SEDIMENTARYPETROLOGY

Clastics in Thin Section

Identification of CommonClastic grains and

Classification

This is not meant as a substitute but a supplement to studying

thin sections with the microscope

Review the Sandstone classification

QuartzarentieLithareniteA

rkos

e

Lith

ic a

rkos

e

Fedlspathic litharenite95%

25%

50 2020

Q

RockFragments

Feldspars(+granite andGneiss clasts)

SublithareniteSubarkose

Volcanic arenite Phyllarenite

Sedarenite

SS/SH areniteChert arenite

Calclithite

Quartz

Dust line

Overgrowth

-low interference colors

Quartzarenite-with Dolomitecement (rhombs)

Feldspars

Microcline (K-feldspar)

quartz

-scotch plaid twin

“Dirty” K-FeldsparAlteration can be used to distinguishuntwinned feldspar from quartz

Plagioclase-note twinning

Plagioclase

Note alteration on large grain

Rock Fragments

Chert-cryptocrystalline quartz

Sandstone rock fragment

Shale rock fragment

Watch out-that was Kerry’sbowling ball

Carbonate rock fragments (CRF)

CRFs commonly contain fossils

Calcite cement

-carbonate, usually calcite with high order interference colors

CRFs show truncation of cementsat grain boundaries

Volcanic rock fragment (VRF)plagioclase laths-ophitic texture

VRF phenocryst calcitecement

Metamorphic rock fragment (MRF)foliated texture (gneiss orschist grain)

MRFs -schist grainsnote mica

Other grains

Muscovite -clear in plain light

Muscovite

biotite-green/brown in plain light, highinterference colors in polarized light, pleochroic

-high interference colors in polarized light

GlauconiteCalcite cement

Chert

CRFs

Classify? Calclithite

Chert

CRFs

Classify? Calclithite

Classify? Volcanic arenite

Classify? CalclithiteNote fossils in upper clastsdolomite in lower clast quartz

Quartz

Dust linesQtz Overgrowths

Classify? Quartzarenite?

??

VRF-Why?

Calcite cement

?

Plagioclase laths?

Classify?Volcanic arenite

K-Feldspar/microcline

QuartzClassify: Arkose

?

SS rock fragment

CRF QTZ? ?

?

Classify:

Cement? Calcite

Sedarenite

?

Classify? Calclithite

Carbonate Rock Fragments

Classify? Chert Arenite

Chert clasts

Quartz and Chalcedony cement

Classify: SS arenite

Cement?

Classify: calclithite

calciteThat was a gutter ball.

That was a 7-10 split.What is the ball madeof?

Classify: sublitharenite

Classify: Volcanic arenite

Cement? calcite

Classify: Calclithite

Classify: Arkose

? mica

Classify: Quatzarenite

Classify: Chert Arenite