Late Cryogenian glaciation in South Australia:Fluctuating ice margin and no extreme or rapid post-glacial sea-level rise  

作　　者：George E.Williams Victor A.Gostin 

机构地区：[1]Department of Earth Sciences,University of Adelaide

出　　处：《Geoscience Frontiers》2019年第4期1397-1408,共12页地学前缘（英文版）

摘　　要：Postulated extreme sea-level rise of up to 1-1.5 km with the late Cryogenian Ghaub deglaciation in Namibia is contentious,as is the great rapidity(<104 yr)of the sea-level rise.Such extreme glacioeustatic events,if real,would have been global and affected all continents.In South Australia,up to six glacial advances and retreats during the late Cryogenian Elatina glaciation indicate a fluctuating ice margin.The latter stage of the Elatina glaciation and the immediate post-glacial environment are examined here for evidence of extreme and rapid sea-level rise.In the central Adelaide Rift Complex,diamictite with faceted and striated clasts occurs at the top of the Elatina Formation<1-2 m beneath the early Ediacaran Nuccaleena Formation’cap carbonate’.One hundred kilometres to the south,~30 m of siltstone and sandstone followed by^6 m of clast-poor diamictite with clasts 10+cm long occur between tidal rhythmites and the cap carbonate.Three hundred kilo metres further south,~70 m of siltsto ne,dolo mitic siltstone and minor dolomite separate tidal rhythmites and early Ediacaran strata.Hence the rhythmites were deposited during a high stand(interstadial or interglacial),not during post-glacial sea-level rise.Storm-generated erosional surfaces within tidal rhythmites at Warren Gorge indicate intermittent rhythmite deposition,and water depth and other palaeoenvironmental factors are uncertain,casting doubt on a published estimate of rapid sea-level rise during rhythmite deposition.The lack of late Cryogenian deeply incised valleys and thick valley-fill deposits in South Australia and central Australia argues against extreme sea-level variations.A hiatus occurred between Elatina deglaciation and deposition of the Nuccaleena cap carbonate,and three palaeomagnetic polarity chrons identified in the cap carbonate imply slow deposition spanning 10^5-10^6 yr.This is supported by independent evidence from magnetic chronostratigraphy for Ediacaran strata in South Australia and California,and by stratigraphic and sedimentologicPostulated extreme sea-level rise of up to 1-1.5 km with the late Cryogenian Ghaub deglaciation in Namibia is contentious,as is the great rapidity(<104 yr)of the sea-level rise.Such extreme glacioeustatic events,if real,would have been global and affected all continents.In South Australia,up to six glacial advances and retreats during the late Cryogenian Elatina glaciation indicate a fluctuating ice margin.The latter stage of the Elatina glaciation and the immediate post-glacial environment are examined here for evidence of extreme and rapid sea-level rise.In the central Adelaide Rift Complex,diamictite with faceted and striated clasts occurs at the top of the Elatina Formation<1-2 m beneath the early Ediacaran Nuccaleena Formation ’cap carbonate’.One hundred kilometres to the south,～30 m of siltstone and sandstone followed by ～6 m of clast-poor diamictite with clasts 10 + cm long occur between tidal rhythmites and the cap carbonate.Three hundred kilo metres further south,～70 m of siltsto ne,dolo mitic siltstone and minor dolomite separate tidal rhythmites and early Ediacaran strata.Hence the rhythmites were deposited during a high stand(interstadial or interglacial),not during post-glacial sea-level rise.Storm-generated erosional surfaces within tidal rhythmites at Warren Gorge indicate intermittent rhythmite deposition,and water depth and other palaeoenvironmental factors are uncertain,casting doubt on a published estimate of rapid sea-level rise during rhythmite deposition.The lack of late Cryogenian deeply incised valleys and thick valley-fill deposits in South Australia and central Australia argues against extreme sea-level variations.A hiatus occurred between Elatina deglaciation and deposition of the Nuccaleena cap carbonate,and three palaeomagnetic polarity chrons identified in the cap carbonate imply slow deposition spanning 10~5-10~6 yr.This is supported by independent evidence from magnetic chronostratigraphy for Ediacaran strata in South Australia and California,and by stratigraphic and sedi

关 键 词：LATE CRYOGENIAN GLACIATION Sea level Adelaide RIFT Complex Elatina FORMATION Nuccaleena FORMATION 

分 类 号：P[天文地球]