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SEDIMENTARY ROCKS.

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Presentation on theme: "SEDIMENTARY ROCKS."— Presentation transcript:

1 SEDIMENTARY ROCKS

2 TERMS Weathering: breakdown of pre-existing rock
Physical or chemical breakdown Transport: movement of sediment on Earth’s surface

3 SEDIMENTARY ROCKS Introduction Detrital Rocks Chemical/Organic Rocks
Classification Lithification Sedimentary Environments Sedimentary Structures

4 Sedimentary Rocks Introduction

5 INTRODUCTION Origin Only form at Earth’s surface
GEOL 131: Sedimentary Rocks INTRODUCTION Origin Only form at Earth’s surface Weathering of pre-existing rock into soluble and insoluble sediments Transport of sediments Deposition of solid sediment or precipitation of dissolved sediment Diagenesis: includes compaction and lithification

6 INTRODUCTION Importance Record of past surface conditions Fossils
GEOL 131: Sedimentary Rocks INTRODUCTION Importance Record of past surface conditions Fossils Economically important materials Fossil fuels, gypsum, phosphates, iron, gravel, etc.

7 Sedimentary Rocks Detrital Rocks

8 Detrital Rocks “Detrital” from “detritus” - debris
GEOL 131: Sedimentary Rocks Detrital Rocks “Detrital” from “detritus” - debris Composed of solid sediment grains Distinguished by size of grains Detrital rock with smaller grains Detrital rock with large grains

9 Detrital Rocks: Common Minerals
GEOL 131: Sedimentary Rocks Detrital Rocks: Common Minerals Quartz Physically durable Feldspars Break down chemically into clays Clay minerals Chemically stable

10 Shale Most abundant sedimentary rock Made of clay grains
GEOL 131: Sedimentary Rocks - Detrital Shale Most abundant sedimentary rock 2/3 of all sedimentary rock is shale Made of clay grains Microscopic sheets From chemical weathering of feldspar

11 Shale GEOL 131: Sedimentary Rocks - Detrital
Scanning electron microscope image of shale showing flat clay grains. Scale bar is cm. From: claysandminerals.com

12 Shale Formation Quiet environment Burial and compaction of clay grains
GEOL 131: Sedimentary Rocks - Detrital Shale Formation Quiet environment Burial and compaction of clay grains Not cemented Weak From: geoexpro.com

13 Sandstone Cemented sand-size grains Sand: 1/16mm – 2mm diameter
GEOL 131: Sedimentary Rocks - Detrital Sandstone Cemented sand-size grains Sand: 1/16mm – 2mm diameter Quartz is predominant mineral

14 Sandstone: Sorting and Shape
GEOL 131: Sedimentary Rocks - Detrital Sandstone: Sorting and Shape Lower energy, shorter transport time Higher energy, longer transport time

15 CONGLOMERATE/BRECCIA
GEOL 131: Sedimentary Rocks - Detrital CONGLOMERATE/BRECCIA Cemented gravel-size grains Gravel: greater than 2mm CONGLOMERATE has rounded gravel BRECCIA has angular gravel

16 Sedimentary Rocks Chemical Rocks

17 GEOL 131: Sedimentary Rocks
Chemical Rocks Dissolved sediment precipitates out of solution as crystals “Inorganic” processes: e.g. evaporation, chemical activity “Biochemical” processes, e.g. growth of shells Bonneville Salt Flats, Utah From: rogerdhansen.wordpress.com

18 Chemical Rocks: Limestones
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Limestones Composed mainly of calcite (CaCO3) Several kinds Some biochemical and some inorganic Most form in marine environments

19 Biochemical Limestones
GEOL 131: Sedimentary Rocks - Chemical Biochemical Limestones From: From: seashellsbymillhill.com From: proprofs.com Chalk Microscopic plankton shells Very soft Fossil limestone Shells + matrix Hard Coquina Shells only Fragile

20 Biochemical Limestones
GEOL 131: Sedimentary Rocks - Chemical Biochemical Limestones Chalk under a scanning electron microscope, showing shells (round) and calcite crystals. Scale bar is cm. From: greenelectron-images.co.uk

21 Inorganic Limestones GEOL 131: Sedimentary Rocks - Chemical
From: russianriverschoolhouse.com From: www4.uwm.edu From: Oolitic limestone Round “ooids” + cement Precipitation of crystals from seawater around a nucleus Rolling back and forth Micrite Microscopic calcite crystals Precipitated from oversaturated seawater Travertine “Cave rock” Porous

22 Inorganic Limestones: Ooids
GEOL 131: Sedimentary Rocks - Chemical Inorganic Limestones: Ooids Calcite layers Seafloor Nucleus Ooid forming Ooid cross-section Ooids form when calcite precipitates from oversaturated seawater onto nuclei being rolled around on seafloor by currents Nucleus can be any small solid particle: sand grain, piece of shell, etc.

23 Chemical Rocks: Dolostone
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Dolostone Composed mainly of dolomite: CaMg(CO3)2 Origin not well understood Most dolostone is probably converted from limestone when Mg is added Mg-rich groundwater? Seawater?

24 Chemical Rocks: Chert Biochemical
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Chert Biochemical Composed mainly of microcrystalline quartz Very hard; sharp edges Made from compacted microscopic plankton shells

25 Chemical Rocks: Evaporites
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Evaporites Inorganic Evaporation of water (usually salt water) Rock salt, rock gypsum Bonneville Salt Flats, the ancient floor of Lake Bonneville, a salty lake now mostly evaporated

26 Organic Rocks: Coal Organic, no minerals
GEOL 131: Sedimentary Rocks - Chemical Organic Rocks: Coal Organic, no minerals Chemically altered dead plant matter Need oxygen-poor water From: eis.uow.edu.au

27 Sedimentary Rocks Classification

28 Classification: Detrital
GEOL 131: Sedimentary Rocks Classification: Detrital

29 Classification: Chemical
GEOL 131: Sedimentary Rocks Classification: Chemical

30 Sedimentary Rocks Lithification

31 Lithification How sediment becomes rock “Lith” = stone
GEOL 131: Sedimentary Rocks - Lithification Lithification How sediment becomes rock “Lith” = stone

32 Lithification Processes
GEOL 131: Sedimentary Rocks - Lithification Lithification Processes Compaction Cementation

33 GEOL 131: Sedimentary Rocks - Lithification
Begins with deposition & burial of sediment under more sediment

34 Compaction Decreases porosity (empty space) Drives out water
GEOL 131: Sedimentary Rocks - Lithification Compaction Decreases porosity (empty space) Drives out water Can make flat grains stick together

35 Cementation New crystals form between grains
GEOL 131: Sedimentary Rocks - Lithification Cementation New crystals form between grains Precipitation out of groundwater Fills in remaining porosity Original sand grain Cement crystals From: northstonematerials.com From: unibe.ch

36 Sedimentary Environments
Sedimentary Rocks Sedimentary Environments

37 Sedimentary Environments
GEOL 131: Sedimentary Rocks - Environments Sedimentary Environments Any place where sediments accumulate Rocks give clues to past environments Reconstruct what Earth’s surface looked like in the past

38 GEOL 131: Sedimentary Rocks - Environments
From: neiu.edu Examples of some sedimentary environments

39 Categories of Sed. Environments
GEOL 131: Sedimentary Rocks - Environments Categories of Sed. Environments Nonmarine Transitional Marine

40 Sed. Rocks Represent Past Environments
GEOL 131: Sedimentary Rocks - Environments Sed. Rocks Represent Past Environments UTAH Bonneville Salt Flats (white areas): rock salt deposits represent ancient lake Ancient Lake Bonneville

41 Sedimentary Structures
Sedimentary Rocks Sedimentary Structures

42 Layers (aka beds or strata)
GEOL 131: Sedimentary Rocks - Sedimentary Structures Layers (aka beds or strata) Most common type of structure Bedding planes: contacts between layers

43 Cross-bedding Cross-beds in a modern sand dune Cross-beds in sandstone
GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding Cross-beds in a modern sand dune Cross-beds in sandstone

44 Cross-bedding shows depositional current’s flow direction
GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding shows depositional current’s flow direction Wind, river, waves, etc. Paleocurrent: ancient depositional current Flow direction Crossbeds

45 Graded beds Grains are sorted by size within a single layer
GEOL 131: Sedimentary Rocks - Sedimentary Structures Graded beds Grains are sorted by size within a single layer

46 Ripple marks & mud cracks
GEOL 131: Sedimentary Rocks - Sedimentary Structures Ripple marks & mud cracks Mud cracks in modern sediment Ripple marks in sandstone

47 End of Sedimentary Rocks Chapter

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