Micro-framework reconstruction from peloidal-dominated mud mounds (Viséan, SW Spain)

Abstract

Currently, the diVerent roles of peloidal micrites are not well understood in matrix-supported bioconstructions such as mud mounds. Upper Viséan outcrops from Guadiato Valley, Cordoba Province, SW Spain provide well-preserved peloidal-dominated mud mounds. Microstructual analysis of these mud mounds has allowed us to establish 13 microfabrics. Although peloids are conspicuous constituents in the microfabrics, they have been diVerentiated into seven peloidal-dominated types, grouped into three categories: (a) homogeneous Wne peloidal types (3 subtypes); (b) homogeneous coarse peloidal types (2 subtypes); and (c) heterogeneous coarse peloidal types (two subtypes). Fast cm-scale microfabric changes were mapped directly onto thin sections. This methodology allows the researcher to recognize the micro-framework of these mud mounds as a complex, multiepisodic organization of microframes and intermicroframes that are formed by primary and secondary automicrites (non-reworked and reworked automicrites, respectively), autochthonous internal sediment, and allomicrite and marine Wbrous cements.The thin-section mapping was also used to estimate the automicrite-allomicrite relationship, which is crucial in separating the microbial and biodetrital mud mounds.

Composition and origin of stromatactis‐bearing mud‐mounds (Upper Devonian, Frasnian), southern Rocky Mountains, western Canada

“…The evolution of mud‐mounds would have been affected potentially by a variety of factors. In discussing Lower Cretaceous examples in north‐eastern Mexico, Murillo‐Muñetón & Dorobek () identified sea‐floor topography, hydrocarbon seeps/hydrothermal vents, upwelling, anoxia in the water column, ramp‐like depositional profile, low background sedimentation rate and relative sea‐level fluctuations as possible controlling factors, in addition to siliciclastic influx and also water depth as it governed illumination and wave action (James & Bourque et al., ; Lees & Miller et al., ; Samankassou, ; Rodríguez‐Martínez et al., ; Samankassou et al., ).…”

“…These depth‐related facies are characterized by different grain type assemblages and are bounded by surfaces like the base of the photic zone, base of the sub‐photic zone, fair‐weather wave base, and storm‐wave base. More detailed subdivision is possible based on light index indicators such as calcareous algae, oncolites and their relative abundance (Bourque et al., ; Rodríguez‐Martínez et al., ). Deeper water mud‐mounds still generally accreted within the photic zone (Pratt, ) but some may have initiated below it.…”

“…The clotted micrite is interpreted as the product mainly of anaerobic heterotrophic bacterial metabolism (Riding, ; Pratt & Haidl et al., ; Rodríguez‐Martínez et al., ). Direct evidence like the close spatial association between bacteria and their byproducts is missing here, like most cases, because of the lack of bacterial relics.…”

Environmental controls on the development of Mississippian microbial carbonate mounds and platform limestones in southern Montagne Noire (France)

“…(e.g. Lees & Miller, ; Della Porta et al ., ; Rodríguez‐Martínez et al ., ; Waters et al ., ), although breccias of the Montagne Noire are commonly poorly exposed which complicate its interpretation.…”

“…The traditionally well‐recognized photic marker is the dasycladales, in which living species are widespread in tropical to warm‐temperate waters, most at 10 to 15 m depths (Berger & Kaever, ), whereas other green algae, for example the bryopsidales, have been recorded in water depths down to 140 m (Hillis‐Colinvaux, ). Koninckopora is the most widely recorded dasycladale in traditional Mississippian mound models, considered as a photic marker (Somerville et al ., , ; Lees & Miller, ), although other authors have interpreted their thalli as platform‐derived material (Bridges & Chapman, ; Rodríguez‐Martínez et al ., ). This taxon is recorded only in the Roc de Murviel Formation, although other dasycladales are as abundant in the Roque Redonde Formation as in the Roc de Murviel Formation.…”