Geology Honor

Nature Study

Requirements

  1. Present the meaning of the following terms:
    • Lithology
    • Layer
    • Fold
    • Fault
    • Delta
    • Meandering river
    • Braided river
    • Straight river
    • Anastomosing river
    • Moraine
    • Alluvial fan
    • Anticline
    • Syncline
    • Antiform
    • Synform
    • Hanging wall
    • Footwall
    • Strike-slip fault
    • Transform fault
    • Normal fault
    • Reverse fault
    • Thrust fault

    Answer: 1) Lithology: the branch of geology that describes and classifies rocks by their physical characteristics (color, mineral composition, texture, grain size). 2) Layer: a stratum of rock, generally sedimentary, with its own appearance and composition, deposited in an approximately parallel manner and separated from neighboring layers by stratification surfaces. 3) Fold: a flexural deformation (undulation) of the rock layers caused by compression stresses, which bends the strata without necessarily breaking them. 4) Fault: a fracture in the rock along which there has been relative displacement of the two blocks (one rises, falls, or slides in relation to the other). 5) Delta: a sedimentary deposit in the shape of a fan or triangle formed at the mouth of a river, where it loses speed on meeting the sea or lake and drops the transported sediments. 6) Meandering river: a single-channel river that describes sinuous curves (meanders) in low-slope terrain. 7) Braided river: a river that divides into several shallow channels that cross and separate around banks of sand/gravel, typical of a large sediment load and variable flow. 8) Straight river: a single-channel river that is practically straight, with few curves, generally controlled by steep slope or by faults/fractures of the terrain. 9) Anastomosing river: a river formed by several relatively stable and permanent channels, separated by vegetated islands, typical of low-slope plains. 10) Moraine: an accumulation of rock material (blocks, sand, clay) transported and deposited by a glacier. 11) Alluvial fan: a fan-shaped sedimentary deposit that forms where a river leaves a mountainous region and spreads its sediments over the plain. 12) Anticline: a fold that is concave downward (in the shape of an arch/A), with the oldest layers in the core and dipping to the sides from the axis. 13) Syncline: a fold that is concave upward (in the shape of a U/V), with the newest layers in the core and dipping toward the axis. 14) Antiform: a fold whose shape is convex upward (concavity downward), used when the relative age of the layers is unknown (a purely geometric definition of an anticline). 15) Synform: a fold whose shape is concave upward, used when the relative age of the layers is unknown (a purely geometric definition of a syncline). 16) Hanging wall: the block of rock located above the plane of an inclined fault. 17) Footwall: the block of rock located below the plane of an inclined fault. 18) Strike-slip fault: a fault in which the blocks slide horizontally in relation to each other, along a vertical plane (lateral movement). 19) Transform fault: a large-scale strike-slip fault that connects segments of tectonic plate boundaries (for example, offsetting oceanic ridges). 20) Normal fault: a fault of vertical movement in which the hanging-wall block descends in relation to the footwall, resulting from extensional (pulling apart) stresses. 21) Reverse fault: a fault of vertical movement in which the hanging-wall block rises in relation to the footwall, resulting from compression stresses. 22) Thrust fault: a low-angle reverse fault (slightly inclined plane), in which one block is pushed over the other, displacing rocks over great distances. — These are basic terms of structural and sedimentary geology. An anticline points upward, a syncline downward. Normal faults occur through extension; reverse ones through compression. Transform faults are those that separate tectonic plates, like the San Andreas fault. The Andes are the product of a thrust fault, with the Nazca plate subducting under the South American one.

  2. Describe:
    • How a glacier moves and what evidence it leaves in its path.
    • Why the banks of a river or stream are often more eroded on the outside of a bend.
    • How a mountain range is formed.

    Answer: You must present to the instructor: 1) A glacier moves slowly through the action of gravity and the weight of the ice, leaving U-shaped valleys, moraines (deposits of debris), striations on rocks, polished stones, and erratic blocks in its path; 2) The outer banks of a curve become more eroded because the water flows faster on the outer part (larger radius), eroding the soil, while it deposits sediments on the inner part (slower). 3) Mountain range — it forms through the collision of tectonic plates: when two plates push against each other (convergence), the layers of rock are compressed, folded, and raised over time, lifting the mountains (e.g., the Andes Mountains, from the collision of the Nazca plate with the South American one). — Glaciers carve U-shaped valleys (Yosemite); rivers carve V-shaped valleys. Differential erosion on curves creates meanders that evolve into oxbow lakes. The Andes (subduction of the Nazca plate), the Himalayas (collision of the Indian plate with the Eurasian one), and the Alps (the African plate with the European one) are classic examples of mountain ranges formed by tectonic collision.

  3. Know in which group of rocks (sedimentary, metamorphic, or igneous) the following rocks are classified:
    • Granite
    • Marble
    • Sandstone
    • Conglomerate
    • Basalt
    • Slate
    • Schist
    • Mudstone
    • Gneiss
    • Quartzite

    Answer: 1) Granite: an igneous (magmatic) rock, formed by the slow cooling of magma at depth. 2) Marble: a metamorphic rock, originating from limestone transformed by heat and pressure. 3) Sandstone: a sedimentary rock, formed by the compaction and cementation of grains of sand. 4) Conglomerate: a sedimentary rock, formed by the cementation of rounded pebbles and gravel. 5) Basalt: an igneous (magmatic) rock, formed by the rapid cooling of lava on the surface. 6) Slate: a metamorphic rock, originating from low-grade metamorphosed mudstone. 7) Schist: a metamorphic rock, with marked foliation and visible minerals (like mica), formed by medium-grade metamorphism. 8) Mudstone (claystone): a sedimentary rock, formed by the compaction of fine particles of clay. 9) Gneiss: a metamorphic rock, high-grade, with light and dark bands (banding), originating from granite or sedimentary rocks. 10) Quartzite: a metamorphic rock, originating from quartz-rich sandstone transformed by heat and pressure. — There are three groups: igneous (cooling of magma — volcanic if on the surface, plutonic if at depth), sedimentary (compaction of sediments), and metamorphic (alteration by pressure and temperature). The rock cycle shows that each one can become another over time. Granite is the most abundant rock in the Earth's continental crust.

  4. Take a photograph or draw each of the following geological features:
    • Ripple marks in sand or mud (If possible, show with an arrow the direction of the current)
    • Erosion
    • Desiccation cracks (these are usually found after a heavy rain or flooding, when the mud begins to dry)
    • Soil profile along the banks of a river or a road (notice how the soil varies in color and grain size in each of the layers)
    • Sandbar (these can usually be found along streams, rivers, or the sea)
    • Sinkhole
    • Fault with displacement of the lithologies

    Answer: You must present to the instructor a portfolio with a photograph or drawing of each feature: ripple marks in the sand/mud (with an arrow indicating the direction of the current); erosion (a furrow on a slope, a gully, a riverbank); desiccation cracks (after rain, in drying mud); a soil profile along a riverbank or a road cut (layers with different colors and grain sizes). — These seven phenomena are classics of field geology. Preserved ripple marks become fossils in ancient sedimentary rocks. Sinkholes are typical of areas with limestone (Bonito-MS, Lagoa Santa-MG). Desiccation cracks appear everywhere mud dries after rain. Road soil profiles are a classic field opportunity for students.