Stratified slope deposits or ''grèzes litées'' (original French name) are accumulations of

debris Debris (, ) is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, as in geology, large rock fragments left by a melting glacier, etc. Depending on context, ''debris'' can refer to ...

that are traditionally associated with

periglaciation Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and ot ...

but that can also form in other settings. The deposits have a weak sorting and a coarse bedding. Stratified slope deposits are usually found at the lower slopes of valleys where thicknesses vary but may exceed 10 meters. Periglacial stratified slope deposits are thought to be the result of rock fragmented by frost being accumulated downslope. A distinction can be made between stratified slope deposits formed in

scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically ...

s and those of ''grèzes litées'' type. The first ones form in slopes with angles in excess of 30°, the latter ones in slopes with angles of 30–28° or as low as 5°. The ''grèzes litées'' type has been reported from

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

mountains, Atlantic Europe,

Central Europe Central Europe is an area of Europe between Western Europe and Eastern Europe, based on a common historical, social and cultural identity. The Thirty Years' War (1618–1648) between Catholicism and Protestantism significantly shaped the a ...

Himalaya The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...

, the

Dry Andes file:Andes_clima.png, 200px, Map of the climatic regions of the Andes. The Dry Andes are shown in yellow. The Tropical Andes are shown in green and the Wet Andes in dark blue. The Dry Andes ( es, Andes áridos) is a climatic and glaciology, glaciol ...

and the

Tropical Andes The Tropical Andes is northern of the three climate-delineated parts of the Andes, the others being the Dry Andes and the Wet Andes. The Tropical Andes' area spans . Geography and ecology file:Andes_clima.png, 200px, Map of the climatic regions ...

. The "biggest known outcrop of ''grèzes litées'' in north-western Europe" lies in the Enscherange in

Luxembourg Luxembourg ( ; lb, Lëtzebuerg ; french: link=no, Luxembourg; german: link=no, Luxemburg), officially the Grand Duchy of Luxembourg, ; french: link=no, Grand-Duché de Luxembourg ; german: link=no, Großherzogtum Luxemburg is a small lan ...

. There are relatively few reports of grèzes litées in the High Arctic, nevertheless these include Svalbard,

Western Greenland Kitaa, originally Vestgrønland ("West Greenland"), is a former administrative division of Greenland. It was by far the most populated of the divisions, being home to almost 90% of the total population. The divisions were de facto replaced by st ...

and Southern Banks Island in the

Canadian Arctic Archipelago The Arctic Archipelago, also known as the Canadian Arctic Archipelago, is an archipelago lying to the north of the Canadian continental mainland, excluding Greenland (an autonomous territory of Denmark). Situated in the northern extremity of ...

Early concept evolution

Stratified slope deposits were first reported under the name of ''grèzes litées'' in Charente, France, in 1951. A few years later André Cailleux described similar deposits calling them ''éboulis ordonnés''. Subsequently,

Jan Dylik Jan Dylik (19 June 1905 – 6 June 1973) was a Polish geography professor at the University of Łódz. He was born in Łódź on 19 June 1905. In 1925 he begain post-secondary studies at Jagiellonian University. He then went on to attend Adam Mick ...

described occurrences in central Poland in the 1960s. In 1968 Jean Tricart argued further for a periglacial origin of ''grèzes litées''. While French scientists gave the term ''grèzes litées'' a constrained definition by attributing them to a

frost weathering Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedg ...

origin and characterizing them granumetrically, its usage by non-French expanded the concept beyond this early definition.

Processes of formation

Periglacial stratified slope deposits form typically in periglacial areas that lack permafrost.

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

-aged stratified slope deposits formed from stone-banked solifluction lobes. In the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

the depth of freezing associated with the formation of stratified slope deposit is estimated at less than 15 cm while in Charente it is 40 to 50 cm. A major process that forms stratified slope deposits in periglacial areas is

solifluction Solifluction is a collective name for gradual processes in which a mass moves down a slope ("mass wasting") related to freeze-thaw activity. This is the standard modern meaning of solifluction, which differs from the original meaning given to it ...

of stone blankets in the form of solifluction lobes and sheets. Other processes include rock fall, flow of ice-coasted

clast Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

s, flow of dry grains,

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

and snow

avalanches An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. Avalanches can be set off spontaneously, by such factors as increased precipitation or snowpack weakening, or by external means such as humans, animals, and earth ...

. Yet more processes contribute to the formation, but that are of lesser importance, include

overland flow Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the s ...

of water caused by rain and the combined action of snow and wind. Stratified slope deposits can form in non-

periglacial Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and o ...

environments, meaning that the presence of stratified slope deposit is not unequivocal evidence for past periglaciation. The reason for the occurrence of stratified slope deposits outside present or past periglacial areas is that many of the processes that lead to their formation are

azonal In geography, azonal is an adjective that refers to processes or things that are not restricted to any climate zone. It can be used to describe soils, landforms, geomorphic processes or vegetation. Volcanism and mountain-related processes are exampl ...

References

{{Periglacial environment Periglacial landforms Sediments Slope landforms