Regolith framework in the Albany-Fraser Orogen/Yilgarn Craton Margin

[摘要] A new conceptual model of the Albany-Fraser Orogen/Yilgarn Craton margin as a paleocoastline with numerous islands and estuarine zones is proposed based on an integrated interpretation of the data presented in this report. The model involves extensive erosion, sedimentation and saprolite development taking place in different styles.“On inland” and “on island” weathering profiles may vary in maturity and saprolite development, with or without a transported cover derived from exotic marine sediments and/or limestones, and also from sediments of the Yilgarn Craton. Such areas are more reliable for understanding geochemical anomaly - basement relationships, whereas the “sea-flooded” areas would require a more thorough and detailed investigation as a result of sediment mixing, mechanical dispersion, rejuvenated weathering profiles and short-term vertical element dispersion processes.Within the above framework, the following four different regolith settings with diverse regolith architecture have been identified and defined. The settings have been named on the type locations where they are best developed. (1) Albany setting: Region dominated by shallow weathered profiles with thin minimum regolith thickness (0-15 m) and abundant basement outcroppings. This regolith stratigraphy is mainly developed at elevations 200 m above sea level. Below this level, erosional features and transported deposits are more abundant, thereby completely removing the saprolite package.(2) Kalgoorlie-Norseman setting: Region dominated by intensely and deeply weathered profiles, with relict landscape having abundant erosional breaks and variable thick regolith profile 20 m. Abundant inverted channels produced by the differential resistance to erosion of the ferruginised channel deposits of paleodrainage networks. Saline lakes, as remnants of paleodrainage are common, concentrating saline groundwater as modern landscape water collectors in combination with elevated evaporation rates.(3) Esperance setting: Regolith dominated by sand dunes with thin surface regolith stratigraphy exposed (5 m). An increased transported cover of the sand dunes systems at the shoreline up to ~20 m thick. Saprolite develops from granitic-gneisses at depth and progresses forming pisolitic units that are overlain by transported sands in packages 2 m thick. In this regolith setting, newly-formed units of ferruginous sandstone occur within the transported sand dune packages. This horizon accumulates transition metals, whereas gold is anomalous in the upper sandy units.(4) Neale setting: Relict, deeply weathered saprolitic profile with the regolith commonly comprising in situ deeply weathered profiles overlain by a transported blanket (2-25m thick). The in situ regolith profile consists of four units from base to top, namely, saprock, dominated by partially weathered granitoids, gneisses and mafic rocks; lower ferruginous saprolite (3-25 m thick) dominated by quartz, feldspars, kaolinite, and goethite after ferromagnesian and sulfide minerals; upper kaolinitic saprolite (10-40 m) dominated by quartz and kaolinite; and silcrete/grit layer (4-20 m thick).In summary, any geochemical sampling, data interpretation and remote sensing technique applied in the region should be framed, and its efficacy evaluated, within regional data of groundwater salinity, pH-Eh, average annual rain fall and geomorphological-sedimentary environment.Mapping the paleocoastlines, islands and estuarine zones, as well as the region of sea limestone/sediment influence, would have remarkable impact for a more efficient planning and implementation of exploration campaigns in the region.

[发布机构] CSIRO

[效力级别] Geomorphology and Regolith and Landscape Evolution [学科分类] 地球科学(综合)