Adam Maloof - Research
The Marinoan Glaciation
Two Neoproterozoic glacigenic units are present on most continents, often interrupting carbonate platform sequences, and sometimes found at the palaeomagnetic equator. Therefore, at least twice during this era, continental glaciers reached sea level in the low-latitudes. Our work, spearheaded by Ph.D. student Catherine Rose, investigates the younger Marinoan low-latitude glacial event in South Australia by pairing detailed mapping and measured stratigraphic sections to high resolution geochemical data. Our purpose is to evaluate the character of the pre-, syn- and post-glacial environments and climates.
Evidence of wet-based glaciers (see subglacial deformation in the figure above), dynamic ice fronts, deep subglacial erosion and/or significant chemical weathering will test important climatic predictions made regarding the Marinoan ice age (e.g., snowball Earth). We are in our third year of a comprehensive facies examination and major element geochemical study of the syn-glacial Elatina Fm. We aim to investigate the nature and style of glaciation, assess the intensity of palaeoweathering processes and ultimately evaluate the thermal regime of equatorial glaciers during the Cryogenian.
Sedimentologically and geochemically distinctive carbonate sequences consistently drape the younger Neoproterozoic `Marinoan' glacial deposit (~635 Ma). The presence of ice-rafted debris in the basal dolostone suggests that at least the lower portion of the cap sequence records deglaciation. Two end-member hypotheses have been proposed for their deposition. An isochronous model proposes that cap dolostones were deposited like a blanket and recorded ocean-wide changes over time subsequent to deglaciation, while a diachronous model proposes that deposition tracked glacioeustatic flooding during deglaciation. Determining which model is correct has specific implications for the time evolution of post-glacial ocean temperature and chemistry.
Over the past three years we have made detailed maps coupled to sedimentological observations and d13C isotopic measurements of the Nuccaleena Fm cap dolostone (in the context of the underlying and overlying stratigraphy). We aim to test the concept that the Nuccaleena Fm was deposited during deglaciation, and attempt to differentiate between diachronous and isochronous models for its deposition to better constrain the evolution of d13C in post-glacial oceans. In the figure above, from left to right, Nick Swanson-Hysell, Catherine Rose and Justin Strauss surf giant wave ripples in dolomite grainstones of the Nuccaleena Formation in the Central Flinders Ranges.