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ItemSilurian trilobites of central Victoria(University of Melbourne, 1996)
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ItemNo Preview AvailableEarly Cretaceous plant biofacies of the Otway and Strzelecki groups, Victoria(University of Melbourne, 2000)The non-marine sediments of the Otway and Strzelecki groups were deposited in the Otway and Gippsland basins, respectively. The basins formed as a result of rifting of Australia from Antarctica during the breakup of east Gondwana, when southeastem Australia was located at approximately 70�S. These sequences incorporate the most continuous record of Early Cretaceous fossil plant assemblages in the Australasian region. They incorporate important reference sections for Australian Early Cretaceous palynostratigraphic and macrofloral biostratigraphic schemes. This study represents the first interdisciplinary investigation using sedimentology and macro- and mesofloral assemblages (biofacies) to assess geographical and temporal changes in fluvial depositional environments and floras within the Lower Cretaceous succession. Measurement of detailed stratigraphic sections and geological mapping resolved stratigraphic relationships within the Neocomian successions of the lowermost Strzelecki Group exposed in the Tyers area, north of Traralgon, Gippsland Basin. This Neocomian portion of the Strzelecki Group is here assigned to the Tyers River Subgroup, incorporating two formations: Tyers Conglomerate and Rintoul Creek Formation. The latter formation is further divided into the Locmany and Exalt members. These units were deposited contemporaneously with the Casterton Formation and Crayfish Subgroup of the Otway Group and are dominated by similar quartzose and lithic sandstones. The sediments were predominantly sourced from the Lachlan Fold Belt to the north. The Aptian-Albian succession is lithologically monotonous in both basins and no further lithostratigraphic subdivision is presently possible. However, this part of the succession is dominated by feldspathic sandstones and together with predominantly westerly-directed palaeocurrents, denotes a major readjustment in drainage systems within the basins after the Neocomian. Fourteen lithofacies characterize distinctive non-marine depositional environments within the Lower Cretaceous sequences and can be assigned to three facies associations characteristic of predominantly braided fluvial systems. Twenty-one biofacies were recognized throughout the Neocomian-Albian on the basis of distinctive macro- and mesofossil associations and preservational characteristics. These biofacies represent distinctive biological associations controlled by both the composition of parent terrestrial communities and taphonomic sorting processes. Biofacies within each major stratigraphic interval (Neocomian, Aptian-lowermost Albian, middle-upper Albian) can be compared closely to one or more biofacies from each of the other intervals, the main contrasts being differences in representation of key species. The recognition of comparable biofacies and lithofacies within each biostratigraphic interval allows interpretation of the evolution of particular depositional environments and plant communities within these lowland basins throughout the Early Cretaceous. Silty fioodbasin deposits are consistently represented by fern-dominated assemblages. Levee and drier floodbasin environments are dominated by small-leafed conifers (Otwayia and Brachyphyllum) in the Neocomian but are gradually replaced by broad-leafed araucarian conifers in the Aptian and Albian. Plant communities occupying floodbasin environments of intermediate substrate moisture levels and fertility are dominated by seedferns and Elatocladus in the Neocomian but are replaced by ginkgophytes in the Aptian, and cheirolepids and podocarps in the Albian. Channel deposits show consistently detrital fossil assemblages. Assemblages within these settings differ in their proportion of woody material, megaspores, fragmentary cuticle and animal secretions/excretions due to fluvial sorting processes. Fossils in these deposits may he derived from a broad range of floodbasin, riparian and even upland community types. Floristic composition and foliar physiognomy in conjunction with palaeomagnetism, isotopic data and sedimentological features suggest that climates underwent a slight cooling from the Neocomian to Aptian with a return to warmer conditions in the Albian. However, application of angiosperm-based morpho-climatic models to the Early Cretaceous floras are inappropriate as many of the Mesozoic gymnosperms belong to extinct groups for which environmental tolerances are poorly known. Documentation of the temporal and fades constraints on plant taxa confirms that the Phyllopteroides laevis, P. serrata and P. dentata macrofloral zones, established by previous workers, represent useful biostratigraphic units. However, some qualifications to their application are needed to take into account facies controls on the distribution of index taxa. The previously established palynostratigraphic and macrofloral biostratigraphic schemes are broadly supported by the establishment of a new biostratigraphic zonation based on abundant and diverse lycophyte and fern megaspores.
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ItemNo Preview AvailableEarly Cretaceous plant biofacies of the Otway and Strzelecki groups, Victoria(University of Melbourne, 2000)The non-marine sediments of the Otway and Strzelecki groups were deposited in the Otway and Gippsland basins, respectively. The basins formed as a result of rifting of Australia from Antarctica during the breakup of east Gondwana, when southeastem Australia was located at approximately 70�S. These sequences incorporate the most continuous record of Early Cretaceous fossil plant assemblages in the Australasian region. They incorporate important reference sections for Australian Early Cretaceous palynostratigraphic and macrofloral biostratigraphic schemes. This study represents the first interdisciplinary investigation using sedimentology and macro- and mesofloral assemblages (biofacies) to assess geographical and temporal changes in fluvial depositional environments and floras within the Lower Cretaceous succession. Measurement of detailed stratigraphic sections and geological mapping resolved stratigraphic relationships within the Neocomian successions of the lowermost Strzelecki Group exposed in the Tyers area, north of Traralgon, Gippsland Basin. This Neocomian portion of the Strzelecki Group is here assigned to the Tyers River Subgroup, incorporating two formations: Tyers Conglomerate and Rintoul Creek Formation. The latter formation is further divided into the Locmany and Exalt members. These units were deposited contemporaneously with the Casterton Formation and Crayfish Subgroup of the Otway Group and are dominated by similar quartzose and lithic sandstones. The sediments were predominantly sourced from the Lachlan Fold Belt to the north. The Aptian-Albian succession is lithologically monotonous in both basins and no further lithostratigraphic subdivision is presently possible. However, this part of the succession is dominated by feldspathic sandstones and together with predominantly westerly-directed palaeocurrents, denotes a major readjustment in drainage systems within the basins after the Neocomian. Fourteen lithofacies characterize distinctive non-marine depositional environments within the Lower Cretaceous sequences and can be assigned to three facies associations characteristic of predominantly braided fluvial systems. Twenty-one biofacies were recognized throughout the Neocomian-Albian on the basis of distinctive macro- and mesofossil associations and preservational characteristics. These biofacies represent distinctive biological associations controlled by both the composition of parent terrestrial communities and taphonomic sorting processes. Biofacies within each major stratigraphic interval (Neocomian, Aptian-lowermost Albian, middle-upper Albian) can be compared closely to one or more biofacies from each of the other intervals, the main contrasts being differences in representation of key species. The recognition of comparable biofacies and lithofacies within each biostratigraphic interval allows interpretation of the evolution of particular depositional environments and plant communities within these lowland basins throughout the Early Cretaceous. Silty fioodbasin deposits are consistently represented by fern-dominated assemblages. Levee and drier floodbasin environments are dominated by small-leafed conifers (Otwayia and Brachyphyllum) in the Neocomian but are gradually replaced by broad-leafed araucarian conifers in the Aptian and Albian. Plant communities occupying floodbasin environments of intermediate substrate moisture levels and fertility are dominated by seedferns and Elatocladus in the Neocomian but are replaced by ginkgophytes in the Aptian, and cheirolepids and podocarps in the Albian. Channel deposits show consistently detrital fossil assemblages. Assemblages within these settings differ in their proportion of woody material, megaspores, fragmentary cuticle and animal secretions/excretions due to fluvial sorting processes. Fossils in these deposits may he derived from a broad range of floodbasin, riparian and even upland community types. Floristic composition and foliar physiognomy in conjunction with palaeomagnetism, isotopic data and sedimentological features suggest that climates underwent a slight cooling from the Neocomian to Aptian with a return to warmer conditions in the Albian. However, application of angiosperm-based morpho-climatic models to the Early Cretaceous floras are inappropriate as many of the Mesozoic gymnosperms belong to extinct groups for which environmental tolerances are poorly known. Documentation of the temporal and fades constraints on plant taxa confirms that the Phyllopteroides laevis, P. serrata and P. dentata macrofloral zones, established by previous workers, represent useful biostratigraphic units. However, some qualifications to their application are needed to take into account facies controls on the distribution of index taxa. The previously established palynostratigraphic and macrofloral biostratigraphic schemes are broadly supported by the establishment of a new biostratigraphic zonation based on abundant and diverse lycophyte and fern megaspores.