What makes a name a lithostratigraphic unit, and the rank/informal-term vocabulary this project actually uses.
Per the definitions note (strict sense): a lithostratigraphic unit needs at least constituent rocks
plus chronology (relative or absolute) or a formally established name — this mirrors the actual
criteria in the North American Stratigraphic Code and the International Stratigraphic Guide: distinctive
lithology, definable boundaries, and (for formal rank) a type section/locality. Fossils and structural
features (faults, suture zones) are a separate, broader category layered on top — see Body types
below, and Stratigraphy for the structural layer itself. Mineral occurrences follow
the same naming logic but are tracked separately (mineria[], not units[]).
Standard lithostratigraphic ranks, highest to lowest. Each rank groups one or more of the rank below it; not every level has to be used for a given succession.
Formation is the fundamental, mappable unit — the one every succession is expected to have. Member and Bed are optional finer subdivisions; Group and Supergroup are optional coarser groupings. Two of the most common rank terms seen in this corpus, side by side:
| Rank | Definition | Example from this corpus |
|---|---|---|
| Formation | The basic mappable lithostratigraphic unit — one dominant lithology or a distinctive interbedded association. | Cieszyn Limestone Formation, Hradiště Formation |
| Member | A named, lithologically distinct part of a formation — doesn't have to cover the whole formation's extent. | Cisownica Member, Piechowka Member (both within the same formation) |
Same base name, different rank word (e.g. "X Group" vs. "X Formation") does not automatically mean
the same unit under two names — the pipeline flags this explicitly as a distinct case
(rank_word_diff() in names.py) rather than merging on name alone, precisely
because a group and a formation with the same root name are sometimes genuinely different bodies.
These aren't part of the formal rank ladder above, but they're common in the tectonic literature this
project draws on and show up constantly as body_type values in the extracted data — this is
the corpus's own GENERIC_TERMS vocabulary (rank words + structural/regional qualifiers that
similar() discounts when comparing names).
| Term | What it marks | Formality |
|---|---|---|
| Nappe / Unit | A thrust sheet — a body defined by tectonic transport, not stratigraphic superposition. | Formal corpus (e.g. Silesian Unit, Magura Nappe) |
| Complex | A body too heterogeneous or structurally reworked for a single lithology/rank — often several formations juxtaposed tectonically. | Usually informal corpus |
| Suite | A group of associated igneous (usually plutonic) bodies sharing origin/age, not stratigraphic superposition. | Formal, IUGS igneous nomenclature |
| Zone | A structural or tectonic domain (e.g. a suture zone) — spatial, not necessarily one lithology. | Informal–formal, context-dependent |
| Basin | A sedimentary depocenter — the area of accumulation, not the rock body itself. | Informal (regional) corpus (e.g. Silesian Basin, Skole Basin) |
| Province | A broad region sharing a genetic/tectonic or igneous character (e.g. an igneous province). | Informal (regional) corpus (e.g. Cieszyn igneous province) |
| Association | A recurring group of rock types interpreted as genetically related, short of formal suite status. | Informal corpus (e.g. teschenite–picrite association) |
"Beds" and "flysch" deserve a flag on their own: both were found doing double duty as a rank word in some
articles and a genuine body-type/lithofacies term in others (the real bug caught while tightening
similar(), 02/09) — when in doubt, check Lexicon for how a specific
name was actually tagged rather than assuming from the word alone.