Relative Age And Stratigraphy Flashcards
Describe Stento’s principle of superposition:
In its plainest form, it states that in under formed stratigraphic sequences, the oldest strata will be at the bottom of the sequence. This important to stratigraphic dating which assumes that the law of super position holds true and that an object can not be older than the materials of which it is composed
Original horizontality
The principle of original horizontality states that layers of sediment are originally deposited horizontally under action of gravity. It is a relative dating technique. The principle is important to the analysis of folded and tilted strata. It was first proposed by the danish geological pioneer Nicholas steno.,
Lateral continuity:
the principle of lateral continuity states that layers of sediment initially extend laterally in all directions; in other words l, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
Laws of cross cutting relationships
The principles of cross cutting relationships states that an igneous intrusion is always younger than the rock it it cuts across.
Inclusions, or foreign bodies, found inside rock are necessarily older than that rock
Law of faunal succession
The principle of faunal succession, also known as the law of faunal succession is based I. The observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeeded each other vertically in a specific, reliable order that can be identified over wide horizontal distances
Uniformitarianism
The theory that changes in the earth’s crust during geological history have resulted from the action of continuous and uniform processes
Catastrophism
The theory that the earth had largely been shaped by sudden, short lived, violent events, possibly in worldwide scope.
Stratigraphy/stratigraphic correlation.
A dictionary of earth sciences. Stratigraphic correlation geologic study concerned with with establishing geochronological relationships between different areas, based on geologic investigations of local successions.
Unconformities
An unconformity is a buried erosion along or non depositional surface separating two rock masses or strata of different ages, indicating that sediment dispositions was not continuous
Disconformity
Is an unconformity between parallel layers of sedimentary rocks which represent a period of erosion or non-deposition
Angular unconformity
Is an unconformity where horizontally parallel strata if sedimentary rock are deposited on tilted and roses layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may be later be deformed and tilted further by price of activity
Non conformity
Exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre existing and eroded metamorphic or igneous rock.
Relative age
Is the age of a rock layer ( or fossils it contains) compared to other layers. It can be determined by looking at the position of rock layers
Numerical (absolute) age
Absolute age is the numeric age of a layer of rocks or fossils. Absolute age can be determined by using radiometric dating
Cross bedding
Is layering within a stratum and at an angle to the main bedding plane.
The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original depositional layering is tilted, such tilting not being the result of post-depositional deformation
Mud cracks
AKA desiccation cracks are sedimentary structures formed as muddy sediment dries and contracts. Crack formation also occurs in clay bearing soils as a result of a reduction in water content
Graded bedding
A graded bed ya one characterized by s systematic Change in grain or clash size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones.
Flame structures
A flame structure is a type of soft sediment detonation that forms in unconsolidated sediments, the eight of an overlying bed forces an underlying bed to push up through the over lying one, generally when both strata are saturated with water.
Law of inclusions
The law of included fragments is a method of relative dating in geology. Essentially, this law states that coasts in a rock are older than the rock itself. One example of this is a demolition, which is a fragment of a country rock that fell passing magma as a rock of stoping
Cross cutting relationships
Cross cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a relative dating technique in geology
Igneous Intrusion (“baked” zone)
An igneous intrusion is a formation in which magma is trapped beneath the surface of the earth and pushed the rock located above it into a dome shape a flat base and a convex upper surface
