Fossilized-Brood Chambers in Nummulites vascus from Libya

Spherical calcite chamber-like objects of almost identical size have been found in a few tests of Nummulites vascus. These Nummulites constitute the dominant benthic foraminifera assembly among the reported foraminiferal assemblage of the Abraq Formation (Late Oligocene) at the Daryanah-Al Abyar Roadcut in Northeast Libya. These structures are identified as brood chambers or cysts formed during reproduction and retained within the mother test, where the embryos was hosted during life. The possibility of a diagenetic origin to these cysts is excluded due to the hollow-nature of these objects which supports a biotic origin rather than diagenesis. Similarly, a symbiotic relationship with microalga is also excluded due to the lack of any cellular microstructure. The existence of calcitic brood chambers in Nummulites is hitherto unknown. Importantly this sample appears to be the first example of a calcified brood pouch fossil or ‘cyst’ in Nummulites (23– 28 Ma) research.


Introduction
The outcrop from which the samples were collected from is located in the northeastern part of Libya, in an area known as Al Jabal Al Akhdar.This section is exposed on both sides of a road-cut located about 40km east of Benghazi city leading from the Daryanah (Tansolukh check point) to Al Abyar village (Figure 1).The road-cut exposes the following rock units the Algal Limestone of Al Bayda Formation, the Al Abraq Formation, the Al Faidiyah Formation and the Benghazi Formation with disconformity surfaces separating them from each other (Figure 2); and a more stratigraphy is noted by (Ewerfalli et al., 2000;and El-Hawat and Abdulsamad, 2004).Nummulites vascus occurs in the lower part of the Upper Oligocene sequence in a bioclastic, marly limestone bed (Figure 3).Three Nummulites tests are documented in this study, quoted (NG1, NG2 and NG3) and are deposited at University of Benghazi, Faculty of Science, Department of Earth Sciences, Benghazi-Libya.

Foraminiferal Content
The section can be subdivided into three foraminiferal assemblages (I-III) from oldest to youngest:

Assemblage III (Nummulitid bed)
Is dominated by nummulitids, including Nummulites vascus, N. fichtelli and Operculina complanata (Figure 3).The Dominance of the primary zonal marker Nummulites fichtelli, in association with N. vascus is strongly indicative of the Oligocene and is assigned to the Nummulites fichtelli Zone of Racey (1995).This zone is well known in the Al Jabal al akhdar area in Oligocene deposits including the Algal limestone of AL Bayda Formation and Al Abraq Formation.It is important to note that the N. vascus has been reported in Oman with a range from Late Eocene-Early Oligocene (Racey, 1995).However, the absence of N. fabianii and the presence of the planktic Globigerina ciperoensis ciperoensis and Cassigerinella chipolensis restrict the age of N. vascus at this section to Late Oligocene and the Globigerina ciperoensis ciperoensis Zone of Bolli and Saunders (1985).
Faculty of Marine Resources, Alasmarya Islamic University, Libya.

Results and Discussion
Brood chambers with crowded embryos occur in chamberlets of living Sorites orbiculus are illustrated by (Kloos, 1984;and Reiss and Hottinger, 1984) from Gulf of Aqaba (Figure 4a-b).Whereas Hottinger (2006) illustrated few examples of last chamber filled with hatchlings in Neorotalia sp. from Spanish Pyrenees, Early Eocene.In addition, Orbitolites sp.exhibits the discrepancy between embryo size and brood chamberlet volumes in material from earliest Eocene, Farafrah Oasis, Egypt.The present study shows three specimens Nummulites vascus size 'brood chambers' for housing the offspring before hatching.Figure (4c) shows ten brood chambers of somewhat identical size; the shape variations being the result of preservation.The last chamber is free and collapsed.They are identical in size (radius 0.25 mm), elliptical in shape (with longest axis within the range of 0.30-40 mm).By comparison with recent examples seen in the illustrated chamberlets of the living Sorites orbiculus (Reiss and Hottinger, 1984) from Gulf of Aqaba (Figures 4a, b In Conclusion, the Al Abraq Formation (Late Oligocene) in the Tansolukh-Al Abyar section has been logged and samples analyzed; which exhibit a wealth of foraminifera from the lower "Bioclastic marly limestone" (Figures 2 and 3).A Late Oligocene age has been assigned to this marly rock sequence now correlated with the Nummulites fichtelli Zone of Racey, (1995) and the equivalent Globigerina ciperoensis Zone of Bolli and Saunders (1985).Hitherto no Nummulites vascus specimens with brood chambers have been documented from the Oligocene sediments of Libya.This phenomenon is also considered unique in fossil Nummulites, although previous comparative studies only focused on living foraminifers and some fossil foraminifera (Hottinger, 2006).The shelf faunal mixing of the planktic and shallow benthic nummulitids in the recorded section is most likely manifested by bottom current and/or the lateral transport of empty tests.

Figure 2 .
Figure 2. The Daryanah -Al Abyar roadcut section, showing the stratigraphical position of the Al Abraq Formation.
Figure 3. Distribution chart of the foraminifers in the studied locality.(*indicates the horizon with in which the Nummulites with brood chambers are recorded) ), it is clearly representative of brood chambers of the agamont generation.During the early examination of this phenomenon, the structures were considered to be of diagenetic origin but closer examination and consultation with colleagues via the ResearchGate website; including Dr. George Stanley University of Montana in Montana State-USA, Dr. Katalin Baldi from Eötvös Loránd University in Budapest-Hungary and Dr. André Klicpera from Leibniz Center for Tropical Marine Ecology in Bremen-Germany; who are much appreciated for their help in confirming the identification and the valuable discussions via the SEM Image herein.