Abstract
The Late Miocene Malbusca outcrop is located in the southeastern coast of Santa Maria Island (Azores, NE Atlantic), interspersed in volcanic formations. At ~20 meters above present sea level, a prominent discontinuous layer of rhodoliths seizes with an extension of ~250 meters. This paper presents the first taxonomic record of fossil rhodolith forming coralline algae for the Miocene of the Azores. The preserved taxonomic features used were the following: (1) arrangement of basal filaments, (2) epithallial cells (when observable), (3) presence of cell fusions, (4) conceptacle type, (5) number of cells layers which conceptacle chamber floors are situated below the surrounding thallus surface and (6) for the sporangial pores, the orientation of the filaments around the conceptacle pores. Based on these characters, six taxa were identified encompassing three Corallinaceae (Lithophyllum prototypum, Lithophyllum sp., Spongites sp. and Hydrolithon sp.) and one Hapalidaceae (Phymatolithon calcareum and cf. Phymatolithon sp.). An unidentified coaxial thallus was also present, the coaxial construction ascribing the specimens to the genus Mesophyllum or Neogoniolithon. Taxonomic accounts for the identified taxa are described, illustrated and an identification key is provided. The report of L. prototypum represents the first Miocene record and the preservation of the specimens is very good. Miocene coralline algae seem very consistent among deposits but some species are relevant for particular areas, like in the Azores.
Highlights
Rhodoliths are nodules of unattached nongeniculate coralline algae (Corallinales and Sporolithales, Rhodophyta)
This paper describes three Corallinaceae and one Hapalidaceae red algal genera comprising six taxa
Identifications were based on the following preserved taxonomic features: (1) arrangement of basal filaments, (2) epithallial cells, (3) presence/ absence of cell fusions or secondary pit connections, (4) conceptacle type, (5) number of cells layers which conceptacle chamber floors are situated below the surrounding thallus surface and (6) for sporangial pores, the orientation of filaments around conceptacle pores
Summary
Rhodoliths are nodules of unattached nongeniculate coralline algae (Corallinales and Sporolithales, Rhodophyta). Coralline algae are common components in Messinian reefs in the Sorbas Basin in SE Spain, with a species composition of Neogoniolithon brassica-florida and Spongites fruticulosus, dominating the shallow-water assemblages; Lithophyllum records peak at the base of reef-core and upper-slope deposits (around 20 m palaeodepth) and Phymatolithon calcareum and species of Lithothamnion are most abundant in deeper slope facies (Braga et al 2009). A few, such as Spongites fruticulosus and Phymatolithon calcareum, have been living in the Mediterranean region for more than 25 Ma. Similar assemblages are present in Macaronesia, in the Miocene (Johnson et al 2012), and younger limestone deposits enriched by rhodoliths and rhodolith-derived sediments are known from the late Pleistocene (Amen et al 2005). It is discussed the limitation and need for a better taxonomical access of the Azorean fossil coralline diversity
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