Teodoro Palacios

Age constraints from small shelly fossils on the early Cambrian terminal Cadomian Phase in Iberia

Abstract The records of biotic and biogeochemical events around the Proterozoic-Cambrian transition are well preserved in sedimentary rock successions in Iberia. Until recently, sparsely fossiliferous siliciclastic and carbonate successions in central Spain were believed to be largely Proterozoic in age and to have suffered late Cadomian deformation. Small shelly fossils identified as Anabarella sp. cf. A. plana are here reported from south-central Spain and are consistent with broadly Ne-makit-Daldynian to Tommotian, early Cambrian age. At a location in southwestern Spain, siliciclastics that yield Platysolenites antiquissimus in association with an unidentified trilobite are interpreted to be coeval with the upper stratigraphic record of P. antiquissimus in Baltica. Both fossil occurrences are nearly time-equivalent to Tommotian-age rocks in North Iberia that yield ichnofossils and acritarchs. These beds unconformably overlie Neoproterozoic turbidites deformed by late Cadomian folding. Small shelly foss...

Precambrian-Cambrian boundary and correlation from southwestern and central part of Spain

This paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcudica and Galaico-Castellana Zones of the Iberian Peninsula. The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Cordoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity ( Skolithos sp., Monomorphichnus sp., Phycodes pedum and Rusophycus sp.) and the rocks with a palynological association ( Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridium sp., aff. Octoedryxium truncatum, Phycomicetes ? sp. and cf. Ooidium sp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity. The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcudica Zone) includes detrital beds with Phycodes pedum, Planolites sp. and Treptichnus sp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genus Micrhystridium are found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids and Bavlinella faveolata are found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds. In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones contain Rusophycus gr. radwanskii, Planolites sp. and Gordia sp. Trace fossils produced by trilobite-like arthropoda ( Monomorphichnus ) have been cited in the upper part of the underlying Pusa Shales. Moreover, Octoedryxium truncatum and Bavlinella faveolata are found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales. Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series. The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.

Size of the earliest mollusks: Did small helcionellids grow to become large adults?

The generally accepted view that early mollusks were millimeter-scale animals is partly based on paleontological data. Millimeter-scale, exquisitely preserved mollusks are important constituents of many small shelly fossil assemblages and have been the focus of most modern studies of Cambrian mollusks. Centimeter-sized mollusks occur in the fossil record as early as the earliest Cambrian but have been neglected for decades in favor of their better-preserved, millimeter-scale counterparts. Here we present a large, limpet-like mollusk from the Lower Cambrian of Spain that preserves an apical shell indistinguishable from the millimeter-scale helcionellids that have come to epitomize the ancestral “conchiferan.” The Spanish fossils provide direct evidence that at least some millimeter-scale helcionellids represent juvenile or larval shells of large, limpet-like mollusks, suggesting that the presumed generalized small size of Cambrian mollusks may be a taphonomic artifact.

Revised biochronology of the Lower Cambrian of the Central Iberian zone, southern Iberian massif, Spain

Trilobites from the upper unit of the Lower Cambrian Pusa Formation (south-central Spain) substantially antedate other Iberian trilobites, according to widely published correlation schemes, and arguably would be among the earliest trilobites globally. These trilobites, previously only briefly mentioned in texts, are here described and illustrated, and their biochronological context examined. The Pusa Formation trilobites are treated in open nomenclature but with suggested affinity to the genus Abadiella. They are associated with small shelly fossils, including Pelagiella sp., chancellorid spicules and Cupitheca sp., and unidentfied archaeocyathans. Trace fossils from the upper unit of the Pusa Formation, down-section of the trilobites, include Dactyloidites isp. and Rusophycus isp., the latter representing the lowest occurrence of this ichnogenus in the region. This biostratigraphical context demonstrates that the Pusa Formation trilobites are substantially younger than had traditionally been thought. In terms of Iberian regional stages they are Ovetian, not Corduban as previously thought. As a consequence of the data presented here, the definitions of Iberian Lower Cambrian regional stages are discussed and a substantially revised correlation between key Lower Cambrian strata of the Central Iberian and Ossa Morena zones is proposed.

A brief review of the fossil record of the Ediacaran–Cambrian transition in the area of Montes de Toledo–Guadalupe, Spain

Abstract The area of western Montes de Toledo to Guadalupe boasts a thick succession of mainly siliciclastic sediment spanning terminal Ediacaran to lower Cambrian strata as indicated by a relatively sparse but diverse palaeontological record. A terminal Ediacaran age is based on the occurrence of Cloudina in platform carbonates of the lower part of the Ibor group and in correlative levels of olistostromes at the base of the Río Huso group. Higher in the Río Huso group are found trace fossils which indicate a Cambrian age, notably Treptichnus bifurcus, which overlaps the local stratigraphic range of macroscopic carbonaceous disc-shaped fossils identified as Beltanelliformis. Strata underlying the Río Huso group contain treptichnids. The fossil record of the terminal Ediacaran–Lower Cambrian of this area is in part comparable to Cloudina-bearing sediments from other regions, in particular Namibia, where treptichnid trace fossils also overlap the range of Cloudina. The possibility of a wider biostratigraphic significance of this should be further tested, including its relation to the base of the Cambrian.

Cambrian–Ordovician acritarchs in the Meguma terrane, Nova Scotia, Canada: Resolution of early Paleozoic stratigraphy and implications for paleogeography

Organic-walled microfossils (acritarchs) provide age constraints for the previously poorly dated Cambrian and Lower Ordovician turbiditic Goldenville and Halifax Groups in the northern Appalachian Meguma terrane of Nova Scotia and address controversies about stratigraphy and provenance. The oldest exposed formation of the ∼8-km-thick Goldenville Group contains the trace fossil Oldhamia , which suggests an age of late Early Cambrian, whereas the coticule-bearing uppermost formation yielded an acritarch species consistent with Middle Cambrian (Epoch 3) age. The conformably overlying ∼5-km-thick Halifax Group includes basal pyritiferous units that yielded a Late Cambrian (Furongian) assemblage of acritarch species, providing further confirmation that the underlying manganese-bearing formations are of Cambrian Epoch 3 age, and not Ordovician as recently claimed. Overlying nonpyritiferous formations contain the Early Ordovician graptolite Rhabdinopora flabelliformis flabelliformis and acritarchs of similar age. Samples collected up section from the graptolite occurrence yielded acritarch species that are indicative of the later Tremadocian and Floian. The new fossil data confirm a gap in age of ∼30 m.y. between the Halifax Group and the overlying Silurian to Lower Devonian Rockville Notch Group. The new ages are consistent with stratigraphic units defined in regional mapping and support recent interpretation of fundamental differences in depositional and tectonic environments between the northwestern and southeastern parts of the Meguma terrane. They also provide new constraints on paleogeography of the terrane by confirming age similarities to stratigraphy in north Wales, with which correlation has been proposed previously based mainly on lithological similarities.

Acritarchs from the Hanford Brook Formation, New Brunswick, Canada: new biochronological constraints on the Protolenus elegans Zone and the Cambrian Series 2–3 transition

Diverse and well-preserved acritarchs are reported from the type section of the Cambrian Hanford Brook Formation at Hanford Brook, southern New Brunswick. This section fills an important gap in acritarch studies by providing the first detailed picture of changing acritarch associations close to the traditional lower–middle Cambrian boundary in Avalonia. Acritarchs from the St Martins Member, at the base of the succession, include Skiagia ciliosa, Heliosphaeridium notatum, H. longum and Liepaina plana and suggest attribution to Cambrian Stage 4. Acritarchs from the Somerset Street Member, in the middle of the formation, include Eliasum llaniscum and Comasphaeridium silesiense . This information adds new biochronological context to an ash bed in the Somerset Street Member previously dated as c . 510 Ma or 508 Ma, and to the endemic trilobites from the same member, including Protolenus elegans . It also places absolute ages on the basal range of stratigraphically important acritarchs. Both the acritarch assemblage and the radiometric age are consistent with a position very close to the traditional lower–middle Cambrian transition and likely within Cambrian Stage 5. Acritarchs from the Long Island Member, at the top of the succession, include additional taxa demonstrating assignment to Cambrian Stage 5. Both the Somerset Street and Long Island members probably correlate with the Morocconus notabilis Zone. The new acritarch species Retisphaeridium striatum Palacios is described. New data are presented on acritarchs from the upper part of the Hell9s Mouth Formation, Wales, and correlation proposed with the Long Island Member.