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Results of a joint paleomagnetic, petrographic, X-ray fluorescence, and stable isotope study of the impact breccias and Paleogene carbonate sediments in the Santa Elena borehole are used to investigate the impact effects and climatic and environmental changes in the Chicxulub crater and Yucatan platform, southern Gulf of Mexico. The Santa Elena borehole reached a depth of 504 m and was continuously cored, sampling the post-impact carbonate sediments and impact breccias. We analyze the section from ~230 m to ~340 m, corresponding to the upper breccias and Paleogene sediments, spanning the breccia-carbonate contact at 332 m depth. The lithological column from macroscopic and thin-section petrographic analyses comprises limestones, dolomitized limestones with thin clay layers, and breccias rich in melt and basement clasts within a melt- or carbonate-rich matrix. Magnetic polarities define a sequence of reverse to normal intervals within chrons 29r to 26r in the impact breccias and basal carbonates. Magnetic susceptibility shows high variable values in the breccias correlating with the clast contents and carbonate or melt-rich matrix. Low paramagnetic or diamagnetic susceptibilities characterize the carbonate sequence. Fe-Ti oxides are dominant magnetic carriers with pseudo-single and multidomain states. In the upper breccias, more complex magnetic mineralogy is observed, with hydrothermal alteration phases. The ∂13C values in the first 20 m interval range from 1.2 to 3.5 ‰ and ∂18O values range from -1.4 to -4.8 ‰. Isotopes show variation trends that correlate with the marine carbon and oxygen isotope patterns for the K-Pg boundary and early Paleocene records. Positive carbon isotopes suggest high productivity, with apparent recovery following the K-Pg extinction. Oxygen isotope values are negative, reflecting regional and local effects. Geochemical data define characteristic trends, with silica decreasing gradually from high values in the breccias, low contents between 320 to 247 m, with intervals of higher variability, particularly between 280 and 247 m, and then increased contents at 247-230 m. Ca shows the opposite trend with low values in the breccias, high in the Paleocene carbonates, and low in the PETM. Major oxides and trace elements show similar patterns, e.g., Fe, Ti, K, and Al, recording changing climatic and depositional conditions in the platform. Results are interpreted in terms of the paleoclimatic and paleoenvironmental evolution of the southern Gulf of Mexico at the Cretaceous-Paleogene boundary, Paleocene and Eocene, including analysis of post-impact processes, hydrothermal activity, platform sedimentation, and sea level changes.

The location, sedimentology, and oceanographic characteristics of the southern Gulf of California make it suitable for investigating the Quaternary climate changes of the Eastern Tropical Pacific Ocean (ETPO). We investigate changes in precipitation, ocean patterns and variations in paleoproductivity in the Eastern Tropical Pacific Ocean related to insolation, migrations, and dynamics of the of Intertropical Convergence Zone (ITCZ), the North America Monsoon (NAM), and inter-hemispheric teleconnections. Proxy records are obtained from sediments in the marginal Alfonso Basin, situated in the southwestern sector of the Gulf of California near its junction with the Pacific Ocean. The age model was based on eleven radiocarbon dates, the MARINE 20 calibration curve, and a reservoir age of 253 + 18 years. High-resolution records of elemental geochemistry, magnetic properties, and radiolarian assemblages are used to track climate changes in the tropical climate system at millennial and centennial time scales over the past 18,500 yr. Geochemical and magnetic proxies revealed an increase of precipitation at ~17,500 and 16,536 yr, in the Bolling Allerod (from ~14,988 to 14,057 yr), and during the early Holocene. Humid conditions predominated between ~7,404 and 5,200 cal yr BP. Records indicate a climatic shift at ~4,860 cal yr BP, suggesting increased aridity and the strength of winds to continue through the late Holocene. Roughly 4000 cal yr BP the productivity increased as a result of the intensification of the winds. Paleoprecipitation changes are associated with ITCZ latitudinal migration and the NAM responding to insolation changes during the Holocene. Aeolian and fluvial inputs, marked by variations in Ti, K, Fe, Zr/Ti and magnetic properties, indicate that precipitation-controlled changes in summer monsoon rainfall primarily forced terrigenous supply throughout the mid-Holocene. We propose that these conditions arise from the northern hemisphere's high insolation at low latitudes, with the average position of the ITCZ migrating northward. Development of the NAM amplifies the seasonality and promotes increased precipitation during summer seasons. During the late Holocene, terrigenous input appears mainly controlled by the intensification of the NW winds. The record indicates a drop-in precipitation and abrupt enhancement of Aeolian activity. Radiolarian assemblages reveal the upper layers of two water masses (TSW and GCW), suggesting that the advection of coastal currents and mesoscale features controlled these conditions. The dominance of Phormostichoartus corbula, Lithomelissa thoracites, and Arachnocorallium calvata, surface dwellers species reveal the Gulf of California Water and relatively high productivity during the BA, and in the transition to the middle to late Holocene, Botryostrobus aquilonaris suggests that during the deglaciation, (~17,468 to 15,426 yr), and at ~12,604 yr the occurrence of the California Current in the Alfonso Basin. Tetrapyle octacantha group represents the dominance of Superficial Tropical Water in the Alfonso basin, associated with conditions of marked stratification in the water column and oligotrophic conditions in the superficial layer during the Holocene Climatic Optimum and the Medieval Warm Period. which fluctuated due to variations in mesoscale gyres and also coastal upwellings off the western coast could contribute.

At the end of the Cretaceous Period (66 Ma), the impact of a meteorite on the Yucatán platform in the southern Gulf of Mexico caused the extinction of 75% of species on Earth, including 90% of planktic microorganisms like foraminifera and calcareous nannoplankton. As the ocean ecosystem struggled to get back on its feet after this calamity, the recovery of marine primary productivity was geographically heterogeneous. Some authors had speculated that this heterogeneity was driven by the uneven distribution of toxic metals in the ocean, and was directly related to distance from the Chicxulub crater. However, results from recent International Ocean Discovery Program/International Continental Drilling Program (IODP/ICDP) joint Expedition 364, which drilled the Chicxulub crater itself, found evidence of the rapid establishment of a healthy, high-productivity ecosystem in the crater within 30 kyr of the impact. This result suggests that the recovery of marine productivity is likely driven by ecological factors like incumbency and competitive exclusion. However, it also raises several additional questions: How long does high productivity last in the crater? Is this high productivity driven by the impact-generated hydrothermal system or is it a Gulf-wide phenomenon? If so, what’s driving it?Here, we examine planktic and benthic foraminifera, calcareous nannoplankton, major, minor, and trace elements, and stable isotopes from the Paleocene interval of IODP Site M0077 in the Chicxulub Crater, and compare it to publically available planktic foraminifer and nannoplankton counts from three oil wells in the northern Gulf of Mexico to determine the long term trends in productivity in the Chicxulub Crater and whether or not they are limited to the crater or extend across the Gulf. We show that the first ~million years of the Paleocene are characterized by a eutrophic surface waters that slowly transition to mesotrophic and then oligotrophic by the middle Paleocene. Foraminiferal data from the northern Gulf of Mexico demonstrates that this trend is regional.