Unit 03 · Sedimentary Rocks & Stratigraphy
Sedimentary rock is Earth's field notebook — weathered fragments and dissolved minerals buried, compacted, and cemented into layers that record the environments that made them. This unit covers clastic rocks like sandstone, shale, and conglomerate, chemical rocks like limestone and rock salt, and organic rock like coal, then turns to the stratigraphic principles — superposition, original horizontality, lateral continuity, and cross-cutting relationships — that let you read a stack of beds as a sequence of time. Mastery means you can name a rock, name the environment that deposited it, and order a cliff face from oldest to youngest.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Sediment to rock: compaction & cementation | Cannot describe how loose sediment becomes rock. | Names compaction or cementation but not both, and not in order. | Traces weathered sediment through burial, compaction, and cementation into solid rock. |
| Clastic, chemical & organic rocks | Groups all sedimentary rock together. | Sorts a few rocks but confuses the three origins. | Classifies sandstone, shale, limestone, rock salt, and coal by clastic, chemical, or organic origin. |
| Depositional environment | Cannot connect a rock to where it formed. | Guesses an environment without using grain size or composition. | Reads grain size, sorting, and composition to name the environment — beach, river, deep sea, or swamp. |
| Stratigraphic principles | Cannot order layers or name a principle. | States superposition but misapplies cross-cutting or original horizontality. | Applies superposition, original horizontality, lateral continuity, and cross-cutting to order any sequence of beds. |
| Unconformities & missing time (lab) | Reads a rock face as one continuous record. | Spots a break in the layers but cannot explain it. | Recognizes an unconformity and explains the erosion or non-deposition that removed the missing time. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“The bottom bed is sandstone with rounded, well-sorted grains, so it’s an old beach. By superposition it’s the oldest layer, and the tilted beds beneath the flat ones mark an unconformity — a long stretch of time that eroded away before the next layers were laid down.”
“It’s just striped rock. The layers are however old. I don’t know why there’s a gap in the middle.”
You demonstrate this unit at the specimen bench and with a stratigraphic column — identifying sedimentary rocks, reading their depositional environments, and ordering a set of beds by the stratigraphic principles aloud — not a multiple-choice test. A criterion counts as mastered only when you can both name the rock and defend the sequence of time it records. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.