SCIENCE · INVESTIGATE AND EXPLAIN

Separate active deposition rate from whole-section apparent rate

A rock column records preserved thickness, not every moment of elapsed time. Deposition can stop, material can be eroded and later compaction can alter thickness. Dividing total preserved thickness by elapsed time therefore answers a different question from the active rate while grains were accumulating.

Learning outcome: Compare different hiatus lengths at the same active rate, then alter active rate while holding hiatus fixed. Reconstruct every diagram vertex and identify the additional dated horizon needed to distinguish continuous slow deposition from faster deposition with a gap.

Starting recap

Distinguish present position, relative event order, numerical age and duration. Preserve calibrated ranges, clock assumptions and missing observations instead of forcing one history.

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Try

At active rate 2 m/Myr and hiatus 6 Myr, active time 15 Myr plus hiatus gives 21 Myr total. Whole-section rate 30/21≈1.42857 m/Myr differs from the active 2 m/Myr.

Open the experiment

Predict

Can unchanged active deposition produce a lower whole-section average rate?

Your prediction and reason

Experiment

Compare different hiatus lengths at the same active rate, then alter active rate while holding hiatus fixed. Reconstruct every diagram vertex and identify the additional dated horizon needed to distinguish continuous slow deposition from faster deposition with a gap.

Separate active accumulation from elapsed stratigraphic time

Worked teaching model · synthetic values · Invented uncompacted30 m section, constant active rate a and one hiatus after15 m. No erosion or later compaction. Total elapsed time30/a+b; whole-section apparent rate30/total. The depth-time discontinuity is absence of deposited material, not a finite layer of empty rock.

Constant active accumulation rate: 2 m/Myr Nondeposition hiatus at half thickness: 6 Myr

Reset keeps your prediction, captures and practice history.

A time interval can be geologically real even when it contributes no preserved thickness.

The horizontal segment in thickness versus elapsed time represents nondeposition. Erosion or compaction would require another observation/model; the slow whole-section rate is not necessarily a slow instantaneous sediment supply.

All plotted values
Time (Myr)	Thickness (m)
0.000000	0.000000
7.500000	15.00000
13.50000	15.00000
21.00000	30.00000

Complete conditional quantities
Quantity	Value	Unit
Preserved thickness	30	m
Active accumulation time	15	Myr
Hiatus duration	6	Myr
Total elapsed time	21	Myr
Whole-section apparent rate	1.428571	m/Myr
Active rate	2	m/Myr

These are invented observation packets and calculations, not mapped field records or laboratory isotope measurements. Retain the source assumptions and first reasoning separately from public feedback.

A time interval can be geologically real even when it contributes no preserved thickness.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Define the time interpretation

2. Connect observations, mechanism and assumptions

The original fictional section preserves 30 m with no compaction or erosion. Deposition proceeds at a constant active rate r, stops for a hiatus H after 15 m and then resumes at the same rate. Active time is 30/r; total elapsed time is 30/r+H; apparent whole-section rate is 30 divided by that total.

The thickness-versus-time diagram contains a horizontal segment during nondeposition. It is not a physical layer of empty space. An age–depth interpretation must represent the time jump at the contact rather than drawing a uniform sedimentation line through it.

Actual accumulation reconstructions require age markers, compaction and erosion evidence and uncertainty. A slowly averaged rate can result from short rapid accumulation separated by long gaps. Neither thickness alone nor a uniform interpolation establishes a unique depositional history.

3. Reconstruct the worked packet

At active rate 2 m/Myr and hiatus 6 Myr, active time 15 Myr plus hiatus gives 21 Myr total. Whole-section rate 30/21≈1.42857 m/Myr differs from the active 2 m/Myr.

4. Predict and investigate

Predict first: Can unchanged active deposition produce a lower whole-section average rate?

5. Test a changed case

Apply the evidence to a changed case

For active rate 3 m/Myr and hiatus 10 Myr, find total elapsed time and apparent rate. How much thickness accumulated during the hiatus?

Retain the chronology, calculations and assumptions before opening public feedback.

Compare a worked response

Active time 10 Myr plus hiatus 10 gives 20 Myr; apparent rate 1.5 m/Myr. No thickness accumulated during the hiatus. This model does not include erosion of an earlier layer.

6. Retain a defensible observation notebook

Preserve the original prediction, complete observations/relationships, calculations, uncertainty convention and rejected alternative. All sections and isotope packets here are invented instructional cases, not actual mapped outcrops or measured isotope analyses. Public practice is not independent reasoning review or supervised field competence.

Method and mechanism reference, checked 30 October 2026. Original prose, diagrams, numerical packets and exercises.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

For active rate 3 m/Myr and hiatus 10 Myr, find total elapsed time and apparent rate. How much thickness accumulated during the hiatus?

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Diagnose clock disagreement without averaging away an open system Next: Resolve plate motion in a common reference frame

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