Climate History, Lake Evolution, and Predicting Organic Richness of the Green River Formation, Piceance Creek Basin, Colorado

Transcription

1 Climate History, Lake Evolution, and Predicting Organic Richness of the Green River Formation, Piceance Creek Basin, Colorado J. Frederick Sarg, Kati Tanavsuu-Milkeviciene, Jufang Feng, and Suriamin Huang Colorado School of Mines, USA

2 The Green River Formation The world s largest known oil shale resources occur in: Eocene lake sediments of Green River Formation Western Colorado and adjacent Utah and Wyoming Piceance Basin largest fraction of reserves Each basin has a unique history Major basins connected at times during history All have periods of evaporite deposition

3 Materials 1. Described cores. In total ft (~3303 m) 6 (available GR Fm. interval) 6 (from R7 to Uinta Fm.) 2. Described outcrops (5). In total 3468 ft (~1057 m) USBM-01A 3. Well data (used ~500; after Bartov and USGS database) Gamma ray Fischer Assay (gal/ton) Outcrops & Lake Center Cores Geochem. Analysis Green River Formation Nahcolite dominated evaporites Halite dominated evaporites

4 Datasets and Methods Source Rock Analyzer Basin Center Section: John Savage 24-1: (117 samples) Shell 23x-2: (46 samples) Basin Margin Section: Lower Douglas (50 samples) Upper Douglas (11 samples) USGS Data Re-evaluation Fischer Assay Database 782 sets of borehole for mapping in Petra Central Well USBM01-A major-oxide concentrations analyzed by WDXRF major-, minor-, and traceelement concentrations analyzed by ICP-AES

5 Sratigraphy Duration ~5Ma Divided into: 1. Members, based on lithofacies 2. Rich and lean zones (R/L), based on kerogen content Volcaniclastic sandstones Dominantly oil shale Dominantly mixed littoral, sublittoral carbonates and siliciclastics Alluvial deposits After Johnson 1984; Dyni 2006; Johnson et al. 2010; Self et al. 2010

6 Littoral, sublittoral facies associations Gradationally based delta mouth bars Prograding delta deposits Sharp based delta mouth bar Distributary channel Littoral, sublittoral oil shale Distributary channel Microbial carbonate 3 cm

7 Organic Richness Variations (Margin)

8 Profundal Facies Associations Oil shale breccia Nahcolite, halite 61 cm 3 cm 2 cm Laminated oil shale

9 Organic Richness Variations (Center)

10 Results Lake margin, littoral, sublittoral zones (7 FAs). Dominantly sandstones and carbonates Deep part of the lake, profundal zone (6 FAs). Dominantly kerogen-rich mudstones (carbonate and clay), oil shale deposits, and evaporites C B (north-south) Deep basin area Margin R4 R6 R5 R7 R3 R2 R1 R0 R8 Littoral, sublittoral deposits Delta Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Profundal deposits Laminated oil shale Softs ediment deformed oil shale Oil shale breccia Turbidites Nahcolite dominated evaporites Halite dominated evaporites

11 Results Lake margin, littoral, sublittoral zones (7 FAs). Dominantly sandstones and carbonates Deep part of the lake, profundal zone (6 FAs). Dominantly kerogen-rich mudstones (carbonate and clay), oil shale deposits, and evaporites Margin S6 Closing Lake S5 High Lake S4 Rising Lake S3 Highly Fluctuating Lake S2 Transitional Lake S1 Fresh Lake Littoral, sublittoral deposits Delta Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Profundal deposits Laminated oil shale Softs ediment deformed oil shale Oil shale breccia Turbidites Nahcolite dominated evaporites Halite dominated evaporites

12 Small-scale (10 s m): Climate, Lake stratigraphy, and Oil shale

13 Organic Carbon Depositional Model Organic Enrichment = Production - Destruction Dilution (after Bohacs, et al., 2005)

14 Arid climate Low runoff Low lake level Lean oil shale 1 cm Littoral, sublittoral siliciclastics Evaporites (halite, nahcolite) Laminated oil shale

15 Increasing precipitation Rising lake level Lean to rich oil shale Person for scale Prograding delta mouth bars Shoreline mudstones Littoral, sublittoral carbonates Delta Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Laminated oil shale Disturbed oil shale deposits Oil shale breccia Silicilastic turbidites Evaporites (halite, nahcolite)

16 Humid climate High runoff High lake level Rich oil shale 1 cm Shoreline mudstones Laminated oil shale Littoral, sublittoral carbonates Disturbed oil shale deposits Delta Oil shale breccia 3 cm Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Silicilastic turbidites Evaporites (halite, nahcolite) 3 cm

17 Results Lake margin, littoral, sublittoral zones (7 FAs). Dominantly sandstones and carbonates Deep part of the lake, profundal zone (6 FAs). Dominantly kerogen-rich mudstones (carbonate and clay), oil shale deposits, and evaporites C B (north-south) Deep basin area Margin R4 R6 R5 R7 R3 R2 R1 R0 R8 Littoral, sublittoral deposits Delta Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Profundal deposits Laminated oil shale Softs ediment deformed oil shale Oil shale breccia Turbidites Nahcolite dominated evaporites Halite dominated evaporites

18 Results Lake margin, littoral, sublittoral zones (7 FAs). Dominantly sandstones and carbonates Deep part of the lake, profundal zone (6 FAs). Dominantly kerogen-rich mudstones (carbonate and clay), oil shale deposits, and evaporites Margin S6 Closing Lake S5 High Lake S4 Rising Lake S3 Highly Fluctuating Lake S2 Transitional Lake S1 Fresh Lake Littoral, sublittoral deposits Delta Littoral, sublittoral siliciclastics Littoral, sublittoral oil shale Profundal deposits Laminated oil shale Softs ediment deformed oil shale Oil shale breccia Turbidites Nahcolite dominated evaporites Halite dominated evaporites

19 Increased Evap. Higher Salinity Basin Margin Isotopic Record Increased Inflow - Freshening Increased Photosyn. High Productivity Increased CO2 uptake - Oxic Oolitic Grainstone

20 OM Deposition Long Term Trends Geochemistry Proxies (USBM-01A Well) High Net Productivity High Dilution High Net Productivity Low Destruction Increased Photosyn. High Productivity Increased CO2 uptake - Oxic

21 Eocene climate and evolution of the Piceance Creek basin (mid- to large-scale complexes) After Zachos et al Age data after Smith et al. 2008, 2010 EECO Early Eocene Climatic Optimum

22 Climate Effects on Productivity & Dilution Stage (Climate) Lake Condition Net Productivity Stage 5 (cooling climate) Stage 4 (beginning of cooling climate) Stage 3 (peak of climate optimum) Stage 2 (beginning of climate optimum) Stage 1 (warm up to climate optimum) Significant runoff & high lake level Runoff increases & increased nutrient influx Increasing salinity. Nutrient supply is restricted and mostly from periodic increases in runoff Increasing lake restriction, brackish to saline water High runoff and nutrient input into fresh lake High Net Productivity (high prod. & low destr.) 30 gal/ton Moderate Net Productivity (mod. Prod. & mod. destr.) 24 gal/ton High Net Productivity, but incr. dilution by evaporites) R5-21 gal/ton R4 36 gal/ton High Net Productivity (mod. prod. & low destr.) R3-25 gal/ton R2-39 gal/ton High Net Productivity (high prod. & mod. destr.) R1-27 gal/ton R0 21 gal/ton