Define and differentiate between lithology and stratigraphy?

Question

Define as it affects its application

Answer 1

Lithology is the study of rocks and minerals. Stratigraphy is the mapping of layers of sediments, perhaps composed of rocks of similar types.

Answer 2

Lithology -
The character of a rock described in terms of its structure, color, mineral composition, grain size, and arrangement of its component parts; all those visible features that in the aggregate impart individuality of the rock. Lithology is the basis of correlation in coal mines and commonly is reliable over a distance of a few miles.

or

The description of rock composition and texture. Lithosphere. The outer solid part of the Earth, including the crust and uppermost mantle. The lithosphere is about 100 km thick, although its thickness is age dependent.The lithosphere below the crust is brittle enough at some locations to produce earthquakes by faulting, such as within a subducted oceanic plate.

Stratigraphy -

Refers to the interpretation of the layers in archaeological deposits. By examining and analyzing the layers (strata) and the artifacts in them, archaeologists can learn how past people lived and what kinds of things they did. Usually, the artifacts found on top are the youngest (most recent), while those on the bottom are the oldest. If the stratigraphy gets mixed up (for example, if someone digs a hole down into it) then interpretation becomes much more difficult, and sometimes impossible.

or
Stratigraphy is a method of dating fossils by observing how deeply a fossil is buried. Sedimentary rock layers (strata) are formed episodically as earth is deposited horizontally over time. Newer layers are formed on top of older layers, pressurizing them into rocks. Paleontologists can estimate the amount of time that has passed since the stratum containing the fossil was formed. Generally, deeper rocks and fossils are older than fossils found above them.

or

The spatial ordering of geological layers or strata. It is usually assumed, and is commonly true, that one layer is laid down upon the previous layer in an orderly progression through time creating a stratigraphy.

Answer 3

Define Lithology

Answer 4

Paul FB's answer is pretty comprehensive...

Lithology - the study of rock types. Sandstone, limestone, shale, whatever... Similar to petrography, which I usually think of in the context of what the rocks are actually made of (minerals, fossils,etc) rather than the characteristics of those rocks (bedding, grainsize, fabric, "facies" etc). Best check in a geological dictionary for the most precise definition if need be.

Stratigraphy - the placing of those rocks in their correct context, usually chronological i.e. time, or age. In the simplest case, as sedimentary rocks are broadly deposited in layers, the oldest rocks will be found underneath the youngest ones (unless later disrupted by faulting, folding, tectonics). Geologist typically use certain types of fossils to categorize the rocks by age (era, period, stage, zone etc, with increasing detail). Types of fossils that have a wide distribution, are easily identified and show rapid evolutionary change are best, as this enables greater accuracy. Ammonites work well in the Jurassic, for example.

Pitfalls in application.... Well imagine sandstone laid down in a Jurassic river bed. The river meandered at some point and changed it's course. A new geologist arrives in the area and maps out the sandstone outcrops (or correlates the sandstone beds between boreholes), and interprets them as one sandstone bed across the whole area. Well, the sandstone all looks pretty much the same (lithologically-speaking)! Later, an experienced geologist then arrives and points out, with the help of fossil data ("biomarkers") that there are at least two sandstone beds of different ages, with different geographic distributions, separated by a gap in geological time (disconformity or unconformity). The river bed sandstone at any given place are time equivalent to swamp mudstones and coals deposited along-side the river, and are not time equivalent to the other sandstones.

This might sound picky, but if you are an geologist wanting to locate an exploratory borehole to find oil in these river-laid sandstones (or any other place!) you could waste millions of dollars of your company's money by drilling in the wrong place.

Answer 5

Petrology is the study of rocks. Lithology is the term for types of rock in a formation, for example the the lithology of the Cotgrave Formation is dominantly mudstones with thin gypsum bands.

Stratigraphy is the science of correlating different formations (usually, but not alway sedimentary) into a relative framework, e.g. the Thanet Sand in London lies above the Upper Chalk but below the Lambeth Group sands and clays.

Note that "above" is purely a stratigraphic term: it means the formation was laid down later. In many cases, following folding and deformation, the "higher" formation can be physically underneath the "lower" one. This is done by a combination of physical observation (you can see the sequence) and fossils (one formation has fossils in it known to be later than another formation, because the relationship has been established elsewhere.

Geochronology then attempts to tie the stratigraphic framework into an absolute timescale, usually in millions of years. In practice, stratigraphy and geochronolgy work han in glove - sometimes the only way you can say that Formation X is younger than Formation Y is because radiometric dates tell you so; they may not be observed anywhere in a position allowing you to tell their relative ages by physical relationship, and one or both have no fossils.

Answer 6

Define Stratigraphy