New insights about the Upper Jurassic – Lower Cretaceous sedimentary successions from Asturias (NW Iberian Peninsula)

Abstract

Detailed mapping of the Jurassic to pre-Albian deposits of central and eastern Asturias (NW of the Iberian Peninsula) allowed several Upper Jurassic and Lower Cretaceous outcrops, previously assigned to other ages, to be identified. Where possible, these outcrops were correlated with the well-known sequences outcropping on the Asturian coast. A new Jurassic stratigraphic unit, the Miyares Formation, was defined, consisting of a conglomerate Lower Unit, a Middle Unit composed mainly of oolitic limestones and an Upper Unit comprising bioclastic and marly limestones with a rich larger foraminiferal fauna. The Lower Unit is interpreted as deposited in a fan delta, the Middle Unit represents a shallow marine high-energy environment, and the Upper Unit deposited on a restricted shallow marine platform. The shallow-water foraminiferal assemblage from the Upper Unit is attributed to the Tithonian and the oldest Cretaceous rocks are Barremian. Therefore, there is a stratigraphic gap recorded in the study area, which might correspond to the latest Jurassic to Early Cretaceous pro parte timespan.Keywords: Late Jurassic, Early Cretaceous, Larger Foraminifera, NW Spain Resumen Una cartografía geológica detallada de los depósitos jurásicos y cretácicos pre-albienses ha permitido identificar varios afloramientos del Jurásico Superior y del Cretácico Inferior, asignados previamente a otras edades. Donde ha sido posible, estos afloramientos han sido correlacionados con las sucesiones bien conocidas que afloran en la costa asturiana. Se ha definido una nueva unidad, la Formación Miyares, formada por una Unidad Inferior conglomerática, una Unidad Media mayoritariamente de calizas oolíticas y una Unidad Superior de calizas bioclásticas y margosas con abundantes macroforaminíferos. La Unidad Inferior se interpreta como depósitos de fan delta, la Unidad Media representa un ambiente marino somero de alta energía, y la Unidad Superior fue depositada en una plataforma marina somera restringida. El conjunto de foraminíferos de agua somera de la Unidad Superior se atribuye al Titoniense y las rocas más antiguas del Cretácico son del Barremiense; existe por lo tanto, en el área de estudio, una laguna estratigráfica que abarca la parte terminal del Jurásico y una parte del Cretácico Inferior.

Constraints Imposed by Rift Inheritance on the Compressional Reactivation of a Hyperextended Margin: Mapping Rift Domains in the North Iberian Margin and in the Cantabrian Mountains

“…Following the Permo‐Triassic rift, a period of thermal subsidence affected the northern Iberian rifts during the Lower and the Middle Jurassic, leading to a general transgression and the development of characteristic marine facies that are progressively younger from west to east (González‐Fernández et al, ; Quintana, ; Riaza, ). These sediments, including dolomites, limestones, and calcareous claystones, have been interpreted as part of the pre‐rift units imaged in the Basque‐Cantabrian Basin and in the Asturian Basin (e.g., Cadenas & Fernández‐Viejo, ; Espina, ).…”

“…These authors proposed a new submarine location for this structure, running N60°W. The Lower to Middle Jurassic sediments correspond to a well‐known marine sequence, which includes dolomites and limestones, displaying a maximum thickness of about 600 m (González‐Fernández et al, ; Valenzuela et al, ). The Upper Jurassic sediments include continental deposits linked to a second rift event, and shallow marine and fluvial deposits developed during the Kimmeridgian‐Tithonian transgressive event (González‐Fernández et al, ).…”

“…The Lower to Middle Jurassic sediments correspond to a well‐known marine sequence, which includes dolomites and limestones, displaying a maximum thickness of about 600 m (González‐Fernández et al, ; Valenzuela et al, ). The Upper Jurassic sediments include continental deposits linked to a second rift event, and shallow marine and fluvial deposits developed during the Kimmeridgian‐Tithonian transgressive event (González‐Fernández et al, ). From the Tithonian to earliest Barremian, González‐Fernández et al () recognized a period of erosion/non‐deposition and defined an Upper Barremian to Aptian transgression accompanied by the deposition of marine facies.…”

“…The Upper Jurassic sediments include continental deposits linked to a second rift event, and shallow marine and fluvial deposits developed during the Kimmeridgian‐Tithonian transgressive event (González‐Fernández et al, ). From the Tithonian to earliest Barremian, González‐Fernández et al () recognized a period of erosion/non‐deposition and defined an Upper Barremian to Aptian transgression accompanied by the deposition of marine facies. The Aptian‐Albian and the Upper Cretaceous deposits, corresponding mainly to siliciclastic sediments with some calcareous levels, are very scarce and disconnected.…”

Revisiting the age and palaeoenvironments of the Upper Jurassic–Lower Cretaceous? dinosaur-bearing sedimentary record of eastern Spain: implications for Iberian palaeogeography

“…Features observed in specimens of A. lusitanica of the studied samples are very similar to those reported in the specimens identified in some Tithonian deposits of Asturias (North Spain), which, in turn, contain similar morphotypes of C. cf. tingitana (González-Fernández et al 2014). Anchispirocyclina lusitanica has been previously attributed to the Portlandian (Hottinger 1967;Pélissié et al 1984) or, since the 90s, to the Tithonian (Septfontaine et al 1991;Velic 2007), which is the age assigned to the deposits containing A. lusitanica of the uppermost part of the Villar del Arzobispo Fm (uppermost part of the SUP; Figs.…”