Foraminiferal Fossil Research Articles

The Foraminifera Fossil Record of the Sedimentary Rock at Kotadjawa, Lampung, Indonesia: The Significance of Marine Paleontological Insight

Kotadjawa, located on the west coast of Lampung, directly faces the Indian Ocean. Lithified calcareous sedimentary beds are prevalently outcropped along this coastline. These beds likely belong to the Simpangaur Formation, which may be associated with the paleocoastal depositional environment and tectonic uplift of the Indian Ocean. Therefore, we investigated the paleontological record, focusing on foraminifera as potential indicators of the paleoenvironment. This study aimed to identify, record, and calculate the relative abundance of benthic foraminifera in the sedimentary beds of Kotadjawa, Lampung. The samples were prepared via chemical treatment of 10% H2O2 for 48 hours. Our results revealed a diversity of benthic foraminiferal fossils within the sedimentary rock. Notably, 11 benthic foraminifera genera were fossilized in the observed outcrop: Textularia (18.4%), Sigmoilopsis (16.5%), Rectobolivina (15.4%), Uvigerina (15.5%), Nodosaria (14.5%), Elphidium (11.5%), Lenticulina (7.7%), Hormosina (6.8%), Bolivina (6.8%), and Globobulimina (5.8%). These results suggested that the sedimentary beds exposed in our study area ranging from the foreshore to the deep ocean floor ecosystem. This suggests that a sediment mixing event, possibly triggered by a paleocatastrophic event, influenced the deposition of these beds. This study provides new insights into marine paleoenvironmental conditions and paleocatastrophic events along the west coast of Lampung, Sumatra.

Geochemical Differences Between Alive, Uncrusted and Dead, Crusted Shells of Neogloboquadrina pachyderma: Implications for Paleoreconstruction

AbstractPlanktic foraminiferal‐based trace element‐calcium ratios (TE/Ca) are a cornerstone in paleoceanographic reconstructions. While TE‐environment calibrations are often established through culturing experiments, shell growth in culture is not always consistent with growth in a natural setting. For example, many species of planktic foraminifera thicken their shell at the end of their life cycle, producing a distinct “gametogenic” crust. Crust is common in fossil foraminifers, however, shells grown in culture do not often develop a thick crust. Here, we investigate potential vital effects associated with the crusting process by comparing the trace element (Mg/Ca, Na/Ca, Ba/Ca, Sr/Ca, Mn/Ca, Zn/Ca) and stable isotope (δ13C, δ18O) composition of alive, fully mature, uncrusted shells to recently deceased, crusted shells of Neogloboquadrina pachyderma collected from the same plankton tows off the Oregon (USA) coast. We find that uncrusted (N = 55) shells yield significantly higher Ba/Ca, Na/Ca, Mn/Ca, and Sr/Ca than crusted (N = 66) shells, and crust calcite records significantly lower TE/Ca values for all elements examined. Isotopic mixing models suggest that the crust calcite accounts for ∼40%–70% of crusted shell volume. Comparison of foraminiferal and seawater isotopes indicate that N. pachyderma lives in the upper 90 m of the water column, and that crust formation occurs slightly deeper than their average living depth habitat. Results highlight the necessity to establish calibrations from crusted shells, as application of calibrations from TE‐enriched uncrusted shells may yield attenuated or misleading paleoceanographic reconstructions.

Distinct responses of abundant and rare foraminifera to environmental variables in the Antarctic region revealed by DNA metabarcoding

The Antarctic region plays a key role in regulating the Earth’s climate and contains a unique record of environmental change. Foraminifera, a group of shell-bearing protists, are widely used as paleoenvironmental proxies. However, core-based reconstructions of Antarctic paleoenvironments are often hindered by the lack of foraminiferal fossil record. Foraminiferal ancient DNA provides new avenues for understanding environmental change, but the correlation between molecular ecological features of foraminifera and environmental conditions remains poorly understood. Here, we obtained surface sediment samples from the Southern Ocean at water depths ranging from 50 to 4399 m and measured eight environmental variables. We generated a DNA metabarcoding dataset of foraminifera and presented the first assessment of relationships between foraminiferal molecular diversity and environmental variables in the Antarctic region. The results showed that the alpha diversity of whole community and abundant subcommunity was positively correlated with water depth and negatively correlated with temperature, chlorophyll a and pheophytin a, while the alpha diversity of rare subcommunity had no linear correlation with the above environmental variables. Both rare and abundant foraminiferal subcommunities exhibited distance-decay relationships, but only the beta diversity of rare subcommunity showed a significant positive correlation with water depth. This study reveals contrasting biogeographical patterns of abundant and rare foraminifera and their different correlations with Antarctic environmental variables, holding promise to provide more proxies for reconstructing past environments using foraminiferal ancient DNA and more information for predicting the impact of future environmental changes on polar biodiversity.

Prehistoric sea-salt manufacture as an adaptation strategy to coastal flooding in East China

Coastal societies are known to be vulnerable to sea-level rise. However, here we report the occurrence of salt manufacturing in the archaeological record of an island of East China that reveals an adaptation strategy by a prehistoric coastal society to sea-level rise through an interdisciplinary study of archaeology and stratigraphy. Archaeological findings and observations of marine microfossils and alkaline earth metals in sediment sequences, together with radiocarbon and optically stimulated luminescence (OSL) dating, reveal that the site was initially occupied at ca. 2900 BCE as an island village with multiple subsistence strategies including hunting, fishing, and stone-tool making associated with the formation of a freshwater dominated coastal plain. Seawater inundation induced by relative sea-level rise occurred at the site at ca. 2400 BCE when Neolithic people constructed elevated mounds and developed specialized sea-salt manufacture in the sheltered tidal flat environment on the island. Evidence from the foraminiferal assemblage suggests that salty soil was scraped from the surface of the adjacent tidal flats and waste material was dumped around the artificial mounds. Micro-structures of the foraminiferal fossils further indicate that these salty soils were air-dried before brine enrichment to produce high-quality salt. Such an economic shift from multiple subsistence into specialized sea-salt manufacture on the island stands in striking contrast to the contemporaneous abandonment of numerous Liangzhu settlements on the adjacent mainland due to coastal flooding. We suggest that prehistoric sea-salt manufacture on the East China coast signifies the resilience of coastal societies in facing the challenge of sea-level rise through exploitation of geographical advantages and marine resources.

Mohammadabad Manganese deposit, southwest Sabzevar basin, Iran: Evidence of sea-floor exhalation and geochemical studies in the late Cretaceous volcano-sedimentary sequence

The southwest Sabzevar basin in northeast Iran is one of the most important areas for volcanogenic stratiform manganese deposits. The Mohammadabad Mn deposit, found in this basin, is hosted by the upper late Cretaceous marly tuffs in a region that has an active history of tectonism. Their geology, mineralogy and geochemistry, including major, trace and rare earth elements (REE), are described in this work. The main ore minerals include pyrolusite, psilomelane, cryptomelane, with minor braunite and manganite. Four styles of manganese mineralization are recognized: (1) layered; (2) nodular; (3) disseminated; and (4) replacement to massive. Regardless of style, pyrolusite, psilomelane, and cryptomelane usually tend to parallel the stratification of sediments, while braunite veins occur in high angle fractures. The replacement of radiolarian and foraminiferal fossils by manganese minerals during diagenesis near the seawater-sediment interface suggests that mineralization occurred in oxygen-rich conditions under the influence of low-temperature hydrothermal fluids. The geochemistry of trace elements of manganese oxides and rare earth elements gives clear evidence of hydrothermal-exhalative origin for Mohammadabad deposit. In general, ore minerals have Co/Ni ratios above 0.12, and U/Th ratios vary from 0.13 to 11.29. The presence of negative Eu anomalies in manganese minerals shows that the ore-forming fluids were generally low-temperature and oxic during mineral formation. In-situ mineralogy studies based on SEM-EDS have distinguished syngeneic and diagenetic Mn systems during the formation of manganese mineralization. The Mohammadabad deposit is considered a typical case of volcanic hydrothermal exhalative-diagenetic Mn mineralization, in which minerals deposited when hydrothermal fluid was released from oxic to dysoxic water columns.

The late Neogene to Quaternary surface water changes as responses from planktonic foraminifera at the transitional Subantarctic Zone

A well preserved and continuous fossil record of planktonic foraminifera could provide insights into global paleoceanographic and surface water changes. We utilize a ~10-million-year record of planktonic foraminifera along with biogenic proxies and stable isotopes from the Ocean Drilling Program (ODP) Site 1088 Hole B, to understand the late Neogene to Quaternary faunal evolution and surface water changes happening in the Subantarctic Zone. Organic carbon and CaCO3 proxy records suggest high productive surface waters linked to the biogenic productivity high in the Indian Ocean between ~9.4 and 8.1 Ma. The planktonic foraminiferal fossil record between ~7.1 and 6.2 Ma shows high relative abundance of surface-dwelling faunas Globigerina bulloides, Globigerinita glutinata and Neogloboquadrina pachyderma simultaneously with high CaCO3 content. The evolution of deep dwelling faunas especially the globoconellids can be tracked between the late Miocene to middle Pliocene as a consequence of deeper export in nutrients and organic matter. At site 1088 the evolution within the Globoconella inflata lineage coincides with changes in hydrographic conditions. The Miocene – Pliocene transition (~6 to 4.5 Ma) marks the appearance of Globorotalia crassaformis and Neogloboquadrina dutertrei at the site. The warmer middle Pliocene assemblage between 4.6 and 3 Ma shows higher abundance of Globoconella inflata and Globoconella puncticulata. An inverse relationship between the polar fauna Neogloboquadrina pachyderma and Globoconella inflata, typical of low to mid lattitudes, suggest a southward position of the subtropical and subantarctic fronts during the middle Pliocene. Enriched organic carbon and ẟ13C values at Site 1088 indicate the presence of nutrient rich surface waters between 4.2 and 4.0 Ma and 3.4 to 3.1 Ma. Transition to a much dynamic Pleistocene saw glacial interglacial variability among the dominant planktonic foraminifera at the site indicating varying surface water conditions controlled by the movement of hydrographic fronts. Our study shows how the large changes in global climate, ocean circulation, nutrient enrichment and frontal movements influenced the abundance, occurrence and evolution of surface and deep dwelling planktonic foraminifera over the last 10 Ma.

A deep-sea foraminiferal assemblage scattered through the late Cenozoic of Antarctic Peninsula and its biostratigraphic and biogeographic implications

AbstractOur knowledge of the foraminiferal fossil record of Antarctica is notoriously patchy but still offers us an overview of its Cenozoic faunas. Few occurrences have been reported for the continent, with deep-sea assemblages described mainly for its eastern portion. Here we describe 21 taxa of large agglutinated foraminifers from the Miocene Hobbs Glacier Formation and the Plio-Pleistocene Weddell Sea Formation on Seymour Island, West Antarctica, including the gigantic Ammodiscus vastus new species. Most of them consist of genera or species typical of deep-sea agglutinated assemblages. All specimens are completely filled and partially covered by lithified micrite. This, along with the postfill fragmentation of some tests, indicates their re-elaboration from older deposits. Because all of these foraminifers share the same taphonomic features and most of them represent taxa associated with deep-sea settings, they probably represent a flysch-type assemblage from an unknown deposit that was eroded and had its microfossils scattered through post-Paleogene sediments. A Paleocene age for this putative assemblage is indicated by the presence of Reticulophragmiun garcilassoi (Frizzell, 1943), a Paleocene index fossil, and by its association with the Cretaceous–Paleocene Ammodiscus pennyi Cushman and Jarvis, 1928. If taken as a coherent foraminiferal assemblage, it represents one of the few deep-sea assemblages known for West Antarctica, and the first flysch-type assemblage recognized for the Antarctic Cenozoic. In addition, it would show that the Paleocene foraminiferal communities of the West Antarctica's deep-sea floor were more like their Pacific counterparts than their Atlantic equivalents.UUID: http://zoobank.org/0d281489-c0c6-47b4-9884-f820806485b7

Shoreline migration paths and depositional architecture of early–mid Miocene deltaic clinoforms in response to sea‐level changes in the north‐eastern shelf margin, South China Sea

AbstractShoreline trajectory analysis improves the understanding of the correlation between clinoform architecture, shoreline and shelf‐edge development, and sea‐level changes. This study uses cores, well‐logs and seismic data to investigate the depositional architecture and shoreline migration paths of early−mid Miocene deltaic clinoforms in the northern Pearl River Mouth basin, South China Sea. Five clinoform types are observed, including sigmoidal, oblique, tangential oblique, parallel oblique and sigmoidal‐oblique clinoforms. Both the rollovers of deltaic clinoforms in seismic sections and the transitional points between delta plain and delta front deposits in well correlation cross‐sections can be used as the indicators for shoreline positions, provided that there are no significantly extended subaqueous deltas. This allows for the identification of three shoreline trajectory types from a single clinoform set and three major stages from the net shoreline trajectory for multiple clinoform sets. A landward‐directed net shoreline trajectory and ascending shoreline trajectories dominate in Stage 1 (23.8 to 17.5 Ma) with sigmoidal clinoforms transitioning into parallel oblique clinoforms, suggesting a rise in third and fourth‐order relative sea level. Stage 2 (17.5 to 13.8 Ma) displays flat or descending trajectories and an overall seaward‐directed net trajectory with a change from parallel to tangential oblique clinoform, indicating a relative sea‐level fall. The reoccurrence of sea‐level rise in Stage 3 (13.8 to 10.5 Ma) was inferred by a landward migration of parallel oblique clinoforms. This study shows that shoreline trajectory and net shoreline trajectory plotted from both seismic and well data is consistent with the regional sea‐level curves estimated from foraminiferal fossil records and the shelf‐edge development, which can be used to estimate the third and fourth‐order relative sea‐level changes in passive margins with wide, low‐gradient shelves. Furthermore, clinoform architecture and migration may have been controlled by the variations of subsidence/uplift and sediment supply produced by tectonic events.

Geochemical and Mineral Properties of Quaternary Deep-Sea Sediments in the Central-Tropical Pacific and Its Response to the Mid-Pleistocene Transition

Global climate and oceanic water masses have undergone profound changes during the middle Pleistocene transition; however, due to a lack of foraminiferal fossils, the nonfossiliferous pelagic deposits were less detected in previous reports. In this work, a gravity core from the Kamehameha Basin in the Central Pacific was studied in terms of magnetostratigraphy, clay mineral and geochemical elements. The main results are: (1) nine magnetozones are recognized in the core, which can be correlated to the geomagnetic polarity timescale from chrons C2n to C1n; (2) smectite is the dominant clay mineral, and the others are illite, chlorite and kaolinite; and (3) the sediments are mainly composed of Al2O3, Fe2O3, MnO, Na2O and TiO2. Based on these results, a geochronological framework for the study area was established, and the depositional rates are estimated as 3–7 m/Myr in the Quaternary, showing an increase during the middle Pleistocene transition. By comparing the findings to various paleoenvironmental processes, it is inferred that the increased sedimentation in the Kamehameha Basin may have resulted from the induced weathering processes and the strengthened aeolian inputs from inner Asia. Moreover, regional circulation related to bottom water evolution has experienced a rapid reorganization across the middle Pleistocene transition. All these findings illustrate the potential of deep-sea sediments in the central tropical Pacific in revealing some key features in paleoclimatology and paleoceanography, which are worthy of further investigation in the future.

The processes of isolation of the Japanese main islands based on stratigraphic analysis of both molluscan and foraminiferal fossils, and the history of the Tokai earthquake

The processes of isolation of the Japanese main islands based on stratigraphic analysis of both molluscan and foraminiferal fossils, and the history of the Tokai earthquake

The Pennsylvanian System in the Sacramento Mountains, New Mexico, USA

Pennsylvanian sedimentary rocks in the Sacramento Mountains, New Mexico, comprise an ~1 km thick stratigraphic section. The Morrowan-Desmoinesian Gobbler Formation was deposited by shallow marine processes in and near the Alamo clastic trough. In this trough, the Desmoinesian-Missourian Gray Mesa Formation (Bug Scuffle Member, Gobbler Formation) is a relatively thin unit (Space History Member) representing the glacioeustatic Amado event. The Missourian-Virgilian Beeman Formation includes the lower, siliciclastic Indian Wells Canyon Member and overlying, carbonate-rich Horse Ridge Member. The Virgilian Holder Formation consists of algal bioherms (Little Dry Canyon Member) overlain by the mixed carbonate-siliciclastic Mill Ridge Member. The Virgilian-Wolfcampian Bursum Formation is mixed siliciclastic-carbonate strata that represent shallow marine and nonmarine paleoenvironments. Animal and plant remains occur throughout the section. Unit age determinations are primarily based on conodont faunas recovered from the Gobbler, Gray Mesa, and Beeman Formations. Many conodont faunas correlate with Midcontinent cyclothems. Extensive algal and foraminiferal fossils also were identified in limestones from the section and contributed to age determinations. The Beeman Formation in particular contains an extensive Missourian macroflora. The macroflora is of “mixed” composition, containing typical wetland elements intimately intermixed with taxa indicative of seasonally dry habitats. A seasonally wet-dry background climate is indicated. It is unlikely that droughttolerant plants were transported exclusively from “uplands.” Some plant remains have arthropod-feeding evidence. Previous analyses identified late Paleozoic ice-age glacioeustasy as the primary depositional driver of Pennsylvanian sedimentation in the Sacramento Mountains. We question this because of problems with those analyses and because of ample evidence of local tectonics and microclimate changes as important drivers of sedimentation in this area. Three Pennsylvanian Ancestral Rocky Mountain orogeny tectonic pulses can be identified in the Sacramento Mountains: Morrowan-Atokan, Missourian, and late Virgilian-Wolfcampian.

Planktonic foraminiferal biostratigraphy of the Limboto Limestone, Gorontalo Province, Indonesia

The limestone research within the Limboto Basin of Gorontalo Province becomes a new challenge, particularly for the study of planktonic foraminiferal biostratigraphy. This study uses the data obtained from the measured section in the north-western part of Limboto Lake. The purpose of this study is to determine the planktonic foraminiferal biozonation and the relative age of Limboto limestones. The analyzed planktonic foraminiferal fossils can be classified as well to moderately preserved of various species, in the context of abundance, categorized as frequent to abundant. There are three recognized planktonic foraminiferal biozones, i.e., two biozones for Miocene age (M13b and M14) and one biozone for Pliocene age (PL1). The Miocene biozones are named as Globorotalia plesiotumida partial range zone (M13b) and Pulleniatina primalis-Globoquadrina dehiscens concurrent range zone (M14), while the name of Pliocene biozone is Globorotalia acostaensis partial range zone (PL1). The results of this study can be a reference to propose an age of Limboto Limestone Formation. Identification and demarcation of the Limboto Limestone Formation are based on the time interval and relative age of the formation based on planktonic foraminifera.

Evolution of the Southwest Australian Rifted Continental Margin During Breakup of East Gondwana: Results From International Ocean Discovery Program Expedition 369

AbstractInternational Ocean Discovery Program Expedition 369 drilled four sites on the southwestern Australian continental margin, in the deep water Mentelle Basin (MB) and on the neighboring Naturaliste Plateau (NP). The drillsites are located on continental crust that continued rifting after seafloor spreading began further north on the Perth Abyssal Plain (PAP) between magnetochrons M11r and M11n (133–132 Ma), ending when spreading began west of the NP between chrons M5n and M3n (126–124 Ma). Drilling recovered the first in situ samples of basalt flows overlying the breakup unconformity on the NP, establishing a magnetostratigraphically constrained eruption age of >131–133 Ma, and confirming a minimal late Valanginian age for the breakup unconformity (coeval with the onset of PAP seafloor spreading). Petrogenetic modeling indicates the basalts were generated by 25% melting at 1.5 GPa and a potential temperature of 1380°C–1410°C, consistent with proximity of the Kerguelen plume during breakup. Benthic foraminiferal fossils indicate that the NP remained at upper bathyal or shallower depths during the last 6 Myr of rifting and for 3–5 Myr after breakup between India and Australia. The limited subsidence is attributed to heat from the nearby Kerguelen plume and PAP spreading ridge. The margin subsided to middle bathyal depths by Albian time and to lower bathyal (NP) or greater (MB) depths by late Paleogene time. Periods of rapid sedimentation accompanied a westward jump of the PAP spreading ridge (108 Ma), rifting on the southern margin (100–84 Ma), and opening of the southern seaway between Australia and Antarctica (60–47 Ma).

Episodic Atlantic Water Inflow Into the Independence Fjord System (Eastern North Greenland) During the Holocene and Last Glacial Period

Four marine sediment cores from two sites in the Independence Fjord system near the Wandel Sea in eastern North Greenland were analyzed for their dinoflagellate cyst (dinocyst) and foraminiferal fossil content to gain insight into the water mass properties and evolution of the outer fjord system over the Holocene and Last Glacial Period. While regarded as a climate-sensitive region, the climatic history of the area remains largely unknown and has been documented through the study of two composite marine sediment cores only once before. The results presented here reveal that Atlantic waters entered the Independence Fjord episodically during the studied interval. High concentrations of dinocysts and foraminifers in the upper few centimeters of the cores are in line with oceanographic measurements clearly illustrating that Atlantic-sourced waters make up the lower part of the water column in the area in modern times. Radiocarbon dating of foraminiferal tests and increasing microfossil concentrations and diversity towards the top of the cores suggest that this inflow has been occurring for at least 2000 years and intensified towards recent times. The core sections below the upper few centimeters are devoid of (Quaternary) dinocysts and calcareous foraminifera with the exception of the lowermost segments of the longer cores. While low foraminiferal test quantities in these lowermost core sections prevent precise age determination, their radiocarbon ages reveal that they were deposited prior to 30 000 years ago, indicating the existence of a pathway for the occasional intrusion of Atlantic-sourced waters into, and thus relatively small local ice caps around, the fjord system prior to the Last Glacial Maximum. The previously documented early Holocene inflow of Atlantic-sourced waters was not detected in our records, likely suggesting a strong topographical and deglacial control on the routing of these water masses during the early Holocene.

Changes of marine productivity and sedimentary environment recorded by biogenic components in the Antarctica Ross Sea since the last deglaciation

Changes in the marine productivity and sedimentary environment since the last deglaciation in the Ross Sea are presented in this paper. Opal has replaced calcium carbonate as the major biogenic component and has a significantly positive correlation with total organic carbon (TOC), which indicates that siliceous phytoplankton controlled the absorption and release of carbon by the biological pump and was the main producer of marine organic matter. Using the AMS 14C age framework, foraminiferal fossils and redox sensitive elements (RSEs), we found that both the sedimentary environment and marine productivity changed clearly in ∼11 cal ka BP, which is more likely related with the melting and retreat of the Ross Ice Shelf. In addition, the increase of marine productivity promoted the sinking of more organic-matter to the seabed. A large proportion of oxygen in the bottom water body was consumed and more carbon dioxide was produced during the decomposition of organic matter, making the bottom water body more soluble to calcium carbonate.

Insights into the procurement and distribution of fossiliferous chert artefacts across southern Australia from the archival record

Following from previous research in Western Australia, this study explores the use of embedded microfossils—including bryozoan and foraminiferal fossil assemblages—to help identify source and distribution of fossiliferous chert artefacts from South Australian archives. Artefacts from key archaeological sites include Allen’s Cave, Koonalda Cave, Wilson’s Bluff, Ooldea and Kongarong. Preliminary analyses indicate a possible differentiation of fossiliferous chert types east and west of the Eyre Peninsula, from Otway Basin and Eucla Basin limestones, respectively. The widespread distribution and trade of fossiliferous chert is supported by ethnographic descriptions of the sources, procurement and trade as recorded by Daisy Bates, Thomas Draper Campbell and Norman Tindale. Further work combining biostratigraphy and lithology with archaeology and ethnography is needed to explore these ideas further.

Mg ∕ Ca and <i xmlns="">δ</i><sup>18</sup>O in living planktic foraminifers from the Caribbean, Gulf of Mexico and Florida Straits

Abstract. Past ocean temperatures and salinities can be approximated from combined stable oxygen isotopes (δ18O) and Mg ∕ Ca measurements in fossil foraminiferal tests with varying success. To further refine this approach, we collected living planktic foraminifers by net sampling and pumping of sea surface water from the Caribbean Sea, the eastern Gulf of Mexico and the Florida Straits. Analyses of δ18O and Mg ∕ Ca in eight living planktic species (Globigerinoides sacculifer, Orbulina universa, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globorotalia menardii, Globorotalia ungulata, Globorotalia truncatulinoides and Globorotalia tumida) were compared to measured in situ properties of the ambient seawater (temperature, salinity and δ18Oseawater) and fossil tests of underlying surface sediments. “Vital effects” such as symbiont activity and test growth cause δ18O disequilibria with respect to the ambient seawater and a large scatter in foraminiferal Mg ∕ Ca. Overall, ocean temperature is the most prominent environmental influence on δ18Ocalcite and Mg ∕ Ca. Enrichment of the heavier 18O isotope in living specimens below the mixed layer and in fossil tests is clearly related to lowered in situ temperatures and gametogenic calcification. Mg ∕ Ca-based temperature estimates of G. sacculifer indicate seasonal maximum accumulation rates on the seafloor in early spring (March) at Caribbean stations and later in the year (May) in the Florida Straits, related to the respective mixed layer temperatures of ∼26 ∘C. Notably, G. sacculifer reveals a weak positive linear relationship between foraminiferal derived δ18Oseawater estimates and both measured in situ δ18Oseawater and salinity. Our results affirm the applicability of existing δ18O and Mg ∕ Ca calibrations for the reconstruction of past ocean temperatures and δ18Oseawater reflecting salinity due to the convincing accordance of proxy data in both living and fossil foraminifers, and in situ environmental parameters. Large vital effects and seasonally varying proxy signals, however, need to be taken into account.

夭折した小沢儀明の残した業績 ―秋吉台の横臥褶曲の発見と微古生物学の体系化―(地学者列伝)

夭折した小沢儀明の残した業績 ―秋吉台の横臥褶曲の発見と微古生物学の体系化―(地学者列伝)

Rich shallow-water benthic ecosystem in Late Miocene East Antarctica (Fisher Bench Fm, Prince Charles Mountains)

Abstract A single shell of a pectenoid bivalve was found in the lower part of the Fisher Bench Formation (Fisher Massif, Prince Charles Mountains). In contrast to glacigenic sediments that form extensive outcrops in this area and are almost barren of foraminifera, small pieces of muddy sand attached to this shell contained a rich assemblage of calcareous and siliceous microfossils. The diatom assemblage associated with this shell was dominated by marine benthic forms with abundant Saeptifera, associated with subordinate marine neritic taxa, and Chaetoceros resting spores. Benthic foraminifera are very abundant but of low diversity, strongly dominated by Rosalina globularis with uniform chambers. It is the first Miocene foraminiferal assemblage reported from East Antarctica excluding the Ross Sea area. These new results confirm the early Late Miocene age of the shell that was dated by Sr isotope values in an earlier study, and suggest an initial phase of deposition in a shallow-water (possibly no > 10 m) marine, cold, and possibly oligotrophic environment. After initial burial in microfossil-bearing sediment that was weakly lithified, the shell was eroded and transported to be incorporated in fossil-poor glacigenic sediments. Since transport from a nearby location could have been facilitated by glacial and/or down-slope movements in this fjordal setting, the shell is considered para-autochthonous. Based on the Antarctic foraminiferal fossil records, it appears that through most of the Cenozoic, those parts of the Antarctic continental shelf that were deeper than a few tens of meters, with the exception of the Ross Sea area, were mostly unfavorable for development and/or preservation of calcareous microfossils.

Paleoceanographic changes in the Northeast Indian Ocean during middle Miocene inferred from carbon and oxygen isotopes of foraminiferal fossil shells

The middle Miocene transition witnessed rapid fluctuations in oceanographic and climatic systems. However, very limited work has been attempted in Miocene sediments of the Northern Indian Ocean to identify these changes. Here we present the first detailed δ13C and δ18O records of surface and deep dwelling foraminifera from ODP site 758 in the Northeast Indian Ocean, located atop the Ninetyeast Ridge. Carbon and oxygen isotopic data on Globigerinoides quadrilobatus (planktonic) and Cibicidoides wuellerstorfi (benthic foraminifera) indicated various global and local successions of oceanographic and climatic importance. The climatic events recorded at ODP 758 are; (a) Mid Miocene climatic Optimum (17–15 Ma), (b) Monterey excursion (17–14 Ma), (c) East Antarctica Ice sheet formation (13.8 Ma), (d) Initiation of Indian Summer Monsoon with waning of Antarctica Ice sheet (12.3–10.4 Ma), and (e) evidence of a cooling event (10.2–9.6Ma).Our benthic foraminifera δ18O record showed almost identical deep water evolution to that of the Indo Pacific for 13.9–11.5 Ma interval. A significant decrease in δ13Cben at ~10.2 Ma was indicative of a complete re-adjustment of the carbon cycle after the Monterey excursion and export of the North Atlantic Deep Water (NADW) towards the southern Ocean to give rise to the Circumpolar Deep Water (CDW), with a δ13C value of ~0.4‰. The formation of the NADW had given rise to modern deep water like conditions at ~10 Ma ago. A comparison of our record with previously published isotopic records from other regions suggested a good correlation between the South Pacific, Indo Pacific and Northeast Indian Ocean during the studied time interval. It appears that a strong westerly Indian Ocean current (MIOjet) may have linked these Oceans from 14 to 9 Ma.