GOD HELP ME (sediments)

Clastic

Formed by erosion of pre-existing rocks (ex. quartz arenite)

Orthochemical

Inorganic precipitates (ex. halite)

Allochemical

Biological precipitates (ex. limestone)

Unidirectional Ripples

• Wave Ripples

• Beach

Graded Bedding

• Evidence of waning current

• Older to younger, larger to smaller grains

Buoma Sequence

Bounded by erosional sedimentary structures at their top and base, evidence of waning current (fines upwards)

• Flute Marks

• Current flow

Convolute Bedding

where semi-consolidated sediment starts to slump

• Flame Structures

• any environment with water saturated sediment

Mudcracks

Drying lakes

Trace Fossils

Signs of biological activity, not actual remains of organisms

Stromatolites

• formed in shallow waters

• from biofilm of cyanobacteria photosynthesis

Most mature minerals (most stable at surface P/T)

Quartz, Zircon, Muscovite

Least mature minerals (least stable at surface P/T)

Pyroxene and olivine

Textural Maturity Signs

• small grain size

• more sorting

• rounder

Conglomerate Depositional Environments

• Beach

• Fluvial

• Alluvial Fans

• Glacial

Where to find very mature

• Eolian dunes

• Beaches

Black Shale

• anoxic, quiet, high organics

• associated with pyrite from H2S production

Red Mudrock

Presence of hematite

Marine Mudstones

Grey, bioturbated

Near Shore Mudstones

Dark grey, identified by floral + fossils

Hemipelagic mudrocks

• Dark grey but can be a variety of colours

• Pelagic fossils

Glacial Mudstones

Contain varves

Calcite Seas

• low-Mg Calcite

• warm water

• high seafloor spreading rates via removal of Mg from cycling through crust

Aragonite Seas

• high-Mg Calcite

• Aragonite

• cool water

Ideal Precipitation Factors of Calcium Carbonate

1. Biological activity

2. Low pressure

3. High temperature

4. High water agitation

5. Less CO2 in water

Ooids

• Non-skeletal

• Inorganically precipitated from excess calcium Carbonate

• Concentrically layered

Oncoids

• Organically precipitated concentrically around a nucleus

• From cyanobacteria photosynthesis (in warm water photic zone)

Folk Scheme

Dunham Classification

Near Shore Environment

• pelmicrites with fenestrae

• stromatolites with bioturbation

Reef System

• Biolithes/Boundstones

• Talus in the fore reef

Carbonate Compensation Depth

Depth below which calcium carbonate cannot accumulate, unless under a layer of clay or siliceous ooze

Starved Basins

• pelagic sedimentation

• turbidites

Processes in the Vadose Zone

• Clay infiltration of pore waters

• Unstable components (pyroxene, amphiboles, plagioclase) degrade

• Growth of authigenic minerals like illite and kaolinite

• Reddening of sediments due to hematite infiltration

Processes in the Phreatic Zone

• Continued alternation and dissolution of grains

• Pressure dissolution of minerals at grain contacts

• Growth of cements: silica as quartz overgrowth, calcite cement

Mudstone Zone 1

• 0-0.5m

• red-brown clays

• oxic zone

• bioturbation

Mudstone Zone 2

• 0.5-10m

• zone of bacterial sulfate (SO₄^2-) → may form H₂S which reacts with Fe³⁺ to produce pyrite

• BLACK PYRITIC SHALES

Mudstone Zone 3

• 10m - 1km

• SULFUR REDUCTION STOPS

• zone of organic fermentation

• expulsion of pore water, increased density

• SIDERITIC MUDSTONES

Mudstones Zone 4

• 1-2.5km

• decarboxylation breaks down organic matter further

• sideritic mudstones

Mudstones Zone 5

• 2.5-7km

• Hydrocarbon Diagenesis

• Remaining organic matter generates petroleum!!

• Expulsion of water moves petroleum into reservoir

Mudstone Zone 6

• >7km

• Metamorphic zone transition

• Illite → Muscovite at 300C

• Kaolinite → Chlorite at 200C

Carbonate Diagenesis

1. Cementation: affected by Mg:Ca ratio and carbonate supply

2. Neomorphism

3. Dissolution: slightly acidic groundwater creates drainage system

4. Compaction: chemical compaction at deep burial causes pressure solution

5. Dolomitization

Carbonate Meteoric Zone

1. Upper Vadose: acidic rainwater dissolves high-Mg calcite and aragonite

2. Lower Vadose: recrystallization of unstable minerals + precipitation of meniscus cements + high-Mg to low-Mg

Carbonate Phreatic Zone

• precipitation of low-Mg cements

• initially isopachous (fine) cements to coarser blades

• syntaxial overgrowths

Carbonate Marine Diagenesis

• micritization

• formation of hardgrounds

• pendant cements

• isopachous fibrous cements, but high-Mg calcite and aragonite!!

Deep Burial Carbonate Diagenesis

• larger crystal size + more iron

• Ferroan calcite = deep burial in ANOXIC conditions

Evaporite - Brine Dolomitization

• evaporation of sea water causes precipitation of gypsum

• Mg-rich brine sinks and causes dolomitization

Evaporative Pumping Dolomitization

• Intense evaporation draws saline water through limestone

• Causes an increase in Mg → dolomitization

Groundwater Mixing Dolomitization

freshwater mixed with 30% marine water suitable for dolomitization

Sea Water Model Dolomitization

• Sea water flushed into sediment pores

• Replenishing influx of fresh sea water puts calcite in contact with Mg

• high tides

Sabkha

Supratidal environments on arid coastlines where saline fluid flows through sediment pores via evaporative pumping

Chicken wire gypsum

50% / 84% / 90% / 96% marine water evaporated precipitates

• 50%: carbonates

• 84%: gypsum

• 90%: halite

• 96%: sylvite

Brine Reflux Model

• repeated influx of sea water of evaporating basin allows evaporite thickening

• brines formed sink / move below

Evaporite Facies

1. K + Mg Salts in Sabkha

2. Halite

3. Halite (during higher salinity) and Anhydrite (during lower salinity)

4. Anhydrite

5. Carbonates

6. Organic rich sediments (where anoxic organic rich shale forms)

Salt Lake vs Bitter Lake

Salt Lake: Halite

Bitter: Sodium Carbonate and Sulfates

Banded Iron Formation Process

1. Archean waters full of Fe2+ of SiO2 → chert continuously precipitated

2. Green sulfur photosynthesis results in oxidation of Fe2+ to Fe3+

3. Increase in stromatolites/cyanobacteria causes excess in oxygen, oxygenated waters drives green sulfur bacteria deeper until photosynthesis is impossible (2.4 Ga)

4. Post GOE - sulfidic ocean forms from hydrogen sulfide produced on land washing into oceans and generates in pyrite in oceans instead of iron minerals (occurred around 1.84 Ga)

Hyaloclastites

When volcanic eruptions interact with water

Eustatic (Global) Sea Level Change

• glacial control on sea

• spreading ridge volume (faster the spread, more sea level rise)

Local Sea Level Change

• crustal deformation

  convergence causes relative sea level fall

• isostatic changes (crustal decompression)