Mineralogical and Geochemical Approaches to Provenance

Abstract

The provenance of siliciclastic sedimentary rocks can be unraveled by tracing their source rocks. The correct recognition of source rocks and areas can add substantially to paleogeographic reconstructions, sediment-budget calculations, and basin analyses. No wonder therefore that, since the emergence of modern geology at the end of the 19 century, such studies have been undertaken frequently. With the advance of technology, new tools and methods have gradually been introduced in provenance studies, and the studies themselves have been moving from purely qualitative descriptions to more rigorous, quantitative analyses. Weltje & Von Eynatten (2004) detail this in a useful synopsis. The 2009 Annual Meeting of the Geological Society of America in Portland devoted a session to sedimentary provenance studies. The book under review, published as GSA Special Paper 487, is a result of this session and consists of eleven independent contributions. The editors, E. Troy Rasbury of Stony Brook University, Sidney R. Hemming of the Lamont-Doherty Earth Observatory, and Nancy R. Riggs of Northern Arizona University, who thoroughly prepared the volume, were also the conveners of the 2009 session. U-Pb geochronology of detrital zircons has become one of the most used and most robust techniques in provenance studies during the last decade. Zircon ubiquity in sedimentary rocks, coupled with the development and availability of SHRIMP (sensitive high-resolution ion microprobe) and LA-ICP mass spectrometry, resulted in a flood of publications that explored this new field. The age spectra of zircons have become almost standard in modern provenance studies. This is also reflected in the contents of this book, in which five contributions concern U-Pb ages of detrital zircons. Interestingly, some of them clearly show that in geologically complex settings, where different source rocks have similar ages, U-Pb zircon geochronology is of limited value only and must be supplemented with other methods. Morton et al. demonstrate that only with the use of a combination of methods it is possible to recognize the various provenances among Paleocene sands of the NE Atlantic. Each single technique, such as a conventional heavy-mineral analysis, geochemistry of detrital garnet and rutile, U-Pb dating of detrital zircon, and a palynofloral analysis, provides only a fragmental picture. Riggs et al. combine U-Pb zircon ages with Th/U ratios in zircon to detect two distinct sources for Late Triassic strata in south-western North America. The isotopic analyses of zircon grains alone are not sufficient to delineate the two sources. In turn, Clements et al. combine detrital-zircon U-Pb ages with zircon Hf-isotopes to unravel the complicated sediment provenance for SE Asia in the Paleogene. Despite the regional and methodological complexity, the authors present the results in an exceptionally interesting way, and the new data allow them to verify some tectonic models for this area. Rothfuss et al. use detrital-zircon geochronology to reveal regional unroofing of Late Cretaceous granitic plutons in SW Montana. The combination of zircon-age populations with traditional sedimentary facies analysis of Paleogene strata allows for the reconstruction of a complex intermontane basin system. Finally, Palmer et al. extracted zircon grains from nunatak moraines of East Antarctica in order to recognize the varied lithology of the icecovered bedrock. They supplement the geochronological zircon study with the identification of the composition of pebbles and coarse sand by optical petrography, and the Ar/Ar analyses of detrital mica and hornblend. The remaining contributions deal with various siliciclastic rocks by means of a wide variety of methods. The only common aspect is that they tackle a provenance problem. Kundic et al. explore single-grain Ar/Ar dating of detrital muscovite to characterize the provenance of Pleistocene loesses on Long Island. An earlier recognition of varied muscovite Ar/Ar ages in potential source areas was a starting point of their study. Downing & Hemming measured Nd, Sr, and Pb isotopes in Sedimentary Record Book Reviews Accepted February 28, 2013