Ivanovia tebagaensiswas a cyathiform Permian codiacean membranous alga with dimorphic cortices

Abstract

Species of Ivanovia (Codiaceae or Udoteaceae, Chlorophyta) have traditionally been characterized as phylloid or leaf-like. Extraordinarily well preserved specimens of I. tebagaensis in limestone from the Upper Permian of southern Tunisia indicate that the thallus was cyathiform or cup-shaped, similar to the broadly conical codiacean Calcipatera and to living Udotea cyathiformis. Ivanovia also shared with Calcipatera the same general membrane structure consisting of bilateral cortices with palisades of utricles, now filled with micrite, and a medulla of tubular coenocytes, now filled with sparry calcite mosaic. A cyathiform thallus would have had an inner and an outer cortex and those of I. tebagaensis were dimorphic. The utricular structure as usually seen in thin sections using transmitted light is much clearer when viewed on polished surfaces of hand specimens using reflected light. Commonly occurring fused membranes suggest that the thalli reproduced vegetatively by budding. The complexity and regularity of the I. tebagaensis membrane structure strongly suggest that a model which proposes that Ivanovia is simply a diagenetic stage in the fossilization of the red alga, Archeolithophyllum, is invalid.

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

“…The model proposed here interprets these mounds as the result of active constructional algal growth, in contrast to the previous hypotheses that they were always passive accumulations of algal thalli within a mud matrix and/or early diagenetic marine cements. Our model is in agreement with growth forms of phylloid algae proposed by Toomey (1976) and Torres (1995Torres ( , 1997. Their position at the top of a transgressive limestone in deepening water probably helped to preserve these mounds from currents and storms that would tend to destroy algal growth forms in shallower water^as might have occurred in the overlying regressive Argentine limestone which contains numerous small algal blades but no mound features like those in Frisbie.…”

“…The remaining space was ¢lled with homogeneous sediments, probably settling of suspended mud from the water column. This model acknowledges the results of trophic analysis by Toomey (1976) and the recently described morphological structures of these algae (Torres, 1995(Torres, , 1997. The frequency and extension of similar mounds need further investigation.…”

“…They are almost always replaced by blocky calcite cement and their systematic position is therefore indeterminable. Similar growth forms have been identi¢ed as Ivanovia and Eugonophyllum (Torres, 1995(Torres, , 1997. The delicate framework and abundance of micrite indicate a position below wave base, as suggested in previous studies of algal mound facies (Toomey, 1976).…”

“…All of these algal cups are similar in size, form, and in¢llings. The thallus form corresponds to the recent reconstruction of bowl-shaped, cyathiform algae (Torres et al, 1992;Torres, 1995). Algal thalli are 20^60 mm in diameter and 0.5^3 mm thick.…”

“…The principal conclusion of this report is that the organisms grouped as phylloid algae were not builders of depositional topography, but rather were a source of building material'. Some recent investigations have re-evaluated the morphology of the conspicuous phylloid algae (Torres, 1995(Torres, , 1997and references cited therein). Considering the revealed growth forms, the fabrics of mounds constructed by these enigmatic plants need to be reconsidered.…”