摘要:

Evolutionary theory is changing in response to two advances: (1) a reappreciation of the significance of the early appearance of most of the major functional designs of organisms (Bauplane) in the Late Precambrian and Early Palaeozoic, and (2) a new understanding of the way that genetic mechanisms, and indeed the genome itself, have changed during geological time. Neo‐Darwinism, the theory that has held sway as the theory of evolutionary mechanism since the early 1940s, is being seen as an explanation for only relatively small modifications of organisms, but not for the production of the major architectural plans. It has become apparent that a more general model of evolutionary mechanisms will have to be produced, and that data from the fossil record, and the interpretation of past environments, will be at a premium. The opportunity for geologists to contribute to the development of a new synthesis of evolutionary theory has never been greater.

ISSN:0812-0099    

DOI:10.1080/08120099008727925

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Two stalagmites from a limestone cave in the Florentine Valley, Tasmania, dated by14C and uranium series methods, provide an estimate of palaeotemperatures on the basis of18O/16O analysis. One of the stalagmites shows continuous deposition between 98 ka and 55 ka BP at a uniform rate of 20 mm/ka. The δ18O data which have a positive relationship with mean annual temperature indicate slightly higher than present day temperatures at 95 ka BP, followed by a gradual decline, culminating in a temperature minimum at about 62 ka BP. This was followed by a rapid temperature rise to a peak still below present‐day temperature at about 57 ka BP.

ISSN:0812-0099    

DOI:10.1080/08120099008727926

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ion microprobe and conventional U‐Pb analyses on single zircons from a felsic porphyry from the Wongan Hills Greenstone Belt in the Western Gneiss Terrain of Western Australia define an age of 3010 ± 7 Ma. This is a minimum age for volcanism in the greenstone belt. A sample of gneiss from near the belt contains two populations of zircons with ages of 2997 ± 47 Ma and 2800 ± 9 Ma. Theca3.0 Ga zircons are interpreted as dating the formation of the granitic parent of the gneiss, and theca2.8 Ga zircons are interpreted as dating gneiss formation. This latter event may be an early manifestation of the major 2.65–2.75 Ga granite‐greenstone episode which affected the entire Yilgarn Craton and is expressed at Wongan Hills by the emplacement of post‐tectonic porphyritic granite dated at 2651 ± 4 Ma, and greenschist facies retrogressive metamorphism, dated at 2646 ± 11 Ma by U‐Pb analyses of cogenetic sphene. The present results confirm the significance ofca3.0 Ga volcanism in the north and western Yilgarn Craton and suggest that this event was coeval with granitoid emplacement. No zircons older than 3.0 Ga, which would support models for an older crustal origin for these rocks, were found in the present samples.

ISSN:0812-0099    

DOI:10.1080/08120099008727927

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Recent work on Australian Tertiary macrofloras has highlighted the importance of the writings of early workers such as Ettingshausen and Deane; placing their localities in a modern stratigraphic context is an important preliminary to further work. The setting of these localities in New England is examined, and age constraints obtained from palynological and isotope studies are used to provide controls on the stratigraphy. A correlation table of Tertiary volcanic stratigraphy in the most significant areas is provided.

ISSN:0812-0099    

DOI:10.1080/08120099008727928

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Gordon Group carbonates consist of biota of the Chlorozoan assemblage, diverse non‐skeletal grains and abundant micrite and dolomite, similar to those of modern warm water carbonates. Cathodoluminescence studies indicate marine, meteoric and some burial cements. Dolomites replacing burrows, mudcracks and micrite formed during early diagenesis.

ISSN:0812-0099    

DOI:10.1080/08120099008727929

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Sedimentation on the northwestern margin of the Eucla Basin has been defined by drilling and palaeontological data to include Early Cretaceous to Miocene sequences. Channel, floodplain and lacustrine deposits of the Loongana Sandstone and Madura Formation indicate that the Early Cretaceous sea did not reach the Kitchener area. Middle to Late Eocene deposits unconformably overlie the Cretaceous sequence and extend up the Lefroy Palaeoriver towards Norseman where they merge with the Bremer Basin sediments. The Hampton Sandstone extends up the Lefroy Palaeoriver and was deposited under shallow high energy marine conditions probably in a well‐flushed large estuary. An erosional break at the top of the Hampton Sandstone and a wedge of fluvial sand in the Chifley palaeochannel provide evidence for a regression. The succeeding Late Eocene transgression covered wide areas around the Lefroy Palaeoriver and led to deposition of the Princess Royal Spongolite. Low oxygen levels and abundant silica, possibly derived from volcanic ash, allowed sponges to thrive in areas with restricted circulation on the basin margin while limestone accumulated in the sediment starved centre of the basin. The break between the Hampton Sandstone and Princess Royal Spongolite in the Harris Lake area is probably equivalent to the major sea level lowstand at 39.5 Ma.

ISSN:0812-0099    

DOI:10.1080/08120099008727930

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Three regional granite associations are resolved by a Sr isotopic traverse across the orogenic structures of southeastern Australia. The associations identified by geochronology and the distribution of maximum initial87Sr/86Sr ratios are (1) western — ∼500 Ma granites of southeastern South Australia with initial ratios up to ∼0.718; (2) central — 400 and 370 Ma granites of central Victoria with maximum initial ratios of ∼0.712; and (3) eastern — 415 Ma granites of the batholiths which parallel the eastern seaboard and have highest initial ratios of ∼0.720. Strontium isotopic compositions preclude granite magma formation by simple melting of a concealed Proterozoic basement comparable with that exposed in the interior of the continent; the latter would be far too radiogenic at the time of magmatism (87Sr/86Sr> 0.73). However, the maximum initial ratios of the western and eastern granite associations correspond to mean values for their respective enclosing Palaeozoic (meta)sedimentary terrains. This link extends to pseudoisochron diagrams of initial87Sr/86Sr vs87Rb/86Sr ratios on which the three associations have distinct trends. The granites are construed to define arrays between the local (meta)sedimentary basement points and a mantle‐like isotopic composition. Granite genesis is described by mixing between a melt derived from the local basement and basaltic material. Crustal sections in the western and eastern associations comprise equivalents of surficial Palaeozoic sequences down to the zone of magma generation. The central association in Victoria is interpreted to contain a concealed ‘isotopically juvenile’ granite source terrain underlying the Ordovician flysch and separated from it by a regional thrust fault. Boundaries between the three regional granite associations are considered the fundamental tectonic discontinuities in southeastern Australia.

ISSN:0812-0099    

DOI:10.1080/08120099008727931

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Four depositional settings interpreted from sedimentary fades associations are present in the non‐marine Early Cretaceous sequence of the Otway Basin: high energy fluvial, low energy fluvial, lacustrine and fluvio‐deltaic facies associations. Organic‐petrological investigation of Otway Group coals delineated four coal types with distinct assemblages of maceral subgroups and individual macerals. The coal types, designated A to D, occur with distinct assemblages of dispersed organic matter (dom) in associated clastics. Specific coal type assemblages in the Otway Group are closely related to changes in sedimentary facies, depositional energy exerting a primary control on the organic facies. High energy deposits of the Pretty Hill Formation and the upper part of the Eumeralla Formation are characterized by a single organic facies. Organic facies in the lower energy lacustrine deposits of the Casterton Formation and the lower part of the Eumeralla Formation appear to be sensitive to subtle changes in environmental settings.

ISSN:0812-0099    

DOI:10.1080/08120099008727932

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120099008727933

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120099008727934

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor