CHRONOMAP: CHRONOSTRATIGRAPHY-GUIDED GEOLOGIC MAPPING AND RESOURCE ASSESSMENT IN THE UNITED STATES

ChronoMap is a collaborative USGS project to create a series of high-res. chronostratigraphic charts, geologic maps (1:500k), time-slice (~2 m.y.) facies distribution maps, and supporting database for US Phanerozoic sedimentary rocks. This effort was inspired by COSUNA, but utilizes integrated sequence stratigraphic techniques underpinned by chemo- and biostratigraphy and refined through differentiation of "traditional" and "time-specific" facies. The temporal resolution of ChronoMap is 10-100x greater than COSUNA. The prototype project focused on the Silurian, the shortest, but also one of the most widely distributed rock sequence in the US.

The Silurian was selected to test the feasibility of the project because: 1) recent NSF- and USGS-funded studies have generated large bio- and chemostratigraphic data sets, 2) the recent development of a global chronostratigraphic composite standard (Cramer et al. 2011), 3) this sequence is widespread in surface exposures and penetrated by >50 publically available cores and >500k wells, 4) hosts a variety of metallic and nonmetallic deposits, and 5) major regional aquifers and aquitards critical in providing drinking water to millions of US citizens. Work progressed from: 1) creation of biostratigraphic and chemostratigraphic composite reference standards, to 2) reinterpretation of the age, stratigraphic correlation, and facies in each column, and 3) creation of regional facies maps and refinement of state-scale geologic maps.

Results of this project demonstrate the feasibility of redefining the stratigraphic architecture of the US. In total 232 geologic columns display the stratigraphic correlation and facies distribution for the Silurian at 100 k.y.-scale. Regional transects illustrate the position of regional unconformities, thicknesses of unconformity bound packages and facies characteristics that redefine Silurian basin/tectonic evolution of the US and sea level fluctuations associated with Silurian climato-oceanic events. Ultimately this prototype project demonstrates a powerful new tool to assess geologic history and natural resource potential of the US and beyond.