Till

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Till

Till is unsorted glacial

Glacier

A glacier is a large, slow-moving mass of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity and high pressure....
sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediment

Sediment

Sediment is any particulate matter that can be sediment transport by fluid dynamics, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers....
s of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier.

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Till is unsorted glacial

Glacier

Sediment

Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
s to mixtures of clay, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters....
, gravel

Gravel

Gravel is rock that is of a specific particle size range. Specifically, it is is any loose rock that is larger than two millimeters in its largest dimension and no more than 64 millimeters ....
and boulder

Boulder

In geology, a boulder is a rock with Particle size of usually no less than 256 mm diameter. While a boulder may be small enough to move or roll manually, others are extremely massive....
s. Clay in till may form in spherical

Sphere

A sphere is a symmetrical geometrical object. In non-mathematical usage, the term is used to refer either to a round ball or to its two-dimensional surface....
shapes called till balls. If a till ball rolls around in a stream, it may pick up rocks from the streambed and become covered by rocks; thence it is known as an armored till ball.

Till is deposited at the terminal moraine

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age....
, along the lateral

Moraine

Continental Glacier

Continental Glacier is located in Bridger-Teton National Forest and Shoshone National Forests, in the U.S. state of Wyoming and straddles the Continental Divide in the northern Wind River Range....
, large amounts of till are washed away and deposited as outwash in sandur

Sandur

A sandur is a Glaciology outwash plain formed of sediments deposited by meltwater at the terminus of a glacier....
s by the river

River

A river is a natural stream of water, usually freshwater, flowing toward an ocean, a lake, or another stream. In some cases a river flows into the ground or dries up completely before reaching another body of water....
s flowing from the glacier and as varve

Varve

A varve is an annual layer of sediment or sedimentary rock.The word 'varve' is derived from the Swedish language word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'....
s in any proglacial lake

Proglacial lake

In geology, a proglacial lake is a lake formed either by the damming action of a moraine or ice dam during the retreat of a melting glacier, or one formed by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice....
s which may form. Till may contain alluvial deposits of gem

Gemstone

A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewellery or other adornments....
s or other valuable ore

Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
minerals picked up by the glacier during its advance, for example the diamond

Diamond

In mineralogy, diamond is the Allotropes of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon....
s found in Wisconsin

Wisconsin

Wisconsin is one of the fifty U.S. state in the United States of America, located in the north central part of the United States. It borders two of the five Great Lakes and four U.S....
, Indiana

Indiana

The State of Indiana was the 19th U.S. state admitted into the union. It is located in the Midwestern United States of the United States of America....
, and Canada

Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
. Prospector

Prospecting

Prospecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.Prospecting is synonymous in some ways with mineral exploration which is an organised, large scale and at least semi-scientific effort undertaken by mineral resource companies to find commercially viable ore deposi...
s use trace minerals in tills as clues to follow the glacier upstream to find kimberlite

Kimberlite

Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley, Northern Cape in South Africa, where the discovery of an diamond in 1871 spawned a diamond rush, eventually creating the Big Hole....
diamond deposits and other types of ore deposits.

Tillite

In cases where till has been indurated or lithified

Lithification

Lithification is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithification is a process of porosity destruction through Compaction and cementation ....
by subsequent burial into solid rock, it is known as the sedimentary rock tillite. Matching beds of ancient tillites on opposite sides of the south Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions; with a total area of about 106.4 million square kilometres . It covers approximately one-fifth of the Earth's surface....
provided early evidence for continental drift

Continental drift

Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912....
. The same tillites also provided the key evidence for the Precambrian

Precambrian

The Precambrian is an informal name for the supereon comprising the eon of the geologic timescale that came before the current Phanerozoic eon....
Snowball Earth

Snowball Earth

Snowball Earth refers to hypotheses regarding paleoclimate global-scale glaciation, claiming that the Earth's surface was nearly or entirely frozen at some points in its past....
glaciation event.

Types of till

There are various types of classifying tills:

primary deposits – these were laid down directly by glacier action
secondary deposits – these have undergone reworking (e.g. fluvial transport, erosion, etc)

Traditionally (e.g. Dreimanis

Aleksis Dreimanis

Aleksis Dreimanis is an award winning Quaternary Geology.Dreimanis was born in Latvia. He first studied geology at the Institute of Palaeontology at the University of Latvia in Riga....
, 1988) a further set of divisions has been made to primary deposits, based upon the method of deposition.

Lodgement tills – sediment which has been deposited by plastering of glacial debris from a sliding glacier bed.
Deformation tills – Sediment which has been disaggregated and (usually) homogenised by shearing in the sub glacial deformed layer.
Melt out tills – Released by melting of stagnant or slowly moving debris-rich glacier ice and deposited without subsequent transport or deformation. Split up into sub glacial melt out till (melting of debris rich ice at the bottom of the glacier) and supraglacial melt-out till (melting of ice on the glacier surface).
Sublimation till – similar to melt out till, except the ice is lost through sublimation rather than melt. Often occurs only in extremely cold and arid conditions, mainly in Antarctica.

Van der Meer et al. 2003 have suggested that these till classifications are outdated and should instead be replaced with only one classification, that of deformation till. The reasons behind this are largely down to the difficulties in accurately classifying different tills, which are often classified based on inferences of the physical setting of the till rather than till fabric or particle size analysis data.

Till

Tillite

Types of till

See also