Marine Micropaleontology: Barbara Lidz
Emeritus Geologist, U.S. Geological Survey (USGS)
Barbara Lidz is a renowned micropaleontologist whose work has spanned the subtropical Caribbean-Florida region, focusing on the Cenozoic era. By studying the microscopic shells of foraminifera, she has unlocked secrets of the Ice Age, tectonic uplift, and the “smoking guns” of sediment transport.
The Full Interview: Deciphering the Geologic Record
When did you first become interested in your field?
As an undergraduate at the University of Southern California, I was taking miscellaneous graduate courses in geology. One of them was foraminiferal micropaleontology, taught by one of the best in the field then, Dr. Orville Bandy. I was captivated. Shortly thereafter, I moved to Miami where Dr. Cesare Emiliani at the Rosenstiel School of Marine and Atmospheric Science would become my mentor. Measuring oxygen-isotope concentrations in planktic foraminifera (forams) from deep-sea cores, Cesare developed the paleotemperature curve that revolutionized understanding of Ice Age oceanic temperatures by showing climatic and glacial/interglacial periodicities. It was he who further inspired and instilled a sense of excitement for the potential and many multidisciplinary ramifications that planktic forams can hold for deciphering the geologic record.
His mentoring and several background factors together stimulated my proficiency in the field. An outdoors person, I’ve had a lifelong love of geology, natural processes, and old and small things. I’d always had a good eye for shapes and was quick to complete jigsaw puzzles, and I’d had a relatively strong background in languages (4 years each of high school Latin and French, 2 years each of college French and Italian). Planktic forams with their myriad shapes and Latin names were a natural attraction. Because of the puzzle-and-language connection, it was easy to learn the different species and their names using published scanning electron microscope pictures as guides. I soon mastered how to interpret and reconstruct the geologic history of the area where the microfossils were collected, whether from deep-sea cores or from onshore outcrops of marine sediments. My area of expertise is the subtropical Caribbean-Florida region and includes all Cenozoic pelagic species from the end of the Cretaceous ~66.5 million years ago to the present. Though I’ve not worked with Cretaceous sediments, I can recognize Cretaceous planktic forams as well.
What are microfossils and why are they important?
Microfossils are the microscopic fossilized remains of marine or terrestrial organisms. There are many kinds of microfossils ranging from terrestrial pollen spores to conodonts (toothlike fossil elements in form but not in function, produced by marine worms) to shells of calcareous marine organisms (for example, pelecypods, ostracods, mollusks, and foraminifera). Nannofossils are extremely small calcareous marine microfossils not visible to the naked eye and include radiolarians and diatoms. A micropaleontologist usually specializes in a single group but is able to recognize organisms from other groups. In general, microfossils are important tools used to determine various aspects of the geologic or climatic record. Some living benthic forams are also used as a measure of pollution.
Foraminifera Forams are protozoans with external chambered calcareous shells. There are two types, planktic and benthic; both are distributed globally.
- Planktic forams are pelagic organisms that float in the open oceans. They live at various depths and construct their shells from elements dissolved in seawater. Species vary depending upon latitude and water temperature. An abundance of fossil pelagic species in deep-sea sediment indicates the overlying water was warm and nutrient-rich. Planktic species are relatively short-lived (a few million to tens of millions of years old) and are used to determine precise geologic age of the sediment or rock in which they are found, called host rock. Planktic forams have many diverse shapes and reveal more than benthic forams about geologic time, processes, past environments and climate.
- Benthic forams are bottom dwellers. They live on or within the top layers of sediment from the shoreline to abyssal depths. Many species are similar in shape. Most benthic forams also build their shells from elements dissolved in seawater, but some species use sand grains from their surroundings to construct their shells. Benthic species are extremely long ranging and are not used for precise age dating. Instead, assemblages consisting of specific species are used to indicate the general setting that existed when the organisms were alive (estuary, inner shelf, outer shelf, slope, abyss, etc.), which implies a general water depth. In a tectonically stable area, general water depth has implications for past position of sea level.
What exactly does a micropaleontologist do?
Basically, a micropaleontologist uses microfossils along with other types of data from the sample site (for instance, type of host rock or sediment, geographic setting, and seismic-survey data) to determine various characteristics of a sample or group of samples. The characteristics are then placed into the context of local geologic history—what happened at the site and when did it happen. Once ‘what’ and ‘when’ are resolved, the data can often be extrapolated into a larger picture—the regional or global record. For example, pollen spores from sediment cores are used to trace the presence and location of terrestrial plants and the movement of tree lines with changing climate through time.
Conodonts become darker with age and thermal pressure through time and are used in the oil and gas industry as indicators of conditions favorable for hydrocarbon formation. When conodonts recovered from a certain subsurface depth within an exploratory well have attained a specific dark color, they verify that organics at that depth have reached the maturation stage to form oil and gas. Like all micropaleontologists, a foraminiferal micropaleontologist uses a binocular microscope and, to a lesser extent, a scanning electron microscope to identify species.
Barbara provided a specific example of her work on St. Croix: “The elongate island consists of volcanic rock at both ends separated by limestone that accreted as pelagic sediments in an ancient seaway before the island was tectonically uplifted. In a series of studies to date the pelagic rocks and sediments, by chance I came across a specific hillside outcrop excavated behind a private residence. The outcrop contained a coarse-grained turbidite encased in massive chalky deep-water limestone. Within the 0.5-m-thick turbidite was a discrete mudball consisting of homogenous clay (visible dimensions 15 x 25 cm). The mudball contained 39 species of reworked planktic Eocene, Oligocene and early Miocene forams; 23 species had not previously been described from the island. These fossils had lived between ~57.8 and 15.2 million years ago. Until the mudball was found, the oldest pelagic sediments identified on the island were early Miocene (~23.0 million years old). To this day, the mudball forams remain the only record known of earlier pelagic sedimentation on St. Croix. The mudball had expanded the timeframe and depositional record of island-history knowledge by 35 million years!”
What is foraminiferal biostratigraphy?
Stratigraphy is the study of the various sedimentary or rock layers (strata) that make up a geologic feature. Such layers are often observed in road cuts. A technique called seismic surveying is used to show subsurface stratigraphy. Biostratigraphy combines the use of seismic and microfossil data to ascertain age of the strata and type of setting in which the strata accumulated.
Biostratigraphy using planktic forams is widely applied in the oil and gas industry. Rock fragments containing microfossils recovered from various intervals during drilling of a well are identified, fossil ages are determined, and the depth interval of the sample is compared to seismic-reflection profiles and other types of data taken in the area. The drilling continues until the fossils indicate that rock layers of a certain age that are known from other wells to contain hydrocarbons are reached.
Biostratigraphy is also used with seismic stratigraphy to determine ages of sediments at the margins of shallow carbonate platforms, important to understanding how carbonate platforms expand and how long it takes. In tectonically active zones, biostratigraphy is used to tell the age of pelagic sediments now above sea level. Knowing the age of uplifted pelagic sediments can help determine when plate-edge tectonics were active in the area or when volcanoes erupted. If there are deep-sea marine sediments onshore in a tectonically stable area, age of the sediments as determined by the microfossils will denote a time when sea level was higher than today.
What other things can foraminifera tell us?
Living planktic foraminifera deposit in their shells different concentrations of carbon and oxygen isotopes and other minerals dissolved in seawater depending on latitude and water temperature. Rapid changes in carbon-isotope concentrations in fossil forams have been linked to sudden releases of frozen methane from the ocean floor, events that are thought to have caused rapid global warming in the past. Variations in oxygen-isotope concentrations in fossil planktic taxa have established ocean temperature and temperature variations through time. Planktic forams can produce abnormally developed shells usually as a response to environmental stress or cold water temperatures.
Benthic foram assemblages are becoming increasingly important as we learn more about the different assemblages that inhabit pristine waters, marginally polluted waters, or survive in heavily polluted areas. Some species contain living algae when alive, as do species of the stony or reef-building corals. Both types of organisms require similar clear ambient oceanic conditions. Stress symptoms that are observed in algae bearing foram populations are comparable to those reported for corals and coral reef communities. Like the planktic taxa, benthic taxa also produce abnormal shells under stress and because sediment is a sink for heavy metals, they incorporate the stored metals into their shells as they grow.
Can you give a couple of examples of what you are researching? The microfossil record in general as a tool for evaluating and monitoring environmental disturbances, both natural and manmade, has proven applications to environmental assessment and remediation. Present studies focus on analyzing geochemical, sedimentological and biological aspects of sediments in Biscayne Bay, Florida, with three objectives:
- Characterize pollution types, dispersal, and concentrations in the bay.
- Compare heavy-metal contaminants with distribution of benthic foram assemblages and abnormalities in foram shells.
- Determine sediment composition through thin-section analyses.
Biscayne Bay backs the largest coral reef in the continental United States and is a vital link to reef vitality. The synergistic effect of natural and human factors has led to the rapid demise of the bay/reef ecosystem.
What has been the most challenging/difficult part of your job?
The most challenging—but exciting—part of my job was dating two long particularly complex carbonate cores recovered from the western margin of the Great Bahama Bank. At onset, the challenge was that the cores were taken in shallow-water sediments that would normally preclude presence of deep-water forams. But they were there, in abundance!
Toward the end of the study, I began finding abundant secondarily deposited (imported or reworked) very old taxa that ranged from ~66.5 to 15.2 million years and identified 82 species. This discovery led to a new direction of research: determining their source. I needed to account for pelagic deposition over 51 million years at the source. The only area in the Caribbean that met all criteria for the source was located somewhere along the tectonically unstable northern coast of Cuba, some 400 to 700 km away. The link between the bank and Cuba implies that the bank margin has advanced seaward primarily but not solely through progradation. Sediments from Cuba had to have been rafted along with the microfossils and therefore have helped build the margin.
Where do you see the future of this field?
In this day of environmental awareness, application of benthic forams as indicators of marine pollution is probably the only viable field of micropaleontology other than palynology (the study of pollen) that may be perceived by some managers as useful. On the other hand, the world is one’s oyster if a micropaleontologist is allowed to decipher parts of the geologic record based on pure science. The more we understand about past climate and the causes that led to changes, the better we can predict what may trigger climate and sea-level change in the future.
What is the best way to prepare for a career in micropaleontology?
That’s a tough one to answer. I guess the most important qualities a person would need are an inquisitive mind, an innate curiosity, enduring patience at the microscope, and the intuition and ability to recognize the numerous and diverse types of information that can be derived from microfossil data. The person should also be able to think independently. Regardless of specialty, a micropaleonologist is a forensic geologist who applies scientific knowledge and logical reasoning to interpret and reconstruct events of the past.
Modern 2026 Perspective
In 2026, the work Barbara Lidz pioneered in Biscayne Bay is more critical than ever. As sea levels rise and ocean acidification impacts coral reefs, “forensic geology” using foraminifera provides the baseline data needed for restoration efforts.