"Rock of the Month # 226, posted for April 2020" ---

Forams are protozoans (Barnes, 1968). They belong to a group of protozoans known as the Sarcodina, which include amoebae, forams, heliozoans and radiolaria (the latter also of geologic note, being largely planktonic and having skeletons composed of silica, or even of strontium sulphate). The shells of forams can be multi-chambered, with apertures linking chambers, which often grow in a spiral manner, the whole being infilled by protoplasm. While many of these relatives of the amoeba are microscopic, they may reach as much as 5 cm in the case of some Nummulites ("coin stones"). The majority are benthic (bottom-dwelling) but some are planktonic, like Globigerina and Orbulina, and float in the sea. They are represented in palaeontology textbooks and collectors' guides (e.g., Woods, 1946; Morley Davies, 1961; Turek et al., 1988; Stinchcombe, 2012), as well as in dedicated monographs (e.g., Loeblich and Tappan, 1964).

Although easily overlooked, forams appeared in the Cambrian, and have been an important part of marine sedimentary sequences from the Carboniferous period to the present, and especially in Cretaceous and Eocene times. They are of worldwide extent. Forams persist to this day, found around, e.g., the coasts of Ireland (Praeger, 1937, pp.342-344). The various kinds range within the limits prescribed for their species by controlling factors such as temperature, depth and salinity. Forams may be so abundant as to assume rock-forming proportions in some sediments. Their contribution is reviewed in petrographic reference works such as Scholle and Ulmer-Scholle (2003, pp.33-50, with examples from Malta to Mexico, and Greenland to New Zealand).

Forams are sufficently varied and widespread that they are useful to geologists for the information they can yield on a) the age of the host rocks (Ogg et al., 2008), b) correlation between outcrops, and c) the paleoecological setting in which they lived. The study of forams plays a part in subdividing large thicknesses of similar rocks, such as the limestones of the Carboniferous of Ireland (Sevastopulo and Wyse Jackson, 2001) As a special example, approaching the Cretaceous-Tertiary boundary (circa 66 Ma), Princeton palaeontologist Gerta Keller, a leading critic of the Alvarez asteroid impact hypothesis, sees a gradual lead-up to the mass extinction, in microfossils such as foraminifera, and also a chemical signature that could be related to the massive volcanic eruption in the Deccan Traps of India. The implication is that, while the end-Cretaceous asteroid impact off the coast of Mexico's Yucatan peninsula may finally have killed off the dinosaurs and other life forms, they may have been in decline, and facing other challenges, for some time before the impact (Bosker, 2018). An example of this work (Keller et al., 2011) details the decline and extinction of planktonic forams, correlating faunal changes to the progression of the gigantic, episodic yet geologically rapid extrusion of over 1 million km³ of lava to form the Deccan volcanic province formed (today, the province covers an area of 512,000 km²).

Gerth (1935) suggested that the larger foraminifera may help solve problems in correlation of Tertiary strata (which are not resolved by the confusing diversity of other fossils such as the bivalves). Gerth reviewed the Tertiary of Java, with brief comparisons with the literature for Borneo and the West Indies. Camerina occurs not only in Java, but also, for example, in Curacao and Cuba. In Java, fossil localities record species of Camerina from the Paleocene to the upper Oligocene.

Fig. 2: The Camerina sample and label at the Museum of CUGB.

The Cretaceous-Eocene fauna is diverse and locally abundant. In Egypt, forams are prominent in the strata along the Nile valley (Alcosser et al., 1991, p.164). Cretaceous and lower Tertiary rocks underlie a 90,000 km² area of Egypt. Correlation is aided by forams such as species of Globigerina (Hermina, 1990).

Forams are especially widespread and well-studied across the Indian subcontinent, and, indeed, along the ancient seaway of the Tethys, across south and west Asia, from Thailand to Turkey (Okay et al., 2001), as a quick search of the MINLIB database affirms. The significance of forams was recognized early in the development of geological sciences in the region, including what are today northern India, Pakistan and Afghanistan (Medlicott and Blanford, 1893). Detailed research continues to this day (e.g., Mathur, 2010; Saraswati et al., 2012). Nummulites as large as 19 mm are reported from Kachchh in Gujarat (Sengupta, 2000).

In addition to serving as time markers, foram species are flags of climatic and environmental conditions. The Middle Eocene Climatic Optimum (MECO) is a long-lasting warming event dated at circa 40 Ma. The MECO event occurs at the Lutetian- Bartonian boundary, and at its maximum, sea surface and deep water seawater temperatures rose circa 5-6°C over a peak lasting >100 ky. Ongoing research at CUGB (Kamran et al., 2020) examines Eocene shallow-marine strata of the Kohat Formation along the Indus Highway section in Pakistan. This study aims to place MECO within a shallow marine carbonate sequence, to document the response and diversity pattern of the LBF (large benthic forams), and to reconstruct the depositional setting based on LBF. The Kohat section is especially rich in LBF such as Nummulites, Alveolina, Assilina, orthophragminids, Lockhartia and Orbitolites, plus a few planktonic and small benthic forams. Foram extinctions at the end of the middle Eocene are referred to as the LFT (large foraminifera turnover) event.

In North America and the Caribbean, detailed studies are available on foram habitat, as in the Bahamas (Cloud, 1962) and Cuba (Thiadens, 1937). In Saskatchewan, the lower Cretaceous strata include the Haplophragmoides gigas marine microfauna, which is dominated by foraminifera (Fraser et al., 1935). These microfossil assemblages extend the known boundaries of ancient seas, in this case (with later research: Koke and Stelck, 1985) across Alberta and beyond the Peace River Arch, to the Hudson Hope area of British Columbia.

References (n=24)

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Bosker,B (2018) What really killed the dinosaurs? Atlantic 322 no.2, 44-55, September.

Cloud,PE (1962) Environment of calcium carbonate deposition west of Andros Island, Bahamas. USGS Prof.Pap. 350, 138pp. plus 10 plates.

Fraser,FJ, McLearn,FH, Russell,LS, Warren,PS and Wickenden,RTD (1935) Geology of Southern Saskatchewan. GSC Memoir 176, 137pp. plus map folder with map 267A plus sections.

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Hermina,M (1990) The surroundings of Kharga, Dakhla and Farafra oases. In `The Geology of Egypt' (Said,R editor), A.A.Balkema, Rotterdam, 734pp., 259-292.

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Koke,KR and Stelck,CR (1985) Foraminifera of a Joli Fou Shale equivalent in the Lower Cretaceous (Albian) Hasler Formation, northeastern British Columbia. Can.J.Earth Sci. 22, 1299-1313.

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