A novel population of composite mounds: their initiation, growth and demise. San Emiliano Formation, Cantabrian Mountains, Spain

Abstract

Purpose Mounds from the Pennsylvanian aged San Emiliano Formation (Cantabrian Mountains, Spain) are commonly well exposed. These mounds range from 2 to 50 m in height and are observed to be primary geological features. The mounds are described and classified and the factors and controls of mound nucleation, growth and demise have been established. Methods Microfacies analysis of 177 thin sections has revealed the composition of the mounds and surrounding carbonates. Results Composite mounds, exhibiting characteristic components of both Cluster mounds and Agglutinated Microbial mounds are described. The mounds are skeletal-microbial/pack-wackestones. Peloidal, homogenous and clotted micrites are the main sedimentological constituents of the mounds. Microfossils are dominant with Donezella, Claracrusta, Rothpletzella and Girvanella being common. Small foraminifera, bryozoans, corals and algae are all present within the mounds, but are more common within off-mound carbonates. Conclusions The formation of the mounds was controlled by a dynamic relationship between Donezellacean algae, and microscopic encrusters, a bio-mechanism not observed in mud mounds elsewhere. Fluctuating environmental conditions lead to the alternate dominance between the two groups, resulting in accretion and stabilisation of carbonate muds. These mounds are compositionally different to their Pennsylvanian counterparts.Keywords Composite mound · Agglutinated microbial mound · Cluster mound · Donezella · Encrusting biota · Microfacies analysis · Pennsylvanian Resumen Propósito Los montículos de la Formación San Emiliano de edad Pensilvaniense (Cantabrian Mountains, España) están comúnmente bien bexpuestos. Estos montículos tienen una altura de 2 a 50 m y se observa que son rasgos geológicos primarios. El los montículos se describen y clasifican y los factores y controles de la nucleación, el crecimiento y la fallecimiento tienen que ver con los siguientes factores se ha establecido. Métodos El análisis de microfacias de 177 sección delgada ha revelado la composición de los montículos y carbonatos circundantes. Resultados Montículos compuestos, que exhiben los componentes característicos de ambos montículos Cluster y Microbial aglutinado. Se describen los montículos. Los montículos son esqueléticos-microbianos lodogranular/lodosa. Peloide, homogéneo y coagulado micrites son los principales componentes sedimentológicos de los montículos. Los microfósiles dominan con Donezella, Claracrusta, Rothpletzella y Girvanella son comunes. Pequeños foraminíferos, briozoarios, corales y algas son todos ellos presente dentro de los montículos, pero son más comunes dentro de los carbonatos fuera del montículos. Conclusiones La formación de los montículos estaba controlada por una relación dinámica entre las algas donezellaceanas, y incrustaciones microscópicas, un mecanismo biológico no observado en montículos de lodo en otras partes. Medio ambiente fluctuante condiciones conducen a la dominación alternada entre los dos grupos, resultando en la creaci...

A microfacies analysis of arid continental carbonates from the Cedar Mesa Sandstone Formation, Utah, USA

“…Encrusting forms such as Rothpletzella and Girvanella have been observed to act as constructors of cavities in other microbially dominated carbonates (Rogers, 2018). Sediments within cavities indicate that the cavities were part of a network through which currents were flowing at the time of primary deposition.…”

“…These encrusting features then join from the base and roof of the voids to form column-like structures that appear preserved as rows of spaced birdseye-like voids. Encrusting forms such as Rothpletzella and Girvanella have been observed to act as constructors of cavities in other microbially dominated carbonates (Rogers, 2018). Laminations and laminoid fenestrae indicate shallow-water to sub-aerial exposure, and they are often used as indicators of sea level.…”

“…They form through complex interactions between ground waters and soils (Spötl and Wright, 1992) within interdune or desert-lacustrine settings (Driese, 1985;Platt, 1989;Seard et al, 2013;Parrish et al, 2017), springs and tufa mounds (Dorney et al, 2017), or from marine incursions Mountney, 2010, 2012). This apparent 'sedimentary bias' is unfavourable as carbonates can provide vital insight into the depositional history, palaeoenvironmental ecology, climate and/or tectonic controls of a basin (May et al, 1999;Rogers, 2018). This apparent 'sedimentary bias' is unfavourable as carbonates can provide vital insight into the depositional history, palaeoenvironmental ecology, climate and/or tectonic controls of a basin (May et al, 1999;Rogers, 2018).…”

“…Despite being recognized frequently, carbonate deposits within arid continental basins are rarely studied in detail Chan, 1988, 1989;Mountney and Jagger, 2004;Moutney, 2012). This apparent 'sedimentary bias' is unfavourable as carbonates can provide vital insight into the depositional history, palaeoenvironmental ecology, climate and/or tectonic controls of a basin (May et al, 1999;Rogers, 2018).…”