Steno’s Laws of Stratigraphy Lesson2 - Earth Steno’s Laws of Stratigraphy

Historical Perspective of Stratigraphy First advances were made in the mid to late 1700s. This was due to advances in mining and canal building.

Historical Perspective of Stratigraphy Abraham Werner, mining geologist In later 1700s he noted that the same strata could be found in the same order at widely separated locations. Implied that local strata could hold clues as to how the global Earth had changed with time. Coined the term “Neptunism” which refers to a now obsolete theory of geo-stratification.

Historical Perspective of Stratigraphy William “Strata” Smith, English canal surveyor and consulting engineer (until 1799) and Father of Geology. Carefully examined strata along canals, roads, railway cuttings and quarries while crisscrossing the English countryside. Found that “the same strata were found always in the same order and contained the same fossils.”

William Smith (1815) First Geologic Map of Great Britain

Historical Perspective of Stratigraphy James Hutton (Founder of Modern Geology; 1726 -1797) Examining the sea coast in England he realized that strata are laid down by deposition of sediment in water. The sediment came from erosion of the continent. Internal forces on the Earth later raised the strata above sea level. The cycle can repeat over and over. Time to form a single strata layer from deposition is many thousands of years.

Stratigraphy (Steno 1669) Law of Original Horizontality-infers that sedimentary rock layers were originally deposited as flat-lying (horizontal) layers.

Stratigraphy (Steno 1669) Law of Original Horizontality-infers that sedimentary rock layers were originally deposited as flat-lying (horizontal) layers. Law of Lateral Continuity-states that sedimentary rock layers are deposited over large areas

Stratigraphy (Steno 1669) Law of Original Horizontality-infers that sedimentary rock layers were originally deposited as flat-lying (horizontal) layers. Law of Lateral Continuity-states that sedimentary rock layers are deposited over large areas Law of Superposition-states that, in a cross-section view, rock layers are oldest at the bottom and become progressively younger upwards.

Stratigraphy (Steno 1669) Law of Original Horizontality-infers that sedimentary rock layers were originally deposited as flat-lying (horizontal) layers. Law of Lateral Continuity-states that sedimentary rock layers are deposited over large areas Law of Superposition-states that, in a cross-section view, rock layers are oldest at the bottom and become progressively younger upwards. Law of Cross-Cutting Relations-infers that a rock body (e.g. igneous dike) cutting through another rock body (sandstone beds) is younger than the layers it intrudes; that is, the igneous dike would be younger than the sandstone beds.

Original Horizontality

Lateral Continuity

Superposition Younger Strata Older Strata Even Older Strata

Cross-cutting relations Fracture is younger than strata because it cuts through the strata.

Let’s recap The story in the rocks.

Something easy. Rank the layers from oldest to youngest B C D

Something easy. Rank the layers from oldest to youngest D, C, B, A from superposition

Little harder. Rank the layers from oldest to youngest C E B Igneous intrusion

Little harder. Rank the layers from oldest to youngest D, C, E, B, A from cross-cut relation and superposition D A C E B Igneous intrusion

Little harder. Rank the layers from oldest to youngest C E B F Igneous intrusion Fault

Rank the layers from oldest to youngest D, C, E, B, A, F Igneous intrusion Fault

What is the youngest feature? D A B C E River Valley

What is the youngest feature? E from cross-cutting relation D A B C E River Valley

Which feature is the youngest?

Which is the youngest? E D B F 0 of 150

Which is older, D or A

Relative Age Date the Features from Oldest to Youngest C B E

Relative Age Date the Features from Oldest to Youngest C, E, B, D, A