Cainozoic igneous activity in eastern australia

During the Cainozoic there was widespread basaltic igneous activity in eastern AustraIia along and adjacent to the Eastern Highlands. The activity commenced about 70 m.y. ago, and has continued through the Cainozoic at a nearly constant rate. More than fifty igneous provinces are recognized. Each province consists of similar volumes of volcanic material and crustal intrusives, the volcanism generally lasting less than 5 m.y. and resulting in lavas that cover a region 50–200 km across. Three main types of igneous province are recognized:

1. (1) central volcano provinces, which are composed predominantly of slightly undersaturated to saturated basaltic lavas, but with some felsic flows and intrusions;

2. (2) lava field provinces, which consist of basaltic flows, commonly strongly undersaturated;

3. (3) a single, mafic, strongly undersaturated, high potassium province.

Within each type of province the average potassium content of the lavas has not changed with time. Most provinces are consistent with an apparent migration of volcanism westward at 5 mm/year across the Eastern Highlands. This migration is thought to be caused by crustal processes. The distribution and age of the slightly undersaturated provinces suggest a migration of the centre of volcanism southward at 66 ± 5 mm/year. Magmas for these provinces are thought to originate from a magma source or sources, with a limited latitudinal extent, within the asthenosphere. The migration is considered to be related to the movement of the Indian (Australian) lithospheric plate relative to the underlying asthenosphere.     

Feldspathoidal rocks from the Cainozoic volcanic province of Ethiopia

A review of the occurrence of feldspathoidal rocks in the Cainozoic volcanic province of Ethiopia is given. Ijolite and melanephelinite are described for the first time from this province. The close relationship between cross-rift transcurrent faults and situation of peralkaline rocks, including the feldspathoidal varieties, is emphasized. No feldspathoidal rocks are known from within the Ethopian rift system, being restricted to the interiors of the Ethiopian and Somalian plateaux.     

The Cainozoic geology of the Middle Shoalhaven Plain

The Middle Shoalhaven Plain is a large, tray‐like depression bounded in the west by the Mulwaree fault and in the east by cliffed Permian sediments. The plain is probably Mesozoic in origin and was partially alluviated during the Early to mid‐Eocene. Much of the plain and sediments were covered by basalts during the Late Eocene. This was followed by an episode of deep weathering, which culminated in the formation of widespread bauxitic and lateritic crusts and manganocrete and silcrete during the mid‐Tertiary. A second minor weathering event is recorded during the latest Tertiary to Early Pleistocene. Two new basalt dates are consistent with earlier ones at about 43 Ma. Palaeomagnetism shows bauxites and ferricretes to be mid‐Tertiary.     

Late Cainozoic activity of the Selwyn Upwarp,Northwest Queensland

An examination of river patterns in northwest Queensland shows that they have recently changed their habit from meandering to braided. This change is attributed to uplift of the Selwyn Upwarp in the late Pleistocene and early to middle Holocene.     

中、新生代吉安盆地沉积环境浅析

运用沉积物物理、化学、生物参数,分析吉安盆地的沉积环境,取得了显著效果,为古沉积环境分析积累了经验,在阐述吉安盆地沉积相,古生物及岩石地球化学的基础上,着重对古气候,古地理进行了探讨。     

Distribution of Cainozoic foraminiferida in the Scott Reef No. 1 well,Western Australia

Micropalaeontological investigation of samples from Scott Reef No. 1 has revealed a thick Cainozoic carbonate sequence. Rich planktonic faunas have enabled the identification of Lower Miocene to Oligocene (N6 to P19) and Lower Eocene to Lower Palaeocene intervals (P6 to Pic). The remainder of the succession has been dated on benthonic evidence and spot age‐determinations on isolated planktonic occurrences. The palaeoenvironmental history of the Cainozoic sequence appears to be regressive from a bathyal situation in the Palaeocene through indeterminate marine Eocene, bathyal to inner shelf Oligocene to Middle Miocene, to reefal conditions which have persisted from the Middle Miocene to the present day.     

Palaeomagnetic dating and stratigraphy of a Cainozoic lake near Cooma,N.S.W.

Palaeomagnetic dates for two sites on the Southern Tablelands of New South Wales, at Bunyan and Bredbo, indicate that basal lake sediments and underlying bedrock were ferruginised during the late Tertiary. The dates provide further evidence of a regional episode of intense weathering and ferruginisation in the late Tertiary.     

Some observations on diamondiferous bedrock gully trapsites on Late Cainozoic, marine-cut platforms of the Sperrgebiet, Namibia

Namibia's southwestern coast, the Sperrgebiet, hosts one of the world's largest gem diamond placer deposits consisting of fluvial, marine and desert deflation/aeolian placer types. To date, the richest onshore placer discovered in the Sperrgebiet comprises several, Plio-Pleistocene to Holocene, littoral marine packages distributed northwards from the Orange River mouth for some 120 km to Chameis Bay. In this zone, known as Mining Area No. 1 (MA1), these Quaternary marine deposits are floored predominantly by siliciclastic rocks of the Late Proterozoic Gariep Belt that have been bevelled into a number of marine-cut platforms during the different Quaternary high sea level stands (notably, at + 30 m, + 8 m, + 4 m and + 2 m). In many places, these bedrock platforms are extensively gullied and potholed, forming abundant fixed trapsites that promote diamond concentration in the Late Cainozoic littoral sediments. Some observations on the distribution, orientation and incision of bedrock gullies in MA1 are presented here.Three principal bedrock gully types, all of which constitute good diamond trapsites, have been identified in the bedrock footwall between the Orange River mouth northwards to Chameis Bay, a distance of some 120 km: (i) swash-parallel gullies in the southern, proximal sector where the bedrock s₂ dips 45°W and the abrasive gravels are most abundant, thus overriding lithological and structural controls in the footwall; (ii) strike-parallel gullies in the central reach where the bedrock s₂ dips between 80° and 85°W and the abrasive bedload is reduced, resistant lithological units promote the formation of such features along the orientation of the metsediments; and (iii) joint gullies in the northern, distal portion where the bedrock s₂ dips 45–60° to the E and coarse abrasive bedload is virtually absent, the structural pattern in the bedrock is exploited by marine erosion.In these Late Cainozoic placers, diamond concentration is further linked to the depth of the gullies incised into the marine-cut platforms. Maximum incision is noted on the seaward margins of the marine-cut platforms where high-energy littoral processes, acting in a micro-tidal range of ca. 1.8 m under strong prevailing southerly wind and South Atlantic derived southwesterly swell regimes, promote marine erosion and deep gully formation.Therefore, the most favourable diamondiferous trapsites in the Late Cainozoic marine packages of the southwestern Sperrgebiet are those developed in deep bedrock gullies of either swash-parallel, strike-parallel or joint pattern origin on the seaward margins of marine-cut platforms that represent discrete high sea level stands during the Quaternary.     

Cainozoic Stratigraphy of the lake Eyre basin and part of the arid region lying to the South

The Cainozoic history of the Lake Eyre region opened with a period of deep weathering during which many of the older rocks were extensively kaolinized. Following erosion and later deposition of a thin sheet of Tertiary fluviatile deposits, a period of weathering resulted in the widespread formation of silcrete. Another period of erosion and deposition was followed by soil formation and minor silici‐fication.

An important period of erosion followed during which some of the main elements of the present landscape were outlined. Warping during this interval gave rise to shallow basins in which lacustrine sediments accumulated. At about the same time, a system of mound springs developed near the western margin of the Great Artesian Basin. Another major period of erosion followed, by which time the main topographic features of the present landscape had evolved. This last event probably took place near the close of the Tertiary. Throughout the Tertiary, drainage was external and ancestral Lake Eyre remained fresh.

The Quaternary was characterized by four periods of aeolian and, to a lesser extent, water erosion and deposition alternating with periods of landscape stability, when weathering and soil formation took place.

Throughout the Cainozoic there was an alternation of relatively humid and dry periods, but true aridity and internal drainage did not appear until the Quaternary. Sand ridges were not formed until the late Quaternary. Intervals of gentle warping occurred from time to time during the Tertiary, but the Quaternary has for the most part been a period of stability. These events have given rise to a sequence of distinctive rock and soil‐stratigraphic units whose characteristics are considered in some detail.     

Late Cainozoic geology,soils, and landscape evolution of the Torrens Creek area,North Queensland

The major features of the geology and geomorphology of the semi‐arid, tropical Torrens Creek area of North Queensland are described. The evolution of the landscape through the late Cainozoic is discussed with reference to three phases of landscape instability and erosion, each separated by phases of stability during which weathering and soil formation proceeded. These erosional periods were probably initiated by episodic uplift of the Great Divide region. Tentative correlations with landscape events in the nearby Nulla Basalt Province suggest that soil profile development probably occurred during late Pliocene (2.3–2.0 m.y. ago), mid‐Pleistocene (1.3–1.1 m.y. ago), and in Quaternary (less than 0.1 m.y. ago) times.