Major Paleoceanographic Events Research Articles

Plio-Pleistocene Planktic Foraminiferal Biochronology of ODP Site 762B, Exmouth Plateau, Southeast Indian Ocean

ABSTRACTThe Indonesian Throughflow region connects the tropical Pacific Ocean with the eastern Indian Ocean, and variability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magnetochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understanding of the coupled histories of the El Niño Southern Oscillation, Western Pacific Warm Pool, Indonesian Throughflow, and the eastern Indian Ocean has greatly benefitted from the chronological framework provided by planktic foraminiferal biostratigraphies from these regions. Ocean Drilling Program (ODP) Hole 762 lies under the influence of the Leeuwin Current, originating from the Indonesian Throughflow. Multiproxy data have been collected from Hole 762B and other nearby sites for paleoceanographic interpretation. However, a detailed planktic foraminiferal biostratigraphy integrated with magnetochronology is not available from this site. We provide here the sequential order of planktic foraminiferal First Occurrence (FO) and Last Occurrence (LO) events, which allowed us to divide the examined section into seven biostratigraphic zones. The biostratigraphy was integrated with magnetostratigraphy using revised ages of magnetochrons, which yielded biochronological age estimates for planktic foraminiferal events. A major planktonic faunal turnover between 3.4 and 2.7 Ma is probably related to the onset of the Northern Hemisphere glaciation and related changes in the Indonesian Throughflow. We have compared our numerical age estimates with published ages from other parts of the world. The diachronism observed probably is related to the local oceanographic setting of ODP Hole 762B, which has been alternatively influenced by changing strengths of the warm Leeuwin Current and the cold west Australian Current. The biochronology established here will be useful for correlating paleoceanographic events in the region.

X‐ray fluorescence core scanning of wet marine sediments: methods to improve quality and reproducibility of high‐resolution paleoenvironmental records

X‐ray fluorescence (XRF) core‐scanning is a convenient non‐destructive tool to rapidly assess elemental variations in unprocessed sediments. However, substantial analytical deviations may occur in such data due to physical sedimentary properties. The consequences of these artifacts on element intensities are important for paleoclimatic studies, but as yet have not been adequately studied for high resolution (≤ 1‐cm interval) records. We have done a high resolution comparison between results from XRF scanning and from two more conventional methods: XRF with beads and inductively coupled plasma optical emission spectrometry (ICP‐OES), both on discrete samples. Our XRF scan data concord reasonably well with those from the conventional methods for most elements. In several discrete intervals large deviations occur that could have been attributed to major paleoceanographic events. However, these deviations appear to be mainly related to water content and distribution. We show that the variability in the water film thickness underneath the plastic foil is highly variable, causing significant apparent variability in all elements from Al to Fe. The unverified use of these elements in ratios can thus lead to deviations in the paleoenvironmental interpretation. Erroneous element (ratio) variability can, however, be recognized and corrected using conventional analytical data of a few discrete samples. The antipathetic behavior of Ca to K or Ti, and their similar behavior to water absorption, leaves their ratios relatively unaffected at variable water film thicknesses. Hence, Ca/K and Ca/Ti ratios are recommended for a preliminary down‐core overview of sedimentary variability and for stratigraphic correlations between unprocessed marine cores.

Ancient origin of the modern deep-sea fauna.

The origin and possible antiquity of the spectacularly diverse modern deep-sea fauna has been debated since the beginning of deep-sea research in the mid-nineteenth century. Recent hypotheses, based on biogeographic patterns and molecular clock estimates, support a latest Mesozoic or early Cenozoic date for the origin of key groups of the present deep-sea fauna (echinoids, octopods). This relatively young age is consistent with hypotheses that argue for extensive extinction during Jurassic and Cretaceous Oceanic Anoxic Events (OAEs) and the mid-Cenozoic cooling of deep-water masses, implying repeated re-colonization by immigration of taxa from shallow-water habitats. Here we report on a well-preserved echinoderm assemblage from deep-sea (1000–1500 m paleodepth) sediments of the NE-Atlantic of Early Cretaceous age (114 Ma). The assemblage is strikingly similar to that of extant bathyal echinoderm communities in composition, including families and genera found exclusively in modern deep-sea habitats. A number of taxa found in the assemblage have no fossil record at shelf depths postdating the assemblage, which precludes the possibility of deep-sea recolonization from shallow habitats following episodic extinction at least for those groups. Our discovery provides the first key fossil evidence that a significant part of the modern deep-sea fauna is considerably older than previously assumed. As a consequence, most major paleoceanographic events had far less impact on the diversity of deep-sea faunas than has been implied. It also suggests that deep-sea biota are more resilient to extinction events than shallow-water forms, and that the unusual deep-sea environment, indeed, provides evolutionary stability which is very rarely punctuated on macroevolutionary time scales.

Evolutionary changes in the biometry of the fossil radiolarian Stichocorys peregrina lineage in the eastern equatorial and eastern North Pacific

Abstract Stichocorys peregrina (Riedel) contributes to paleoceanography as a valuable stratigraphic tool for correlation of deep-sea siliceous sediments in world oceans and as a paleoceanographic indicator. This paper documents the evolutionary morphologic changes of the S. peregrina lineage from the middle Miocene to late Pliocene in the eastern equatorial and eastern North Pacific (IODP Site U1335 and ODP Site 887, respectively). The size and shape changes show that there are at least two geographical variations in the S. peregrina lineage. In the eastern equatorial Pacific, two significant morphological shifts took place about 11.0 and 7.0 Ma, but the morphology remained relatively stable from 7.0 to 3.0 Ma. Coincident with morphological changes in the S. peregrina lineage were changes in biogenic productivity. These changes suggest that there is a close correspondence between major paleoceanographic events in the late Neogene and evolutionary changes of the S. peregrina lineage in the low latitudes. In the high latitudes, the ratio of the third segment to fourth segment in width and height showed a maximum from 9.5 to 8.0 Ma, and decreased stepwise at about 8.0 and 6.5 Ma. However, the radiolarian data in the high latitudes do not show a clear relationship between the paleoceanographic events and size variation of this lineage. The evolutionary transition from Stichocorys delmontensis to S. peregrina can be used as a primary biostratigraphic marker in the low latitudes. However, it is not easy to use the evolutionary transition for biostratigraphic correlation and age determination in the high latitudes, because there is no obvious change in the ratio of the third to fourth segment widths that can be used to distinguish S. delmontensis from the descendant S. peregrina .

High resolution Holocene palynological record from the Scotian Shelf

Because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold Labrador Current and the Gulf Stream, the Atlantic Provinces experience some of the most dynamic climate conditions in Canada. Major climate changes occurred during the Holocene, as shown by pollen records from lakes, but previous paleoceanographic studies, based on low-resolution proxy-data records do not show major changes during the past 8000 years. Therefore, the Holocene history of Canada's Atlantic region was examined using a high-resolution palynological record from the Scotian Shelf (La Have Basin). Sea surface conditions were reconstructed using proxy-data from dinoflagellate cysts and paleobioclimatic transfer functions. Ocean–atmosphere interactions are determined by onshore–offshore correlation of marine and pollen records from Nova Scotia. Results show a succession of major paleoceanographic events. Sea surface temperatures (SST) (February and August) up to 5°C higher than today's average and slightly higher salinity are reconstructed between 10.5 and 8.5 ka. The last pulse of meltwater from the residual ice sheet affected the shelf waters between 8.5 and 6.5 ka by lowering the SST (in February) and the salinity. Most previous studies failed to record this event. Since 6.5 ka, August temperature generally remained around today's value, while February temperature was generally 2°C above it, except for recurring colder and lower salinity intervals. These cold intervals have a recurrence of about 1000 years. A slight cooling of summer SST is recorded in the last 500 years. Comparison with climatic reconstructions from Nova Scotia pollen records shows a difference in timing between ocean and atmosphere. The onset of the climatic optimum (hypsithermal) in Nova Scotia lags by about 2000 years (until 8 ka) relative to the ocean but it lasted longer. The Neoglacial cooling in Atlantic Canada however, started earlier (2 ka) than the late Holocene ocean cooling. La Have Basin's Holocene paleoceanography presents some differences from most other studies from the region: (1) the hypsithermal started earlier; (2) the last pulse of meltwater is recorded; (3) the last 6500 years are punctuated by colder intervals. Increased productivity and blooms of toxic algae in the early Holocene are probably due to a combination of factors: increased nutrients and a greater stability of the water column because of meltwaters, higher SST and increased upwelling or storm activity.

Stratigraphy and structure of the Lower Cretaceous of Lampazos, Sonora, (northwest Mexico) and its relationship to the Gulf Coast succession

The stratigraphy and structure of the Lower Cretaceous (Aptian-Albian) rocks exposed in the area of Lampazos, Sonora, are redefined and correlated to well-known stratigraphic successions of Chihuahua and northeast Mexico (Coahuila and Nuevo Leon). Originally, seven stratigraphic units were proposed for the Cretaceous rocks exposed in the Lampazos area, but in this article only five units (El Aliso, Agua Salada, Lampazos, Espinazo del Diablo, and Los Picachos formations) have been used, and we propose herein to discontinue usage of the other two (Nogal and La Mesa formations). This Aptian-Albian succession of east-central Sonora yields facies and fossil content remarkably similar to coeval sequences in the Gulf of Mexico realm (Chihuahua, Coahuila, and Nuevo Leon). These sections contain abundant microfossils (benthic and planktonic foraminifera, colomiellids, nannoconids, and radiolarians) that permit detailed biostratigraphic determinations. A complete Aptian-lower Albian section (base of K-6 through top of K-15 of the biochronologic scheme of Longoria, 1984) was identified. Abrupt lithic changes through the Aptian-Albian section of Lampazos revealed three major paleoceanographic events having an overall regional marine transgression, including an early Aptian (K-6 to K-7) event, a late Aptian (K-10 to K-11) event, and an early Albian (K-13 to K-14) maximum flooding phase. We used physical and biochronologic data to tie the aforementioned events to geochemically constrained Aptian-Albian oceanic anoxic events (OAEs) in Santa Rosa Canyon of Nuevo Leon. The close correlation between the oceanic events in east Sonora (northwest Mexico) and central Nuevo Leon (northeast Mexico) invokes the closer paleogeographic development of the two regions and undoubtedly links the area of Lampazos to a rapid encroachment of the paleo-Gulf of Mexico through north-central Mexico (the Mexican Sea) into northwestern Mexico (Chihuahua trough and Sonoran basin). The early Aptian (biozones K-6 to K-7) transgression has its maximum extension during the early Albian (biozones K-13 to K-14), culminating with the drowning of the carbonate platforms. The Lower Cretaceous rocks exposed in the Lampazos area are complexly folded and faulted. The more conspicuous structures are isoclinal and box-shaped folds and thrust faults, mostly oriented north-south and northwest-southeast, having vergences to both the northeast and southwest. A very conspicuous feature is the opposite vergence of thrust faults, either converging or diverging. Two dextral strike-slip faults (northeast-southwest and east-west) separate the area into three large blocks that have different patterns of folds and thrust faults. Also, it is evident that the area was affected by at least two episodes of normal faulting. Furthermore, the structural style of deformation present in the Lampazos succession is remarkably similar to the style of deformation of coeval rocks in northeastern Mexico, especially to the structure of the Chihuahua tectonic belt. The Lampazos succession is paleogeographically and tectonically related to the Chihuahua tectonic belt, and it is considered to be the westernmost extension of the ancestral Gulf of Mexico. The fact that the Lampazos succession can be lithocorrelated to known sequences in northeastern Chihuahua (Lucero, Ahumada, and Loma Plata formations) and northeast Mexico (Cupido, San Angel, La Pena, and Tamaulipas formations), which are know to be source rocks in exploration wells in Nuevo Leon and Coahuila, makes the Lampazos area of Sonora potentially attractive as an exploration target.

Ecological structuring and evolution of deep sea agglutinated foraminifera — a review

Recent agglutinated foraminiferal communities exhibit both simple and complex ecological structuring within habitats. Simple ecological structuring (i.e. a limitation of the entire fauna at or close to the sediment-water interface and absence of erect suspension feeding forms) is mainly observed under low oxygen conditions and high organic flux or after severe substrate disturbance. Oligotrophic deep sea conditions with low vertical particle flux and little substrate disturbance as in the central areas of the modern oceans lead to the development of complex ecological structuring with various highly adapted “specialists” (i.e. mobile infaunal forms, a variety of epifaunal suspension feeders, and epifaunal deposit feeders with special mechanisms to avoid energy loss and use food resources not exploitable by other organisms). The paleontologic record of species diversity and habitat preferences since the late Jurassic exhibits two trends: (1) a general trend from simple to complex ecological structuring within habitats leads to an overall increase in diversity; (2) fluctuations in this trend coinciding with major paleoceanographic events, i.e. changes in deep water oxygenation and paleoproductivity. From a comparison of Recent and fossil communities from various trophic situations we conclude, that the ecological structuring of agglutinated foraminifera within habitats may have been one of the most important driving forces (selection mechanisms) in the evolution of this special group of protists.

Paleocene-Pleistocene benthic foraminiferal evidence of major paleoceanographic events in the eastern South Atlantic (DSDP Site 525, Walvis Ridge)

Benthic foraminifers in the size-fraction greater than 0.073 mm were studied in 88 Paleocene to Pleistocene samples from Deep Sea Drilling Project Site 525 (Hole 525A, Walvis Ridge, eastern south Atlantic). Clustering of the samples on the basis of the 86 most abundant foraminifers (in total, 331 taxa were identified) allowed separating two major assemblage zones: the Paleocene to Eocene interval, and the Oligocene to Pleistocene interval. Each of these, in turn, were subdivided into three minor subzones as follows: lower upper Paleocene (approx. 62.4 to 57.8 Ma); upper upper Paleocene (56.6 to 56.2 Ma); lower and middle Eocene (55.3 to 46.8 Ma); upper Oligocene to middle Miocene (25.3 to 16 Ma); middle Miocene to Pliocene (15.7 to 4.2 Ma); and lower Pleistocene (0.4 to 0.02 Ma), with only minor differences with the previous zone. Some very abundant taxa span most of the column studies ( Bolivina huneri, Cassidulina subglobosa, Eponides bradyi, E. weddellensis, Gavelinella micra, Oridorsalis umbonatus, etc.). Several of the faunal breaks recorded coincide with conspicuous minima in the specific diversity curve, thus suggesting that the corresponding turnovers signal the final stages of periods of faunal impoverishment. At least one major bottom-water temperature drop (as derived from δ 18O data) is synchronous with a decrease in the foraminiferal specific diversity. On the other hand, a specific diversity maximum in the middle Miocene might be associated with a δ 13C increase at approx. 16 to 12 Ma. Highest foraminiferal abundances (up to 600–800 individuals per gram of dry sediment) occurred in the late Paleocene and in the early Pleistocene, in coincidence with the lowest diversity figures calculated. The magnitude of the most important faunal turnover recorded, between the middle Eocene and the late Oligocene, is magnified in our data set by the large hiatus which separates the middle Eocene from the upper Oligocene sediments. Considerably smaller overturns occurred within the late Paleocene (in coincidence with changes in the specific diversity, absolute abundance of foraminiferal tests, and δ 13C), and in the middle Miocene (in coincidence with a specific diversity maximum and a δ 13C excursion). New information on the morphology and the stratigraphic ranges of several species is furnished. For all the taxa recorded the number of occurrences, total number of individuals identified and first and last appearances are listed.

Mesozoic calcareous nannofossil evolution: Relation to paleoceanographic events

The taxonomic evolution of Jurassic and Cretaceous calcareous nannofossil species is described using the following indices: species diversity, rate of speciation, rate of extinction, rate of diversification, rate of turnover, survivorship, and species accretion. The Jurassic prior to the late Oxfordian is characterized by positive diversification rates, that is, rates of speciation exceeded rates of extinction. Highest rates of diversification occurred in the late Lias and early Oxfordian. During the generally regressive latest Jurassic, diversification rates remained low and rates of extinctions exceed rates of speciation. In the early Cretaceous, rates of diversification are positive and peak in the early Valanginian, early Aptian, and middle Albian, after which time rates of extinction generally exceed rates of speciation. Such peaks in rate of evolution coincide with times of increased accumulation of organic carbon in the ocean (“anoxic events”). Peaks in rates of extinction result in very high rates of turnover during times of major regressions, in particular, in the Tithonian and Maastrichtian. Survivorship analyses for three datum planes (74.5, 144, and 160 Ma) show relatively constant extinction rates with some stepping in the older part; they are best explained by a temporally fluctuating abiotic environment causing changes in the probability of extinction. Species accretion curves are also relatively linear with some indication of changing rates of speciation. The coincidences of major changes in evolutionary rates with major paleoceanographic events are indicative of a predominantly abiotic control of nannoplankton evolution. Relationships of evolutionary rates of calcareous nannoplankton with deep ocean ventilation, sea level, and ocean fertility indicates that global tectonic processes are the ultimate causes of evolutionary change.

Evolutionary changes in some Late Neogene planktonic foraminiferal lineages and their relationships to paleoceanographic changes

The timing of evolutionary changes in some late Neogene lineages of planktonic foraminifers and major paleoceanographic events are evaluated to assess possible correspondences between paleoclimatic change (in a broad sense) and evolutionary innovations. Previously published data on evolutionary changes in the Globorotalia inflata lineage, the Globorotalia tumida lineage, and the Globorotalia truncatulinoides lineage, and new data on the Sphaeroidinella dehiscens lineage, are used in the study. Most evolutionary rate changes in these lineages are shown to occur near times of major paleoceanographic events. For example, rapid increase in conicality and weakening of the keel in the G. inflata lineage in the latest Miocene coincided with the 6.2‐Ma event (global cooling, sea level regression, and shift in carbon isotope ratios in foraminiferal tests). Disappearance of keeled morphotypes (Globorotalia conomiozea) in the same lineage, and appearance of nonkeeled forms with rounded periphery (Globorotalia puncticulata) coincided with the return of warmer, more stable climatic conditions, and transgressions at the Miocene/Pliocene boundary (5.3 Ma). Phyletic transformation from Globorotalia plesiotumida into G. tumida also took place across this boundary, and supplementary apertures first developed in the S. dehiscens lineage. Supplementary apertures in the S. dehiscens lineage were rare through the early Pliocene but became rapidly dominant in the populations in the interval between 3.4 and 3.3 Ma, where major paleoceanographic changes occurred (the 3.4‐to 3.2‐Ma event marked by cooling of surface waters and increased production of bottom waters at high latitudes, resulting in strengthening of ocean vertical and horizontal gradients). Forms without a supplementary aperture became extinct only 0.3–0.4 m.y. later (3.0 Ma), and at about the same time, G. inflata appeared in the fossil record. Although evolutionary change exhibits striking temporal correlation with climatic change, some evolutionary time series do not show any obvious relationship to paleoclimate: chamber number in the final whorl in the G. inflata lineage and conicality in G. truncatulinoides.

Earth movements, paleoceanography, paleoclimatology and eustasy: Major Cenozoic events in the North Atlantic

Abstract A geodynamic balance between movements of the Fennoscandian Shield and the North Atlantic ocean floor (the Faeroe-Iceland Ridge region) is proposed: a vertical movement in one area is balanced by counter-movements in the other area due to the transfer of a low viscosity mass in the asthenosphere. A rapid uplift of the Fennoscandian Shield (and the Barents Sea region) of at least 600 m around the Oligocene-Miocene transition (22.5 Ma) was compensated for by subsidence of the Faeroe-Iceland Ridge area of the order of 1000–1500 m. A significant subsidence of the Fennoscandian Shield at about 0.9–0.8 Ma (of about 600 m) is likely to have been compensated by an uplift of the Faeroe-Iceland Ridge area (explaining a major paleoclimatic change at this time). Major paleoceanographic events occurred at about 38 Ma, 22.5 Ma and 3.2 Ma. A drastic paleoclimatic event — the beginning of the north hemisphere continental glaciations — occurred at about 2.5 Ma. Eustasy is much more complex than originally assumed...