LE3 .A278 2012

2012

Pufahl, Peir

Acadia University

Master of Science

Masters

Geology

Earth & Environmental Sciences

The Paleoproterozoic Frere Formation (ca. 1.80 Ga) of Western Australia is a 600 m thick sedimentary succession of iron formation and siltstone that accumulated in shallow water environments on an unrimmed continental margin. Lithofacies suggest that deposition occurred during a marine transgression punctuated by higher frequency relative sea level fluctuations that produced five parasequences. Parasequences are decameter-scale and defined by a basal flooding surface overlain by interbedded magnetite-bearing, hummocky cross-stratified sandstone that grade into microbially laminated, hematite-rich mudstone and trough cross-stratified grainstone. Each cycle is interpreted to record progradation of intertidal and tidal channel sediments over middle shelf deposits. The presence of eolian dunes, beach facies, mud cracks, absence of coarse clastics, and preponderance of siltstone and very fine-grained sandstone indicate deposition along an arid coastline marked by input of wind-blown sediment. Iron formation of the Frere Formation is restricted to peritidal and middle-shelf paleoenvironments, contrasting with older Paleoproterozoic iron formations in North America, which accumulated in the full spectrum of shelf environments. Lithofacies associations and paragenetic pathways identified within the Frere Formation also suggest deposition in seawater with a prominent oxygen chemocline. Dilution by clastic input to middle-shelf environments is interpreted to have prevented iron formation from developing in deeper settings. The absence of pyrite in middle shelf lithofacies implies upwelled bottom water was not euxinic, supporting recent studies that demonstrate the Paleoproterozoic transition to a sulfidic ocean was not as widespread as previously surmised.

The author retains copyright in this thesis. Any substantial copying or any other actions that exceed fair dealing or other exceptions in the Copyright Act require the permission of the author.

https://scholar.acadiau.ca/islandora/object/theses:228