Regional trends in clay mineral fluxes to the Queensland margin and ties to middle Miocene global cooling

Abstract

Three ODP sites located on the Marion Plateau, Northeast Australian margin, were investigated for clay mineral and bulk mineralogy changes through the early to middle Miocene. Kaolinite to smectite (K/S) ratios, as well as mass accumulation rates of clays, point to a marked decrease in accumulation of smectite associated with an increase in accumulation of kaolinite starting at 15.6 Ma, followed by a second increase in accumulation of kaolinite at~13.2 Ma. Both of these increases are correlative to an increase in the calcite to detritus ratio. Comparison of our record with published precipitation proxies from continental Queensland indicates that increases in kaolinite did not correspond to more intense tropical-humid conditions, but instead to periods of greater aridity. Three mechanisms are explored to explain the temporal trends in clay on the Marion Plateau: sea-level changes, changes in oceanic currents, and denudation of the Australian continent followed by reworking and eolian transport of clays. Though low mass accumulation rates of kaolinite are compatible with a possible contribution of eolian material after 14 Ma, when Australia became more arid, the lateral distribution of kaolinite along slope indicates mainly fluvial input for all clays and thus rules out this mechanism as well as oceanic current transport as the main controls behind clay accumulation on the plateau. We propose a model explaining the good correlation between long-term sea-level fall, decrease in smectite accumulation, increase in kaolinite accumulation and increase in carbonate input to the distal slope locations. We hypothesize that during low sea level and thus periods of drier continental climate in Queensland, early Miocene kaolinite-rich lacustrine deposits were being reworked, and that the progradation of the heterozoan carbonate platforms towards the basin center favored input of carbonate to the distal slope sites. The major find of our study is that increase kaolinite fluxes on the Queensland margin during the early and middle Miocene did not reflect the establishment of a tropical climate, and this stresses that care must be taken when reconstructing Australian climate based on deep-sea clay records alone.

Diagenetic Implications of Stylolitization In Pelagic Carbonates, Canterbury Basin, Offshore New Zealand

“…Operating conditions for the first series were 45 kV and 40 mA, scanning range between 2.5u and 70u 2h, step of 0.02u 2h, and acquisition time of 2 seconds per step, while for the second series a scanning range between 2.5 and 40u (for air dried clay) or 2.5u and 26u 2h (for heated and glycolized clay), step of 0.015u 2h, and acquisition time of 1 second per step. Quantitative estimates of the minerals present in the bulk analysis are based on the equations derived from Cuff (1969) for mixtures of calcite with other minerals (quartz in this study), whereas the quantification of clay is based on John et al (2006).…”

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“…Kaolinite can crystallize in permeable sandstone 24 . The decrease of montmorillonite content, along with an increase in kaolinite and illite in the upper units, suggests that the climate changed and that there was a greater sediment supply from the land 25 .The magnetostratigraphy suggests the age of the lower lignite between 12.4 to 13.0 million years ago 6,7 . Thus, the climate changed at about 13 million years ago.…”

Observing the past to better understand thefuture: a synthesis of the Neogene climate inEurope and its perspectives on present climatechange

“…macromammal faunas [70], iv) vegetation changes (typically from evergreen to deciduous) [72,73], v) benthic foraminiferal oxygen isotope ratios (δ 18 O) [69,74], vi) subpolar planktonic foraminiferal species [69], vii) echinoderm fauna [50], viii) and others such as changes in the hydrological cycle and in water-atmosphere transfer energy [75,76]. In addition, δ 18 [59].…”