• arkL
  • notes
  • introduction and login
  • notes on sequence data
  • notes on data table creation
  • view data
  • multicolumn view
  • dataset view
  • column view
  • event view
  • interval view
  • references
  • taxon links
  • data upload & integration
  • upload data
  • populate (integrate and check data)

Sequences and sea-level

A sequence is defined by 5 age-onlap points.

Their ages and levels are calculated from the ages and long term sea level values of the seq bdy/ls and mfs plus the offlap-magnitude of the cycle.

label age onlap 1 top prev_SBage mfs actual sl 2 crest 0.5 * (3 -> 1) 0.75 * 3 -> 1) 3 mfs - maximum flooding surface mfsage 0.5 * (1 -> 5) 4 lst - lowstand tract 0.333 * (5 -> 3) 0.667 * (5 -> 3) 5 SB - sequence boundary SBage SB actual sl 6 control SBage 0 Table listing the 6 points that define a sequence and the equations to calculate them

NOTES In the program we have a function to calculate the set of 5 age-onlap values, using the equations in the table. The equations are positions between points – eg. 0.333 * (5->3) represents one third of distance from point 5 to 3. Calculation sequence is 1,5,3,2,4 point 6 is an optional control point to seqment the curve mfs actual sl = longterm sl value SB actual sl = (longerm sl value – sl_change)

sl_change

• in the Jurassic sequences are ranked as minor, medium or major and sl_change values of 20, 45 or 80m assigned.
• In the Cretaceous separate sl_change values are given for each sequence

Long term sl curve

Types of TSC columns generated from sequence & sea-level data

Sequence plot – shows sb (solid line with label) and mfs events (dotted line) plus blue triangles with width at the mfs set by the seq_scale value of the mfs T-R Cycles – events are typically a subset of the sequence events but may include some extra. Special fields TR_cycle (values: T-minor; T.medium; T-major; R) and TR_names indicate which events are used and the cycle names. Mega T-R Trends – subset of T-R Cycle events. A separate field Mega_TR_cycle defines which events are used and the Transgression magnitude. Some names differ from std sequences so there is also a TR_names field Coastal onlap segmented – based on the sequence data as shown in previous slide. NB In TSC they clearly use curve fitting as opposed to joining the points with straight line segments so my output looks a bit crude but it shows the pattern Coastal onlap – as above but without plotting of sb lines. Short-Term Phanerozoic – this is probably just a smoothed curve through the mfs and sb values. Mean Sea Level (intermediate term; synthetic) – this is probably a curve through the average of the mfs & SB values. Long Term Phanerozoic – simple plot of values from the longterm_sl field

How this is handled in the database

Events

All the column types, are essentially event-based. A single sequence is defined by a sequence boundary (SB) followed by a maximum flooding surface (MFS). Optionally the low stand tract (LST) may also be defined as a separate event. These are given the suffixes SB, MFS and LST and the event_types: => seq bdy, mfs, lst.

In the events table there are several extra fields for this column type: seq_scale (values: major/medium/minor); longterm_sl; sl_change; sea_level_notes; TR_cycle (values: T-minor/T-medium/T-major/R); Mega_TR_cycle (values: T-minor/T-medium/T-major/R). sl_change needs to be given to generate the onlap curves, and it is a positive number.

query to see all the sequence/sea-level data in the events table: select id, age, eventx, event_type, seq_scale, sl_change, longterm_sl, sl_correction_applied, sea_level_notes, TR_cycle, Mega_TR_cycle, TR_name from arkL_events where dataset_id=31 order by age
NB Since several columns use the same data we cannot use the column_id in the data selection query, instead we need to use dataset_id and sub_dataset_id. This is a case where subdatasets are definitely needed, since in some datasets there is more than one one sets of sequences - notably the "sequences Perm-Carb-Dev NAm".

Intervals

How this is handled in the program

For the onlap columns the same basic query is used, but then a separate function is used to calculate the set of five points for each sequence - using the equations given in the table above. The final ouptut is a long list of age-onlap pairs which then are passed to the graphic script for plotting.