Intra-volcanic sedimentary rock in North Ethiopia

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Coordinates: 13°39′19″N 39°10′23″E / 13.6552°N 39.1731°E / 13.6552; 39.1731
Source: Wikipedia, the free encyclopedia.
Intra-volcanic sedimentary rock
Stratigraphic range: Oligocene
Approximate paleocoordinates
0°N 0°E / 0°N 0°E / 0; 0
RegionTigray
Country Ethiopia
ExtentNorthern Ethiopian Highlands
Type section
Named byIt:Giovanni Merla
Intra-volcanic sedimentary rock in North Ethiopia is located in Ethiopia
Intra-volcanic sedimentary rock in North Ethiopia

Between 29 and 27 million years ago, the extrusion of Ethiopia’s flood basalts was interrupted and deposition of continental sediments occurred. Inter-trappean beds outcrop in many places of the Ethiopian highlands. They consist of fluvio-lacustrine deposits, that are generally a few tens of metres thick. Often, these interbedded fluvio-lacustrine deposits are very visible because their bright colours strongly contrast with the basalt environment.[1]

Name and definition

The formation, also called silicified limestone and interbedded lacustrine deposits was first extensively characterised in the 1930s by Merla and Minucci.[2]

Stratigraphic context

The formation is generally at the interface between the lower Ashangi Basalts, and the upper Alaji Basalts.

Environment

The sediments were deposited in shallow lakes and marshes in large topographic depressions. The dense vegetation hosted mammals and birds, which found their food between the reeds of the lake shores. The decomposing vegetation sometimes deprived the water of oxygen, what led to large dy-offs, particularly when temperatures raised. In addition, water levels were variable, and annually some of the lakes could dry up completely. Relatively few species could adapt to such variable conditions.[3]

Dogu’a Tembien, Tigray Region

Lithology

Khunale

The intra-volcanic rocks comprise

Dogu’a Tembien), roadcuts show around 45 metres thick sedimentary deposits. The fossilised calcareous beds, locally contain cherty nodules and wavy laminations. The loose to massive sediments of the uppermost part of the formation show well-developed bedding; they are black in colour. This is peat, the result of organic decomposition, that was then covered by the Alaji Basalts, the second phase of basalt eruption.[4][2]

Life

The inter-trappean beds contain a

gastropods themselves, particularly their faeces, have contributed to the silicification, more in particular to the formation of pelletoidal wackestone, that ultimately changed into cherts.[3]

Geographical extent

The formation occurs widely in the

Dogu’a Tembien, particularly around Hagere Selam they reach a thickness of around 100 metres lying above one hundred metres of basalts.[1]

The Geramba Rock-Hewn Church in Intra-volcanic Silicified Mudstone

In the Ethiopian flood basalts,

Tembien highlands to sculpt the Geramba rock church. It is the only rock church carved from this formation. The church is designed as a basilica; it holds a flat ceiling and three bays. On the rock wall, there are some ancient paintings.[4][5][6]

References

  1. ^
    ISBN 978-3-030-04954-6
    .
  2. ^ a b c Merla, G.; Minucci, E. (1938). Missione geologica nel Tigrai. In: La serie dei terreni, vol. 1. Rome, Italy: Regia Accademia d’Italia, Centro Studi per l’Africa Orientale Italiana.
  3. ^
    ISBN 978-3-030-04954-6
    .
  4. ^
    ISBN 978-3-030-04954-6
    .
  5. ^ Plant, R.; Buxton, D. (1970). "Rock-hewn churches of the Tigre province". Ethiopia Observer. 12 (3): 267.
  6. ISBN 978-3-030-04954-6
    .
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