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Mariscal Canyon, Southernmost Big Bend National Park:

Mariscal Canyon, Southernmost Big Bend National Park: Contractional and Extensional Deformation and A Recently Exhumed Rhyolite Ignimbrite. Patricia Wood Dickerson South-Central GSA, March 2012. Mariscal Canyon — Talley to Solis. Lower Cretaceous Stratigraphy.

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Mariscal Canyon, Southernmost Big Bend National Park:

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  1. Mariscal Canyon, Southernmost Big Bend National Park: Contractional and Extensional Deformation and A Recently Exhumed Rhyolite Ignimbrite Patricia Wood Dickerson South-Central GSA, March 2012

  2. Mariscal Canyon — Talley to Solis

  3. Lower Cretaceous Stratigraphy Santa Elena - massive limestone cliff-former Sue Peaks - shale & thin limestone slope-former Del Carmen - massive limestone cliff-former Confirmed exposures of Kdc and Ksp in Mariscal Mountain. Ksp somewhat thinner than in Sierra del Carmen, Santa Elena Canyon.

  4. WSW-Striking Fault & Thrust Detail

  5. Rio Grande Flooding, September 2008 Boquillas Hot Springs - note bathhouse

  6. Thrust Fault in Central Canyon North riverbank – exhumed by flooding Ksp and Kse are thrust, overturned to E Thrust is cut by N-striking normal fault; thin-bedded, overturned Ksp against massive, near-horizontal Kse; thick breccia carapace Ksp is oldest unit at river level on N bank

  7. Thrust Fault & Normal Fault, Central Canyon River flows in WNW-striking normal fault that cuts thrust. South bank is upthrown, exposing thrusted Kdc, Ksp & Kse. Kdc is not present on north riverbank and was not seen east of this reach of the Canyon.

  8. Cross Canyon Detail

  9. Cross Canyon - View NW Kse rolling over along thrust crest, dips to ~30° E Kbo folded to east of thrust

  10. Newly Exhumed Ignimbrite (gray, foreground) • Densely welded rhyolite tuff • Dips 25 degrees SSW • Discordant with respect to • deformed Cretaceous strata • N contact buried beneath sand • and gravel; E, S & W contacts • submerged • Probable remnant of more • extensive deposit, preserved • in depression in K rocks • Foundered into a solution- • collapse cavity? (common on • Mariscal Mt.) • Let down due to undercutting • by the river & removal of • fractured, less resistant K rock?

  11. Solution Collapse Features – Foundered Rhyolite Sill, NE Flank of Mariscal Mt. (Dickerson et al., 2010, BEG Misc. Map 48)

  12. Cross Canyon — Fold in Footwall of N-Striking Thrust Kbu in fold flank Kbu and folded Kbo

  13. Slickenside Camp — Flower Structure

  14. Slickensided Fault Wall, Flower Structure L-L fault, striae rake 40° SE Fault breccia at striated wall

  15. Eastern Flower Structure Fault Kse dips 11º SW east of fault, 21º WSW on west Contractional fault at cliff base Undulating shear planes 

  16. Western Flower Structure Fault Variable S and W dips on slabs between shears 1 or 2 m vertical offsets Contractional fault at lower left Horizontal Kse approaching flower structure from W 

  17. Flower Structure Diagram (Goetz in Goetz & Dickerson, 1985)

  18. Eastern Range-Front Fault Kbo downdropped against Kse on normal fault Kse dips 12° E, Kbo dips 14 ° E

  19. Mariscal Canyon – more to explore… Thanks to Commander & Crew: Marcos Paredes, NPS Jim Bones Mary Bridges Bones

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