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Stratigraphic Plug Alignment (SPA)

Source: R/spa_align.R
spa_align.Rd

Linearly interpolates plug-based measurements (e.g., TOC, porosity, XRD) onto a high-resolution reference depth grid (e.g., XRF). The procedure uses base R's approx() with rule = 1 (default) to prevent extrapolation beyond the observed depth range, ensuring stratigraphically consistent alignment of all datasets.

Usage

spa_align(
  ref,
  ...,
  depth_col = "Depth_m",
  rule = 1,
  add_suffix = TRUE,
  trim = FALSE
)

Arguments

ref

A data.frame containing the reference depth grid and (optionally) high-resolution variables (e.g., XRF). Must contain the depth column specified in depth_col.

...

One or more named data.frames containing plug-based measurements to be interpolated (e.g., xrd = xrd_df, plugs = plug_df).

depth_col

A character string giving the name of the depth column shared by all input datasets. Defaults to "Depth_m". The depth column may use any unit (e.g., meters, feet, centimeters); "Depth_m" is only a column label and does not require depths to be in meters. However, all input datasets must use the same depth unit for interpolation to be meaningful.

rule

Integer passed to approx() (default 1). rule = 1 prevents extrapolation outside the observed depth range. rule = 2 performs constant extrapolation (end-point hold).

add_suffix

Logical; if TRUE, variable names are suffixed with the dataset name (e.g., TOC_plugs, Quartz_xrd).

trim

Logical; if TRUE, drops rows where any interpolated column is NA. Default FALSE (preserves all reference depths).

Value

A data.frame containing the reference depth grid and interpolated variables aligned to the same resolution.

Details

SPA is intended for vertically ordered core or log data, where measurements are indexed by depth along a stratigraphic profile.

Examples

ref <- data.frame(Depth_m = 0:10, Ca = runif(11, 100, 200))
xrd <- data.frame(Depth_m = c(2, 5, 7), Quartz = c(54, 60, 58))
plugs <- data.frame(Depth_m = c(3, 7, 9), TOC = c(3.0, 3.3, 3.5))

# Default: preserves reference depth grid
aligned <- spa_align(ref, xrd = xrd, plugs = plugs)
head(aligned)
#>   Depth_m       Ca Quartz_xrd TOC_plugs
#> 1       0 160.0761         NA        NA
#> 2       1 115.7208         NA        NA
#> 3       2 100.7399         54        NA
#> 4       3 146.6393         56     3.000
#> 5       4 149.7777         58     3.075
#> 6       5 128.9767         60     3.150

# Overlap-only alignment
aligned_overlap <- spa_align(ref, xrd = xrd, plugs = plugs, trim = TRUE)