Exercises: Fieldwork and geological heritage

Name three classic instruments used by field geologists and briefly explain what each is used for.

What is geodiversity? Give two examples of geological heritage features that deserve protection.

GPS and mobile phones have been incorporated into fieldwork. Explain two specific advantages they offer over traditional methods.

List at least five minimum pieces of information that you must record in your notebook when describing an outcrop.

What is a geopark? State how it differs from a natural park and what aims it pursues in terms of conservation, education and local development.

Name four basic safety and behaviour rules for a geological field trip, related to equipment, weather, respect for property and the conservation of geosites.

Explain how a map is oriented in the field with the help of a compass and two known points on the terrain, and why this is the first operation on arriving at a work station.

Describe how to take and label a rock sample correctly in the field, and explain why a sample without a reference to its collection point loses almost all its scientific value.

The diagram represents in plan view the measurement that a geologist has taken on inclined sandstone strata: "strike N $45^\circ$ E, dip $30^\circ$ SE".

1. a) Explain what each of the two values that make up this measurement means (strike and dip).

1. b) Identify which element of the diagram (the blue line or the orange arrow) represents each one, and justify your answer based on its orientation relative to north.

What are a hand lens and a steel scratch point used for in the field when describing a rock? Relate these observations to the mineral identification that will be carried out later in the laboratory.

A local council proposes opening a quarry on a hillside where dinosaur footprints (fossil tracks) outcrop. Argue why this action would damage geological heritage and propose an alternative compatible with economic activity.

A student writes "dip 60° SW" in their notebook but forgets the strike of the stratum. Explain why the measurement remains incomplete and which two notations for the direction (azimuth and quadrants) they could have used.

Field sketches are still used even though we all carry a camera on our phones. Explain what an interpreted drawing — selection of features, scale, annotations — provides that a photograph does not record by itself.

Why is it advisable to sample fresh rock, removing the weathered rind, and to take several samples from the same level? Relate this practice to the reliability of subsequent laboratory analyses.

An outdoor fossil footprint site is deteriorating due to weathering and visitors. Propose three protection measures compatible with visiting it and one prior documentation measure (casts or three-dimensional scanning), justifying them.

The strike and dip measurements taken in the field end up represented on the geological map. Explain how one goes from the notebook annotations to drawing the contacts and the structural symbols on the map, and why it is advisable to review them the same day.

Two volcanic outcrops in the same district are competing for a limited budget allocation for their designation and development as a Geosite (Geological Site of Interest, LIG):

• Site A: A morphologically well-preserved Strombolian cone, but composed of lapilli deposits that are very common in the region, located next to a paved regional road and 2 km from a secondary school. It is at risk of anthropogenic degradation due to ongoing plundering of volcanic bombs.

• Site B: A highly eroded, exhumed phonolitic plug whose original relief has been dismantled, but which contains peridotite xenoliths from the upper mantle that are unique in the peninsular geological record. It is located in a rugged area that requires a two-hour hike on foot across steep terrain.

1. a) Evaluate and compare the scientific value versus the educational and outreach potential of both sites.
2. b) Knowing that the methodological criteria of the IGME weight representativeness, rarity, vulnerability, and accessibility, justify in a reasoned manner which of the two sites should be prioritized as a Geosite if the primary objective is to prevent the irreparable loss of unique geological heritage.
3. c) Design a conservation and management measure for the selected site that mitigates its primary risk factor without hindering scientific research.

A technical team must assess the stability of a 45 m high vertical scarp in karstified limestones above a frequently traveled road. Two methodologies are proposed: a conventional survey at the toe of the slope using a geologist's compass and a laser rangefinder, or a photogrammetric drone survey supported by surface GPS-RTN targets.

1. a) Interpret what systematic structural biases (for example, Terzaghi's orientation bias) will affect the fracture data if direct compass measurements are only taken from the base of the scarp accessible on foot.
2. b) A technician states that the high-resolution three-dimensional digital model obtained by the drone completely replaces visiting the outcrop, allowing one to determine with total reliability the lithology, the actual aperture of the joints, and the presence of residual decalcification clay in the discontinuities. Technically refute this statement by pointing out the limitations of photogrammetric remote sensing compared to in situ geological examination.
3. c) Design an integrated field protocol that combines the advantages of both techniques to characterize the rockfall risk while minimizing the physical exposure of geologists at the toe of the slope.

While mapping a straight road cut oriented N030°E with vertical walls, you observe sandstone beds that dip on the cut wall itself with an apparent dip of 25° towards the NE. In a nearby quarry located within the same formation, you verify that the true strike of the bedding is N090°E (E-W) dipping towards the N.

1. a) Justify geometrically, using spatial reasoning or relying on a mental block diagram, why the angle measured on the road-cut wall (25°) is necessarily less than or equal to the true dip of the bed.
2. b) The trigonometric relationship between the apparent dip ($\alpha$), the true dip ($\beta$), and the horizontal angle between the wall of the cut and the strike of the bed ($\theta$) is given by $\tan(\alpha) = \tan(\beta) \cdot \sin(\theta)$. Knowing that the angle between the road cut (N030°E) and the bed strike (N090°E) is $\theta = 60°$, calculate the true dip ($\beta$) of the beds (use $\tan(25°) \approx 0,466$ and $\sin(60°) \approx 0,866$).
3. c) If you were on a slope where you cannot measure the bed in three dimensions and you do not have the trigonometric formula at hand, explain what direct geometric technique allows you to determine the trace of the true dip in the field using a clinometer and water or a pencil.

You are mapping a coastal section of turbidite flysch where you suspect the presence of overturned series due to synsedimentary or tectonic folding. At three consecutive stations aligned from west to east (spaced 50 m apart), you record the following data:

• Station 1: Strike N000°E, dip 60° to the E. At the base of the sandstone beds, flute casts and normal grading (grain size decreasing towards the east) are observed.

• Station 2: Strike N000°E, dip 90° (vertical strata).

• Station 3: Strike N000°E, dip 70° to the E. Cross-lamination and basal load casts face towards the geographic west.

1. a) Determine and interpret the stratigraphic polarity (younging direction: normal series or overturned series) at stations 1 and 3, justifying which sedimentological criteria support your deduction.
2. b) Reconstruct the underlying tectonic structure: deduce whether the succession corresponds to the limb of an overturned fold (indicating whether it is an anticline or a syncline) and in which direction its axial surface dips.
3. c) Predict what serious mistake a geologist would make when calculating the true stratigraphic thickness of the formation if they had only taken strike and dip measurements while ignoring the polarity criteria.

On a limestone slope dipping at 35°, a surface with bipedal and quadrupedal dinosaur tracks has been discovered on a bed of marly limestone that is highly friable and vulnerable to freeze-thaw weathering. The local town hall proposes opening the site to the public without restrictions, allowing tourists to walk on the bed to take plaster casts and anchoring metal walkways directly onto the fossiliferous rock using drilled bolts.

1. a) Critically evaluate the municipal project: identify two physical and chemical degradation processes that this design would accelerate and justify the irreversibility of the damage to the footprints.
2. b) The paleontological study finds that the sauropod trackways show well-preserved mud expulsion rims (cushions) oriented N-S, while fossil wave ripple marks and desiccation cracks are perpendicularly superimposed on them. Interpret the evolution of the sedimentary environment and explain how you would translate this temporal sequence into accessible language for an interpretive field panel.
3. c) Design an alternative in situ intervention and musealization plan that balances educational display with the strict preservation of the bed, specifying access infrastructure, climate protection, and monitoring.

On a forested mountain slope with thick soil cover, there are no continuous rock outcrops. You must accurately locate the stratigraphic contact between a lower formation of impermeable Paleozoic slates and an overlying horizontal formation of permeable Mesozoic limestones. While hiking up the slope, you record the following data:

• Elevation 700 m: Dark clayey soil with angular, shiny clasts of slaty rock; gentle slope (12°); oak forest.

• Elevation 840 m: The slope steepens abruptly to 38°; a horizontal line of springs and waterlogged areas with hygrophilic vegetation (rushes and mosses) appears.

• Elevation 870 m: Shallow soil with grayish limestone scree that reacts with 10% HCl; xerophilic scrub vegetation.

1. a) Deduce and interpret at approximately what elevation the lithological contact is located, justifying your deduction based on the observed hydrogeological behavior, geomorphological landforms, and botany.
2. b) If at the contact elevation you were to find a breccia with angular fragments of both rocks cemented by iron oxides, along with striations (slickensides) on the block walls, reason whether the contact is still a stratigraphic unconformity or if it has been reactivated as a fault.
3. c) Explain how you would represent this contact on the geological map according to official cartographic standards (observed contact vs. inferred or concealed contact), and justify which surface geophysical method (electrical resistivity tomography or seismic refraction) would allow you to verify its depth beneath the colluvial mantle without drilling boreholes.

During the mapping of the flank of a fold in fluvial sandstones, three students measure the dip of the same rock stratum at points separated by only 3 metres from each other, obtaining discordant values: Student A: 27° to the E; Student B: 48° to the E; Student C: 34° to the E.

Upon reviewing the field notes, it is verified that:

• Student A placed the clinometer on the inclined surface of an internal lamina of trough cross-bedding.

• Student B rested the compass on an open decompression joint plane at the edge of the scarp.

• Student C used the notebook as an auxiliary plane resting on the flat base of the stratum containing basal load casts, measuring along the line of maximum slope (perpendicular to the strike).

1. a) Diagnose the validity of the data from A and B: explain the conceptual error of each and why their measurements do not represent the tectonic dip of the formation.
2. b) A fourth student proposes calculating the arithmetic mean of the three measurements: $(27° + 48° + 34°)/3 = 36,3°$ to record it on the map. Rebut this proposal, justifying why averaging structural data without geological discrimination distorts the geometry of the mapping.
3. c) Describe with technical precision the standardised cartographic symbol that must be drawn on the map to reflect the correct measurement of student C (strike N000°E and dip 34°E), detailing the orientation of its strokes and the numerical value.

Following an episode of torrential rains (130 mm in 24 h), a slope movement is triggered in a river valley through which a hiking trail runs. Upon inspecting the terrain, you observe:

• A semicircular main scarp with a 2,5 m displacement at the head, with tension cracks open in the ground up to 20 m uphill from the scarp.

• Leaning pine trunks with curvature at their base ("pistol-butt trees") along the entire affected slope.

• At the base, a disorganised mass of waterlogged Miocene gypsiferous clays invading the riverbed, reducing its natural channel by half.

1. a) Identify the kinematic typology of the movement (rotational slide, translational slide, or mudflow) and deduce, based on botanical and geomorphological evidence, whether it is a completely new phenomenon or the reactivation of a pre-existing unstable mass.
2. b) The town council proposes bringing in heavy machinery immediately to excavate and remove the earth from the toe of the landslide and reopen the path. Predict the geotechnical impact of this action on the overall stability of the slope and reason what will happen to the cracks at the head.
3. c) Design a stepped action plan in three phases (urgent safety intervention, corrective drainage/stabilisation measures, and monitoring or surveillance system) that the technical report must fulfil before permitting pedestrian traffic.

Unit challenge. Become a technical consultant for the geological heritage of your surroundings! Your mission is to design an educational and conservation proposal for an official Geosurface/Geological Site of Interest (LIG) in your province.

Follow these stages:

1. Sources and data: Access the viewer of the Spanish Inventory of Geological Sites of Interest (IELIG) of the IGME and select a nearby LIG. Collect its geographical coordinates, its typology of interest (stratigraphic, geomorphological, etc.), the age of the materials, and the dominant lithology.

2. Representation tools: Download the corresponding National Geological Map sheet (MAGNA at $1:50\,000$ scale) from the IGME viewer. Interpret the legend and draw a simple sketch of the geological cross-section or the arrangement of the layers (strike and dip).

3. Fieldwork and heritage: Draft a brief field report (maximum $1,5$ pages) detailing the basic equipment necessary for in situ sampling or observation, the description of the outreach stop, and two justified proposals for the preservation of this heritage against anthropogenic impact.

Assessment criteria:

• Rigor in data collection through the official IGME viewers.

• Accuracy when interpreting and sketching the geological cartography.

• Scientific coherence of the fieldwork proposal and relevance of the heritage conservation measures.