The Fauna of The Pahi Greensands
General collection, including G.S. Localities 544 and 732 and Dr Marshall's collection.
G.S. Localities 3292 and 3327, Pahi Peninsula, West Shore.
G.S. Locality 3289, Coates' Landing, Hukatere Peninsula.
|Nucula cf. sagittata Suter||X||A|
|Nuculana (Saccella) semiteres (Hutton)||X||X||A, B|
|Nuculana (Saccella) pahiensis n.sp.||X||X||A|
|Nuculana (Jupiteria) ferrari n.sp.||X||X||A|
|Neilo cf. sinangula Fin.||X||A|
|Cucullaea cf. waihaoensis Allan||X||X||A, D|
|Limopsis cf. campa Allan||X||X||A. D|
|Serripecte n.sp. aff. tioriensis Marwick||X||C|
|Cubitostrea gudexi (Suter)||X||X||A, B|
|Pinna cf. distans Hutton||X||X||A, B, D|
|Venericardia healyi n.sp||X||X||C|
|Venericardia bartrumi n.sp||X||X||A, D|
|Lucinoma arapaoa n.sp||X||X||A, D|
|Divaricella (Divalucina) notocenica King||X||A|
|“Angulus” pahiensis n.sp||X||X||A|
|Finlayella marshalli n.sp||X||X||X||A, D|
|Dosinia (Kakahuia) n.sp||X||A, D|
|Marama (Hina) sp.||X||X||X||D|
|Hedycardium brunneri (Hector)||X||A|
|Notocorbula aff. humerosa (Hutton)||X||A|
|Offadesma marwicki n.sp||X||A|
|Panope worthingtoni Hutton||X||X||X||A, B, D|
|Zeacolpus n.sp||X||X||X||A, B|
|Monalaria concinna (Suter)||X||X||A, B|
|Sigapatella n.sp. aff. mapalia Marw||X||X||X||A, B|
|Magnatica. cf. fons Finlay||X||X||A, B|
|Cypraea (? Eocypraea) murdochi n.sp.||X||B|
|Cypraea (? Bernayia) n.sp.||X|
|Tatara pahiensis (Marshall)||X||A|
|Falsicolus n.sp. cf. allani Fin||X||X||X||A|
|Falsicolus cf. solidus Suter||X||A|
|Waihaoia suteri Marw||X||X||X||A, B, D|
|Eoturris cf. neglectus (Suter)||X||A.|
|Marshallaria, aff. spiralis (Allan)||X||A|
|Notogenota pahiensis Powell||X||X||A|
|Speightia spinosa (Suter)||X||B|
|Acteon cf. n.sp. B. (Finlay & Marwick, 1937)||X||A|
|Aturia (Brazaturia) n.sp||X||A, D|
|Laevidentalium cf. pareorense (P. and S.)||X||A|
|Carcharodon auriculatus (Blainville)||X||G|
|Odontaspis elegans (Agassiz)||X||C|
Facies and Conditions of Deposition. There are a number of different facies within the Pahi greensands at both localities, and some of the molluscan species are restricted to one or more of such facies. In the faunal list the lithology with which each species was associated is indicated by the following symbols:
Calcareous glauconitic silty sandstone.
Hard calcareous concretionary bands in A.
Coarse conglomerate with pebbles of dark green and black argillite in a gritty calcareous cement.
Shell rock; tightly packed mollusca in moderately hard glauconitic sandy limestone.
Tim fauna of A includes such forms as Nuculana, Divaricella, the Tellinidae, Hedycardium, Offadesma, Sigapatella, Austroassia, Galeodea, Falsicolus, Turridae, Act eon, suggesting sublittoral euraline waters of moderate depth, perhaps about 10 to 25 fathoms.
The concretions (B) have formed around cores of shell material probably in much the same way as noted by Bartrum (1917) in recent sediments at similar depths. Facies C and D represent current-scoured channels at similar depths, such as have been mapped by Powell (1937) in the Waitemata Harbour. Indeed, a shell-rock composed chiefly of Venericardia n.sp. represents conditions closely akin to his Venericardia-Tawera association, while the conglomeratic lenses (C) with a fauna of Serripecten, Venericardia, and pelagic sharks, are more suggestive of benthic conditions with strong bottom currents caused by tidal flow in confined channels (comparable with Powell's bottom formations, 3 to 3c) than of littoral deltaic conditions. Finlay (1939, p. 521, p. 538) has presented micropalaeontological evidence for the upper (= true) Bortonian age of the Pahi white marl, outcropping only half a mile from the greensands and associated rocks. If the greensands and marl are contemporaneous, the latter finegrained calcic facies represents a deeper deposit, below the limit of effective operation of bottom currents and waves, and the presence of such a rock as the lateral equivalent of the nearby sublittoral greensands and conglomerates emphasizes the poverty of terrigenous material supplied to the Bortonian seas. Conditions for the formation of glauconite are also claimed (Galliher, 1935) to occur where the deposition of marine sediments is slow in depths of 10 to 50 fathoms, so that the Pahi greensands may be considered merely a local bathymetric variant of the widespread fine-grained deeper-water sediments comprising part (at least) of Ferrar's Onerahi Series, the distinction being due more to their relations to the wave base than to differences in the supply of sediment.
One further stratigraphical implication may be noted. Ferrar (1934, p. 35) mapped the Pahi greeusands, and other similar rocks (see, for example, a note under Lopha gudexi Suter below) in his Whangarei Series and then used the Pahi fauna as evidence of the Eocene age of part of that series. The Whangarei Series, as typically developed, consists of basal coal-measures unconformably overlying older rocks followed by a marine sequence and, though there is little definite faunal evidence of the age of the Whangarei beds, it is probable that their basal members represent, in North Auckland, the Whaingaroan (mid Oligocene) transgression so widespread in South-West Auckland. The Whangarei beds certainly follow the Onerahi sediments after a period of non-deposition, possible injection of peridotites, and erosion, and the association of the Pahi Eocene green-sands with the Onorahi beds allows such a period (the Kaiatan Stage, Upper Eocene) for elevation prior to the Whaingaroan transgression.
Finlay and Marwick (1940, pp. 109, 110) have noted the rarity of Kaiatan (“Tahuian”) sediments in the North Island, and it is possible, in view of the above considerations, that the early Tertiary orogeny in North Auckland (Bartrum and Turner, 1929) may prove to fill the gap in North Auckland stratigraphy representing the Tahuian and Kaiatan Stages (now considered synonymous) of the Upper Eocene.