U-PB DATING OF CALCITE CONCRETIONS FROM CAMBRIAN BLACK SHALES AND THEPHANEROZOIC TIME-SCALE

Citation
C. Israelson et al., U-PB DATING OF CALCITE CONCRETIONS FROM CAMBRIAN BLACK SHALES AND THEPHANEROZOIC TIME-SCALE, Earth and planetary science letters, 141(1-4), 1996, pp. 153-159
Citations number
24
Categorie Soggetti
Geochemitry & Geophysics
ISSN journal
0012821X
Volume
141
Issue
1-4
Year of publication
1996
Pages
153 - 159
Database
ISI
SICI code
0012-821X(1996)141:1-4<153:UDOCCF>2.0.ZU;2-F
Abstract
The U-Pb dating of carbonate offers considerable potential for accurat e and direct dating of sedimentary rocks. Here we show that carbonate concretions from the Upper Cambrian black shales in southern Scandinav ia have remarkably high U to Pb ratios (U-238/Pb-206 up to 288,000) pe rmitting precise geochronology. A fine-crystalline early diagenetic co ncretion yields an age of 509.8 +/- 5.1 Ma, providing an accurate age for the late Cambrian, whereas a coarse 'cone-in-cone' concretion has yielded an age of 478.2 +/- 4.9 Ma, defining the final stage of sedime nt compaction and indicating a protracted dewatering and diagenetic hi story. These results demonstrate the power of this method for directly calibrating the geological time scale and constraining diagenetic his tories.