Post on 17-Dec-2015
A FORMAL MODEL FOR THE GEOLOGICAL TIMESCALE
AND GSSP
Simon J.D. COX CSIRO Exploration and Mining, ARRC
Stephen M. RICHARD, Arizona Geol Survey and U. S. Geological Survey
Goal
• Formal Model for time-scale information
Why?• ensures accurate communication within
sub-discipline • harmonization with other info systems,
geoscience & other• software generation and implementation
“Ordinal Temporal Reference System” - ISO 19108
• Temporal position described in terms of an ordered, hierarchical set of named eras– E.g. “Lopingian”
• Compare with • Temporal Coordinate System – number and scale – e.g. “260 Ma”
• Calendar– day/month/year (western, Hebrew, Japanese, etc)
• Node – event, point in time, associated with a time instant
Theory: Temporal Topological Complex
• Edges are joined at nodes
• Edge – directed, has begin & end nodes, realized as a time period
Object introduces an identifiable information item
Theory: Ordinal Reference System
• Reference system ⇒ relative positions of any two edges is unique– Before, After, Begins, Ends, During, Equals, Contains, Overlaps, Meets, OverlappedBy, MetBy, BegunBy, EndedBy
• ≡ Constrained Topologic Complex– Any path between nodes may only be subdivided in one way
• Different subdivision = different “system”– Each system has a “domain of validity” – multiple systems may exist simultaneously provided their scope does not overlap
B1
B4
B5
B2 B3
B21
B23B22
B24
Ba Bc
Bb
A DCB
Geologic Time Scale
• Era = named edge– Hierarchically ranked
• Boundary = temporal node
• Traditional studies focused on eras– Where the rocks and
fossils are!
EraName=“Permian”Rank=“System”
EraName=“Lopingian”
Rank=“Series”
NodeName=“Base of Artinskian”
NodeName=“Base of Permian”
GSSPGlobal Standard Stratotype Section and Point
EraName=“Permian”Rank=“System”
EraName=“Lopingian”
Rank=“Series”
NodeName=“Base of Artinskian”
NodeName=“Base of Permian”
• GSSP focuses on boundaries– the “temporal nodes”– associated with stratigraphic events
• GSSP boundary stratotype– Stratigraphic section at a specific
location– Position in section that shows evidence
of the event (‘point’, ‘golden spike’)
• Calibration is based on age measurements made on specimen(s) collected from the stratotype – Result of Measurement = estimated
temporal position of boundary
Standard Global Numerical Age*
• Boundary position is assigned, rather than estimated
• Used for pre-Ediacaran timescale– preCambrian eras still comprise an
Ordinal Temporal Reference System – More common to use chronostratigraphy
(= Temporal Coordinate System)
* Global Standard Stratigraphic Age (GSSA), nomenclature revision proposed by Walsh et al, 2004
Formal model of Geologic Time System and GSSP
• Hierarchical ordinal system, in which the eras are ranked (e.g. era, period, epoch)
• Temporal position assigned to interval bounds based on measurements on specimens from GSSP, or from Standard Global Numerical Age
Geologic Time System
1 +begin Initiation 1..*+nextStratEra1
+end Termination
1..*
+previousStratEra
TM_Complex
TM_TopologicalComplex
TM_ReferenceSystem
GeologicTimeScale
UnambiguousTemporalTopoComplex
0..*
1+basis
1..*
M_Node
StratNodeTM_OrdinalEra
StratEra
1
0..1
+Name
TM_TopologicalPrimitive
TM_Edge
Name
1+Definition
TM_ prefix indicates parent model element in ISO 19108
GSSP-- StratNode
TM_ prefix indicates parent model element in ISO 19108
StratNode
TM_Primitive
TM_GeometricPrimitive
StratAgeInterpretation
0..1
TimeLocation
1
GeologicEvent
StratigraphicEvent
1..*Manifestation
1..*Feature
Stratotype0..1 Containment 1
+contains
TM_Node
GeologicSurface
BoundaryLevel
EventNode
1
1
DefinedNode
TM_TemporalPosition
«Data Type»TM_Coordinate
+ coordinateValue: Number
0..*
1+position
Numerical age interpretation
Specimen
0..*
Sample
10..*
1..*+target
Observation
DateDetermination0..*
Evidence
1..*
Feature
Stratotype
TM_Primitive
TM_GeometricPrimitive
StratAgeInterpretation
GeologicSurface
BoundaryLevel
EventNode
0..1
TimeLocation
1
0..1 Containment 1
+contains
1
1
LithostratigraphicUnitMicrostratigraphicUnit
1..* {ordered}
1
Important concepts from outside of stratigraphy
• position – Geospatial e.g. of stratotype or specimen – Temporal – e.g. of stratigraphic boundary
• Specimen – object on which observations may be made– e.g. particular piece of rock
• Observation/Measurement – use of a procedure on a specimen, to estimate the value of a property– e.g. isotopic age, chemical composition– the property value is the result of an observation
Implementation
• Formal model (UML) can “automatically” generate software:– XML transfer format– relational database schema
Conclusions
• ISO 19108 standard provides standard model for temporal reference systems
• XMML provides a standard model for specimens and measurements
• Combine these to model important aspects of geologic time systems based on GSSP
• Some refinement still needed– constrained temporal topological complex– some details of relationships involving
stratEvent/stratBoundary/specimen/stratotype etc
These are the GSSP selected
and ratified components for
the given boundary node
EraName=“Permian”Rank=“System”
EraName=“Lopingian”
Rank=“Series”
NodeName=“Base of Artinskian”
NodeName=“Base of Permian”
Eventdescription=“Conodont,
lowest occurrence of Streptognathodus isolatus”
Eventdescription=“Conodont,
disappearance of Foo bar”
Stratotypedescription=“27 m above base of Bed 19,
Aidaralash Creek, Aktöbe, southern Ural Mountains, northern Kazakhstan”
Stratotypedescription=“Some other place”
These are ordinal
timescale components
These are components required
for correlation and timescale calibration
AgeMeasurementresult=“-299 Ma”
AgeMeasurementresult=“-298 Ma”
Preferred age for this node