much softer mudstone, which has been deeply eroded along a well-defined depression extending from the coast at the mouth of the Punakaiki River to the Fox River.
Access.—Access is by track only, and two routes are available. The one most commonly used is by the Fox River Track from the coast along the gorges the river has cut through the two limestone escarpments, and the other is by the Inland Track through the erosional depression between the two limestone escarpments.
The mouth of Fox River is almost midway along the 68 mile coastal road which connects the West Coast towns of Westport and Greymouth. The Fox River Track leaves the road on the south side of the river, crossing and re-crossing it several times before reaching the steep slopes of the lower-limestone gorge where the track is cut on the south side of the gorge well above river level. At the mouth of Dilemma Creek, which is only crossed with difficulty when the stream is high, the bed of the river widens and the track descends to river level following grassy flats on alternate sides of the river until the upper end of the gorge is reached. A small hut, still in fair condition, stands at the upper end of the gorge on the north bank of the river, a mile from Dilemma Creek junction and six miles from the coast. From the hut a small flat extends to the upper limestone gorge, in which the river is confined until the mouth of Henniker Creek is reached, and the valley widens for the last time at the fault-angle depression before entering the Paparoa Range.
The Inland Track leaves the coastal road at the south side of the Punakaiki River, 10 miles south of Fox River. It follows the erosional depression controlled by the soft mudstone between the two limestone escarpments and crosses the Punakaiki and Porarairi Rivers and Bullock Creek before reaching the headwaters of Fox River at the junction of Fossil and Dilemma Creeks. The track is formed and was once suitable for pack horses, but is now very overgrown. From the creek junction the track follows the bed of Dilemma Creek to the Fox River and the Fox River Track.
Outline of Geology.
The valley of Fox River has already been described by Henderson as part of the Reefton Subdivision (N.Z.G.S. Bulletin 18) and a geological map (Map of Brighton and Punakaiki S.D.'s) which covers the area described in this report published on a scale of one mile to an inch. The present re-survey was made for two purposes: to examine the anthracite deposits, and to examine the marine sequence. No important anthracite deposits were found, but the marine sequence was found to contain an unconformity and a disconformity, neither of which had previously been mapped.
The Lower Buller Fault Zone, a major fault zone mapped and described by Henderson, divides the region into two distinct topographic and geologic parts. West of the fault Tertiary beds dip east at low angles and the structure is simple; but east of the fault an irregular belt of complexly deformed coal measures and breccia lies to the west of the granite and greywacke that form the mass of the Paparoa Range, and the structure is complex. The fault zone is made up of several sub-parallel faults of at least two different
ages. The relationship between the Tertiary beds and these faults provides information which is of critical importance in the study of the Paparoa Range, and suggestive of application to other New Zealand mountain ranges.
In this report eleven stratigraphic units (formations) are distinguished; seven are marine, three terrestrial, and one the undermass. The approximate thickness and most probable age of these proposed formations is shown by the following table. No attempt has been made to find unique local formations names, but each is given a different number and distinguished by the prefix Fx from other West Coast Tertiary formation numbers (Koiterangi; Gage and Wellman, 1944. Ross; Gage, 1945. Garden Gully and Fitzgerald Creek; Gage and Wellman, 1945).
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Period||Stage||Formation.||Feet (approx)||Lithology.||Henderson 1918 (Map)|
|Miocene||Pre-Taranakian post-Awamoan||Fx 11||200||Sandy mudstone with basal conglomerate||Pareora Series|
|Hutchinsonian||Fx 10||500||Calcareous medium sandstone.|
|Oligocene||Upper Waitakian||Fx 9||500||Calcareous medium sandstone, calcareous mudstone, thin basal greensand.||Upper Oamar [ unclear: ] u Series|
|Waitakian Duntroonian||Fx 8||1000||Hard crenulate limestone.|
|Whaingaroan||Fx 7||5||Glauconitic sandy limestone.|
|Kaiatan||Fx 6||100||Hard calcareous sandstone with bands of impure limestone, micaceous sandstone and mudstone.|
|Bortonian ?||Fx 5||?||Slightly calcareous fine sandstone.|
|Quartzose Coal Measures||Fx 4||100||Leached; quartz sandstone quartz conglomerate, shale and coal seams.||Lower Oamaru Series|
|Upper Cretaceous||Arkositic Coal Measures||Fx 3||1000 ?||Unleached; sandstone, conglomerate, shale and coal seams.|
|Hawk Crag Breccia||Fx 2||2000 ?||Breccia and conglomerate.||Mawheranui Series|
|Palaeozoic||Undermass||Fx 1||Greywacke, argillite and granite.||Aorere Series and Granite|
All the beds described in the above table do not outcrop within the mapped area, but as they underlie the mapped area and have been shown in the cross-section their outcrops will be described briefly. The most complete section of the lower covering beds is provided by coastal cliffs near the mouth of Fox River. The lowest formation, Fx2, is exposed over less than a square mile at the mouth
of the Fox River; many good outcrops show red-stained breccia with angular and sub-angular fragments of granite of all sizes up to several feet in diameter. The breccia is similar to that described below from the headwaters of the Fox River, and the breccia from both areas has been correlated by Henderson (1918, p. 80) with the breccia at Hawk Crag in the Buller Gorge. This correlation is based entirely on lithology, but the lithology is so unusual and the resemblance so striking that this correlation is usually accepted (for correlation with similar beds elsewhere see Gage and Wellman, 1944, p. 355). The next overlying formation, the arkositic coal measures, is not represented at the coast, and the breccia is directly and unconformably overlain by the quartzose coal measures Fx4. The contact has recently been exposed by a scrub fire, and is now clearly visible from the Greymouth-Westport road a few chains south of the Fox River bridge. From the road the flat-dipping quartzose coal measures can be seen to rest on an almost horizontal, even surface, which cuts across the bedding of the breccia. The dip of the breccia is irregular and not well defined at most places, but at this place it appears to dip north-west at 20°. This important angular unconformity has already been discussed by Morgan (1914) and Henderson (1918, p. 83), but the actual contact between the two sets of beds has not previously been described. The marine beds which overlic the quartzose coal measures are not well exposed immediately above the unconformity, but a clear section can be built up from exposures near the coast and not far from the mouth of the Fox River. The slightly calcareous fine sandstone described later from Henniker Creek does not appear, and the quartzose coal measures are directly overlain north of the Fox River at St, Kilda by highly micaceous sandstones and mudstones, the lower part of the Fx6 formation. A micro-fauna from these beds (G.S. 3175) is described later by Dr. Finlay as lower Kaiatan. The upper part of the formation is obscured by limestone debris at St. Kilda, but is well exposed on the coast immediately east of Seal Island, and shows calcareous mudstone with scattered large concretions grading up into hard calcareous sandstone with bands of blue sandy limestone. Several micro-fossil samples were taken and are shown below to be of upper Kaiatan age. Above Fx6 comes the thin Fx7 formation, which is represented by a 5ft. band of glauconitic limestone with many macro-fossils. The age of this formation is uncertain, but is probably either Duntroonian or Whaingaroan. The main limestone, Fx8, directly overlies Fx7. This hard and unusually thick limestone, the lowest bed in the western part of the mapped area, forms conspicuous escarpments.
The marine beds within the mapped area are described in greater detail later, but it is convenient to describe each formation briefly before passing on to the detailed descriptions. Above the hard limestone comes the band of softer calcareous mudstone which forms the topographic depression. This band varies considerably in thickness, thinning to the north and disappearing before Fox River is reached. The calcareous mudstone grades upwards into a thick bed of calcareous sandstone which forms a well-marked
lithologic unit distinct from the underlying mudstone. Foraminiferal faunas studied by Dr. Finlay also showed a well-defined difference, but the faunal break occurs not at the lithologic change, but higher in the section within the sandstone, the mudstone, and the lower part of the sandstone being both of Upper Waitakian age, and the upper part of the sandstone Hutchinsonian.
It will be shown later (p. 227) that failing lithologic differences it is not inconsistent with accepted practise to use fossils to define formations, and the Upper Waitakian beds have consequently been included in one formation, Fx9; the mudstone and sandstone portions being distinguished on the map and section as Fx9a and Fx9b respectively. The Upper Hutchinsonian part of the sandstone forms the whole of the Fx10 formation.
The uppermost formation, Fx11, unconformably overlies the calcareous sandstone Fx10 and overlaps on to the arkositic coal measures. It contains a well-defined basal conglomerate and for a West Coast locality is richly fossiliferous. Both macro-fossil and micro-fossil faunas show that the formation is intermediate in age between the Awamoan and Taranakian stages and that it does not fit into the latest-published New Zealand Tertiary stage classification scheme of Finlay and Marwick (1940), but represents an unnamed stage which has become well known faunally since that time.
The relation between the proposed classification and Henderson's is given by the column on the right hand side of the table of formations, and a fuller description is given later (p. 227).
Fx 1; Greywacke and Granite. (Undermass.)
The greywacke of the Paparoa Range is one of the many New Zealand greywacke formations of unknown age. Henderson placed this greywacke together with the greywacke of the Victoria Range in the Aorere Series, and this implies a correlation with the type Aorere Series of the Collingwood district, part of which is known to contain Ordovician fossils. This correlation is uncertain, for no fossils have been found in the greywacke of the Paparoa Range. The lithology, moreover, is different, for the type Aorere Series contains beds with a large range of lithology including quartzites and marble as well as greywacke and argillite similar to that of the Paparoa Range. Neither the upper nor lower contacts of the Paparoa undermass are known, and although it must be many thousands of feet thick there are no reliable sections to give a minimum thickness. The one characteristic feature, which may have diagnostic importance, is the trend of the folds. The greywacke has been closely folded and the strike of the fold axes will not differ much from the strike of the beds. The most common strike as mapped and noted by Henderson (1918, p. 70) is north-west almost at right angles to the trend of the Paparoa Range and to the strike of the greywackes near Reefton, but parallel to the strike of the greywackes of the coastal ranges at least as far south as Ross. The greywackes at Ross form the type Greenland Series of Morgan (1908), and Morgan (1911) used the same name for similar greywacke near Greymouth at the southern end of the Paparoa Range.
There is no lithologic reason for distinguishing the undermass at the southern end of the Paparoa Range from that at Fox River, for they are both part of the same belt of rocks and have already been correlated by Henderson (1918, p. 68).
It is obviously unsatisfactory to have two series names for the same rock group, and equally unsatisfactory to have only one name for rocks which may belong to different rock units. The difference in trend of folds may or may not have age significance, but it is the only known mappable characteristic with regional significance, and the author suggests that it would be convenient, until better evidence is forthcoming, to use the name Greenland Series for the north-west striking coastal greywackes and to find a new name for the north to north-north-cast striking greywackes near Reefton to distinguish them from the type Aorere Series.
Fx2 and Fx3: Basal Breccia and Arkositic Coal Measures.
Distribution and Coal Occurrences.—The belt of coal measures and breccia near the Lower Buller Fault are so severely crushed and so complexly folded that it is not convenient to describe the distribution of the two formations separately. The outcrops are described in order from south to north, starting at the head of Fossil Creek and ending at Fox River. In Fossil Creek coal-measures detritus is not uncommon; but the only coal-measure outcrop seen was on the south side of the creek, in fault contact with calcareous sandstone. Crushed breccia forms a conspicuous bluff on the opposite bank a few chains upstream. Still farther upstream coal-measure detritus becomes rare and none was seen above the junction of a large north-east-flowing tributary. No detrital coal was seen. On the ridge between Fossil and Dilemma Creeks coal measures were seen in place only at the head of a small stream which flows north to Dilemma Creek. No coal seams were observed and detrital coal is rare. In the lower part of this stream outerops of breccia are not uncommon, and ten chains from its junction with Dilemma Creek a fault contact between the breccia and Fx10 calcareous sandstone is clearly exposed. The throw of this fault is probably large, perhaps exceeding 1,000 ft., and although the calcareous mudstone is not crushed and the fault plane well defined, the breccia is so pulverized that its constituent fragments are unrecognisable and undistinguishable from crushed granite. The fault plane dips east at 60° and is almost parallel to bands of coarse sand and angular fragments of granite, marking the bedding of the calcareous sandstone. A few chains north in Dilemma Creek the whole width of the fault zone is occupied by Recent gravels and neither coal measures nor breccia outcrops.
The next outcrops seen, arkositic sandstone and grit with irregular films of coal, are about halfway between Dilemma and Henniker Creeks near the head of a small stream that flows west to Dilemma Creek. The beds dip west at 20°, and are not crushed, but five chains downstream a vertical outcrop indicates considerable deformation. The next two outcrops in Henniker Creek are small and show no solid coal, but both are structurally important. The most westerly is on the south side of the stream 60 chains above its junc-
tion with Fox River; horizontal sandy mudstone unconformably overlies tilted coal measures which dip north-west at 20°. The other outcrop is on the opposite side of the stream 15 chains farther upstream, where severely crushed coal measures are involved in a major fault. No well-defined seam was observed, but fragments of fault-involved coal are not uncommon (A5 in table of analyses). The significance of these two outcrops in the interpretation of the structure is discussed later and shown by the cross-section.
North of Henniker Creek the belt of coal measures widens, and detrital coal becomes common and more widespread. Bacon Creek is the name given to a small stream that enters Henniker Creek 40 chains above the Henniker Creek-Fox River junction. In this creek fragments of coal are common and are derived from two seams exposed on the eastern side of the major fault mentioned above and half a mile from the mouth of the creek. Downstream from the fault Bacon Creek flows through a narrow gorge formed by 200ft. cliffs of sandy mudstone, but upstream from the fault the mudstone is replaced by crushed coal measures and the cliffs are abruptly replaced by gentle slopes. A coal seam five chains from the fault is crushed and not well exposed, but may be as much as 10 ft. thick. A less crushed seam five chains farther upstream was sampled (A4 in table of analyses) and traced for two chains across a low spur near the head of the creek.
At Fox River, 30 chains north, the two rock types are still clearly distinguishable by their characteristic topography, the position of the fault-contact between the coal measures and the sandy mudstone being marked by the termination of the steep cliffs and the beginning of the even slopes. Detrital coal is again common east of the fault, but only two thick seams were observed, both on the south side of the river. The more westerly, 25 chains east of the fault, dips east at 20° and forms part of the following section exposed in a bluff at near river level five chain from the present river bank.
|Granite sandstone and granite conglomerate||100|
|Dirty crushed coal (A3 in table of analyses)||6|
|Carbonaceous micaceous sandstone||20|
The other seam, 15 chains upstream from the one just described, has recently been exposed by a slip. The seam is vertical and is probably the 26ft. seam mentioned by Henderson (1918, p. 204). The slip shows:—
|Hard quartz sandstone and conglomerate||10|
|Coal with occasional pebbles (A1 in table of analyses)||22|
|Not exposed, may be coal||10|
|Quartz-mica sandstone with coal lenses and bands of conglomerate||14|
Breccia is exposed at a few places between the 22 ft. seam and the first granite outcrop 10 chains farther upstream. The breccia contains angular and sub-angular fragments of granite with a large range in size, fragments of pegmatite with inch flakes of mica being
conspicuous. It is more indurated than the breccia at the mouth of the Fox River, but shows no other significant difference.
The area between Fox River and Four Mile Stream, two miles north, was not examined, but the presence of much detrital coal in a small stream that drains the area, and enters Fox River 25 chains below the junction of Henniker Creek, makes it probable that further coal outcrops will be found in this direction.
Content and Relation to Underlying Reds.—The coal measures contain no quartzose beds and consist entirely of arkositic sediments which range in grade from shale to coarse sandstone and conglomerate. Breccia grades up into rounded granite conglomerate, and the conglomerate into coal-measure sandstone, both at Fox River and six miles south, outside the mapped area, at Bovis Creek. Both breccia and coal measures are composed of granite-derived material with an admixture of hornfelsie greywacke, and both probably were derived from the same source. Although the contact was not seen, it is almost certain that the breccia rests directly and unconformably on the underrmass.
Age and Correlation of the Coal Measures.—The Paparoa coal measures of the Greymouth district (30 miles south) are stated by Morgan (1911, p. 56) to grade up from a basal conglomerate known to be similar to that of the Fox River district. The Paparoa beds contain many seams of coal; all have a sulphur content of less than one per cent. Above the Paparoa beds, and perhaps resting on them unconformably, are the quartzose Brunner beds with medium-to-high-sulphur coal. The Brunner beds grade up into the marine Island Sandstone (Bortonian) and the Kaiata Mudstone (Kaiatan).
There is no evidence against correlating with the Paparoa beds the low-sulphur arkositic coal measures, and breccia of the Upper Fox River; and with Brunner beds the high-sulphur quartzose coal measures near the coast, which unconformably overly the basal breccia and grade up into marine beds of Kaiatan age. The above correlation is indirect, but no better attempt can be made until the coal-measure leaf impressions have been reliably described.
Appearance of Coal.—The thick high-rank 22 ft. seam has attracted the greatest attention. The coal, only slightly dirty to the touch, is bright and has a sub-metallic lustre. According to the American Society for Testing Materials proposed classification of coal by rank (1938, Supplement to book of A.S.T.M. Standards) this coal, having more than 86 and less than 92 per cent, fixed carbon on a dry ash-free basis, is placed in the semi-anthracite group of the anthracite class of coal. The high rank of this coal is of some interest, for with the exception of the Canterbury anthracites, which are lignites locally changed by igneous intrusions (Evans, 1899), no other thick seams of anthracite are known in New Zealand.
Although the coal is classified as a semi-anthracite, it shows in hand specimens a greater resemblance to the low volatile bituminous coals produced from the Paparoa Mine than it does to true anthracites, being soft and friable and intersected by numerous shear planes, and not hard like a full anthracite.
It might be thought that these numerous shear planes are solely a result of the intensity of deformation suffered by the coal measures, but this is probably not the case, for Campbell (1930, p. 694) when discussing the stages in the progressive metamorphism of coal has shown that in the United States bituminous coal becomes progressively more cleaved and friable as the volatile content is reduced and reaches maximum friability or “softness” at low-volatile bituminous or semi-anthracite rank; with increasing metamorphism the individual fragments become re-cemented to form typical hard anthracite. It would appear likely that the friability of the Fox River coal is as much due to its rank as to its extreme deformation; for it is probable that the generalizations made by Campbell—which are irrespective of special deformation—will apply also to New Zealand. Consequently any other high-rank seams found, even if less deformed, will also be friable.
Analyses and Rank of Coal.—In spite of the soft nature of the coal and its inaccessability its obvious high rank has attracted several prospectors and many ill located samples have been analysed. Several of these analyses have been assembled by Henderson (1918, p. 204). It will be shown later, however, that the rank of the coal changes so rapidly in a direction normal to the Lower Buller Fault Zone that individual analyses are of little value unless the precise locality from which the samples were obtained is known, consequently the only anaysis reproduced in the table below is the one which was collected from a known locality by Henderson himself. This analysis is of some importance, for it shows (in agreement with the other analyses quoted by Henderson) that the sulphur content is low and considerably less than one per cent. The sulphur content of coals from different New Zealand formations show large and consistent differences and the low-sulphur content of this coal has already been referred to when discussing the correlation of the coal measures.
With the exception of A2 quoted from Henderson (1918, p. 204) to give the sulphur content, all of the following analyses have been made by Mr. Doherty of the State Mines Department, Rewanui, and are published here by the courtesy of that department. The origin, of the samples is marked on the plan with the analysis numbers given in the table below.
|Al. Fox River, 22–30 ft||9.4||1.3||9.2||87.0||2.5|
|A2. Fox River, 0–3 ft.||6.8||0.7||12.1||82.1||5.1||0.07|
|A3. Fox River, 6ft.||4.5||1.0||17.5||79.5||2.0|
|A4. Bacon Creek, 2.5 ft||3.0||1.0||19.0||57.0||23.0|
|A5. Henniker Creek, loose||2.7||0.8||22.2||60.8||16.2|
|A6. Bovis Creek, loose||1.1||7.0||37.5||41.5||14.0|
A1. Picked lump of hard coal from 22 ft. seam, upper Fox River.
A2. Sample near large seam (Henderson, p. 204, No. 7).
A3. From 6ft. seam, 25 chains east of fault (picked sample).
A4. Seam at Bacon Creek.
A5. Fault-involved coal, Henniker Creek.
A6. Loose coal, Bovis Creek.
The wide variation in the value of the fuel ratios (ratio of fixed carbon to volatile matter) indicates that coals of very different ranks occur within the limited area of the upper Fox River Basin. The analyses when plotted on a map show a rapid but regular decrease
in rank from east to west, the most easterly samples from the Fox River being a semi-anthracite, and the most westerly sample from Bovis Creek being a non-coking sub-bituminous coal, the intermediate samples being coking bituminous coals. No direct reason for this unusually rapid change in rank is apparent, but many of the explanations invoked elsewhere (for example, age, permeability of enclosing rock, contact metamorphism, or original composition) can be shown to be non-effective here. Difference of age is often given as a cause, but it is highly improbable that the Bovis Creek coal measures can differ appreciably in age from those at Fox River for both grade up from the basal breccia and neither can be as young as the quartzose coal measures at the coast (Fx 4).
The well defined differences in the degree of induration of the coal measures no doubt cause corresponding differences in permeability. But these differences are the opposite of those needed to explain the differences in rank, for the high-rank low-volatile anthracite is associated with the more indurated coal measures, and the low-rank high-volatile coal with the less indurated. An early view of Campbell's (1905) was that joints significantly increase the permeability, permit the escape of volatile matter, and increase the rank of coal; but no direct relation between coal rank and jointing can be shown at Fox River. In any case, a general and uniform increase in the rank of coal with depth is usually admitted (Hilt's Law) and, in general, increase in rank means decrease in volatile, matter, but this is directly opposed to the supposed effect of permeability, for the deeper the coal the more difficult will it be for the volatile products to escape. If permeability be important, we should expect the volatile matter to increase with depth, and yet no such regular increase of volatile matter with depth has been reported from any bituminous coalfield, and neither permeability nor jointing can be accepted as a cause of increase in coal rank. The most probable explanation of the increase of induration and jointing with rise of rank is that all three variables—induration, jointing, and rank—are the result of increasing metamorphism; jointing thus having indirect but no direct connection with the amount of volatile matter in the coal.
Anthracite in Canterbury has been convincingly explained as lignite altered by intrusion of igneous rock. (Evans, 1899.) The thermal effect of these intrusions is always local and often irregular and some part of the intrusive rock is usually found without difficulty. But deep erosion has exposed no such intrusive rock in the Fox River area, and, indeed, the regular way in which rank changes show that we have to deal with regional rather than contact metamorphism.
Differences in the coal-forming vegetation have also been suggested as the cause of variations in rank, but it is unlikely that anthracite was deposited as such. Also, if the original material is important, why should variation be regional and irrespective of seam?
Although most of the coal measures in the upper Fox River Valley have been extremely crushed and deformed, a few small blocks have escaped, but the distribution of these uncrushed blocks is irregular and certainly shows no obvious relation to the change in rank. The table of analyses makes this clear, for pulverized coal from the
fault at Henniker Creek (A5) is of lower rank than the relatively undisturbed seam at Fox River (A3). Local influences will not suffice and the explanation must lie in some form of regional metamorphism, either that due to horizontal pressure as suggested by David White (1925) or that due to the loading effect of super-adjacent sediments as recently restated by Heck (1943). It is impossible to test these rival theories in the Fox River district, for the overlying beds have been either stripped off or deeply buried so as to be non-measurable, but it is known that the thickness of the covering strata must have been considerable.
The coal-measure outcrops described are usually both complexly folded and extremely crushed, and Henderson (1918, p. 205) states that “the strata are so shattered that there is no likelihood of commercially valuable seams ever being found in them.” Several thousand tons of anthracite could be won from the thick vertical seam at Fox River, but the cost of providing access would be prohibitive. All the outcrops are near the fault zone, and it is very probable that deformation will decrease rapidly westward, and it is perhaps significant that the outcrop in Henniker Creek dips only at 20° and is less crushed than the others nearer the fault zone. The analyses show that the rank of coal decreases rapidly westward and it is almost certain that if the coal seams extend west below the upper Tertiary beds, as is not unlikely, the rank of the coal will be sub-bituminous, probably slightly higher in rank than that at the coast.
Fx 4, Fx 5, Fx 6, Fx 7, and Fx 8 Formations.
Distribution.—The limestone is separated from the Fx 3 coal measures and the Fx 2 breccia by several hundred feet of beds included in the Fx 4, Fx 6, and Fx 7 formations which outcrop near the coast and have already been briefly described. The Fx 5 formation is exposed only at Henniker Creek, and a brief description is given on p. 224.
The limestone (Fx 8) covers only a small part of the north-west corner of the mapped area in the middle reaches of Fox River and in the lower part of Dilemma Creek, but it extends beyond without major interruption as a prominent escarpment, south to Cave Point and north, less continuously, for 20 miles to Cape Foulwind.
Content.—The limestone is hard, white to pink in colour, and of general high grade except for bands with granules of quartz. Bedding is usually well marked by crenulate layers, and current bedding is not uncommon. Macro-fossils are rare and poorly preserved, and no bands seen were soft enough for foraminiferal samples.
Age and Correlation.—As no fossils have been obtained from the limestone, its age is uncertain, but as it is overlain by Fx 9 mudstone of upper Waitakian age and underlain by Fx 7 calcareous sandstone of either Duntroonian or Whaingaroan age, it is probably either Duntroonian or Waitakian, and consequently of about the same age as the upper part of the Cobden Limestone. (Finlay and Marwick. 1940. p. 112).
Fx 9A. Calcareous Mudstone.
Distribution.—In the area under consideration, the mudstone is thin and of limited extent, but it thickens southward, reaching the
coast immediately north of Punakaiki River. The lower part is exposed near the month of Fossil Creek, the middle part in Fossil Creek between the two crossings of the Inland Track, and the upper part in the south bank of Dilemma Creek 20 chains above the month of Fossil Creek. North of Fox River it is absent and Fx 9B calcareous sandstone rests directly on limestone.
Content.—The lower part is massive, light blue-grey, very calcareous mudstone. At the coast the lower foot or so is glauconitic and rests on an eroded limestone surface. The upper part contains harder 2–6 in. bands of calcareous sandstone which increase in thickness to form the massive calcareous sandstone that overlies.
Age and Correlation.—No macro-fossils were seen, but a foraminiferal sample from the middle of the formation taken from Fossil Creek (F.6380) is considered by Dr. Finlay to be upper Waitakian in age.
Fx 9B and Fx 10 Calcareous Sandstone.
Distribution.—Calcareous sandstone is the most widespread formation in the valley of the upper Fox River and its tributaries. It is particularly well exposed in Welsh Creek, north of Fox River, where it forms low cliffs on both sides of the stream. These cliffs are steep, but not vertical, and have weathered into smooth rounded curves, broken by infrequent bedding planes. Similar cliffs flank the Fox River from a few chains above the hut to near the junction of Henniker Creek. It is also well exposed for half a mile as cliffs in Dilemma Creek, where there is little change in lithology until the steep-dipping upper and coarser part is reached. In Fossil Creek, the next creek to the south, outcrops are less continuous and recent gravels obscure the middle of the formation.
Content.—The bulk of the formation is very calcareous medium sandstone, with occasional bands of sandy limestone, some of which contain calcareous nodules and scattered brachiopods. The uppermost beds,* exposed in Dilemma and Fossil Creeks, are coarser and consist of 6 in. bands of hard, micaceous, gritty sandstone alternating with soft micaceous sandstone in which quarter-inch angular fragments of granite and hornfels are not uncommon. The coarse facies does not show north of Dilemma Creek, and Fx 11 sandy mudstone rests unconformably on calcareous sandstone similar to the bulk of the formation.
Relation to Underlying Beds.—North of Fox River calcareous sandstone rests disconformably on limestone, but south-west it rests on and grades into an increasing thickness of Fx 9 mudstone. The disconformable contact with the limestone is well shown in Welsh Creek north of the Fox River hut, and is emphasized by pronounced differential weathering, the rounded outlines of the calcareous sandstone contrasting with the angular flutings cut in the harder but more soluble limestone. The contact zone is softer than either formation and has weathered back several feet from the face of the cliff. There is
[Footnote] * The only sample collected from the coarse beds contained a Kaiatan fauna, but owing to the possibility of error in labelling, it was considered better to leave the beds, as originally mapped, and await the collection of further samples.
no measurable angular unconformity although the contact is exposed for several chains, but glauconite becomes increasingly common towards the base of the calcareous sandstone, and glauconite fills borings which penetrate several inches into the underlying limestone.
Age and Correlation.—Only a few poorly preserved brachiopods were found, but several foraminiferal samples were taken. The lowest stratigraphically is F.6380A from the glauconitic base of the formation at Welsh Creek. Also from Welsh Creek, and 50 ft. higher, is F.6381. Two samples from near the top of the formation were taken from the east bank of Fox River. F.6382, the stratigraphically lower sample, is from 10 chains, below the mouth of Henniker Creek and F.6383, the upper, is only 3 ft. below the unconformable contact of the overlying sandy mudstone and from 20 chains above the month of Henniker Creek. It has already been explained that these samples fall into two groups, the two lower, from Welsh Creek, being of upper Waitakian age–the same age as the underlying calcareous mudstone—and the two upper, from Fox River, being of Hutchinsonian age. It is unfortunate that as no samples were taken from the middle of the calcareous sandstone it is not known if the contact between the upper Waitakian and Hutchinsonian parts is a sharp break or a gradation. The position of the contact is shown only approximately on the map.
Fx 11. Sandy Mudstone.
Distribution.—The sandy mudstone, the uppermost and most easterly marine bed, is separated from coal measures and basal breccia to the east by a major fault, and unconformably overlies Fx 10 calcareous sandstone or, more rarely, Fx 3 coal measures. The most southerly occurrence known is a small faulted outlier on the ridge between Dilemma Creek and a small northern tributary of that creek. To the north it occupies the fault-angle depression as a gradually widening sheet, the full extent of which is not known.
Content.—The bluffs at Fox River, Henniker Creek, and Bacon Creek present many good sections of massive, moderately soft, sandy mudstone, with calcareous concretions aligned along bedding planes. The base of the formation is marked by a 1–10 ft. conglomerate band composed of scattered pebbles, up to 3 in. across, of greywacke, granite, calcareous sandstone, and coal measures. Coal pebbles are not uncommon; they range up to an inch, but are usually no more than an eighth of an inch across. Analyses of two pebbles from the south of Fox River are given below together with the analysis of a coal pebble collected by Henderson (1918, p. 91) from somewhat older beds on the Inland Track north of the Punakaiki River.
|A7. Fox River (pebble)||5.8||43.0||47.7||3.5|
|A8. Fox River (pebble)||17.0||39.5||37.2||0.3|
|A0. North of Punakaiki R. (pebble)||9.2||35.2||45.4||10.2||0.71|
|A7 and 8. Coal pebbles from near the base of sandy mudstone, Fox River.|
|A9. Coal pebbles from calcareous sandstone, north of Punakaiki River. (Henderson, 1918, p. 91.)|
The two coal pebbles from the Fox River differ somewhat in rank and type, but both are of considerably lower rank than the nearest coal seams now exposed. The Punakaiki coal pebble is intermediate in composition to the Fox River ones. A discussion on the origin of
these coal pebbles is perhaps best postponed until further pebbles are collected and their rank and sulphur content determined. It is worth mentioning, however, that the complete absence of semi-anthracite can be in part explained by its extreme friability. The difference in friability between the semi-anthracite and the coal pebbles is well shown by their difference in resistance to erosion. Semi-anthracite is rapidly pulverized by stream gravels, whereas the coal pebbles, although they form but a small proportion of the rock, tend to weather out and accumulate in stream eddies.
Relation to Underlying and Overlying Beds.—The unconformable contact between Fx 11 sandy mudstone and underlying beds warrants detailed description, for an important orogenic movement disturbed older beds before the sandy mudstone was deposited. The unconformity is best shown at Henniker Creek. As the almost horizontal base of the mudstone is traced upstream from the junction of this creek with Fox River it can be seen to rest indifferently on Fx 10 calcareous sandstone, Fx 3 coal measures, and a rock, Fx 5, which has been tentatively correlated with the Bortonian Island Sandstone of Grey-mouth. Near Fox River, the contact with calcareous sandstone is clearly exposed in continuous outcrops near the base of bluffs; a sharp break separates the conglomerate at the base of the sandy mudstone from the eroded top of the calcareous sandstone. There is no angular discordance. On the east bank, near the mouth of Bacon Creek, the basal conglomerate contains many 3 in. pebbles of calcareous sandstone. On the same side of the river and 20 chains farther upstream Fx 11 sandy mudstone and Fx 10 calcareous sandstone both show in a long outcrop a few feet above river level. At the southern end, fossiliferous muddy conglomerate, the basal part of the sandy mudstone, rests with no angular discordance on calcareous sandstone in the same way as at the outcrop farther downstream, but when traced north pebbles and fragments of coal measures become increasingly common and finally make up the whole of the lower part of the outcrop. There is no evidence for a fault and the fragments are so similar that they were almost certainly derived from the same coal measures. On the south side of the river three chains farther upstream a 50 ft. bluff is being undermined by the river. The upper part is sandy mudstone grading down to the usual muddy conglomerate at the contact; but the calcareous sandstone is absent and the conglomerate rests, without sign of faulting, on coal measures which dip downstream at 20°. Ten chains farther upstream, but on the north side of the river, a small rill flowing from the north has initiated a slip in crushed rock, and a large area has been stripped of soil and vegetation. The lower part is extremely jointed, hard, slightly calcareous, light-bluegrey fine sandstone different from either the coal measures or the Fx 9 sandstone but similar to the Island Sandstone of Greymouth. About 50 ft. above river level this sandstone is unconformably overlain by the sandy-mudstone conglomerate which dips east at 10°. A few feet east the sandy mudstone is in fault contac with coal measures, the fault plane being a well-exposed smooth surface dipping east at 30°. An analysis of coal from this fault is given as A5 in the table of analyses.
The marine beds that once overlay the sandy mudstone have been eroded from the Fox River area, and the mudstone is now directly overlain by thin Recent or Pleistocene stream gravels. It is probable,
however, that the overlying marine beds will be preserved in the fault-angle depression to the north, where no recent geological examination has been made.
Age and Correlation.—The whole of the formation is fossiliferous, and several collections were made. The best fossil locality, and one of the best on the West Coast, is the bluffs on the north side of the Fox River from 5 to 15 chains above the junction of Henniker Creek (G.S.3485). Collections were also made from bluffs on the opposite side of the river, both from the upper part of the formation (G.S.3182) and from the base of the formation (G.S.3181). South of Fox River a collection was made from concretions and boulders in Bacon Creek 60 chains above Fox River (G.S.3486).
These macro-fossils were examined by Dr. Marwick and his description is given below.
Mollusca from Fx 11 Formation, Upper Fox River District.
|Neilo cf. australis (Q. & G.)||X||X|
|Veletuceta cf; trelissickensis (Marw.)||X|
|Manaia cf. hurupiensis (Marw.)||X||X|
|Anomia trigonopsis Hutt.||X|
|Lima cf. waipip [ unclear: ] ensis March. and Murd.||X|
|Venericardia aff. subintermedia Suter||X||?|
|Divaricella notocenica King||X|
|Maorimactra cf. chrydaea (Suter)||X|
|Angulus aff. edgari (Iredaie)||X|
|Dosinia aff. lambata (Gould)||X|
|" " (Raina) cf. cottoni Marw.||X||X||?|
|" " (Kereia) cf. chathamensis Marw.||X|
|Atamarcia thomsoni Marw.||X||X||X|
|Gari cf. stangeri (Gray)||X||X|
|Panopea cf. w [ unclear: ] thingtoni Hutt.||X|
|Zegalerus cf. crater Fin.||X|
|Maoricrypta wilckensi Fin.||X|
|Polinices huttoni Ther.||X||X|
|Polinella scalpta (Marw.)||X||X|
|Nassicola aff. speighti Marw.||X|
|Zelandiella cf. calcarata Marw.||X|
|Xymene aff. dre [ unclear: ] i (Hutt.)||X|
|" " aff. robusta Marw.||X|
|" " aff. reflexa Marw.||X|
|Raryspira cf. hebera (Hutt.)||X||X|
|" " cf. novaezelandiae (Sowby.)||X|
|Olivella neozelanica Hutt.||X||X|
|Austrotoma minor (Fin.)||X||X|
|Neoguraleus aff. subobsoletus Pow.||X|
|Zeacuminia aff. pareoraensis (Suter)||X|
|Dentalium n.sp. A||X||X|
|" " B||X|
G.S.3181. Brighton Surv, Dist. South side Fox River at 220° from Trig. Fr, 15 ft. above pebble band and unconformity. H. W. Wellman coll.
G.S.3182. Brighton Surv. Dist. South side Fox River, 30 chains at 180° from Trig. Fr. H. W. Wellman coll.
G.S.3485. Brighton Surv. Dist. North bank Fox River, 17 chains above Henniken Creek junction. H. W. Wellman coll.
G.S.3486. Brighton Surv. Dist. Bacon Creek, 45 chains above junction with Fox River. H. W. Wellman coll.
These four faunules can be regarded as one fauna, the age of which is, fairly obviously, Upper Miocene. This is shown by many lines of evidence, of which it is sufficient to cite the combination of Cucullaea, Olivella and Polinices huttoni. To make a precise correlation on the New Zealand age scale, however, is not so easy. Affinities of most of the significant forms are closer to the Tongaporutuan and Urenuian than to the Awamoan, for example, Cucullaea n.sp., Manaia hurupiensis, Dosinia cottoni, Atamarcia thomsoni, Zeacolpus n.sp., Sigapatella n.sp., Austrosipho n.sp., Zelandiella calcarata, and Dentalium n.sp. A. Most of the Awamoan affinities are not exclusively Awamoan, but are presented by long-ranging pelecypods, e.g., Limopsis, Zenatia, Anomia, Divaricella, Notocorbula, Panope.
On the present stratigraphic scale, correlation would have to be with the Taranakian, for there is no special resemblance to Tongaporutuan rather than to Urenuian. But there is a lack of definite Taranakian specific identities and a presence of elements suggesting a pre-Taranakian, post-Awamoan age. For instance, the Manoia differs from the Taranakian rapanuiensis, is closer to hurupiensis, which may be pre-Taranakian, and agrees with an unnamed species from East Grey shell-bed. Bartrumia is not known as high as Taranakian. Atamarcia thomsoni and the Zeacolpus n.sp. occur at Hurupi Creek, Palliser Bay. The only other Lyria known in New Zealand is from Clifden band 6C.
Owing to the noticeable break in evolution of common molluscan lineages, it has long been felt that the Taranakian does not follow directly upon the Awamoan (Fin. and Marw., 1940, p. 122), but that a considerable period of time intervened. The significance of this period is now becoming more apparent from Dr. Finlay's foraminiferal studies, and it will be found, below, that the foraminiferal evidence in regard to these beds is more definite than the molluscan.
In his map Henderson divided the beds into five Tertiary groups:
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Lower Pliocene and Upper Miocene||Pareora Series||(5)||Marine sandstone and claystone. often calcareous.|
|(4)||Limestone and calcareous grit, sandstone, and claystone|
|Miocene||Oamaru Series||(3)||Marine sandstone and claystone and littoral conglomerate, grit, sandstone, and shale with coal seams.|
|(2)||Conglomerate, grit, sandstone, and shale with coal seams.|
|Eocene||Mawheranui Series||(1)||Breccia and breccia conglomerate.|
It would have been convenient to have adopted Henderson's series names and to have used them as a basis for the proposed classification, but there are two reasons against this. The first is that the series names he used are taken from a New Zealand Tertiary stage classification which has long been superseded, and the second is that his series are not well enough defined, by type locality or otherwise, to permit closer subdivision. Consequently a new classification scheme is needed. It would be possible to classify the marine strata according to the stage classification proposed by Finlay and Marwick (1940) and now generally accepted. But such a simple scheme in which the same name is applied to both the time units and stratigraphic units is not fully satisfactory, for if the stage classification scheme prove inadequate in the future, and were to be superseded by an even more detailed one, as is not unlikely, corresponding changes would be required in the names of the marine strata, and the scheme would then lay itself open to the same criticism as is now directed at Henderson's.
The only satisfactory procedure is first to divide the strata into formations according to lithology and fossil content; then to name and define each formation according to its distribution and outcrop; and only then to correlate these formations (stratigraphic units) with the corresponding time units (Tertiary stages). In this way the stratigraphic units will be defined and named independently of the Tertiary stage classification and will not be affected by possible future changes in the time-unit classification. The relative consideration to be given to the fossils and to the lithology in defining the stratigraphic units has now to be considered. No problem arises when the lithologic breaks coincide with the faunal breaks, or when then are several lithologic units within a faunal unit, for then field mapping alone will suffice to define the boundaries of the stratigraphic units. When, however, an apparently uniform lithologic unit can only be subdivided after the field samples have been examined in the laboratory, there is a tendency to consider that such examinations only define the age of the rocks and should be neglected in the mapping and naming of the stratigraphic units (but not, of course, in the time correlation). A different attitude is adopted towards easily identified macro-fossils, for example Maitaia is usually accepted as a criterion for the Maitai Series, and the presence of ammonites or belemnites would be considered good reason for separating the bed which contained them from overlying beds with similar lithology and Tertiary fossils. The author can see no reason for adopting a different attitude for the less conspicuous micro-fossils. The stages are generalizations made from the fossil evidence and are subject to progressive modification as stratigraphic and fossil evidence accumulates, but the occurrence or non-occurrence of fossils within the strata will not change and is part of the same order of basic facts as is the lithology.
In the proposed classification the strata have been divided as closely as possible, subject, however, to the stratigraphic units having more than local significance.
The relation between the proposed classification and Henderson's is shown by the column on the right hand side of the table. The boundaries of Henderson's marine series are not clearly defined in his text,
but it is possible to deduce from his map that the Pareora Series includes the beds now included in Fx 11 and Fx 10 formations; the upper Oamaru Series the Fx 9, Fx 8, and Fx 7 formations; and the lower Oamaru the Fx 6, Fx 5, and Fx 4 formations. With regard to regional West Coast correlation it should be mentioned that Henderson (p. 83) has correlated his upper Oamaru Series, which includes most of the predominantly calcareous beds, with the Cobden limestone (Morgan, 1911, p. 62), and his Pareora Series, which includes the overlying marine beds, with the Blue Bottom (Bell, 1906, p. 85, and Morgan, 1911, p. 62). Later palaeontological studies have shown that this correlation is substantially correct, but unconformities and erosion intervals make detailed correlation more complex than was envisaged by the earlier geologists.
It will be noticed that the Pareora and upper Oamaru Series as used by Henderson both include beds separated by noticeable breaks, the Pareora Series being interrupted by the angular unconformity at the base of the Fx 11 sandy mudstone and the upper Miocene series by the disconformity at the base of the Fx 9 formation. Henderson did not recognise these breaks at the headwaters of the Fox River, but found evidence for “marked discordance between the Blue Bottom and earlier Miocene beds” (Henderson, 1918, p. 90) at two places in the inland part of the Reefton Subdivision. Also on the same page, he remarked that “the passage from the Cobden limestone to the Blue Bottom is, in one locality (near the mouth of the Punakaiki), abrupt and marked by the occurrence of water-worm pieces of coal.” It is now known that the beds containing the coal fragments partly fill the time interval represented by the unconformity at the base of the Fx 11 sandy mudstone, and the erosion and deposition of that coal must be one of the minor results of the deformation which is represented by the angular unconformity at Fox River headwaters already discussed.
Fig. 1—Cross-section along line A–B, Plate 24.
Structure and Geological History.
The area mapped is too small to warrant a complete geological history, and the following description will be confined to a discussion of those events which are particularly well recorded within the area. These events are closely related to the interpretation given to the
structure near the Lower Buller Fault Zone. This structure is illustrated by a cross-section (Fig. 1) taken through the valleys of Fox River and Henniker Creek in a south-easterly direction almost at right angles to the fault.
The lower marine beds, which outcrop only at the coast, have been shown for completeness. The eastward thickening of the Fx 6 mudstone (Kaiata Mudstone) is hypothetical, but in accordance with the increase in thickness which is known to take place on the same, side of the Paparoa Range both to the north and south at Westport and Greymouth, the correctness or incorrectness of this assumption in no way affects the conclusions to be drawn from the evidence provided by the upper beds. The eastern end of the section is complex and several interpretations of the outcrops are possible. The cross-section is probably the simplest explanation of the facts known at present, but further exploration would probably make a still more complex picture necessary.
Two faults are shown, one older than, and one younger than the Fx 10 sandy-mudstone. There is no doubt about the position and the dip of the younger fault, for the fault plane is clearly exposed in the slip at Henniker Creek, and the fault shown to be a low-angle reverse fault. The older fault is not exposed in Henniker Creek, but the evidence for it, although indirect, is good and is based on the appearance of low-dipping coal measures only 10 chains from horizontal Fx 10 sandstone at least 1,000 ft. higher stratigraphically. The fault probably extends south to beyond Fossil Creek as the major fault which separates coal measures from calcareous sandstone, and the dip of the fault on the cross-section has been assumed to be the same as that observed just south of Dilemma Creek. Having two faults, one older and one younger than the Fx 11 mudstone, it is certain that we also have two periods of deformation, one older and one younger than the mudstone. Little more can be said of the age of the younger period of deformation, for the only unfaulted beds in the vicinity are high-level gravels, either Pleistocene or Recent in age.
It is certain, however, that the older fault must have been active during the interval of time between the deposition of the Hutchinsonian Fx 10 sandstone and the pre-Taranakian but post-Awamoan Fx 11 mudstone. According to the Tertiary stage classification proposed by Finlay and Marwick (1940) the Taranakian stage immediately follows the Awamoan and the Awamoan the Hutchinsonian, and the faulting must have been restricted to the relatively short interval of time represented by the Awamoán Stage. The faulting, however, is probably not restricted to such a short interval as would appear from that classification, for Finlay and Marwick have considered for some years past and have evidence in preparation that a considerable interval of time separates the Awamoan from the Taranakian; a period represented by as-yet-unnamed Tertiary stages, and the deformation may have taken place at any time during this interval. All West Coast Tertiary sections recently examined in detail show a break which represents either an unconformity or a disconformity between the Cobden Limestone and the Blue Bottom (both names being used in the wide sense), but no good purpose would
be served by comparing these sections with the one at Fox River until stage names have been allotted to the Awamoan-Taranakian time interval.
Although the throw on the older fault must have been considerable, in Henniker Creek only a few chains west of the inferred fault the Fx 10 sandstone is parallel to the overlying Fx 11 mudstone, and the disturbance must have been essentially one of block faulting, the angular disturbance of the blocks being small.
It is not difficult to explain the fragments of Fx 3 coal measures between the Fx 11 mudstone and the Fx 10 sandstone in Henniker Creek as the unconsumed remnants of a Miocene landslide derived from the major fault a few chains east, a landslide which must have taken place after the deformation but before the deposition of the Fx 11 mudstone. After the landslide the topographic relief caused by the fault was planed off by the sea, which advanced across the fault and deposited the Fx 11 mudstone. How far this sea advanced eastwards is not known. The sea may not have covered the whole of the area now occupied by the Paparoa Range, but it is certain from the nature of the Fx 11 sediments that the range was then lower than now.
The younger fault which forms the eastern limit of the Fx 11 mudstone is the result of a deformation similar to the first, in which the coal measures were again thrust westwards over younger beds, but this time it was the Fx 11 mudstone which was directly overthrust by the coal measures. This younger fault has also been planed off during a comparatively recent erosion cycle and a layer of gravels, not shown on either plan or section, deposited indifferently on both the coal measures and the Fx 11 mudstone. These recent gravels now have the same relation to the mudstone (disconformity) and the coal measures (angular unconformity) as has the mudstone to the sandstone and the coal measures.
It is not improbable that faulting similar to that just described has played an important part in the building of both the Paparoa Range and other New Zealand ranges. The essential features of this type of deformation considered with respect to time and space is the periodic elevation of positive blocks and the probably equally periodic subsidence of the negative blocks. Both the positive and negative blocks form parts of crustal folds, but the wave length of these folds is so large that the numerous breaks in the sedimentary sequence do not show as other than disconformities within the limits of the contacts exposed at any one place.
Much of the diastrophic history of such areas will be deciphered only from a study of the fault zones, for it will be there that definite evidence of unconformity and overlap will be exposed, although often confused and sometimes rendered illegible by the result of the latest deformation.
Notes on the Microfaunas from Fox River Area.
By H. J. Finlay,
(Micropalaeontologist, N.Z. Geological Survey).
Faunas from outside the locality dealt with, but within the general area, and from formations referred to in the text.
Fx 6. This is the lowest horizon from which microfaunas could be obtained. No definite Bortonian microfaunas have yet been recognised from the West Coast, and a Bortonian age for basal “Island Sandstone” still rests on casts of such mollusca as Monalaria, found at but one locality. Matrix, associated with mollusca from G.S.3175 (cliffs east of road from St. Kilda, Brighton S.D., slide number F6415) yielded a fair microfauna which included:—
Siphotextularia cf. heterostoma (Forn.), Bolivinopsis cubensis C. and B., Robulus cultratus Mont., Vaginulina aff. cristellata (Staehe), Marginulinopsis spinulosa (Stache), Siphonodosaria cf. globulifera (Kreuz.), Nodosaria cf. raphanistrum Linne, Bolivinita n.sp. of Kaiatan, Uvigerina bortotara (Fin.), Trifarina aff. bradyi Cush., Bulimina pupula Stache, Cassidulina subglobosa Brady, Cerobertina kakahoica Fin., Nonion aff. pompilioides (P. and M.), N. maoricum (Stache), Anomalina eosuturalis Fin., Gyroidina cf. orbicularis d'Orb., G. scrobiculata Fin., Epistomina elegans d'Orb., Alabamina tenuimarginata (C. P. and C.), Notorotalia n.sp., Cibicides parki Fin., C. pseudoconvexus Parr, C. thiara (Stache), Sphaeroidina n.sp.
This is a Kaiatan assemblage, and is very close in general style to the five faunas from the less sandy mudstone above it, but there are enough differences to warrant reference to the lower Kaiatan, of which the Tahuian is an equivalent. Compare remarks made on faunas F.6283 and F.6284 from Garden Gully (Trans. N.Z. Inst., vol. 75, pt. 3, p. 362).
Five samples from the micaceous mudstone overlying the previous locality yielded good microfaunas, the highest being from 140 ft. below the limestone at sea-level below Trig. Bh. The faunas are all Upper Kaiatan and are so similar that they are best tabulated as follows:—
|Cyolammina incisa Stache||X|
|Rolivinopsis cubensis C. & B.||X||X||X||X|
|Gaudryina reussi Stache||X||X||X|
|Arenodosaria antipoda (Stache)||X||X||X||X||X|
|Martinottiella communis (d'Orb.)||X||X||X||X||X|
|Massilina tenuis (Czj.)||X||X||X||X|
|Robulus ouliratus Mont.||X||X||X||X|
|Vaginulinopsis asprocostulata (Stache)||X||X||X||X||X|
|Marginulinopsis spinulosa (Stache)||X||X||X||X||X|
|Dentalina substrigata (Stache)||X||X||X||X|
|Nodosaria cf. raphanistrum Linne||X||X|
|Siphonodosaria cf. globulifera (Krenz.)||X||X||X||X||X|
|Glandulina aperta Stache||X||X||X|
|Guttulina communis, d'Orb.||X||X||X||X|
|" " aff. seguenzana Brady||X||X||X|
|Bolivinita n.sp. of Kaiatan||X|
|Bolivina pontis Fin.||X||X||X||X||X|
|Virgulina aff. schreibersiana Czj.||X|
|Uvigerina bortara (Fin.)||X|
|Angulogerina aff. rugoplicata Cush||X||X|
|Bulimina truncanella Fin.||X||X||X|
|Cassidulina subglobosa Brady||X||X||X||X||X|
|Cerobertina kakahoica Fin.||X|
|N. gen. of Robertinidae||X||X|
|Nonion aff. pompilioides (F. & M.)||X||X||X||X||X|
|" " maoricum (Stache)||X||X||X||X||X|
|" " " " smooth form||X||X||X|
|Anomalina esouturalis Fin.||X||X||X||X|
|" " n.sp.||X||X||X||X||X|
|Gyroidina scrobiculata Fin.||X||X||X||X||X|
|" " cf. orbicularis d'Orb.||X||X|
|Epistomina elegans d'Orb.||X|
|Asterigerina n.sp. of Omotumotu||X||X||X|
|Notorotalia n.sp. of Kaiatan||X||X||X||X||X|
|Carpenteria rotaliformis C. and C.||X||X|
|Cibicides parki Fin. X||X||X||X||X|
|" " thiara (Stache)||X||X||X||X||X|
|" " aff. novozelandicus (Karr.)||X||X||X||X|
|" " maculatus (Stache)||X||X||X||X||X|
|" " pseudoconvexus Parr||X||X||X||X|
|" " n.sp||X||X||X||X|
|Discorbis scopos Fin.||X||X||X||X||X|
F.6416. Brighton Suivey District, 380 ft. stratigraphically below bed at sea-level under Trig. Bh.
F.6417. Brighton S.D., 340 ft. stratigraphically below bed at sea-level under Trig. Bh.
F.6418. Brighton S.D., 290 ft. stratigraphically below bed at sea-level under Trig. Bh.
F.6419. Brighton S.D., 290 ft. stratigraphically below bed at sea-level under Trig. Bh.
P.6410. Brighton S.D., 240ft. statigraphically below bed at sea-level under Trig. Bh.
F × 7. One sample from G.S.3180 (5 ft. below the limestone at sea-level below Trig. Bh; slide number F6421) was associated with molluscs such as Chlamys aff. venosus (Hutt.). Since the few known occurrences of venosus are in beds of upper Kaiatan age, this related species might indicate either about the same age or something younger such as Whaingaroan. Unfortunately, the microfauna allows of no decision on the matter. It is very small and of unusual nature:—
Cyclammina incisa Stache, Dorothia n.sp., Arenodosaria antipoda (Stache), Martinottiella communis (d'Orb.), Cassidulina subglobosa Brady, Nonion cf. pompilioides (F. & M.), Anomalina n.sp., Gyroidina zelandica Fin., Notorotalia n.sp., Cibicides thiara (Stache), Cibicides mediocris Fin.
Little can be said about this assemblage except that it could be Kaiatan, Whaingaroan, or Duntroonian. None of the usual key species is present, and the fauna is obviously from an unusual facies and must await knowledge of other sections before it can be placed. It has some points of resemblance to one from 100 ft. below the limestone at Ngapara, also to one from G.S.1424 (Waitahu Bridge, Reefton) and also to one from G.S.3171 (Perpendicular Point, Brighton S.D.); the last-named contains true Chlamys venosus and underlies a good upper Kaiatan microfauna. Tentative correlation may be made in the meantime with the Whaingaroan, but the possibility of uppermost Kaiatan is not ruled out.
Fx 8. One sample from the base of the limestone at the same locality as the last sample yielded a better but also somewhat indeterminable fauna:—
Semivulvulina capitata (Stache), Textularia n.sp., T. n.sp. aff. miozea Fin., T. n.sp. aff, cuspis Fin., Flabellammina sp., Dorothia
minima (Karr.), Martinottiella communis (d'Orb.), Karreriella novozelandica Cush., Arenodosaria antipoda (Stache), A. robusta (Stache), Gaudryina reussi Stache, G. crespinae Cush., Vaginulina cristellata Stache, Marginulina allani Fin., Glandulina aperta Stache, Lagenoglandulina subovata (Stache), Guttulina communis d'Orb., Bulimina pupula Stache, Cassidulina subglobosa Brady, Ellipsonodosaria subconica (Kreuz.), Nonion cf. pompilioides (F. and M.), N. maoricum (Stache), Anomalina n.sp., Eponides concentricus (F. and M.), Gyroidina allani Fin., Notorotalia stachei Fin., Cibicides thiara (Stache), C. maculatus (Stache), C. pseudoconvexus Parr, C. n.sp. This is certainly either a Whaingaroan or Duntroonian fauna, but the absence of key species really characteristic of either makes a decision difficult. Rotaliatina would certainly be expected in this facies if it were Whaingaroan, yet the Textularia n.sp. aff. cuspis has not been seen above Whaingaroan. Tentatively a Duntroonian age is suggested, but Whaingaroan is quite possible. The main mass of the hard limestone is probably Duntroonian-Waitakian.
Faunas from the locality dealt with; below the erosional unconformity.
Fx 9. One sample from the calcareous mudstone (F.6380) and two from the base of the calcareous sandstone (F.6380A and F.6381) yielded large and well-preserved faunas, and were obviously similar. They indicate an Upper Waitakian fauna, about midway between type Waitakian and type Hutchinsonian, so that there is some time gap between these and the last fauna, at least partially accounted for by the disconformity between.
The faunas from here onwards are tabulated together at the end in order to save space, since they are nearly all large.
Fx 10. Two samples from near the top of the calcareous sandstone supplied faunas considerably different from those in Fx 9. The lower one (F.6382), some 50ft. or more below the top, was poor and of itself indecisive, but similar in general to the upper one (F.6383), only 3ft. below the unconformity. The latter contained such forms as Plectofrondicularia parri Fin., Virgulopsis pustulata Fin., Pseudononion stachei (Cush.), Cancris amplus Fin., Nonion pompilioides (F. and M.), Notorotalia n.sp. aff. tenuissima (Karr.), etc., which indicate a horizon at least as high as Hutchinsonian; there are no distinctive Awamoan forms.
This fauna is so distinct from those of Fx 9, and both are so characteristic of horizons known in sections elsewhere that a time break within the calcareous sandstone has to be assumed. It may be mentioned, for example, that Fx 9 corresponds in faunas with the lowest greensands at All Day Bay and with the Waipara “Grey Marls,” while Fx 10 is the equivalent of the All Day Bay sandstone just below the A wamoan blue clays and of some or all of Thomson's brachiopod limestones of the Waipara, except the top one “E”.
Faunas from the locality dealt with; above the erosional unconformity.
Fx 11. Four samples from varying heights above the unconformity and conglomerate were examined, two associated with mollusca, two without macro-fauna. All these had a uniform fauna, strikingly
different in background and in key species from all the faunas below. The association of such forms as Textularia miozea Fin., Robulus calcar Mont., Plectofrondicalaria aff. pohana Fin., Bolivina aff. parri Cush., Rectobolivina mdoria, Fin., Loxostomum n.sp., Uvigerina miozea Fin., Nonion n.sp. aff. Nonionella, N. aff. halkyardi H.A. and E., N. cf. simplex (Karr), Notorotalia aff. zelandica Fin., Globorotalia miozea Fin., etc., shows a much younger fauna and indicates a long lapse of time since Fx 10. There are a few Taranakian affinities in these faunas, but they are definitely not as young as that. Correlation is plainly indicated with the Uppermost Tutamoe, as evidenced by faunas from the type Tutamoe section. The East and West Grey shell beds, the top of mudstone part of the Westland “Blue Bottom” (when not eroded off) and many other important localities are also correlatives. In the meantime the age may be referred to as pre-Taranakian and post-A wamoan.
|Angulogerina australis H.A. & E.||X||X||X|
|Amphistegina lessoni d'Orb.||X||X||X||X|
|A. macraglabra Fin.||X|
|A. miosuturalis Fin.||X||X|
|A. parvumbilia Fin.||X|
|A. pinguiglabra Fin.||X||X||X||X||X||X||X|
|A. subnonionoides Fin.||X|
|Arenodosaria antipoda (Stache)||X||X|
|Astrononion cf. novozelandicum C. & E.||X||X||X||X|
|Bolivina anastomosa Fin.||X||X||X||X||X|
|B. lapsus Fin||X||X||X||X||X|
|B. cf. parri Cush||X||X||X||X|
|B. punctata d'Orb.||X||X|
|Bulimina pupula Stacche||X||X|
|B. truncanella Fin.||X|
|Buliminella cf. apiculata Chap.||X|
|Buliminoides cf. williamsonianus (Brady||X|
|Buningia oreeki Fin||X||X|
|Cancris amplus Fin.||X|
|C. lateralis Fin.||X|
|Cassidulina carinata Cush.||X||X||X||X|
|Cassidulinoides orientalis (Cush.)||X||X|
|C. aff. parkeriana (Brady)||X||X||X||X|
|Cibicides catillus Fin.||X|
|C. ihungia Fin.||X||X|
|C. mediocris Fin.||X||X||X|
|C. novozelandicus (Karr.)||X||X||X|
|C. maculatus (Stache)||X||X|
|Dentalina soluta Reuss.||X||X||X|
|D. subcostata Chap.||X||X|
|Discorbis scopos Fin.||X||X||X||X|
|Dorothia minima (Karr.)||X||X||X|
|Dyocibicides biserialis C. & V.||X|
|Ehrenbergina marwicki Fin.||X||X|
|Ellipsoglandulina, subconica (Kreuz.)||X|
|Elphidium crespinae Cush.||?|
|E. striatissimum (Karr.)||X||X|
|Eponides broeckhianus (Karr.)||X||X|
|E. concentrious (F. & M.)||X|
|E. ecuadorensis G. & M.||X||X|
|Frondicularia cf. spathulata Brady||X|
|Gaudryina crespinae Cush.||X||X|
|Gaudryina cf. quadrangularis Cush.||X||X||X|
|Glandulina aperta Stache||X||X||X|
|G. laevigata d'Orb.||X||X||X||X||X||X|
|G. bulloides d'Orb.||X||X||X||X||X||X|
|Globorotalia dehiscens C.P. & C.||X||X||X||X||X||X||X|
|G. miozea Fin.||X||X|
|G. scitula (d'Orb.)||X||X||X||X|
|Gyroidina neosoldani Brot||X||X||X|
|G. zelandica Fin.||X||X||X||X|
|Haeuslerella hectori Fin.||X||X|
|H. cf. pukeuriensis Parr.||X|
|Lagenonodosaria hirsuta (d'Orb.)||X||X||X||X||X|
|L. scalaris (Batsch)||X||X|
|Liebusella soldani (J. & P.)||X||X|
|Lenticulina mamilligera (Karr.)||X||X||X|
|Loxostomum n.sp. (a)||X||X|
|L. n.sp. (b)||X|
|Marginulina subbullata Hantk.||X|
|Martinottiella communis (d'Orb.)||X||X|
|Massilina tenuis (Czj.)||X||X|
|Nodosaria cf. raphanistrum Linne||X|
|Nonion halkyardi Cush.||X||X||X|
|N. maoricum var. (smooth)||X|
|N. maoricum var. (stout)||X|
|N. n.sp. aff. Nonionella||X||X||X||X|
|N. cf. pompilioides (F. & M.)||X||X|
|N. aff. simplex (Karr.)||X||X||X||X|
|Nonionella magnalingua Fin.||X||X|
|N. novozelandica Cush.||X|
|N. zenitens Fin.||X|
|Notorotalia spinosa (Chap.)|
|N. tenuissima (Karr.)||X|
|N. n.sp. aff. tenuissima|
|N. aff. zelndica Fin.||X||X||X||X|
|Palmula taranakia Fin|
|Parvicarinina deflata Fin.||X|
|Plectofrondicularia parri Fin.||X|
|P. n.sp. aff. parri Fin.||X||X|
|P. n.sp. aff. pohana Fin.||X|
|P. wahaingaroica (Stache)||X||X||X|
|Pleurostomella subnodosa Reuss.||X|
|Pseudononion stachei (Cush.)||X||X||X||X||X|
|Pullenia bulloides d'Orb.||X||X||X|
|Reatobolivina mooria Fin.||X||X|
|R. maoriella Fin.||X||X||X|
|Robulus cf. calcar (d'Orb.)||X|
|R. dicampylus (Franz.)||X|
|R. vortex (F. & M.)||X||X||X|
|Saraoenaria italica Defr.||X||X||X|
|Siphonina australis Cush||X|
|Siphonodosaria aff. lepidula (Schw.)||X||X||X|
|S. verneuili (d'Orb.)||X||X||X|
|S. challengeriana (Thal.)||X||X|
|S. heterostoma (Forn.)||X||X|
|S. n.sp. aff. awamoana Fin.||X||X|
|Sphaeroidina bulloides d'Orb.||X||X|
|Spiroloculina novo-zealandica Cush. & Todd||X||X|
|Tewtularia miozea Fin.||X||X||X|
|T. n.sp. aff. miozea Fin.||X||X||X||X|
|Trifarina bradyi Cush||X||X||X||X|
|Uvigerina canariensis d'Orb.||X||X||X|
|U. dorreeni Fin.||X||X||X||X|
|U. miozea Fin.||X||X||X||X|
|Vagocibicides maoria Fin.||X||X||X||X|
|Virgulina aff. schreibersiana Czj.||X|
|V. aff. bramlettei G. & M.||X||X|
|Virgulopsis pustulata Fin.||X|
F.6380. Lower Fossil Creek, Brighton S.D.; 193 chs. at 238° from Trig. Fr.
F.6380A. Welsh Creek, from contact of upper and lower limestone; 149 chs. at 293° from Trig. Fr. A very bryozoan facies, which was not sorted and mounted completely when F.6381 was seen to be so like F.6380.
F.6381. Welsh Creek, N. branch Fox River; 50 ft. above contact of upper and lower limestone; 139 chs. at 295° from Trig. Fr.
F.6382. Fox River, 10 chs. below mouth of Henniker Creek; 60 chs. at 245° from Trig. Fr.
F.6383. South bank, Fox River; 20 chs. above mouth of Henniker Creek, 3 ft. below unconformity; 70 chs. at 220° from Trig. Fr.
F.6384. Ibid.; 10 ft. above pebble band and unconformity.
F.6385 (= G.S.3182). S. bank Fox River; 30 chs. at 180° from Trig. Fr.
F.6386. 75 chs. up Henniker Creek from junction with Fox River; 100 chs. at 182° from Trig. Fr.
F.6387 (= G.S.3485). N. bank, Fox River, 17 chs. above Henniker Creek junction.
Bell, J. M., 1906. The Geology of the Hokitika Sheet. N.Z.G.S. Bull. 1, p. 85.
—— 1930. Coal as a Recorder of Incipient Rock Metamorphism. Economic Geology, vol. 25, p. 694.
Evans, W. P., 1899. Contact Metamorphism at the New Brockley Coal Mine. Trans. N.Z. Inst., vol. 31, p. 557.
—— 1945. Age Revision of Tertiary Sediments at Garden Gully and Fitzgerald Creek near Blackball, Westland. Trans. Roy. Soc. N.Z., vol. 75.
Heck, E. T., 1943. Regional Metamorphism of Coal in South-eastern West Virginia. Bull. Am. Assoc., Petrol. Geol., vol. 27, no. 9, pp. 1194–1227.
Henderson, J., 1918. The Geology of the Reefton Subdivision. N.Z.G.S. Bull. 18.
Morgan, P. G., 1908. The Geology of the Mikonui Subdivision. N.Z.G.S. Bull. 13.
—— 1911. The Geology of the Greymouth Subdivision. N.Z.G.S. Bull. 13.