1 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks Wacke – Sandstone with 10-15% matrix (silt- and/or clay-size material between grains; e.g., with various clay minerals like chlorite, illite, etc.).

2 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks Quartz arenite Feldspathic arenite Lithic arenite

3 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks Quartz arenite Feldspathic arenite Lithic arenite

4 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Greywacke – Informal term for dark-grey, coarse-grained sandstones, consisting of poorly sorted, angular to sub-angular grains of quartz, feldspar, dark minerals and lithic fragments in a fine-grained, compact and clay-rich matrix. Often used to describe turbiditic sandstones. If possible, its use should be avoided.

5 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Turbidites – Result from turbidity current deposits, which are derived from underwater avalanches. Turbidite flows are responsible for distributing vast amounts of clastic sediment into the deep ocean.

6 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Greensands – Term for green sands or green sandstones applied to shallow marine deposits with large quantities of rounded, green grains (glauconite). Roadcut – Lionel Mt. Sandstone (Cambrian), lower unit (TX). Glauconitic Sandstone.Glauconite and quartz – plane light.

7 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Physical setting examples for different sandstone types. Greywacke Quartz arenite Feldspathic arenite Lithic arenite

8 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Common cements. Calcite cement Quartz cement Hematitic cement

9 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Common cements. Lower Silurian Red Mt. Fm. – quartz arenite A – Sutured contact (red arrow) between quartz grains. Un-modified grain margins (black arrows) extend to overlap (red dashed lines) at the contact. B – Same area, x-polarized light. Cements syntaxial on the two pressure dissolved grains meet with cement syntaxial to a third are a common point (black arrow). Suture – red arrow.

10 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Quartz. - What do the terms “monocrystalline”, “polycrystalline” and “undulose extinction” mean? What, if anything, might the use of these terms tell us about the sediment or rock being examined? Rounded monocrystalline quartzPolycrystalline quartzPolycrystalline quartz – undulose extinction

11 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Quartz. - Monocrystalline quartz – Typically indicative of an igneous source rock – Often the major constituent (60% - 70%) of quartz arenites. - Polycrystalline quartz – Often a relatively minor (< 40%) constituent of quartz arenites – Can indicate metamorphic source rock (quartzite) if polygonal crystal boundaries are evident and if a large number (3 + ) of quartz crystals form individual grains – Can also indicate a granitic source rock if fewer crystals form individual grains and no or very little intercrystal suturing is evident. - Would you expect to see a difference in weathering stability between these quartz varieties? Why or why not?

12 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Feldspars. Potassium feldspars - Orthoclase Microcline – x-hatched crystal twinning

13 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Feldspars. Plagioclase feldsparsPlagioclase striations – polysynthetic twinning

14 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Accessory minerals. - Other common accessory minerals include pyroxene, corundum, zircon, tourmaline, garnet, magnetite and rutile. - What can the dominance of particular accessory minerals tell us, if anything? Chlorite Muscovite mica BiotiteOlivine

15 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Lithic arenites – Sandstones with > 5% lithic fragments, often having a clayey matrix. Lithic arenite – Wolfville Fm. (Jurassic), at Red Head Nova Scotia. Top: plane light, bottom: x-polarized light.

16 EES 450: Sedimentary Geology ARENITES (SANDSTONES) AND THEIR CLASSIFICATION 20% - 25% of all sedimentary rocks ● Common arenite matrices. ClaysSericite – fine micasMicrite