• Time Scale of 1800’s good, but relative
• Strata change facies and are usually diachronous
• Separate concepts of rock units and time units

• Lithostratigraphy versus Chronostratigraphy
• Formations
• Sedimentary Facies
• Sea-level Changes
• Unconformities

• Geologic Mapping in Northern Europe led to the modern relative time scale through:
• Principle of superposition and….
• Principle of fossil Correlation...

Principle of Fossil Correlation 

Like assemblages of fossils are the same age and therefore strata containing these particular fossils are also the same age.

• Smith and Cuvier’s maps
• Wernerian Chronology

• Alluvial rocks (Arduino’s Tertiary)
• Secondary Rocks (Flotz)
• Transition Rocks
• Primitive or Primary

Undertook massive project of naming the entire European succession of strata.

• Sedgwick mapped deformed, poorly fossiliferous strata in Cambria (Wales).

• Murchison mapped below the base of the Old Red Sandstone (Silurian).

• Old Red Sandstone (Devonian)

• Silurian (Murchison)

• Ordovician (after S & W were dead)

• Cambrian

• Phanerozoic Eon: visible life
• Paleozoic Era: dominated by invertebrates
• Eras subdivided into Periods
• Younger periods subdivided into Epochs

• Igneous and metamorphic rocks (primitive) were not all older than rocks with fossils

Eon Eonothem

Era Erathem

Period System

Epoch Series

Age Stage (working unit)

• Lithostratigraphy: dividing rock sequence into units
• Chronostratigraphy: relating rock units to geologic time

• Extending local patterns allow recognition of big picture patterns:
• Unconformities
• Change in grain size
• Thickness of sediments

• Formation: local unit of stratigraphy
• "Originated From the same formative processes" 1770
• We now break it into much finer subdivisions

• Group (largest division)
• Formation
• Member
• Stratum (thinnest rock unit observable) now called "cycle" or "parasequence"

• Distinguished by:
• mineral composition
• color
• textural properties
• thickness, geometry of body
• organic remains
• outcrop character
• Total is Lithology

• Locally named formations do not extend indefinitely without changing
• Fossils in a formation change laterally with rock type
• Similarities of fossils in similar sedimentary rocks reflect environmental factors rather than age equivalence

• Term used to characterize laterally adjacent strata that are more or less time equivalent but differ in lithology and fossils

• Extending local facies patterns allow recognition of big picture patterns
• Original lateral continuity suggests presence of sedimentary facies where they are now missing due to erosion…powerful

• Attempts to relate the rock record to geologic time difficult:
• Subsequent deformation
• Erosion
• Faulting
• Time is continuous whereas the rock record is riddled with missing units

• The deposition of a formation usually takes 1 to 3 million years and records a lot of shifting environments

• Sea-level is not constant but has changed repeatedly throughout Earth History

• Transgressive Facies Pattern: upward progression in rock sequence from shallower to deeper-water deposits
• Sediments become finer up the section
• From Base to Top:
• conglomerate-sandstone-siltstone-shale-limestone

• Deeper-water deposits give way up the section to shallower-water deposits
• Sediments become courser up the section
• From Base to Top:
• Limestone-shale-siltstone-sandstone-conglomerate

• Regional facies patterns can reflect local subsidence and uplift or…
• Eustatic (global) changes in sea level

• Global (eustatic) sea-level changes over Earth History attributed to:
• Continental glaciation
• Increase in volume of mid-ocean ridges
• Periods of intense mountain building
• Other factors

• Transgressions and Regressions locally controlled by:
• Crustal uplift or subsidence
• Rates of sedimentation

• Occurs when sedimentation is fast enough so that shorelines build outward even if global sea-level is rising
• Causes a local regression

• A local transgression will occur if:
• Rate of local subsidence is slower than rate of sea-level rise
• Rate of local subsidence is faster than the rate of sea-level fall

• If the rate of local uplift is faster than the rate of sea-level fall, a regression will occur
• If the rate of local subsidence or uplift is equal to the rate of sea-level rise or fall, no net change in sea-level will occur locally

• Erosional surfaces or intervals of missing strata
• Can be traced and mapped over large distances
• Can vary in age from place to place
• Amount of missing rock section can also vary from place to place

• Can represent profound crustal upheaval and deep erosion associated with mountain building
• In other cases, unconformity may represent very little erosion or simply be a surface of non-deposition without erosion

• Disconformity: no discordance between strata above or below
• Angular Unconformity: angular discordance between older strata below and younger strata above
• Nonconformity: underlying rocks igneous or metamorphic