Representation tools

On geological maps, the orientation of strata is represented with a "T"-shaped symbol. Explain what its long stroke and its short stroke with its figure indicate (strike and dip).

In the key of a geological map, colours, patterns and acronyms like "Pz" or "K" appear. Explain what each of these three graphical elements represents.

The legend of a geological map orders the units from the oldest at the bottom to the youngest at the top. Explain which principle this order reflects and why it makes the map easier to read and interpret.

What is a stratigraphic column and what information does it provide about rock layers? State at least three items of data that must appear on it.

What is the difference between the stratigraphic column of a specific outcrop and the composite column of a region? Explain how the latter is built from several partial columns.

The figure shows the stratigraphic column of an outcrop with five undeformed layers, numbered from bottom to top. State which layer is the oldest and which is the youngest, and state the geological principle you have applied.

In a stratigraphic column, marls pass gradually into limestones with abundant shallow-water marine fossils. Interpret this change in terms of sea-level variation and justify whether it corresponds to a transgression or a regression.

A stratigraphic column is drawn at a vertical scale of $1:2\,000$. A marl formation measures $7,5\ \text{cm}$ on paper. Calculate its actual thickness in metres.

Explain the difference between a geological map and a geological cross-section. What can be seen in the cross-section that cannot be seen on the map?

What is a geological cross-section? Describe the steps to draw one from a geological map and a chosen section line.

In a schematic geological cross-section, the vertical scale is exaggerated five times relative to the horizontal. Explain what this vertical exaggeration means and what error in interpretation it can cause when estimating terrain gradients.

In a geological cross-section, a dyke of igneous rock cuts across all the strata and also across a fault. Which principle allows you to order the dyke, the strata and the fault in time? Could the dyke be older than any of the layers? Justify your answer.

The schematic cross-section shows strata A, B and C, an erosional surface (unconformity), strata D and E, fault F and igneous dyke G. Place the eight geological events represented (including the erosion) in chronological order from oldest to newest, and justify each relationship using the applied principle.

A cross-section shows, from bottom to top: slates (A), an undulating erosion surface, conglomerates (B), sandstones (C), a fault that displaces B and C, and silts (D) that cover the fault without being affected by it.

1. a) Order all the events from oldest to most recent;
2. b) state the principle that justifies each relationship;
3. c) explain what type of unconformity separates A from B.

On a map, the contacts between strata draw parallel bands that repeat in symmetrical order on both sides of a central band. What tectonic structure do you interpret? What additional data do you need to decide whether it is an anticline or a syncline?

On a geological map, a contact cuts obliquely across all the units it traverses. Explain which two types of contact (intrusive or fault) can show such a trace and which observations on the map and in the field allow them to be distinguished.

On a map, a limestone stratum draws a "V" where it crosses a valley.

1. a) Explain the relationship between the shape of the contact on the map, the relief and the dip of the stratum (the rule of V's);
2. b) describe how the contact would be traced if the stratum were horizontal;
3. c) and if it were vertical?

You can do it on paper and send a photo with your answer.

A flowchart represents the sequence weathering → erosion → transport → deposition. What is the advantage of representing a geological process with a flowchart compared to a written description?

What is a conceptual model or diagram in geology? State one advantage and one limitation of simplifying reality in a diagram.

Design, describing its stages and arrows, a flowchart explaining how the erosion of granite in a mountain range can end up forming a sandy beach. Indicate which agent is involved in each stage.