Sediment colour as recorder of climate and tectonics: Cenozoic continental red beds of the Himalayan foreland basin in NW India

摘要

The Cenozoic Himalayan foreland basin sedimentary facies are widely studied by researchers as they preserve record of complex interplay between tectonics, sedimentation and climate. Palaeoclimate reconstructions from these sediments have been done using various proxy tools. Colour of sedimentary facies is considered as one of the diagnostic palaeoclimate/climate indicator and the red colour is commonly associated to be with hot, arid climate. The Himalayan foreland basin (HFB) sediments from the oldest to the youngest, comprise almost all red and grey shades and the bright red facies greatly fascinate Earth Scientists. These red to grey coloured Himalayan foreland basin sediments preserve a record of global to regional climatic cycles and tectonic pulses. Studies pertaining to red colour and climate, specifically its association with hot, arid climate, are overwhelming. In general, studies focusing on continental red beds with specific climate are contradictory and confusing till date. Paradoxically, we now know more about red colour and climate than about red color and tectonics. Therefore, representative Himalayan foreland basin red beds of different times in the NW Himalaya have been selected for the present study. The HFB red beds of Oligocene, middle Miocene and upper Pliocene age have been investigated to find out any specific relationship of tectonics and/or particular climate cycles with red colour of these sediments on the basis of compilation of morphological, micromorphological, sub-microscopic and geochemical studies. It has been found that the bright red and grey colour shades are reliably shown by finer facies, particularly palaeosols, and coarser facies of the HFB sediments respectively, whether formed in cool, humid conditions or warm, arid conditions. This suggests greater role of tectonics during foreland basin sedimentation for preservation of sediment colour. Also, the purpose of this study is to highlight the need for more such investigations at various temporal and spatial scales in foreland basin sediments so that the colour of sediment can be appropriately used in future investigations dealing with sediment colour as an indicator of specific climate.