UGA 50:11 - Geochemical Studies of the Green River Formation in the Piceance Basin, Colorado: II. Chemofacies from Hierarchical Cluster Analysis Off-Canvas Toggle Member Login Donate About Publications Geology of the Intermountain West Guidebooks UGA Geosites Special Publications UGA 28 Topical Papers Members Member Benefits Become a Member Resources Newsletter Meeting Minutes Geologic Road Signs Geology Links UGA Constitution Outreach Student Scholarship Fund Teacher of the Year Become a Sponsor UGA Sponsors & Affiliates Lehi Hintze Award Events Contact UGF About UGF Donate to UGF Off-Canvas Toggle About Publications Geology of the Intermountain West Guidebooks UGA Geosites Special Publications UGA 28 Topical Papers Members Member Benefits Become a Member Resources Newsletter Meeting Minutes Geologic Road Signs Geology Links UGA Constitution Outreach Student Scholarship Fund Teacher of the Year Become a Sponsor UGA Sponsors & Affiliates Lehi Hintze Award Events Contact UGF About UGF Donate to UGF Off-Canvas Toggle thisistheplace2.jpeg subpage1.jpeg subpage2.jpeg subpage3.jpeg UGA 50:11 - Geochemical Studies of the Green River Formation in the Piceance Basin, Colorado: II. Chemofacies from Hierarchical Cluster Analysis Tengfei Wu - School of Geosciences, University of Oklahoma Jeremy Boak - Hurricane Peak Geosciences Justin E. Birdwell - U.S. Geological Survey DOI: https://doi.org/10.31711/ugap.v50i.115 Abstract Hierarchical cluster analysis (HCA) was applied to a geochemical dataset representing the Eocene Green River Formation in the Piceance Basin of Colorado to identify chemofacies in core and outcrop samples from the basin margin and the basin center. The input dataset consisted of inductively coupled plasma optical emission spectroscopy and mass spectrometry and total organic carbon (TOC) content analyses of 186 basin margin outcrop samples and 190 basin center core samples discussed in Part 1 of this study (this volume). TOC values and twenty-five major and trace elements were used as variables to define statistical clusters of samples for the overall dataset, for the two basin center cores, and for each separate core or outcrop dataset by HCA applying Euclidean distance and Ward’s method algorithms. For each dataset, five cluster-defined chemofacies were identified. The chemofacies for each dataset show chemical affinities with five informally defined rock types– mudstone, marlstone, carbonate-rich mudstone, siliciclastic-rich mudstone/siltstone/sandstone, and Na-rich (saline) mudstone, with each showing variations in TOC content and abundance of redox sensitive minor and trace elements. A close relationship between enrichment of redox sensitive elements, particularly As and Mo, and TOC is identified in the basin center. Whereas enrichment factors (relative to average shale) are relatively low for many Period IV (PIV) transition metals, as discussed in Part 1 of this study, their consistent coherence in enrichment or depletion in HCA-defined chemofacies demonstrates the expected relationship between redox state and organic richness. Enrichment in PIV transition metals also shows a correlation to enrichment in elements with affinity for siliciclastic sediment. Enrichment/depletion among several groups of redox indicators is not everywhere consistent, with some chemofacies showing, for example, enrichment of PIV transition metals and depletion of sulfur and arsenic. Early timing of saline conditions in the basin margin is clearly displayed in the chemofacies log display, consistent with observations based on geochemical interpretations of concentrations and elemental ratios discussed in Part 1. Overall, the chemofacies are consistent with major mineralogical units and lake history stages defined in previous work, but provide more detail on the fluctuations in lake chemistry that occurred during deposition of Green River oil shale in the Piceance Basin. Order It ($5.00) Cart Your cart is empty Login Form Login for discounted rates on document downloads and to access members only content Username Password Show Password Remember Me Log in Forgot your password? Forgot your username? Create an account Utah Geological Association P.O. Box 526356 Salt Lake City, UT 84152-0100  Facebook  YouTube © 2025 Utah Geological Society | Site by Third Sun MEMBER LOGIN Off-Canvas Toggle About Publications Geology of the Intermountain West Guidebooks UGA Geosites Special Publications UGA 28 Topical Papers Members Member Benefits Become a Member Resources Newsletter Meeting Minutes Geologic Road Signs Geology Links UGA Constitution Outreach Student Scholarship Fund Teacher of the Year Become a Sponsor UGA Sponsors & Affiliates Lehi Hintze Award Events Contact UGF About UGF Donate to UGF