Systematic position and palaeoecology of the Upper Jurassic to Tertiary alga Marinella lugeoni Pfender.-
Zitteliana, 20, 105-122, München.
The alga Marinella lugeoni Pfender commonly occurs in Upper Jurassic and Lower Cretaceous sediments, and is known until the Oligocene. Originally described as a cyanophyte, most authors attributed the alga to the codiaceans whereas some reckoned a solenoporan character. Features detected in the rich material from the Portuguese Upper Jurassic support a red algal character and reveal close relationships to the corallinaceans. Criteria for such interpretation are: (1) The microcrystalline character of tissue walls, (2) Noticeable enrichment of Mg and lack of Sr indicating an originally Mg-calcite skeleton, (3) the small size of filaments which are subdivided by horizontal walls and occasionally bifurcate, (4) partial tissue differentiation, resulting in the development of an epithallial layer and probably of megacells, (5) auto-dissolution of skeletal material resulting in voids with pores which can be interpreted as reproductive organs, and (5) the frequent rhodolite growth form.
The simple structure of most of the thallial tissue and the radial arrangement of cell threads in Marinella are also features of solenoporacean red algae. Despite its similarities with both corallinaceans and solenoporaceans Marinella should not be taken as a 'missing link'. The longevity of the relative simple tissue features of Marinella indicates that corallinaceans did neither develop from solenoporaceans nor from Marinella but probably had a common, possibly uncalcified ancestor with Marinella.
Marinella occurs in a wide variety of marine shallow-water environments, but is most frequent in particle-rich, partly clayey limestones. It also occurs in settings of fluctuating salinities, where it indicates the more marine phases. Its success in highly abrasive settings such as unstabilised, quartz-rich ooid sands seems to be related to a high regeneration ability, a pathway which is followed by modern coralline algae.
Last changes Nov. 2004 by Reinhold Leinfelder