Sequence stratigraphy is a relatively new branch of geology that attempts to link prehistoric sea-level changes to sedimentary deposits. Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ... Prehistory (Greek words προ = before and ιστορία = history) is the period of human history prior to the advent of writing (which marks the beginning of recorded history). ... // Definition Mean sea level (MSL) is the average height of the sea, with reference to a suitable reference surface. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ...

The 'sequence' part of the name refers to cyclic sedimentary deposits. The term 'stratigraphy' refers to the geologic knowledge about the processes by which sedimentary deposits form and how those deposits change through time and space on the Earth's surface. Stratigraphy, a branch of geology, is basically the study of rock layers and layering (stratification). ...

Sea level through geologic time

Comparison of two sea level reconstructions during the last 500 Myr. The scale of change during the last glacial/interglacial transition is indicated with a black bar.

Sea level changes over geologic time. The graph on the right illustrates two recent interpretations of sea level changes during the Phanerozoic. Today's date is on the far left side, labeled N for Neogene. The blue spikes near date zero represent the sea level changes associated with the most recent ice age, which reached its maximum extent about 20,000 years Before Present (BP). During this glaciation event, the world's sea level was about 320 feet (98 meters) lower than today, due to the large amount of sea water that had evaporated and been deposited as snow and ice in Northern Hemisphere glaciers. When the world's sea level was at this "low stand", former sea bed sediments were subjected to subaerial weathering (erosion by rain, frost, rivers, etc.) and a new shoreline was established at the new level, sometimes miles basinward of the former shoreline if the sea floor was shallowly inclined. Description This figure compares the Hallam et al. ... Description This figure compares the Hallam et al. ... The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ... Neogene Period: A unit of geologic time consisting of the Miocene and Pliocene Epochs. ... The Wisconsin (in North America), Weichsel (in Scandinavia), Devensian (in the British Isles) or Würm glaciation (in the Alps) is the most recent period of the Ice Age, and ended some 10,000 Before Present (BP). ... Before Present is a year numbering system, used for the far past times, relating dates to the year 1950. ... This article is about a foot as a unit of length. ... metre or meter, see meter (disambiguation) The metre is the basic unit of length in the International System of Units. ... For information on water from a sea or ocean, see sea water. ... A fresh snowfall in Colorados (USA) high forests. ... ICE can refer to: InterCity Express, a German high-speed train Internal combustion engine, a fuel engine In-car entertainment In-circuit emulator, a computer hardware device In case of emergency, emergency number in mobile phones Institution of Civil Engineers, British civil engineer guild Immigrations and Customs Enforcement, U.S... The Northern Hemisphere is the half of a planets surface (or celestial sphere) that is north of the equator (the word hemisphere literally means half ball). On Earth, the Northern Hemisphere contains most of the land and population. ... Mouth of the glacier Schlatenkees near Innergschlöß, Austria. ... Look up Erosion on Wiktionary, the free dictionary Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, movement in response to gravity, or living organisms (in the case...

Today, sea level is at a relative "high stand" because the majority of the glaciers had melted by about 10,000 BP and minor glacial melting has slowly continued (with occasional reversals) throughout recorded human history. The ancient shoreline of the last ice age is now under approximately 390 feet (120 meters) of water. For this reason, most early civilization seaport cities are currently under water (this may be the historic origin of the biblical Noah story). Noah or Nóach (Rest, Standard Hebrew נוֹחַ Nóaḥ, Tiberian Hebrew נֹחַ Nōªḥ; Arabic نوح Nūḥ), is a Biblical figure who according to Genesis built an ark to save his family and a selection of the worlds animals from the Deluge (an example of divine retribution). ...

In the distant past, sea level has been significantly higher than today. During the Cretaceous (labeled K on the graph), sea level was so high that a seaway extended across the center of North America from Texas to the Arctic Ocean (see reconstruction here)along a structural downwarp in front of a developing mountain range (the Sevier thrust belt).

These alternating high and low sea level stands repeat at several time scales. The smallest of these cycles is approximately 20,000 years, and corresponds to the rate of precession of the Earth's rotational axis (see Milankovitch cycles) and are commonly referred to as '5th order' cycles. The next larger cycle ('4th order') is about 40,000 years and approximately matches the rate at which the Earth's inclination to the Sun varies (again explained by Milankovitch). The next larger cycle ('3rd order') is about 110,000 years and corresponds to the rate at which the Earth's orbit oscillates from elliptical to circular. Lower order cycles are recognized, which seem to result from plate tectonic events like the opening of new ocean basins by splitting continental masses. Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ... Milankovitch cycles is the name given to the collective effect of changes in the Earths movements upon its climate. ... The Sun is the star at the centre of our Solar system. ... The tectonic plates of the world were mapped in the second half of the 20th century. ...

Hundreds of similar glacial cycles have occurred throughout the Earth's history. The earth scientists who study the positions of coastal sediment deposits through time ("sequence stratigraphers") have noted dozens of similar basinward shifts of shorelines associated with a later recovery. The largest of these sedimentary cycles can in some cases be correlated around the world with great confidence.

Economic Significance

These events have economic significance because these changes in sea level cause large lateral shifts in the depositional patterns of seafloor sediments. These lateral shifts in deposition create alternating layers of good reservoir quality rock (porous and permeable sands) and poorer-quality mudstones (capable of providing a reservoir "seal" to prevent the leakage of any accumulated hydrocarbons that may have migrated into the sandstones). Hydrocarbon prospectors look for places in the world where porous and permeable sands are overlain by low permeability rocks, and where conditions are right for hydrocarbons to be generated and migrate into these "traps".

External links

• A chart of sea level for the past 140,000 years (The different orders of cyclicity can be seen as higher frequency chatter on an overall asymmetric cycle. Today's date is on the right side of this chart.)
• An Online Guide to Sequence Stratigraphy by the University of Georgia's Stratigraphy Lab.