Sedimentary Rocks and Geological Processes

Lecture 3 Overview

• Lecture 3 covers geosystems, geology, geomorphology
• It details endogenic and exogenic systems including all driving forces
• It explains time spans, into which Earth's geologic history is divided, particularly focusing on the Anthropocene
• Guiding principles & laws in geology are also covered
• Including the principles of uniformitarianism and superposition
• The lecture includes a review of Earth's Structure and Internal Energy and a breakdown of Earth Materials and the Rock Cycle

Introduction

• Comprehending the natural environment is crucial for recognizing our reliance on it, addressing environmental concerns, and its own inherent value
• The natural environment comprises four interconnected spheres: the Atmosphere, Hydrosphere, Lithosphere, and Biosphere
• The Earth operates as a dynamic system with an array of subsystems
• The Earth features a multitude of interconnected processes across diverse spatial and temporal scales

Two Broad Earth Systems

• The earth features endogenic and exogenic systems
• The Endogenic system encompasses internal processes that drive heat and material from deep within the Earth's crust
• Its energy source includes heat from pressure (gravity) and radioactive decay
• A related branch of science includes geology
• The Exogenic system consists of external processes on Earth's surface, propelled by air, water, and ice
• Its energy source is primarily solar energy and the energy of atmospheric motion
• A related branch of science is geomorphology
• The endogenic system and exogenic system are input into rock and mineral transformation and tectonic processes
• This results in the output of crustal deformation and volcanism
• This process outputs various landforms: karst, fluvial, eolian, glacial, and coastal.
• Human activity acts as hazards that affects the geomorphic processes

Geologic Time Scale

• The order of scale is Eon > Era > Period > Epoch
• The Earth is >4.567 billion years old
• The Precambrian Eon makes up 88.3% of the Earth's history
• .04% of Earth's history happened in the last 2 Ma (Mega annum)
• The last 570 million years has seen a large number of era's

The Anthropocene

• Human activity impacts the Earth's systems to a greater extent compared to natural forces
• Notably, human activities influence Earth's systems more rapidly than natural forces.
• The 'Anthropocene' is referred to as 'the human epoch' and it spans approximately 250 to 6000 years Before Present (B.P.)
• The formalization of the Anthropocene at the Epoch level is backed by novel stratigraphic signatures.

Guiding Principles Laws in Geology: Dating

• Absolute Time: Refers to the exact measurement of years before present (BP), often determined through scientific techniques like radiometric dating
• Relative Time: Involves arranging events in the order they occurred
• Relative dating relies on assessing the positions of rock strata relative to each other, examined through stratigraphy
• The oldest rock on Earth is about 4.0 billion years old, and the oldest known fossil is about 3.5 billion years old
• Radiometric Dating is defined by half-life: the time it takes for half of the unstable atoms in a rock sample to decay

Historical Contributors to Geology

• 1669 –Steno, N. codified the Law of superposition
• Hooke, R. recognized Fossils as dating instruments
• 1786 -Cuvier discovered Extinctions
• 1799 –Smith, W. developed the Law of faunal succession
• 1841 saw the First global geological record
• The 20th century developed Radio-dating and aligned palaeo with geological records

Geology Principles

• Stratigraphy involves an extensive study of rock layers, applying principles to understand stratigraphic units and their formation
• Relative dating enables the placement of rock layers and geological occurrences in chronological order through stratigraphy
• Principle of Original Horizontality: States that sedimentary layers are initially deposited horizontally
• Principle of Lateral Continuity: States that sedimentary layers extend continuously in all directions until they thin out or encounter a barrier
• Principle of Superposition: States the bedrock is arranged with the youngest bed toward the top
• Principle of Cross-Cutting Relations: States that a rock or fault is younger than any rock or structure that it cuts
• Law of Inclusions: States that if rock A contains fragments of rock B, rock A must be younger
• Law of Faunal Succession: States that fossil organisms succeed one another in a definite and determinable order

Superposition and Uniformitarianism Definitions

• Superposition: Rock and sediment are invariably ordered with strata towards the top
• Uniformitarianism: suggests that the same physical processes that occur today have been operating throughout geologic time

Unconformities Definition

• Unconformity is a pattern observed in rock groups that reveals prior erosion, sedimentary rock involvement, sea-level changes, and orogenic uplift

Unconformities Types

• Disconformity: Characterized by the rocks below the erosion surface being significantly older than those above
• Nonconformity: Occurs when sedimentary rock layers are laid directly over eroded igneous or metamorphic bedrock
• Angular unconformity: Characterized by horizontal sedimentary layers positioned atop tilted and lifted layers of older sedimentary rocks
• Paraconformity: The rock lacks signs of erosion with only a pause in sedimentary deposits with a large gap in time

Earth's Structure and Internal Energy

• The Earth formed from a nebula 4.6 billion years ago
• The formation consisted primarily of silica and iron
• As temperature decreased, the Earth solidified, and gravity sorted the materials by density
• The core's mass equates to one-third of the Earth's total mass
• The core's volume accounts for one-sixth of the Earth's total volume
• The magnetic poles and the geographic poles are different
• The fluid outer core generates 90% of Earth's magnetic field
• Since the outer core is composed of liquid molten metallic iron
• The north magnetic pole (NMP) is currently migrating at 85.1°N, 134°W
• Each layer in the Earth's structure is distinct in its composition and temperature
• Heat energy moves upwards through conduction and convection in plastic or fluid layers
• Seismic tomography identifies the boundaries of the layers
• Density variations can cause seismic waves to reflect and refract.
• Earths Mantle: Accounts for 80% of the planet's volume, with a density of 4.5g/cm3
• The Moho discontinuity is the boundary between the uppermost mantle and the crust
• Continental crust is low in density at 2700 kg/m3 and is classified mostly granite
• Sial is a compound of silica and aluminum
• Oceanic crust is denser at 3000 kg/m3 and is classified mostly basalt
• Sima is a compound of silica and magnesium

Asthenosphere and Lithosphere

• Asthenosphere: Located between the upper mantle and uppermost mantle it exhibits plastic-like characteristics
  • The material flows when force is applied
• Lithosphere: Comprised of the crust and the uppermost portion of the mantle
• The average thickness of oceanic crust is 5 km, while continental crust averages 30 km

Earth's Buoyancy and Isostasy

• Buoyancy explains that less dense materials float in denser ones
• Earth's crust floats on denser, elastic layers beneath it
• Earth's crust maintains a continuous state of adjustment described as Isostasy
• The earth is greater where a load is greater, the crust tends to compress. This is also known as isostatic rebound
• 46.6% of the Earth's crust is Oxygen
• 27.7% of the Earth's crust is Silicon

Rock Types

• A mineral is an inorganic natural compound with a specific chemical composition and crystal structure
• A rock is an assemblage of minerals, undifferentiated material, or solid organic material
• Three basic rock types are Igneous, Sedimentary, and Metamorphic
• Igneous rocks can be intrusive or extrusive
• Sedimentary rocks are lithified sediments via cementation, compaction, dehydration, or heating.
• Metamorphic rocks undergo alteration via heat, pressure, compressions, or sheer
• The rock cycle consists of to hydrologic and tectonic cycles that drive rock formations

Igneous Rocks

• Igneous rocks are the most abundant class of rock on Earth and are formed from molten material
• Rapid cooling results in fine texture
• Slow cooling results in coarse texture
• Intrusive igneous rocks cool from magma beneath the earth
• Granite is example
• Extrusive igneous rocks cool from lava on the surface
• Basalt is an example
• Plutons are intrusive igneous body
• It includes batholiths, laccoliths, sills, and dikes

Sedimentary Rocks

• Formed from the breakdown of existing rock
• Formed by lithification with minerals dying
• Can be classified into shale, sandstone, and conglomerate
• Chemical sedimentary rocks produces from shells or precipitation
• Biogeochemical sedimentary rocks form from organic plant and animal matter

Metamorphic Rocks

• Metamorphic rocks Form by physical alteration through high pressure, extreme heat, or both
• The rocks are resistant to weathering and erosion
• Contact metamorphism occurs when intrusion magma cooks the rocks
• Regional metamorphism occurs when rock turns metamorphic.
• Foliated rocks has a banded appearance
• Slate, Gneiss, and Schist are examples of such rock
• Marble and Quartzite are Nonfoliated

Explore sedimentary rock formation, classification (clastic, chemical, biogeochemical), and their role in landscapes like karst topography. Understand exogenic and endogenic systems, relative dating principles, and Earth's spheres involved in geological processes.