Reefal and mud mound facies development in the Lower Devonian La Vid Group at the Colle outcrops (León province, Cantabrian Zone, NW Spain)

Abstract

In the locality of Colle (Cantabrian Zone, NW Spain), the upper part of the Valporquero Shale Formation (Emsian, La Vid Group) contains an interval of shales and marlstones (barren, greenish-grey shales and fossiliferous, greenish-grey or reddish shales/marlstones) with beds and packages of homogeneous and cross-bedded skeletal limestones. Metre-scale mud mounds and coral biostromes occur encased in the fossiliferous reddish and greenish-grey shale/marlstones, respectively, with the coral biostromes overlying conspicuous skeletal limestone bodies. These rocks were deposited on a carbonate ramp, ranging from above storm wave base for the cross-bedded skeletal limestones to below the storm wave base for the remaining deposits, organic buildups included. The vertical stacking of these facies and the occurrence of the two types of buildups are interpreted to reflect the interplay among several (possibly 4th and 5th) orders of relative sea-level variations, during a 3rd-order highstand. Coral biostromes occur in early 5th-order transgressive system tracts developed within late 4th-order highstand, and are interpreted to have thrived on a stable granular substrate (skeletal limestones) in non-turbid waters, being later aborted by the onset of muddy sedimentation. Biostrome features suggest that they developed under environmental conditions essentially different from those related to the sedimentation of their granular substrate. Mud mounds occur in 5th-order transgressive and early highstand system tracts tied to early 4th-order sea-level rise. Field relationships suggest that mud mounds grew coevally with muddy sedimentation, with high-frequency variations in carbonate vs. terrigenous mud sedimentation influencing their development.

First fossil sponge from Antarctica and its paleobiogeographical significance

“…Modified after Fernández et al (2006). was initially reported on by Fernández et al (2006). From these rocks we describe the first chambered hexactinellid sponge from the Palaeozoic.…”

“…The siliceous sponge-bearing, polymicritic bryozoan mudmounds and the surrounding fossiliferous sedimentary deposits (reddish shale/marlstone; facies C of Fernández et al 2006) formed in a low-energy, fairly deep marine environment below the storm wave base, but apparently still under the influence of periodic storms. The latter is attested to by the occurrence of thin skeletal beds, which we interpret as distal tempestites, formed by storm-induced offshore directed bottom currents (storm surge) capable of transporting their suspension load even beyond the storm wave base (cf.…”

“…The Colle outcrops have been well known for their well-preserved and abundant invertebrate fossils since the 19th century (e.g., Verneuil 1850; Mallada 1875; Comte 1938Comte , 1959Truyols-Massoni 1981;Alvarez 1999;Schröder and Soto 2003). Fernández et al (2006) conducted a facies analysis and sequence stratigraphic interpretation of the studied interval that focused on the development of reef complexes composed of coral biostromes and mud mounds. The latter yield an hexactinellid sponge fauna that Fig.…”

“…Based on Lobato et al (1984). Modified after Fernández et al (2006). was initially reported on by Fernández et al (2006).…”

“…This interval corresponds to the Sagüera Member of the Esla Formation named by Keller (1988) and the Intermediate Limestone Member of Leweke (1982). According to the facies and sequence stratigraphic analysis by Fernández et al (2006) Lithostratigraphy of the astur-leonese facies …”