Towards a new NGDC sediment classification scheme

1. 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”

2. Current system for lithologic description Determine field for primary lithology and then select name from code list (components)

3. 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)

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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.

12. 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