Sediment, Rocks, and Weathering Processes

This set of flashcards covers key concepts related to sediment transport history, sedimentary rock classification, weathering processes, and volcanic activity.

Well-rounded grains

Indicate prolonged transport history, suggesting the sediment has traveled far from its source in a high-energy environment.

Angular grains

Suggest a limited transport history and that the sediment is likely deposited close to its source in a low-energy environment.

Well sorted sediment

Indicates uniform grain size, likely formed in a stable environment with consistent energy conditions.

Poorly sorted sediment

Indicates a range of grain sizes, suggesting varied energy conditions during deposition.

Grain size and energy environment

Larger grain sizes indicate high-energy environments, while smaller grain sizes indicate low-energy environments.

Rank of clastic grain size

Clay, Silt, Sand, Granule, Pebble, Cobbles, Boulders.

Clastic rock classification

Based on grain size: sandstone (sand), siltstone (silt), shale (clay).

Mechanical weathering

Physical processes that break down rocks without changing their chemical composition, e.g., freeze-thaw, thermal expansion.

Chemical weathering

The chemical alteration of minerals in rocks, e.g., dissolution of minerals, that can increase the rate of mechanical weathering.

Example of chemical weathering

Carbonic acid dissolving limestone, leading to karst landscape formation.

Example of mechanical weathering

Freeze-thaw cycles that cause rocks to break apart.

Chemical sedimentary rocks

Formed from the precipitation of minerals from solution, e.g., limestone, chert.

Biogenic chemical sedimentary rocks

Formed with the influence of organisms, e.g., coal, limestone from shells.

Chert vs. limestone

Both are sedimentary rocks; chert is silica-based, while limestone is predominantly calcium carbonate.

Naturally occurring acids

Carbonic acid (from CO2 in water) and sulfuric acid (from sulfur oxides); limestone and marble are vulnerable.

Example of non-biogenic chemical sedimentary rock

Evaporites such as rock salt, formed by evaporation of saline water.

Depositional environment

The setting in which sediment is deposited, influencing rock type and characteristics.

Paleocurrent interpretation

Analyzing sedimentary structures to determine the direction of ancient water flow.

Sedimentary structures

Features formed during sediment deposition that provide insights into sedimentary environments.

Phaneritic vs. aphanitic rocks

Phaneritic rocks form underground with larger crystals, while aphanitic rocks form on the surface with smaller crystals.

Porphyritic texture

Indicates a two-stage cooling process, where larger crystals form before finer crystals.

Types of pyroclasts

Tephra, lapilli, ash, in order of increasing size.

Types of lava

Pahoehoe (smooth) and a'a (rough), with pillow lava forming under water.

Pyroclastic flow

A fast-moving current of hot gas and volcanic matter.

Volcano types

Shield, stratovolcano, cinder cone, and lava dome, distinguished by size and shape.

Magma composition

Varies by type of volcano and influences eruptive products.

Fractional crystallization

Process where different minerals crystallize out of magma at different temperatures.

Partial melting

Results in magma composition differing from the original rock due to differences in melting temperatures of minerals.

Magma mixing vs. assimilation

Magma mixing is the blending of two magmas; assimilation involves the incorporation of surrounding rock material.