Mid Miocene Research Articles

Plate tectonic significance of Late Oligocene/Early Miocene deep sea sedimentation at Maewo, Vanuatu (New Hebrides)

Eight lithofacies representing a westward trending, deep sea fan, dominantly deposited from mass flow mechanisms, are recognised in geologic sections in the lower part of the Sarava Formation, of Late Oligocene/Early Miocene age, on Maewo Island, Vanuatu, New Hebrides. Also present representing the floor on which the deep sea fan prograded are non-calcareous, red siltstone and minor green siltstone which indicate deposition beyond the calcareous compensation depth, i.e. a depth greater than 4.25 km, and rare thin airfall ash. Previous workers proposed that rifting occurred in the area now occupied by Maewo during the Mid Miocene. However, the great depth at which the Late Oligocene/Early Miocene strata were deposited suggests that rifting occurred prior to the Late Oligocene. Rifting may have occurred even earlier because Pentecost Island, which lies south of Maewo, has a dismembered ophiolite suite which ranges in age from 35-28 Ma (Oligocene). The ophiolite suite may have formed in an interarc environment. The writer's reconstruction of the Oligocene arc system of the New Hebrides is an analogue of the present day Mariana Arc System. Interarc rifting ceased by the Early Miocene and during the Mid-Late Miocene the subduction of zone may have migrated westwards to lie along the Maewo-Pentecost axis.

Volcanic geology of the Waipoua area, Northland, New Zealand

Abstract Waipoua Basalt Formation is closely associated with coeval mid Miocene sediments of Waipoua Subgroup. The formation consists of lava flows (2–25 m thick), typically separated by layers of tephra (up to 2 m thick), and intruded by dike swarms in a zone extending 15 km north from Maunganui Bluff. Lava from both flows and dikes is a glomeroporphyritic plagioclase-olivine-augite basalt. In the Kaihu area Whatoro Breccia Member (new) is a breccia of assorted igneous Hthologies, mostly of Waipoua Basalt origin, in a tuffaceous matrix. Although eruption may have occurred in the dike-intruded zone, evidence suggests that the main volcanic centre lay a short distance offshore from Maunganui Bluff.

Eruptive history of the early to mid miocene Waitakere volcanic arc, and palaeogeography of the Waitemata Basin, Northern New Zealand

Abstract Geophysical anomalies, volcaniclastic basinal sediments and exposures of intrusive and extrusive igneous rocks (Waitakere Group) indicate that a line of volcanoes (Waitakere Volcanic Arc) was active along west Northland during early and mid Miocene times (22–15 m.y. B.P.). The Arc is inferred to have been generated above a west-dipping Benioff zone that paralleled the boundary between the Indian and Pacific plates. The region between the Arc and a postulated eastern trench (arc-trench gap) consisted of a terrestrial basement high, an elongate basin (Waitemata Basin) and a northern land mass. Calc-alkaline volcanism was active at at least three major centres along the Arc and began in the Waitakian and early Otaian, supplying volcanic detritus to the Waitemata Basin. The two southern centres were the most active, continuing to erupt well into the Altonian. Eastward advance of the active margins of these centres and associated uplift, first at Kaipara and later in the Waitakere Ranges, saw bathyal ...

Cainozoic sedimentation in basins adjacent to a major continental transform boundary in southern New Zealand

The Indo-Australian/Pacific plate boundary crosses the New Zealand continental block as the Alpine fault system, an oblique continental transform. Plate tectonic calculations for the SW Pacific imply the inception of this plate boundary in the latest Eocene. In western South Island, rapidly subsiding flysch basins were established at this time. Southeast of the Alpine Fault, basins developed along an active tectonic trend, the Moonlight Tectonic Zone. Early Oligocene infilling by thick submarine fan sequences was accompanied by regional subsidence, so that by late Oligocene, deep marine mudstone was dominant in basins and limestone on adjacent shelf areas. In contrast, early to mid Miocene time was characterized by contemporaneous uplift and subsidence, with tectonic activity on basin margins and development of new source areas adjacent to the Alpine Fault. Reverse faulting, folding and uplift developed at about 12 Ma and continues today. The sedimentary history is consistent with the development of the plate boundary from a zone of slow oblique extension, to a through-going continental transform, to a compressive transform system. Continental transform boundaries appear to be characterized by small, tectonically active basins, and by a complex tectonic history, particularly when close to the pole of relative rotation. Although difficult to recognise, they may be important in the geologic record.

A new owlet night–jar from the early to mid–Miocene of eastern New South Wales

A new owlet night–jar from the early to mid–Miocene of eastern New South Wales

Phylogenetic position of the southern rock lizard Australolacerta australis within the Lacertidae radiation

The southern rock lizard Australolacerta australis is a rock-dwelling lizard endemic to South Africa. The phylogenetic relationships of this species with other lacertid lizards are still not clear and have never been assessed in any phylogeny of Lacertidae using DNA sequence data. In this study we employed 3 044 base pairs from mitochondrial cytochrome b, 12S and 16S rRNA genes to investigate the phylogenetic position and the evolutionary history of A. australis. We performed phylogenetic analyses under the assumptions of Maximum Likelihood and Bayesian inference and estimated the timing of the cladogenic events related to A. australis by using a relaxed molecular clock method. Our phylogenetic reconstruction clearly placed A. australis within the southern African branch of the tribe Eremiadini including genera Tropidosaura, Meroles, and Pedioplanis. The former genus constitutes with A. australis a clade endemic to southernmost mountains of Africa. The radiation of this southern African clade is estimated to have occurred during the Mid Miocene (14.7–11.5 Mya), and it was likely due to the climate changes that occurred in the South African region at that time.