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Towards a new NGDC sediment classification scheme. Steve Carey, Paula Worstell, Guy Rothwell, June Wilson, Tom Janecek. Objective: Devise a new classification scheme that:. 1. Is easy to understand and use 2. Maintains a large degree of consistency between the existing ODP and the NGDC

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towards a new ngdc sediment classification scheme
Towards a new NGDC sediment classification scheme

Steve Carey, Paula Worstell, Guy Rothwell, June Wilson, Tom Janecek

Objective: Devise a new classification scheme that:

1. Is easy to understand and use

2. Maintains a large degree of consistency between the existing ODP and the NGDC

3. Is useful to database users

4. Avoids cumbersome and uninformative terms, e.g. “mixed sediments”

slide2

Current system for lithologic description

Determine field for primary lithology and then select name

from code list (components)

slide3

Lack of consensus

1. Extent to which the sediment classification

should be devoid of any genetic interpretations

2. Retention of the neritic sediment class

3. Exact scope of potential data entry

Present two models for discussion:

1. Descriptive sediment classification (Ternary)

2. Simple sediment classification (SSC)

slide4

Ternary Sediment Classification

Paula Worstell, SIO

Objective: modify ODP sediment classification for use

With NGDC/curator’s database

Major Points:

1. Completely descriptive approach

2. Input data with increasing levels of detail

3. Base component listings on those that can be recognized

in smear slide and gross lithologic descriptions

4. Use a ternary system of classification based on three major

sediment classes

slide5

100% biogenic

50% biogenic

(all forms)

Biogenic

Class

(all forms)

30% biogenic

(monomineralic)

Biogenic

(similar forms)

Biogenic

(similar forms)

Mineral/Lithic

Class

Glass Class

100% glass

100% mineral/lithics

Classes for Granular Sediments

1. Biogenic: components include forams, coccoliths, diatoms,

shell fragments, coral fragments, etc.

2. Glass: components include mafic and acidic glass,

microtectites, palagonite

3. Mineral/lithic: components include quartz, feldspar, clay

minerals, zeolites, heavy minerals, etc.

Class Ternary Diagram

slide6

Naming Conventions for Granular Sediments

Prinicipal name: determined from ternary diagram and

selection from list unique to the class

Major modifer: precedes principal name and corresponds

to components of:

1. >15% for biogenic class

2. >25% for glass and mineral/lithic classes

Minor modifer:follows the principal name, linked by

“with”. Corresponds to components of:

1. 5-15% for biogenic class

2. 10-25% for glass and mineral/lithic classes

Examples:

1.Biogenic: foraminfer ooze with quartz

2.Glass: feldspar tuff with rock fragments

3. Mineral/lithic: quartz sand with feldspar

slide7

Data Input for Ternary Sediment Classification

Component data entered as numeric values and

by a series of pop-up menus

Example:

Total % Biogenic- enter numeric value

Total % Glass- enter numeric value

Total % Mineral/lithic- enter numeric value

Physical state- via pop-up menu

Major component (>25%): via pop-up menu

Minor component (10-25%): via pop-up menu

Pop-up selections to be arranged in a

hierarchical structure with increasing detail

slide8

Simple Sediment Classification (SSC)

Steve Carey, GSO/URI

Objective: modify ODP Sed. Classification for use with NGDC/curator’s database

Major Points:

1. Retain four major sediment classes of the ODP scheme

2. Eliminate the mixed sediment class

3. Minimize the number of component data inputs needed

to classify sediment

4. Reduce the amount of data entry required for the database

slide9

Ratio of

siliciclastic

to

volcaniclastic

grains

Classes for Granular Sediments

1. Pelagic: fine grained organic debris of open ocean microflora

and microfauna, e.g. forams, radiolarians, ccccoliths

2. Volcaniclastic: rock fragments and minerals derived from

volcanic sources

3. Siliciclastics: mineral and rock fragments derived from

plutonic, sedimentary or metamorphic rocks

4. Neritic: coarse-grained calcareous skeletal debris, etc.

Class Diagram

1:1

>1:1

<1:1

0

100

Volcaniclastic

Siliciclastic

sediment

sediment

%Siliciclastic and volcaniclastic grains

%pelagic and neritic grains

50

50

Neritic

Pelagic

sediment

sediment

0

100

1:1

>1:1

<1:1

Ratio of pelagic to neritic grains

slide10

Naming Conventions for Granular Sediments

Prinicipal name: determined from class diagram and

selection from list unique to the class

Major modifer: precedes principal name and corresponds

to components of:

1. >25%

Minor modifer:follows the principal name, linked by

“with”. Corresponds to components of:

1. 10-25% for biogenic class

Examples:

1.Pelagic: foraminfer ooze with quartz

2.Neritic: pellet grainstone with bioclasts

2.Volcaniclastic: feldspar tuff with rock fragments

3.Siliciclastic: quartz sand with feldspar

slide11

Data Input for Simple Sediment Classification

Component data entered as absolute % of major group with major and minor

components identified by pull-down menus

Example:

Total% pelagic components 35

Major pelagic component forams

Minor pelagic component

Total % siliclastic component 10

Major pelagic component

Minor siliclastic component quartz

A minimum of 16 potential data inputs related to component abundances are needed to classify sediment.

slide12

Advantages

1. Implemented with moderate training of sediment describer

2. Does not assume any genetic interpretation

Disadvantages

1. Potential for unusual sediment classification

2. More extensive data input

Simple Sediment Classification

Advantages

1. Implemented with less training of sediment describer

2. More similar to ODP convention

3. Easy data entry

Disadvantages

1. Sacrifices details of individual component analysis

2. Retains sediment classes with genetic implications

3. Concerned mainly with main sedimentary components

Summary

Ternary Sediment Classification