Stratigraphy of the Cordubian-Ovetian (Lower Cambrian) Transition in the Occidental Iberian Chain (Spain)

[Resumen] Este trabajo analiza los afloramientos de la Formación Embid (Cámbrico Inferior) existentes en el borde nororiental de la Cadena Ibérica Occidental, entre las localidades de Torrijo de la Cañada y Villalengua (unidad estructural de Moros). Con este objetivo se han realizado dos perfiles estratigráficos y estudiado sus litofacies. Asimismo, se pone de manifiesto el contenido paleoicnológico más representativo. La aparición de distintos ejemplares del icnogénero Astropolichnus separados 200 m. en la serie estratigráfica plantea la necesidad de reconsiderar la precisión de este incofósil como indicador bioestratigráfico. Debido a la ausencia de afloramientos superficiales de la Formación Bámbola, estos materiales constituyen las rocas más antiguas.de esta Cadena. Finalmente, se propone al perfil To1 como hipoestratotipo de la Formación Embid en la Cadena Ibérica Occidental.[Abstract] This work presents a study of the Embid Formation, the oldest formation cropped out in the Occidental Iberian Chain (NE Spain). This outcrop is placed in the nucleus of the Moros structural unit (ALVARO et al., 1992), located in the nonheastern contact of this Chain with the Calatayud-Teruel Teniary basin, between Villalengua and Torrijo de la Cañada localities (Zaragoza Province). We have studied two sections of the Embid Formation (To1 and T02). The first one, 250 m. thick, is the most complete and shows the best exposition of the area. It is proposed as the hipostratotype of the Embid Formation in this Chain. In To1, four terms (El to E4) of this formation and other at the beginning of the Jalón Formation al) have been recognized, according to the sandstone/shale ratio. The ichnofossils and other sedimentary structures studied here suggest, for terms E2 and E4-J1, a litoral to shallow sublitoral environment (tidal flat and tidal channels, influenced by tidal and wave effects), and a sublitoral (circalitoral) environment with episodic levels influenced by storms currents and/or hard tides, for the terms El and E3. The northeastwards To2 section, 150 m. thick, shows a similar evolution, but a more distal character. The wide development of subtidal sand bodies as well as the low diversity and wealth of biogenic structures, suggest a shoreface sedimentation, with a intercalated episode influenced by tidal action. The materials of this section are assigned to the Embid Formation for its lithology, the lack of white quarzites (that characterize the underlying Bámbola Formation) and the ichnofossil record. In spite of palichnological, lithological and sedjmentological affinities between both profils, we can not give an accurate correlation of both sequences. The section To1 records a shallower episode (E2), reaching subaerial exposure in the Cordubian-Ovetian transition. It is the first time this episode has been recognized in the Iberian Chains, and it is considered as a local process. A second shallower episode is placed in the transition of the Embid-Jalón Formations (E4-J1). It has been recognized in other outcrops of the Iberian Chains and LIÑAN & GAMEZ (in press) have proposed a correlation of this regressive episode with the Woodlands Regression (BRASIER, 1985). On the other hand, Astropolichnus ichnogenus is recorded in different levels of same section (200 m. separated), for the first-time in the Iberian Chains. This fact will force to reconsider the accuracy of this ichnofossil as biostratigraphical marker. Finally, a progresive eastwards distallity of the sediments is inferred by comparison with similar outcrops of the Oriental Iberian Chain, by the existence of the first local"shallower episode, placed in the more suroccidental outcrop of the basin (To1), and by the northeastwards paleocurrents directions. These data support the existence of an emerged area beside the occidental margin of the Cantabrian-Iberian Basin as was pointed by LOTZE (1961), and also proposed in the cantabrian sector of this basin by ARAMBURU el al. (1992)

The Cambrian of the Iberian Peninsula : an overview

This work is a brief overview of the Cambrian in the Iberian Peninsula, along with an updated review of lithostratigraphic and biostratigraphic data. A Cambrian correlation chart between the different stratigraphical units that have been established in the Iberian Peninsula is given. We also reappraise the Lower and Middle Cambrian regional stages in the light of new palaeontological data, and the different biozonations proposed with several palaeontological groups

A new occurence of the genus Tonkinella in northern Spain and the Middle Cambrian intercontinental correlation

The genus Tonkinella is a typical polimeroid trilobite in lower Middle Cambrian rocks from Vietnam, Canada, U.S.A., India, Korea, Siberia, China and Argentina. It has recently been found in the Mediterranean region (Iberian Chain, northeastern Spain). In this paper we refer the finding of Tonkinella aff. breviceps in the Leonian (lower Middle Cambrian) of the Cantabrian Mountains (northern Spain), analysing its stratigraphical position, fossil assemblages, biochronology and utility for intercontinental correlation. The presence of this taxon allows us to make a more accurate correlation between the Middle Cambrian biochronological scales of Laurentia, the Mediterranean area and China

LITHOSTRATIGRAPHY AND PALAEONTOLOGY OF THE ‘BLACK SHALE’ FACIES OF THE SEMANGGOL FORMATION (CHERT UNIT) AT BUKIT MERAH (PERAK, PENINSULAR MALAYSIA)

In the Semanggol formation cropping out in Northern Perak, a ‘black shale’ facies was identified at the lowermost level of the chert unit at Bukit Merah, containing trace and body fossils. Despite some recent contributions made in Northern Perak outcrops, some questions about the origin of the ‘black shale’ facies remain open, particularly its depositional palaeoenvironment, palaeo-oxygenation history and biochronological age. Moreover, the presence of trace and body fossils in the facies contradicts ‘classical’ views of the ‘black shales’ of the Semanggol formation. Therefore, this study aims to describe the lithostratigraphic and palaeontological contents of the facies, as well as to apply sedimentological, palaeoichnological, petrographical and geochemical analyses for ascertaining the origin of it. The results revealed a shallow marine, sublittoral setting based on the identification of the Cruziana ichnofacies. The coarsening- and the thickening-upward trend observed in the studied stratigraphic section is compatible with a prograding, distal deltaic sequence. Two sources of additional oxygen are identifying as the episodic storm events and the presence of microbial mats, which frequently replenished the oxygen levels at the seafloor. Hence, the deposition occurred under relatively well-oxygenated conditions. Finally, the age of the succession is Early Triassic based on the presence of the bivalve genus Claraia

First report of Crumillospongia (Demospongea) from the Cambrian of Europe (Murero biota, Spain)

The demosponge genus Crumillospongia, originally described from the Burgess Shale (middle Cambrian of Canada), has only been cited from lower and middle Cambrian localities of North America and China. The taxon is now also described from uppermost lower Cambrian rocks of the Murero Lagerstätte (Zaragoza Province, NE Spain). Crumillospongia mureroensis sp. nov. is a small to medium sized sack-shaped to elongate demosponge characterized by the presence of densely packed pores of three sizes, considerably larger than those in any other species of the genus. The Spanish material represents a link in the chronostratigraphical gap between the Chinese and North American material.Peer reviewe

Biostratigraphy of the Ribota and Huérmeda formations (Cambrian Series 2) in the Comarca del Aranda (Zaragoza province), Iberian Chains (NE Spain).

This article presents a detailed biostratigraphic analysis of the Cambrian Series 2 Ribota and Huérmeda formations of four sections of the Iberian Chains (NE Spain), and a systematic study of their trilobite faunas. We identified four major assemblages: two in the middle part of the Ribota Formation, one at the base of the Huérmeda Formation and one at the top of the Huérmeda Formation. The studied species permit the assignment of these formations to the middle and upper Marianian and probably lower Bilbilian stages in the regional stratigraphic chart for the Iberian Peninsula, which correlates with an interval around the Cambrian Stage 3-4 boundary. The assemblages exhibit a great correlation potential with the presence of Termierella and the first figured material of Andalusiana from the Iberian Chains, two characteristic taxa of the Marianian of the Ossa-Morena Zone, having been also recorded from the Central Iberian Zone and Morocco. In addition, specimens tentatively assigned to Hebediscus are recorded for the first time from the region, a taxon with a wide geographic distribution which allows a good international correlation in the Cambrian Series 2

Cambrian bioestratigraphy and environmental evolution of the Borobia area (Province of Soria, Oriental Iberian Chain, Spain)

[Resumen] Se estudian dos secciones estratigráficas en los afloramientos cámbricos más septentrionales de la Cadena Ibérica Oriental, las cuales incluyen a las formaciones Jalón, Ribota, Huérmeda, Daroca, Valdemiedes, Murero y Acón. Los datos estratigráficos, mineralógicos, petrológicos y paleontológicos sugieren la existencia de tres geoventos de tipo eustático. El primero de ellos (Transgresión del Cámbrico inferior) comienza con depósitos litorales en condiciones áridas y ambiente oxidante, para evolucionar a un medio sublitoral carbonatado y posteriormente a otro de plataforma siliciclástica abierta. El segundo geoevento (Regresión Hawke Bay) estaría representado por las areniscas y lutitas de la Formación Daroca. El inicio del tercer geoevento (transgresión generalizada del Cámbrico medio) produce la instauración de una plataforma mixta (terrígeno-carbonatada) con pulsos regresivos asociados, representados por la base de la Formación Acón. La presencia de los trilobites Strenuaeva ineondita, Aeadolenus sp., Asturiaspis inopinatus; Paradoxides (Eeeaparadoxides) suleatus; P. (Eee.) rouvillez: P. (Bee.) barehyrhaehis, Badulesia tenera, Badulesia pasehz: Badulesia granien: Solenopleuropsis verdiagana, Solenopleuropsis truneata y Pardazlhaina sp.; junto a los acritarcos Skiagia ezliosa, Heliosphaen'dium dissimzlare, Arehaeodiseina umbonulata, Cristallinium eambn'ensis, Eliasum Ilaniseum, Timofeevia fosfonOtiea y Timofeevia lanearae sugiere que los pisos Marianiense, Bilbiliense, Leoniense y Caesaraugustiense del Cámbrico inferior-medio están representados. Estos datos paleontológicos permiten una primera comparación entre la biozonación española de trilobites y la de acritarcos, y proceder así a la correlación de los materiales del Cámbrico inferior y medio de la Península Ibérica con los de la Plataforma Oriental Europea.[Abstract] Two stratigraphical sections from the more septentrional Cambrian outcrops of the Oriental Iberian Chain 'are studied, including theJalón, Ribota, Huérmeda, Daroca, Valdemiedes, Murero and Acón formations (Lower-Middle Cambrian). The stratigraphical, mineralogical, petrological and paleontological data suggest the presence of three eustatic geoevents. The first one (Lower Cambrian Transgression) started with litoral deposits on arid and oxidant conditions that changed to sublitoral deposits (carbonate shelf) and posteriorly to an open siliciclastic shelf. The second eustatic geoevent (Hawke Bay Regression) is represented by the sandstones and lutites of the Daroca formation. The third geoevent (Middle Cambrian Transgression) began with the establishment of a mixed shelf (terrigenous- carbonated) and shows sorne regressive pulses represented by the basal leveIs of the Acón Formation. The presence of the trilobites Strenuaeva ineondita, Aeadolenus sp., Asturiaspis inopinatus, Paradoxides (Eceaparadoxides) suleatus, P. (Eee.) rouvillei, P. (Bee.) barehyrhaehis, Badulesia tenera, Badulesia pasehz~ Badulesia granien', Solenopleuropsis verdiagana, Solenopleuropsis truneata and Paradazlhania sp.; and the acritarchs Skiagia ezliosa, Heiosphaen'dium dissimzlare, Arehaeodiseina umbonulata, Cristallinium eambn'ensis, Eliasum Ilaniseum, Timofeevia fosfontiea and timofeevia lanearae suggest a Lower-Middle Cambrian age (Marianian to Caesaraugustian stages). These biostratigraphical data allow a comparison between the trilobite and acritarch biozonations for the first time in Spain as well as the correlation of the Península Ibérica's Lower-Middle Cambrian materials with the East European Platform ones.

Presence of Naraoia Walcott, 1912 (Nektaspida, Arthropoda) in the middle Cambrian of Europe (Murero, NE Spain).

The genus Naraoia Walcott, 1912, a Burgess Shale-type fossil known from the lower and middle Cambrian of British Columbia (Canada), Idaho and Utah (USA), as well as from Yunnan and Guizhou provinces (China), is now reported from the middle Cambrian of Murero (Zaragoza, Spain), which is the first record in the Acadobaltic province. The only fragmented specimen found is determined as Naraoia sp., its age being Pardailhania multispinosa Zone (Drumian Stage). This new datum reinforces the hypothesis of the existence of a cosmopolitan faunal substrate in early Cambrian times, which is to some extent refl ected in the mid Cambrian by faunal groups of low evolutionary potential as the family Naraoiidae and other soft-bodied fossil taxa