Estibaliz Apellaniz

THE PALEOCENE–EOCENE THERMAL MAXIMUM: NEW DATA ON MICROFOSSIL TURNOVER AT THE ZUMAIA SECTION, SPAIN

The benthic foraminiferal turnover and extinction event (BEE) associated with the negative carbon isotope excursion (CIE) across the Paleocene–Eocene Thermal Maximum (PETM) is analyzed in the Zumaia section (Spain), one of the most complete and expanded deep-water sequences known worldwide. New biostratigraphic, paleoecologic, and paleoenvironmental data on benthic foraminifera are correlated to information on planktic foraminiferal and calcareous nannofossil turnover in order to evaluate possible causes and consequences of the PETM. Gradual but rapid extinction of 18% of the benthic foraminiferal species starts at the onset of the CIE, after the initial ocean warming (as inferred from calcareous nannofossils) recorded in the last 46 kyr of the Paleocene. This gradual extinction event culminated ∼10.5 kyr after the onset of the CIE and led to the main BEE, affecting 37% of the species. Therefore, extinctions across the PETM affected a total of 55% of the benthic foraminiferal species at Zumaia. The gradual extinction occurred under inferred oxic conditions without evidence for carbonate dissolution, indicating that carbonate corrosivity and oxygenation of the ocean bottom waters were not the main cause of the event. An interval characterized by dissolution occurs above the main BEE, suggesting that bottom waters became corrosive after the main extinction. Carbonate is progressively better preserved through the overlying deposits, and carbon isotope values gradually return to background levels. These data are consistent with a slow deepening of the carbonate compensation depth after its initial rise owing to abrupt acidification of the oceans. Microfossil data support a rapid onset of the PETM, followed by long-term effects on calcareous plankton and benthic foraminifera.

Did the Late Paleocene thermal maximum affect the evolution of larger foraminifers? Evidence from calcareous plankton of the Campo Section (Pyrenees, Spain)

The larger foraminifer turnover (LFT), which marks the base of the Ilerdian stage, may be related to the Late Paleocene Thermal Maximum (LPTM), or be at least nearly coeval with that climatic event. Thus, the impact of the LPTM may have been greater than hitherto realised, having also affected mid-latitude shallow-marine biota. This conclusion has been reached after a re-study of the calcareous plankton of the uppermost Paleocene and lowermost Eocene interval of the Campo section in the central southern Pyrenees. Campo is an important reference section because it contains larger foraminifers, planktic foraminifers and calcareous nannofossils, and their co-occurrence was used to intercalibrate their respective zonal schemes. Previous studies at Campo placed the onset of planktic foraminiferal Zone P5 near the base of the Ilerdian, and the calcareous nannofossil NP9/NP10 chronal boundary (sensu Bybell, L.M., Self-Trail, J.M., 1995. Evolutionary, biostratigraphic and taxonomic study of calcareous nannofossils from a continuous Paleocene/Eocene boundary section in New Jersey. US Geol. Surv. Prof. Pap. 1554, pp. 1‐36) not less than 150 m above the Ilerdian lower limit. By these estimates, the LPTM (known to have occurred in the middle part of Zone P5 and just before the NP9/NP10 boundary) would be an event much younger than the LFT. However, our reexamination of planktic foraminifers suggests that the base of the Ilerdian is probably situated at the middle of Zone P5 (a possibility proposed by Hillebrandt in 1965, but denied by later authors). For instance, Morozovella occlusa has been found for the first time in the Campo section. Its Last Appearance Datum (LAD), which in the Pyrenees was approximately coeval with that of Morozovella velascoensis (event used to place the top of Zone P5), has been identified in beds situated less than 70 m above the base of the Ilerdian. Such thickness represents a time span of a similar magnitude as the one which separated the LPTM and the LAD of M. occlusa in the deep-water hemipelagic succession of the Basque Basin, in the western Pyrenees. Autochthonous calcareous nannofossils are neither abundant nor well preserved in most of the studied interval, with Rhomboaster bramlettei (the marker of the base of Zone NP10) being extremely rare in lower and middle Ilerdian beds, a fact that makes it very difficult to fix the position of the NP9/NP10 boundary in the Campo section. However, the bases of zones NP9 and NP11 have been located, and they support the zonation with planktic foraminifers. These new data suggest that the LFT and the LPTM may have been coeval or nearly so, a possibility reinforced by correlation with sections of the Basque Basin. Specialists of larger benthic foraminifers can easily delineate the LFT in shallow water carbonate successions of the Tethys domain, and they propose to place the Paleocene/Eocene boundary at the base of the Ilerdian stage. On the other hand, the deep

Correlation of the Thanetian-Ilerdian turnover of larger foraminifera and the Paleocene-Eocene thermal maximum: confirming evidence from the Campo area (Pyrenees, Spain)

It has long been known that a major larger foraminifera turnover (LFT) occurred at the boundary between the Thanetian and Ilerdian stages, but its possible correlation with the Paleocene-Eocene thermal maximum (PETM) was unsuspected until the work of Baceta (1996), and has been controversial ever since. After summarizing the history of this controversy, we present information from three new sections that conclusively resolve the issue, all of them placed less than 2 km to the east of the classical Campo section in the southern Pyrenees. In these three sections, an up to 7 meter-thick intercalation of continental deposits rich in pedogenic carbonate nodules is sandwiched between uppermost Thanetian and lowermost Ilerdian shallow marine carbonates. The d13C composition of 42 pedogenic nodules collected from two of these sections (San Martin and La Cinglera) ranges between –11.4 and -14.3‰ and averages –12.9‰, values that conclusively represent the PETM and for the first time are recorded in sections where the LFT is clearly represented. Further, a high-resolution lithological correlation between Campo and the three new sections across the P-E interval unquestionably demonstrates that the lowermost marine beds with autochthonous specimens of Alveolina vredenburgi (a tell-tale of the LFT) are laterally interfingered –and are therefore coeval- with the nodule-bearing PETM continental deposits. On the basis of the new evidence, the temporal coincidence of the PETM and the LFT can no longer be doubted.

Redefinition of the Ilerdian Stage (early Eocene)

The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO’s of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a “silver spike” to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy.

Biostratigraphy and magnetostratigraphy of the Cretaceous/Tertiary Sopelana section (Basque country)

Remarkably thick sequences of upper Cretaceous and lower Tertiary sediments outcrop on the northern coast of the Basque country. We have sampled the well exposed section along the Sopelana beach over 150 m, spanning roughly from middle Maastrichtian (71 Ma) to lower Paleocene (66 Ma), for both biostratigraphic and magnetostratigraphic studies. Thermal demagnetization of ∼ 400 specimens revealed both normal and reversed recent overprints unblocked below 200°C, and both normal and reversed characteristic directions at higher temperatures (200–450°C in the grey limestones; 350–550°C in the redder marls and limestones). Thermal and AF demagnetization and monitoring of weak field susceptibility are consistent with some form of (titano-) magnetite as the main carrier of magnetization. 259 demagnetization diagrams yielded two nearly antipodal clusters of directions, which are still polluted by some 20% remaining recent overprint. The overall mean direction in stratigraphic coordinates is D = 356°, I = 51° (α = 3°), consistent with what is expected for Eurasia at KTB time. Magnetic stratigraphy outlines a succession of eight polarity intervals and is rather straightforward, except for two highly complex zones (52 to 40 m, and 28 to 26 m below the KTB) where the magnetic polarity appears to flip at an unreasonable rate. Biostratigraphic check allows unambiguous assignment of several chrons, with the recognition of the Gansserina gansseri, Abathomphalus mayaroensis, “Globigerina” eugubina, Eoglobigerina edita ( = E. pseudobulloides) and E. trinidadensis zones. The magnetostratigraphic section therefore begins in chron 31R and ends in 29N. Further detailed study of the complex zones reveals that specimens there have a distinct magnetic behaviour: susceptibility increases beyond 400°C, indicating instability and mineralogical change, intensities are higher than elsewhere and more scattered, and a higher unblocking temperature/higher coercivity magnetic component is uncovered. This component, which is absent from the rest of the section, could be an early chemical remagnetization. Indeed the complex zones contain larger amounts of chlorite, a sign of more intense diagenesis. We have therefore discarded samples showing this anomalous behaviour, and have retained only the 223 samples where demagnetization was achieved by 450°C. The thicker, lower complex zone reduces to a reversed chron which we propose to correlate with 30R. We have identified an extra short reversed event within chron 30N, for which independent support is found in DSDP Sites 524 and 577a, and possibly in Gubbio. Finally, the high-sedimentation rate section at Sopelana (25 m/Ma in the Maastrichtian, 7 m/Ma in the Danian) displays one of the best resolved on-land magnetostratigraphies around KTB time. The two complex zones of early remagnetization form an “echo” which may have been generated some 100 kyr after deposition of the sediments. The KTB itself occurs approximately halfway to 3/5 up 29R in terms of time.

On the age of the Early/Middle Eocene boundary and other related events: cyclostratigraphic refinements from the Pyrenean Otsakar section and the Lutetian GSSP

An integrated bio-, magneto- and cyclostratigraphic study of the Ypresian/Lutetian (Early/Middle Eocene) transition along the Otsakar section resulted in the identification of the C22n/C21r chron boundary and of the calcareous nannofossil CP12a/b zonal boundary; the latter is the main correlation criterion of the Lutetian Global Stratotype Section and Point (GSSP) recently defined at Gorrondatxe (Basque Country). By counting precession-related mudstone–marl couplets of 21 ka, the time lapse between both events was calculated to be 819 ka. This suggests that the age of the CP12a/b boundary, and hence that of the Early/Middle Eocene boundary, is 47.76 Ma, 250 ka younger than previously thought. This age agrees with, and is supported by, estimates from Gorrondatxe based on the time lapse between the Lutetian GSSP and the C21r/C21n boundary. The duration of Chron C21r is estimated at 1.326 Ma. Given that the base of the Eocene is dated at 55.8 Ma, the duration of the Early Eocene is 8 Ma, 0.8 Ma longer than in current time scales. The Otsakar results further show that the bases of planktonic foraminiferal zones E8 and P10 are younger than the CP12a/b boundary. The first occurrence of Turborotalia frontosa , being approximately 550 ka older that the CP12a/b boundary, is the planktonic foraminiferal event that lies closest to the Early/Middle Eocene boundary. The larger foraminiferal SBZ12/13 boundary is located close to the CP12a/b boundary and correlates with Chron C21r, not with the C22n/C21r boundary.

An early Lutetian carbon‐cycle perturbation: Insights from the Gorrondatxe section (western Pyrenees, Bay of Biscay)

turbidites and kaolinite, a 3‰ decline in the bulk d 13 C record, a >1‰ decline in benthic foraminiferal d 13 C followed by a gradual recovery, a distinct deterioration in foraminiferal preservation, high proportions of warm-water planktic foraminifera and opportunistic benthic foraminifera, and reduced trace fossil and benthic foraminiferal diversity, thus recording a significant environmental perturbation. The onset of the perturbation correlates with the C21r-H6 event recently defined in the Atlantic and Pacific oceans, which caused a 2C warming of the seafloor and increased carbonate dissolution. The perturbation was likely caused by the input of 13 C-depleted carbon into the ocean-atmosphere system, thus presenting many of the hallmarks of Paleogene hyperthermal deposits. However, from the available data it is not possible to conclusively state that the event was associated with extreme global warming. Based on our analysis, the perturbation lasted 226 kyr, from 47.44 to 47.214 Ma, and although this duration suggests that the triggering mechanism may have been similar to that of the Paleocene-Eocene Thermal Maximum (PETM), the magnitude of the carbon input and the subsequent environmental perturbation during the early Lutetian event were not as severe as in the PETM.

Early Eocene climatic optimum: Environmental impact on the North Iberian continental margin

The early Eocene climatic optimum, which constituted the peak of the long-term early Cenozoic global warming, had a significant impact on the environmental evolution of terrestrial and oceanic areas. Surprisingly, however, its influence on continental margins is poorly known. New insights are provided from a sedimentological, stable isotope, mineralogical, and micropaleontological study of an 1100-m-thick Lower-Middle Eocene deep-marine succession that accumulated on the North Iberian continental margin. The early Eocene climatic optimum is represented by a 410-m-thick interval characterized by scarcity of hemipelagic limestones, abundance of dark marls, which record a reduction in calcium carbonate content and an increase in kaolinite, and the occurrence of conspicuous red layers with high siderite and pyrite content. Series of stratigraphically significant events frame the early Eocene climatic optimum. Based on this analysis, the environmental influence of the early Eocene climatic optimum started at 52.6 Ma and lasted ~2.3 m.y. Its onset is marked by rapid drops in δ13C and δ18O, which record the addition of 13C-depletedcarbon into the ocean-atmosphere system for 80 k.y. and a concomitant warming. A hotter climate and a perennial rainfall regime increased the supply of terrestrial clays, organicmatter, and iron oxides into the sea. Eventually, these changes affected the deepsea bottom 270 k.y. after the onset of the early Eocene climatic optimum, creating conditions in which opportunistic benthic foraminifera thrived, and leading to increased methanogenesis in the subsurface, which caused the formation of siderite. A subsequent gradual recovery culminated abruptly at 50.3 Ma with a global cooling episode, which is locally recorded by the accumulation of lowstand resedimentation deposits.

Modification of the original stratigraphic distribution of Globigerina hillebrandti Orue-Etxebarria, 1985 and its inclusion in another genus; one more planktonic foraminifer species surviving the mass extinction of the K/T boundary

The detailed study of K/T sections in western Pyrenees, SE of the Iberian Peninsula and Tunisia demonstrate that Hedbergella hillebrandti previously thought to be restricted to the Lower Paleocene also occurs from the Upper Maastrichtian. This species originally attributed to the genus Globigerina is transferred in Hedbergella and is one of the planktonic foraminifers surviving the mass extinction of the K/T boundary.

In Search of the Bartonian (Middle Eocene) GSSP (I): Potential in the Basque–Cantabrian and Aquitanian Basins (Western Pyrenees)

The Global Stratotype Section and Point (GSSP) for the base of the Bartonian (middle Eocene) stage is as yet undefined. Herein we assess the GSSP potential of the successions found in the Basque–Cantabrian and Aquitanian basins (western Pyrenees). On the basis of the available data, no outcrop in the Biarritz and Pamplona areas fulfilled the requirements outlined by the International Commission on Stratigraphy. However, the succession exposed on the eastern side of the Cape of Oyambre (San Vicente de la Barquera, province of Cantabria, northern Spain) did so, and yielded positive preliminary results.