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Sedimentary Geochemistry

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sedimentary-geochemistry diagenesis provenance chemostratigraphy

Core Idea

Sedimentary geochemistry examines the chemical processes and signatures in sediments and sedimentary rocks, from their formation through weathering and transport to their burial and diagenetic transformation. Sediment chemistry records source rock composition (provenance), weathering intensity, redox conditions in the depositional environment, and post-depositional diagenetic modifications. Key tools include major-element weathering indices (CIA, CIW), REE patterns for provenance, redox-sensitive trace elements (Mo, U, V, Re) for paleoenvironmental reconstruction, and stable isotope chemostratigraphy (delta-13C, delta-34S, delta-18O) for global biogeochemical changes. Sedimentary rocks are the archive of Earth's surface conditions through time.

Explainer

Sedimentary rocks are Earth's memory. They record the chemistry of past oceans, atmospheres, weathering regimes, and biological systems in mineral assemblages, major and trace element concentrations, and isotopic compositions that can be measured billions of years after deposition. Sedimentary geochemistry reads this archive.

Provenance analysis uses immobile elements and their ratios to identify the tectonic setting and lithology of the source terrain. REE patterns (Eu anomaly, LREE/HREE slope), Th/Sc ratios (felsic sources have high Th/Sc), and Cr/Th ratios (mafic sources have high Cr) discriminate between felsic continental, mafic oceanic, and recycled sedimentary sources. These ratios survive weathering, transport, and moderate diagenesis, preserving source information in ancient sediments.

Paleoenvironmental reconstruction relies on elements whose behavior changes dramatically with redox conditions. In modern oceans, Mo, V, Re, and U are dissolved under oxygenated conditions but become insoluble and accumulate in sediments under anoxic or euxinic conditions. By measuring their enrichments in ancient sediments and calibrating against modern analogs (Black Sea, Cariaco Basin), geochemists reconstruct the redox state of past water bodies. The secular record of these elements through Earth history documents major oxygenation events, ocean anoxic events, and the long-term evolution of marine redox chemistry.

Diagenesis -- the chemical and physical changes occurring after deposition -- modifies the primary geochemical signal. Organic matter is microbially degraded through the terminal electron acceptor sequence. Pore waters evolve as minerals dissolve and precipitate. Authigenic minerals (pyrite, siderite, dolomite, glauconite) form in the sediment column. Understanding diagenesis is essential for interpreting primary signals correctly and for recognizing which geochemical proxies survive burial and which are overprinted.

Practice Questions 3 questions

Prerequisite Chain

Counting to 10 → Counting to 20 → Understanding Zero → The Number Zero → Counting to Five → One-to-One Correspondence → Combining Small Groups Within 5 → Addition Within 10 → Addition Within 20 → Two-Digit Addition Without Regrouping → Two-Digit Addition with Regrouping → Addition Within 100 → Repeated Addition as Multiplication → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Two-Digit by One-Digit Division → Division with Remainders → Remainders and Quotients in Division → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Reading and Writing Decimals → Comparing and Ordering Decimals → Adding and Subtracting Decimals → Multiplying Decimals → Dividing Decimals → Dividing Fractions → Mixed Number Arithmetic → Order of Operations → Integer Order of Operations → Variable Expressions → Combining Like Terms → One-Step Equations → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Iterated Integrals and Fubini's Theorem → Double Integrals in Cartesian Coordinates → Double Integrals over Rectangular Regions → Double Integrals in Polar Coordinates → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Green's Theorem → Surface Integrals and Flux of Vector Fields → Surface Integrals and Flux of Vector Fields → Divergence Theorem: Flux and Outflow → Divergence Theorem → Electric Flux → Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → The Electromagnetic Spectrum → Blackbody Radiation and Planck's Law → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → Heisenberg Uncertainty Principle → Wavefunction and the Born Rule → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → Quantum Entanglement → Bell Theorem and Bell Inequalities → Postulates of Quantum Mechanics → Scattering Theory → Introduction to Scattering Theory → Partial Wave Analysis in Scattering → Spin Angular Momentum → Electron Spin and Intrinsic Magnetic Moment → Stern-Gerlach Experiment: Spin Quantization and Measurement → Electron Diffraction and Matter Wave Properties → Davisson-Germer Experiment: Crystal Diffraction of Electrons → Electron Diffraction and Matter Wave Interference → Wavefunctions and Probability Density Interpretation → Quantum Superposition and Linear Combinations of States → Quantum Operators and Observables → Canonical Commutation Relations and Uncertainty → Heisenberg Uncertainty Principle and Measurement Limits → Time-Independent Schrödinger Equation and Eigenvalues → Hydrogen Atom in Quantum Mechanics → Spectral Lines and Energy Transitions → Selection Rules for Atomic Transitions → LS and jj Coupling Schemes in Multi-Electron Atoms → Pauli Exclusion Principle and Antisymmetric Wavefunctions → Electron Configuration and the Aufbau Principle → The Periodic Table and Atomic Electronic Structure → The Periodic Table → Electron Configuration → Periodic Trends → Ionization Energy → Ionic Bonding → Lewis Structures → Resonance Structures and Delocalized Electrons → Resonance and Formal Charge → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Solubility Equilibria → Phase Diagrams and Clausius-Clapeyron Equation → Chemical Potential and Thermodynamic Equilibrium → Geochemical Thermodynamics → Trace Element Geochemistry → Partition Coefficients → REE Patterns in Geochemistry → Sedimentary Geochemistry

Longest path: 173 steps · 809 total prerequisite topics

Prerequisites (3)

Aqueous Geochemistryhard Redox Geochemistrysoft REE Patterns in Geochemistrysoft

Leads To (1)

Organic Geochemistrysoft