{{Short description|Geological formation in Ethiopia}} {{Infobox rockunit | name = Antalo Limestone | image = Antalo_Limestone_at_Kurkura.jpg | caption = Formation at Kurkura village [[Degua Tembien|(Dogua Tembien)]], holding St. Mika'el's cave | type = [[Geological formation]] | period = Kimmeridgian | age = [[Oxfordian (stage)|Oxfordian]]-[[Kimmeridgian]]<br />~{{fossilrange|163|153}} | prilithology = [[Limestone]], [[marl]], [[calcareous]] [[sandstone]] | otherlithology = [[Grainstone]], [[wackestone]] | namedfor = [[Antalo]] town | namedby = [[William Thomas Blanford]] | year_ts = 1868 | region = [[Tigray Region|Tigray]] | country = [[Ethiopia]], [[Eritrea]] | coordinates = {{coord|13.5977|N|39.2772|E|display=inline,title}} | paleocoordinates = {{coord|7.5|S|26.6|E|display=inline}} | unitof = | subunits = | underlies = [[Mugher Mudstone]] | overlies = [[Adigrat Sandstone]] | thickness = {{convert|800|m|ft|abbr=on}} | extent = [[Mekelle]] Outlier, [[Danakil Alps]] | area = | map = {{Location map+ | Ethiopia | relief = 1 | width = 250 | float = center | places = {{Location map~ | Ethiopia | lat_deg = 13.6 | lon_deg = 39.3 | mark = Blue pog.svg | marksize = 12 }} }} | map_caption = }}
The '''Antalo Limestone''', also known as the '''Antalo Sequence''', is a [[geological formation]] in [[Ethiopia]]. It is between 300 and 800 metres thick and comprises [[fossiliferous]] [[limestone]]s and [[marl]]s that were deposited in a reef. Marine microfossils have shown an age between 165 and 150 million years.<ref>{{cite book |last1=Sembroni |first1=A. |last2=Molin |first2=P. |last3=Dramis |first3=F. |title=Regional geology of the Dogu'a Tembien massif. In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District |date=2019 |publisher=SpringerNature |isbn=978-3-030-04954-6 |url=https://www.springer.com/gp/book/9783030049546}}</ref><ref name="bosellini">{{cite journal |last1=Bosellini |first1=A. |last2=Russo |first2=A. |last3=Fantozzi |first3=P.L. |last4=Assefa |first4=G. |last5=Tadesse |first5=S. |title=The Mesozoic succession of the Mekelle Outlier (Tigrai Province, Ethiopia) |journal=Mem. Sci. Geol. |date=1997 |volume=49 |pages=95–116}}</ref>
== Name and definition == The Antalo Supersequence includes two main stratigraphic units: the '''Antalo Sequence''' and the '''Agula Group'''.<ref name="bosellini"/><ref name="dramis2019">{{cite book |last1=Dramis |first1=F. |title=Geo-trekking in Ethiopia's Tropical Mountains |last2=Fubelli |first2=G. |chapter=Limestone, Karst and Tufa Dams in the Western Part of the Mekelle Outlier |date=2019 |publisher=SpringerNature |location=Cham (CH) |pages=107–119 |doi=10.1007/978-3-030-04955-3_7 |series=GeoGuide |isbn=978-3-030-04954-6 |s2cid=199102740 }}</ref> The Antalo Sequence, or Antalo Limestone has been named after the town of [[Hintalo]] in [[Tigray Region|Tigray]], Ethiopia. The name of the formation was coined by geologist [[William Thomas Blanford]], who accompanied the [[British Expedition to Abyssinia]] in 1868.<ref>{{cite book |last1=Blanford |first1=W.T. |title=Observations on the geology and zoology of Abyssinia, made during the progress of the British expedition to that country in 1867-68 |url=https://archive.org/details/cu31924024736666 |date=1870 |publisher=Macmillan and Co. |location=London}}</ref> At that time, Hintalo was a major town on the route of the invading British army.<ref>{{cite book |last1=Markham |first1=C. |last2=Prideaux |first2=W. |title=A history of the Abyssinian expedition |date=1869 |publisher=Macmillan}}</ref> So far the nomenclature has not been proposed for recognition to the [[International Commission on Stratigraphy]].
== Geographical extent == The sedimentary succession is found in Ethiopia, in the [[Mekelle]] Outlier, in the [[Blue Nile]] gorge, in the [[Harrar]] Plateau and around [[Dire Dawa]].<ref name="bosellini"/>
== Stratigraphic context == The Antalo Limestone overlies the [[Adigrat Sandstone]], and is covered by the [[Agula Group]] or [[Agula Shale]] and the [[Mugher Mudstone]].
== Environment == The Antalo Limestone comprises sediment that was deposited in a shallow tropical sea in the [[upper Jurassic]]. As the region had undergone a [[marine transgression]], it was below the sea level. At that time, what would become Ethiopia was positioned just south of the equator.<ref name="lerouge&aerts">{{cite book |last1=Lerouge |first1=F. |last2=Aerts |first2=R. |title=Fossil evidence of Dogu'a Tembien's environmental past. In: Geo-Trekking in Ethiopia's Tropical Mountains, the Dogu'a Tembien District. |date=2019 |publisher=SpringerNature |isbn=978-3-030-04954-6 |url=https://www.springer.com/gp/book/9783030049546}}</ref>
== Lithology == [[File:May_Qarano_quarry_in_Antalo_Limestone.jpg|thumb|left|Quarry in the third member of Antalo Limestone at May [[Qarano]] in [[Degua Tembien|Dogu'a Tembien]]]] The limestones and [[marl]]s of the Antalo Sequence also hold [[shale]] and [[calcareous]] sandstone layers. The Antalo Limestone comprises four members: (1) a basal member with [[grainstone]] and [[wackestone]] lithologies, with marly interlayers and in the upper part [[stromatoporoid]] coral-like level; (2) sandy limestone deposited in [[estuaries]] and [[lagoons]]; (3) [[Micrite|micritic]] (very fine grained) limestone with intercalations of wackestone and [[coquina]] beds deposited in relatively deep water; and (4) a succession of marls and limestone, with [[chert]]y limestone at the base.<ref name="bosellini"/><ref name="dramis2019"/> [[File:Rock sample 11 Sandy limestone Addi Idaga.jpg|thumb|left|Rock sample of sandy limestone (second member), collected in [[Addi Idaga]]]] [[File:Rock sample 7 Upper limestone formation Miheno.jpg|thumb|Rock sample from the fourth (upper) member, collected in [[Miheno]]]]
== Fossil content == [[File:Rock sample 6 Limestone with mollusks Azef.jpg|thumb|Rock sample of Antalo Limestone with mollusks, collected in [[Azef]]]] The Antalo Limestone sediments were deposited at the time of dinosaurs and primitive birds. Well away from coasts, coral reefs formed the edge of the continental shelf. At shallow depth, the sea bottom was made of large [[mudflats]], with sand bars and [[spit (landform)|spit]]s near river mouths.<ref name="lerouge&aerts"/> This sea bed hosted many invertebrate animals: [[echinoderm]]s, [[crustacean]]s, [[bivalves]] and [[gastropod]]s were common. There was also fish. As it was not a nutrient-rich ecosystem, larger predators were rare, maybe some marine reptiles like crocodiles. A striking scavenger in this fauna was a [[cephalopod]] mollusc, a giant [[nautilus]] with a characteristic spiral shell.<ref name="lerouge&aerts"/>
===Invertebrates=== ; Bivalves {| class="wikitable" align="center" |- ! colspan="6" align="center" | '''[[Bivalve]]s of the Antalo Limestone.'''<ref name=":1">{{Cite journal |last1=Kiessling |first1=Wolfgang |last2=Pandey |first2=Dhirendra Kumar |last3=Schemm-Gregory |first3=Mena |last4=Mewis |first4=Heike |last5=Aberhan |first5=Martin |date=2011 |title=Marine benthic invertebrates from the Upper Jurassic of northern Ethiopia and their biogeographic affinities |url=https://www.academia.edu/12856498 |journal=Journal of African Earth Sciences |volume=59 |issue=2–3 |page=195 |doi=10.1016/j.jafrearsci.2010.10.006 |bibcode=2011JAfES..59..195K |issn=1464-343X}}</ref> |- ! Genus !! Species !! Presence !'''Material'''!! Notes !! Images |- |''[[Actinostreon]]'' |''A. solitarium'' |10 specimens from AL1, 65 from AL2. |75 specimens. |A [[Palaeolophidae|palaeolophid]]. | |- | ''[[Arcomytilus]]'' |''A. laitmairensis'' | AL1 and AL2. |3 left valves, 1 right valve and 4 articulated specimens. | A [[Mytilidae|mytilid]]. | |- |''[[Eopecten]]'' |''E. velatus'' |AL1. |1 left valve. |A [[Pectinidae|pectinid]]. | |- |''[[Gryphaea]]'' |''G.? (Bilobissa?) balli'' |AL1. |1 left valve. |A [[Gryphaeidae|gryphaeid]]. | |- |''[[Integricardium]]'' |''I. (Integricardium)'' cf. ''bannesianum'' |7 specimens from AL1, 1 from AL2. |4 left valves, 1 right valves and 3 double-valved specimens. |A [[Cardiidae|cardiid]]. | |- |''[[Liostrea]]'' |''L.'' sp. |AL1 and AL2. |2 specimens. |An [[Ostreida|ostreid]]. | |- |''"[[Lucina (bivalve)|Lucina]]"'' |''"L."'' cf. ''cecchii'' |AL2. |4 double-valved specimens. |A [[Lucinidae|lucinid]]. | |- |''[[Modiolus (bivalve)|Modiolus]]'' |''M. (Modiolus) imbricatus'' |2 specimens from AL1, 1 from AL2. |3 double-valved specimens. |A [[Mytilidae|mytilid]]. | |- |''[[Musculus (bivalve)|Musculus]]'' |''M. (Musculus) somaliensis'' |AL1 and AL2. |2 articulated specimens. |A [[Mytilidae|mytilid]]. | |- |''[[Nanogyra]]'' |''N. nana'' |AL2. |2 articulated specimens. |A [[Gryphaeidae|gryphaeid]]. | |- |rowspan=2|''[[Pholadomya]]'' |''P. (Bucardiomya) somaliensis'' |1 specimen from AL1, 6 from AL2. |7 double-valved specimens. |A [[Pholadomyidae|pholadomyid]]. | |- |''P. (Bucardiomya) lirata'' |AL2. |1 double-valved specimen. |A [[Pholadomyidae|pholadomyid]]. | |- | rowspan="2" |''[[Plagiostoma (bivalve)|Plagiostoma]]'' |''P. harronis'' |AL1 and AL2. |3 left valves, 5 right valves and 2 articulated specimens. |A [[Limidae|limid]]. | |- |''P. sublaeviusculum'' |AL2. |1 left valve 1 right valve and 1 articulated specimen. |A [[Limidae|limid]]. | |- |''[[Seebachia]]'' |''S. ("Eoseebachia") sowerbyana'' |AL2. |2 left valves. |An [[Astartidae|astartid]]. | |- |''[[Spondylopecten]]'' |''S. (Spondylopecten) palinurus'' |AL1. |2 left valves. |A [[Pectinidae|pectinid]]. | |- |''[[Stegoconcha]]'' |''S. gmuelleri'' |AL2. |2 articulated specimens. |A [[Pinnidae|pinnid]]. | |- |} ; Brachiopods
{| class="wikitable" align="center" |- ! colspan="6" align="center" | '''[[Brachiopod]]s of the Antalo Limestone'''<ref name=":1" /> |- ! Genus !! Species !! Presence !'''Material'''!! Notes !! Images |- |cf. ''[[Amydroptychus]]'' |cf. ''A.'' sp. |Base of AL2. |10 individuals. |A [[Rhynchonellida|rhynchonellid]]. | |- |''[[Cererithyris]]'' |''C.'' sp. |1 from AL1, 105 from AL2 . |106 individuals. |A [[Terebratulida|terebratulid]]. | |- |''[[Cymatorhynchia]]'' |''C.'' sp. |AL2. |16 individuals. |A [[Rhynchonellida|rhynchonellid]]. | |- |''[[Daghanirhynchia]]'' |''D.'' sp. |3 individuals from AL1, 51 from AL2. |54 individuals. |A [[Rhynchonellida|rhynchonellid]]. | |- |''[[Monsardithyris]]'' |''M.'' sp. |AL2. |20 individuals. |A [[Terebratulida|terebratulid]]. | |- | ''[[Somalirhynchia]]'' |''S. africana'' | Mostly from AL2. |More than 100 individuals. | A [[Rhynchonellida|rhynchonellid]]. |[[File:Sonalirhynchia brachial valve.jpg|center|150 px]] |- |}
; Cnidarian {| class="wikitable" align="center" |- ! colspan="6" align="center" | '''[[Cnidarian]]s of the Antalo Limestone'''<ref name=":1"/> |- ! Genus !! Species !! Presence !'''Material'''!! Notes !! Images |- | ''[[Actinastrea]]'' |''A. crassoramosa'' | 47 specimens from AL1, 13 from AL2. |60 larger fragments of colonies. | A [[stony coral]]. | |- |''[[Coenastraea]]'' |''C. arabica'' |AL2. |1 specimen. |A [[stony coral]]. | |- |''[[Collignonastraea]]'' |''C.'' cf. ''grossouvrei'' |AL2. |1 specimen. |A [[stony coral]]. | |- |''[[Columnocoenia]]'' |''C. gemmans'' |AL1. |2 specimens. |A [[stony coral]]. | |- |''[[Comoseris]]'' |''C. meandrinoides'' |AL3. |1 complete colony. |A [[stony coral]]. | |- |''[[Cladophyllia]]'' |''C. excelsa'' |AL3. |1 specimen. |A [[stony coral]]. | |- |''[[Cryptocoenia]]'' |''C. slovenica'' |7 specimens from AL1, 4 specimens from AL2. |11 specimens. |A [[stony coral]]. | |- |''[[Ironella]]'' |''I. arabica'' |AL1. |12 specimens. |A [[stony coral]]. | |- |''[[Isastrea]]'' |''I. bernensis'' |20 specimens from AL1, 22 specimens from AL2. |42 specimens. |A [[stony coral]]. | |- |''[[Kobyastraea]]'' |''K. lomontiana'' |AL1. |1 specimen. |A [[stony coral]]. | |- |''[[Latiastrea]]'' |''L. greppini'' |2 from AL1, 3 from AL2. |5 specimens. |A [[stony coral]]. | |- |''[[Lochmaeosmilia]]'' |''L. trapeziformis'' |AL1. |16 karger fragments of colonies. |A [[stony coral]]. | |- |''[[Ovalastrea]]'' |''O. michelini'' |AL2. |3 specimens (including 1 complete colony). |A [[stony coral]]. | |- |}
; Echinoderms {| class="wikitable" align="center" |- ! colspan="6" align="center" | '''[[Echinoderm]]s of the Antalo Limestone''' |- ! Genus !! Species !! Presence !'''Material'''!! Notes !! Images |- | ''[[Ausichicrinites]]'' |''A. zelenskyyi'' | |Nearly complete specimen.<ref>{{Cite journal |last1=Salamon |first1=Mariusz A. |last2=Jain |first2=Sreepat |last3=Brachaniec |first3=Tomasz |last4=Duda |first4=Piotr |last5=Płachno |first5=Bartosz J. |last6=Gorzelak |first6=Przemysław |title=Ausichicrinites zelenskyyi gen. et sp. nov., a first nearly complete feather star (Crinoidea) from the Upper Jurassic of Africa |journal=Royal Society Open Science |year=2022 |volume=9 |issue=7 |article-number=220345 |doi=10.1098/rsos.220345 |doi-access=free|pmc=9297031 |pmid=35875469|bibcode=2022RSOS....920345S }}</ref> | A [[Comatulida|comatulid]]. | [[File:Ausichicrinites zelenskyyi gen. et sp. nov.jpg|center|150 px]] |- |''[[Pygurus]]'' |''P. meslei'' |Upper part of the formation.<ref>{{Cite journal |last1=Radwańska |first1=Urszula |last2=Jain |first2=Sreepat |date=2020-10-01 |title=First Late Jurassic echinoid record of Pygurus meslei Gauthier from the Antalo Limestone Formation (Blue Nile Basin, Ethiopia) |url=https://www.sciencedirect.com/science/article/pii/S1464343X20301497 |journal=Journal of African Earth Sciences |language=en |volume=170 |article-number=103898 |doi=10.1016/j.jafrearsci.2020.103898 |bibcode=2020JAfES.17003898R |s2cid=219739555 |issn=1464-343X|url-access=subscription }}</ref> | |A [[sea urchin]]. | |- |} ; Molluscs {| class="wikitable" align="center" |- ! colspan="6" align="center" | '''[[Mollusc]]s of the Antalo Limestone'''<ref name=":0">{{Cite journal |last1=Jain |first1=Sreepat |last2=Schmerold |first2=Roland |date=2021 |title=Callovian and Kimmeridgian fossils and stratigraphy of the Blue Nile Basin (central western Ethiopia) |journal=Annales Societatis Geologorum Poloniae |doi=10.14241/asgp.2021.11 |s2cid=239211851 |issn=0208-9068|doi-access=free }}</ref> |- ! Genus !! Species !! Presence !'''Material'''!! Notes !! Images |- |''[[Orthosphinctes]]'' |''O.'' aff. ''tiziani'' |Top part of sub-unit II. |5 fragmentary specimens. |An [[Ataxioceratidae|ataxioceratid]] [[ammonite]]. | |- |''[[Pachyceras]]'' |''P.'' cf. ''lalandeanum'' |From the middle part of sub-unit II, GPS location 10°02′39.7″N, 38°13′53.7″E. |One poorly preserved specimen (no. AF020). |A [[Pachyceratidae|pachyceratid]] [[ammonite]]. |[[File:Pachyceratidae - Pachyceras lalandeanum.JPG|center|150 px|]] |- | rowspan="4" |''[[Paracenoceras]]'' |''P.'' cf. ''ennianus'' |Top part of sub-unit II. |1 specimen (no. AF012). |A [[nautiloid]]. | |- |''P.'' aff. ''prohexagonum'' | Lower Limestone Member.<ref>{{Cite journal |last=Jain |first=Sreepat |date=2019-01-01 |title=First Bathonian (Middle Jurassic) nautiloid Paracenoceras Spath from Ethiopia |url=https://typeset.io/papers/first-bathonian-middle-jurassic-nautiloid-paracenoceras-29cc2a6iuu |journal=Journal of African Earth Sciences |language=en |volume=149 |pages=84–96 |doi=10.1016/J.JAFREARSCI.2018.07.027 |bibcode=2019JAfES.149...84J |s2cid=134655647 |issn=1464-343X|url-access=subscription }}</ref> | | A [[nautiloid]]. | |- |''P.'' cf. ''kumagunense'' |Top part of sub-unit II. |1 specimen (no. AF004). |A [[nautiloid]]. | |- |''P.'' cf. ''giganteum'' |Middle part of sub-unit II. |1 specimen (no. AF005). |A [[nautiloid]]. | |- |''[[Purpuroidea]]'' |''P.'' aff. ''gigas'' |One specimen (AF025) from the top part of sub-unit I; One specimen (AF026) from the top part of sub-unit II.
|2 specimen (AF025 and AF026). |A [[Gastropoda|gastropod]]. | |- |}
== Limestone and karst geomorphology == [[File:Santarfas washing place.jpg|thumb|left|A spring in Antalo Limestone at [[Santarfa]]]] The layering is sub-horizontal, the same as that of the underlying sedimentary formations.<ref name="dramis2019"/> This gives rise to a structural sub-horizontal [[terrain|relief]], with alternating cliffs and flats. Dissolution processes in limestone lead to the occurrence of caves. Most described caves in Mesozoic limestone in Ethiopia are located in the [[Harrar]] region (Sof Omar cave) and in the [[Degua Tembien|Dogu'a Tembien]] district of [[Tigray Region|Tigray]].<ref name="catlin">{{cite journal |last1=Catlin |first1=D |last2=Largen |first2=M |last3=Monod |first3=T |last4=Morton |first4=W |title=The caves of Ethiopia. |journal=Transactions of the Cave Research Group of Great Britain |date=1973 |volume=15 |pages=107–168}}</ref>
== Traditional uses of Antalo Limestone == [[File:Antalo_Limestone_as_building_material_-_house_in_Addi_Ateroman_in_Dogu'a_Tembien.jpg|thumb|Antalo Limestone is commonly used for house building; here a homestead in Addi Ateroman in [[Degua Tembien|Dogu'a Tembien]]]] Given its nearly rectangular shape and its strength, the hard layers of Antalo Limestone are used for :* House building. Traditionally, fermented mud will be used as mortar :* Fencing of homesteads, generally in [[dry stone|dry masonry]] :* Milling stone: for this purpose plucked-bedrock pits, small rock-cut basins that naturally occur in rivers with [[kolk (vortex)|kolks]], are excavated from the river bed and further shaped. [[Mill (grinding)|Milling]] is done at home using an elongated small boulder ([[mano (stone)|mano]])<ref>{{cite book |last1=Nixon-Darcus |first1=L.A. |title=The cultural context of food grinding equipment in Northern Ethiopia: an ethnoarchaeological approach. PhD thesis |date=2014 |publisher=Simon Frazer University |location=Canada |url=http://summit.sfu.ca/item/14597}}</ref><ref>{{cite book |last1=Gebre Teklu |title=Ethnoarchaeological study of grind stones at Lakia'a in Adwa, Tigray Regional State, Ethiopia. PhD diss. |date=2012 |publisher=Addis Ababa University |url=http://213.55.95.56/bitstream/handle/123456789/439/Gebre%20Teklu.pdf?sequence=1&isAllowed=y}}</ref> :* Door and window [[lintels]] :* Footpath [[Paving stone|paving]] :* [[Terrace (agriculture)|Stone bunds]] or ''gedeba'': terrace walls in [[dry stone|dry masonry]], typically laid out along the contour for sake of [[soil conservation|soil and water conservation]] :* [[Check dam]]s in [[gullies]] for sake of [[gully erosion]] control :* [[Cobble stone]]s, sold to the towns for paving secondary streets ==See also== *[[Ausichicrinites]]
== References == {{Reflist}}
[[Category:Geologic formations of Eritrea]] [[Category:Geologic formations of Ethiopia]] [[Category:Jurassic System of Africa]] [[Category:Oxfordian Stage]] [[Category:Kimmeridgian Stage]] [[Category:Limestone formations]] [[Category:Marl formations]] [[Category:Shallow marine deposits]] [[Category:Paleontology in Eritrea]] [[Category:Paleontology in Ethiopia]] [[Category:Tigray Region|Formations]]