Sedimentary Structures - PowerPoint PPT Presentation

1 / 8
About This Presentation
Title:

Sedimentary Structures

Description:

Bedding - layering! Layering of sediments is common due to ... Cross-bedding (inside ... large scale cross-bedding in these sandstones (interpreted ... – PowerPoint PPT presentation

Number of Views:699
Avg rating:3.0/5.0
Slides: 9
Provided by: westfiel
Category:

less

Transcript and Presenter's Notes

Title: Sedimentary Structures


1
Sedimentary Structures
  • Clues to depositional environments

2
Bedding - layering!
  • Layering of sediments is common due to episodic
    deposition
  • In most cases the layers are close to horizontal
    at the time of deposition
  • Layering may survive lithification

Loose sediment - Merrimack Valley
East Berlin formation - Holyoke
3
What does a geologist see?
Colorado River - Grand Canyon National Park, AZ
4
Ripple marks - indicate currents
Pyramid Lake, NV
Grand Canyon Natl. Park, AZ
  • Ripples form on the surface of sediment (mud or
    sand) over which a current of wind or water is
    flowing
  • Current direction may be indicated by the
    asymmetry of the ripples (steep side upstream)

5
Cross-bedding (inside ripples or dunes)
  • Sediment layers on the front slope of a ripple or
    dune will be inclined at the time of deposition
  • Current direction is indicated by the direction
    of tilt of those cross-beds

Interior of ripples in outwash - NH
De Chelley sandstone - AZ
6
  • Note large scale cross-bedding in these
    sandstones (interpreted as old desert dunes,
    lithified to stone!)

Canyon de Chelly, AZ
7
Mudcracks (drying of fine sediment)
In sediment, near Albany, NY
In mudstone, Glacier Natl. Park, MT
  • Mudcracks form when wet, muddy sediment dries out
    and shrinks
  • Other sediment may fill in the cracks, preserving
    these features after lithification

8
Implications for environments?
  • Bedding - episodic deposition, undisturbed
    sediment (no burrowers)
  • Ripples marks - margins of streams, windy
    environments (current of wind or water)
  • Cross-bedding - margins of streams, desert dunes
    (similar to ripples - the cross-beds are inside!)
  • Mudcracks - seasonal lakes, margins of rivers or
    lakes (occasional drying out of environment)
Write a Comment
User Comments (0)
About PowerShow.com