Contacts, Units and Intervals

A project names its stratigraphy in three lists. A contact is a picked boundary: a formation top, a marker bed, a sequence boundary, an unconformity. A unit (stratigraphic unit) is the interval between two contacts: a formation, a member, a bed. Ordered from younger to older, the units make up the project's stratigraphic column. An interval is a named span between a younger and an older contact, one or more units thick, which is followed from log to log: a formation, a channel belt, any package you want to correlate.

Object	Takes a	Shown in its properties as
Polyline (a trace)	contact	Contact
Fault	contact	Contact
Orientation measured on bedding	unit or interval	Unit
Geobody	unit or interval	Unit
Scan line	unit
Stratigraphic unit	unit, bounded by two contacts	Unit, Younger Contact, Older Contact
Bed of a geological log	interval	the log's interval bar (2D Log tab)

A trace follows a boundary, so it sits on a contact; a measurement, a body or a scan line sits within a unit, and a measurement or a body may sit within an interval instead. The Active Descriptor panel of the Interpretations ribbon tab holds an active contact and an active unit, its Unit dropdown lists the intervals too, and its Apply button gives each selected object the one it takes (see the Active Descriptor).

Contacts

The Contacts branch (called Picks in earlier versions) holds the project's named contacts. Interpretations refer to them: a polyline records the contact it traces in its Contact property, a log pick ties the contact to a depth in a geological log, correlation panels join the same contact across logs, and a stratigraphic unit or an interval is bounded by a younger and an older contact. Because contacts are project-wide, one contact can be followed across every section, log and polyline in the study.

Select a contact to see it in the Properties panel:

Property	Meaning
Name, ID	The contact's name and its numeric ID.
Contact Type	How the contact formed: Unspecified, Conformable, Erosional (unconformity), Intrusive or Faulted. Or the sequence-stratigraphic surface it is: Sequence boundary (SB), Transgressive surface (TS), Maximum flooding surface (MFS) or Flooding surface (FS), which a correlation panel draws by type. Contacts from projects saved before contact types existed open as Unspecified.
Enabled	Show the contact in logs.
Age	The age of the contact.
Color, Opacity	How the contact is drawn.

The contact type is a property of the stratigraphic contact. It is separate from the Base Contacts list, which describes the contact at the base of a bed in a geological log (sharp, erosive and so on).

Units

The Units branch holds the project's named stratigraphic units. An orientation measured on bedding names the unit it lies in in its Unit property, and geobodies, scan lines and stratigraphic units carry a unit too. A stratigraphic unit is filled in its unit's colour, an orientation coloured by Stratigraphy takes its unit's colour, and the stereonet's Stratigraphy colours come from both lists.

Select a unit to see its Name, ID, Age, Color and Opacity in the Properties panel.

Projects saved before contacts and units were separate

Older projects kept one list, Picks, for both. That list opens as Contacts, and every unit name already in use by an orientation, geobody, scan line or stratigraphic unit is added to Units automatically, with the colour and age of the contact of the same name. One line in the messages panel says how many units were created. Nothing needs re-assigning.

Intervals

The Intervals branch (called Correlations in earlier versions) holds the project's named intervals. Select one to see it in the Properties panel:

Property	Meaning
Name, ID	The interval's name and its numeric ID.
Younger Contact	The contact on the interval's upper side, from the Contacts list.
Older Contact	The contact on the interval's lower side.
Parent Interval	The interval this one is part of: a member's formation, a parasequence's sequence. Neither the interval itself nor any interval inside it can be its parent.
Rank	Its rank in the hierarchy: Group, Formation, Member, Bed, Sequence, Systems Tract, Parasequence, Channel Belt, Storey, Element, Bed Set, or a rank you type.
Age	The age of the interval.
Color, Opacity	How the interval is drawn on logs and in correlation panels.

Intervals are used in three places:

• On a geological log, a run of beds takes an interval with Assign Interval on the 2D Log tab. An interval is one unbroken run of beds on a log, and neighbouring logs in a correlation panel that hold the same interval are joined by a band. See Intervals.
• A geobody or an orientation can lie in an interval rather than a unit: its Unit row, and the Active Descriptor's Unit dropdown, list the intervals after the units.
• On a log through a geopolygon, the geopolygon's base and top can be placed as picks of the interval's Older Contact and Younger Contact, and the beds between them can take the interval. See 3D interpretations on the log.

Entries made in the old Correlations list open as intervals with no contacts; set them on each interval's properties.

Intervals nest: each is listed under its Parent Interval. A log's beds can be given the finest interval and are counted in the ones above it too. See Nested intervals.

Adding, deleting and exporting

• New on the Contacts, Units or Intervals header adds an entry: give it a name, an ID and an age. A new entry becomes the active contact, unit or interval. New Contact and New Unit on the Interpretations ribbon tab, and the new-interval button beside the Interval dropdown on the 2D Log tab, do the same.
• Delete on an entry removes it. A deleted contact, unit or interval stays deleted when the project is reopened. A deleted interval is taken off every bed that had it, and the intervals inside it move up to its parent.
• Export on the Contacts or Units header writes the list to a CSV file, one name,ID row per entry. On the Intervals header it writes a table with a header row, name,id,younger_contact,older_contact, and one row per interval with its name, ID and its younger and older contacts.

Context menus

All three branch headers show the standard group menu, and each contact, unit or interval shows the standard item menu. Both menus are listed on the Standard Item and Group Menus page.