Moncharmontia compressa ( De Castro, 1966 )

SIMMONS, MICHAEL & BIDGOOD, MICHAEL, 2023, “ Larger ” Benthic Foraminifera Of The Cenomanian. A Review Of The Identity And The Stratigraphic And Palaeogeographic Distribution Of Non-Fusiform Planispiral (Or Near-Planispiral) Forms, Acta Palaeontologica Romaniae 19 (2), pp. 39-169 : 77-79

Moncharmontia compressa ( De Castro, 1966)

Reference Illustration & Description

[Note: also misspelled as Montcharmontia in several publications]

Tasli et al. (2006), Fig. 7 (J-K) for illustration.

The original comprehensive description of the genus and the two species ( M. apenninica and M. compressa ) by De Castro (1966) only states two differences between the species by referring to M. compressa as having heartshaped chambers in axial view and only one row of apertural openings compared with M. apenninica . However, the test is also clearly more laterally compressed than M. apenninica and has a more subrounded to subangular periphery.

These and other differences between M. apenninica and M. compressa are tabulated and illustrated by Tešović et al. (2001) and can be summarised by M. compressa being smaller (with an equatorial diameter of <0.34mm), more compressed umbilically and with a smaller proloculus (<0.08mm) compared with M. apenninica . Test wall thickness is also less in M. compressa (<0.012mm). M. apenninica has a well-rounded periphery (some specimens can be almost subglobular in overall shape) compared with the somewhat more subangular periphery (broad lenticular and more obviously biumbilicate) of M. compressa . Both species have similar number of chambers in the first (7-8) and second whorls (9-10). See the Species Key Chart (Appendix) for diagnostic and other characteristics.

The records of Fleuryana adriatica from the Turonian of SW Turkey by Solak et al. (2020) are virtually indistinguishable from those of M. compressa (De Castro) . The only taxonomic difference between the two is that F. adriatica has a single apertural slit whereas M. compressa has a single row of apertural openings. This may be extremely difficult to see in thin section views. F. adriatica also ranges to the Maastrichtian and more work needs to be done to establish the degree of separation of these two taxa. Koch et al. (1998) have provided more compelling illustrations of F. adriatica from Turonian strata.

Stratigraphic Distribution

Early Cenomanian? – Maastrichtian.

Most plausible and definite illustrated records of M. compressa are confined to post-Cenomanian strata, ranging up into the Maastrichtian ( Sinanoğlu, 2021, from Turkey). An illustrated form attributed to M. apenninica was recorded from the early Cenomanian of Syria ( Ghanem et al., 2012) but the illustration has characteristics closer to M. compressa . Solak et al. (2017) illustrate a form they describe as “ Moncharmontia (?) sp.” from the mid- late Cenomanian of the Turkish Taurides. From the material illustrated this might be M. compressa or B. bentori .

Unillustrated records from the Cenomanian include from the Natih Formation of Oman by Piuz & Meister (2013) and Piuz et al. (2014). Berthou & Lauverjat (1979) record a form they term “ Moncharmontia (?) cf. apenninica compressa ” from the late Albian of Portugal. However, they provide no illustration.

Cenomanian Paleogeographic Distribution

Probably Eastern Neotethys.

Records of M. compressa from Cenomanian strata are all uncertain. The species is more widely and confidently reported from younger stratigraphy.

Cenomanian “cyclamminids”

As throughout much of the Jurassic and Cretaceous, Cenomanian shallow-water carbonate platform sedimentary rocks (including marls) often contain relatively large, planispiral agglutinating foraminifera with alveolar walls. These are included in genera such as Pseudocyclammina Yabe & Hanzawa , Buccicrenata Loeblich & Tappan , and Hemicyclammina Maync , and can informally be termed “cyclamminids”, although their higher- level classification continues to be debated (e.g., Mikhalevich 2004a & b; Kaminski, 2014; Albrich et al., 2015 and see above). Despite records of such taxa being known for several decades, there remains uncertainty on the precise identity and taxonomy of some of the genera involved, and a thorough taxonomic revision is required that is outside the scope of this primarily biostratigraphic review.

The genus Hemicyclammina has recently been revised by Simmons & Bidgood (2022). That review is summarised herein, with a small amount of additional information that has come to light subsequently. More problematic are Buccicrenata and Pseudocyclammina and the species assigned to these genera. Further complications are introduced in that it is not always possible to see key features such as the nature of the aperture in random thin-sections, with even the presence of an alveolar wall sometimes being doubtful, especially in coarsely agglutinating specimens. Certainly, there are occurrences of Pseudocyclammina and Buccicrenata reported in the literature that would be better assigned to the non-alveolar walled genera Ammobaculites Cushman or Lituola Lamarck. On the other hand, disaggregated, three-dimensional specimens will not show critical internal features.

Figures

Fig. 7 Representative illustrations of Daxia cenomana: a Equatorial section, Arnaud-Vanneau & Prestat in Schroeder & Neumann (1985, pl. 1, fig. 2, France); b Axial section, Arnaud-Vanneau & Prestat in Schroeder & Neumann (1985, pl. 1, fig.7, France).