Paleocene Radiolaria from DSDP Leg 36-Site 329, Maurice Ewing Bank, Malvinas Plateau: biostratigraphic response

The carbonatic succession of the Maurice Ewing Bank in the Malvinas Plateau, presents records of remarkable paleoceanographic changes in the South Atlantic Ocean, and documents the interval between its opening and the stabilization of the circumpolar current. A report of the Paleocene radiolarian fauna recovered in the Cores 33 and 32 (Section 4) of the DSDP Leg 36-Site 329 is presented herein. The samples, composed mainly by micritic limestones, were chemically treated with a solution of hydrogen peroxide (H2O2) and sodium hexametaphosphate (Na16P14O43). Afterward, they were soaked in a solution of chloridric acid (HCl). The studied microfauna shows low diversity and abundance and is composed by the genera Amphisphaera, Haliomma, Amphymenium, Spongodiscus, Lithelius, Dictyomitra, Dendrospyris, Bathropyramis and Siphocampe. The original biostratigraphic framework proposed for the DSDP Leg 36-Site 329 (based on nannofossils and foraminifers) assigns a Paleocene age to the rocks of the Cores 33 and 32 (Section 4). Radiolarian absence in the Paleocene-Oligocene interval is due to the poor preservation of the specimens. However, the co-occurrence of Amphisphaera priva (Foreman) Hollis and Dictyomitra andersoni (Campbell and Clark) Foreman allows us to sustain at least a Late Paleocene age for the Core 33. The assemblages recovered in the Cores 33 and 32 (Section 4) exhibit some similarity with Paleocene faunas reported in the New Zealand region. Forthcoming studies based on this radiolarian microfauna can provide relevant paleoceanographic data about the South Atlantic Ocean during the Late Paleocene.Simposio VI: Microfósiles del Mesozoico y Cenozoico de América del Sur y Antártida. Nuevas aplicaciones y problemáticas asociadasFacultad de Ciencias Naturales y Muse

Maastrichtian microfossils of the Shallow Marine Umir Formation, Northeastern Colombia

During the Late Cretaceous, northern South America was characterized by broad epicontinental seas, with variable surface productivity and changing bottom-water oxygenation. Global sea-level fluctuations and local tectonic shifts caused their disappearance in the latest Cretaceous. We present an integrated micropaleontological and geochemical study of a section comprising the Umir Formation and its lower stratigraphic contact with the La Luna Formation, in the Middle Magdalena Valley, northeastern Colombia. Foraminiferal assemblages were moderately diverse and mainly dominated by benthic taxa, characterizing the biozones Siphogenerinoides bramlettei and Ammobaculites colombiana (Maastrichtian). Planktonic foraminiferal assemblages were less diversified, being species assigned to Heterohelicidae and scarce keeled forms (Globotruncana spp.) the most recurrent taxa. Ostracod recovery was very scarce, and we could only identify the genus Actinocythereis. In contrast, calcareous nannofossil assemblages were moderately diversified along the section, and composed of typical Late Cretaceous low-latitude taxa such as Micula staurophora, Cribrosphaerella ehrenbergii, Gartnerago segmentatum. The identified microfossils indicate a transition from middle-inner shelf conditions, with moderately oxygenated bottom waters within the La Luna Formation, to a shallower marine setting within the Umir Formation. This interpretation is supported by Sr/Ba and log(Fe/Ca) ratios measured in bulk sediment, which indicate increased continental runoff and terrigenous input in the upper part of the section. Moreover, a significant biotic turnover was identified at the base of the section, suggesting the presence of a xenoconformity at the La Luna-Umir contact, which has been previously described and proposed as a regional stratigraphic feature. El Cretácico Tardío del norte de Sudamérica estuvo dominado por mares epicontinentales extensos, con fluctuaciones de la productividad superficial y oxigenación del agua de fondo. Cambios en los regímenes tectónicos locales y descensos globales en el nivel del mar, llevaron a la desaparición de dichos ambientes hacia fines del Cretácico. Presentamos un estudio micropaleontológico y geoquímico integrado de una sección de la Formación Umir y su contacto basal con la Formación La Luna en el Valle Medio del Magdalena, noreste de Colombia. Las asociaciones de foraminíferos fueron moderadamente diversas y estuvieron dominadas por formas bentónicas que definen las biozonas de asociación locales Siphogenerinoides bramlettei y Ammobaculites colombiana (Maastrichtiano). Las formas planctónicas, menos diversas, incluyeron ejemplares de Heterohelicidae y escasas formas quilladas (Globotruncana spp.). El registro de ostrácodos fue muy escaso, sólo pudimos reconocer al género Actinocythereis. En contraste, las asociaciones de nanofósiles calcáreos fueron moderadamente diversas y comprendieron formas típicas de bajas latitudes del Cretácico Tardío como Micula staurophora, Cribrosphaerella ehrenbergii, Gartnerago segmentatum. Las asociaciones de microfósiles indican una transición de condiciones de plataforma media-interna, moderadamente oxigenada en la Formación La Luna, a un ambiente más somero en la Formación Umir. Esta interpretación es corroborada por las relaciones de Sr/Ba y log(Fe/Ca) del sedimento que indican un aumento en la escorrentía continental y el aporte de terrígenos hacia la parte superior de la sección. De igual forma, la variación significativa en las asociaciones de microfósiles hacia la base sugiere la presencia de una xenoconformidad en el contacto La Luna-Umir, que fue previamente reportada como de carácter regional

The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

We integrate benthic foraminiferal stable isotopes, X‐ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon

The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

金沢大学理工研究域地球社会基盤学系We integrate benthic foraminiferal stable isotopes, X-ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon. ©2019. American Geophysical Union. All Rights Reserved.Embargo Period 6 month

Mita regina ? (Campbell & Clark 1944

Mita regina ? (Campbell & Clark, 1944) (Fig. 4G) FIGURED SPECIMEN. — ULVG-8312. MATERIAL. — One specimen (recovered with the acetic acid method). REMARKS Preservation obscures some characteristics attributed to the species in its original description. Family AMPHIPYNDACIDAE Riedel, 1967Published as part of Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1) on pages 10-12, DOI: 10.5252/g2013n1a1, http://zenodo.org/record/453801

Botryometra heros

Botryometra heros (Campbell & Clark, 1944) (Fig. 5B) Lithomelissa (Micromelissa) heros Campbell & Clark, 1944: 25, pl. 7, fig. 23. ? Lithomelissa heros – Foreman 1968: 25, pl. 3, fig. 5a, b. Botryometra heros – Moix et al. 2009: fig. 4K. FIGURED SPECIMEN. — ULVG-7331. MATERIAL. — Five specimens (recovered with the hydrogen peroxide method). OCCURRENCE. — Maastrichtian of California (Campbell & Clark 1944; Foreman 1968); Campanian of Turkey (Moix et al. 2009). REMARKS This species was not assigned to? Lithomelissa hoplites Foreman, 1968 due the absence of ridges extending from the apical horn on to the cephalis, as well as the absence of upward-directed spiny projections on these ridges. Likewise,? L. hoplites possesses a poreless cephalis and dorsal and primary wings extended from the three edges of the triangular thorax (Foreman 1968).Published as part of Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1) on page 13, DOI: 10.5252/g2013n1a1, http://zenodo.org/record/453801

Spumellaria Ehrenberg 1875

Spumellaria gen. et sp. indet. (Fig. 5L) FIGURED SPECIMEN. — ULVG-7341. MATERIAL. — Four specimens (recovered with the hydrogen peroxide method); two specimens (recovered with the acetic acid method). DESCRIPTION Test ellipsoidal, possibly composed of a spongy meshwork and without radial spines. Pores are of sub-circular outline and the skeleton surface is smooth. REMARKS The absence of diagnostic features does not enable a precise identification.Published as part of Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1) on pages 16-17, DOI: 10.5252/g2013n1a1, http://zenodo.org/record/453801

Theocapsomma Haeckel 1887

<i>Theocapsomma</i> sp. <p>(Fig. 5D) FIGURED SPECIMEN. — ULVG-7333.</p> <p>MATERIAL. — One specimen (recovered with the acetic acid method).</p> <p>DESCRIPTION</p> <p>Test of three segments. Cephalis completely encased in thorax, generating a dome shaped cephalo-thoracic portion, and bearing a small apical spine. Thorax hemispherical with subcircular pores enclosed in polygonal pore frames, with small nodes protruding from the corners. Lumbar stricture moderately defined externally. Thorax subcylindrical with subcircular pores longitudinally arranged. Distal margin probably ragged.</p> <p> REMARKS The absence of a vertical tube does not enable a direct comparison to <i>Theocampe daseia</i> Foreman, 1968 and <i>T. bassilis</i> Foreman, 1968.</p>Published as part of <i>Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1)</i> on page 14, DOI: 10.5252/g2013n1a1, <a href="http://zenodo.org/record/4538016">http://zenodo.org/record/4538016</a&gt

Orbiculiforma Pessagno 1973

Orbiculiforma sp. 2 (Fig. 5I) FIGURED SPECIMEN. — ULVG-7338. MATERIAL. — Three specimens (recovered with the hydrogen peroxide method); two specimens (recovered with the acetic acid method). DESCRIPTION Test is circular in outline, with or without peripheral spines. The center of test is shallowly depressed (central cavity); the central cavity is flanked by a poor-developed rim. There are small circular pores, irregularly distributed over the test. The periphery of the external rim presents a rough aspect. REMARKS There is a small nassellarian attached to the figured specimen.Published as part of Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1) on page 16, DOI: 10.5252/g2013n1a1, http://zenodo.org/record/453801

Dictyomitra Zittel 1876

Dictyomitra sp. 1 (Fig. 4E) FIGURED SPECIMEN. — ULVG-7322. MATERIAL. — One specimen (recovered with the hydrogen peroxide method); seven specimens (recovered with the acetic acid method). DESCRIPTION Test conical proximally and becoming somewhat cylindrical distally; lobulate and costate throughout (about 11 costae in lateral view). Cephalis sharply pointed apically, with costae converging in the cephalic area. Post-cephalic segments somewhat cylindrical. Distal margin ragged,with poor-developed costal projections. REMARKS The poor preservation of the specimens does not assure the specific identification.Published as part of Kochhann, Karlos G. D., Baecker-Fauth, Simone & Fauth, Gerson, 2013, Late Maastrichtian Radiolaria from ODP Leg 165 - Site 999 B, Colombian Basin, pp. 5-20 in Geodiversitas 35 (1) on page 10, DOI: 10.5252/g2013n1a1, http://zenodo.org/record/453801