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Ghost Ranch, New Mexico, Project Overview – GEO 660, Summer 20006

Explore the physical response of aeolian sands seas to wind changes over 100,000 years in Ghost Ranch, New Mexico. Study Entrada and Todilto formations, rock record of migrating dunes, and dune preservation. Interpret depositional settings and paleotopography.

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Ghost Ranch, New Mexico, Project Overview – GEO 660, Summer 20006

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  1. Ghost Ranch, New Mexico, Project Overview – GEO 660, Summer 20006 Physical Response of Aeolian Sands Seas to Changes in Wind Regime Over the Last 100,000 Years – An Approach From System Self-Organization Gary Kocurek

  2. Overview of project Your preparation More time in field looking at the geology and less lecture Objectives of Pre-Class Meeting

  3. Regional paleogeography Review of aeolian systems and their rock record Ghost Ranch Project Middle Jurassic Entrada & Todilto Formations What is unique about Entrada dune record Some parts of the explanation Project assignment Topics Addressed

  4. Middle Jurassic World View

  5. Western North America • Subduction complex • Interior seaway • Entrada Desert

  6. Entrada Sand Sea (In Part!)

  7. Entrada & Todilto Paleogeography

  8. Todilto Formation Facies • Inland sea • Bull’s eye facies pattern • Surrounded by Entrada dunes • Marine and sabkha facies to north and west

  9. Ghost Ranch Outcrop

  10. What Is The Rock Record Of Migrating Aeolian Sand Dunes?

  11. Ancient Aeolian Record • Sets of dune cross-strata • Each set is produced by one migrating dune • Transport direction determined by foreset dip directions • Interdune surface and overlying flat interdune strata

  12. Ancient Aeolian Record

  13. Ancient Aeolian Record

  14. Stratification Types of Dune Foresets • Lee-face deposits • Grainflow • Grainfall • Wind ripples • Textural differences reflected in diagensis

  15. Grainflow & Grainfall Strata

  16. Grainflow & Wind-Ripple Strata

  17. Wind-Ripple Laminae

  18. Grainflow Cross-Strata

  19. Grainflow, Wind-Ripple & Flat Strata

  20. Ghost Ranch Outcrop: What Is Special Regarding Dune Preservation?

  21. Entrada/Todilto Outcrop • L & G are Todilto facies • M represents subaqueous mass flow deposits • D is the last Entrada dune • Compare D to underlying Entrada strata

  22. “Right” Wall of Entrada/Todilto Outcrop

  23. “Left” Wall of Entrada/Todilto Outcrop

  24. Todilto Facies I: Well Laminated Limestone

  25. Todilto Facies I In Thin-Section

  26. Todilto Facies II: Brecciated Laminae Limestone

  27. Todilto Facies III: Wavy Laminae Limestone

  28. Todilto Facies IV: Micro Laminae Limestone

  29. Todilto Facies V: Gypsum

  30. Explain the occurrence of preserved Entrada dune paleo-topography (one of 3 known examples globally!) Components Draw for yourself the outcrop walls of the Entrada & Todilto By a series of connected measured sections, document the relationship of the Todilto facies to the Entrada paleotopography Interpret/contrast depositional settings of Entrada dune, mass flows, and Todilto facies What to hand in Two drawings No more than 2 pages of text that gives your interpretation with support (exclude irrelevant material!) Ghost Ranch Project

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