Sandstone composition of the Valdez and Orca groups, Prince William Sound, Alaska

Citations Over Time

Abstract

Introduction 1 Acknowledgments 2 General geology 2 Valdez Group and correlative rocks 2 Orca Group and correlative rocks 5 The Contact fault system 5 Previous petrographic studies 7 Methodology 8 Results of studies of Valdez Group samples 8 West, central, and east Valdez areas 8 Differences between west Valdez-and central Valdez-area samples 10 Provenance 12 Anomalous Valdez Group samples 13 Results of studies of Orca Group samples 14 Eastern exposures of the Orca Group 14 Western exposures of the Orca Group 19 Anomalous Orca Group samples 22 Comparison of results of studies of the Orca Group with previous work 25 Tectonic models and the placement of the Valdez-Orca boundary 25 Evidence for the northward displacement of the Valdez and Orca Groups 26 Petrographic constraints on the significance and location of the Valdez-Orca boundary 27 The existence of a terrane boundary 27 Alternative locations of a terrane boundary 27 Johnstone Bay fault 27 Bainbridge fault 28 Montague Strait fault 28 Placer River fault 28 Imbricate faulting along terrane boundary 28 Summary 28 Areas that have anomalous sandstone petrography Mount Denson area 29 Areas spatially associated with rna fie rocks 29 Resurrection Peninsula area 29 Knight Island area 30 Ellamar area 30 Montague Island and Ragged Mountain areas 30 Petrography 31 Age 31 Metamorphic-grade relationships 33 Structural style 34 Sedimentary facies 34 Conclusions 34 References cited 34 FIGURES 1. Generalized geologic-tectonic setting of the Prince William Sound area, Alaska.Terrane boundaries 2 2. Geologic map of the Prince William Sound area 3 3. Turbidites of the Valdez Group in the Port Wells area, western Prince William Sound 4 4. Fossil localities and location of Valdez Group-Orca Group contact in western Prince William Sound as delineated •by previous workers 6 Ill 5. Location of petrographic areas and samples point-counted for this study 7 6.Modal analyses of sandstone of the Valdez Group from the west Valdez, east Valdez, and central Valdez areas 10 7. Photomicrographs in transmitted light of thin sections of sandstones from the Valdez Group 11 8. Modal analyses of sandstone from the Valdez Group and (at least partly) correlative lithostratigraphic units 12 9. Modal analyses of sandstone of the Valdez Group from the Mount Denson and Resurrection Peninsula areas compared with analyses of sandstone of the Orca Group from the Port Gravina-Cordova area 15 10.Modal analyses of sandstone of the Valdez Group from the Mount Denson and Resurrection Peninsula areas compared with those from the west Valdez, central Valdez, and east Valdez areas 16 11.Modal analyses of sandstone of the Orca Group from the Port Gravina and Cordova areas compared with analyses of sandstone of the Orca Group from the Hinchinbrook Island area 17 12.Photomicrographs in transmitted light of thin sections of sandstones from the Orca Group 18 13.Modal analyses of sandstone of the Orca Group from the Sargent Icefield and Chenega areas compared with analyses of the Ghost Rocks Formation 20 14.Comparison of sandstone modal analyses from the Valdez and Orca Groups 21 15.Modal analyses of sandstone of the Orca Group from the Ellamar and Knight Island areas 23 16.Comparison of modal analyses of sandstone from the Knight Island-Ellamar (combined), Montague Island, and Ragged Mountain areas with those from the Port Gravina-Cordova area 24 17.Modal analyses for sandstone of the Orca Group from the Montague Island and Ragged Mountain areas compared with analyses from the Zodiac fan and from the Sitkalidak Formation 32 18.Ratio of volcanic clasts to total lithic fragments in Zodiac fan sediment, Sitkalidak Formation sandstone, and Orca Group sandstone from the Montague Island and Ragged Mountain areas 33 TABLES 1. Composition of sandstone from the west Valdez, east Valdez, and central Valdez areas 9 2. Geochemical analyses of selected Valdez and Orca Group sandstone samples 13 3-5.Composition of sandstones: 3. From the Valdez Group: Mount Denson and Resurrection Peninsula areas 14 4. From the Orca Group: Cordova and Port Gravina areas 16 5.From the Orca Group: Sargent Icefield and Chenega areas 19 6. Statistical summary of first-degree trend surface for point-count data 21 7-8.Composition of sandstones: 7. From the Orca Group: Knight Island and Ella mar areas 22 8. From the Orca Group: Montague Island and Ragged Mountain areas 31 I.VF-L = 41.5-34.5-24).These rocks show similarities in petrography age, metamorphic grade, structural style, and sedimentary facies, to the Sitkalidak Formation, 400 km to the west, as well as petrographic similarities to the sediments of the Zodiac fan.Preliminary petrographic investigations (Mitchell, 1979;Winkler, 1976) suggested that the sandstone composition of the Valdez Group and its lateral equivalents is distinct from that of the Orca Group.The present study was undertaken in order to characterize the sandstone composition of the two groups throughout the Prince William Sound area and particularly to test whether a Introduction 1significant change in sandstone composition may help define the placement of the contact between the Valdez and Orca Groups.

Related Papers

• → Variability of subtidal current structure in a fjord estuary: Puget Sound, Washington(1985)31 cited
• → Seasonal oceanographic studies in McMurdo Sound, Antarctica(1962)40 cited
• Marine sedimentological data for the inland waters of Washington state (Strait of Juan de Fuca and Puget Sound)(1974)
• → A 35 mm microfilm compilation of collected bathymetry data from Cruise 77024, Labrador Sea, Davis Strait, Baffin Bay, Lancaster Sound, Jones Sound and Smith Sound, eastern Arctic(1989)
• → ON SOUND SCATTERING IN THE UPPER LAYERAND ON THE SHELF OF THE NORTH-WEST PACIFIC OCEAN(2020)