geol 440 sedimentology and stratigraphy: processes...
TRANSCRIPT
GEOL 440 Sedimentology and stratigraphy: processes, environments and deposits
Lecture 10: Sedimentary Environments and facies: an introduction; Controls on deposition,
preservation and accumulation
So, why do we need to understand the deposits of differing environments?
sedimentary & geological history (small-large scale)
economic importance - e.g. hydrocarbons, water
economic importance -minerals and metals (e.g. gold-diamonds-gypsum-aggregates)
prediction/management of contemporary environments
What do we need to quantify in order to characterise the deposits of differing environments?
grain size & typesedimentary structures - type, size, distribution larger-scale attributes - e.g. sandbody sizepalaeocurrentsbody/trace fossilsvertical and lateral variations (time & space)
Sedimentary Facies….….the essential sedimentary & palaeontological attributes of a
sedimentary environment….examine an environment - ancient and/or moderncharacterise key attributes - vertical and lateralestablish a ‘facies model’ - a key summaryof the environment
One key tool-the vertical profile or log(tho’ never neglect lateral variability &
characteristics)
height
grain size
cl si f m c gravelsand
Sedy structures
Tracefossils
CLASTIC CARBONATE
height
grain typemu wa pa gr
Body fossils
Trace fossils
Diagenetic features; vugs
Johannes Walther (1860-1937)
Walther’s Law: ‘Facies adjacent to one another in a continuous vertical sequence also
accumulated adjacent to one another laterally’
Facies Successions
Facies Succession – a progressive change in certain facies properties in a specific direction (vertically or laterally).
* Removes the environmental ambiguity of individual facies.
from today make sure you can…….
Reading:•Boggs, Part IV•Harold Reading (Ed): Chapter 2 (Controls on the sedimentary rock record)•Walker, Roger. Chapter 1, Facies Models revisited (in: Posamentier and Walker)
•Define a facies and facies association•Appreciate general approach to defining a facies•Think of the data you’d need to define a facies
Now…think of the advantages AND disadvantages of facies modelling…what are the possible pitfalls?