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Trilobites between Lower and Upper Kellwasser events, Mrirt area, Morocco (Devonian of Morocco)

Where: Morocco (33.2° N, 5.6° W: paleocoordinates 38.4° S, 8.3° E)

• coordinate based on political unit

• local area-level geographic resolution

When: Late/Upper Frasnian (379.5 - 376.1 Ma)

• Late Devonian cephalopod limestones in olistolithic slabs contained within Visean shales. Collections come from between the Lower and Upper Kellwasser events. Late Palmatolepis rhenana Zone.

• group of beds-level stratigraphic resolution

Environment/lithology: marine; gray lime mudstone

• The association of reduced-eyed and

•blind trilobites with predominantly necto-benthonic organ-

•isms characterizes the well oxygenated cephalopod realm of a

•moderately deep outer platform environment. Accumulations

•of shelly debris that do not exhibit any evidence of corrosion

•and size sorting might result from intermittently slow sedi-

•mentation rates rather than from physical transport.

• "In this area the latest Frasnian succession is characterized

•by the occurrence of two dark-grey hypoxic limestone levels

•of Kellwasser-Kalk facies, the Lower (LKW) and Upper

•(UKW) Kellwasser levels (Lazreq 1992). They are separated

•by 80 cm of intervening grey-beige oxic calcilutites assigned

•to the Late Palmatolepis rhenana Zone by Lazreq (1992,

•1999). The trilobites were recovered in section 1 from two

•levels: the older is situated 13 cm above theLKW, the younger

•18 cm below the base of theUKW(horizons 1A and 1B in

•Fig. 1B). The sample collected in section 2 corresponds to

•the younger fauna of section 1. Associated conodonts recov-

•ered from matrix material of the trilobite-bearing rocks were

•determined by Catherine Girard and Gilbert Klapper as fol-

•lows: the lower trilobite horizon yields Palmatolepis hassi

•sensu stricto and Pa. bogartensis which indicates the lower

•part ofMNZone 13 (for correlation of conodont zonations, see

•Klapper and Becker 1999); the upper trilobite bearing horizon

•yields Pa. rhenana, Pa. boogaardi, abundant Pa. bogartensis,

•Ancyrognathus asymmetricus and Polygnathus webbi (but

•neither Pa. linguiformis nor An. ubiquitus were found), indi-

•cating correlation with the upper part of MN Zone 13.

•Trilobite debris of exclusively disarticulated exuviae is

•concentrated in thin layers within the biomicritic limestone,

•along with mass occurrences of conodonts, homoctenid tenta-

•culites and fewer manticoceratid goniatites, smooth brachio-

•pods and crinoid ossicles. The association of reduced-eyed and

•blind trilobites with predominantly necto-benthonic organ-

•isms characterizes the well oxygenated cephalopod realm of a

•moderately deep outer platform environment. Accumulations

•of shelly debris that do not exhibit any evidence of corrosion

•and size sorting might result from intermittently slow sedi-

•mentation rates rather than from physical transport.

Primary reference: R. Feist. 2002. Trilobites from the latest Frasnian Kellwasser Crisis in North Africa (Mrirt, central Moroccan Meseta). Acta Palaeontologica Polonica 47(2):203-210 [M. Foote/M. Foote/M. Foote] more details

Purpose of describing collection: biostratigraphic analysis

PaleoDB collection 35385: authorized by Michael Foote, entered by Michael Foote on 09.12.2003

Creative Commons license: CC BY (attribution)