Lec-4

Classification of Sandstone

1. Introduction

• Overview of classification focus.

• Key topics include petrography and sandstone types, provenance, and mineral compositions.

2. Petrography and Origin of Principal Sandstone Types

• A. Quartz Arenites

• B. Arkoses

• C. Litharenites

• D. Greywackes

3. Provenance and Significance of Mineral Compositions

• 3.1. Genetic Classification of Quartz Grains

• 3.2. Paleoclimate

• 3.3. Tectonic Setting by Detrital Modes

4. References

• Dr. Muhamed F.Omer, Ph.D. in Sedimentology, Postdoctoral - Warsaw University, 2014.

Classification of Sandstone

- Introduction

• Petrographic classification.

• Microscopic studies; grain types assessed (400 grains recommended).

• Field estimates via hand lens.

• Triangular Diagram Usage

  • End members: Quartz (+Chert), Feldspar, Rock Fragments.

  • Fields named by modal analysis.

- Groups of Sandstones

• Arenites: Clean sands (>25% feldspar).

• Litharenite: >25% rock fragments, more than feldspar.

• Wackes: Dirty sands (>15% matrix).

Classification of Sand-Grain Types

• Quartzose Grains: Qt = Qm + Qp

• Lithic Fragments: Included based on content.

• Feldspar Grains: F = P + K (P = plagioclase, K = potassium feldspar).

Types of Sandstone

1. Quartz Arenite

• At least 95% quartz.

• Well-rounded, well-sorted, high textural maturity.

• Cements: quartz overgrowths, calcite common.

• Heavy minerals: well-rounded ZTR.

• Typical deposition: shallow marine shelves.

• Example: Khabour Formation, Iraq.

2. Arkose

• 25% feldspar; red/pink color.

• Poorly to well-sorted grains.

• Cemented by calcite, quartz, clay.

• Derived from granites and gneisses.

• Example: Injana Formation, Iraq.

3. Litharenites

• High content of unstable rock fragments.

• Poorly sorted; fluvial and deltaic settings.

• Bulk composition: high Al2O3, low Na2O/MgO.

• Example: Qalandar Formation, Iraq.

4. Greywacke

• Texturally immature; >15% matrix.

• Fine-grained matrix: chlorite, sericite.

• Rich in Al2O3; deposited by turbidity currents.

Provenance Significance of Mineral Compositions

• Mineralogy affects sediment transport distance, climate.

• Provenance studies help reconstruct pre-depositional history.

3.1. Genetic Classification of Quartz Grains

• Monocrystalline types: non-undulose, slightly undulose, undulose.

• Polycrystalline types differentiated by crystal units.

3.2. Paleoclimate

• Sandstone mineralogy reflects ancient conditions.

3.3. Tectonic Setting by Detrital Modes

• Relates detrital composition to tectonic settings.

• Provenance terrains: stable craton, basement uplift, magmatic arcs, recycled orogen.

References

• Academic references on sandstones and classifications.