(1) University of Aberdeen, Aberdeen, United Kingdom
Abstract: Genetic relationships between alluvial, shallow marine and deep-water sandstones elucidated by mineral-chemical stratigraphy
Alluvial basins are the ultimate source of almost all sand grains. During transportation and storage in alluvial basins the sensitivity of different minerals to the processes of weathering and erosion determines sand composition, generally dominated by quartz. Heavy minerals, although not abundant, provide a high-resolution record of changes that occurred during evolution of alluvial basins. In the rock record variations in heavy mineralogy and their associated trace element geochemistry are useful lithostratigraphic data that, in alluvial basins, resolve stratigraphic units on a meter-scale. Shallow marine sandstones have lower frequency variations (decimeter-scale) and are generally more homogeneous mineral-chemistry than alluvial sandstones. Their mineral-chemical signature is interpreted to have formed from a more diverse mineral-chemistry derived from adjacent alluvial systems by sedimentary reworking and mixing on the shallow marine shelf. Deep-marine sandstones may have high or low frequency variations in mineral-chemistry. Where high-frequency mineral-chemical variations are present they have similar meter-scale frequency to alluvial sandstones.
The similar frequency between deep-water and alluvial sandstones is interpreted to reflect a direct derivation of sand in a deep-water system from an alluvial basin (bypass of any contemporary shallow marine shelf). More homogeneous mineral-chemical signatures in deep-marine system are interpreted to reflect the derivation of sand from an adjacent shallow marine shelf. Thus, in deep-marine systems mineral-chemistry has the potential for differentiating between sand derived by shelf bypass or from the shelf. By focussing on stable minerals and low solubility trace elements possible diagenetic affects can be excluded.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana