Reading

Sedimentary • Stanley, S.M., 2015, Sedimentary Environments, – Ch. 5. Systems History Rocks and • On Ecampus Sedimentary Basins

What is a Sedimentary Basin? Sedimentary Rocks – A thick accumulation of – Necessary conditions: •Intro 1. A () • Origin of sedimentary rocks 2. Sediment Supply – Clastic Rocks – Carbonate Sedimentary Rocks • Interpreting Sedimentary Rocks – Environment of • Implications for the System

World Map of Sedimentary Basins Where are the Sedimentary Basins?

6 A B Watts Our Peculiar Planet: The Cycle Liquid Water and

Hydrologic Cycle

Tectonics

http://www.dnr.sc.gov/geology/images/Rockcycle-pg.pdf 8

SEDIMENT 3 Basic Types of Sedimentary Rocks • Unconsolidated products of Weathering & • Detrital ( = Clastic) – Loose , gravel, silt, mud, etc. – Made of Rock Fragments – Transported by , wind, glaciers, currents, etc. • Biochemical – Formed by Organisms • : – Consolidated sediment • Chemical – Lithified sediment – Precipitated from Chemical Solution

Detrital Material Transported by a Formation of a Sedimentary Rocks 1. Weathering – mechanical & chemical 2. Transport – by river, wind, glacier, ocean, etc. 3. Deposition – in a point , moraine, beach, ocean basin, etc 4. Lithification – loose sediment turns to solid rock Processes during Transport • 1. Sorting – Grain size is related to energy of transport – Boulders  high energy environment – Mud  low energy

Facies: Rock unit characteristic of a depositional environment

Processes during Transport: 2. Rounding Significance for Petroleum System? Sand Grains • : Fine grain, clay rick?, very low energy environ., low permeability, high organic content? → Source rocks, Seals, Permeability barriers

• : Coarse grain, -rich, high energy env., low organic content, high porosity? → Reservoirs, Migration pathways is progressive – angular grains  near source – rounded grains  long transport

Petroleum System Implications Well rounded Well sorted Good Quartz Reservoir! High porosity and Permeability

Bimodal rounding Poorly sorted Poor Reservoir! Lithic sandstone Many depositional environments with particular Low porosity and characteristics: Permeability Lithification : Porosity vs. • Compaction Depth Curve • Decrease in pore space • Due to increasing lithostatic pressure with burial

• Cementation • Pores filled Φ =41.73 e –z/8197 ft • Quartz or calcite cements Φ =41.73 e –z/2498 m • Recrystallization • New mineral growth • Beginning of metamorphism • Can kill porosity Schmoker and Halley, 1982

Lithification Petroleum System Implications • Determines the nature of the reservoir • Critical for economic viability • Highly variable • Hard to predict ahead of the drill

Rock Lithification of Shale Fragment Dewatering of shale • Overpressure? • Expulsion of hydrocarbons? Cement qtz

SEM-CL image- Frontier Fm. -Lithic Sandstone

Reed, UT Austin Classification of Clastic Detrital Rock • Based on Particle size Names – Gravel (more than 2 mm) • Pebbles (small) (Driveway gravel) • Cobbles (medium) (Plum to melon size) Conglomerate • Boulders (large) (Melon to bus size) –Sand(2 mm - 1/16 mm) – Silt (1/16 - 1/256 mm) Shale –Clay(< 1/256 mm)

CARBONATE SEDIMENTARY Biochemical Sedimentary Rocks ROCKS • Carbonate Rocks •Madeof Calcium Carbonate or Mg -Ca Carbonate – Limestone  calcite (CaCO3 ) • Precipitated from seawater – Dolostone  dolomite (Ca,Mg (CO ) ) 3 2 – Mostly by organisms (biochemical) • algae, shells, corals • – In some cases chemically (inorganic) • Organic-rich shales have large biochemical component – Do not confuse with organic Carbon-rich rocks

Chalk- Microscopic algae Chalk Sedimentary Environments Fields in the produce from fractured chalk • Type and geometry of sedimentary White Cliffs of Dover, UK rocks • Key to paleogegraphy • Prediction of distribution of source rocks and reservoirs • Use the modern to interpret the ancient

Carbonate - Bahamas

Coral Reef

Coral Reef Carbonates Sedimentary Environments of Deposition Non-Marine Environments How do we recognize them?

• Glacial • Rock Types • Deserts • • Alluvial Fans • Lakes • •Swamps •Geometry • Braided • Meandering Streams

Deserts Modern Jurassic Dunes (160 million years old) Utah •Very good sorting •Great reservoirs •Rarely preserved

Alluvial Fans Types of River • Conglomerates Mountain • Poorly sorted • Not so great! Delta Braided

Meandering Meandering Fluvial Environments (Rivers) Braided Stream Meandering Stream

Channel and Development of

Time Kimberley, Australia National Geographic Photo

Channel Sandstone Sandstone Mudstone

Sandstone

Conglomerate Vertical Well log Response sequence of rocks left by a meandering river

Peoria Field, CO

Wiki.apg.org

Log signature of Sedimentary Rocks fine River coarse

Delta-marine

coarse Barrier Island fine

Transgressive sand

Atkinson et al., 1988 52

Take home Points

• Sedimentary Environments produce recognizable rock sequences • Useful for predicting the lateral rock changes in the subsurface • Control reservoir properties • Non-Marine Environments • Deserts • Rivers • Electrical logs produce patterns for different environments are distinctive