Construction versus accumulation in phylloid algal mounds: an example of a small constructed mound in the Pennsylvanian of Kansas, USA

Abstract

Most phylloid algal mounds are currently interpreted as no more than accumulations of leaf-like thalli supported by mud. We report here phylloid algae from the Upper Pennsylvanian (Late Carboniferous) Frisbie Limestone Member in Kansas, USA, which built small mounds with recognizable primary topographic relief. Cup-shaped algal thalli, growing closely packed and juxtaposed near and above one another, produced a framework in the shapes of topographically conspicuous mounds from smaller, centimeter-scale to meter-scale features. Meter-scale mounds are composites of smaller, juxtaposed, centimeter-scale mounds and intramound areas contain crinoid debris, sponges, bryozoans, brachiopods, and skeletal grains. The intercup voids enclosed in the framework fabrics of individual thalli are filled with a variety of matrix and cements: (1) peloidal grains, both in clotted wackestone and grainstone; (2) early marine cement; (3) microbial encrustations, often oriented against gravity; and (4) mudstone. Bedded limestones equivalent to and overlying the mounds are bioclastic wackestone and differ fundamentally from the mound limestone in facies, biotic components, absence of both frameworks and of peloidal clotted grains. Topographic relief above the sea floor, the growth fabrics with a framework including primary intramound and intercup voids and their complex infillings, and the lithic and biotic differences between mound and off-mound intervals fulfil the stratigraphic and biological criteria characterizing reefs. The model proposed here interprets these mounds as the result of active constructional algal growth, in contrast to published hypotheses that most phylloid algal mounds were passive accumulations of algal thalli within a mud matrix and/or early diagenetic marine cements.

The influence of terrestrial run off on marine biotic communities: An example from a thrust-top carbonate ramp (Upper Pennsylvanian foreland basin, Picos de Europa, NW Spain)

“…Samankassou and West (2002) and Forsythe (2003) documented cup-shaped phylloid algae that actively contributed to mound growth displaying similar features to those of some phylloid algal mounds described herein.…”

Internal structure and depositional environment of Late Carboniferous mounds from the San Emiliano Formation, Cármenes Syncline, Cantabrian Mountains, Northern Spain

“…Although phylloid algae are the major mound builders, mounds built by other algae have been reported, e.g., Anthracoporella dasycladalean algal mounds (Samankassou, 1998). The growth fabric of algal mounds is an important aspect, which has not been investigated in detail: whether they consist of detrital accumulations of algal thalli (Ball et al, 1977) or of in situ thalli, implying a framework (examples in Samankassou, 1998;Samankassou and West, 2000) needs further investigation. Another important topic is the role of microbial activity in the accumulation, consolidation, and lithification of the mound structure (Pratt, 1982(Pratt, , 1995Webb, 1996;Kirkland et al, 1998).…”

Paleoecology of Pennsylvanian phylloid algal buildups in south Guizhou, China

“…4), and brachiopods (Choristes sp., Neospirifer orientalis, and Orthotichia marmerea) are commonly associated with the phylloid algal facies. The high-diversity assemblages are not conWned to cavities as commonly seen in similar reefs elsewhere (Toomey 1976(Toomey , 1980Samankassou and West 2002;Forsythe 2003): e.g., the co-occurring auloporid corals locally form patches consisting of boundstone (Fig. 4b).…”