GEOLOGI UKM Paling Gempak!

Clastic Sedimentary rock : Sandstone

Clastic sedimentary rock
Clast or piece of minerals or fragments of rock
Form from cemented grains
Aggregates of minerals : quartx, feldspar, muscovite, biotite,hornblende, pyroxene
Colour : brown, white, red, grey, yellow, orange, pink and black
Texture : arenaceous sediment
Sixe : 1/16mm- 2mm (0.0625mm-2mm)
May include finer and coarser material
< 30% of gravel/pebble
3 kinds of materials in it : clast particles, matrix and cement
Cements : calcite, silica & iron oxide (they may fill the spaces where there is no matrix)
Matrix (fine grained stuff) silt-clay
High matrix = poorly sorted --- >15% matrix = wacke (dirty) maybe subangular
Little matrix = well sorted --- <15% matrix, little cement = arenit (clean) maybe well rounded
Sandstone > 25% of feldspar (Arkose : alluvial fan)
Sandstone made of volcanic particle – tuff (volcanoclast)
Sandstone with pieces of rock fragments : Lithic sandstone
Not usually contain good fossils because of energertic environment
Oxygen rich environment – oxidation take place – become red colour iron oxide
Reduced environment – darker- grey colour
High porosity – good aquifier and petroleum reservoir : 5.0 % - 25.0%
High Permeability
High resistance to weathering
Electrical resistivity of pure sandstone = 10 ohm
Specific gravity : 2.2 - 2.8
Arenaceous sediment become sandstone when it is compacted by pressure of overlying deposit

· Sedimentary structure :

Ripples can indicate the local water currents or wind directions.
Load structures sole marks, rip-up clasts and similar features are fossil footprints of ancient currents.
Liesegang bands are signs of chemical action after burial of the sand.