Presentation on theme: "Stratigraphy Rocks, Fossils, and Time. Introduction Stratigraphy crucial to Historical Helps us understand vertical and lateral changes in rocks/environments."— Presentation transcript:
Stratigraphy Rocks, Fossils, and Time
Introduction Stratigraphy crucial to Historical Helps us understand vertical and lateral changes in rocks/environments with time Helps us understand paleogeograpy e.g. where the land was, where the ocean was, where the mountains were, etc
What is Stratigraphy? A branch of geology concerned with composition, origin, age relationships, and geographic extent of layered or stratified rocks Valley of the Gods, Utah
Stratigraphy Stratigraphic section –Tracing stratigraphic sections from outcrops leads to correlation of rock units – Sequence of sedimentary rocks on a bed-by-bed basis – Demonstrates equivalency across an area
Sedimentary Facies Body of sediment/rock characterized by physical, chemical, and biological attributes Sediment/rock makes it recognizable and different from laterally adjacent rock –Could be textures –Could be fossils –Could be composition Transgression – Sea Level rises, environments march landward Regression– Sea Level drops, environments march seaward
Lateral Changes in Stratigraphy Beds may change laterally in thickness or lithology –Differences due to changes in sedimentation rate or depositional environment
Walther’s Law Those facies found in a conformable (no faults, unconformities, folds) lateral sequence will replace one another vertically
Conformable Vertical Successions Transgression Regression Facies are time transgressive Ages of facies vary from place to place Sea level ↑; shoreline moves inalnd Sea level ↓; shoreline moves seaward
Did sea level rise or fall?
Transgressive Sequence Note time lines cut across units
Transgressive and Regressive Sequence V-shaped pattern produced by migrating facies during a transgression followed by a regression – Three stratigraphic sections illustrate facies generated in vertical succession at three different locations
Causes of Transgressions and Regressions Cold and warm climates –Cold climate glaciation – Warm climate ice melt Uplift and Subsidence Uplift regression Subsidence transgression Seafloor spreading Fast spreading transgression Slow spreading regression
Fossils and Correlation William Smith – Determined relative ages of rocks using fossils and assemblages of fossils – Established Principle of Faunal Succession
Principle of Fossil Succession Fossils succeed one another through time in a regular and determinable order Because of this, any time period can be recognized by its fossil content
Fossil Assemblages Species have a time of origination and a time of extinction Because of this, different times have different fauna and flora If sedimentary rocks from different places contain the same fossils, they were deposited at the same time –If fossil A range = 40 – 20 my –If fossil B range = 25 – present –What is age of rocks containing last appearance of A & first appearance of B.
Establishing Correlation of Units How do we establish correlation or equivalency of units?