| Zdroj: |
Global Biogeochemical Cycles; Dec2005, Vol. 19 Issue 4, p480-501, 22p, 2 Diagrams, 7 Charts, 1 Graph, 1 Map |
| Abstrakt: |
A new digital map of the lithology of the continental surfaces is proposed in vector mode (n ≈ 8300, reaggregated at 0.5° × 0.5° resolution) for 15 rock types (plus water and ice) targeted to surficial Earth system analysis (chemical weathering, land erosion, carbon cycling, sediment formation, riverine fluxes, aquifer typology, coastal erosion). These types include acid (0.98% at global scale) and basic (5.75%) volcanics, acid (7.23%) and basic (0.20%) plutonics, Precambrian basement (11.52%) and metamorphic rocks (4.07%), consolidated siliciclastic rocks (16.28%), mixed sedimentary (7.75%), carbonates (10.40%), semi- to un-consolidated sedimentary rocks (10.05%), alluvial deposits (15.48%), loess (2.62%), dunes (1.54%) and evaporites (0.12%). Where sediments, volcanics and metamorphosed rocks are too intimately mixed, a complex lithology (5.45%) class is added. Average composition is then tabulated for continents, ocean drainage basins, relief types (n = 7), 10° latitudinal bands, geological periods (n = 7), and exorheic versus endorheic domain and for formerly glaciated regions. Surficial lithology is highly heterogeneous and major differences are noted in any of these ensembles. Expected findings include the importance of alluvium and unconsolidated deposits in plains and lowlands, of Precambrian and metamorphic rocks in mid-mountain areas, the occurrence of loess, dunes and evaporites in dry regions, and of carbonates in Europe. Less expected are the large occurrences of volcanics (74% of their outcrops) in highly dissected relief and the importance of loess in South America. Prevalence of carbonate rocks between 15°N and 65°N and of Precambrian plus metamorphics in two bands (25°S-15°N and north of 55°N) is confirmed. Asia and the Atlantic Ocean drainage basin, without Mediterranean and Black Sea, are the most representative ensembles. In cratons the influence of ancient geological periods is often masked by young sediments, while active orogens have a specific composition. [ABSTRACT FROM AUTHOR] |
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