Stratigraphy & the Stratigraphic Column

VRGS can attach a stratigraphy to an object — an internationally recognised chronostratigraphic unit, your own group / formation / member naming, and measured ages where you have them — and draw a stratigraphic column beside the 3D view showing where everything sits in geological time.

Two things carry a stratigraphy today:

A triangulated mesh	What a whole outcrop is.
A stratigraphic marker	An age pinned to one location — a measured horizon, a dated sample, a picked contact.

Giving an object a stratigraphy

Select the object and open the Stratigraphy group in its property sheet. It offers three independent descriptions, any of which you can leave blank.

Chronostratigraphy — picked from the ICS chart

Chosen as a cascade: System → Series → Stage, each list filtered by the one above. Choosing the Cretaceous drops the stage list from 102 entries to twelve, which is what makes it usable — a flat chart dropdown is 171 units and nobody can find anything in it.

Row	What it is
System	Period / System. Narrows the two lists below it.
Series	Epoch / Series within the chosen System.
Stage	Age / Stage within the chosen Series (or System).

You do not have to fill all three: the most specific level you have chosen is the one that counts, so a System on its own is perfectly valid. Choosing a blank clears that level and everything below it.

The lists re-filter as you go

Changing a level rebuilds the rows below it, so pick top-down. If you switch the System from Cretaceous to Jurassic, a stale Turonian in the Stage row is cleared rather than left sitting there meaning nothing.

Lithostratigraphy — your own naming

Group, Formation and Member are free text: what you call the rock. They are deliberately never matched against the ICS chart — "top unit 1" is a perfectly good formation name and means nothing to the chart. They are purely descriptive and never move the column.

Measured ages

Age (Ma) — millions of years before present — refines that end rather than replacing it. So an object can say "Turonian, but I have dated the base at 92.1 Ma" and get a tighter interval than the stage alone would give.

Two ends, for an object that spans an unconformity

Meshes get Top (younger) and Base (older) groups, each carrying the full set — chronostratigraphy, lithostratigraphy and a measured age — because an outcrop spanning an unconformity really is different rock at the top than at the base.

Leave the Base group blank for anything sitting within a single unit.

A read-back row at the bottom of the group shows the resolved age range — 66 – 100.5 Ma — or says "no age (descriptive only)" when only lithostratigraphy was given, or "not set". That row is how you catch a unit name the chart does not recognise, rather than only noticing later that the column is quietly ignoring the object.

Stratigraphic markers

A marker is a point in the model carrying an age. Place one from the Interpretations tab's Strat Marker command: click the spot on the outcrop, then say what it is in its property sheet — the same way samples and waypoints are placed.

• A marker is a single point in time by default, so it gets one Age group rather than Top and Base. Mark it as spanning an unconformity to get both.
• The marker captions itself with the most specific stratigraphy it carries — member, else formation, else group, else the ICS unit — because that is what identifies it on the outcrop. Its object name (Strat Marker_3) says nothing. A marker with no stratigraphy yet falls back to its name.
• Markers take their colour from the official CGMW colour of the ICS unit they carry, so a scene of markers reads as the same palette as the column beside it.
• They are listed under Stratigraphic Markers in the Data tree, with the usual point-annotation group options: Show Labels, Label Size, Maintain Size, Display Size and LOD.

The stratigraphic column overlay

Switch it on from Home → Options → Overlays → Strat Column. It draws a column of geological time down the side of the 3D view, with each unit in its official CGMW colour.

The chart is generated from the Macrostrat international timescale (CC-BY 4.0, ICS-derived): 171 units from Eon down to Stage, including all 102 stages.

What it shows

• Bands at the finest rank that is legible at the current size. Where stages fit, the column draws up to three strips — Period | Epoch | Stage — because a bare Epoch beside a stage is not enough context.
• Markers for the objects in the scene that carry a stratigraphy, at the ages they resolve to.
• The picked object's own range. Click a mesh or a marker in the 3D view and the column brackets where it sits, captioned with the object's name. A bracket rather than a filled band, because filling would hide the very bands the selection is meant to be read against; a caret in the left margin keeps a selection only a pixel or two tall findable.

Choosing the age window

Priority, highest first:

1. Mouse-wheel zoom over the column. It zooms the age axis about the cursor, so the age under the pointer stays put across notches. It is clamped to the chart at one end and to the shortest stage at the other, and slides rather than truncating at the ends.
2. The project's age range, if you set one. In the project property grid's Stratigraphy group: tick Set Age Range and give Top Age (Ma) (the younger end) and Base Age (Ma). A Book Cliffs project is Top 66, Base 100.5. It is the opening view, not a limit — the wheel can still take you outside it.
3. Worked out from the model — the span of whatever stratigraphy the visible objects carry.
4. The whole chart, when nothing else applies.

Getting back to auto-ranging

There is no reset button. Switching the column off clears the wheel zoom, so turning it off and on again returns it to the project range or to the model's own extent.

Renderer differences

Wheel zoom over the column is Vulkan only. The OpenGL view still draws the column and still honours the project age range.

How the age is resolved

For each end of an assignment:

1. If a measured age was given, that is the age.
2. Otherwise the most specific chronostratigraphic level filled in supplies the boundary — its younger boundary for the top, its older boundary for the base.
3. Lithostratigraphy never contributes an age. An object described only by formation name has no age and does not appear on the column; the read-back row says "no age (descriptive only)" so you can see that is what happened.

Stratigraphy and Athos

An object's stratigraphy is appended to its description in the same tagged form the rest of VRGS uses, so it reads as prose and is findable — a question like "which surfaces are Turonian?" has something to match. Any free text you have already written in the object's LLM Context row is kept; the stratigraphy is added to it, not substituted for it.

Tips and troubleshooting

• The object does not appear on the column. It has no resolvable age — check the read-back row in its Stratigraphy group. Lithostratigraphy alone is descriptive and carries no age.
• A unit name is not recognised. The read-back row says so. Names are matched against the shipped ICS chart; re-pick the unit from the cascade rather than typing it.
• The Stage list is enormous. Pick a System first — that is what the cascade is for.
• The column shows a range I did not ask for. Something has priority over the project range: you have wheel-zoomed. Switch the column off and on again.
• A marker is grey. It has no ICS unit yet — markers take their colour from the chart.

See also

• Project Properties — where the project age range is set.
• Display Properties — the overlay toggles.
• Stereonet User Guide — colouring orientations by stratigraphy.