Igneous and Metamorphic Rock Forming Minerals. Department of Geology Mr. Victor Tibane SGM 210_2013

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1 Igneous and Metamorphic Rock Forming Minerals Department of Geology Mr. Victor Tibane 1 SGM 210_2013

2 Classification of sedimentary rocks Sedimentary rocks are products of weathered, fragmented or dissolved, transported, deposited and lithified components of other rocks Rock cycle! During these processes, the components become sorted and separated from each other or from components of different rocks, of different provenance, become mixed and deposited together.

3 Classification of sedimentary rocks The processes of disassembly of rocks are Physical weathering = Dismembering deposition & cementation. Chemical weathering = dissolution weathering precipitation from solution. Bio-weathering = dissolution & fragmentation biological precipitation and cementation of particles.

4 Classification of sedimentary rocks Walther s facies law (simplified after Johannes Walther, 1894) laterally migrating depositional facies (facies shift) successively overlap each other. Thus, in a vertical profile, only neighbouring sedimentary facies can be superimposed directly on each other. Thus, in a geological profile, the vertical sequence of sedimentary deposits equals the lateral facies migration of the past. Walther s facies law does not permits therefore, that e.g. deep marine facies directly overlies or underlies desert deposits. If such a sequence can be found, than both depositional facies must be separated by a tectonic or time gap - erosional boundary (unconformity).

5 Classification of sedimentary rocks Valley fill of sediments Fine alluvial sediments Mud flats sediments Brackish mud flats Shallow marine sands Marine limestone marine shale lacustrine sediments Transgression! coal seams pedogenic mud (soil) lacustrine limestone mud flat deposit basal sand sheath

6 Common sedimentary facies: lake desert glacier tidal flats river beach delta Press & Siever, 1995

7 clay < mm φ Silt = mm φ fine silt = mm φ middle silt = mm φ coarse silt = mm φ Sand mm φ fine sand = mm φ middle sand = mm φ coarse sand = mm φ Gravel > 2.0 mm φ fine = mm φ middle = mm φ coarse = mm φ

8 The ϕ-scale = negative logarithm at basis 2 of the measured grain size in mm (sieve grain size) ϕ = -log 2 D φ = diametre [mm] The phi-scale subdivides the grain sizes into equally large units whereby ϕ = 0 equals the diametre of 1.0 mm ϕ positive < 1 mm ϕ negative > 1mm ϕ=8 : φ =2-8 = 1/2 8 = 1/256 = mm

9 j > (-1) -1 (-6) mm: < 1/256 1/256 1/16 1/ clay silt sand gravel, cobbles < 0.002mm mm mm mm mudstone/claystone siltstone sandstone conglomerate Pelite Psammite Psephite Lutite Arenite Rudite

10 Wentworth-Udden grain size scale for sediments mm mm < 0.002mm mm

11 conglomerate breccia sandstone claystone Grains (clasts): Indicators of transportation process, distance, and provenance

12 Shape, size, mineralogy, surface texture and the arrangement of sedimentary grains allow for reconstruction of their source, transport distance and depositional facies Grain size large: short transport but highly energetic small: long transport (energy?) Grain roundness Maturity of sediment angular: short transport well rounded: long transport (multiple?) Feldspar present: short transport (climate?) Feldspar absent: long transport (protolith?)

13 Sieve analysis: Sieve diagrams transport information? Content Hontent in in (%) [%] Sorting poorly well moderately Grain diametre [mm] good: e.g. aeolian sediment moderate: e.g. fluviatile sediment poore: e.g. glacigenic sediment, mud flows debris flows, turbidites

14 Properties of sedimentary bedding Bed parallel lamination and lenses: current flow, laminar? Layer and lamina boundaries: non-sedimentation? Crossbedding: dunes, ripples, shallow / deep water, river, lake, ocean Grading of grain sizes: Turbidite; current? Grading of mineralogy: changing solutions?

15 Transport of clastic sediment fragments: Laminar flow Turbulent flow

16 Transport of sediment: Water surface Fine clay particles are overall suspended in the flow Solution load Current direction Suspension load Small grains are overall suspended in the flow River bed, coarse grained Bottom load Press & Siever, 1995

17 Transport of clastic sediment fragments:

18 Sedimentary structures Ripples: asymmetrical: river, current, wind transport symmetrical: oscillation, beach, wind agitated standing, shallow water

19 Sedimentary structures: Ripple marks and crossbedding Asymmetrical current ripples Symmetrical oscillation ripples

20 Transport of clastic sediment fragments: Asymmetrical current ripples Flat luv side Flow direction Steep lee side

21 Transport of clastic sediment fragments: Similar angle of slope Wave movement h Symmetrical ripples (strand) λ Flat luv slope Steep lee slope Current flow direction

22 Transport of clastic sediment fragments: Erosion on luv side sedimentation on lee side Lower flow velocity Water surface higher flow velocity Movement direction of water, ripples and dunes

23 Transport of clastic sediment fragments: Flat-top symmetrical ripples at a strand, and fossil symmetrical ripples

24 Transport of clastic sediment fragments: Imbrication of conglomerate clasts by current Imbrication of river flat pebbles Flow direction Large clasts move mostly as bed load saltation or roll freight.

25 Graded Bedding Turbulent flow 3. Turbidite 2. Turbidite 1. Turbidite

26 Turbulent flow Fine grained Coarse grained Graded turbiditic deposit

27 Sediment garin surfaces frosting: desert, aeolian (wind) transport aeolian transport aquatic transport 1 mm 1 mm Quartz Sand Monazite Sand

28 Sediment Garin Surfaces aeolian aquatic Kalahari SEM - Quartz x SEM - Monazite x Beach sand

29 Sediment Garin Surfaces aeolian aquatic SEM - Quartz SEM - Monazite

30 Sediment Garin Surfaces aeolian transport aquatic transport 1µm 1µm AFM - Quartz AFM - Monazite

31 Provenance of sediments Heavy mineral content (r > 2.9 g/cm 3 ): E.g. zircon: magmatic provenance E.g. garnet: metamorphic provenance E.g. mica: metamorphic or magmatic provenance

32 Nomenclature (classification) Grain size mm : Arenite = Sandstone E.g. quartz-arenite, calc-arenite Feldspar Rich in feldspar: = Arkosis

33 Classification according to composition lithische Lithic Komponenten fragments Litharenite Graywacke, when 15-75% clay matrix Quarz Quartz Quartz-Arenite Arkosis Press & Siever, 1995 Feldspar Feldspat QFL Quartz Feldspar Lithic fragments

34 Roundness of grains and distance of transportation Rounded components cm: Conglomerate Angular components cm : Breccia

35 Roundness of grains and distance of transportation Roundness and sphericity of grains are related to the distance of transportation, but some rocks produce only platy to elongated grains spheroidal sub-spheroidal elongated platy

36 Grain and Matrix - supported texture sandstones, conglomerates and breccias Grain supported Matrix supported Conglomerate Breccia

37 Maturity of the sediment: compositional maturity monomineralic-monomict structural maturity well rounded and spheroidal mature sediment: 100% quartz grains well rounded spheroidal

38 Low maturity sedimentary rocks: Conglomerates and breccias structurally? compositionally?

39 Old-Red- Conglomerate (Scotland)

40 Low maturity sedimentary rocks : Collapse or dissolution breccias Structurally? Compositionally?