SCIENCE · INVESTIGATE AND EXPLAIN

Connect sedimentary texture to compaction and cementation

Clastic sedimentary rocks contain transported fragments. Gravel-sized clasts exceed about 2 mm; sand lies roughly between 1/16 and 2 mm, while finer particles include silt and clay-sized material. Size is not composition: clay-sized particles and clay minerals are related but distinct categories. Sorting and rounding reflect transport and source history, not a unique environment by themselves.

Learning outcome: Compare different compaction porosities without cement, then add cement at one fixed compaction state. Keep original grains, added solids, pore volume and bulk volume separate. Explain what a measured grain-volume loss would imply about this model.

Starting recap

Separate observation, material inventory, process model and historical inference. State units and the evidence that could reject a proposed explanation.

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Try

At pre-cement porosity 0.2, bulk volume is 75 cm³ and pores 15 cm³. Filling one-quarter of those pores adds 3.75 cm³ cement, leaves 11.25 cm³ pores and gives final porosity 0.15.

Open the experiment

Predict

Which volume is preserved during compaction, and which changes when cement arrives?

Your prediction and reason

Experiment

Compare different compaction porosities without cement, then add cement at one fixed compaction state. Keep original grains, added solids, pore volume and bulk volume separate. Explain what a measured grain-volume loss would imply about this model.

Preserve solid volume while pores and cement change

Worked teaching model · synthetic values · Original deposit bulk100 cm³, porosity0.4 and original grains60 cm³. Compaction conserves original grain volume; then cement fills b of remaining pore volume without further bulk-volume change. Cement is an external solid addition; original-grain volume is not total final solid volume.

Final porosity before cement: 0.2 fraction Pore space later filled by externally supplied cement: 0.25 fraction

Reset keeps your prediction, captures and practice history.

Compaction rearranges grains; cementation adds a new solid phase in pore space.

Grain size, sorting, rounding and sedimentary structures constrain transport and deposition, not a unique environment by themselves. The model excludes grain crushing, dissolution and further framework collapse.

Light fill: original grains. Dark fill: added cement. Unfilled space: pores. This is a volume accounting diagram, not an image of actual grain geometry.

Complete quantities under the stated assumptions
Quantity	Value	Unit
Original grain volume	60	cm³
Bulk volume after compaction	75	cm³
Pore volume before cement	15	cm³
Externally added cement volume	3.750000	cm³
Final solid volume	63.75000	cm³
Final pore volume	11.25000	cm³
Final porosity	0.1500000	fraction
Compaction bulk-volume loss	25	cm³

Retain the prediction and settings before comparing explanations. Replayed supplied observations are not new specimens, independent field samples or practical certification.

Compaction rearranges grains; cementation adds a new solid phase in pore space.

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 geological question

2. Build the mechanism and evidence ledger

Conglomerate commonly contains rounded gravel clasts; breccia contains angular ones; sandstone is sand-dominated. Mud-rich rocks can split along bedding. Chemical and biochemical sedimentary rocks instead involve precipitation or biological accumulation, such as evaporites or many carbonate deposits. Structures including cross-bedding and graded layers add evidence about depositional processes.

Compaction reduces pore space as grains rearrange, while cementation precipitates additional solid in pores. The original 100 cm³ deposit has porosity 0.4, leaving 60 cm³ original grains. At new porosity φ, conserving those grains gives bulk volume 60/(1−φ). It is incorrect to keep bulk volume fixed during this compaction step.

After compaction the model adds external cement to a chosen fraction of the remaining pore space, holding bulk volume fixed during that second step. Final solid volume includes original grains plus cement. Dissolution, grain crushing and further collapse are excluded, so actual rock histories may require a more complete material balance.

3. Reconstruct a worked example

At pre-cement porosity 0.2, bulk volume is 75 cm³ and pores 15 cm³. Filling one-quarter of those pores adds 3.75 cm³ cement, leaves 11.25 cm³ pores and gives final porosity 0.15.

4. Predict and investigate

Predict first: Which volume is preserved during compaction, and which changes when cement arrives?

5. Test a changed case

Apply the mechanism to a changed case

At pre-cement porosity 0.4 with half the pores cemented, find bulk volume, cement volume, final solid volume and final porosity.

Retain the calculation, evidence and assumptions before opening public feedback.

Compare a worked response

Bulk remains 100 cm³, initial pores 40, cement adds 20, final solids are 80 and final pores 20 cm³: porosity 0.2. No compaction occurred in this setting, but cementation did.

6. Retain evidence and its limits

Keep the first prediction, complete ledger, changed case and rejected alternative in the lesson notebook. Supplied observations and bounded CPU models are not actual specimen handling, fieldwork or independently assessed competence. Record source purpose and uncertainty rather than treating public feedback as independent reasoning.

Mechanism and classification reference, checked 30 October 2026. Original teaching prose, numerical packets and questions; no source illustration or exercise is copied.

Apply

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

At pre-cement porosity 0.4 with half the pores cemented, find bulk volume, cement volume, final solid volume and final porosity.

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: Distinguish chemical transformation from mechanical fragmentation Next: Separate burial pressure, temperature and differential stress

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