Art. XXIV.—Remarks on Bulletin No. 20 (New Series) of the New Zealand Geological Survey.
[Read before the Wellington Philosophical Society, 6th December, 1919; received by Editor, 31st December, 1919; issued separately, 15th June, 1920.]
The “Two-limestone” Theory.
Description of the Hutchinsonian and Awamoan Stages as interpreted by Park.
Hutchinsonian and Awamoan Localities.
Bortonian and Waiarekan Localities.
Summary and Conclusion.
In Bulletin No. 20 (New Series) of the Geological Survey Branch of the Mines Department Professor Park has described the geology of the Oamaru district of North Otago. The present writer has examined this area in some detail, and his observations have been recorded in several papers read before this society. In several important matters he finds himself at variance with Professor Park, and some notes on the latter's recent work are given in the following pages. The paper deals with the “two-limestone” theory of Professor Park, with his classification of the fossiliferous tufaceous beds, and with his subdivision and correlation of the beds of north-eastern Otago. The evidence on which the present writer's conclusions are based has been detailed in former papers.
Park first formulated his “two-limestone” theory in an attempt to reconcile the differences of opinion that had long existed between Captain Hutton and other geologists as to the position of the so-called “Pareora fauna” The present writer (1916, p. 25) showed that the “two-1 mestone” theory was not tenable in the Oamaru coastal district, and that the Awamoan (Pareora) beds lie above the limestone and Hutchinson Quarry beds. In Bulletin No. 20 Park has accepted this interpretation in part, for he places the Awamoan (Pareora) beds at the top of the series; but the so-called Waitaki stone is now placed in the Upper Hutchinsonian,
immediately below the Awamoan beds. The classifications adopted by Park (1905, p. 492) and later in Bulletin No. 20 indicate the change in his views.
|Awamoan||Awamoan beds||Awamoan beds.|
|Hutchinsonian||Hutchinson Quarry beds||(a.) Upper Hutchinsonian = Waitaki stone. (b.) Lower Hutchinsonian.|
|Ototaran||Ototara limestone||Ototara limestone.|
It will be seen that the Hutchinson Quarry beds (Hutchinsonian) have been subdivided, the Lower Hutchinsonian being the well-known Hutchinson Quarry greensands, which are said to lie beneath the so-called Waitaki stone (Upper Hutchinsonian).
That Park's latest view has not gained general acceptance is clearly indicated by the following quotation from the letter of transmittal to the Minister of Mines which prefaces Bulletin No. 20. Mr. P. G. Morgan, Director of the Geological Survey, writes: “Although quite agreeing with most of the conclusions reached, I cannot follow Professor Park in all respects, more particularly in his views regarding the relative ages of the Oamaru and Waitaki stones.” The present writer, has also found considerable difficulty in following Professor Park in his arguments for the differentiation of two-limestone horizons. In discussing the “two-limestone” theory, as formulated in Bulletin No. 20, it will be contended (1) that Park's Upper Hutchinsonian in the area between Kakanui and Target Gully, Oamaru, is really the base of the Awamoan; (2) that his Upper Hutchinsonian of the Landon Creek area is the equivalent of his Lower Hutchinsonian in the district between Kakanui and Target Gully; (3) that no evidence is brought forward to show that the Upper Hutchinsonian is present in the Flume Creek area; (4) that the correlation of the rocks called “Upper Hutchinsonian” in the Oamaru and Papakaio districts with the limestone of the Waitaki Valley (Waitaki stone) is not justified by the evidence brought forward in Bulletin No. 20. The discussion on the Bortonian and Upper Waiarekan of Park aims at showing that lists of fossils ascribed to these stages must be considerably reduced, as the horizons are very doubtful. References to Bulletin No. 20 will be made by quoting merely the pages of that publication.
II. The “Two-Limestone” Theory.
Park's “two-limestone” theory, as stated above, was an attempt to solve the problem of the “Pareora fauna.” This problem first presented itself to the New Zealand geologists when Haast submitted four collections of fossils from different localities to Hutton (1887, p. 430) for identification. The latter referred all the shells to the Pareora (Awamoan) horizon above the limestone. Haast himself was convinced that one of the collections had been obtained from beds which lay below the limestone. Other collections of fossils examined by Hutton were determined by him as “Pareora,” and in all cases he referred the beds to an horizon above the limestone. Haast and the officers of the old Geological Survey agreed with Hutton that some of his “Pareora” faunas came from above the limestone, but the field evidence convinced them that other collections of fossils determined by Hutton as “Pareora” came from below the limestone. Park (1905, p. 491) clearly recognized the difficulties, and attempted
a solution by his theory that there were two limestone horizons, separated by the Hutchinson Quarry and Awamoan beds (Pareora); or, in other words, that there was but one “Pareora fauna,” lying between two limestones, the lower being called the Ototaran stone and the upper the Waitaki stone.
The present writer (refer to Thomson, 1915, p. 123), after an excursion to the Waihao district of South Canterbury, was convinced that, where the full series was developed, there was but one limestone present. An examination of the fauna beneath the limestone showed that it bore a remarkable resemblance to the fauna above the limestone in the Waihao district, where the beds occur in the same section. This view was supported by Thomson (1915, p. 123), who subsequently visited the Waihao district. Park, however (1905, p. 510), had given a section at Kakanui in which his two limestones were shown separated by the fossiliferous beds. The present writer (1916, pp. 22–25) sought to prove that this section had been misinterpreted, and that only one limestone was present, with the fossiliferous beds lying above it. Park in his latest work has evidently accepted this interpretation of the section, for the Awamoan beds are now placed at the top of the sequence in the Oamaru and Kakanui districts. As pointed out above, however, he still maintains that the limestone of the Waitaki Valley is distinct from the limestone of the Oamaru district.
III. Description of the Hutchinsonian and Awamoan Stages as Interpreted by Park.
Before discussing the sections described in Bulletin No. 20 it will be necessary to form a clear conception of Park's various subdivisions of the beds above the Ototaran. Correlation of beds is possible on palaeonto logical or lithological evidence, or by direct stratigraphical connection, and it seems to the writer that Park has relied mainly on the lithological evidence in establishing his Upper Hutchinsonian horizon. The following quotations will indicate his conception of the post-Ototaran beds.
(1.) Awamoan Beds.
“The Awamoan strata consist of blue or bluish-green marine sandy clays that in some places pass into bluish-green sea-muds, in other places into very soft sandstones. In most places they are interbedded at distant intervals with hard calcareous bands that are sometimes sandy, in others argillaceous and crowded with shells. In some places the hard bands are replaced by calcareous nodular concretionary masses and flaggy lenses, occurring in more or less well-defined horizons.”
It will be shown that these hard calcareous bands in the Awamoan are referred by Park to the Upper Hutchinsonian in the Target Gully locality.
(2.) Hutchinsonian Beds.
The Hutchinsonian is subdivided lithologically, in descending order, into—(a) Glauconitic sandstone (Upper Hutchinsonian); (b) Glauconitic greensands (Lower Hutchinsonian); (c) Conglomerate, mainly basaltic.
The glauconitic sandstone (a) is said to represent the Waitaki stone of Upper Hutchinsonian age. He describes this horizon as follows: “The glauconitic sandstone follows the greensands conformably… it consists of soft glauconitic sandstone interbedded with hard yellowish brown sandstone bands… it is a compact yellowish-brown calcareous
glauconitic sandstone.” The glauconitic greensands (Lower Hutchinsonian) are described in the following extracts: “The glauconitic sandy beds at All Day Bay, Kakanui, Hutchinson's Quarry, and Grant's Creek are loose and incoherent, but at the upper end of Target Gully, at Landon Creek, and in the Waitaki area they form fairly compact glauconitic sandstones” (p. 78). Further, it is stated that “the fauna of this horizon [Lower Hutchinsonian] is distinguished by the abundance of the brachiopod Pachymagas parki (Hutt.), by the presence of the corals Isis dactyla Ten.-Woods and Mopsea hamiltoni (Thomson), and of the cup-shaped bryozoan Celleporaria nummularia Busk. Besides these there occur many pectens and other molluscs. Pachymagas parki (Hutt.) is present almost everywhere, but the other fossils mentioned may be abundant at one place and absent at another” (p. 78). “Pachymagas parki (Hutt.) occurs in great abundance in the Lower Hutchinsonian, usually to the exclusion of all other brachiopods except Rhizothyris rhizoida (Hutt.), which is nearly always present with it” (p. 109). “The Lower Hutchinsonian is the most distinctive and persistent horizon of the Oamaruian system; it always overlies the Oamaru stone. In the Oamaru area it consists of calcareous glauconitic greensands that at Landon Creek and the lower Waitaki Valley are partly or wholly replaced by calcareous glauconitic sandstone. But whether greensands or glauconitic sandstone, the characteristic brachiopod Pachymagas parki (Hutt.) and the peculiar corals Isis dactyla Ten.-Woods and Mopsea hamiltoni (Thomson) are always present. The Waitaki stone is underlain by the greensands” (p. 110).
It will be shown that these sandstone bands in the Landon Creek area are referred to the Upper Hutchinsonian, although from Park's description of the characteristic fossils they should belong to his Lower Hutchinsonian (Hutchinsonian of Thomson).
As pointed out by the present writer (1916, pp. 20–21), the fossil Pachymagas parki (Hutt.) occurs in abundance in a well-defined band of hard glauconitic sandstone. In the present paper this band is called the “parki” band. It is ofter accompanied by Rhizothyris rhizoida (Hutt.), to the exclusion of all other brachiopods. This hardened band is underlain in many places in the district by looser greensands, also glauconitic, but characterized also by a constant assemblage of fossils—Aetheia gaulteri (Morris), Terebratulina suessi (Hutt.), Isis dactyla Ten.-Woods, and Mopsea hamiltoni (Thomson), which are all very abundant. This bed usually contains many specimens of Pachymagas parki (Hutt.), but in these looser greensands the individuals of this species are on the average distinctly smaller than in the upper “parki” band, and their external characters are far more constant. In the hardened upper band, where it is usually accompanied by Rhizothyris rhizoida (Hutt.), the specimens assigned to the “parki” species are extremely variable in external shape. As pointed out by Park in the extracts quoted, above, this greensand horizon is a most distinctive one; it is, the typical Hutchinsonian of the Oamaru system, and always lies above a nodular band (Park's conglomerate). Park, however, would term these “Isis” greensands, and the “parki” greensands Lower Hutchinsonian; and states that they are separated from the Awamoan by the Upper Hutchinsonian (Waitaki stone). The writer contends that the “Isis” greensands and the overlying “parki” greensands constitute the Hutchinsonian, and are followed directly by the Awamoan beds.
In the localities discussed below an attempt is made to show that where the Awamoan beds are present, as in the Oamaru area, the hard calcareous bands at their base are called Upper Hutchinsonian; where the Awamoan beds are not present, as at Landon Creek (west branch), the “fairly compact glauconitic sandstone” (the “parki” band) is called Upper Hutchinsonian; where the “parki” band is absent, as in Landon Creek (Papakaio district), the upper glauconitic portion of the limestone is called Upper Hutchinsonian (p. 64). The various localities in which the post-Ototaran beds occur will now be discussed.
IV. Hutchinsonian and Awamoan Localities.
(1.) All Day Bay (p. 56).
The section in this locality has been described by the writer (1916, p. 20), and by Park in Bulletin No. 20. Both agree that the “darker and tougher greensands” (the “parki” band) are followed directly by the Awamoan beds. The section in this locality is most important, as it illustrates the typical character of the beds above the limestone. Here we have in one section, as shown by Park, the limestone much hardened towards its upper surface, which is corroded (nodular). This surface is immediately followed by the “Isis” greensands, capped by the hard “parki” band, which is directly overlain by the Awamoan beds. In this locality there is no Upper Hutchinsonian horizon, and Park's so-called Lower Hutchinsonian is conformably overlain by the Awamoan, which contains “hard sandstone layers.” Park does not recognize an Upper Hutchinsonian in this locality.
(2.) Deborah (p. 59).
In this section the highest bed exposed is the “parki” band, which is underlain by “6 ft. of greensands [which] contain many molluscs and brachiopods.” The braclfiopods present in these underlying greeensands are Terebratulina suessi (Hutt.) and Aetheia gaulteri (Morris), which are again accompanied by the same species of Isis and Mopsea. At the base of these greensands lies the nodular surface of the hard limestone which closed the Ototaran at All Day Bay. No Upper Hutchinsonian is present at Deborah.
(3.) Coast North of Kakanui Quarry (p. 70).
In this section Park shows the sequence of beds closed by a “hard semi-crystalline limestone.” The present writer has figured the complete section along the coast (1916, p. 23, fig. 2). The beds form a syncline, and to the north east this hard limestone is nodular at the surface, and followed by the “Isis” greensands, but the hard “parki” band has been denuded. The sequence is exactly similar to that at All Day Bay and Deborah. The surface of the hard limestone is nodular, and pieces of rolled volcanic rock occurs at the base of the “Isis” beds and represent Park's conglomerate at the base of the Hutchinsonian. In this coastal section the Upper Hutchinsonian is not stated to be present, though the limestone in this locality was formerly (1905, p. 510) called Waitaki stone (Upper Hutchinsonian).
(4.) Oamaru Rifle Butts.
In his discussion on the Hutchinsonian stage (chapter vii, p. 77) Park makes no reference to the Hutchinsonian beds at the Rifle Butts, but he
gives a section (pl. ii, fig. A) in which are shown “the greensands with Pachymagas parki” followed by a glauconitic shell-bed (bed i), a hard brown limonitic sandstone (bed h), and soft glauconitic sands (bed g), and all these beds are classed as Hutchinsonian. These beds above the “parki” green-sands are Park's Upper Hutchinsonian. The Awamoan beds are said to lie above this so-called Upper Hutchinsonian. Now, the glauconitic sandy shell-bed (bed i) is crowded with molluscan casts and extremely fragile shells, and there is no doubt that it is similar to the shell-beds at Target Gully and Ardgowan, which all geologists recognize as Awamoan, and its position immediately above the “parki” band confirms this (compare Park's section at All Day Bay, p. 56). These beds (g, h, i, of pl. ii, fig. A) are undoubtedly Awamoan, and there is, therefore, no Upper Hutchinsonian at the Rifle Butts.
(5.) Hutchinson's Quarry (pp. 60–61).
In this locality the junction of the greensands with the limestone is not clear, although they undoubtedly overlie it. As the Upper Hutchinsonian is not stated to be present, it is unnecessary to discuss the section further.
(6.) Target Gully (pp. 79–80).
In this locality the Awamoan and Upper Hutchinsonian are said to be present in the same section. From the description given it is difficult to judge exactly which beds are referred to the Upper Hutchinsonian. The following statement occurs on page 79: “The glauconitic sandstone [Upper Hutchinsonian] follows the greensands conformably at the shell-bed (Target Gully).” These greensands are Lower Hutchinsonian (p. 78). On the same page it is stated that “at the shell-bed, Target Gully, it [the glauconitic sandstone] consists of soft glauconitic sandstone interbedded with hard yellowish-brown sandstone bands.” In the section given on page 80 the horizons of the beds are not indicated; the fossiliferous greensands (bed c), which are the lowest greensands exposed in the section, must, according to Park's first statement quoted above, belong to his Lower Hutchinsonian, leaving a hard yellowish-brown glauconitic sandstone (2 ft. to 4 ft. thick) to represent the Waitaki stone (Upper Hutchinsonian). The fossils in this sandstone are in the form of casts, and no palaeontological or other evidence is offered to support the contention that the bed is at the horizon of the limestone in the Waitaki Valley (the so-called Upper Hutchinsonian). If Park refers all the greensands to his Upper Hutchinsonian, as would appear from the second statement quoted above, there is still no evidence to support this view. Of the seventy-two species of Mollusca listed from bed c, sixty-seven species occur in Park's list of Awamoan fossils (pp. 97–105), three forms are Recent, and the other two are not characteristic. The percentage of Recent species is said to be 40–3; and, as the percentage, of Recent species in the Awamoan of the Oamaru district is stated by Park to be 32.9, there would seem to be no justification for separating these beds from the Awamoan horizon. Pachymagas parki (Hutt.), however, is said to occur in the form of casts in bed d, and as the same fossil is recorded from bed c, and this is the characteristic fossil of Park's Lower Hutchinsonian, the beds might equally well be referred to his Lower Hutchinsonian. As a matter of fact, in the absence of a brachiopod fauna it is a difficult matter to distinguish the Hutchinsonian from the Awamoan. As Park says (p. 53), “the relationship existing between the Hutchinsonian and Awamoan is generally so close that it is difficult to define where the one ends and the other begins.”
If, however, in addition to a molluscan fauna the brachiopods are present, the line of demarcation is a sharp one in the Oamaru and Papakaio districts, the close of the Hutchinsonian being marked by a glauconitic band crowded with Pachymagas parki (Hutt)., which is often accompanied by Rhizothyris rhizoida (Hutt.). The writer believes that the “parki” beds in the present locality are followed directly by the Awamoan, and, as the former beds are Park's Lower, Hutchinsonian, it follows that there is no Upper Hutchinsonian in the Target Gully locality. Yet Park states (p. 25) that “on palaeontological grounds the Hutchinsonian might be divided into two sub-stages—the lower or true Hutchinsonian including the glauconitic greensands, the upper comprising the glauconitic calcareous sandstone that forms the Waitaki stone or Waitakian.” The writer has been unable to find in Park's latest work these palaeontological grounds.
When the writer examined the Target Gully section the junctions of the various beds were obscured by slope deposits, in which were collected fossils from the shell-bed (Awamoan), specimens of Pachymagas parki (Hutt.), and Rhizothyris rhizoida (Hutt.), and this would indicate that the true Hutchinsonian (Park's Lower Hutchinsonian) is present below the shell-bed. Putting aside this obscurity of the section, however, it is contended that no evidence has been adduced to justify any bed in the section being differentiated as a separate Upper Hutchinsonian horizon. The fossils from bed c are Awamoan, and the hard glauconitic sandstone is exactly similar to the bands that occur in Park's Awamoan at All Day Bay.
(7.) Upper Target Gully (p. 82).
Two sections are exposed in this locality. In fig. 37 a “rusty-brown glauconitic sandstone; 9 ft. exposed; contains Pachymagas parki (Hutt).” In fig. 38 a glauconitic sandstone is shown. It is said to be crowded with Pachymagas parki (Hutt). According to Park's definition of the beds, neither the Awamoan nor the so-called Upper Hutchinsonian is present.
(8.) Ardgowan Shell-bed (p. 81).
The section in this locality (fig. 36) shows the Ardgowan shell-beds resting directly on a “soft brown sandstone,” from which twelve fossils were collected; eleven of which are found in typical Awamoan localities. The other fossil, Lima suteri Dall, is apparently not found elsewhere in the Oamaru district. Park's Lower Hutchinsonian is not present in the section, and no reason is assigned for separating this “slightly glauconitic sandstone” from the Awamoan. As pointed out above, these sandstone bands are characteristic of the Awamoan, and there is no evidence to show why they should be placed at an Upper Hutchinsonian horizon.
(9.) Devil's Bridge (pp. 62, 82).
The section at the outlet end of Devil's Basin shows “a soft friable glauconitic sandstone, 12 ft. thick, crowded with Pachymagas parki (Hutt.),” and accompanied by Rhizothyris rhizoida (Hutt.), overlain directly by a brown calcareous glauconitic sandstone, 30 ft. thick, from which seventeen forms, were obtained, thirteen of which occur in the Awamoan, one is not found elsewhere, two are recorded from the “Lower Hutchinsonian” elsewhere (that is, from the “parki” greensands), while Emarginula wannonensis Harris occurs in the Ototaran. This so-called Upper Hutchinsonian cannot be separated from the Awamoan, particularly as it rests hard upon the “parki“
greensands, its normal position as shown by Park in his section at All Day Bay (p. 56). The writer (1918b, p. 121) described this locality, and showed that the “parki” band lay some distance above the limestone, which was nodular at its surface, and according to Park the upper part of the limestone is “a hard semi-crystalline limestone from 2 ft. to 4 ft. thick.” The sequence is similar to that at All Day Bay, although the small exposure of looser greensands between the nodular surface of the limestone and the “parki” band has not yet proved fossiliferous. The sands above the “parki” band are glauconitic, and in this respect are similar to the Awamoan at All Day Bay. In the present locality no reasons have been adduced to show that the Upper Hutchinsonian is present.
All the localities in the Oamaru district where Park has described the Hutchinsonian have now been discussed, and the writer has attempted to show that the band of glauconitic sandstone (the so-called Upper Hutchinsonian of Park) is part of the Awamoan. The description in Bulletin No. 20 of the Awamoan beds shows that they may assume the character of an indurated sandstone. In the absence of palaeontological evidence, the placing of a thin band of sandstone in an Upper Hutchinsonian is unwarranted. The fossils that have been recorded by Park are Awamoan, as shown above. In his classification of the beds of north-east Otago, Thomson (1916, p. 35) defined the Hutchinsonian as the beds lying between the Ototara imestone and the shell-bed at Target Gully. This shell-bed undoubtedly forms the base of the Awamoan at the Rifle Butts, but from its very nature t is not likely to be a widely extended horizon (it is known to occur at only three places—Rifle Butts, Target Gully, and Ardgowan). These shell-beds appear to be the remains of shell-banks of the Awamoan seas, and, although confined to the lower part of the Awamoan, they may not always represent the basal bed. At All Day Bay the basal bed of the Awamoan, which lies directly on the “parki” band (Hutchinsonian), contains similar fossils to the shell-bed, but no shell-bed occurs in the locality. As pointed out above, the, “parki” band marks a definite horizon, the close of the Hutchinsonian, and it seems preferable to make this band the upward limit of this stage. This would mean that Park's Waitaki stone (Upper Hutchinsonian) would be driven into the Awamoan, but it would not in any way lower the value of the evidence he has brought forward to prove that this limestone is at a different horizon from the Ototaran stone.
(10.) Landon Creek and Flume Creek.
The Awamoan beds are not present in these localities, but certain hard glauconitic bands are present in the upper beds. Some of these are referred to the Upper Hutchinsonian horizon. The present writer contends that these so-called Upper Hutchinsonian bands represent the “parki” band, in other cases lower beds, and are therefore, according to Park's definition, his Lower Hutchinsonian. As the “parki” band is the highest horizon in the Landon Creek and Flume Creek areas, the so-called Upper Hutchinsonian cannot be present.
In fig. 25 (p. 63) a section is given showing “rusty-brown glauconitic greensands crowded with Pachymagas parki (Hutt.)” at the top of the sequence. According to Park's definition, this is his Lower Hutchinsonian horizon, and the Upper Hutchinsonian cannot be present. We must note, however, that a “brown calcareous glauconitic sandstone” 6 ft. thick is said to lie 4½ ft. below the “parki” bed. This band of sandstone is again shown in fig. 26, where the “parki” band is not shown. In both figures
this glauconitic sandstone lies directly on the Oamaru stone (Ototaran), and in fig. 25 is separated from the “parki” band by nodular greensands. In fig. 27 (p. 64) the “parki” band is not present, but 24 ft. of glauconitic sandstone is shown lying above the limestone and classified as Hutchinsonian, but whether Upper or Lower is not stated. In figs. 26 and 27, then, this glauconitic sandstone cannot represent the Upper Hutchinsonian.
In fig. 15 a section is given in Landon Creek showing at the top of the Hutchinsonian a “hard brown calcareous sandstone, thickness of 6 ft. exposed,” from which were obtained the brachiopods Pachymagas parki (Hutt.) and Rhizothyris rhizoida (Hutt.). This is Park's Lower Hutchinsonian, and the Upper Hutchinsonian is therefore absent. Fig. 15 is important, as it enables us to correlate the beds in the Landon Creek area with those in the Oamaru area. It will be noted that the upper part of the Oamaru stone is a bed of “hard semi-crystalline limestone,” which is overlain by looser greensands containing Isis dactyla Ten-Woods, and these are capped by “a hard brown calcareous sandstone containing Pachymagas parki (Hutt.) and Rhizothyris rhizoida (Hutt.).” The sequence is the same as at All Day Bay, only in the present locality the nodular surface of the hard limestone is not so evident.
On page 46 Park gives a classification of the beds in Landon Creek, and shows that the limestone beneath the “hard semi-crystalline limestone” is glauconitic. This is the case in the whole of the Landon Creek area, and it is extremely probable that bed b of fig. 25, bed b of fig. 26 (both of which underlie nodular greensands), and bed b of fig. 27 represent this upper glauconitic portion of the limestone. The nodular greensands (”Isis” beds) just referred to contain Isis dactyla Ten.-Woods, Aetheia gaulteri (Morris), and Terebratulina suessi (Hutt.), and they lie immediately beneath the “parki” band. The fossils collected by the writer from these beds have already been published (1918b, pp. 122, 123), and, although these lists are incomplete, they indicate that the sequence is similar to that of the Kakanui district. In the Landon Creek area, then, the highest beds present are the “parki” beds (Park's Lower Hutchinsonian of the Oamaru-Kakanui areas discussed above), and his Upper Hutchinsonian is non existent.
The writer has attempted to show that in the coastal district, where the Awamoan beds occur above the greensands, the base of the Awamoan is termed Upper, Hutchinsonian; that in the Landon Creek area, where the “parki” band is the highest horizon present, either this bed or underlying beds are termed Upper Hutchinsonian. In other words, the Hutchinsonian greensands with Pachymagas parki are overlain directly by the Awamoan beds, and the “Upper Hutchinsonian” of Park is applied to different horizons in different parts of the district, and is therefore inadmissible in classification.
On page 48 a section is given in which the Oamaru stone is shown capped by a bed of hard semi-crystalline limestone, which represents the upward limit of the Ototaran. The sequence is similar to that at All Day Bay (p. 56), west branch of Landon Creek (p. 46), Deborah (p. 59), Kakanui (p. 70). In the present locality and in the localities just mentioned the overlying greensands contain Isis dactyla Ten.-Woods, Mopsea hamiltoni (Thomson), Aetheia gaulteri (Morris), Terebratulina suessi (Hutt.), and there is no doubt that these greensands are all at the same horizon—the base of the Hutchinsonian. Now, these greensands (bed m of fig. 17) are said to be the same as bed g of fig. 28, and the latter bed is said to be Upper Hutchinsonian (Waitaki stone), which is impossible, as the fossils are the fossils of
Park's Lower Hutchinsonian of the coastal area (see p. 78). Further, from Park's description of the beds at Big Flume Creek on page 48 and page 65, bed m of fig. 17 should be correlated with bed f of fig. 28, not bed g, as both lie hard on the “band of semi-crystalline limestone” and represent the “Isis” greensands, and the fossils of the latter horizon also occur in the lower portion of bed g. The writer was unable to find the glauconitic sandstone overlying these “Isis” beds, and after visiting the Big Flume Creek during the present year was only confirmed in his own interpretation of the section as given in a former paper (1918, p. 123). As indicated there, the section is a discontinuous one, and the beds are probably faulted. The highest beds exposed in the section, which crop out on the right bank of the creek between the water-race and the Oamaru-Kurow main road, are the “Isis” greensands capping the “hard semi-crystalline limestone,” and the writer found no beds above them.
In regard to this section Park (p. 65) says, “This section is important, as it shows not only the relationship of the Oamaru stone to the Hutchinsonian, but also—what is of greater significance—the relationship of the Oamaru stone to the Waitaki stone.” Even if the glauconitic sandstone (bed g of fig. 28) does occur as shown in section above the “Isis” beds (the present writer was unable to find it), no evidence has been presented to show that it is the equivalent of the limestone of the Waitaki Valley near Duntroon. A section is given on page 83 of the rocks near Duntroon, where Park's typical Waitaki stone is shown overlying a fossiliferous glauconitic greensand. From the description of this stone in the legend it would appear that the rock is a very impure limestone, but it is as pure in many parts as the typical Ototaran limestone; it is certainly arenaceous and glauconitic in places, but it is undoubtedly a limestone. The analyses given on page 115 (especially analysis No. 4) confirm this.
Park gives a list of brachiopods from the glauconitic sandstone at the base of the Waitaki stone (p. 83). These brachiopods have also been collected from the upper part of the glauconitic limestone of Landon Creek. Wherever the limestone becomes very glauconitic the brachiopods appear. The upper glauconitic part of the limestone in the Landon Creek area and in the Flume Creek area increases considerably in thickness, and it is this portion that yields fossils similar to those at the base of the limestone near Duntroon. As pointed out in a former paper, these fossils are not restricted to this base. At White Rocks and at Duntroon the lower glauconitic part of the limestone increases considerably in thickness, and these brachiopods are found a considerable distance above the base of the limestone. Detailed correlation is not possible until we know the downward range of this brachiopod fauna in the Oamaru limestone, and its upper range in the rocks of the Waitaki Valley. At present all we can state is that the brachiopod fauna of the limestone in the Waitaki Valley and in the limestone of the Landon Creek area is undoubtedly Ototaran.
V. Bortonian and Waiarekan Localities.
In his table of the Oamaruian Mollusca (p. 97) Park states that sixty-four species were obtained from the Bortonian and sixty-four species from the Upper Waiarekan (Waiareka tuffs). This subdivision of the Waiarekan of Thomson into a Lower Waiarekan (Bortonian) and an Upper Waiarekan has much to recommend it. In many places in North Otago the coal-grits are overlain by fine micaceous quartzose greensands, and near their base hardened calcareous concretionary bands occur in which fossils are
very abundant, but unfortunately mainly in the form of casts. From this horizon at Black Point, McKay and Park made extensive collections, and forty-three species were determined by the late Mr. Henry Suter, and referred by Park to his Bortonian. In another paper in this volume the writer has given a list of fossils, also determined by Suter, which were collected from an horizon about 30 ft. above the coal-grits, and almost certainly represent the Bortonian horizon. At Ngapara a similar fossiliferous bed is found lying a short distance above the coal-rocks. In the bed of the Kakanui River, near Gemmel's crossing, this fossiliferous horizon occurs beneath glauconitic greensands, which dip beneath the Waiarekan tuffs of the Oamaru district. The introduction of a Bortonian horizon should be favourably received by geologists. Park has stated that “for a classification to be a trustworthy standard of reference it is an essential requirement that the subdivision shall be made in a district where the component subdivisions are in such intimate association that their relationship to one another can never be in doubt.” All will accord hearty approval to this dictum; but we may also add that, if an attempt is being made to work out a distinctive fauna for each of these component subdivisions, it is also an essential requirement that the fossils shall be definitely ascertained to have come from a definite horizon. This does not mean that fossil lists should be discarded merely because their horizon is doubtful, but it does mean that these doubtful fossils should be rejected, temporarily probably, when lists typical of the various stages of a system are being compiled. The species listed by Park as Bortonian and Upper Waiarekan call for some comment in the light of the principles just enunciated. The fossils from the beds at Black Point number forty-three species (p. 34), and were gathered from Park's typical Bortonian locality, and the horizon is undoubted. On page 35 a fist of thirteen species of Mollusca is given from brown sandstones which lie “about 80 ft. above the lignitic quartzose beds of the Ngaparan stage, and may represent a somewhat higher horizon than the Bortonian.” On the same page is given a list of fossils gathered from fossiliferous blocks, but “these masses could not be traced to their source.” As the horizon of the first collection is doubtful, and as the second was derived from rocks that were not in situ, these fossils cannot be included in the typical Bortonian. The list of sixty-four species must therefore be reduced to forty-three species.
(2.) Upper Waiarekan.
The writer (1918a, p. 107) attempted to define the horizons of the volcanic rocks in the Oamaru district, and concluded that there was a period of volcanic activity prior to the deposition of the Ototaran limestone, represented by the Waiareka tuffs (Upper Waiarekan of Park), and that there was a later period—perhaps two later periods—of activity represented by the volcanic rocks that occur interbedded with the Ototaran limestone near Oamaru. Park recognizes three periods, the second and third being Ototaran, while the first period is Upper Waiarekan. These volcanic rocks form fragmental tufaceous beds for the most part, and were probably all accumulations from submarine eruptions; they are often fossiliferous, Fossils gathered from tufaceous rocks may therefore be either Ototaran or Waiarekan, and before the fossils are assigned to either of these horizons the position of the bed must be indisputable. The fossils listed as Upper Waiarekan by Park have in nearly all cases been gathered from beds interbedded with limestone, and the writer believes that they belong to the limestone period—that is, they are of Ototaran age. Park himself indicates
that his Waiarekan tuffs at Cape Wanbrow may be partially Ototaran, for he states that in this locality the Waiarekan tuffs are “over 600 ft. thick—though it is possible that a portion of the latter may belong to the Ototaran.” The writer is in accord with this statement, and would assign to the Ototaran the interbedded tuffs and limestone bands in the Shirley Creek section near the Rifle Butts, which form the top of Park's Upper Waiarekan. The beds immediately below the lower pillow-lava near Boatman's Harbour should also be Ototaran. The various localities where the Waiarekan tuffs are said to occur will now be discussed.
(a.) Kakanui South.—In Bulletin No. 20, section 19, page 52, shows the tuffs lying beneath the Ototaran limestone, and they are doubtfully referred to the Waiarekan. Above them lie 71 ft. of limestone, 24 ft. of marly clays, and tufaceous matter is plentiful throughout the section. The limestone (bed a) is evidently at or near the base of the Ototaran. If so, the under-lying tuffs are probably Waiarekan, but they have yielded no fossils.
(b.) Boatman's Harbour, Cape Wanbrow.—Park in a measured section (pl. ii, sec. B) shows the beds in excellent detail. A well-marked break is shown below bed h2. Discussing this unconformity, Park says that it is “apparently due to contemporaneous erosion.” He further states that the Oamaru building-stone “is absent, and, if not wholly, is partly represented by the fossiliferous tuffs and limestones at Boatman's Harbour [i.e., by the beds above the lower pillow-lava]. The brachiopods from the upper of the two limestone bands at that cove are mostly those of the Kakanui limestone horizon of the Ototaran [i.e., Upper Ototaran], as also are the brachiopods from the lower of the two limestone bands underlying the pillow-lava.” The beds referred to are shown in plate ii, section B, but in the legend these lower limestone bands and interbedded volcanic rocks are not referred to any horizon, although from the title of the section they are probably to be placed in the Waiarekan; yet the description of the beds does not indicate where the upper limit of the Waiarekan should be placed. From the quotation given above it is clear that the lowest fossiliferous band in the section contains characteristic Ototaran brachiopods, and underlying this band unconformably is a great thickness of volcanic tuffs which have not yielded any fossils. The fauna from this locality cannot be referred to the Waiarekan.
(c.) Shirley Creek (see pl. ii, fig. A).—Park states that “at Shirley Creek the Waiarekan tuffs are overlain unconformably by the Oamaru stone and associated beds…. The unconformity cannot be regarded as other than intra-formational.” When the writer examined this section he formed the opinion that the beds above and below this so-called unconformity had the same dip (1918a, p. 110/fig. 2). It is true that the upper bed (pl. ii, fig. A, bed c) is a limestone band containing masses of volcanic rocks, as shown by the writer in the paper just referred to; but this is a common feature in the limestone bands interbedded with tuffs, as shown by Park on page 37, where he writes in reference to the two bands below the pillow-lava that “these limestone beds are brecciated with angular blocks of vesicular basalt.” The beds referred to the Waiarekan at Shirley Creek are calcareous tuffs interstratified with polyzoan limestone bands, and they contain the typical Ototaran brachiopod Liothyrella oamarutica (Boehm), and there would appear to be no reason for separating the beds between bed q and bed w from the Ototaran. At the top of bed w there is an undoubted physical unconformity, which probably represents the break at Boatman's Harbour below bed h2 of plate ii, fig. B, as the beds that lie beneath these unconformities are unfossiliferous tuffs of similar composition.
(d.) Awamoa Creek, near Deborah (p. 41).—The base of the section (fig. 5) is a basalt showing pillow-structure similar to the lower pillow-lava at Boatman's Harbour. The two rocks have been described by the writer (1918a, p. 113), and there is little doubt that they are at the same horizon. The rock at Boatman's Harbour has been shown to be almost certainly Ototaran, and the pillow-lava in the present locality must be referred to the same stage. The highest bed of the section is a brecciated pillow-lava exactly similar to the highest bed in the section at Boatman's Harbour, while the intermediate beds are calcareous fossiliferous tuffs and limestones. The fossils recorded from the tufaceous beds above the lower pillow-lava in the present locality are in rather poor condition, and the percentage of Recent species as determined by Suter is 37.5. The evidence is scareely sufficient to warrant these rocks being classed as Waiarekan.
(e.) Grant's Creek (p. 45).—In fig. 14 a section is given on the east bank of Grant's Creek, near Oamaru. It shows the Oamaru stone with interbedded bands of basaltic conglomerate, and the soft friable greenish glauconitic calcareous tuffs underlying are called Waiarekan. These beds are horizontal, and it is stated that “less than 50 yards higher up the stream, and on the same side, the Oamaru stone is followed by the Hutchinsonian greensands crowded with Pachymagas parki (Hutt.).” The maximum thickness of the rocks above the tuffs is 21 ft., and, as the rocks are horizontal, and the Hutchinsonian beds occur a short distance away capping the limestone, these tufaceous beds are certainly not Waiarekan. The development in the present section is very similar to the section exposed lower down the stream and described by the writer (1918b, p. 121, fig. 3). In that section 20 ft. of limestone separates the volcanic rocks of Oamaru Creek from the Hutchinsonian greensands, and Park rightly considers these volcanic rocks as Upper Ototaran (see geological map, Bulletin 20). The tufaceous beds in the present locality are therefore Ototaran. These beds mapped by him in the basin of Grant's Creek as Waiarekan are similar to those developed at Upper Target Gully which he has mapped as Upper Ototaran. A comparison of the sections shown on page 82 at Upper Target Gully (figs. 37 and 38) will indicate the similarity of the rocks in the basin of Grant's Stream to those at Upper Target Gully. Similar sections occur at Hutchinson's Quarry (1918a, p. 111) Lower Target Gully (Bulletin 20, p. 80), and Eden Street, Oamaru (Bulletin 20, p. 60). The present writer, in his description of the Hutchinson Quarry and neighbourhood (1918a, p. 112), showed that the fossiliferous beds at Boatman's Harbour which lie beneath the brecciated pillow-lava are certainly not Hutchinsonian, as contended by former geologists, and Park in his latest work has reached the same conclusion, as his geological map clearly shows. The writer's argument was based solely on the correlation of the upper volcanic rocks at Boatman's Harbour and Oamaru Creek near the junction of Grant's Stream, and as Park also correlates these volcanic horizons there can be no doubt that the volcanic horizon in the present section is not Waiarekan but Ototaran (Upper Ototaran).
In the localities that have been discussed, if these so-called Waiarekan tuffs are Ototaran tuffs, then Park's fauna of the Upper Waiarekan is reduced from sixty-four species to the seventeen species detailed on pages 43 and 44 of Bulletin No. 20. The brachiopods quoted there are characteristic Ototaran fossils, four of the Mollusca are new species, Clio annulata (Tate) is not found elsewhere in New Zealand, Amusium zitteli (Hutt.) is not recorded from any other locality in North Otago, and the remaining
fossils are either found in higher beds or are Recent. The horizon of these tuffs is doubtful, but the association of these calcareous tuffs with chalky clays and marls is similar to the beds near the base of the Ototaran in the section exposed on the right bank of the Kakanui River (p. 57, fig. 19). The writer has also observed these marly beds and tuffs near the base of the limestone in the old quarry at Fortification Hill, near the village of Alma.
VI. Summary and Conclusion.
It has been contended that the sequence and subdivision of the Tertiary beds of North Otago as detailed in Bulletin No. 20 requires certain modifications, and the following conclusions have been reached by the writer:—
(1.) Park's Lower Hutchinsonian is the true Hutchinsonian of Thomson, and is characterized by the fossils Pachymagas parki (Hutt.), Aetheia gaulteri (Morris), Terebratulina suessi (Hutt.), Isis dactyla Ten.-Woods, and Mopsea hamiltoni (Thomson).
(2.) No evidence has been brought forward in the bulletin for the establishment of an Upper Hutchinsonian horizon in the area lying between All Day Bay and Upper Target Gully. The beds referred to this horizon are Awamoan, and lie immediately on the “parki” greensands.
(3.) The highest beds present in the Landon Creek area are the “parki” greensands, and in the Flume Creek area the “Isis” greensands, which constitute Park's Lower Hutchinsonian; there cannot, therefore, be an Upper Hutchinsonian horizon in these localities.
(4.) No evidence is presented in Bulletin No. 20 to show that the Ototaran limestone in the Oamaru and Papakaio districts correlates with the beds below the limestone in the Waitaki Valley. Both limestones contain several brachiopods which are restricted to the Ototaran of the typical Oamaru district, and must be classed as Ototaran.
(5.) The nature of the limestone (polyzoan limestone) interbedded with the tuffs beneath the lower pillow-lava at Boatman's Harbour and Shirley Creek, and the brachiopods obtained from these bands, strongly suggest that their age is Ototaran, not Waiarekan.
(6.) The occurrence of Awamoan fossils in the beds (Otiake beds) above the limestone of the Waitaki Valley, and the fact that the Awamoan and Hutchinsonian are “part and parcel of the same series,” as Hutton, McKay, and Park have asserted, further strengthens the argument that this limestone is Ototaran.
(7.) Nevertheless, the brachiopod fauna of the greensands in the Oamaru coastal district enables a clear line of demarcation to be drawn in that area between the Hutchinsonian and Awamoan.
Hutton, F. W., 1887. Note on the Geology of the Valley of the Waihao, in South Canterbury, Trans. N.Z. Inst., vol. 19, pp. 430–33.
Park, J., 1905. On the Marine Tertiaries of Otago and South Canterbury, Trans. N.Z. Inst., vol. 37, pp. 489–551.
Thomson, J. A., 1915. Classification and Correlation of the Tertiary Rocks, 8th Ann. Rep. N.Z. Geol. Surv., pp. 123–24.
—— 1916. On Stage Names applicable to the Divisions of the Tertiary in New Zealand, Trans. N.Z. Inst., vol. 48, pp. 28–40.
Uttley, G. H., 1916. Geology of the Neighbourhood of Kakanui, Trans. N.Z. Inst., vol. 48, pp. 19–27.
—— 1918a. The Volcanic Rocks of Oamaru, Trans. N.Z. Inst., vol. 50, pp. 106–17.
—— 1918b. Geology of the Oamaru-Papakaio District, Trans. N.Z. Inst., vol. 50, pp. 118–24.