Hematite-rich concretions from Mesoproterozoic Vindhyan sandstone in northern India: a terrestrial Martian 'blueberries' analogue with a difference

摘要

We report here hematite-rich concretions observed in the sandstone of the Mesoproterozoic Vindhyan Supergroup of rocks occurring in parts of Bihariya, Uttar Pradesh, northern India. These concretions are similar to `blueberries' from Mars and their terrestrial analogues reported from the Jurassic Navajo Sandstone in Utah, USA. The presence of diagenetically formed hematite concretions gave the first confirmation of the presence of liquid water in the red planet in the past. We report here the detailed morphology, petrography, mineral chemistry, magnetic susceptibility characteristics and spectral radiometric data of hematite-rich concretions observed in the Vindhyan sandstone. These are compared with `blueberries' from Mars and other similar terrestrial analogues reported from different parts of the world. In spite of similarities, these hematite-rich concretions are strikingly distinct in having a nucleus and alternate iron-rich and iron-poor rims unlike other global occurrences. In addition, we document here outcrop scale evidence of possible fluid pathways considered responsible for the development of the concretions.