Sporolithon cf. airoldii

Dey, Rikee, Basso, Daniela, Chakraborty, Arindam, Roy, Lopamudra, Bhaumik, Ajoy Kumar & Ghosh, Amit K., 2023, Rhodolith-forming coralline red algae in the CaCO biofactory - A case study from the Serravallian of tropical northeastern Indian Ocean, Comptes Rendus Palevol 22 (26), pp. 541-567 : 551-554

Sporolithon cf. airoldii

( Fig. 5D)

DESCRIPTION

Encrusting to warty growth form, thallus monomerous, dorsiventral, non-coaxial VC. The cells of VC are rectangular in shape that measure 8 to 16 µm in length and 3 to 8 µm in diameter. Cells of PF are more or less squarish with no distinct zonation, 5 to 12 µm in length and 4 to 10 µm in diameter. Cell fusions present. Epithallial cells and trichocytes are indiscernible. Sporangia elliptical, formed within calcified compartments and grouped into sori. Each sporangium measures 80 to 120 µm in height and 35 to 48 µm in diameter ( Table 1).

REMARKS

The specimen is comparable to Sporolithon airoldii described from the lower Oligocene of NW Iran ( Basso et al. 2019) in having small size of the vegetative cells and other anatomical features, but the maximum length of the sporangia exceeds that of the specimens described by Basso et al. (2019) as well as the type material of S. airoldii . Vannucci et al. (2010) re-described S. airoldii from the upper Rupelian-Chattian of Sassello while re-assessing Airoldi’s (1932) specimens. Sporolithon airoldii was recorded earlier from the Oligocene of Molare Formation of the Tertiary Piedmont Basin, NW Italy ( Vannucci et al. 2010), from the lower and middle Rupelian of Prasco and Ovrano, Alessandria ( Mastrorilli 1968), Val Lemme, Carrosio, Alessandria ( Fravega et al. 1988), from the upper Rupelian to Chattian of Sassello, Savona ( Airoldi 1932; Fravega et al. 1987), from the upper Burdigalian to Serravallian of St. Florent, N. Corsica and Bonifacio, Cala de Labra, S. Corsica (Mastrorilli in Bellini & Mastrorilli 1975) and from the lower Oligocene of NW Iran ( Basso et al. 2019).

Sporolithon praeerythraeum (Airoldi) Vannucci, Piazza, Fravega & Basso, 2000

( Fig. 5E, F)

Archaeolithothamnium praeerithraeum Airoldi, 1932: 63 , pl. 9, fig. 2.

Sporolithon praeerythraeum (Airoldi) Vannucci, Piazza, Fravega & Basso, 2000: 193 .

DESCRIPTION

Lumpy to protuberant thallus, VC filaments indiscernible. The peripheral filaments (PF) show horizontal layers of elliptical cells. Cell fusions are present in the PF, the cells of PF measure 14 to 26 µm in length and 10 to 12 µm in diameter. Sporangia grouped in sori, individual sporangia measuring 30 to 36 µm in diameter and 59 to 68 µm in height ( Table 1).

REMARKS

Vannucci et al. (2000) revised and re-documented this species of Sporolithon and transferred Airoldi’s (1932) Archaeolithothamnium praeerythraeum under the genus Sporolithon with a new combination. The species has been identified from the late Eocene to early Oligocene of Italy and Bulgaria ( Francavilla et al. 1970; Bakalova 1983). The overall thallus organization, shape and size of the sporangia and the arrangement of the sporangia are closely comparable to the middle Miocene specimens recorded by Vannucci et al. (2000) and Chelaru & Bucur (2016).

BENTHIC AND PLANKTONIC FORAMINIFERS

In addition to the above mentioned coralline red algae, some benthic and planktonic foraminifers are also present, but owing to their poor preservation they are identifiable only up to generic level. The commonly occurring benthic foraminifers are represented by Amphistegina sp. ( Fig. 5G, H), Cycloclypeus sp. ( Fig. 5I, J), Heterostegina sp. ( Figs 5K; 6A, B), unidentified nummulitids ( Fig. 6C), Operculina sp. ( Fig. 6D), Quinqueloculina sp. ( Fig. 6E), Triloculina sp. ( Fig. 6F), Biloculina sp. ( Fig. 6G). The planktonic foraminifers are indeed difficult to identify in thin sections, however, on the basis of some distinguishing features some of them are identifiable up to genus level, namely Globigerinoides sp. ( Fig. 6 H-J), and Dentoglobigerina sp. ( Fig. 6K, L).

FACIES AND SEDIMENTOLOGY

The different types of facies along with sedimentological features recognized in each outcrop are described as follows: