Data definition and standardization

One of the key aspects of FAKTS is the classification of each case study example and parts thereof on the basis of traditional classification schemes (e.g. dominant transport mechanism, channel/river pattern), external controlling factors (e.g.

description of climatic and tectonic context), and associated dependent variables (e.g. basin vegetation type and density, suspended sediment load component).

This context-descriptive information is linked to combinations of quantitative (hard) and qualitative (soft) data which describe fluvial architecture. Soft data stemming from interpretations (typically acquired from the published literature, though also from direct outcrop study) are used for defining the types of constituent units that build sedimentary architecture (assigned to predefined sets of classes; e.g. facies type) and some of their features (e.g. bounding surface order). These soft data are related to hard data, which are derived from measurement or observation (e.g.

dimensional parameters, spatial relationships, grain size). Since we rely on interpretations, a standardization of fluvial architecture is required for consistency:

common classifications are used, and a set of rules and criteria that define a procedure for translating the source data into FAKTS has been established to keep both data definition and data entry practice as objective and coherent as possible.

Fluvial systems are subdivided at the largest scale into subsets that have no given geological meaning, but are instead defined according to the two following types of criteria.

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Each representation of data about a geological subject (e.g. outcrop sketch, cross-section, log, correlation panel) that is named/numbered separately in the source work, is assigned a single subset. If data about one subject are originally split in the source work (e.g. sedimentological logs and architectural panels in separate figures but covering the same outcrop), the original datasets are merged into one single subset, and the associated type of spatial observation is the result of their composition.

Each dataset that is characterized by demonstrated or inferred changes in some of the attributes is split to obtain subsets with homogeneous attributes, thereby defining subsets as stratigraphic windows or planform segments with homogeneous attributes and no given scale. For example, outcrop panel stratigraphy can be subdivided into subsets on the basis of inferred basinal climate type. An alternative example is the distinction of modern river planform subsets on the basis of channel pattern.

These two criteria are not mutually exclusive and can be combined, for example where many outcrop profiles are considered, each being subdivided into several subsets on the basis of inferred changes in external parameters and controls.

Depositional elements are simply classified as channel-complex or floodplain elements. Channel-complexes represent channel-bodies (and their infills) that are defined on the basis of flexible but unambiguous geometrical criteria (see appendix A), and are not related to any particular genetic significance or spatial or temporal scale (cf. Dalrymple 2001; Gibling 2006); they range from the infills of individual channels cutting through the floodplain to compound, multi-storey valley-fills. This definition facilitates the inclusion of datasets that are poorly characterized in terms of the geological meaning of these objects and their bounding surfaces, and this is especially the case for most subsurface datasets. Floodplain depositional elements are also defined on the basis of unambiguous geometrical criteria, and their segmentation is subsequent to channel-complex definition, as floodplain deposits are subdivided according to the lateral arrangement of channel-complexes (see the hypothetical example in figure 2.2).

Figure 2.2: hypothetical example showing object indexing of subsets, depositional elements, architectural elements and facies units and illustrating how the nested containment of each order of objects is implemented in the tables by making use of the unique indices. Facies types follow Miall’s (1996) classification; architectural element types follow a classification that is purposely defined for FAKTS database, and derives from Miall’s (1996) scheme.

Following Miall’s (1985; 1996) concepts, architectural elements are defined as components of a fluvial depositional system with the characteristic facies associations that compose individual elements interpretable in terms of sub-environments. FAKTS is designed for storing architectural element types classified according to both Miall’s (1996) classification and also to a classification derived by modifying some Miall’s classes (table 2.1) in order to make them more consistent in terms of their geomorphological expression, so that working with datasets from modern rivers is easier. Architectural elements described according to any other alternative scheme are translated into both classifications following the criteria outlined by Miall (1996) for their definition.

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Table 2.1: Architectural element type classification adopted in FAKTS; codes are modified after Miall (1996).

Code Architectural element type – geomorphic significance CH Vertically accreting (aggradational) channel (fill)

DA Downstream accreting macroform LA Laterally accreting macroform

DLA Downstream + laterally accreting macroform and undefined accretion direction macroform

SG Sediment gravity flow body HO Scour hollow fill

LV Levee

AC Abandoned channel (fill) FF Overbank fines

SF Sandy unconfined sheetflood dominated floodplain CR Crevasse channel

CS Crevasse splay LC Floodplain lake C Coal body

In FAKTS, facies units are defined as genetic bodies characterized by homogeneous lithofacies type down to the centimetre-scale, bounded by second- or higher-order (Miall 1996) bounding surfaces. Lithofacies types are based on textural and structural characters; facies classification follows Miall’s (1996) scheme, with minor additions (e.g. texture-only classes – gravel to boulder, sand, fines – for cases where information regarding sedimentary structures is not provided) (table 2.2). Both facies type and architectural element type classifications can be expanded and edited at any time: classes can be added as they are recognized, and others deleted in order to keep the new classes mutually exclusive.

Table 2.2: Lithofacies classification adopted in FAKTS; modified after Miall (1996).

Code Characteristics

G-

Gravel deposits with undefined structure and undefined additional textural characteristics. Gravel-grade sediment (granule to boulder) usually constitutes the majority of the unit by volume, as the graded or massive structure of bi- or pluri-modal matrix-supported conglomerates/gravels is very likely to be recognized.

Gmm Matrix-supported, massive or crudely-bedded gravel.

Gmg Matrix-supported, graded gravel.

Gcm Clast-supported, massive gravel.

Gci Clast-supported, inversely-graded gravel.

Gh Clast-supported, horizontally- or crudely-bedded gravel; possibly imbricated.

Gt Trough cross-stratified gravel.

Gp Planar cross-stratified gravel.

S- Sand deposits with undefined structure. Sand-grade sediment must constitute the majority of the package by volume.

Ss Faintly laminated/cross-bedded, massive or graded sandy fill of a shallow scour.

Sm Massive sand; possibly locally graded or faintly laminated.

Sd Soft-sediment deformed sand.

Sw Symmetrical ripple cross-laminated sand.

F- Fine-grained (silt/clay) deposits with undefined structure. Fine-grained sediment must constitute the majority of the package by volume.

Fl Interlaminated very-fine sand, silt and clay; thin cross-laminated sandy lenses may be included into these heterolitic packages.

Fsm Laminated to massive silt and clay.

Fm Massive clay.

Fr Fine-grained root bed.

P Pedogenic carbonate.

C Coal or highly carbonaceous mud.