Archive for August 18th, 2013

Wooster’s Fossils of the Week: A foraminiferal ooze from the Pleistocene of Italy

August 18th, 2013

YCM forams 1On a recent field trip to Sicily, our paleontological party visited outcrops at Cala Sant’Antonino on the western side of the Milazzo Peninsula in the northwestern part of the island. We saw there an Early Pleistocene sedimentary unit informally called the “Yellow Calcareous Marls”. With a handlens you would see a close view of the rock like the image above. It consists almost entirely of tiny hollow white spheres with occasional dark flecks. In the lab back home these little calcitic balls were revealed to be tests (skeletons) of foraminiferans known as Globorotalia inflata (d’Orbigny, 1839). This is a classic example of a biogenic sediment called foraminiferal ooze, samples of which are now in Wooster’s paleontological and sedimentological teaching collections.
Foram-Marl-060913This is the outcrop of the “Yellow Calcareous Marls” at Cala Sant’Antonino from which the above samples were collected. The rock is very soft and powdery to the touch.

YCM forams 2In this closer view of the rock the individual foraminiferal tests are more apparent. Near the center is one example showing the connected bulbous chambers (making it multilocular) and the slit-like aperture between them. These tests are slightly recrystallized, giving them a sugary look. The dark bits are sand-sized volcaniclastic grains derived from early eruptions of the Mount Etna complex.

Globorotalia_inflataThese are modern examples of Globorotalia inflata. (The scale bars are 0.1 mm.) The bumpy surface texture, bulbous chambers and distinctive aperture make identification of the fossil examples fairly easy. The images were taken by Bruce Hayward.

Globorotalia inflata is a long-lived planktonic species, meaning it floats about near the top of the water column throughout the oceans. In life these single-celled organisms extend thin strands of material (pseudopodia) into the water around them to collect organic material and the occasional diatom or radiolarian for nutrition. They live in populations with billions of individuals, so under the right conditions their tests can accumulate on the seafloor in numbers so vast they form thick deposits, our foraminiferal oozes. Our particular ooze in this story formed in relatively deep (epibathyal), cool waters during one of the early glacial intervals. This foraminiferan turns out to be a critical guide to the age of the unit as well as its paleoenvironmental context.

References:

Fois, E. 1990. Stratigraphy and palaeogeography of the Capo Milazzo area (NE Sicily, Italy): clues to the evolution of the southern margin of the Tyrrhenian Basin during the Neogene. Palaeogeography, Palaeoclimatology, Palaeoecology 78: 87–108.

Sciuto, F. 2012. Bythocythere solisdeus n. sp. and Cytheropteron eleonorae n. sp. (Crustacea, Ostracoda) from the Early Pleistocene bathyal sediments of Cape Milazzo (NE, Sicily). Geosciences 2012 2: 147-156.