The team’s most significant technical achievement is the first foraminiferal zonation ever produced for the London Clay Formation. Earlier researchers, working as far back as the 1880s, had despaired of ever building such a scheme. Sherborn and Chapman noted in 1886 that regional variability among the shells was so pronounced that the word species should often be replaced by variety, and Bowen concluded in 1954 that no zonal scheme could be advanced for the formation based on foraminifera. Hart and his colleagues overturned that pessimism by carefully recording the first and last appearances of key taxa through the Whitecliff Bay and Alum Bay successions, defining eight zones they call Hampshire Basin Benthic zones, or HBB 1 to 8. Each zone is anchored on easily identified species such as Lobatula lobatula, Eilohedra vitrea and Cibicidoides alleni, and the scheme can be correlated between the two Isle of Wight sections using a distinctive planktonic datum first recognised by C. A. Wright in 1972.

Sampling the London Clay is far from straightforward. The cliffs are unstable, riddled with mudflows that tend to recur in the same places year after year, and the steeply dipping beds are subject to modern weathering that can selectively destroy fossils. The researchers found that samples taken from the foreshore, after storms had stripped away the modern beach, often yielded better preserved and more complete assemblages than cliff samples from the same horizons. They processed roughly two-kilogram samples using the white spirit method, which breaks down claystones and siltstones completely without damaging the microfossils, then washed the residues on a 63-micrometre sieve and examined four separate size fractions under the microscope. Erosion surfaces overlain by mudstone clasts and phosphatic nodules revealed hiatuses in the succession, suggesting that the London Clay of Whitecliff Bay and Alum Bay may be incomplete, a feature the authors suspect is the norm but is rarely described.

With the zonation in place, the team turned to palaeoecology. Using morphogroup analysis, planktic to benthic ratios, agglutinated to calcareous ratios, dominance and diversity indices, and Murray’s classic triangular plots, they reconstructed water depths through the London Clay. Their interpretation ranges from hyposaline, possibly river-mouth conditions to an open shelf environment between roughly 5 and 105 metres deep. Crucially, the maximum water depth in both Whitecliff Bay and Alum Bay falls within the interval of the Early Eocene Climatic Optimum, a prolonged hyperthermal spanning approximately 54 to 48 million years ago. When the two depth curves are superimposed, they overlap closely, and the planktonic datum coincides with the inferred maximum flooding in both sections. The authors suggest this sea level rise and fall within the EECO might represent a glacio-eustatic response to the warming, an intriguing possibility given that the event occurred in a hothouse world.

That interpretation, however, comes with caveats the authors are careful to spell out. The PETM, which occurred close in time to the EECO, is widely thought to have taken place in an ice-free world, making ice-driven sea level change difficult to invoke for the early Eocene. Modern calculations of ocean thermal expansion, based on NASA and NOAA data, suggest that warming of 0.6 to 1.0 degrees Celsius produces only a few centimetres of sea level rise, far too little to be detected in compacted Eocene mudstones. Alternative mechanisms remain on the table, including tectonic movements on the Sandown Pericline, as proposed by Stamp in 1921, or dynamic topography driven by the Iceland mantle plume, which Gale and Lovell have argued influenced sea level in the Anglo-Paris Basin into the Lutetian. The absence of any significant facies change accompanying the early Eocene depth maximum argues against a strong tectonic control, leaving the question open.

The second half of the story belongs to larger benthic foraminifera, the giants of the micropalaeontological world. These complex, symbiont-bearing shells, including the discoidal nummulitids and the cigar-shaped, porcelain-white alveolinids, are normally restricted to tropical and subtropical shallow carbonate shelves. Finding them in the clay-rich mid-Eocene sediments of southern England, at relatively northern palaeolatitudes, is highly unusual and points to a substantial warming episode. In the Whitecliff Bay succession, larger foraminifera appear in the Earnley Sand Formation and continue into the Barton Clay Formation, an interval embracing the uppermost Lutetian and lowermost Bartonian that straddles the Late Lutetian Thermal Event and the Middle Eocene Climatic Optimum, a short-lived warming of roughly 500,000 years duration around 40 million years ago.

The alveolinids are the star witnesses. Known in England from only three localities, including Fisher’s Beds 21 and 22 at Selsey Bill in Sussex and the uppermost Selsey Sand Formation in Whitecliff Bay, these fusiform shells also occur in pale limestones dredged from the sea floor of the English Channel. Dennis Curry collected such limestones from the R.V. Sarsia in 1955, and samples held by the British Geological Survey were re-examined for this study, with several confirmed to contain visible alveolinids. A vibro-core drilled between Jersey and the Cotentin Peninsula in 2009 recovered Eocene sediments with worn but unmistakable larger foraminifera, close to in situ mid-Eocene deposits near Valognes in Normandy. Taken together, these occurrences mark the northernmost known limit of Alveolina in northwestern Europe and sketch a picture of a warm, shallow sea covering much of the Channel region during the Lutetian.

The authors argue that this warm-water assemblage responds to the Late Lutetian Thermal Event, while the extension of the ranges of nummulitid species such as Nummulites prestwichianus and N. rectus into the lowermost Barton Clay Formation suggests that warm conditions persisted into the MECO, whose isotope signal lies low in that formation. Following Dawber and colleagues, they suggest both events may record a slight glacio-eustatic rise, and the presence of carbonate sediments resting directly on the basement of the Cotentin Peninsula supports a transgressive event in a marginal setting. Unlike the early Eocene case, mid-Eocene glaciation is more plausible, since ice-rafted debris has been reported from marine cores near Greenland back to around 44 million years ago.

What makes this study remarkable is its blend of Victorian field geology and modern micropalaeontological technique. The Whitecliff Bay succession was first described by Prestwich in 1846, and the larger foraminifera were figured by Carpenter and Dixon in 1850, yet the London Clay had never yielded a workable zonation until now. The paper is also a memorial to two giants of British micropalaeontology, John Murray, whose 1974 monograph with Chris Wright remains foundational, and Mark Alex-Sanders, whose doctoral-level work on the London Clay foraminifera underpins the new zonation and who died before his research could be published. The eight HBB zones, though of local application only, give the Hampshire Basin a biostratigraphical framework comparable to those long established elsewhere in the Anglo-Paris Basin.

For anyone wondering why shells smaller than a grain of sand matter, the answer lies in the deep-time perspective they provide. The Eocene hyperthermals are the closest analogues in the geological record to the greenhouse warming now under way, and understanding how sea level, water depth and marine ecosystems responded to those events helps calibrate expectations for the future. That a walk along an English beach at low tide, sampling vertically dipping clays once drowned under a warm shelf sea, can still yield new insights into global climate dynamics more than 250 years after the first fossil collections from these cliffs is a testament to the enduring power of patient, meticulous field science.

Subject of Research: Eocene foraminiferal biostratigraphy and palaeoecology of the Hampshire Basin, UK, in relation to Eocene hyperthermal events

Article Title: Can the distribution of foraminifera locate the Early Eocene Climatic Optimum (EECO) and Middle Eocene Climatic Optimum (MECO) events in the Eocene succession of the Isle of Wight (UK)?

Article References: Hart, M. B., Alex-Sanders, M. E. A., & Smart, C. W. (2026). Can the distribution of foraminifera locate the Early Eocene Climatic Optimum (EECO) and Middle Eocene Climatic Optimum (MECO) events in the Eocene succession of the Isle of Wight (UK)?. Journal of Micropalaeontology, 45(1), 315-334. https://doi.org/10.5194/jm-45-315-2026

Image Credits: AI Generated

DOI: 10.5194/jm-45-315-2026

Keywords: foraminifera, Isle of Wight, Eocene, EECO, MECO, London Clay Formation, hyperthermal events, palaeoecology, biostratigraphy, sea level change, larger benthic foraminifera, Hampshire Basin

The stakes of this work are considerable. Today, humanity is pumping carbon dioxide into the atmosphere at a rate of roughly 10 petagrams of carbon per year, a pace that scientists say is unprecedented across the last 66 million years. The only comparable episode in the geological record is the late Paleocene–early Eocene, when atmospheric carbon dioxide climbed to levels even higher than today’s, albeit roughly nine to ten times more slowly, at about 1.1 petagrams of carbon per year. During the Paleocene–Eocene Thermal Maximum, or PETM, deep ocean and high-latitude surface temperatures rose by 6 to 8 degrees Celsius, triggering widespread extinction of benthic foraminifera and profound ecological disruption in both marine and terrestrial ecosystems. Understanding how that ancient greenhouse world responded is one of the best natural experiments available for anticipating our own future.

The new study focuses on bulk organic carbon isotopes, a technique that measures the ratio of the light isotope carbon-12 to the heavier carbon-13 in the organic matter preserved within sediments. When enormous quantities of carbon-12-enriched carbon, whether from volcanic methane, destabilised gas hydrates, or other reservoirs, flood the ocean–atmosphere system, the isotopic signature of everything that grows and dies within it shifts sharply negative. Geologists call these shifts negative carbon isotope excursions, and they are the primary diagnostic tool for identifying hyperthermal events in the rock record. At Jerain–Dauki, the team collected thirty-six stratigraphically constrained samples spanning coal seams, sandstones, shales, siltstones and carbonaceous horizons across a vertical profile stretching from just 5 centimetres to more than 16 metres above the base of the section.

The results are striking. The δ¹³C values of the organic matter range from −23.1 to −32.5 per mil, a total variability of 9.4 per mil, and within that spread the researchers identified two major negative excursions of roughly 6 to 6.5 per mil and two minor ones of about 3 to 4 per mil. The first major excursion appears abruptly at about 4.87 metres up the section, where values plunge by around 6 per mil before slowly recovering. A smaller shift of roughly 3 per mil follows at 8.10 metres, then a second major excursion of about 6.5 per mil strikes at 11.60 metres, and a final minor excursion of around 4 per mil appears at 15.50 metres. The pattern of sharp drops followed by gradual recoveries suggests a complex, multi-phase history of carbon release rather than a single catastrophic injection.

Correlating these excursions with specific global events remains provisional, but the stratigraphy offers tantalising clues. The major excursion recorded between samples JD-8 and JD-9 may broadly correspond to the PETM itself, while one of the excursions higher in the section may be comparable to ETM-2, a smaller early Eocene hyperthermal that followed roughly two million years later. The dinoflagellate cyst assemblages recovered from the section, though sparse, include species such as Apectodinium longispinosum and Homotryblium tasmaniense that support a late Paleocene to early Eocene age, placing the excursions squarely within the window of globally recognised hyperthermal activity. The researchers stress that the presence of multiple negative excursions separated by intervals of partial recovery points to repeated pulses of isotopically light carbon entering the exogenic reservoir.

One of the most surprising findings concerns where the biggest isotopic shifts occur. Intuitively, one might expect the most negative carbon isotope values in the coal seams and carbonaceous shales, where organic matter is most abundant and best preserved. Instead, the largest excursions, at samples JD-9 and JD-25, occur within sandstone-dominated intervals. The team tested whether this could be an artefact of lithology, reworking, or organic matter mixing, and found the evidence against such a explanation compelling. If lithological control were dominant, the carbonaceous units would show the most negative values, yet those units remain relatively stable at around −25 to −26 per mil. Moreover, a statistical cross-plot of δ¹³C against total organic carbon content reveals essentially no correlation, with a coefficient of determination of just 0.05. The excursions, in other words, reflect genuine changes in the isotopic composition of the global carbon reservoir, not local quirks of sedimentation or preservation.

The palynological evidence also paints a vivid picture of the ancient environment. The samples are dominated by terrestrial material, including plant cuticles, degraded debris, black oxidised plant fragments and charcoal, along with mangrove pollen of the genus Spinizonocolpites, which is associated with the Nypa palm that fringed tropical coastlines of the Tethys Ocean. Marine indicators, including dinoflagellate cysts such as Apectodinium, Diphyes colligerum, Homotryblium tasmaniense, Hystrichokolpoma rigaudiae and Spiniferites, appear only in low abundances and in a handful of horizons. Together, these assemblages indicate deposition in a restricted marginal-marine setting, likely a coastal swamp or lagoon that was episodically inundated by marine waters. Earlier work from the region had documented an Apectodinium acme, a burst of this warm-water dinoflagellate that marks the PETM worldwide, in equivalent rocks of the Shillong Plateau, lending further support to the regional correlation.

Placed in a global context, the magnitude of the Jerain–Dauki excursions is remarkable. Open-ocean carbonate archives typically record PETM-related shifts of only about 2.5 to 4 per mil, whereas the major excursions here reach 6 to 6.5 per mil. Comparable large values have been reported from the Tingri section of Tibet, where excursions reach about 7 per mil, from Arctic Ocean higher-plant n-alkanes at 6 to 8 per mil, and from bulk carbonate records on the Atlantic Coastal Plain. Within India itself, the new record exceeds the excursions documented from western Indian lignite successions such as Vastan, Tadkeshwar, Giral and Panandhro, as well as the roughly 3.4 per mil excursion recorded in the Sylhet Lakadong Limestone. This variability highlights how differently the same global perturbation can be expressed across depositional settings, latitudes and proxy types, with marginal-marine and terrestrial organic records often showing amplified responses relative to deep-marine carbonates.

The broader significance of the study lies in filling a conspicuous gap. Most hyperthermal records come from sub-tropical to temperate regions of the Northern Hemisphere and from deep-sea cores, while genuinely tropical archives remain scarce. The Jerain–Dauki section demonstrates that tropical continental-margin systems were highly sensitive to Paleocene–Early Eocene carbon cycle perturbations and capable of preserving high-amplitude isotopic signals. Recent paleoclimate modelling suggests that these carbon release events were accompanied by enhanced terrestrial methane emissions and an intensified hydrological cycle, with increased global precipitation and evaporation under elevated atmospheric carbon dioxide, and the new record is consistent with those inferences. The authors note that future compound-specific biomarker analyses could further disentangle organic matter sources and local environmental influences from the global signal.

For a world once again conducting an uncontrolled experiment with the carbon cycle, the message from the ancient swamps of Meghalaya is sobering. Fifty-six million years ago, a slower but still enormous release of carbon-12-enriched carbon reshaped climates, acidified oceans, reorganised ecosystems and left its isotopic signature in sediments from the Arctic to the tropics. The fact that a restricted coastal bay on the Indian plate recorded these events so clearly, and in some cases more dramatically than the open ocean, underscores both the global reach of hyperthermal carbon injection and the value of tropical marginal-marine archives in constraining the magnitude, structure and mechanisms of early Cenozoic climate disruption. As researchers continue to assemble the global picture, records like Jerain–Dauki will be essential for testing how Earth’s climate system responds when the carbon cycle is pushed far beyond its normal operating range.

Subject of Research: Paleocene–Early Eocene carbon isotope excursions recorded in the tropical marginal-marine Lakadong Sandstone of north-eastern India

Article Title: A tropical marginal-marine record of Paleocene–Early Eocene carbon isotope excursions from the Lakadong Sandstone, South Shillong Plateau, India

Article References: Sharma, A., Uddandam, P. R., Shukla, M. K., & Agrawal, S. (2026). A tropical marginal-marine record of Paleocene–Early Eocene carbon isotope excursions from the Lakadong Sandstone, South Shillong Plateau, India. Discover Geoscience, 4(1), Article 355. https://doi.org/10.1007/s44288-026-00713-0

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00713-0

Keywords: PETM, carbon isotope excursion, Paleocene–Eocene, hyperthermal events, Lakadong Sandstone, South Shillong Plateau, Meghalaya, dinoflagellate cysts, marginal-marine, paleoclimate, carbon cycle, tropics