Evaluating the biosignature potential of ammonium in Proterozoic red beds and implications for the search for life on Mars  

作　　者：Eva E.Stüeken Philip Fralick Stephen Hillier Anthony R.Prave 

机构地区：[1]School of Earth and Environmental Sciences,University of St Andrews,St Andrews,KY169TS,UK [2]Department of Geology,Lakehead University,Thunder Bay,ON P7B 5E1,Canada [3]The James Hutton Institute,Craigiebuckler,Aberdeen,AB158QH,UK [4]Department of Soil and Environment,Swedish University of Agricultural Sciences(SLU),SE-75007 Uppsala,Sweden

出　　处：《Earth and Planetary Physics》2024年第6期836-853,共18页地球与行星物理（英文版）

基　　金：EES acknowledges funding from a NERC Frontiers grant(NE/V010824/1);Leverhulme Trust research grant(RPG-2022-313).

摘　　要：Over the past two decades,it has become increasingly apparent that early Mars may once have been warmer,wetter and more habitable for microbial life than it is today,which has spurred discussions about potential biosignatures that may be preserved in Martian sediments.An impediment to this line of research is the pervasive oxidation of Mars’surface due to photochemical oxidants that have likely destroyed remnants of organic matter.Here,we investigate whether nitrogen(N)transferred from biomass to phyllosilicate minerals during diagenesis can be preserved in oxidized mudrocks.We investigate two sequences of terrestrial Proterozoic red beds,namely the Sibley Group(1.4 Ga)in Canada and the Stoer Group(1.2 Ga)in Scotland,and we find enrichments in authigenic N in the range of several tens of ppm in both units.The highest concentrations(ca.100 ppm on average)are found in the most desiccated red beds of the Stoer Group,concurrent with enrichments in potassium(K).We discuss similarities and differences between the two sets of rocks with regards to salinity,pH,biological productivity and K-metasomatism,and we conclude that the ideal mechanism for the preservation of biogenic N in red beds may be in-situ release of ammonium from microbial mats into the clay substrate,possibly facilitated by early diagenetic,biologically induced illitization.Illite and smectite have been observed on Mars,and experiments suggest that Martian waters contained moderate amounts of dissolved K.Hence,it is conceivable that a similar K and N enrichment process could have occurred as to what we document for the Proterozoic,preserving evidence of life that may have survived to the modern day.

关 键 词：red beds BIOSIGNATURE MARS NITROGEN AMMONIUM clay minerals 

分 类 号：P185.3[天文地球—天文学]