Civil Rights
Movements, leaders, victories and the continuing fight for equality.
q2K BHP
Black History Portal
THE BHP WIRE —
HIDDEN TRUTHS
What's New!
Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
| Port Askaig Tillite Formation | |
|---|---|
| Stratigraphic range: 717–660 Ma | |
 One of the diamictite beds on Garbh Eileach | |
| Type | Geological formation |
| Unit of | Argyll Group |
| Underlies | Bonahaven Formation |
| Overlies | Garbh Eileach Formation, Lossit Limestone Formation |
| Thickness | up to 1,100 metres (3,610 ft) |
| Lithology | |
| Primary | Diamictite, sandstone |
| Other | Siltstone, dolomite |
| Location | |
| Country | Scotland, Ireland |
| Type section | |
| Named for | Port Askaig |
The Port Askaig Tillite Formation (PATF) (also known as the Port Askaig Formation) is a sequence of glacigenic sedimentary rocks deposited during the Cryogenian period of the Neoproterozoic era, forming part of the Dalradian Supergroup.[1] It is exposed along the Dalradian outcrop from Galway, Mayo and Donegal in Ireland in the west through Islay and the Garvellachs in the Inner Hebrides to Schiehallion, Braemar and Fordyce to the east on mainland Scotland.[2] The formation records a time in Earth's history where there were repeated glaciations where ice sheets extended to low latitudes, sometimes referred to as a Snowball Earth.[3]
The PATF forms scattered outcrops along the whole ca. 600 km extent of the Dalradian Supergroup. It is always metamorphosed and variably deformed as a result of the Grampian Orogeny. The thickness of this unit varies greatly across the outcrop, with its thickest development, estimated at 1,100 m,[3] in the Inner Hebrides on the Garvallachs and Islay. The type section is found on Islay, near Port Askaig, for which the formation is named. This area has been identified as a major depocentre for the Argyll Group, possibly as a result of active extensional faulting. Even in this area the unit thins markedly to the west and the base is marked by an unconformity with the underlying Lossit Limestone Formation, part of the older Appin Group. On Garbh Eileach, the largest island of the Garvallachs, the base of the PATF is conformable, following on from the Garbh Eileach Formation of the uppermost Appin Group. On Islay the top of the PATF is marked by a transition to the mixed siliciclastic-carbonate Bonahaven Formation. In this central area the sequence is extremely well exposed and the deformation state is generally low, meaning that original sedimentary structures are well-preserved, allowing for confident environmental interpretation.[2]
The PATF is subdivided into five members the lowest (oldest) three of which are particularly well-exposed on the Garvallachs. The sequence contains 48 beds of diamictite interbedded with sandstones of non-glacial origin, forming 35–40% of the unit, typically deposited in deltaic to shallow water marine environments. The rest of the formation is made up of minor amounts of siltstones and dolomites. The diamictites, rocks consisting of large to very large clasts set in a finer-grained matrix, are interpreted to be tillites of glacial origin. The sediments are organised into units interpreted to represent 28 periods of glaciation, 25 periods where glacial conditions were close (peri-glacial) and 23 non-glacial episodes. The onset of the earliest of the glacial cycles is recognised within the uppermost part of the Garbh Eileach Formation. The end of the overall glacial interval is unclear, although the uppermost member only has a few, thin diamictite beds. There is nothing within the overlying Bonahaven Formation that matches a typical Cap carbonate.[3]
During the Neoproterozoic cold period, the Cryogenian, there are two globally distributed glacial sequences, the older Sturtian glaciation (~717–660 million years ago} and the younger Marinoan glaciation (<654–632 million years ago), both of which are regarded as probable examples of a Snowball Earth, where ice sheets extended to very low latitudes. The PATF has been correlated with both of these.[3][4] A number of techniques have been used to reduce the uncertainty. Rhenium–osmium dating has been carried out on pyrite grains found within layered baryte deposits that are part of the Easdale Subgroup of the Argyll Group. This gives values of 604.0 ± 7.2 Ma and 612.1 ± 18.6 Ma, which can be compared to earlier dating of the Tayvallich Volcanic Formation within the overlying Tayvallich Subgroup, of 595 ± 4 Ma and 601 ± 4 Ma, using U-Pb and Sm-Nd methods. These results suggest that the PATF is best correlated with the Marinoan glaciation.[4] Detrital zircon analysis has also been carried out on zircon grains from the sandstones interbedded within the PATF. The results support the sequence being Sturtian in age, with "youngest single grains" throughout being consistent with the likely depositional ages.[3]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The Port Askaig Tillite Formation (PATF) (also known as the Port Askaig Formation) is a sequence of glacigenic sedimentary rocks deposited during the Cryogenian period of the Neoproterozoic era, forming part of the Dalradian Supergroup. It is exposed along the Dalradian outcrop from Galway, Mayo and Donegal in Ireland in the west through Islay and the Garvellachs in the Inner Hebrides to Schiehallion, Braemar and Fordyce to the east on mainland Scotland. The formation records a time in Earth's history where there were repeated glaciations where ice sheets extended to low latitudes, sometimes referred to as a Snowball Earth.
Diamictite ( ; from Ancient Greek dia- (δια): 'through' and meiktós (µεικτός): 'mixed') is a type of lithified sedimentary rock that consists of unsorted to poorly sorted terrigenous sediment containing particles that range in size from clay to boulders, suspended in a matrix of mudstone or sandstone. The term was coined by Richard Foster Flint and others as a purely descriptive term, devoid of any reference to a particular origin. Some geologists restrict the usage to unsorted or poorly sorted conglomerate or breccia that consists of sparse, terrigenous gravel suspended in either a mud or sand matrix. Unlithified diamictite is referred to as diamicton. The term diamictite is often applied to unsorted or poorly sorted, lithified glacial deposits such as glacial tillite and boulder clay. Diamictites in general are often understood to have been formed by ancient glaciers, for example the Snowball Earth hypothesis rests on this explanation. However the most common origin for diamictites is deposition by submarine mass flows like turbidites and olistostromes in tectonically active areas, and they can be produced by a range of geological conditions. A list of theorized origins include: glacial meltwater flow deposition unsorted moraine glacial till basal melt-out ice rafted sediments deposited by melting icebergs or disintegrating ice sheets (dropstones) volcanic lahars lahar mass flows entering the ocean marine debris flow turbiditic olistostromes mixing of sediments by submarine landslides tectonic fault gouge erosional regolith, in the form of a debris flow other mass wasting events extraterrestrial impact breccia
The Smalfjord diamictite, Bigganjargga Tillite or Reusch's Moraine is a diamictite in Finnmark, northern Norway. The rock was first identified as a tillite by Hans Reusch in 1891, hence its name. The tillite overlies sandstone whose contact surface is striated. Reusch's Moraine belongs to the Smalfjord Formation, a geological formation of Neoproterozoic age. The tillite possibly formed during the Sturtian glaciation in connection to a global glaciation. Reusch's Moraine was among the first sites discovered to bear evidence of Precambrian glaciations, being only preceded by findings in Scotland (1871), Australia (1884) and India (1887). The site is remarkably illustrative and Reusch's 1891 sketch has been labeled "iconic" by Paul F. Hoffman. The area has been protected by law at least since the 1960s and it is forbidden to hammer the rocks.
The Cancañiri Formation, also named as Cancañiri Tillite, is a Katian to Hirnantian geologic formation of central Bolivia. The pebbly, argillaceous sandstones, shales and siltstones of the up to 1,500 metres (4,900 ft) thick formation, were deposited in a glacial foreshore to deep water turbiditic environment. The formation is named after Cancañiri, a mining town close to Llallagua, where a local legend of a possessed woman is believed. The formation overlies the San Benito Formation in Cochabamba and the Amutara Formation in other parts. The Cancañiri Formation is overlain by the Uncía Formation.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →The Greenwood District.
