The Cambrian of the Moroccan Atlas regions. - Beringeria Special issue 2: 7-46,14 text-figs.; Wllr.l.- burg. Abstract. The characteristics of the Cambrian of the ...
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THE LOWER-MIDDLE CAMBRIAN STANDARD OF WESTERN GONDWANA
Introduction, Field Guide, Abstracts, and Proceedings of the First Conference of the Lower Cambrian Stage Subdivision Working Group and I. G. C. P. Project 366 Ecological Aspects of the Cambrian Radiation
Edited by Gerd Geyer & Ed Landing
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Beringeria Special Issue 2 WUrzburg 1995
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1001' 366 C1IMBRIRN ECOLOGII
The Cambrian of the Moroccan Atlas regions GERD GEYER & ED LANDING
GEYER, G. &
LANDING,
E. 1995. The Cambrian of the Moroccan Atlas regions. - Beringeria Special issue 2: 7-46,14 text-figs.; Wllr.l.-
burg. Abstract. The characteristics of the Cambrian of the Moroccan Atlas regions are described and illustrated. Such major depositional controls as "Grand cycles" and tectonic environments arc discussed briefly. The lithostratigraphic units for the uppermost Prolcrozoic(?) to the Upper Cambrian of the Moroccan Anti-Atlas and High Atlas mountains are reviewed and partly revised. The descriptions characterize lithology, depositional environment, fossil content, and synonymy of each lithostratigraphic unit. The Jbcl Tichinchine Formation is abandoned. The bio- and chronostratigraphy of the Atlas regions are summarized with their (formal and informal) subdivisions including new biostratigraphical units in the Middle Cambrian. Detailed stratigraphy permits a recognition of evidence for diachroneity of several formational contacts. Controversial data and problems of the Moroccan Precambrian-Cambrian boundary arc discussed in detail. The available evidence does not permit any degree of certainty in correlations even at the stage-level with Lower Cambrian sections on other Cambrian continents.
• Uppermosl Proterozoic, Lower Cambrian, Middle Cambrian, Upper Cambrian, lithoslratigraphy, environment, bioslratigraphy, chronoslratigraphy, diachroneity. Morocco. Zusammcnfassung: Die Hauptmerkmale des Karnbriums in der marokkanischen Atlas-Region werden vorgestellt. Die kontrollierenden Faktoren der Ablagerung (wie "Grand cycles" und tektonische Rahrnenbedingungen) werden kurz diskutiert. Die lithostratigraphischen Einhcitcn yom vermutlichen obersten Proterozoikurn bis zurn Ober-Karnbrium im Anti-Atlas und Hohcn Atlas werden vorgestellt und teilweise revidicrt. Die Bcschreibungen bcinhalten die Charakterisierung von Lithologie, Ablagerungsbedingungen, Fossilinhalt und Synonymic jeder lithostratigraphischen Einheit. Die Jbel Tichinchinc Formation wird aufgehoben. Bio- und Chronostratigraphic der Atlas-Gebiete werden mit ihren formcllen und informellen Einheiten summarisch dargestellt und weitere erkennbare biostratigraphische Einhcitcn fllr das Mittelkambrium cingefUhrt. Fcinstratigraphische Aufnahmen liefern Beweisc fur Diachronismen einiger Formationsgrenzen. Kontrovcrse Daten und Probleme im Zusammenhang mit der Grenze zwischen Prakambrium und Kambrium in MarQkko werden detailliert diskutuert. Dabei zeigt sieh, daB die augenblicklichen Daten keine brauchbare Korrelation der Abfolgen mit anderen kambrischen Kontincnten, sci cs auch nur den Bereich der Stufen, erlauben.
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• Obersles Prolerozoikum, Unter-Kambrium, Miuel-Kambrium, Ober-Kambrium. Lilhoslraligraphie, Ablagertmgsgeschichle, Bioslraligraphie, Chronoslratigraphie, Diachronismus, Marokko. Addresses of the authors: Dr. GERO GEYER, Institut fur Palaontologic, Bayerische Julius-Maximilians-Universitat, Plcichcrwall 1, 097070 WUrzburg; Dr. E. LANDING, New York State Geological Survey, New York State Museum, Empire State Plaza, Albany, N.V. 12230, U.S.A.
Introduction The Atlas regions of Moroco have the most complete and best studied Cambrian successions in Africa. These relatively fossiliferous rocks are well exposed and compose the most important reference area for the Lower and lower Middle Cambrian in western Gondwana. The Anti-Atlas range has comparatively complete, very fossiliferous, and particularly weakly metamorphosed sequences that may extend upward from the uppermost Proterozoic (Fig. I). Additional Cambrian outcrop areas include the central High Atlas Mountains, the Jbilet and Rehamma regions, and the
coastal Meseta, where the rocks were affected by the Hercynian orogeny. In some areas, such as the Rehamna, tectonic activity caused marked metamorphism. In addition, nappe implacement and faulting during the Atlasian phase of the Alpine orogeny created tectonic slices that affected the entire Moroccan part of the Hercynian massif. This report summarizes the stratigraphic succession of the uppermost Proterozoic(?) and Cambrian of the Moroccan Atlas regions. It follows earlier summaries and stratigraphic revisions by GEYER (1989a, 1990a,
G. GEYER &
8
1990b) but provides additional details that have led to a somewhat modified view of depositional architecture and controls (Table I). The two earlier summaries attempted to provide improved definitions for lithostratigraphic assignments and to overcome the traditional confusion of litho- and biostratigraphic terms that appears in reports on the Moroccan uppermost
E.
LANDING
Proterozoic(?) and Cambrian. It might be noted here that the Lower Cambrian in reports by CI'IOUBERT (1952b) and HUPE (1953) began with the lowest, abundantly fossiliferous unit in Morocco, the Amouslek Formation in modem terminology (Table I), and reports after the mid-1970s have greatly extended the lower range of the Cambrian System.
•
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rig. I. Sketch map or the High Atlas and Anti-Atlas regions, Morocco, illustrating known areas ofNeoproterozoie(?)-Cambrian rock (densely stippled), areas presumed Dr known to include Neoproterozoie(?)-Cambrian rock (small stipples), and outcrops of older Neoproterozoic rock and crystalline basement (crosses).
Major depositional controls The late Proterozoic ("Pan african") orogeny in Morocco and northwestern Africa was followed by deposition of an uppermost Proterozoic(?)-Cambrian cover sequence (see Fig. 2 and discussed in detail below). This cover sequence illustrates an important, long-term transition in lithofacies associations that is well illustrated the more complete successions of the western and central Anti-Atlas.
Carbonate-siliciclastic transition The cover includes a thick interval of carbonate-dominated rocks followed by siliciclastic-dominated rocks
higher in the Cambrian in the western Anti-Atlas. The uppermost Proterozoic(?)-Lower Cambrian in this region (Le., Adoudou, Lie de vin, and Igoudine Formations) is dominated by restricted marine platform limestones and dolostones and is overlain by a shale-carbonate "Grand cycle" in the upper Lower Cambrian (Le., Amouslek Formation). Uppermost Lower Cambrian units include fine-grained siliciclastics with relatively minor nodular and bedded limestones (Issafen Formation) overlain by higher energy, shallow marine, sandstone-dominated facies (Le., Asrir and Tazlaft Formations). Limited carbonates also characterize the
The Cambrian of the Moroccan Atlas region
lower Middle Cambrian, and fossil-hash limestone beds are regularly encountered only in the lower part of the Jbel Wawrmast Formation (see Breche a Micmacca Member in Table I). TI-IEOKRlTOFF's (1979) early suggestion that Morocco came under progressively stronger, higher latitude influences during the Cambrian seems to be appropriate in explaining the decrease in limestones from the latest Precambrian(?)Lower Cambrian, in the loss of archaeocyathan buildups higher in the Lower Cambrian, and in development of paleoenvironments that permitted trilobite immigration in the Lower-Middle Cambrian boundary interval between the separate continents of Gondwana and Avalon (LANDING, in press). A rapid motion of the Moroccan margin of Gondwana seems to have taken place from the low latitude position (BuRRErI' et aI., 1990) suggested by latest Proterozoic(?)-Lower Cambrian carbonate facies to the high south temperate latitudes indicated by late Early and Middle Cambrian paleomagnetic work (e.g., SCOTESE et aI., 1979; SMITII et aI., 1981). Tectonic setting The presence of volcanic rocks and a volcanoclastic component of sedimentary rocks has long been recognized in the uppermost Proterozoic(?)-Middle Cambrian cover sequence of Morocco (e.g., DESTOMBES et aI., 1985; BUGGISCI-t & FLOGEL, 1988; BUGGtSCI-I & SIEGERT, 1988). These volcanic rocks indicate that deposition of the shallow water cover sequence did not take place on a completely "passive margin". However, the relative amount of volcanic rocks is much less in the cover sequence than in parts of the underlying Panafrican orogen, and different tectonic environments are represented. It might be noted that ignimbrites in the upper part of the Serie d'Ouarzazate under the cover sequence in the central Anti-Atlas (EI Graara massif) have reported U/Pb volcanic zircon and RblSr whole rock ages (ca. 586-563 Ma) that are late Proterozoic (see review in BUGGISCI-I & FLOGEL, 1988). Published accounts and our field work indicate that two important intervals of volcanism are recorded in the cover sequence and that these volcanic intervals correspond to basin reorganizations. Volcanic ashes and flows are interbedded locally in the lower on lap dolostones of the Adoudou Formation in the lowest part of the cover sequence (e.g., Ci-IOUBERT & FAUREMURET, 1970). One source for these ashes is dramatically preserved as the "Volcano of Alougoum" in the eastern EI Graara massif (CHOUBERT, 1952a; CHOUBERT et aI., 1979). An early U/Pb date of 534 ± 10 Ma
9
from the Volcano of Alougoum (DUCROT et aI., 1976, recalculated by DUCROT & LANCELOT, 1977) suggests that deposition of the Adoudou Formation began in the middle part of the sub-trilobitic Lower Cambrian (i.e., middle Placentian Series and Manykaian-equivalent; see ISACHSEN et aI., 1994; LANDING, 1994, 1995a) and that the Precambrian-Cambrian boundary in the AntiAtlas may lie at the unconformity between the Panafrican orogen and overlying, middle Lower Cambrian(?) Adoudou Formation. The temporal relationship of volcanism and marine on lap holds not only in the earliest Cambrian but also in the Lower-Middle Cambrian boundary interval. BUGGISCH & SIEGERT (1988) proposed a northwestern source of volcanoclastic debris in the upper Lower Cambrian of the Anti-Atlas. VILAND (1972), BOUDDA et al. (1972), DESTOMBES et al. (1985), and our field work indicate that thin K-bentonites and local pillowed flows are regularly encountered as thin layers in the lower part of the Jbel Wawrmast Formation of the central and western Anti-Atlas, the Jbel Sarhro, and the High Atlas. This volcanism accompanied unconfonnable onlap of the lower Middle Cambrian across the lower Lower Cambrian on the south side of the Jbel Sarhro and across the Panafrican orogen on the north side of the Jbel Sarhro and eastern High Atlas. The association of lower Lower and lower Middle Cambrian on lap with volcanism suggests that epeirogenic processes in a pull-apart (strike-slip or transtensional) regime may have defined the Cambrian depositional basin in Morocco. Minor volcanism is recorded through most of the Cambrian of Morocco, but other volcanic intervals do not seem to have a relationship to basin reorganization. For example, COMI'STON et al. (1990, 1992) determined a SHRIMP date (discussed below) on a thin ash in the higher Lie de vin Formation. Our stratigraphic reevaluation shows that the thin volcanic debris layers of the "Serie de Jebel Tichinchine" (designation abandoned, below) reported by BUGGISCI-I & SIEGERT (1988) actually occur in the upper Lower Cambrian Issafen Formation. Ashes in the upper Issafen Formation at Amouslek in the central Anti-Atlas and in approximately coeval strata of the Lemdad Formation will be seen in the course of the MOROCCO '95 field trip (see Field program, May 5 and May 7; this volume). Beds of volcanic ash in the upper Middle Cambrian Tabanite Group are also noted in maps of the Jbel Sarhro area published by the Service Geologique du Maroc have been determined to be non-volcanogenic arkoses (E. LANDING and W. HELDMAIER, unpubl. data).
10
GERD GEYER
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'FORM'A,T,I'ON··································· . .. . . . .,. . . . . . . . . . ..·uI::AG .... . . . . . . . . . . . . . . . .. .,
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Souss Basin The uppermost Proterozoic-Cambrian cover sequence of the Anti-Atlas and High Atlas mountains was deposited in a sedimentary basin that persisted into the Silurian, This Souss Basin (GEYER, 1989a) is generally similar to an epicratonic basin, with exception of the continuing volcanism, The axis of the basin roughly coincides with the modern trend of the Anti-Atlas (Fig. I). The depocenter of the Souss Basin obviously underwent a counter-clockwise reorientation from a NWtrend during Adoudou Formation deposition to a WSW-trend during deposition of the lbel Afraou Formation and, possibly, the formations of the Tabanite Group. The lower part of the cover sequence has been di-
vided into groups that reflect more-or-Iess asymmetrical transgressive-regressive cycles. Depositional environments changed through time with shoreline offlap and the increasing influx of detrital material derived from the east. Biostratigraphic evidence for diachroneity in formation contacts also suggests that on lapofflap cycles are recognizable in the Cambrian of Morocco (Fig. 2). However, formational contacts are "traditionally defined" through seemingly gradational intervals in the Moroccan Cambrian, and it is possible that stratigraphic reevaluation may lead to an understanding of the interval as a series of unconformitybounded sequences. In the course of this field trip, we wi II examine the evidence for and against a regional sequence boundary at the Lower-Middle Cambrian boundary in Morocco.
Cambrian stratigraphy Taroudant Group The lowest part of the Moroccan COver sequence is known from the western and central Anti-Atlas and
and volcanic complexes of the late Proterozoic PanAfrican orogen. Vast areas of the western Anti-Atlas are underlain by the Taroudant Group, and a distinc-
frol11 the western and, probably, the eastern margins of
five topography is developed 011 Clle.: group.
the Adrar n'Dren massif of the central High Atlas. The Taroudant Group rests unconformably on metamorphic
The Taroudant Group has received special interest because Illany workers have assumed that the Precam-
The Cambrian of'thc Moroccan Atlas region
brian-Cambrian boundary is located within it. Even though the available biostratigraphic data is limited and provides no resolution in Lower Cambrian correlation, carbon isotope, magnetostratigraphic, and geochronologic investigations have been published on the group. The assumption in these studies that non-conventional correlation techniques can be used for interregional correlation is problematical because these techniques cannot be related to an adequate biostratigraphic standard in the Taroudant Group (see section on Precambrian-Cambrian boundary, below). In any case, a 534 ± 10 Ma date on the lower Adoudou Formation (cited above) suggests that all of the Taroudant Group is Lower Cambrian. Our work with S. A. BOWRING on U/Pb volcanic zircon dates on the underlying, upper part of the Serie d'Ouarzazate, the lower Adoudou Formation, and middle Lie de vin Formation are expected to provide precise dates to bracket the Pan-African orogen-lower Taroudant Group unconformity and deternline approximate rates of lowest
II
Cambrian accumulation in the Anti-Atlas. The Taroudant Group is of interest because of its lithofacies associations. The group includes a depositional cycle developed on a shallow marine carbonate platform (Adoudou Formation) and the higher carbonate-shale sequence (Lie de vin Formation) is the best preserved, seemingly continuous sequence through lowest Cambrian, extremely shallow marine environments. Adoudou Formation Lithology and regional development The Adoudou Formation, named arler Oued Adoudou in the western Anti-Atlas, has a relatively thin (up to 140-150 m locally), lower unit composed of conglomeratic, dolomitic, and siliciclastic beds with local volcanic ashes and flows. This Basal Member is overlain by limestones and dolostones of the upper Limestone Member. nle formation fonm a broad outcrop belt in
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Fig. 3. Sketch map of the High Atlas and Anti-Atlas regions, Morocco, illustrating distribution of thc Adoudou Fonnation and tentative paleogeography during its deposition. The line that starts at Agadir indicates a zone of thrust faults, which separate the Anti-Atlas domain from the Hercynian fold belt. Coarse stipples indicate the probable limits of the distribution of the l3asal Member (sensu stricto). Irregular pattern reprcsents non-dcpositional arcas; small stipplcs = marginal clastic belt; irrcgularly hachured = areas with significant content of volcanic rocks; isopach lines indicate probablc thicknesses (in meters). Modified from GEYER (1989a: Fig. 2), based on data from G. C110UBERT and unpublished data from G. GEYER.
12
GERD GEYER
the core of the western and central Anti-Atlas where it is primarily responsible for the topography. However, the formation wedges out at the margins of the numerous Proterozoic inliers to the east (BOUDDA et aI., 1979; VAN LOOY, 1985). In addition, the formation is known from the south-central High Atlas Mountains (e.g., the Lemdad syncline and Agoundis sections). The thickness of the Limestone Member ranges from 500 to more than 1,000 m. A west-to-east lithofacies change takes place in the Adoudou Formation. Relatively pure carbonates in the west are replaced by a more siliciclastic-rich facies in the central Anti-Atlas. The change in facies is generally a lateral transition rather than an interfingering of the different facies. Although the Adoudou Formation is one of the thickest and best exposed units in Morocco, detailed information about its lateral and vertical facies changes and the continuity of its deposition is limited. Detailed studies are only available on the Tiout section (MONNINGER, 1979; see May 3 of the MOROCCO '95 field trip, this volume) and, to a more limited extent, for the Tamjout section (CI-lAZAN, 1954). A more-orless detailed investigation on the carbon isotope signatures of the Adoudou Formation was published by MAGARITZ et al. (199 I) that they claimed permitted a comparison with the Siberian Yudoma and Pestrotsvet Formations (see Precambrian-Cambrian boundary discussion, below). Depositional environment Adoudou Formation carbonates reflect deposition primarily under shallow subtidal to intertidal marine conditions. An interesting lithofacies association includes the interbedded rhyolitic or syenitic explosive volcanics and planar-laminated, stromatolitic, pinkishbrown dolostones with scattered anhydrite molds at the western end of the EI Graara massif (i.e., BUGGISCH & FLUGEL, 1986; LANDING & HELDMAIER, unpub. data). CI-lOUBERT (I 952a) documented intercalations of trachyandesitic rocks in the formation. The volcanic source at Jbel Bokho (Jebel Boho) near Alougoum is still recognizable as a volcano (CHOU BERT, 1952a; BOUDDA et aI., 1979), and the middle of the Adoudou Formation in the surrounding area is dominated by volcanic rock. On lap of the formation took place across an erosion surface on the late Proterozoic Pan-African orogen. The transition from the Basal into the Limestone Member reflects a change from a more clastic onlap sequence into a predominantly carbonate sequence
&
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with probable shoreline transgression. Fossils Reports on Adoudou Formation fossils are limited. CHOUBERT et al. (1950, 1952a, 1952b, 1987), BUGGISCH et al. (1978), BUGGISCH & HEINITZ (1984), and VAN LOOY (1985) reported stromatolites from the Limestone Member in the Anti-Atlas. The presence of a skeletal alga-referred to Kundatia composita has been described from the central Anti-Atlas (BUGGISCH & FLUGEL, 1986) although this determination must be regarded as erroneous (see below under chapter "Moroccan Precambrian-Cambrian boundary". CHOUBERT et al. (1979) reported a number of acritarchs from the Basal Member at localities in the western AntiAtlas. Synonyms Calcaires inferieurs (CHOU BERT, 1952b, CI-lOUBERT in HUPE, 1953); "Serie de base" plus "Calcaires inferieurs" (CI-lOUBERT in HUPE, 1953); Adoudounien (CIIOUIJERT, 1956, 1958, 1959); Adoudounien inferieur (CIIOUIJERT, 1963, CHOUBERT et. aI., 1975); Dolomies et Calcaires inferieurs (BoUDDA & CI-lOUIJERT, 1972, CI-lOUBERT et aI., 1975); Serie de base plus Calcaires et Dolomies inferieurs (BOUDDA et aI., 1979); Adoudounien p. p. (BOUDDA et aI., 1979); Adoudounien s. s. (CI-lOUIJERT & FAURE-MuRET, 1987); Lower Limestones and Dolomites Formation (HOLLARD, 1985); Serie des calcaires inferieurs (BuGGISCI-l & FLOGEL, 1988); Adoudou Formation (GEYER, 1989a); Adoudon Formation (MAGARITZ et aI., 1991). The term "Calcaires inferieurs" has been misspelled several ways in recent, English language publications. Basal Member The Basal Member (Serie de base; Ci-IOUBERT, 1952b) is an approximately 100 m-thick, transgressive unit. Three units are distinguished in completely developed sections of the Basal Member in the western Anti-Atlas: (I) lower, massive conglomerates, (2) middle, diagenetically recrystallized dolostones and limestones, and (3) an upper, shale-dominated interval with conglomeratic, quartz arenite, or arkose beds and limestone and dolostone layers (BOUDDA et aI., 1979; HOLLARD, 1985). Conglomerates replace the carbonates towards the eastern margin of the basin. The Basal Member is not known with certainty east of the Jbel Sirwa massif. A facies change into siliciclastic rocks takes place west of the Adrar n'Dren massif in the Agoundis area of the High Atlas, where VILAND
The Cambrian of the Moroccan Atlas region
(1972) noted the association of green shales with subordinate sandstones and carbonates. Limestone Member The Limestone Member (Calcaires inferieures s.s.) is a rather monotonous sequence of shallow marine car· bonates that reaches about 1,000 m in the western Anti-Atlas but only 200 m in the Bou Azzer area of the central Anti-Atlas (EI Graara massif). Outcrops in the central High Atlas are composed of massive, light-grey dolostones that lack distinct bedding. The light colored, massive dolostone and subordinate limestone of • the member are interbedded in most sections with mudstones, shales, and sandstones. Slumps and other syn-sedimentary deformational structures are common (BUGGISCH & HEINITZ, 1984; HEINITZ, 1984). Ripple marks and reworked argillaceous clasts are common, and local evidence for subaerial dessication is present (MONNINGER, 1979). The prominent dolomitization, particularly in the lower and middle part of the Adoudou Formation, is striking by comparison with overlying formations and has been linked to an increased Mg/Ca ratio or a higher partial pressure of CO 2 in the Precambrian by TUCKER (1992). This explanation for Adoudou dolostones is considered unlikely; the lower Adoudou Formation is lowest Cambrian on the basis of available geochronologic data, and the dominant carbonate mineral in earIiest Cambrian sediments elsewhere has been noted to be aragonite (LANDING, 1992). The dolomitic sequence of the Adoudou Formation may simply reflect highly restricted inner platform deposition or even burial dolomitization by fluids during Hercynian or Alpine oro-
13
geny. CHAZAN (1954) described a lower submember of the Limestone Member ("Assise de Tamjour") characterized by silicified dolostones with isolated chert lenses. The siliceous intercalations or silicified carbonates are often variably mineralized. Lie de vin Formation Lithology and regional extent The Lie de vin Formation consists of fine-grained siliciclastic rocks with numerous limestone and dolostone beds. The term Iie-de-vin (CHOU BERT, 1942) refers to the typical purple color of the shales in the unit and not to a geographic place and type section, which actually should be the basis for the name of any lithostratigraphic unit. The known thicknesses range from 300 m at Warzazate (BOUDDA et aI., 1979) to about 950 m in the type section at Tiout (MONNINGER, 1979). These measurements illustrate the easterly thinning of the unit to about 25 m at the southeastern rim of Jbel Sarhro (DESTOMBES, unpublished data). The Lie de vin Formation usually overlies the Adoudou Formation, but it locally rests unconformably on the late Proterozoic Pan-African basement east of the Sirwa dome. The rocks of the Lie de vin Formation vary in the relative proportion of carbonates and siliciclastics. The increase in siliciclastics over the Adoudou Fornlation reflects a relative regression. Red sandstones and conglomerates dominate at the basin margin in the east. In the central Anti-Atlas, the middle part of the formation is a completely detrital succession dominated by sandstones that interfinger with finer-grained
Fig, 4, Tiout section, northern llank of western Anti-Atlas. View from top of Adoudou Formation shows Lie de vin Formation (dark, well banded outcrops) and Igoudine Fornlation (massive beds on nose of mountain). Note Souss plain and southern rim of High Atlas in the background.
GERD GEYER
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l00km
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MARRAKECH
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Fig. 5. Sketch map of the High Atlas and Anti-Atlas regions, Morocco, illustrating distribution of the Lie de vin Formation and tentative paleogeography during its deposition. The line that starls at Agadir indicatcs a zone of thrust faults, which separalc thc Anti-Atlas domain from the Hercynian fold belt. Irregular pattem represents non-depositional areas; small stipples = marginal clastic belt; brick signature = areas witb considerable to dominant carbonale deposils; isopach lines indicate probable thicknesses (in mcters). Modified from GEYER (1989a: Fig. 3) and based on data from G. CI'IOUilERT and unpublished data Irom G. GEYER. sediments. This lithofacies association progrades from the east of Warzazate into the central Anti-Atlas. This siliciclastic interval is the Tikirt Member (from Gres de Tikirt; GENTIL, 1912) that crops OUt from the westcentral Anti-Atlas to the Jbel Sarhro in the east. Characteristic Lie de vin Formation sections are found on the southem slope of the westem Anti-Atlas, where sections are dominated by purple shales. Dolostones and limestones become increasingly common towards the top of the formation, especially in the upper third of the sequence (HOLLARD, 1985). The type section at Tiout is somewhat atypical in the dominance by massive, brownish weathering limestones and dolostones with relatively thin siltstones. The Lie de vin Formation corresponds more-or-Iess to the earlier terms "Schistes lie de vin" (CHOUBERT, 1952b), "Serie regressive lie-de-vin" (CHOUBERT in HUPE, 1953), "Serie lie de vin" (CHOU BERT, 1963), "Adoudounien moyen" (CHOUBERT & FAURE-MuRET, 1970), "Adoudounien superieur" (BOUDDA & CHOU-
BERT, 1972), and "Taliwinien" (CHOUBERT et aI., 1975). Depositional environment The Tiout section shows a complex interbedding of lithofacies that has been interpreted as cyclicity (see MONNINGER, 1979; TUCKER, 1986b; GEYER, 1989b). Dolomitic, limy, marly, and silty sediment were deposited under persistant low energy, shallow, relatively hypersaline conditions (MONNINGER, 1979). The alternating lithofacies probably reflect some combination of changes in clastic input, salinity, or climate or small-scale sea level changes. These conditions led to symmetrical cycles (or alternations) that include tidal flat dolostones with cyanobacterial laminates and such indicators of hypersaline conditions as pseudomorphs after halite and anhydrite or gypsum (MONNINGER, 1979). The evaporitic facies pass offshore into micritic, peloidal, and oolitic limestone with stromatolite and thrombolite bioherms (SCHMITr,
Thc Cambrian of the Moroccan Atlas region
1979a; TUCKER, 1986a). The lower part of the Lie de vin Fonnation, in particular, has facies that suggest a non-marine origin (LATHAM, 1990). The Tikirt Member in the middle Lie de vin Fonnation is a coarser, siliciclastic facies that reflects regression and terrigenous input. The lower part of the Tikirt has flute and load casts (BUGGISCH et aI., 1978). Fossils The Lie de vin Formation is locally fossiliferous, but animal body fossils are not yet known. Stromatolites and thrombolites are locally conspicuous and fonn large biohenns in the Anti-Atlas. They were studied in detail at Tiout and include LineI/o, TlIngllssia, Pa/omia, Nimbophy/on, and Igolldinia (SCHMIlT, I979a, 1979b). However, their biostratigraphic interpretation has generated controversy (BERTRAND-SArATI, 1981; compare CHOUBERT & FAURE-MURET, 1987, and SDZUY & GEYER, 1988) and does not contribute to the problem of correlation. Thrombolite construction is related to the occurrence of the probable cyanobacteria Tar/hinia, Renalcis, and Kordephy/on, an assemblage claimed by LATHAM & RIDING (1990) to indicate an equivanency with the Siberian Tommotian Stage or higher. The upper part of the fonnation in the western AntiAtlas has complex metazoan traces such as Diplocra/erion (LATHAM & RIDING, 1990), which are best interpreted as indicating a Cambrian age. Trilobites which were claimed to be found at the top of the Lie de vin Fonnation in the Lemdad River section in the central High Atlas (BOUDDA & CHOUBERT, 1972) were reinterpreted to come the base of the Lemdad Fonnation (SDZUY, 1978; assigned to "Calcaire Superieur"; see discussion under May 6 of the MOROCCO '95 field guide, this volume). Trace fossils are also in the upper part of the Tikirt Member, including Diplichni/es-type traces (see Id Boukhtir section in GEYER et aI., this volume). Synonyms Serie regressive lie-de-vin (CHOUBERT, 1952b); Serie regressive des schistes lie de vin (CHOUBERT, 1952b); Schistes lie de vin (CHOUBERT, 1952b); Serie regressive lie de vin (CHOUBERT in HUPE, 1953); Georgien inferieur p. p. (CHOU BERT, 1956, 1958); Adoudounien superieur p. p. (CHOU BERT, 1963); Adoudounien moyen (CHOU BERT & FAURE-MuRET, 1970); Serie lie de vin (CHOUBERT, 1963, BOUDDA & CHOUBERT, 1972, CHOUBERT et aI., 1975); Adoudounien superieur (BOUDDA & CHOUBERT, 1972, CHOUBERT et aI.,
15
1975); Taliwinien (CHOUBERT et aI., 1975, BOUDDA et aI., 1979); Lie de vin Fonnation (GEYER, 1989a, 1989b).
Tata Group The Tata Group crops out in the western and central Anti-Atlas and in the bloc occiden/al of the Adrar n'Dren massif, central High Atlas. The group composes the remainder of the Lower Cambrian above the Lie de vin Fonnation. GEYER'S (e.g., 1990a) recognition of the HlIpeolenlls Zone from the upper Asrir Fonnatioll means that the Tata Group extends into the lowest Middle Cambrian (lowest Tassafinian Stage) of Morocco. The alternative explanation that the abrupt faunal change from the Moroccan upper Lower Cambrian Sec/igena Zone into the HlIpeolenlls Zone corresponds to a cryptic, but major, sequence boundary and unconformity within the Asrir Fonnation is not supported by fossil evidence from the Lemdad syncline (see MOROCCO '95 field guide, this volume). Tata Group outcrops cover large areas in the well developed sections in the western Anti-Atlas. This region is the classic Lower Cambrian field region for such pioneers of the Moroccan Cambrian as the late GEORGES CHOUBERT and PIERRE HUPE (e.g., HUPE 1952,1953; CHOUBERT, 1953). Igoudine Formation Lithology and regional development The Igoudine Formation is composed of massive limestone and dolostone beds (MONNINGER, 1979; GEYER, 1989a). It forms large outcrops along the border of the western and central Anti-Atlas. The thickness varies regionally and reaches almost 400 m in the Tiznit area. Deposition of the Igoudine Fonnation was initiated by regional deepening from the restricted marine interval of the underlying Lie de vin Fonnation. The base of the fonnation is usually sharp and marked by the appearance of massive carbonates with thin shales. The fonnation consists mainly of dark dolostones and limestones and subordinate light grey to pink carbonates. Conspicuous regional and vertical changes are present in the Igoudine Fonnation. The fonnation is composed of massive carbonates that are largely dolomitic at the base and become increasingly calcareous upward in the southern Anti-Atlas. Red, pink, or light colored cavernous limestones and brown marlstones are intercalated in the fonnation in this region (HOLLARD, 1985). However, shales and sandstones with ripple marks, cross-beds, intraclasts, and re-worked, low-am-
16
GERD GEYER
plitude cyanobacterial mats are more frequent on the southern nank of the lbel Sarhro (BUGGISCH et aI., 1978) and indicate higher energy conditions locally in lhe upper part of the (goudine Formation. Syn-sedimentary deformations are conspicuous in the vicinity of the lbel Sirwa (see BUGGISCH & HEINITZ, 1984, and HElNITZ, 1984, for analysis). An important Hthofacies change can be identified in several sections. This includes a change from black, often laminated, lime mudstones and dolosiltites into
& ED LANDING
overlying, massive, dark oolitic pack- and grainstones with intraclasts and marlstones with thin quartz sandstone interbeds. The overlying lithofacies is the Tiout Member (i.e., "Transition layers" sensu MONNINGER, 1979, and SCHMITr, I979a, and possibly "Calcaires de base" sensu BUGGISCH et aI., 1978). The Tiout Member has a thickness of about 110 m at Tiout, slightly more than 50 m in the Amouslek region, and about 20 m south of lbel Kissane.
~ .,-;:iiifi
o
""~.::~::'
prl!~~RJ=O\e~i6"ip/::~:~:}~
l00km
MARRAKECH
"-+," = ~ - Timoulaye IzOOr Asrir
Fig. 6. Sketch map of the High Atlas and Anti-Atlas regions, Morocco, illustrating distribution of the Igoudine, Amouslek, Lemdad, and Tislit Fomlalions and tenlative paleogeography during their deposition. The line that slarts at Agadir indieales a zone of thrust faults, which separate the Anti-Atlas domain from the Hercynian fold belt. Irregular pattem represents non-depositional areas; large stipples = marginal clastic belt; small stipples = tentative distribution of Tislit Formation; spotted brick signature = tentative distribution of Lcmdad Formation; brick signature = areas with considerable to dominant carbonate deposits in the Amouslek Formation. Based on maps from GEYER (1989a: Fig. 4) and CtlOUBERT and unpublished data from GEVER.
Depositional environment TIle Igoudine Formation was deposited under shallow marine conditions. BUGGISCH et al. (1978) noted dessication cracks and ignimbrite horizons as evidence for subaerial exposure. Higher energy conditions, possibly associated with slightly deeper and less restricted marine conditions, are recorded by the Tiout Member (MONNINGER, 1979). The development of the Tiout
Member facies may mark a transition from near shore to open shelf conditions. The appearance of a skeletalized fauna in the Tiout Member is probably linked to these facies changes. Fossils The low energy facies of the lower part of the formation are frequently stromatolitic. Reports on these
The Cambrian of the Moroccan Atlas region
build-ups are based on sections near the Jbel Sirwa massif (BUGGISCH & HEiNITZ, 1984; HEINITZ, 1984), and biostromal and biohermal stromatol ites are also known from the southern Jbel Sarhro (BUGGISCH et aI., 1978)'. The most comprehensive study on these stromatolites deals with the lower Igoudine Formation at Tiout (ScIiMITr, 1978, 1979a, 1979b), where trace fossils also occur. The stromatolites Acaciella sp. cf. A. angepena and the endemic Tiol/lella bOl/ddai (ScHMrrr, 1979a) occur at Tiou!. Horizons with thrombolites are also known from the lower member of the Igoudine Formation at Tiout (SCI-IMIH & MONNINGER, 1977; SCIiMITr, 1979a). Studies on trace fossi Is have not been done. The Tiout Member has the oldest known skeletal fossils known from Morocco. They include trilobites, archaeocyathans, chancellorids, hyoliths, Hyolilhellus, Coleoloides, and the "skeletal algae" (including probable cyanobacteria) Renalcis, £piphylon, Tolypo/hrix, Girvanella, and others (SDZUY, 1978; DEBRENNE & DEBRENNE, 1978, and this volume; and unpubl. information). The trilobites include species of £ofallo/aspis, HI/pelina anliql/a, and yet undescribed "bigotinoid" redlichiaceans (SDZUY, 1978, 1981). Archaeocyathans form bioherms in some beds of the Tiout Member (DEBRENNE, 1960, 1975; DEBRENNE & DEB RENNE, 1976, 1978). Similar faunas are known to occur al Tazemmourt and Amouslek (SDZUY, 1978; DEBRENNE, 1960; DEBRENNE & DEBRENNE, this volume). Synonyms Calcaires superieurs (CHOUBERT, 1952b, CHOUBERT in HUI'E, 1953); Georgien inferieur p. p. (CHOU BERT, 1956, 1958); Calcaires georgiens (0 IOU BERT, 1958); Adoudoun ien superieur p. p. (CHOU BERT, 1963); Adoudounien superieur (CIIOUBERT & FAURE-MURET, 1970); Calcaires superieurs avec Collenia (BOUDDA & CIIOUBERT, 1972, OIOUI3ERT et aI., 1975); Ouneinien (BOUDDA & OIOUBERT, 1972); Etage Ouneinien (CHOU BERT et aI., 1975); Upper limestone formation p. p. (HOLLARD, 1985); Upper Limestones Formation p. p. (HOLLARD, 1985); Serie des calcaires superieurs + Calcaires de base (BUGGISCH & FLOGEL, 1988); Igoudine Formation (GEYER, 1989a, 1989b, 1990b). Amouslck Formation Lithology and regional development The lowest part of the classical Lower Cambrian (i.e., Georgien) of HUPE (1953) includes an alternation of generally dark limestones and lighter siliciclastic mud-
17
stones first termed the "Serie schisto-calcaire (CHOU BERT, 1952b) and now known as the Amouslek Formation (GEYER, 1989a, 1990b). The "Amouslekien" of CHOUBERT et al. (1975) is not identical to HUPE'S (1960) "Etage d'Amouslek". The latter is a biostratigraphic unit and differs from the diachronous "Serie schisto-calcaire". TI,e Amouslek Formation is a sequence of greenish, purple, or grey shales (often slaty) with intercalated limestones, the latter often containing archaeocyathan bioherms. The unit is widely distributed in the AntiAtlas and ranges from about 220 m in thickness at the Amouslek type section to about 40 m south of Jbel Kissane. It wedges out towards the eastern part of the Jbel Sarhro (BOUDDA et aI., 1979). The amount of siliciclastic content increases in the shallower water environments to the east (CHOUBERT, 1964) with a lateral transition into the Tislit Formation in the Tazenakht area. Volcanic material is present at some localities, as at Tazemmourt (SCHAER in BOUDDA et aI., 1979), but significant volcanic activity is not recorded by the formation. A typical lithologic sequence is exposed at Amouslek on the northern slope of the western Anti-Atlas. The type section of the Amouslek Formation consists of: (I) lower green slates, (2) a middle unit of grey sandy or red muddy slates, and (3) a thick upper unit of limestones with green and light yellow argillaceous shales. Shale-oolite alternations occur in this part of the section in the northwestern Anti-Atlas. These asymmetric cycles/alternations commence with olive shales that grade up into quartz arenites and oolitic limestones with desiccation (or synaeresis?) cracks and symmetrical and interference ripples and finally into cross-bedded oolites (TUCKER, 1986b). The tops of these alternations locally have thrombolite buildups. The increase and dominance of shoal-water limestones upward through the Amouslek Formation and the abrupt transition into overlying shales of the Issafen Formation are similar to lithofacies changes through Grand cycles in the southern Canadian Rockies (e.g., AtTKEN, 1966, 1972). This same shale-carbonate transition and an abrupt change into overlying shales is seen near Timoulaye Izder in the western Anti-Atlas. Dark Iimestones largely replace the shales in the lower part of the formation in the Tiznit region (CHOUIlERT, 1963; BOUDDA et aI., 1979; BERNEKER & GEYER, 1990). However, the lower part of the formation in the southwestern and western parts of the Anti-
18
GERD GEYER
Atlas are dominantly shale (i.e., the "schistes de Timoulay" of CHOUBERT, 1963). In the northwestern Anti-Atlas and parts of the western and southwestern Anti-Atlas, the succession locally consists of massive limestone with thin intercalated shales ("Calcaires massifs de Tiznit" of CHOUBERT et aI., 1975). These limestones consist of a framework of calcareous algae with local archaeocyathan build-ups. Depositional environment The vertical succession of the Amouslek Formation is a macroscale (Grand cycle) variation that seems to include a relative sea-level rise or increase in rate of sealevel rise. This transition is well illustrated at Timoulaye Izder where shale-dominated facies of the lower Amouslek Formation sharply overlie the peritidal, carbonate-dominated Igoudine Formation and are progressively replaced upward by trilobite-hash limestones, archaeocyathan-algal build-ups, ooid limestones, and uppermost, cyanobacterial mats with mud cracks. The transition from the trilobite hash limestones into the archaeocyathan build-ups is marked by a 3-4 m-thick interval of slump-folded strata at this section (W. HELDMAIER & E. LANDING, un pub. data). TUCK ER (I 986b) reconstructed mesoscale, peritidal cycles or alternations and transgressive cycles in the upper, carbonate-dominated part of the Amouslek Formation in the northwestern Anti-Atlas. These alternations include a lower, lagoonal-tidal flat unit overlain by a high energy ooid shoal cap interpreted to have been formed during minor sea-level rises. The amount of siliciclastic material in the Amouslek Formation increases to the east (GEYER, 1989a). The decrease in development of the carbonate upper part of the Amouslek suggests an easterly transition from the middle carbonate platform into more inner detrital belt facies. Fossils The Amouslek Formation locally has abundant shelly fossils. HUPE (1953) described many trilobite species from the formation. Amouslek archaeocyathans include the most diverse assemblages from Morocco and were dealt with in detail by F. DEBRENNE (DEBRENNE, 1958, 1959, I960a, 1960b, 1961, 1964, 1992a, DEBRENNE & DEBRENNE, 1965, 1975, and this volume, DEBRENNE et aI., 1990). The massive limestones of the formation are often dominated by a framework consisting of calcareous algae and subordinate archaeocyathans. These limestones grade into bioherms composed primarily of archaeocyathans with
&
ED LANDING
associated trilobites and echinoderm fragments. Other common fossil groups include brachiopods (GEYER, 1994a, I994b), hyoliths, chancellorids and other SSFs, and calcareous algae. Biostratigraphically important sections include Amouslek and Tazemmourt, and archaeocyathans are well developed at Amouslek, Tazemmourt, and at the Jbel Ta'lssa. Stromatolites and low cyanobacterial mats occur in the upper carbonate half-cycle at many localities and have been discllssed from Jbel Kissane (BUGGISCH et aI., 1978). Synonyms Serie schisto-calcaire (CHOUBERT, 1943, CliOUBERT & FAURE-MURET, 1970); Serie des Schistes verts et Calcaires intermediaires (HUPE, 1953); Serie schisto-calcaire de l'Anti-Atlas (CIIOUBERT, 1956); Serie schistocalcaire ou Etage d'Amouslek (BOUDDA et aI., 1974); Etage Amouslekien (CIIOUBER~ et aI., 1975); Slatelimestone formation p. p. (HOLLARD, 1985); Slates and sandstones Formation (HOLLARJ), 1985; probably a writing mistake); Amouslek Fonnation (GEYER, 1989a, 1990b). Lemdad Formation Lithology and regional development The Lemdad Fonnation (GEYER, 1989a, 1990b) is a geographically restricted sequence of brownish, red, and greenish marlstones and siltstones with thick limestones and dolostones and volcanic ash or volcanoclastic intercalations. It is described only from the "bloc occidental" of the "Massif ancien" (i.e., Adrar n'Dren or Promontoire d'Ouzellarh) of the High Atlas. The lithologic variability of this unit is due to the vertical changes in volcanic content. Its thickness is estimated to be 500 m in the Lemdad syncl ine. The type section at Oued EI Mdad (section Le I; MOROCCO '95 field trip stop May 6, this volume) consists of a relatively rhythmic alternation of marland siltstones with limestones and dolostones. The lower part of the formation is rich in oolitic and oncoidal limestones and dark lime mudstones. The carbonates are replaced upward by finely crystalline dolostones and light colored, somewhat sparitic limestones (BOUDDA et aI., 1975; GEYER, 1989a). This change is accompanied by a decrease in carbonate bed abundance and thickness. The average thickness of the carbonatedominated intervals is about 30 to 40 m. Towards the top of the fonnation, archaeocyathans fonn conspicuous build-ups at Oued EI Mdad, but they do not extend laterally. The fine-grained siliciclastic beds are
The Cambrian ofthc Moroccan Atlas region
variable, but are largely composed of unfossiliferous slaty si Itstones that are brown, red, or grey in the lower parl and increasingly grey or green upward. Thin, often nodular marlstones and less abundant, micaceous or feldspathic quartz arenites are present. Basic to intermediate volcanic intercalations mask the sccming cyclicity of the type section. The volcanoclastics occur as distinct beds within the fine-grained siliciclastics, but are less easily distinguishable within carbonate-dominated intervals. Spilites and keratophyres are known as boulders (BOUDDA, 1968) and probably represent clasts reworked from lower levels of the formation. The Lemdad Formation of the central High Atlas overlies the Lie de vin Formation, underlies the Issafen Formation, and correlates with the Igoudine and Amouslek Formations. GEYER (1989a) proposed the Lemdad Fonnation because this post-Lie de vin and pre-Issafen interval could not be subdivided on the available evidence into an Igoudine and Amouslek interval, as in the Anti-Atlas, and because of the importance of volcanic interbeds. It is possible that further work may allow recognition and correlation of the carbonate-shale break at the Igoudine-Amouslek contact in the Anti-Atlas into the Lemdad Formation. This correlation would allow recognition of volcanic-rich facies of the Igoudine and Amouslek Formations and suppression of the Lemdad Formation. Deposi tional en vironment Little investigation of the paleoenvironments of the Lemdad Formation has been done. The formation represents shallow marine depositional environments with varying siliciclastic and volcanic input. Wave activity was moderate, but stronger ambient energies are indicated by occasional coarser beds. Field observations suggest that the formation, at least in its upper part, is a regressive or aggradational mesoscale cycle that is best illustrated by carbonate microfacies. Fossils Details on the fossil sequence are known only from the Lemdad syncline, but most of the species are still undescribed. SCHMIlT (1979a, 1979b) described the endemic stromatolites Ve/ella safar/iae and Madigani/es /emdadensis from the lower part of the formation in the Lemdad syncline. Trilobites are common in some horizons through the unit. Several species of Lemdadella occur in the lower part of the Lemdad (SDZUY, 1978), and /-/ebedisclls, Bondonella, Antal/asia, Berabichia, and
19
many others appear in the middle and upper part (GEYER, 1988b, I990c). Fallolaspis occurs in green slates near the Tizi n'Test (GEYER, J 989a). Additional shelly fossils include brachiopods, hyoliths, HyoIi/hellus, and various phosphatic microfossils. Archaeocyathans form large bioherms in the middle to upper part of the formation, and have been partly described by DEI3RENNE et al. (1992) and DEI3RENNE & DEI3RENNE (this volume). Calcareous "algae" (e.g., Epiphy/on, Girvanella, and Rena/cis) are frequently intergrown as a framework in the archaeocyathan build-ups. Synonyms Serie schisto-calcaire p. p. (CHOUI3ERT, 1952b, 1958); Serie schisteuse (CHOUBERT, 1952b, CHOUBERT, 1956); Complexe schisteux (CIIOUI3ERT in HUI'E, 1953); Etage d'issafene (CHOUBERT, 1963, BOUDDA & CHOUBERT, 1972, C/-IOUBERT et aI., 1975); Assise schisteuse ou etage d'issafene (BOUDDA et aI., 1974); Etage Issafenien (CHOUBERT et al. 1975); Sous-etage d'issafene (BOUDDA et aI., 1979); Green and purple slate and rubbly limestone formation (HOLLARD, 1985); Green and purple slates and Scoriaceous limestones Formation (HOLLARD, 1985 [probably a writing mistake]); Schistes de l'lssafene (SIEGERT, 1986); Schistes de I'lssafene (BUGGISCH & SIEGERT, 1988); Lemdad Formation (GEYER, 1989a, 1990b). Other names which are probably spelling errors are not listed. Tislit Formation Lithology and regional development The Tisli! Formation (GEYER, 1989a, I990b) crops out east of the Lemdad, Igoudine, and Amouslek Formations in the central and east-central Anti-Atlas and has its westernmost outcrops in the Tazenakht area. It is a heterolithic unit of alternating, red or purple siltstones and fine-grained quartz arenites with thick intervals of largely dolomitic carbonates. The siltstones are generally argillaceous but range into fine-grained, feldspathic quartz arenites towards the east. Greenish shales that occur in the formation are commonly laminated and become rare to the east. As other Lower Cambrian units, siliciclastic content increases to the basin margin in the east and north (VAN LOOY, 1985; GEYER, 1989a). However, mediumto coarse-grained sandstones appear even in the westernmost sections. Ripple marks, cross-beds, dessication cracks, and large mud clasts occur in the sand-
20
GERD GEYER
stones (BUGGISCII et aI., 1978; VAN LOOY, 1985). Pseudomorph halite crystals are known from the cover of the El Graara massif (DESTOMIlES, unpublished). The lateral changes in lithology accompany an easterly thinning of the formation from a maximum estimated thicknesses of more 300 m to its feather edge in the eastern Jbel Sarhro or at the Jbel Ougnate (VAN LOOY, 1985; BOUDDA et aI., 1979). Sedimentary cycles are reported south of the Jbel Sarhro (BUGGISCH et aI., 1978). Reddish or grey, often calcareous dolostones dominate the carbonate beds of the formation, particularly in the lower part. VAN LOOY (1985) described numerous oolitic and intraclast limestones from the upper part of the formation in the Hmam and Tislit-n-Tamassine synclines. These limestones were correlated with a carbonate interval with low cyanobacterial mats in the Tislit-n-Ait-Douchchene syncline. BUGGISCII et al. (1978) described an interval of black, bituminous limestones, grey dolostones, and green and red marlstones and shales just below the lowest occurrence of trilobites at sections south of Jbel Kissane. These "Calcaires de base" were interpreted to mark an interval of more normal marine salinity and were regarded as an analog and correlate of the Tiout Member. VAN LOOY (1985) assumed a volcanic origin for the abundant detrital quartz in the calcareous dolostones at the type section. In addition, BUGGISCH et al. (1978) described crystal tuffs from the lower part of the formation in the Jbel Sarhro. In general, however, volcanic ash is an insignificant component of the formation.
&
ED LANDING
Depositional environment Apparent sedimentary cycles in the Tislit Formation south of the Jbel Sarhro indicate extremely shallow marine depositional environments (BUGGISCH et aI., 1978). These alternations include stromatolitic carbonates that are overlain by siltstones with cross-beds and ripples. Dessication cracks point to subaerial exposure. The top of the cycles are composed of shale with halite pseudomorphs formed under hypersaline conditions (SIEGERT, 1986). Oolitic limestones with intraclasts in the western part of the formation's outcrop belt suggest high energy shoal environments that may be transitional laterally into the Igoudine Formation. These environments were replaced to the east by lagoonal facies and supratidal flats. Fossils Skeletal fossils are relatively rare in the Tislit Formation. Trilobites, hyoliths, and calcareous algae are known from a number of calcareous horizons through the formation, but none of them have been formally described. Domal and mat-like stromatolites and thrombol ites are abundant in parts of the formation in the Jbel Sarhro (BUGGISCH et aI., 1978). Synonyms Serie schisto-calcaire, a facies orientale (CHOU BERT, 1952b); Calcaires superieurs [pro parte] (BUGGISCH et aI., 1978); Calcaires de base [pro parte] (BUGGISCH et aI., 1978, BUGGISCH & FLOGEL, 1988, Serie schistocalcaire [pro parte] (BuGGISCH et aI., 1978); Serie
Fig. 7. Section north of Alougoum,
southwestern rim of EI Graara block. Escarpment consists of upper part of
Tislit Formation, overlain by soft shales of the Issafcn and resistant quartz arcn~ ites of the Tazlaft Formation. Rocks composing the lower and middle slope
arc the Issafcn Formation and show conspicuous units of rubbly limestones (Co/caire scoriace). The top of the hill is fonned by the lower part of the ASTir Fonnation.
21
The Cambrian ofLhc Moroccan ALIas region
o
l00km
MARRAKECH
•
.
.".-
Fig. 8. Sketeh map of the High Atlas and Anti-Atlas reginns, Morocco, illustrating lenlativc facies distribution during deposition of the lower Issafen, uppermost Lemdad, upper Tislit, and Akerouz Formations and tentative paleogeography during their depusition. The line that starts at Agadir indicates a zone of thrust faults, which separate the Anti-Atlas domain rrom the Hercynian fold belt. Irregular wavy pattern represents non-depositional areas; large stipples = tentative distribution or Tislit f'ormation: spotted brick signature
= tentative distribution
or Lemdad Formation; horizontal hachures
= areas with significant amounts of Co/caire scoriace beds in the Issafcn f-ormation. 5) and CIlOUBERT and on unpublished data from G. GEYER and W. I-IELDMAIER.
schisto-calcaire orientale (CI-IOUBERT et aI., 1975, BOUDDA et aI., 1979); Serie Schisto-calcaire orientale (V AN LOOY, 1985); Serie des calcaires superieurs [pro parle] (BUGGISCII & FLOGEL, 1988); Tislit Formation (GEYER, 1989a, 1990b). Issafen Formation Lithology and regional development The Issafen Formation consists of grey, yellowish, reddish, and purple slaty shales and siltstones with only a few calcareous and/or quartz arenite beds in the lower part and rubbly or nodular limestones (Ca/caire scoriae.!) in the upper part. The unil is widely exposed along the rim of the Anti-Atlas and the southern slope of the High Atlas. Known thicknesses range from 26 m in parts of the Tazenakht region (VAN LOOY, 1985) 10 100 m between Akka and Tata and up to 180 m at Amouslek.
=
Issaren Formation; brick signature
Based on maps from GEYER (1989a: Fig.
The lower part of the Issafen typically consists of slightly micaceous, finely laminated, light shale and siltstone, often with a slaty cleavage. The fresh color of the rock is greenish to light yellow and weathers to very light grey to white, sometimes with light yellow to light brown lines marking calcareous laminae. The fine-grained siliciclastics are usually planar-laminated, with local cross-bedding and burrow churning. Fossil grainstones and marlstones are locally present, but limestones are a minor component in the sequence. Towards the lOp of the Issafen, increasingly common siltstones and fine-grained quartz arenites and rare volcanic ashes appear. The Issafen Formation has local archaeocyathan build-ups that may form topographically conspicuous ribs within the soft slaty shales and siltstones. Closely packed calcareous nodules with a shale matrix (i.e., "scoriaceous limestones") are confined in the Issafen Formation to the western Anti-Atlas. These
22
GERD GEYER
&
ED LANDING
Fig. 9. Amouslek section, northern nank of western
Anti-Atlas.
Rocks com-
posing the lower and middle slope are the 155afc" Formation and show conspicuous units of rubbly limestones (Co/caire scoriace). The top of !.he hill is formed by the lower part of the Asrir Formation.
calcaires sCO/'iace beds form the base and top and thin intervals within the formation. Co/caire scoriace has been interpreted as diagenetically altered beds of finegrained terrigenous clastic and subordinate volcanoclastic sediment and calcareous interbeds (DE KO lNG, 1957; HUPE, 1959). However, a more probable origin lies in diagenetic redistribution of calcareous material within green, purple, and red siliciclastic muds and the growth of nodules within burrow-churned sediment (e.g., LANDING, 1995b). The Issafen Formation coarsens into red siltstones and intercalated, fine-grained quartz arenites of the Tislit Formation in the central Anti-Atlas. Restudy of the series of shales with subordinated limestone beds at the type section of the "Serie von Jbel Tichinchine" (SIEGERT, 1986; see below) near Timoulaye Izder in the western Anti-Atlas proves extreme lithologic similarity with the Issafen Formation (W. HELDMAIER, E. LANDING, and G. GEYER, unpub. data) and indicates that the "Jbel Tichinchine Formation" (designation abandoned herein) is simply the Issa fen Formation. Fossils The remarkable archaeocyathans of the Issafen Formation have been examined by F. DEBRENNE (DEBRENNE, 1964; DEBRENNE & DEBRENNE, 1975, I992a; DEBRENNE et aI., 1992) at the famous Amagour and Tamezrhar-Aguerd localities (DEBRENNE & DEBRENNE, 1965). The first reported African archaeocyathans were discovered in 1925 in massive bluish limestones of the formation at Sidi Moussa d'Aglou (BOURCART, 1927;
BOURCART & LE VILLAIN, I928a, 1928b, 1931). In addition, hyoliths, brachiopods, echinoderms, chancellorids, and cyanobacterial mats are known from the formation (BERNEKER & GEYER, 1990; GEYER, unpubl ished data). Synonyms Serie schisto-calcaire p. p. (C110UBERT, 1952b, 1958); Serie schisteuse (CI-IOUBERT, 1952b, CI-IOUBERT, 1956); Complexe schisteux (CHOUBERT in HUI'E, • 1953); Gres noiratres (in part) (HUI'E, 1959); Etage d'issafene (CHOUBERT, 1963, BOUDDA & CIIOUBERT, 1972, C!'IOUBERT et aI., 1975); Assise schisteuse ou • etage d'issafene (BOUDDA et aI., 1974); Etage Issafenien (CIIOUBERT et al. 1975); Sous-etage d'issafene (BOUDDA et aI., 1979); Green and purple slate and rubbly limestone formation (HOLLARD, 1985); Green and purple slates and Scoriaceous limestones Formation (I-IOLLARD, 1985 [probably a spelling error]); Schistes de l'lssafene (SIEGERT, 1986); Schistes de l'lssafene (BUGGISCH & SIEGERT, 1988); Issafen Formation (GEYER, 1989a, 1990b); additional names which are probably spelling mistakes are not listed.
Jbel Tiehinehine (term abandoned herein) Discussion As noted above, the lower part of the type section of the "Jbcl Tichinchine Formation" (SIEGERT, 1986; BUGGISCII & SIEGERT, 1988 GEYER, 1989a, I990b) near Bou lzakarn in the western Anti-Atlas is lithologically comparable and correlative with the Issafen
Thc Cambrian orthc Moroccan Atlas region
23
Tichinchine, Serie d'Jebel Tichinchine (BUGGISCI-I & SIEGERT, 1988); Jbel Tichinchine Formation (GEYER, 1989a, I990b). Asrir Formation
Lithology and regional development
Fig. 10. Lcmdad syneline, section I.e I (sec MOROCCO '95 field guide, this volume). Lower half or slope ronncd by Issalcn Formation with limestone beds, upper slope by ollen volcanodctrital deposits or the Asrir Formation.
Formation. The middle and higher beds of the "Jbel Tichinchine" are purplish grey and grey shales and siltstones with rare, thin shell hash beds, calcareous nodules, several calcaire scoriace units, and a few, very thin (up to I cm) ash or volcaniclastic lenses (W. HELDMAIER, E. LANDING, and G. GEYER, unpub. data). Interpretations of the "Jbel Tichinchine Formation" as a lithologically distinct facies in the western AntiAtlas that correlates with most of the uppermost Lower Cambrian (upper Issafen-Asrir Formations) and the lower Middle Cambrian (BUGGISCI-I & SIEGERT, 1988) and is a persistant, carbonate-rich unit (BUGGISCI-I & SIEGERT, 1988; GEYER, 1989a, 1990b) are incorrect. The "Jbel Tichinchine" includes the Issafen Formation near Bou Izkarn and is succeeded to Ihe east in the center of the syncline, after a long covered interval, by the lower Middle Cambrian Tamanart Formation. Synonyms Gres noiriltres [pro parte] (HuPE, 1959); Serie von Jbel Tichinchine (SIEGERT, 1986); Series [Serie] of Jebel
The Asrir Formation is an erosionally resistant, heterolithic succession of green, grey, or purple sandy shales, quartz arenites, and thin volcanic ashes. It has a broad outcrop along the margin of the Anti-Atlas and also occurs in the "Bloc occidental" of the "Massif ancien" in the High Atlas. Known thicknesses of the formation vary considerably. BUGGISCH et al. (1978) reported 30-180 m in the Jbel Kissane region, and 175 m is present in the Tata area (BOUDDA et aI., 1979). The Asrir Formation is usually conformable on the Issafen Formation, but locally lies on Precambrian III (BOUDDA et aI., 1974). Differences in sandstone coarseness and amount of volcanic material result in variable lithology and color of the Asrir Formation. Lower Cambrian volcanic activity seems to have reached a maximum during deposition of this unit; the centers of volcanism are believed to lie in the western High Atlas region or somewhat farther north and northwest in the late Early Cambrian (CHOUI3ERT & FAURE-MURET, 1956; SCHAER, 1964; BOUDDA et aI., 1979; BUGGISCH & SIEGERT, 1988). Multiple eruptions have been considered responsible for sedimentary alternations with a lower unit of dark green, slaty ashes (SIEGERT, 1986). The Asrir Formation in the western Anti-Atlas consists of alternating shale and sandstone intervals that are several tens of meters in thickness. The red, olivegreen, and green-grey shales have large amounts of fine-grained quartz sand and may be highly micaceous. The associated sandstones are green-grey or light green, quartz-rich or feldspathic, and often highly micaceous. Lithic arenites ("greywackes") and arkoses higher in the section often have large pyroclastic or, rarely, ferruginous patches. A few pyritic sandstones with abundant Skolithoslike, vertical burrows extend over wide areas in the southwestern Anti-Atlas (HuPE, 1959; DESTOMI3ES, 1985; BERNEKER & GEYER, 1990). Planolites-like traces are locally abundant. Depositional environments Siliciclastic mudstone clasts, cross-beds, and ripple marks are known from the Asrir Formation in the western Anti-Atlas and High Atlas Mountains (SIEGERT,
24
GERD GEYER & ED LANDING
1986; BERNEKER & GEYER, 1990; see field trip stops May 5, May 9, this volume). Deposition of the Asrir records an increase in coarser siliciclastic debris over the Issafen Formation. In most parts of the western Anti-Atlas, coarsening- and fining-up sequences are intrepreted as evidence for progradational events of a delta complex (see Aguerd Fonnation). However, it is unlikely that the area was part of a wave-influenced, nearshore system. Parts of the formation with occasional cross-beds and quartz arenites with Skolithos-like traces may represent littoral sands (BERNEKER & GEYER, 1990). SIEGERT (1986) showed that burrowmottled mudstones and siltstones dominate in the southern Anti-Atlas, and regarded this as a lagoonal facies. Towards the east, the Asrir Fonnation is regarded as laterally transitional into the Tazlaft Formation, a monotonous alternation of red argillaceous siltstones, fine- to medium-grained quartz arenites, and arkoses (BUGGISCH et aI., 1978; BOUDDA et aI., 1979; SIEGERT, 1986). An interfingering of the Asrir and Aguerd Formations (marine and fluvial facies, respectively) occurs in sections between Tata and Timguissilt. Fossils Body fossils are rare in the Asrir Formation, and the abrupt change in trilobite faunas marked by the appearance of the lowest Middle Cambrian (lower Tassafinian Stage) Hupeolenus Zone in beds assigned to the uppermost Asrir Formation will be discussed in the course of this trip. Numerous trilobites are found in a calcareous, tuffaceous arkose at Amouslek (field trip stop, May 5, this volume). Several other localities yield limited faunas with trilobites (HUPE, 1953, 1959, 1960; GEYER, 1990a, 1990b). In addition to trilobites, monoplacophoran-like mollusks, hyoliths, and brachiopods have been found. SIEGERT (1986) mentioned a carbonate bed with archaeocyathans from east of Tata.
mistake]); Serie volcano detritique d'Jbel Issendalen [sic] (SIEGERT, 1986); "Serie volcano-detritique" of Issendalen (BUGGISCH & SIEGERT, 1988); Asrir Formation (GEYER, 1989a, 1990b). Tazlaft Formation Lithology and regional development The Tazlaft Fonnation (GEYER, 1989a, I990b), a monotonous series of reddish or purple, fine- to mediumgrained feldspathic sandstones with rare, red argillaceous siltstones, crops out in the east-central and eastern Anti-Atlas (BUGGISCH et aI., 1978; BOUDDA et aI., 1979). It thins to the east and south. The type section is 115 m-thick, and the Tinifift locality has the greatest known thickness, 160 m (SIEGERT, 1986). In other east-central Anti-Atlas localities, the Tazlaft Formation is less than 20 m-thick. The sandstones are frequently trough cross-bedded, 0.2-3.0 m-thick units that form lenses up to 15 m-thick (SIEGERT, 1986). These lenses frequently show basal lag deposits and represent channel-fill and accretionary point bar deposits. Dessication cracks have been described only from the lower part of the formation, where the characteristic cross-beds are not developed
Synonyms Gres terminaux (CHOUBERT, 1952b, CHOUBERT in I-IUPE, 1953, CHOUBERT & FAURE-MuRET, 1970); Serie greseuse et volcanique (CHOUBERT, 1958); Serie greso-calcaire p. p., (MOUSSU, 1959); Etage d'Asrir (CHOU BERT, 1963, BOUDDA & CHOUBERT, 1972, Choubert et aI., 1975); Gres terminaux ou etage d'Asrhir (BOUDDA et aI., 1974); Asririen (CHOUIJERT et aI., 1975); Niveau d'Asrir (BOUDDA et aI., 1979); Tenninal slates, sandstones, and tuffs formation (HOLLARD, J 985); Terminal slates sandstones and tuffites Fonnation (HOLLARD, 1985 [probably a spelling
Fig. 11. Well bedded, cross-stratified quartz arenites of the Tazlaft Fonnation at Tizi n'Tclganc (between Jbcl Sarhro and Jbel
Ougnalc).
The Cambrian of the Moroccan Atlas region
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25
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Fig. 12. Sketch map of the High Atlas and Anti-Atlas regions. Morocco. illustrating tentative facies distribution during deposition of the Asrir, Aguerd, Tazlal1 and Akerouz Formations and tentative paleogeographic situation during their deposition. The line thal starts at Agadir indicates a bundle of thrust faults which separate the Anti-Alias domain from the Ilereynian fold belt. Irregular wavy pattern = non-depositional arcas; large stipples = tentative distribution of upper Akerouz Formation~ mediumsized stipples = tentative distribution ofTazlafl Fonnation: small regular stipples = arcas with coarser-grained Asrir Formation: minute stipples areas with finer-grained Asrir Formation: irregularly stippled = distribution of Aguerd Formation during deposition of the upper Asrir Fonnalion. Arrows indicate directions of sediment transport. l3ased on maps from GEYER (1989a: Fig. 6). S,EGERT (1986), and C"OUBERT and on unpublished data from G. GEYER and W. IIELDMAtER.
(SIEGERT, 1986; BUGGISCH & SIEGERT, 1988). Unidirectional paleocurrents toward the west to westsouthwest in the southern Jbel Sarhro and toward the west to west-northwest in the EI Graara massif are indicated by the cross-beds (SIEGERT, 1986; W. HELDMAIER, unpubl. data).
The thickest sections of the Tazlaft Formation in the region of Alnif have low energy calcarenites and siltstones. SIEGERT (1986) proposed that these sediments indicate limnic conditions ("Lake of Alnir'), although low energy, inner shelf conditions seem more appropriate.
Depositional environment
Fossils
SIEGERT (1986) and BUGGISCI-I & SIEGERT (1988) proposed a depositional setting that was controlled by two deltaic complexes. These were regarded as "braided river systems," even though the depositional structures of the relatively fine grained sandstones of the Tazlaft Formation are better regarded as the product of a meandering now regime. The transitional facies between the Tazlaft and Asrir Formations has been regarded as marking a change into a tide-dominated delta system «BUGGISCII & SIEGERT, 1988).
Biological remains are not reported. Synonyms Gres tcrminaux [po p.] (CIIOUIJERT & FAURE-MURET, 1970, BOUDI)A et aI., 1979); Gres roses it innuences continentales (CIlOUIlERT et aI., 1975, BOUDDA et aI., 1979); Gres rouges [po p.] (CIIOUI3ERT et aI., 1975, BOUDDA et aI., 1979); Gres rouge (SIEGERT, 1986); Gres rouges (BUGGISCH & SIEGERT, 1988); Tazlaft Formation (GEYER, 1989a, 1990b).
26
GERD GEYER
Aguerd Formation Lithology and depositional environment The thin (10-20 m) Aguerd Formation (SIEGERT, 1986) includes cross-bedded and quartzose, coarse-grained arenites and conglomerates. The formation crops out on the southern margin of the western Anti-Atlas from Ihe Tata area west to the area of EI Aioun du Draa and east into the Jbel Ougnate area. Planar bedding changes into asymmetrical ripples and trough cross-beds upward through this massively bedded unit. The cross beds indicate northerly transport. Burrow mottled layers and Skolithos occur only in Ihe lowest part of the formation. The recognition and utility of the Aguerd Formation in mapping is problematical because the formation was based primarily on granulometric study (SIEGERT, 1986). Indeed, characters that might be appropriate for confident definition of the Aguerd, Tazlaft, Asrir, and Akerouz Formations require further investigation. Fossils Trace fossils, almost exclusively Skolithos tubes ("Pipe rock"), from the lower part of the formation are the only known biological remains. Synonyms
&
ED LANDING
(1986) believed that the Akerouz was a condensed equivalent of the entire Lower Cambrian elsewhere in Morocco, with the calcarenite bed at its base correlative with the deepening event at the Amouslek-Issafen formational contact. All of these hypotheses require testing by biostratigraphic study and lithostratigraphic correlation. Depositional environment SIEGERT (1986) interpreted this unit as the product of fluvial deposition under the influence of northerly to northwesterly flow. BUGGISCH & SIEGERT (1988) reported caliche in the Akerouz Formation and proposed that subaerial conditions are recorded. Fossils No fossils are known from the Akerouz Formation. Synonyms Gres rouges [pro parle] (BOUDDA et aI., 1979); Serie von Akerouz (Georgien continental) (SIEGERT, 1986); Serie von Akerouz (BUGGISCH & SIEGERT, 1988); Serie d'Akerouz (BUGGISCH & SIEGERT, 1988); Akerouz Formation (GEYER, 1989a, 1990b).
Feijas internes Group
Gres verts marins (CHOUI3ERT et aI., 1975, BOUDDA et aI., 1979); Konglomerat[e] von Aguerd (SIEGERT, 1986); Conglomerate[s] of Aguerd, Conglomerate d'Aguerd (BUGGISCH & SIEGERT, 1988); Aguerd Formation (GEYER, 1989a, 1990b). Akerouz Formation Lithology and regional development The Akerouz Formation (SIEGERT, 1986) is known only from the eastern Anti-Atlas at localities 60 km WNW of Erfoud. The formation was first assigned to the "Gres rouges" (BOUDDA et aI., 1979) and includes 70 m of white and grey quartz arenites and purple siltstones and mudstones at the type locality. According to SIEGERT (1986), the lower 35 m are a heterolithic alternation of grey to yellowish sandstone, micro-conglomerate, and reddish shale units that are up to several meters in thickness. The upper part is characterized by grey and whitish sandstones. Largescale cross-beds, scour surfaces, ripples, thin laminations, and mud pebbles within the sandstones are reported by SIEGERT (1986). The Akerouz Formation rests on Precambrian or Cambrian(?) sandstones and conglomerates. SIEGERT
The Feijas internes Group (DESTOMI3ES, 1985), based on the "Schistes de Feijas internes" (CHOU BERT, 1942), is an informal lithostratigraphic term (i.e., a name that is not based on a geographic or mapped cultural feature) for lower Middle Cambrian rocks that underlie a elongate lowland (i.e., jeijas) in the Akka-Tata type area. DESTOMI3ES (1985) distinguished a lower, siltstone and fine sandstone-dominated Jbel Wawrmast Formation and an upper, sandstone-dominated Jbel Afraou Formation in the central and eastern Anti-Atlas. Three laterally correlative formations are established west of Akka: the Tamanart Formation ("Lower shale formation of the inner Feijas"), the overlying, resistant sandstone of the Goulimine Formation, and the upper Akka Formation ("Upper shale formation of the inner Feijas") (GEYER, 1989a). Recent investigations suggest that an interfingering of these facies occurs and a clear regional differentiation of the lithostratigraphic units may not be possible (W. HELDMAIER, unpub. data). The base of the Jbel Wawrmast and Tamanart Formations (and base of the Feijas internes Group) is discordant. The transgressive character of the base of the group is best demonstrated in the central High Atlas
The Cambrian of the Moroccan Atlas region
and northern Jbel Sarhro, where the group rests nonconformably on the Proterozoic basement. That area may represent either: I) a persistant morphologic high following the late Panafrican collision of a plate in the north with the West African craton that was first inundated by the Feijas internes Group or 2) a block uplifted in the late Early Cambrian by a change in the strike-slip tectonic regime on the margin of the West African craton. Jbel Wawrmast Formation Lithology and regional development The Jbel Wawrmast Formation (DESTOMBES, 1985) largely consists of yellowish-weathering, fine-grained sandstones and green and blue-green siltstones. The lower part of the unit is characterized by thin, lithologically variable limestones. This part of the formation is tenned the Breche a Micmacca Member (described below). The Jbel Wawrmast Formation crops out from the western High Atlas to the eastern and west-central Anti-Atlas. The greatest thickness is more than 300 m in the Tagragra syncline southeast of Tazenakht (VAN LOOY, 1985). This thickness decreases to approximately 100 m and less in the Jbel Ougnate (DESTOM13ES, 1985; compare section Tarhoucht in GEYER et aI., this volume). Breche a Micmacca Member The Breche a Micmacca Member is the lower part of the Jbel Wawrmast Formation, and locally, the Tamanart Formation. It is composed of frequently trilobite-, echinoderm-, and brachiopod-rich, bedded and nodular limestones that alternate with shale or sandstone inter-
27
vals. The limestone beds often cap color cycles that extend upward from yellowish green to bluish and finally red. Thin (up to 5 Col) volcanic ashes (frequently K-bentonites in the High Atlas and Jbel Sarhro) occur in the member, and pillowed flows lie at the base of the member locally in the Jbel Sarhro (W. HELDMAIER and E. LANDING, unpub. data). Reworked clasts of the underlying siliciclastics, glauconite grains, submarine corrosion surfaces, and stromatolitic laminae frequently occur in the thin, frequently amalgamated limestone (up to 40 Col) beds. A number of these reddish to greenish shelly limestones can be interpreted to mark erosive intervals that developed during oftlap-onlap events. The member crops out from the eastern and eastern Adrar n'Dren massif of the High Atlas to the western Jbel Sarhro region (Agdz and Skoura areas) and the EI Graara massif. The recognition of this informally named member was based on limestones exposed near Ourika Wawrmast, 100 km to the southeast of Tizi n'Tichka in the north-central Anti-Atlas (BONDON & NEl.TNER, 1933). The Breche a Micmacca Member commences with a few meters of purple or grey tuffitic and somewhat arenaceous slates in this "type" section. The overlying interval has ferruginous limestones that are up to several decimeters in thickness and have abundant shelly fossils (field guide by GEYER et aI., this volume). The thickness and lithology of these beds varies greatly. The name "Breche a Micmacca" was originally applied to a lithology that bears a superficial resemblence to a breccia formed of intraclasts, fossil fragments, and local calcite crystals. Calcareous, tuffitic, dark shale and conglomeratic or oolitic iron ore clasts occur, as well. These limestones normally include well-washed, fossil
Fig. 13. Tatelt section, Jbcl Kissane area. Typical suite of fine-grained sandstones and fossiliferous, limonitic limestone beds of the Breche a Miemaeeo Member in the foreground, higher part of Jbel Wawrmast Fom13tion in the midground.
GERD GEYER & ED LANDING
28
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