Kaihikuan rocks at Corbies Creek and Mt. St. Mary, North Otago
Year:
Project type:
Advisers:
Abstract:
Marine fossils of Kaihikuan age (Middle Triassic) are known from two discrete areas within Torlesse Supergroup "greywackes" to the south-west of the Middle Waitaki Valley.
At Corbies Creek, five moles west of Otematata, fossils are abundant in a sequence of indurated, shallow marine sandstones and siltstones that resemble the Murihiku Supergroup rocks in facies, but are of the arkosic mineralogy characteristic of the Torlesse Supergroup. The 4000 ft thick sequence has been divided into the following formations (in ascending order): Rabbiters Hut Sandstone (790 ft), Elderberry Formation (530 ft), Taylor Siltstone (185 ft). Charlie Free Sandstone (305 ft), Matagouri Siltstone (830 ft), Putakitaki Sandstone (305 ft), Umu Siltstone (145 ft), One O'Clock Formation (750 ft), and Long Gully Formation (250+ ft). The Corbies Creek Group is proposed for these rocks.
A rich Kaihikuan fauna, including many new species is unevenly distributed throughout the lower 3500 ft, plant fossils appearing in the uppermost 250 ft. The apparently conformable relationship of fossil flora to fossil fauna would indicate an upper Kaihikuan or Lower Oretian age for the plant fossils, this being at variance with the tentative uppermost Triassic or Lowest Jurassic date suggested by palaeobotanical correlations.
Corbies Creek Group rocks occupy a downfaulted strip extending from the Otematata River, nine miles in the Corbies Creek-Backyards area. The strip is faulted against Chlorite 2 surface semischists to the south-west and against unfossiliferous, deep-water greywackes to the north-east. Sediments within the strip are semi-isoclinally folded about axes that plunge moderately towards the southwest.
In the St. Mary Range, eight miles west of Kurow, Kaihikuan fossils occur in a largely overturned sequence of similar, but incipiently schistose sediments. A sequence of 3000 ft has been divided into 6 informal units - labelled M1 to M6. Although diagnostic Kaihikuan fossils are restricted to the upper 1200 ft, populous shellbeds of the trigoniid Agonisca are found throughout the full sequence, and define a zone extending north-west - south-east got at least 7 miles. These rocks are isoclinally folded about an anticlinal axis plunging gently north-west. Fossils are compressed perpendicular to cleavage.
Massive unfossiliferous greywackes, adjacent to and between the two areas of fossiliferous shelf sediments, would seem to have been deposited in deep water as they are intimately associated with undoubted turbidites. Reconnaissance structural observations would suggest that they are complexly folded about steeply plunging axes.
At Corbies Creek, five moles west of Otematata, fossils are abundant in a sequence of indurated, shallow marine sandstones and siltstones that resemble the Murihiku Supergroup rocks in facies, but are of the arkosic mineralogy characteristic of the Torlesse Supergroup. The 4000 ft thick sequence has been divided into the following formations (in ascending order): Rabbiters Hut Sandstone (790 ft), Elderberry Formation (530 ft), Taylor Siltstone (185 ft). Charlie Free Sandstone (305 ft), Matagouri Siltstone (830 ft), Putakitaki Sandstone (305 ft), Umu Siltstone (145 ft), One O'Clock Formation (750 ft), and Long Gully Formation (250+ ft). The Corbies Creek Group is proposed for these rocks.
A rich Kaihikuan fauna, including many new species is unevenly distributed throughout the lower 3500 ft, plant fossils appearing in the uppermost 250 ft. The apparently conformable relationship of fossil flora to fossil fauna would indicate an upper Kaihikuan or Lower Oretian age for the plant fossils, this being at variance with the tentative uppermost Triassic or Lowest Jurassic date suggested by palaeobotanical correlations.
Corbies Creek Group rocks occupy a downfaulted strip extending from the Otematata River, nine miles in the Corbies Creek-Backyards area. The strip is faulted against Chlorite 2 surface semischists to the south-west and against unfossiliferous, deep-water greywackes to the north-east. Sediments within the strip are semi-isoclinally folded about axes that plunge moderately towards the southwest.
In the St. Mary Range, eight miles west of Kurow, Kaihikuan fossils occur in a largely overturned sequence of similar, but incipiently schistose sediments. A sequence of 3000 ft has been divided into 6 informal units - labelled M1 to M6. Although diagnostic Kaihikuan fossils are restricted to the upper 1200 ft, populous shellbeds of the trigoniid Agonisca are found throughout the full sequence, and define a zone extending north-west - south-east got at least 7 miles. These rocks are isoclinally folded about an anticlinal axis plunging gently north-west. Fossils are compressed perpendicular to cleavage.
Massive unfossiliferous greywackes, adjacent to and between the two areas of fossiliferous shelf sediments, would seem to have been deposited in deep water as they are intimately associated with undoubted turbidites. Reconnaissance structural observations would suggest that they are complexly folded about steeply plunging axes.
Thesis description:
100 leaves : illus., diagrs., maps (fold. in pocket) ; 27 cm.
Department:
OU geology Identifier:
1967Ryburn
OURArchive handle:
OURArchive access level:
Location (WKT, WGS84):
POLYGON ((170.367115240000089 -44.701216147999958,170.3717349530001 -44.713340813999935,170.371560619000093 -44.7196216899999,170.37152122800012 -44.721079451999969,170.371193667000057 -44.733020377999935,170.371190275000117 -44.733096835999959,170.370833066000046 -44.746059014999958,170.370274747000053 -44.766323322999938,170.231722366000099 -44.763630177999971,170.231249769000101 -44.763330808999967,170.181107609000037 -44.731359544999975,170.180647724000096 -44.731069263999984,170.011278615000037 -44.620779906999985,170.010891045000108 -44.620526775999963,170.012058319000062 -44.597831035999945,170.01245196800005 -44.59021334199997,170.013263241000118 -44.574433699999986,170.051219320000087 -44.570744289999936,170.08702177400005 -44.567253986999958,170.097224005000044 -44.566257895999968,170.140695973000106 -44.5822002699999,170.166580760000102 -44.591677850999986,170.178072264000093 -44.595883834999938,170.182977836000077 -44.597677843999975,170.203916553000113 -44.605333603999952,170.227977937000105 -44.614126959999965,170.23620199800007 -44.617141290999939,170.300628977000088 -44.640733886999953,170.302055533000043 -44.641257718999952,170.329489930000022 -44.663181296999937,170.357380513000066 -44.685450170999957,170.365829093000116 -44.697842068999933,170.367115240000089 -44.701216147999958))
Files
Collection
Citation
Ryburn, Roderick James., “Kaihikuan rocks at Corbies Creek and Mt. St. Mary, North Otago,” Otago Geology Theses, accessed May 15, 2025, https://theses.otagogeology.org.nz/items/show/28.