About Events

Overview

This is a guide to the concepts and processes involved in using StrataBugs Events.

Dictionary events

An Event is a stratigraphic occurrence of a taxon or other marker, which could be observed in space (at a depth in a well) or time (part of a composite standard or event scheme). Dictionary events can be be defined as having tops, bases, or occur at a single point in time/space.

Top events or base events can occur in space: as the FDO - first downhole occurrence and LDO - last downhole occurrence; or in time as extinctions (LAD - last appearance datum) or inceptions (FAD - first appearance datum). The position (in space or time) of a event pair (FDO/LDO or LAD/FAD) is determined in part by its absence: the FDO or LAD is the point above or after which there are no more occurrences.
Conversely, single events can logically only occur at only one point in space or time, and are marked by a recognisable presence of something - e.g. a flood of a particular taxon.

Events are usually related to a particular species, and in StrataBugs they usually linked to a taxon from the taxonomic database. Events can also include acmes, increases or decreases in abundance, or other similar variations in occurrence believed to have stratigraphic value. Note that these abundance events still have stratigraphic range, and they can therefore be paired events, for which a top and base can be identified. An event can sometimes be marked by one or more taxa in an assemblage, in which case you can elect not to link the event to any particular taxon name. Non-biostratigraphic events such as lithostratigraphic markers (e.g. ash beds, log picks) may also be considered as events but are of course not linked to taxon names in the database.

The dictionary events can be defined with a number of prefixes to the event name, which are used in different scenarios. The prefixes to be used for tops could be Top, FDO for the true stratigraphic top, or maybe FCO for First Common occurrence, or FAO for first Abundant occurrence etc. the dictionary defines which event types are allowed for each dictionary event. It will be likely therefore that any given taxon may have a number of different events defined for it.

Well events

When you recognise an event in a well, you can record it by linking the dictionary event to a depth (sample) in the well. You can record an event as either a top (FDO), base (LDO), or single. Well events can be displayed on charts, and provide a means of correlation from one well section to another. Well events are stored within interpretation Versions, so you can have multiple event lists for one well.

Composite standard events

A composite standard event is an event from the dictionary with an assigned age (in CSUs- Composite Standard Units or Ma). An ordered list of these events is called a Composite standard - a stratigraphic scheme of events. Pairs of events can occur as tops (LADs) and bases (FADs). For an event based on a species, the LAD and FAD bound the species' stratigraphic range - which can be displayed on a stratigraphic range chart. Different composite standards can be created for different geographical regions, or could be based on different chronostratigraphic timescales.

Composite Standards can 'inherit' the events of a parent composite standard. This allows a regional composite standard to redefine local ranges for selected events while inheriting the rest of the events from its parent composite standard. They can also be chained, such that the parent itself can inherit events from its parent, and so on.

Comparison of events in a well section with events in a composite standard can help when interpreting the stratigraphy of a well. This is the first step in graphic correlation.

The Event Dictionary

To view the event dictionary, open the Taxonomic Database module and select Events | Event Dictionary... from the menu. The Events window shows a table with the event type, name, taxon and top/base option. Double click on an event to open the Event: Edit dialog - see this page for more details on these fields. Like the taxon dictionary, the event dictionary applies to the whole database, i.e. all users and all wells.

You can add events to the event dictionary via the Taxonomic Database window. On the main menu, select Events | Add event... to open the Event: Add/Edit dialog - see this page for more details on these fields. If you have a taxon selected in the Taxon window, the dialog will be pre-populated with that taxon name. This makes it easy to first find your event taxon using the controls in Taxonomic Database, and then to add an event linked to that taxon to the event dictionary.

Well Events

Well events are linked to a dictionary event (i.e. the event must exist in the event dictionary before you can record it in a well), but are also linked to a sample depth. Various other attributes, including analyst and source details, can be stored with well events.

Remember that events are stored in interpretation versions; make sure you have the correct version selected on the interpretations tab before you enter event data.

Methods for recording well events:

In Samples & Interpretations, open the Interpretations tab for your well, and select the Events tab. Add events individually by pressing Add... to open the Event: Add to Well dialog. If the event isn't in the dictionary, you can add from this dialog if necessary. To edit any recorded event, double-click it in the table or select it and press Edit.
Generate events based on occurrences previously recorded in the well, by pressing Generate... to opens the Events: Generate dialog.
Display a composite standard in the Stratigraphic Schemes pane in Samples & Interpretations, and double-click an event name to add it as a well event. The currently selected sample on the samples tab will be used to prepopulate the dialog.
Pick events directly from the distribution chart: right-click in a Taxon Panel on the Standard Chart when the cursor is hovered over both a sample and an occurrence (both will show in the tool tip). Select Pick event at cursor position... If there are no dictionary events for the occurrence taxon, you will have to add one before you can add a well event. If there are multiple dictionary events for the taxon, you will have to select one. If there is only one dictionary event for the taxon you will be taken directly to the Well Event dialog (but you can add a new event from here if you wish). You will be warned if (and which) events for that taxon have already been picked in the well before you proceed.

Composite Standard Events

Composite standards are stratigraphic schemes comprised of events (from the event dictionary) with ages (in Ma or CSUs). Add or Edit composite standards in the Schemes and Interpretations module (select Schemes | Stratigraphic schemes, and select type as composite standard) or in the Taxon Database module (select Events | Composite Standards). More about working with composite standards...

Page last updated: 01-Nov-2022 14:37