INTEGRATING DETRITAL ZIRCON GEOCHRONOLOGY AND SEQUENCE STRATIGRAPHY

Analytical determination of large populations of detrital zircons has progressed rapidly with the advent of the Laser Ablation Inductively Coupled Mass Spectrometer (LA-ICPMS). The age sprectra of large populations of detrital zircons commonly are used to address a variety of tectonic and provenance questions. By integrating detrital zircon geochronology with sequence stratigraphic principles developed since the mid-1970's we can make predictions regarding sediment dispersal and provenance, especially on the 2nd- and 3rd-order time frame (a few millions to a few 10's of millions of years). For example during long-term Lowstand Systems Tracts (LST's) continental bedrock and older siliciclastic sediments surrounding basins are exposed becoming a source for detrital zircons. Seafloor fans sourced from these surrounding areas may originate from incised valleys limiting the recycling of sediments produced in the immediately preceding sequence. During Transgressive Systems Tracts (TST's) rapid flooding of continents or basin margins will limit the source of detrital zircons to continental interiors or distal sources far from the basin; additionally the sources of detrital zircons will migrate landward as sea level rises. During Highstand Systems Tracts (HST's) siliciclastic sediment will build basinward burying older sediments there may be a large degree of homogenization of detrital zircon populations from disparate sources as sedimentary processes on the shelf mix multiple sediment sources. Additionally the burial of underlying sediment will keep them from being re-worked until later erosion. During Falling State Systems Tracts (FSST's) siliciclastic sediments along the shelf may be re-worked and mixed with sediments derived from sources more proximal to the basin. An ongoing study of Middle-Late Ordovician quartzites (Eureka and equivalents) of the western U.S. is being used to test these predictions. Preliminary data from this study will be presented.