JT, '14 1

the tools and techniques

GEOL 202: Earth Surface Processes and Deposits

Practical Basin Analysis

JT, '14

Mostly - adding the subsurface dimension

drilling

remote sensing

2

three-dimensional visualization and analysis

JT, '14

Applicability: Energy resources: oil, gas, coal, nuke,

geothermal,

Minerals

Groundwater

Seismic hazards

Engineering applications

Environmental studies

?

3

JT, '14

measured section (review) what it will show

lithology (symbols)

grain size of

individual beds

grain-size trends

in beds

among beds

interpretation

4

JT, '14

what about subsurface data? mudlog

core

geophysics

5

JT, '14

lithologic log - mud-logging

6

data aquired as the drill-bit goes down

cuttings

JT, '14

subsurface measured sections from wells well logs and well

data

sample cuttings

and core

drop electrical

probes down the hole

7

how does this work?

JT, '14

Reverse-circulation drilling

8

JT, '14

subsurface measured sections from wells remember cuttings

are returned from the top, down!

data will be

gathered in reverse order of stratigraphy

9

how does this work?

JT, '14

and core samples lots of information

and very expensive

10

JT, '14

down-hole electric logs pull the drill-string and lower a variety of

probes to determine whats down there

11

JT, '14

basic electric log response SP - spontaneous

potential

voltage between

the surface and the depth

resistivity - between two probes in the hole

gamma radiation

12

JT, '14

combined well logs

the lithology log here is symbolic (to make it all digital)

based on well ...

cuttings brought

up in the circulating mud

core

13

Kansas Geological Survey

JT, '14

geophysical logs

left - gamma ray log

SGR = total

CGR = w/o uranium

right - resistivity log

14

Kansas Geological Survey

JT, '14 15

example of the end product, delivered by contractors

this is all the exploration geologist sees, most of the time

JT, '14

logging other aspects

composition

cuttings

geophysical

properties

17

% composition plots

JT, '14

down-hole imaging Schlumbergers latest flashy

technology - virtual core

18

JT, '14

what other kinds of data can we gather?

from outcrop

from geophysical attributes

19

JT, '14 20

High-resolution stratigraphy - very detailed logs of outcrop or well data

usually only a few (or one) components at a time

Systematic sampling strategy - e.g. a regular interval like every 10cm, or ?

advantages

disadvantages

practicality?

JT, '14

high-resolution stratigraphy (cont.)

Choosing the data suite

geochemical

climate, biological activity, alteration

geophysical

best for cryptic sections?

petrological

component sources

other component

21

JT, '14

chemo-stratigraphy

an example:

carbon isotope

ratios in limestone record changes in sea-level

22

next slide

JT, '14

close-up detail - carbon isotope fluctuations reflect sea-level change

23

JT, '14

another example - gamma-ray

log of outcrop

24Pawellek & Aigner, 2003

JT, '14 25

sedimentology-based data: Paleocurrent analysis

detailed information about environmental systems based on paleocurrent indicators

key issues

identifying type of indicator

data distribution

statistically significant numbers

JT, '14

how to display data? rose diagram

a circular

histogram of directions

length of petal shows number of measurements

direction of petal is orientation

26

JT, '14 27

paleoflow scale hierarchy: example from one riverEach hypothetical rose averages the box area. Which one is outcrop scale?

smallest scale: crevasse in river bar face

largest scale: delta system

largest area

smallest area

JT, '14 28

Interpret data spread Meandering river with

laterally migrating bars

Average is not far o, but

Range is wide, some are

upstream

Importance of enough data!

JT, '14 29

Stratigraphic analysis with paleocurrents

Fluvial section, shows different trends for:

in-channel sand

laterally aggrading bars

bar tops

JT, '14 30

K Gallup Ss.: offshore to backshore prograding beach system

Note: Oscillatory indicators (NE-SW) in shoreface (shallow, fair weather) and in offshore (deep, storms)

Longshore drift indicators (NW-SE) in upper shoreface

Harms et al., 75

Stratigraphic analysis with paleocurrents

JT, '14 31

Regional analysis - paleocurrents

Devonian conglomerate clastic section with stratigraphically AND regionally consistent paleoflow to the WSW

(Nilsen et al. 1981)

JT, '14 33

Three-dimensional correlation Placing stratigraphic sections on a map

defining axes

x and y axes are often north and east

z axis is almost always thickness

JT, '14 34

Fence diagrams 3-dimensional correlation of sections

on a map base

tie together two or more cross-section

false perspective view

(unless map is tipped, too!)

allows analysis of spatial distribution

JT, '14

example - parking lot substrate, an engineering study

35

Tina Marja Hariu

JT, '14

with many fence posts... better 3D

distribution

problems:

perspective

hidden panels

36

JT, '14 37

Maps that interpret stratigraphy - isopleth maps

Structure contour maps

Isopach maps

Isochore maps

Isolith maps

Facies maps

Paleogeographic maps

isopleth maps defined - any map that represents data at geospatially located points in a continuum that can be contoured

JT, '14 38

Structure contour maps a contour map on a surface, usually a

lithosome (formation) boundary

datum is sea-level

negative elevations possible and common

data are surface elevation

JT, '14

visualize topography on the

top of a key bed

slopes = bedding

dip

hills & valleys =

anticlines and synclines

39Schlumberger

JT, '14

example: structure contours on a doubly plunging syncline Salem, KY

note:

closed

contours

parallel

fold limbs

41

JT, '14

more complex subsurface shapes

42

anticline

syncline

JT, '14 43

Isopach maps contour maps of stratigraphic

thickness

USGS

JT, '14

isopach maps, the rules: datum is base, or (usually) top of unit

(why?)

data are measured *true thickness

*corrected for dip

special features

no negative values (i.e. no thickness less

than zero)

zero line is pinch-out

44

JT, '14

stratigraphic vs. vertical thickness problems if dips are steep

45

thickness for isopach maps

cross section

JT, '14

using isopach maps to define an impact structure in California Jared Morrow and Bennett Spevak (2007)

46

isopach maps on crater fill

seismic section across crater 3D reconstruction

JT, '14

regional isopach maps Pennsylvanian

tectonic basins, thickness indicates

depth

accommodation

47

interpreting this map?

JT, '14 48

Ron Blakeys paleogeography

same scales

JT, '14 49

Isochore maps drilled vertical thickness

thickness for isochore maps

JT, '14

tephra thickness isopach Rio Blanco tephra (3500ybp), Costa Rica

51

JT, '14

structure and isopachs note thickening over structure high

52Schlumberger

JT, '14 53

Isolith (lithofacies) maps Percentage maps

contours of equal percentage of some value

e.g. % mud, % plagioclase feldspar

Ratio maps

contours of ratio values

commonly thickness ratios

favorite version - clastic ratio map

ratio of siliciclastic to carbonate rocks within

a given section

JT, '14

lithofacies map example

54

facies are determined from a ternary plot (Young et al., 1976)

JT, '14

example of a clastic ratio map the ratio is

contoured

55

JT, '14 56

Facies distribution maps Interpretive facies maps

Paleogeographic (time-

slice) maps

JT, '14 57

geologic subcrop maps pick a unit or an age, and remove

everything above/younger

e.g. a Triassic subcrop map includes all

Triassic and older rocks.

JT, '14

example: Mississippian in Kansas

58

Kansas state map of major structural elements

Mississippian subcrop map

Schaben oilfield

Kansas Geol. Survey

JT, '14

zoom in to the Schaben oilfield

60

cross section based on well logs

Miss. subcrop map

shows a west-dipping angular unconformity

JT, '14

Newer geophysical analyses seismic exploration

62

layers are acoustic events and thickness is really time.

JT, '14

Newer geophysical analyses 3D seismic

63

JT, '14

combine 3D seismic with side-scan sonar

64