Machaeridians from the Middle and Upper Ordovician of the Argentine Precordillera

ORTEGA G., ALBANESI G.L. AND ZEBALLO F.J.

GEOLOGICAL JOURNAL (CHICHESTER)

JOHN WILEY & SONS LTD

Año: 2012 vol. 48 p. 212 - 221

0072-1050

The machaeridians are marine Palaeozoic annelids, which developed a dorsal skeletoncomposed of calcite plates, achieving a world wide distribution from the EarlyOrdovician to the Middle Permian. The absence of records from this group is notable inArgentina in spite of intense studies of Palaeozoic rocks. This fact can be assigned tobiases in the sampling or because of preservation problems. Machaeridian sclerites ofthe families Plumulitidae and Turrilepadidae collected in Middle and Upper Ordovicianrocks from the San Juan Precordillera, Argentine, are described here for the first time.Plumulites sp. is recorded in early Darriwilian strata from the Gualcamayo Formationexposed in the western flank of the Cerro La Chilca locality. Plumulitid and turrilepadidsclerites are described from the upper member of the Los Azules Formation (lateSandbian) in the Cerro Viejo de Huaco area. The material of the Los Azules Formationis the first record of turrilepadid in Sandbian rocks, which are scarce in Ordoviciansuccessions. The referred strata bear pelagic, benthic and nektobenthic faunalassemblages, constituting a similar taphocoenosis preserved in shales and calcareoussilty shales related to transgressive events. The record of machaeridians expands ourknowledge of the Ordovician biotas from Argentina and provides new information onthe palaeobiogeographical distribution of this Palaeozoic annelid group.