Sediment diagenesis in high latitude sedimentary systems: Climate influences on mineral and geochemical processes during early diagenesis
|Location||International Geological Congress,oslo 2008|
|Holding Date||04 October 2008|
Primary variables controlling early diagenetic (post-depositional) processes in sandstones include temperature, vegetation richness, humidity, hinterland geology (controlling sediment supply) and the specific site of sediment accumulation. Early diagenetic processes in marine clastic sediments are mainly controlled by sulphate and other reduction processes and are potentially little affected by latitude. In contrast, fluvial, deltaic and estuarine clastic sediments are potentially strongly affected by latitude.
Primary sediment supply can be strongly affected by climate since temperature and humidity influence the extent of chemical weathering. Cold and arid climates lead to low degrees of chemical weathering and feed lithic fragments to the accumulating sediment resulting in mineralogically immature sediment (e.g. rich in feldspar minerals). Cold and arid climates also lead to formation and sedimentation of smectite clay minerals in contrast to warm and humid climates that result in formation of kaolinite. The relatively low temperature of high latitude systems will thus encourage the accumulation of mineralogically-immature and smectite-rich sediments.
The lushness of vegetation in the sediment hinterland, and at the site of deposition, has a major effect on diagenetic processes. Where vegetation is rich, there will be much organic carbon buried with sediments. Under these circumstances, widespread bacterial processes result in excess CO2 generation. This in turn will encourage the widespread formation of carbonate minerals in the sediment including siderite in fluvial and delta plain settings and calcite in lower delta and estuarine settings. Where vegetation is limited, for example at high latitudes, there will be limited organic matter, limited bacterial activity and CO2-generation and muted formation of carbonate cements in the sediment.
Sediment accumulation rates may be higher at higher latitudes (less trapping by vegetation) leading to faster isolation of pre-existing sediment from oxidising surface waters. Animal-sediment interaction (burrowing, digestion) serves to both modify primary depositional structures and alter the mineralogy of sediments (exacerbate weathering processes, paradoxically under reducing conditions, leading to bio-clays such as berthierine). In organically-lean sediments at low temperatures, animal populations will be limited and both bioturbation and the formation of bio-clays will be relatively muted. Thus high latitude sedimentary systems will be little influenced by animal activity in the sediment matrix and leading to less bioturbation and less significant generation of new clay minerals. In summary, high latitude clastic sediments will tend to have higher smectite-kaolinite ratios, have less carbonate cement and be mineralogically more reactive than lower latitude sediments. High latitude sediments will be highly susceptible to a wide range of mineral alteration processes as they are buried.