The Neoproterozoic “Blood Falls” in Tarim Craton and Their Possible Connection With Snowball Earth

Abstract

Blood Falls refers to the outflow of iron-rich brine plumes under the Taylor Glacier in Antarctica, which have distinctive blood-like red color. It was proposed that during the Cryogenian, Fe oxides of terrestrial origin accumulated under glaciers via a mechanism similar to the modern Blood Falls, although reports of iron deposits of such novel origin are lacking in literature. The Quruqsay iron formation is hosted in Neoproterozoic glacial sequences in the northern margin of the Tarim Craton in NW China and consist of 15 lenticular iron orebodies. The iron ores are mainly composed of fine Fe-oxide aggregate and clastics, with the latter sometimes occurring as dropstones indicating glacial fluvial deposition. The hematite minerals show positive Ce and Y anomalies but lack positive Eu anomalies, with flat shale-normalized rare Earth elements patterns. The hematite minerals also display remarkably negative ε Nd values and close-to-0 δ 56 Fe values, which collectively indicate that iron was sourced from continents rather than mid-ocean ridge hydrothermal vents. Additionally, δ 18 O values of the hematite are consistent with the large ice-volume during the Snowball Earth event. Evidence from the Quruqsay iron deposit suggest oxidation of terrestrial sub-glacier iron-bearing discharge in oceans of extensive glaciation, correlating with the predicted Blood Falls-type iron deposits in the Neoproterozoic. The Quruqsay iron formation is a unique hematite-rich iron deposit implying that subglacial lakes can be a significant repository for Fe 2+ and that the volume of the Neoproterozoic glaciers may be much higher than the current glacier.