Ch 9 GEOL 215 Sedimentary Rocks

disintegration & main types

Breaking to smaller fragments. Surface area increase leads to more weathering

Main types:

Jointing (decompression included)

Frost action

Biological processes

decomposition & main types

Changes in composition by chem and biochemical reactions.

Types:

Dissolution (dissolving)

Ion Exchange (clay formation, breaks down feldspar minerals)

Hydrolysis (Add H+ or OH-)

Hydration/dehydration (+H2O or reduce H2O)

Oxidation (electron transfer usually with O)

Chelation (see next slide)

Chelation and products

organic hydrocarbon complexes produced by lichen and humus decay. produces dissolved metals in organic ring complexes

Hydrolysis decomposition products

Clay minerals such as kaolinite, illite, smectite

Ion exchange decomposition products

Dissolved solids including Na+1 and K+1

Climate needed for high decomposition

warm and wet climate

Climate needed for high disintegration

cool and dry climates

Mineral stability lowest to highest

Halite

Calcite

Olivine

Pyroxenes (augite)

Calcic Plag

Amphiboles (hornblende)

Sodic Plag (albite)

Biotite

Orthoclase

Muscovite

Clay minerals

Zircon, rutile, tourmaline

Quartz

Al oxides (gibbsite)

Iron Oxides (hematite)

Goldich's series

classifications of sediments

Clastic (sandstone, shale)

Chemical (limestone, Gypsum)

Organic (coal, chalk)

Sedimentary cycle

Weathering and erosion

Sediment transport

Deposition

Diagenesis

Compaction

Cementation

Uplift and exposure of source rocks; Restarts

Types of sediments

Detrital (sandstone, shale)

Biochemical (limestone, gypsum)

Organic (coal, chalk)

Environments of Sediment Formation

Terrestrial (Eolian, Stream, Glacial environments, etc)

Transitional or Paralic (Estuarine, delta, shore environments, etc)

Marine (deep marine, shallow marine)

Princ of original Horizontality

Everything is originally flat, any tilting is after the layering occurred) with the exception of crossbedding of dunes

Superposition of strata

Younger rocks are originally on top of older rocks

Thick strata

> 1cm; Beds

Thin Strata

<1 cm; lamination

Fluid Flows

water, wind. No shear strength so the smallest stress sets them in motion, leads to significant sediment transport

Plastic Flows

Glaciers. have shear strength so requires some stress to set in motion such as gravity

Laminar Flow

Flow with smooth, layered fluid. Typically high viscosity, low speed fluids in smaller channels

Turbulent Flow

Flow with chaotic, mixed fluid. Typically low viscosity, high speed fluids in wider channels

Sediment transportation by water diagram

Traction is part of bed load

Suspension is in suspended load

Solution is dissolved (ions)

Hjustrom's diagram

Entrainment (eroded) transportation, and deposition are determined by this graph

Unidirectional flow regime

Flows in one direction over time

Wavebase

depth in water at which waves at surface do not affect

Glacial Sediments

Glacial till

Lithified --> tillites

Varves

Lake freezes in winter and thaws in summer. Darker=organic-rich, summer

Dropstones

Dropped from glaciers, disturbs laminations

Sediment transport by wind diagram

Dependent on grain size

Clay and silt: suspension

Coarse silt and sand: saltation

Fine to coarse sand and gravel: creep

Eolian sediment characteristics

Well-sorted

Downwind sequences:

Deflation

dune fields -> deposited via traction

Well-sorted mud deposits from suspension (Loess soils)

Deflation in Eolian sediments

coarse lag gravels where finer material has been removed

Sand dune morphologies

Straight crested - transverse dunes

Curve-crested - Barchan and parabolic

Classification of Sediment transport by mass flows dependent on:

Internal cohesiveness of rock

Proportion of sed:water

how sediments are supported in the flow

Max flow speed

Cohesive flows

Caused by lack of cohesion of rock mass and substrate, but maintains mass cohesion as it moves. Ex: rockslides and slumps

Granular Flows

Large prop of sed to water; >80 (sediments) : <20 (water) +air. Ex: avalanches, debris flow, soil creep

Slurry Flows (liquefied flows)

Movement that can be faster (100km/hr) and water is important. Smaller proportion of sediments to water; 60-80 (sed) : 20-40 (water). Ex: debris flow and mud flows

Hyperconcentrated flows

Water important to maintain this flow. Low proportion of sed particles; 20-60 (sed) : 40-80 (water). Ex: subaqueous turbidity flows

How to recognize debris flow

Poor sorting by size

Crude/no internal stratification

Inverse grading (big to small)

Boulders and pebbles dispersed in fine matrix

Turbidity Current

Dense water flow with sediment suspended due to turbulence, in higher energy areas. Not turbulent flow, different concept. Deposits called turbidites

Bouma sequence

describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers