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Unformatted text preview: Interpretation of Reivilo Spherule Layer : All of the known Archean to Paleoproterozoic spherule layers occur as discrete layers rich in coarse sand-size grains with predominantly spherical shapes and a heterogeneous suite of internal textures indicating they were formerly molten; geochemical evidence of extraterrestrial material has been detected in most of them [1-5]. We interpret the Reivilo spherule layer as impact ejecta because it fits the pattern texturally, even though we have no geochemical data as yet. If the Reivilo spherules are like those in the other layers, they were probably generated by an object very roughly the size of the K/T impactor and represent silicate melt droplets with a low silica composition along the lines of basalt . The well-sorted nature of the layer and the abrupt transition to silt at the top further suggest that the layer was deposited under the influence of high- energy waves and/or currents, perhaps generated by the impact itself, as shown by many of the other layers [2,4]. After the Reivilo spherules came to rest on the seafloor, they were compacted as overburden slowly increased and original crystals were replaced with authigenic K-feldspar. However, shapes and internal textures were sufficiently original crystals were replaced with authigenic K-feldspar....
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- Spring '08