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Sedimentary patterns across the Lower-Middle Cambrian transition in the Esla nappe (Cantabrian Mountains, northern Spain) Álvaro, J.J. Vennin, E. Moreno González De Eiris, Elena Perejón, A. Bechstädt, T. 551.7"621.2" Patch reefs Carbonates Sedimentology W. Gondwana Cambrian Geología Geología estratigráfica 2506.18 Sedimentología 2506.19 Estratigrafía Financial support was provided by the Spanish Projects PB 93-0591 and PB 96-0842, a French `Coup de Pouce' Project and some projects funded by the German Research Foundation (DFG). This paper is a contribution to IGCP Project 380 `Biosedimentology of microbial buildups' In the carbonate platforms of the western Gondwana margin, the extinction recorded at the Lower–Middle Cambrian boundary is accompanied by a profound change in the style of carbonate deposition. The Láncara Formation of the Esla nappe (Cantabrian Mountains, northern Spain) contains a distinct sedimentary turnover due to a combination of tectonism, eustatic fluctuations, and immigration and colonization of new benthic communities, such as the youngest archaeocyathan assemblage of the entire Iberian Peninsula. During latest Early Cambrian times, a regressive trend is recorded in the Láncara Formation. This regression was recorded on a peritidal-dominant, homoclinal ramp that is topped by a tectonically induced discontinuity (D1). The latter surface marks the beginning of a last prograding, regressive tendency recorded on an intra-shelf ramp with ooidal/bioclastic shoals protecting archaeocyathan-microbial patch reefs. The overlying discontinuity (D2) corresponds to a major erosive unconformity, which coincides with the Lower–Middle Cambrian boundary in the Cantabrian Mountains. The subsequent, long-term, earliest Middle Cambrian rise in relative sea-level allowed deposition of low-relief, bioclastic shoals bearing a diverse and cosmopolitan assemblage of benthic fauna. Finally, the previous evolution is bounded by a third discontinuity (D3), which marks the beginning of a rhythmic sedimentation indicative of a major phase of tectonic breakdown and drowning of platforms recognised throughout southwestern Europe. Two associations of calcimicrobes occur in the latest Early Cambrian regressive trend of the Láncara Formation: (i) Proaulopora and Subtiflora are identified in peritidal, high-energy settings, lacking self-supported structures, whereas (ii) intergrowths of Epiphyton, Renalcis and Girvanella encrusted branching colonies and solitary archaeocyaths in protected (back-shoal) patch reefs. The latest Early Cambrian regression is correlated in southwestern Europe in both siliciclastic (Iberian Chains and Ossa–Morena) and carbonate-dominant platforms (Cantabrian Mountains, Montagne Noire and Sardinia). Its tops are recognised as diachronous unconformities ranging in age from early Bilbilian to the Bilbilian–Leonian or Lower–Middle Cambrian boundary. Depto. de Geodinámica, Estratigrafía y Paleontología Fac. de Ciencias Geológicas TRUE pub 2024-07-31T12:47:54Z 2024-07-31T12:47:54Z 2000 journal article VoR https://hdl.handle.net/20.500.14352/107327 0037-0738 10.1016/S0037-0738(00)00134-2 eng info:eu-repo/grantAgreement//PB 93-0591 info:eu-repo/grantAgreement//PB 96-0842 Álvaro et al. (2000): «Sedimentary patterns across the Lower-Middle Cambrian transition in the Esla nappe (Cantabrian Mountains, northern Spain)», Sedimentary Geology, 137(1-2), pp. 43-61. Disponible en: https://doi.org/10.1016/S0037-0738(00)00134-2. restricted access application/pdf Elsevier