Facies variation in Waulsortian buildups. Part 2; Mid‐Dinantian buildups from Europe and North America

Abstract

Using detailed petrographic analysis and a new method of handling similarity coefficients, samples from over 30 Mid-Dinantian (Upper Tournaisian-Lower Visean) carbonate buildups from Europe and North America are compared with the Waulsortian facies of Belgium. The same component types are present and they bear very similar relationships to one another. This is very significant because the assemblages of components in Belgium have recently been interpreted in terms of water depth (Lees er al. 1985).Four Waulsortian Phases are recognized, corresponding to the Belgian depth-related assemblages. They represent growth in a range of marine environments from fairly deep, aphotic (probably more than 300 m) through to the photic zone (less than 120 m).Logging and mapping of phases allows growth patterns of individual buildups and buildup complexes to be interpreted as products of changing depositional environments. The very existence of the phases provides new information on the origin of the buildups. It also reveals that there was a fundamental growth mechanism independent of the preserved biota.

Transgressive–regressive sequence stratigraphy of Pennsylvanian Donezella bioherms in a foreland basin (Lena Group, Cantabrian Zone, NW Spain)

“…In some intervals, carbonate mud is the main component of mounds, showing heterogeneous microfabrics (Fig. 4d), such as homogeneous, laminated, peloidal and clotted micrite (polymuds of Lees and Miller 1985). Stromatactic-like cavities are poorly developed.…”

Microbial‐sponge and microbial‐metazoan buildups in the Late Viséan basin‐fill sequence of the Jerada Massif (Carboniferous, NE Morocco)

“…If this premise is correct, and considering a maximum water depth of c. 20 AE 5 m for the grainy facies, buildup thickness below the first occurrence of plurilocular foraminifers will give a 'static model estimate' for the depth of buildup initiation, c. 60 AE 5 m. Since the lower limit of stacheiinid red algae is about 20 m above the base of the buildup, dysphotic to aphotic conditions should prevail below a water depth of c. 40 AE 5 m. This extremely shallow estimate is well correlated with the assumed dimmed light conditions due to water turbidity. Even a wave base close to the top of the buildup, at the first occurrence of cortoids (Lees and Miller 1985: 'shallow water'), would shift depth limits shallowwards, to somewhat less than 20 m.…”

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

“…In Mississippian mud mounds, the 'multi-component mudstone' of Lees (1964) and the later 'polymuds' fabrics (Lees and Miller 1985) are reference terms or concepts in the mesostructural study of their internal organization. However, the accretion mechanisms are not so clear when both massive or leiolitic fabrics and aphanitic micritic microfabrics occur simultaneously and are dominant.…”