Temporal and spatial scales of an Anthropocene Series
Abstract
The Anthropocene is under consideration as a potential addition to the Geological Time Scale. Within current stratigraphic guidelines, it needs be analysed both as a unit of geological time of geochronology sensu stricto (for example, an Anthropocene Epoch) and also as a parallel, material chronostratigraphic (or 'time-rock') unit: an Anthropocene Series, comprising strata formed since the beginning of the Epoch. From a deep-time, far-future perspective the base of such a chronostratigraphic unit will likely appear sharp, synchronous and precisely correlatable using lithologic, biostratigraphic, chemostratigraphic and sequence stratigraphic proxies, given the rate and scale of human perturbation of the Earth System. While some lithostratigraphic effects will persist only as long as does the anthropogenic driver, others (chemo- and sequence stratigraphic) will be geologically longer-lived and yet others (biostratigraphic) will have permanent consequences, to give rise to a substantial and well-characterized unit. However, a prospective Anthropocene Epoch/Series needs be for current use, even though the phenomenon is in its early stages: not least (though not exclusively) by stratigraphers working on geologically young deposits, seeking annual/decadal time resolution. One may explore a 'short' Anthropocene, beginning ~1950 CE, that post-dates much anthropogenic change in long-settled areas, but coincides with marked global acceleration in population, energy use, urbanization and habitat/species loss. It slightly post-dates a 13C/12C shift caused by fossil fuel burning but closely coincides with near-synchronous spread of man-made radionuclides and marked changes in N isotopes in far-field lakes. On land, such an Anthropocene Series might comprise post-war constructions and their foundations (as the 'Artificial Ground' of geological maps), surface components of soils (esp. agricultural) and terrestrial sedimentary systems (aeolian, fluvial, lacustrine, deltaic) that vary from pristine to strongly anthropogenically perturbed. Offshore an Anthropocene Series may comprise marine strata with thicknesses ranging from metres in rapidly aggrading coastal systems to decimetres in shelf regions, to millimetres or less in distal deep-ocean settings. Human-produced signals here would include effects of bottom trawling (most shelves), variations in sediment input (from coastal engineering/upriver dam construction) and chemistry (including 'dead zones') and biotic changes including species invasions. A further lithofacies comprises subsurface intrusions, through deep building foundations, mining, tunnelling and drilling, with associated diagenetic change. The lower boundary of an Anthropocene Series varies from simple (most lake deposits) to geometrically complex and intergradational (as in 'Artificial Ground' of long-settled urban areas) to poorly separable (as in slowly aggrading deep sea environments where Anthropocene deposits are being inter-bioturbated with Holocene ones). Boundary recognition is a factor in the formalization debate. However, attempts to distinguish an Anthropocene Series, and to discriminate facies within it, would provide useful perspective on the extent and nature of global change.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGC51H..01Z
- Keywords:
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- 1600 GLOBAL CHANGE