Abstract
Abstract. Geologic dating methods for the most part do not directly measure ages. Instead, interpreting a geochemical observation as a geologically useful parameter – an age or a rate – requires an interpretive middle layer of calculations and supporting data sets. These are the subject of active research and evolve rapidly, so any synoptic analysis requires repeated recalculation of large numbers of ages from a growing data set of raw observations, using a constantly improving calculation method. Many important applications of geochronology involve regional or global analyses of large and growing data sets, so this characteristic is an obstacle to progress in these applications. This paper describes the ICE-D (Informal Cosmogenic-Nuclide Exposure-age Database) database project, a prototype computational infrastructure for dealing with this obstacle in one geochronological application – cosmogenic-nuclide exposure dating – that aims to enable visualization or analysis of diverse data sets by making middle-layer calculations dynamic and transparent to the user. An important aspect of this concept is that it is designed as a forward-looking research tool rather than a backward-looking archive: only observational data (which do not become obsolete) are stored, and derived data (which become obsolete as soon as the middle-layer calculations are improved) are not stored but instead calculated dynamically at the time data are needed by an analysis application. This minimizes “lock-in” effects associated with archiving derived results subject to rapid obsolescence and allows assimilation of both new observational data and improvements to middle-layer calculations without creating additional overhead at the level of the analysis application.
Highlights
Cosmogenic-nuclide exposure dating is a geologic dating method that relies on the production of rare nuclides by cosmic-ray interactions with rocks and minerals at the Earth’s surface
The observable data for exposure-dating applications are (i) measurements of the concentrations in common minerals of trace nuclides that are diagnostic of cosmic-ray exposure, for example, beryllium-10, aluminum-26, or helium-3, and (ii) ancillary data describing the location, geometry, and physical and chemical properties of the sample. Interpreting these measurements as the exposure age of a rock surface is simple in principle: one measures the concentration of one of these nuclides, estimates the rate at which it is produced by cosmic-ray interactions, and divides the concentration by the production rate to obtain the exposure age
It is much more complex in practice, because the cosmic-ray flux varies with position in the atmosphere and the Earth’s magnetic field, and the production rate depends on the chemistry and physical properties of the mineral and the rock matrix
Summary
Geologic dating methods, saving a few exceptions like varve or tree ring counting, do not directly measure ages or time spans. Interpreting the measurement as a geologically useful parameter such as an age or rate requires some sort of calculation and a variety of independently measured or assumed data such as radioactive decay constants, initial compositions or ratios, nuclide production rates, or nuclear cross sections (Fig. 1). Even though the geochemical measurements themselves in archived or previously published studies are valid indefinitely, the derived ages become obsolete This is an obstacle for analysis of geochronological data collected over a long period of time or, sometimes, from multiple laboratories or research groups who have different approaches to middle-layer calculations, because any comparison requires repeatedly recalculating all the derived ages from source data using a common method.
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