Stratigraphy and sedimentation of the Caversham formation at Puketeraki, Karitane Peninsula and Matanaka farm, Northeast Otago, New Zealand

Toha, Budianto.

Stratigraphy and sedimentation of the Caversham Formation at Puketeraki, Karitane Peninsula, and Matanaka Farm have been studied using vertical profile analysis. The study places emphasis on micropaleontology; sedimentology, including carbonate-terrigenous sediments ratio, grainsize analysis of the terrigenous sand fraction, sedimentary petrography and provenance; and sequence stratigraphy. Three measured sections, totalling 95 meters in thickness, are considered to represent a complete section through the onland stratigraphy of the Caversham Formation of East Otago. The sections, therefore, are proposed either as a supplement to the original reference sections or as standard sections.
The Caversham Formation is characteristically a uniform greyish-white, mixed carbonate-siliciclastic rock which is yellowish when weathered and in which bioclastic and quartz grains are dominant. The carbonate content ranges from 27% to 77%, terrigenous sand from 5% to about 40%, and terrigenous mud from about 25% to 52%. Heavy minerals include zircon, apatite, epidote, garnet, rutile, and opaques. Terrigenous sediments are most likely derived from Haast Schist, Fiordland and Stewart Island (Western Province). Bedding planes are generally visible only in large, somewhat weathered, outcrops such as high seacliffs. Overall, the vertical section indicates a coarsening upward interval which is succeeded by fining upward, suggesting a shallowing and deepening upward facies succession.
The base of the Caversham Formation is characterized by irregular erosion surface (either scoured structures or bioerosion) with glauconite sand, bioclastics and calcareous nodule resting on it. The lower member ( Puketeraki section) is made up of high frequency cyclothems dominated by alternating "hard-soft" beds of muddy allochemic limestone and intercalated allochemic mudrock. This member was deposited during Otaian to early Altonian times, and corresponds to a period of gradual shallowing upward from outer shelf to mid-outer shelf. The middle member (Karitane Peninsula section) consists of heterolithic bedded allochemic sandstone, muddy allochemic sandstone, sandy allochem limestone, and muddy allochem limestone. This member was deposited during middle Altonian time and coincided with ensuing shallowing upward from middle to inner shelf, possibly in a storm dominated environment. The upper member ( Matanaka Farm section ) which is composed of a poorly bedded muddy allochem limestone, muddy micrite, and carbonaceous micritic shale was deposited during late middle Altonian time in response to deepening water from inner to mid-outer shelf. This upper member is unconformably overlain by the Goodwood Limestone, forming a gentle angular discordance surface.
The sequence stratigraphy concept is applied with limited success to the Caversham Formation. The formation can be subdivided into two depositional sequences, namely S 1 and S2. The first sequence consists of a typical highstand system tract (HST) which shows a coarsening and shallowing upward facies succession from Puketeraki to Karitane Peninsula sections. This sequence rests on a condensed section of the Concord Greensand, and terminates in a type 2 sequence boundary. The second sequence which rests on the type 2 sequence boundary indicates a fining upward facies succession and can be subdivided into shelf margin wedge (SMW) and transgressive system tract (TST) units. This sequence comprises the upper Karitane and Matanaka sections, and is overlain by a condensed section/ maximum flooding surface (MPS). While deposition of the Caversham Formation seems to correspond to a period of gradual global rise in sea-level which peaked at about 16 Ma, near the base of the Clifdenian Stage, the likely overriding control was exerted by tectonism with periodic uplifting of basement blocks due to reactivation of the Titri and Waihemo Fault Systems beginning in early Miocene time.
Due to variation in rock composition, the use of term "Caversham Sandstone" (Benson, 1969) for this unit is inapproriate, and "Caversham Formation" is proposed for its subtitution.

vi, 142 leaves (some folded) : col. ill., maps ; 30 cm.

1993Toha