A Proto-Caribbean Record of the Weissert Event from Cuba

In the Sierra de los Órganos in western Cuba, the steep limestone hills preserve sediments that accumulated on the floor of the ancient Caribbean Sea, about 135 million years ago. Thin dark, organic-matter-rich bands alternate with paler grey beds, forming a barcode-like pattern laid down by an ocean whose deeper waters were periodically starved of oxygen. These strata record one of the earliest major climate disturbances of the Cretaceous world: this has been called an Oceanic Anoxic Event or OAE.

In our recently published open-access article in Frontiers in Earth Science, we analyzed sediments from a quarry near the town of Pons, in the Sierra de los Órganos, to reconstruct how the early Proto-Caribbean responded when Earth’s carbon cycle shifted into a different state.
During the Valanginian (Early Cretaceous Period), greenhouse conditions were already in place, but something pushed the system further. Some scientists think in terms of volcanic outgassing, high CO₂, intensified weathering, and nutrient-rich runoff. The oceans stored this disturbance in the only way they can, by changing how they circulate, how they feed life, and how much oxygen reaches the depths. In many basins worldwide, that change shows up as intervals of dark, organic-rich sediments and a global shift in carbon isotopes. This coupled package of carbon-cycle disruption and marine deoxygenation is what we call the Weissert Event.

La Lata sits on what was then a marine slope along the margin of the young Proto-Caribbean Basin, between the evolving Americas and the Tethyan realm. Today it’s an active quarry. In the early Cretaceous it was a quiet pelagic seafloor, slowly accumulating the skeletal rain of coccolithophores, radiolarians, and tiny foraminifera. In that setting, any disturbance in oxygen, productivity, or sediment flux is recorded very efficiently.

We focused on just the lowermost ~4 meters of a ~30-meter section of the Pons Formation. At first glance it seems simple: comparatively thick, medium-gray limestones rich in carbonate are interbedded with much thinner, darker, carbonaceous marls and marly limestones. Under the microscope, however, this “barcode” resolves into five distinct microfacies, ranging from bioturbated, fossil-rich limestones to laminated, nearly barren, organic-rich levels with abundant sulphate minerals, like pyrite.

The first key result is how carbon cycle is distributed and sequestered within the sediments. The dark marls contain total organic carbon up to ~10-11 wt%, while the paler limestones usually sit around 1-3 wt%. Total inorganic carbon behaves in the opposite way: carbonate-rich in the thick gray beds, diluted where organic matter and clay concentrate. That alternation already hints at fluctuating conditions at the seafloor. These were intervals more favorable to the preservation of organic matter, separated by more “normal” background sedimentation.

Superimposed on that fabric is a clear negative excursion in δ¹³Corg of about 1.7‰. That excursion is not random in time. Biostratigraphic markers, especially the presence of specific calcareous nanoplankton place this interval in the late Valanginian subzone NK3B, the very window classically associated with the Weissert Event elsewhere in the world, and linking our local curve to the global record.

The dark beds do more than carry isotopes. They are loaded with mineral and microscopic evidence that oxygen in bottom waters dropped sharply during certain pulses. Under SEM we see framboidal pyrite and small cubic aggregates, often growing inside foraminiferal tests, mingled with illite-smectite clays and microbial fabrics. Redox-sensitive trace elements peak in the same horizons: vanadium, nickel, chromium, molybdenum, uranium, thallium, and sulfur all show marked enrichments where total organic carbon is highest. At the same levels, detrital indicators such as Al, Si, Ti, and Li also increase, suggesting stronger terrigenous flux -probably the fingerprint of enhanced runoff and weathering on land.

Bioturbation tells a complementary story. In the thick gray limestones, burrows are common and the bioturbation index often reaches 3–4: the seafloor was oxygenated enough for infauna to churn the sediment. In the organic-rich marls, the index drops to 1–2, and X-ray images reveal only faint, incomplete structures. These are intervals where oxygen availability was restricted enough to suppress most benthic activity.

Put together, the picture that emerges is not a single, monolithic “black shale” horizon but a series of deoxygenation pulses, closely tracking the negative carbon isotope excursion. During those pulses, Los Órganos lay beneath waters that were more stagnant or less ventilated, but more superficially nutrient-rich. Organic matter arriving at the seafloor was less efficiently destroyed, sediment input from land was boosted, and trace metals were scavenged from the water column into the accumulating muds.

Why does this matter beyond the satisfaction of matching a Cuban cliff to a named global event? First, it demonstrates that the Proto-Caribbean Seaway did not sit on the sidelines of Valanginian climate change. It participated fully in the Weissert disturbance. The same isotope signal, the same style of organic-rich sedimentation, and comparable redox signatures appear here as in better-known Tethyan sections. Second, the section at La Lata shows how a marginal to hemipelagic basin can register global forcing factors like higher CO₂, weathering, in its own local language of facies, microfossils, and chemical inventories.

Finally, there is an uncomfortable echo with the present. The rocks at La Lata, Sierra de los Órganos, formed under long-term CO₂ buildup, intensified weathering, and nutrient loading. The ocean responded by reorganizing circulation and oxygen distribution, carving “dead-zone” intervals into the sedimentary archive. Today we are driving the carbon cycle far faster, but the physics and chemistry of seawater have not changed. Ancient barcodes like those of the Pons Formation are not predictions, but warnings. When the carbon cycle is pushed hard, oceans everywhere, from open basins to narrow seaways, can slide toward deoxygenation affecting not just the carbon cycle, but all life in earth.

In that sense, each black band in the quarry is both a record of a vanished ocean and a quiet reminder that Earth’s climate system has thresholds. Our goal at La Lata was to read that record as clearly as possible, and to place the Proto-Caribbean firmly on the map of ocean anoxic event research. The story those limestones tell is simple and stark = when the planet breathes carbon too quickly, the oceans are often the first to lose their breath.

Recommended paper

Our pen-access article: Orihuela J., Melinte Dobrinescu M.C. and Maurrasse F.J-M.R. (2025) “Characterization of the Weissert oceanic anoxic event in lower Cretaceous limestones of the Guaniguanico terrain, Sierra de los Órganos, Western Cuba,” published in Frontiers in Earth Science (Vol. 13, 1549274) on 20 April 2025 (doi: 10.3389/feart.2025.1549274).

Jurassic Ferns from the Girón Group: A Window into Ancient Tropical Ecosystems

A new study published in the Journal of South American Earth Sciences opens a small window on the flora and environmental conditions of tropical South America during the Late Jurassic. 

The paper, "Jurassic fern Piazopteris from the Girón Group, Colombia: A taxonomic and paleoenvironmental evaluation," presents the discovery and analysis of six fossil fern specimens from the Eastern Cordillera of Colombia, helping expand a bit of knowledge of Jurassic plant life in the paleo-Caribbean region.

The fossils were collected from the carbonaceous mudstones of La Honda Creek, part of the Girón Group—an important but underexplored sedimentary unit that preserves traces of Mesozoic terrestrial ecosystems. The ferns are tentatively identified as Piazopteris cf. branneri, a member of the now-extinct genus of the Matoniaceae. Piazopteris once thrived in humid, equatorial climates.

What makes this study particularly compelling is its multidisciplinary approach. Using thin-section petrography, scanning electron microscopy (SEM), and carbon geochemistry—including total organic carbon (TOC) and stable isotope (δ¹³Corg) analyses—the researchers aproximated the depositional environment and climate context of these fossils. The results point to a low-energy, swamp-like setting with significant organic accumulation, likely influenced by a humid, tropical to subtropical climate. The geochemical data not only support this interpretation but also provide a valuable window into the carbon cycling and preservation conditions of Jurassic terrestrial environments.

The genus Piazopteris is a biostratigraphically and paleoecologically relevant genus, typically associated with Jurassic-Cretaceous floras of Gondwanan affinity. The occurrence of Piazopteris cf. branneri in Colombia contributes to a growing record of Jurassic ferns in South America and provides important taxonomic refinements for this group, which has often been misidentified or found poorly preserved.

Importantly, this work also underscores the scientific potential of the Girón Group as a paleobotanical archive. While the Girón Group has been recognized for its sedimentological and tectonic significance, its paleontological potential remains vastly underutilized. This new contribution highlights the need for further research, particularly stratigraphic refinement, paleobotanical and geochemical work in this region.

This study was carried out by a multidisciplinary team of geologists and paleontologists from several institutions in Colombia and abroad, including the Universidad Industrial de Santander (UIS), Florida International University (FIU), and research institutes focused on stratigraphy and paleontology. The collaboration brought together the fields of sedimentology, paleobotany, geochemistry, and microscopy to advance understanding of Jurassic floras in tropical settings. 

Special thanks go to all who helped make this discovery and research possible.

Citation:

Torres-Parada, J.M., Orihuela, J., Alarcón Gómez, C.M., Diaz Villamizar, J.S., Gómez-Coronado, J.S., Márquez-Prada, J.J., Lizarazo-Pabón, J.A., Patarroyo, G. (2025). Jurassic fern Piazopteris from the Girón Group, Colombia: A taxonomic and paleoenvironmental evaluation. Journal of South American Earth Sciences, 158, 105488. https://doi.org/10.1016/j.jsames.2025.105488

Images created with AI (ChatGPT Image creator, 2025). 

Ancient Sand Dollars Reveal a Lost Caribbean Ecosystem: New Findings from South-Central Cuba

The fossil record offers glimpses into ancient worlds, and a new study on Clypeaster echinoids from Cuba’s Damují Formation provides valuable insights into the Caribbean’s past. These fossils, dating from the Late Eocene to Early Oligocene, represent some of the earliest known occurrences of this genus in the region.

The research, conducted in Rodas, south-central Cuba, extends the known temporal and geographical range of Clypeaster, a genus of sand dollars that still thrives in tropical and subtropical oceans today. While previous studies focused on Oligocene and Miocene specimens, these newly examined fossils fill a gap in our understanding of how echinoids evolved and dispersed during a critical period of climatic transition—the Eocene-Oligocene boundary.

The geological context of the Damují Formation suggests that Clypeaster lived in a diverse marine environment, alongside large foraminifera, corals, and small fish. The presence of these fossils indicates that warm, shallow-water reef systems persisted in the Caribbean despite global cooling trends at the time. This challenges previous assumptions that echinoid diversification in the region occurred later, during the Miocene.

The study also raises intriguing questions about the role of the Caribbean as a migration corridor for marine life during the Paleogene. Were these Clypeaster populations early colonizers, or did they represent a more ancient lineage persisting through climatic shifts? Future research, including detailed morphological analyses and comparisons with other fossil sites, may help unravel the evolutionary pathways of these echinoids.

By documenting these fossils, this study contributes to our understanding of past ecosystems and the biogeographical history of echinoids. It also underscores the importance of Cuba’s fossil record in reconstructing ancient marine environments and refining our models of species distribution during critical periods of Earth’s history.

This work was made possible through the contributions of coauthors Carlos Rafael Borges-Sellén, Alberto F. Arano-Ruiz, Johanset Orihuela, and Yasmani Ceballos-Izquierdo, whose efforts in fieldwork, analysis, and writing were fundamental to this research. The full paper is available for download here.

The study is published in POEYANA, a peer-reviewed open-access journal (ISSN: 2410-7492, RNPS: 2403) that has been a cornerstone of zoological research in Cuba, the Caribbean, and the Neotropics since its founding in 1964. Originally established at the former Institute of Zoology of the Cuban Academy of Sciences, POEYANA is now edited by the Institute of Ecology and Systematics under the Ministry of Science, Technology, and Environment (CITMA). With over 500 published articles spanning more than five decades, the journal continues to serve as a platform for scientific contributions from Cuban and international researchers in the field of natural sciences.

Fossil News! First Pliocene Land Vertebrate Fossils from Cuba

I’m thrilled to announce the publication of our latest research paper, "First Record of Terrestrial Vertebrates from a Late Pliocene-Early Pleistocene Deposit in Cuba," which uncovers the first documented Pliocene land vertebrate fossils in Cuba’s history to date. Found at the El Abra outcrop in Matanzas, these fossils offer a rare glimpse into the prehistoric fauna of the Greater Antilles, hinting at unique evolutionary patterns and diversity, plus providing new insight into the biodiversity and biogeographic history of the Caribbean region.

While we recognize that possible land vertebrate fossils of older age may exist in the caves of Pinar del Río, these remain untested and are generally assumed to be Pleistocene, and even later in the Pleistocene, in age. As such, our findings from El Abra represent the earliest confirmed fossils within the Late Pliocene-Early Pleistocene range, adding a new dimension to our understanding of Caribbean vertebrate evolution.

One particularly exciting aspect of this discovery includes previously undocumented remains of capromyine rodents (so called hutias or jutias), showcasing unique dental characteristics that hint at possible connections with species in Hispaniola. This find challenges and enriches our understanding of Caribbean vertebrate dispersal and diversification, underscoring the importance of examining overlooked fossil records or outcrop deposits to piece together new evolutionary histories.

I am immensely grateful to my colleagues and co-authors Yasmani Ceballos, Lazaro Viñola, Logel Lorenzo and Alberto Clark, who collaborated on this project, contributing their expertise and dedication to each step of this investigation. Further thanks are due to the friends and institutions, for logistics, conversations, sharing of ideas, knowledge, and collecting permits. 

Take a look and join us in exploring this new chapter of Cuba's fossil record and its broader implications for Caribbean paleontology!

Source: 

Orihuela, J., Viñola-Lopez, L. W., Lorenzo, L., Clark, A., & Ceballos-Izquierdo, Y. (2024). First Record of Terrestrial Vertebrates from a Late Pliocene-Early Pleistocene deposit in Cuba. Journal of South American Earth Sciences, 105200.

Carnivorous Fish of the Cretaceous: New Fossil Discoveries Unearthed in Colombia’s La Luna Formation

Beneath the hills of Colombia’s Eastern Cordillera lies an ancient record, preserved in the layers of rock known as the La Luna Formation. Dating back to the Upper Cretaceous, about 90 million years ago, this formation provides a glimpse into vast marine ecosystems, when warm seas covered much of what is now South America. Yet, despite its potential, the fossil record from this period in Colombia has remained surprisingly sparse.

In a groundbreaking discovery, a team of researchers has unearthed fossilized remains of the extinct fish family Enchodontidae from the La Luna Formation in the municipality of Matanza, Santander Department. These fossils, which include jaw and skull fragments, represent the first comprehensive report of Enchodus, a genus within the Enchodontidae family, from this region. Enchodus was a predatory fish, easily recognized by its distinctive sharp teeth, which made it one of the dominant marine predators of its time.

The fossils collected from the field were embedded in calcareous mudstone and concretions. The team utilized morphological analyses, along with computed tomography (CT) scans, to study the specimens in detail. These scans revealed not only the external features of the fossils but also internal structures hidden within the rock matrix — features crucial for taxonomic classification.

One of the most exciting aspects of this discovery is its contribution to understanding the diversity and distribution of Enchodus. The genus was already known to have a wide geographic range, with fossils found across North America, Europe, and Africa, but records from South America, particularly Colombia, have been rare. These newly uncovered specimens, some of which show distinctive morphological features, may even point to the presence of new, yet undescribed species of Enchodus.

The fossils were found in the Galembo Member of the La Luna Formation, a sedimentary sequence rich in organic material and known for its preservation of marine life. The environment in which these fish lived was likely a shallow, oxygen-starved sea, contributing to the preservation of skeletal remains. Despite the disarticulated nature of the fossils — a sign of active sea-bottom conditions and scavenger activity — the bones and teeth of these ancient predators offer a fascinating look at marine ecosystems during the Late Cretaceous.

This discovery not only fills a gap in Colombia’s fossil record but also raises intriguing questions about the factors that influenced the preservation and fossilization of marine life in the region. Why, in a period known for rich marine biodiversity, are fossils from the Colombian Upper Cretaceous so hard to come by? The answers to these questions may lie in the geological and environmental conditions of the time, but further research is needed to unravel these mysteries.

The findings also highlight the potential for future discoveries in the La Luna Formation. As more specimens are uncovered and analyzed, we may uncover further evidence of marine vertebrate diversity in this region. Each fossil tells a story, and these new specimens of Enchodus are beginning to piece together a chapter of the evolutionary history of marine life in South America.

These findings are detailed in the recently published article:

Torres-Parada, J.M., Orihuela León, J., Patarroyo Camargo, G.D., Alarcón Gómez, C.M., Diaz Villamizar, J.S., Gómez-Coronado, J.S., Márquez Prada, J.J. (2024). Upper Cretaceous Enchodontidae (Actinopterygii: Aulopiformes) in the La Luna Formation, Eastern Cordillera, Colombia: A new report. Journal of South American Earth Sciences, 148, 105160.

I extend warm thanks to Jose M. Torres-Parada for the opportunity to collaborate on this project. May many more come our way!