Patrimoine Naturel Et Développement Durable

ROYAUME DU MAROC Académie Hassan II des Sciences et Techniques

ACTES DE LA SESSION PLÉNIÈRE SOLENNELLE Année 2020

Thème: Patrimoine naturel et développement durable

Rabat, 25 - 27 février 2020 Communications affichées 397

THE TAZEMMOURT SECTION: FEATURING THE FIRST CAMBRIAN FOSSIL LAGERSTATTE KNOWN FROMAFRICA

1 1 3 4 Gerd Geyer , Ed Landing , Miguel Caldera Pais , Nasrrddine Youbi .s and Moulay Ahmed Boumehdi 4,s

1-lnstitut fiir Geographie und Geologie, Bayerische J11U11s-Maximilians-Universitiit Würzburg, Germany 2-New York Staœ Museum, 222 Madison Avenue, Albany, NY, U.S.A. 3- Mediterranic Store, 7780-133 Castro Verde, Portugal 4- Dep11rtment of Geology, Faculty ofSciences Semlalia, CadiAyyad University Marrakech, Morocco 5- Instituto Dom Luiz, University ofLisbon, Portugal

The Tazemmourt section (Figure 1) is composed of lower Cambrian strata with a total thickness of ca. 350 m. It includes rocks of the Igoudine and Amouslek formations. The section is fairly well studied (e.g., [1]-[6]), but is particularly famous for its superbly preserved trilobites (extinct marine arthropods with dorsal skeletons mineralized by calcium carbonate). These trilobites are offered for sale on the global fossil market and find their way into numerous international museum collections (e.g., [7]). Many trilobite species were described from the Tazemmourt section for the first time and have their type localities here ([l], [8]). In addition, the vertical sequence of fossils seen in the section is the basis for the biostratigraphical subdivision in the Atlas Ranges. This fossil-based zonation is part of the most important relative time subdivisions of the Cambrian Period in the West Gondwana paleocontinent and globally (e.g., [l], [6], [9]-[11]).

Recent work has revealed that several horizons in the Daguinaspis Zone (based on trilobite fossils) of the Amouslek Formation yield animal remains with well preserved, internai soft-parts. These occurrences were termed the Souss La.gerstlitte, and this is the first Cambrian fossil Lagerstiitte known fromAfrica ([12], [13]). Accordingly, the Tazemmourt section certainly deserves a protected status and should be regarded as one of the key geotopes in Morocco. 398 Actes de la session plénière solennelle, Rabat, 25 - 27 février 2020

Figure l : 'làzemmourt Main Sedlon, 'riew towards nol1h from mld-sectfon. 1)pkal shale-domlnated mlddle and upper parts of the Amoo.slek Formation are 'risible

The Tazemmourt section is located south of the village of Tazemmourt, about 10 km SSE of 'Throudannt (Lambert coordinates 171.41382.4, ca. N 30° 23' 45" W 8° 49' 30"). The rocks dip northward, and the top of the section at the southem rim. of Tazemmourt is covered by the alluvial sediments of the Souss plain (Figure 1). The base of the section, about 2 km south ofTazemmourt, is in an east-west striking valley formed on the lgoudine Formation. The conspicuous transverse ridge to the north of that valley is fonned by resistant limestones that lie about at the level of unit 17 in Jean Abadie's uupublished thesis (Figure 2).

The Igoudine Formation in the Tazemmourt section is dominated by massive limestones. The succession through the 'Iiout Member that fonns the upper Igoudine Formation is the best example of that member, apart from the Tiout section, and includes numerous horizons with an::haeocyaths (studied by F. Debrenne, (14)-(18]). Archaeocyaths are important for regional and intercontinental fossil-based correlation in ancient tropical marine rock successions. Associated fossil hasb limestones contain Hupetina antiqua, the oldest known t:rilobite that i.s described from Mo:rocco ((19]). Communications affichées 399

A. hol/ardi ·---,-.. Zone ...... ,-..

~~ ~ ,....., .!!? ~i ~ ] 0 Q. i « t/) Cl) 111 c .s 0 """'- S,N -~ - c! ~ ~ / { z SOU SS 0 _:I_ LAGER ~ 'T STATTE :E 0 a::: 0 ·-"""'- u.. ~------0 ------· :::.:: 0 w ,-.. ..J ...... Choubertella en :::::> Zone 0 :E ,....., < ·--o,-..

0 50m ~ ,-..

Fallotaspis plana Zone

0 0 ë>;.:. A

Figure 2 : Stratigraphie profile ol the middle and upper part ol the Tazemmourt main ledion showing lmown OCCU1'J.UiCa of Crilobites. atehaeocyatbt, and other shelly fouils. The stratigraphie range of the SoWl8 Lagerstitte. with uceptionaJ. preservation of fOlll.Îlll, is shown. Modified. from [2] and based. on unpublished. data. 400 Actes de la session plénière solennelle, Rabat, 25 - 27 février 2020

The Amouslek Formation in the 'làzemmourt section is composed of cyclic alternations of rock do:minated by green, grey and subordinate pwple shales with intercalatcd marlstone and limestone beds that include some archaeocyath buildups. The formation includes the only known contact of the top of the Choubertella and base of the Daguinaspis zones (an interval which includes an unpublished important faunal association). The shales of the middle and bigher Daguinaspis Zone are rich in trilobites, which are exploited in nume:rous small quanies in the main section. Eighteen different trilobite species we:re first descn'bcd :from the Amouslek Formation of this section ([1], [7], [11)), and this mean.s this is one of the most important trilobite localiti.es in Morocco and in West Gondwana (e.g., Figure 3). This part of the section was the basis for proposing the :first sophisticatcd b:i.osttatigraphic :zonation of the lower Cambrian for use on a global scale [1].

In addition, preservation of soft-part in various groups of fossils was reœntly described from the middle to uppe.r part of the Daguinaspis Zone [13), and particularly well preserved specimens were recovered from the Tazemmourt section, including the preservation of the digestive tract in several species of trilobites (Fi.gure 4), but also :from seta.e and parts of the visceral mass in brachiopods (Figure S).

Figure 3 : Bolotype of Pfmûor fallotl (Bupé, 1953), whb partly aposecl ventral dde of Che aoskeleCon (llbrlgenae, h)'pOltome, and rœû'al plate under the head reglon), œlledecl ln 1949 from 1he Amouslek Fonndon ofthe 'làzemmourt sedfon. Collectfon of the MU9éum Communications affichées 401

Figure 4 : Exoshleton of Che trilobite spccies Dapinalpi.s ambroggii trom Che Dlzemmourt sedion with paired. parC5 of the digestive tract preserved. io. the cqih•lon and anterior part ol the thora:. Collection Devoille DEV C4.2

l1gure 5 : Tbe unusual braddopod Mluolcludla ampltltrile from the 'làzemmourt section w:lth reUct, poorly preserved setae (splne.lfke structura) near the margln of the Tains (left) and clark stalnlng of soft parts tbat lmpregnates tbe shell materfal (arrows). Collection Barbe CGB 24b. 402 Actes de la session plénière solennelle, Rabat, 25 - 27 février 2020

Acknowledgement and funding

The studies on the section was supported by funds of the Deutsche Forschungsgemeinschaft to GG (DFG grants GE 549n-l, GE 549/13-1, GE 549/22-1), by funds of the National Science Foundation to EL, and by funds of the Academy Hassan II of Science and Technology of Morocco AcadHIIST/SDU/2016-02 to A. El Albani and NY. The Academician Prof. Ahmed El Bassani is gratefully acknowledged for the handling of this manuscript, bis patience and support.

References

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[3] G. Choubert,A. Faure-Muret, et al., Livret-guide de l'excursionAnti-Atlas occidental et central. Notes et Mémoires du Service Géologique du Maroc 229 (1970), 259 pp. [4] G. Choubert, A. Boudda, and A. Faure-Muret, Essai de stratigraphie de la couverture sédimentaire del'Anti-Atlas: Adoudounien - Cambrien inférieur. Reunion de la Limite Cambrien-Précambrien, Agadir-Rabat 1975, Dok. I A, Texte (1975), 57 pp.

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[8] G. Geyer, The Moroccan fallotaspidid trilobites revisited. Beringeria 18 (1996), 89- 199. [9] G. Geyer, Late Precambrian to early Middle Cambrian lithostratigraphy of southem Morocco. Beringeria 1 (1989), 115-143.

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[15] F. Debrenne, Archaeocyatha. Contribution à l'étude des faunes cambriennes du Maroc, de Sardaigne et de France. Notes et Mémoires du Service Géologique du Maroc 179 (1964), 371 pp.

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[17] F. Debrenne, M. Debrenne, and A. Faure-Muret, Faune d' Archéocyathes de l' Anti Atlas occidental (bordures Nord et Sud) et du Haut Atlas occidental. Cambrien inférieur, Maroc. Géologie Méditerranéenne XVII (1992), 177-211.

[18] F. Debrenne, and M. Debrenne, Archaeocyaths of the Lower Cambrian of Morocco. Beringeria Special Issue 2 (1995), 121-145.

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