Paleoecology and proliferation of the bivalve Chondrodonta joannae (Choffat) in the upper Cenomanian (Upper Cretaceous) Adriatic Carbonate Platform of Istria (Croatia)

Chondrodonta joannae (Choffat) is a morphologically variable oyster-like bivalve with a predominately calcitic shell. An exceptional exposure of C. joannae-bearing strata of late Cenomanian age crops out along the seaside in northern Istria (Croatia) and permits a taphonomical and functional analysis in order to define the life habit and growth strategies of this bivalve. The C. joannae population from the studied succession is characterized by highly-elongated, large and curved shells, reaching about 50 cm in height and 5 cm in length. This shell shape is typical of the club-like bivalve morphotype, which was adapted to soft-bottom substrates with high sediment accumulation. The shell is slightly inequivalve and characterized by a reduced body cavity, a few centimetres high, and a dorsal region up to 10 times longer. The shell opening mechanism was mostly based on the resilium located between the chondrophores which protrude in the body cavity. The abandoned dorsal cavity is filled by a calcite hinge plate, the ventral edge of which acted as fulcrum for the valve flexibility. In the hinge plate, the function of chondrophores changed. They acted as a hinge to keep tightly interlocked the valves, which considerably emerged above the sediment-water interface. The individuals were arranged in low shrub-type congregations, which produced low-relief mounds. The functional morphology and taphonomic signature suggest that C. joannae individuals collected food at a greater distance from the bottom with respect to the co-occurring rudists. We speculate that the C. joannae proliferation could be related to a late Cenomanian phase of environmental instability predating the OAE2 with fluctuating climatic conditions and ocean fertility

Strontium isotope stratigraphy of late Cenozoic fossiliferous marine deposits in North Borneo (Brunei, and Sarawak, Malaysia)

Neogene marine deposits of North Borneo are locally very rich in fossils that provide glimpses into the past biodiversity. However, dating these onshore sediments with biostratigraphy is often hampered by the lack and/or the poor preservation state of index fossils. Therefore, the fossiliferous sites were targeted with strontium isotope stratigraphy (SIS) to obtain higher precision relative dating. Well-preserved macrofossils were screened using a multidisciplinary approach, and 87Sr/86Sr ratios of the most pristine remains were used to date the embedding sediments. Most of the measured ages fall in the expected chronostratigraphic framework established by large scale studies for the region. The oldest, Burdigalian (early Miocene) ages were measured for the Sibuti Formation in Sarawak (17.71 \ub1 0.2My and 16.7 \ub1 0.2My) followed by a Serravallian (middle Miocene) age within the Belait Fm in Brunei (12.1 +1.4/-1.2My). Eight localities from the younger units, the Miri and Seria formations in Brunei, gave a range in age from 10.5 \ub1 1 to 7.0 +0.9/-0.5My (Tortonian-Messinian). Reworked fossil assemblages from Tutong beach were also investigated and the SIS ages of Late Miocene support an origin from the younger part of the Seria Fm. One locality, in Lumapas where limestone crops out in Brunei, gave an unexpected younger age (Tortonian, late Miocene, 10.6 \ub1 1My) compared to estimates projected for its assumed stratigraphic position in the lower Belait Formation (late Burdigalian). These challenging data require more research, yet if the young age is accepted, the stratigraphic situation of the limestone needs further revision

Atherfieldastacus rapax (Harbort, 1905) (Glypheidae, Mecochiridae) from the Lower Cretaceous of the Maestrat Basin (NE Spain)

Three specimens of the lobster 'Meyeria rapax', which represent the first record of this species in Spain, were collected in the Artoles Formation cropping out in the surroundings of the town of Ares del Maestrat in the Maestrat Basin. Microfacies and paleontological analyses of the sedimentary succession containing the fossil lobsters allow us to infer a near-coastal depositional setting. Numerical ages derived from Sr-isotope analyses combined with previous chronostratigraphic studies of the Artoles Formation suggest an early Barremian age for the stratigraphic interval, which is located around the middle part of the formation, with lobsters studied. The study of the morphological features observed in the record of the 'Meyeria rapax' specimens from Spain supports the ascription of the species to the new genus Atherfieldastacus proposed recently for the Mecochiridae family

THE MIDDLE EOCENE CLIMATIC OPTIMUM (MECO) IMPACT ON THE BENTHIC AND PLANKTIC FORAMINIFERAL RESILIENCE FROM A SHALLOW-WATER SEDIMENTARY RECORD

We present here new quantitative analyses of planktic and benthic foraminifera to assess the impact of the Middle Eocene Climatic Optimum (MECO, ~40 Ma) on these biotic groups studied along a shallow-water succession rich in larger benthic foraminifera (Sealza, Liguria, NW Italy). The MECO is one of the major Eocene global warming events, characterized by ~4–6°C warming, shifts in the global carbon cycle, and rise in atmospheric pCO2. The Sealza succession is interpreted as the product of a drowning ramp influenced by tectonic activity and provides an exceptional chance to compare biotic variations in shallow-water assemblages with deep-water communities across the MECO. In the section, the MECO interval is tentatively constrained by stable isotope oxygen data and calcareous plankton biostratigraphy. The marked decline in abundance of the epifaunal benthic Cibicidoides across the lower-middle part of the MECO suggests a decrease in oxygenation at the seafloor. Further evidence of oxygen depletion is the increase in organic matter content (TOC) of the sediment and the presence of infaunal genera Uvigerina and Bolivina. The planktic foraminiferal assemblages record the MECO warming in the upper water column as the mixed-layer warm index genera Acarinina and Morozovelloides markedly increase in abundance. In the post-MECO interval, here poorly exposed, cooler conditions are indicated by the dominance of the cold-water index genus Subbotina. Remarkably, Acarinina decline in abundance in the upper MECO interval and never recover. The MECO perturbance permanently impacted the benthic and planktic communities at Sealza that exceeded the tipping point to move to a new regime, thus proving the fauna to be not resilient, but also not recording any extinctions.

Rotaloidean foraminifera from the Upper Cretaceous carbonates of Central and Southern Italy and their chronostratigraphic age

New rotaloidean foraminifera from the Upper Cretaceous shallow-water carbonates of Central and Southern Italy have been described, thus widening the knowledge on the Late Cretaceous rotaloidean foraminifera in the Central Tethyan realm. Rotorbinella lepina sp. nov., Rotalispira vitigliana sp. nov. and R. maxima sp. nov., belong to the family Rotaliidae (subfamilies Rotaliinae and Lockhartiinae, respectively). Pilatorotalia pignattii gen. nov. sp. nov. and Neorotalia? cretacea sp. nov. are placed in the family Pararotaliidae. Moreover, further studies are carried out on the associated Rotalispira scarsellai and âStensioeinaâ surrentina. The age assignment of these rotaloideans has been calibrated by means of strontium isotope stratigraphy to late Santonian?-middle Campanian

Platform-wide shift to microbial carbonate production during the late Aptian

In the aftermath of major Phanerozoic biocrises, diverse metazoan-dominated reef ecosystems were commonly replaced by microbial carbonate-producing communities. Apart from the loss of metazoan competitors, the factors causing pervasive microbial carbonate production in shallow-water platform settings are not completely understood. Amongst others, outstanding warm temperatures coupled with low-oxygen waters were proposed as possible triggers. This study focuses on late Aptian shallow marine carbonates deposited on the Apennine carbonate platform (ACP) in the central Tethys. By establishing an integrated high-resolution chemostratigraphic framework for two sections of the ACP, the coeval onset of pervasive bacinelloid growth is discovered, indicating a platform-wide shift from a metazoan-dominated ecosystem to microbial carbonate production. The initial phase of microbial proliferation coincides with the final stage of the so-called late Aptian “cold snap” and the subsequent temperature increase, which was paralleled by a significant sea-level rise. Our results contrast with observations from the early Aptian Oceanic Anoxic Event 1a, where a similar shift toward microbial “bacinelloid” carbonate production has been linked to exceptionally warm conditions and hypoxia

Neritic isotope and sedimentary records of the Eocene–Oligocene greenhouse–icehouse transition: The Calcare di Nago Formation (northern Italy) in a global context

From the Middle Eocene to Early Oligocene, the Earth experienced the most significant climatic cooling of the Cenozoic era. The Eocene–Oligocene transition (EOT) represents the culmination of this climatic cooling, leading to the onset of the Antarctic glaciation and, consequently, to the beginning of the present-day icehouse world. Whereas the response of deep-sea systems to this climate transition has been widely studied, its impact on the shallow-water carbonate realm is poorly constrained. Here, the sedimentary expression of the EOT in two shallow-marine carbonate successions (Nago and San Valentino, northern Italy) belonging to the Calcare di Nago Formation is presented. The chronostratigraphic framework was constructed by integrating litho-, bio-, and isotope-stratigraphic data (C and Sr isotopes), allowing to correlate these shallow-marine successions with pelagic sections in central Italy (Massignano), Tanzania (TDP Sites 12 and 17), and the Indian Ocean (ODP Site 744). Within several sections in northern Italy, including Nago and San Valentino, a Priabonian (Late Eocene) transgression is recorded. Oxygen isotopes of ODP Site 744 show a coeval negative shift of 0.4‰, suggesting a glacio-eustatic origin for this transgression. In the Nago and San Valentino sections, no prominent sequence boundary has been detected that would indicate a rapid sea-level drop occurring together with the positive shift in δ¹⁸O defining the EOT-1 cooling event. Instead, a gradual shallowing of the depositional environment is observed. At TDP Sites 12 and 17, the EOT-1 is followed by a negative shift in δ¹⁸O of around 0.4‰, which correlates with a relative deepening of the environment in the studied sections and suggests a melting pulse between EOT-1 and the Oligocene isotope event 1 (Oi-1). The positive δ¹⁸O shift related to the Oi-1 translates in San Valentino into a change in carbonate factory from a photozoan association dominated by larger benthic foraminifera, corals, and red algae to a heterozoan association dominated by bryozoans. The same bryozoan facies occurs in several Italian localities near the Eocene–Oligocene boundary. This facies is interpreted to represent an analogue of modern cool-water carbonates and results from a cooling pulse of at least regional scale, associated to the Oi-1 event

Reticulinella kaeveri CHERCHI, RADOIÄ\u8cIÄ\u86 & SCHROEDER: A marker for the middle-upper Turonian in the shallow-water carbonate facies of the peri-Adriatic area

Reticulinella kaeveri CHERCHI, RADOIÄ\u8cIÄ\u86 & SCHROEDER is recorded for the first time in the Upper Cretaceous shallow-water carbonates of the southern Apennines. The narrow stratigraphical range and the wide geographical distribution of this species makes it a very valuable biostratigraphic marker in the Turonian of the peri-Adriatic carbonate platforms. Strontium isotope stratigraphy of well preserved rudist shells from levels containing Reticulinella kaeveri, or immediately above its last occurrence, allows the chronostratigraphic age of this species to be defined more precisely. However, owing to the presence of a distinct late Turonian minimum in the marine reference curve, the strontium isotope ratios of the studied samples are compatible both with a late middle Turonian (upper part of the Romaniceras deverianum ammonite zone) and with a late Turonian age (Subprionocyclus neptuni ammonite zone)

Late Cretaceous alveolinaceans (larger foraminifera) of the Caribbean palaeobioprovince and their stratigraphic distribution

Architectural analysis of the Late Cretaceous alveolinaceans of the Caribbean palaeobioprovince has made it possible to separate four genera: Praechubbina, Chubbinella gen. nov., Chubbina and Caribalveolina. The first three genera belong to the family Rhapydioninidae, while the fourth is placed in the family Alveolinidae. Two species, Praechubbina breviclaustra and P. oxchucensis sp. nov., represent the primitive genus Praechubbina, while the species cardenasensis and obesa, previously ascribed to this genus, must be reassigned respectively to Chubbinella gen. nov. and Caribalveolina. The species Chubbina jamaicensis, C. macgillavryi and C. fourcadei sp. nov. complete the inventory of Chubbina. The alveolinid genus Caribalveolina comprises two species, C. obesa and C. michaudi. Caribbean alveolinaceans include two successive assemblages. The lower assemblage is characterized by Praechubbina oxchucensis, P. brevisclaustra, Chubbinella cardenasensis and Caribalveolina obesa. The upper assemblage is represented by the genus Chubbina, with C. fourcadei, C. jamaicensis and C. macgillavryi, and Caribalveolina michaudi. The age of the lower assemblage is uncertain (probably Late Campanian-Early Maastrichtian), while the upper assemblage has been dated by strontium isotope stratigraphy as Late Maastrichtian. © 2013 Natural History Museum