The Selandian-Thanetian Transition Event (STTE) represents a relatively understudied interval of carbon cycle instability and environmental disruption during the Paleocene. This study presents a comprehensive sedimentological, palynological, and geochemical record of the STTE based on two shallow marine wells (Moczygemba VT #11 and Vogelsang Frieda #1) from the Texas Gulf Coast, USA. Our multiproxy approach integrates palynology and nannofossil biostratigraphy to establish age constraints and track ecological changes, organic carbon isotopes to detect regional preservation of the STTE, and elemental ratios to infer chemical weathering intensity and mean annual precipitation. Results indicate that the STTE along the Gulf Coast was characterized by elevated weathering rates under semiarid to humid climatic conditions. Palynological assemblages show a marked increase in Thomsonipollis magnificus, suggesting the expansion of mangrove or coastal swamp taxa during inferred warming phases. Notably, negative excursions in organic carbon isotopes, along with increased terrestrial input of organic matter in both cores, confirm the regional expression and impact of the STTE. These findings provide critical constraints on the STTE by linking carbon cycle perturbations to continental-scale sourceto-sink responses across North America and demonstrate how deltaic systems along the Gulf Coast recorded and responded to mid-Paleocene global warming.

The coccolithophore Reticulofenestra is key to understanding late Cenozoic climate change, but taxonomic identification remains challenging. This study uses morphometric and mixture analysis to evaluate taxonomic criteria for late Eocene to early Oligocene Reticulofenestra. The method enables a systematic comparison between the taxonomic morphotypes and the components recognized through Gaussian mixture modeling of parameters of distal shield length, circularity, and central opening ratio. At the species level, a total of nine morphotypes were studied from 6700 data points collected across three study sites in the mid-low latitude Atlantic-Indian Oceans. The results demonstrate that length and circularity effectively distinguish groups, validating their uses as primary taxonomic criteria. Nevertheless, central opening ratio exhibits high intra-group variability, limiting its standalone application. In addition, our integrated data reveal three evolutionary phases: (1) initial diversification during late Eocene cooling; (2) extinction following peak diversity after the Eocene-Oligocene Transition; and (3) early Oligocene stabilization reflecting adaptation in smaller species. This work provides statistical references for the validation of semi-quantitative morphologic descriptions, which may help establish a robust framework for identifying this ecologically vital lineage and enhance our understanding of phytoplankton responses to past environmental changes. Future genomic studies will be crucial for elucidating genotype- phenotype-environment relationships in Reticulofenestra evolution.

We report a new ecological refugium for the Cheirolepidiaceae family (pollen form genus Classopollis) in the Paleocene Lower Wilcox Group in the Gulf Coast of southeastern Texas based on palynological analysis of four wells. The Cheirolepidiaceae were once thought to have gone extinct at the Cretaceous-Paleogene (K/Pg) boundary or earlier in North America; however, similar ecological refugia for this family in the Paleocene have previously been reported in China, Argentina, and potentially the Rocky Mountains of the United States. The highest relative abundances of Classopollis pollen were found in delta front, lagoon, and shoreface depositional paleoenvironments marked by high mud-fraction Sr/Ba (a geochemi-cal proxy for salinity), and abundances generally increased down section in older Paleocene strata. The high relative abundance of Classopollis pollen in the well samples, the rarity of reworked Mesozoic palynomorphs, the generally good preservation of Classopollis pollen, and the similarity of Classopollis fluorescence spectra to other in situ Paleocene pollen all provide strong evidence for the survival of the Cheirolepidiaceae family in the coastal salt marshes of Texas through at least the late Paleocene.

The first size reduction (FSR) in the Reticulofenestra-Gephyrocapsa-Emiliania ( RGE ) lineage (order Isochrysidales), which occurred in the early Oligocene (~32 Ma), is of great significance for understanding the Lilliput effect that has affected coccolithophore communities from the late Eocene to this day. We conducted a morphologic analysis on the coccoliths of Reticulofenestra species that lived during the late middle Eocene to early Oligocene (~40–31 Ma), using marine sediments from the South Atlantic Ocean. Our data show increasing size and decreasing abundance of the large species during the late Eocene, leading to their disappearance at the FSR, and a concurrent decrease in the size variability of the small- to medium-sized coccoliths whose central opening diameter had become very reduced. Although the cosmopolitan late Paleogene through Neogene size decrease in coccolithophores has been linked to the concomitant long-term decline in global p CO 2 , we suggest here that the FSR was the result of environmental destabilization caused by the expansion of eutrophic environments following the late Eocene establishment of overturning circulation associated with ice buildup on Antarctica. This study also leads us to propose a hypothetical model that links coccolith morphology of species of the RGE lineage and trophic resources in the upper ocean: the small- to medium-sized, r-selected coccolithophores with smaller coccolith central openings live in nutrient-rich waters where they rely mostly on photosynthesis and little on mixotrophy, whereas the larger, K-selected species with larger coccolith central openings live in oligotrophic waters where they are more dependent on mixotrophy.

Four tropical ODP/IODP sites were quantitatively investigated to enhance the Oligocene calcareous nannofossil biostratigraphy between 24-30 Ma. Despite the low diversity in the Oligocene, our data show additional bioevents and a new taxon-range zone in the tropical region. Sphenolithus avis appeared in upper Zone NP23 in the Indian Ocean, providing an additional bioevent between the base events of S. distentus and S. ciperoensis. Sphenolithus ciperoensis appeared to be rare and sporadic but an increase in abundance was synchronously found in the tropics at 28.73 Ma which is correlated with middle Chron C10 r in Hole 1237B. Sharp extinction levels include the top events of Helicosphaera compacta and S. predistentus in which the latter is more distinguishable than the top of S. distentus. The base of Triquetrorhabdulus carinatus differs within our tropical sites by showing inconsistent ages. Slightly prior to the NP24/25 boundary, S. ciperoensis reached its highest abundance during the decline of S. distentus and S. predistentus in the tropics. Confined to the early part of that abundance shift, an acme of gigantic S. ciperoensis, with a spine ratio (T/B) larger than 1.23, was observed together with S. ciperoensis s.s only in the Indian and Pacific Oceans which was probably related to fertility changes in the photic zone. The acme of gigantism lasted longer in the SE Pacific Ocean for about similar to 500 kyr, which is correlated with the lower-middle part of Chron C9 n (27.41-26.86 Ma), while in the Indian Ocean it was only found with low abundance at 26.86 Ma. Chiasmolithus altus, which was only observed in the western Pacific Ocean, abruptly terminated at 26.60 Ma. We introduce here the new Crassidiscus backmanii taxon-range zone, observed in our four tropical and mid latitude sites with a significant short duration. The base of C. backmanii is correlated with upper Chron C8 r in Hole 1237B at 26.19 Ma, while it is correlated with lower Chron C8 n in Hole U1438B at 25.78 Ma; hence the reliability of this biozone needs further examination. An event of a maximum abundance, however, shows similar ages in our tropical sites yielding an age of 25.75 Ma correlated to middle Chron C8n.2 n in Hole 1237B and of 25.71 Ma correlated with lower Chron C8 n in Hole U1438B. The top of S. avis occurs slightly below the top of S. ciperoensis, thereby, providing an additional bioevent in the Chattian.

Pseudo-cryptic speciation occurs commonly in living oceanic plankton. In the coccolithophores, recent genetic studies have revealed that Braarudosphaera bigelowii has a number of unique genotypes that correlate well with pentalith size, indicating that this coccolithophore “species” actually contains multiple pseudo-cryptic taxa. In order to look for evidence of pseudo-cryptic speciation in the past, we measured the radii of 2800 B. bigelowii pentaliths from the Braarudosphaera-rich limestones that contain the GSSP for the Lower/Middle Paleocene (Danian/Selandian) boundary at Zumaia, Spain. Analysis of the radius measurements using the Expectation-Maximization algorithm yielded two size groups, herein termed form X (<4.5μm) and form Y (≥4.5μm). This result suggests the possibility of at least two pseudo-cryptic species in the Early Paleocene taxon B. bigelowii. In addition, there is a sharp increase in overall B. bigelowii abundance near the Paleocene Magnetochron C27n/26r reversal in the Zumaia section, forming an acme zone that spans approximately four meters. Isotopic analyses of organic matter show that an abrupt negative excursion of 3.5‰ in δ13Corg coincided with the onset of the B. bigelowii acme. Biostratigraphic correlation between this section and the Danian/Selandian boundary section at Qreiya, Egypt confirmed that this isotopic shift correlates with a hyperthermal event (Latest Danian Event), and suggests that B. bigelowii abundance may have been affected by changing climatic conditions.

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The Qreiya section (Upper Egypt) contains a well-preserved record of the first radiation of the fasciculiths, an evolutionary event that affected the coccolithophores of the Order Discoasterales during the late Danian. At Qreiya it unfolds across the so-called Neo-Duwi Event. We describe the morphostructural changes that affected coccoliths and document a trend towards increased surface area of the coccoliths of the Order Discoasterales. Our isotopic data do not support earlier interpretation(s) that the Neo-Duwi Event may correspond to a Paleocene hyperthermal. We interpret the first radiation of the fasciculiths as an adaptive response to increased oceanic oligotrophy through the appearance of coccoliths adapted to food collection in nutrient-poor oceanic waters.

Three new genera of coccolithophores are introduced and one genus is emended. Six new species are described. They are part of the so-called first radiation of the fascicultihs that began in the latest Danian and constitute a marker for correlation of the Danian/Selandian boundary.

Patterns of diversification and longevity in Paleogene coccolithophorids are analyzed by combining the temporal history of selected genera, families, and orders with the number of discrete morphospecies in them. The coccolithophorids underwent an abrupt mass extinction at the Cretaceous/Paleogene boundary, and a rapid (~1 m.y.-long) global turnover at the Paleocene/Eocene boundary. In contrast, they underwent a diachronous turnover at the Eocene/Oligocene boundary that spread over 6–7 m.y. at mid- and low-latitudes. The turnover included sequential extinctions and speciations of short-lived taxa, beginning slightly before 37 Ma, and losses of taxa that dominated mid- and low latitudes at 34.2 Ma and high latitudes at 32.3 Ma. It is also marked by a few evolutionary appearances, in particular, that of the Family Syracosphaeraceae, which is the most diversified of the living coccolithophorids. Most importantly, the turnover resulted in a shift in the balance between families across several orders, such that families that dominated during the Eocene dwindled during the turnover, and, conversely, families that were little diversified during the Eocene became dominant. Thus, members of Family Coccolithaceae and the genus Heliodiscoaster typify Eocene communities; members of the Family Calcidiscaceae and the genus Eudiscoaster characterize Neogene communities. This shift was accompanied by a decrease in the robustness of coccoliths, suggesting that the Eocene/Oligocene event had a marked effect on the physiology of Eocene coccolithophorids. Bolide impacts and the emplacement of large basaltic provinces provide mechanisms to explain large biotic events. Such mechanisms, however, can be ruled out in the case of the Eocene/Oligocene turnover, which was undoubtedly related to climatic cooling and glaciation. The filtering effect of environmental stress on late Eocene diversity remains to be explained.

We have conducted a preliminary analysis of the history of size change of coccoliths through the Jurassic and Cretaceous. This is essentially based on a compilation of literature data. The results demonstrate that the average size of coccoliths has increased from early Jurassic through the Santonian, stabilized until the Campanian and decreased during the Maastrichtian. Remarkably, this size history parallels the diversity (species richness) history of the Mesozoic Coccolithophorids, and constitutes an illustration of Cope's rule. The amplitude of change of the average size through time appears to have remained small, which may result from competition by other, larger, contemporaneous calcareous nannoplanktonic groups.

We describe the use of LABVIEW to automate data collection and instrument control for the Franck–Hertz experiment and for the popular Tel-X-Ometer x-ray machine. Such automation permits the rapid collection and reduction of large amounts of data, thus facilitating exploration of the basic physics of these experiments. The use of industry-standard software packages, such as ORIGIN and MATHEMATICA, provides students with valuable exposure to professional tools for the display and analysis of data.