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Coral bioherms and biostromes in the muddy bottomset of a fandelta system (Oligocene, Tertiary Piedmont Basin, Italy)
No full textTurbid-water coral assemblages: a case study from the Oligocene Tertiary Piedmont Basin (N Italy)
No full textIn the geological record, but also at the present time, coral assemblages thriving in
permanently or episodically turbid waters as a result of terrigenous input are much
more common than what is expected, thinking to the conventional optimal conditions
for coral reef growth (i.e. warm, well-illuminated, oligothrophic shallow waters of the
tropics and subtropics). Despite, in fact, relatively high turbidity conditions, restricted
light penetration, and the presence of often mobile terrigenous sediment substrates,
active coral growth is well developed and many coral bioconstructions in the past are
actually associated with marly and mixed carbonate-siliciclastic sediments.
In the Tertiary Piedmont Basin (northern Italy) coral assemblages and associated bioconstructions
developed under terrigenous sedimentation during the Oligocene. They
occur in siliciclastic conglomerates and sandstone of fan delta and clay-rich prodelta
settings.
Collected data provide information basically about the composition of the coral assemblages,
facies and depositional products of coral growth together with taphonomic
aspects.
The succession is characterized by the episodic production of abundant coral rubble of
the branching corals Acropora and Stylophora. These rudstone and floatstone facies
are distinguished on the base of their sedimentological and paleontological aspects,
and taphonomic features such as bioerosion and encrustation provide useful information
about the different effetcts of turbidity and sediment accumulation. Coral rubble
deposits are often buried or occasionaly represent a hard substrate for successive coral
growth.
Corals in growth position also occur and consist of a suite of phaceloid and massive
colonies (Caulastrea, Goniopora, Astreopora, Diploria, Favia, Antiguastrea) with
growth habits and morphological characters typical of sediment-resistant corals. These
corals form monospecific clusters or, especially towards the top of the succession, can
co-exist together to form a small “framework”. Diversity and thickness of these coral
bioconstructions, however, are quite reduced compared to many other Oligocene coral
assemblages, suggesting that sediment imput, restricted light penetration, and maybe
episodic high concentration of nutrients, were major controls on coral growth and
carbonate production
Minor Coral Diversity Loss but Long‐Lasting Coral Reef Crises in the Early Paleogene Hothouse
Full text linkThe future of tropical coral reefs is severely threatened by rising global temperatures and relies on the persistence of two key attributes: (a) coral biodiversity, and (b) the reef-building capacity. In order to understand how these attributes responded to a climate warming, we investigated corals and coral reefs in the early Paleogene “hothouse” interval. We focused on the Mediterranean region, which was the global center of reef coral diversity and provides the most complete record for this time interval. We computed biodiversity dynamics of reef corals based on a new compilation of Paleocene to Eocene reef coral occurrences and compared these with coral reef development recorded in the PaleoReefs Database. Extinctions and diversity were within background fluctuations across the Paleocene-Eocene Thermal Maximum (PETM). Coral diversity increased rapidly in the aftermath of the PETM and remained high across the entire Eocene. But reef building collapsed at the PETM and recovered to late Paleocene levels only by the late Eocene. We document that reef corals have demonstrated an excellent resilience within the hothouse, whereas coral reefs were much more vulnerable and took much longer to recover. Our findings suggest that although coral reefs might disappear in the near future, corals will persist and could begin reconstructing reefs once environmental conditions allow
Oligocene nearshore benthic assemblages and coral facies of the northern Gargano Promontory
No full textShallow water carbonate successions of Oligocene age are quite well distributed in the Apulia domain and are often associated with the development of luxuriant coral reef systems (Salento Peninsula, Maiella Mountain). The dominant biogenic components generally consist of rich associations of scleractinian corals and larger foraminifera.
In the Gargano Promontory, the Oligocene has been recently reported for the first time and a new carbonate unit informally established and named as Grotta S.Michele limestone (Morsilli et al., 2005). The aim of the present study is thus to investigate the type locality of this unit in order to describe and interprete its lithologic composition and biotic content through facies analysis.
The stratigraphic succession consists of grainstones-rudstones to wackestones-mudstones, reaches a maximum thickness of about 28 m and clearly shows a fining-upward trend.
The fossil fauna is mainly characterized by abundant scleractinian corals, associated with benthic forams and coralline algae. Corals are represented by very few genera and basically consist of globose colonies of Goniopora near the base of the succession, followed by floatstones-rudstones rich in branched Acropora, Stylophora, Alveopora and phaceloid colonies of Caulastrea towards the top. Similarly, also the foraminiferal assemblages, dominated by miliolids and soritids, are rather poor, often with a small number of specimens and low taxonomic diversity. Some larger foraminifera such as Archaias, Austrotrillina, Nephrolepidina, and Nummulites also occur, thus indicating an Oligocene age (Chattian).
Several facies types have been identified on the basis of macroscopic observations in the field and microfacies analysis. Data are provided in particular for the distribution and relative abundance of the main biotic components, including coralline algae, bivalve and gastropod fragments, together with textural features.
The facies association suggests a nearshore, sheltered, shallow-water marine paleoenvironment with possible evidence of changes in hydrodynamic conditions from very low to moderate-high energy. Within this setting, the unusual low-diversified coral assemblages and the absence of a true framework can be interpreted as a response to stressed conditions probably controlled by the inherited paleotopography
Mar Rosso, Aprile 2009. il primo corso italiano di bio-geologia delle scogliere coralline
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Paving the way: Accomplishments of the first Field Course on coral reef Biogeology held in the Red Sea (Marsa Alam, Egypt, 19-24 April 2009)
No full textA taphonomic approach to coral reefs study: Examples from the Oligocene of the Piedmont Basin (NW Italy) and Gornji Grad Beds (Slovenia)
No full textUnparallel resilience of shallow-water tropical calcifiers (foraminifera and scleractinian reef corals) during the early Paleogene global warming intervals
Full text linkInvestigating the fossil record to provide evidence about the response of shallow-water tropical calcifiers to past warming events is crucial considering that they are severely threatened by current global warming. We thus focused our attention on scleractinian reef corals (SRC) and shallow-water foraminifera (SWF), both mainly symbiont-bearing organisms, analysing and comparing their diversity patterns during the Paleocene and Eocene from datasets of the Neothetyan circum-Mediterranean region. In particular, at both genus and species level, we analysed changes in diversity, together with origination and extinction rates. Despite some biases related to biostratigraphic resolution of SRC and SWF data, our results show that they reacted differently to the major warming events of the Early Paleogene. The K/Pg mass extinction caused the disappearance of almost all SWF, whereas several corals passed this crisis and persisted up to the end of Paleocene, when the Paleocene-Eocene Thermal Maximum (PETM) caused a relatively small decrease of coral diversity together with a global collapse of coral reefs. On the other hand, a rapid radiation of nummulitids and alveolinids occurred at species level. The impact of the Early Eocene Climatic Optimum (EECO) was apparently more severe for SWF than for SRC. After the Middle Eocene Climatic Optimum (MECO), the general cooling trend led to the fading of Eocene SWF genera and species, whereas SRC began their rapid diversification from Bartonian to Priabonian and culminating in the Chattian. Our results suggest that rapid warming events favoured speciation in SWF, whereas the slow cooling trend (e.g., after the MECO) favoured diversification of SRC. Our data also underline that SWF reacted differently to warming events as compared to deep-sea smaller benthic foraminifera and that the same events in the planktonic realm are not strictly coeval with those occurring in shallow-water environments. On a wider perspective, we observe that shallow-water calcifiers demonstrate a good degree of resilience to global temperature increases, even if undergoing to more or less marked reduction of biodiversity. We provide evidences for the recovery of past ecosystems from both short and long stressors
Rhodalgal lithofacies of the Porto Badisco Calcarenite (Upper Chattian, Apulia Italy).
No full textThere are few detailed studies on the evolution from the Oligocene to Miocene carbonate facies. This is anomalous considering the transition form the warmth of the late Oligocene to the Neogene ‘Icehouse’, with a series of major changes in climate, ice volume, ocean circulation and carbonate factories (from chlorozoan to rhodalgal dominated). In literature it is accepted that rhodalgal lithofacies became most widespread during the Neogene, with thick accumulations of rhodolith-dominated facies known mostly from the Miocene of the Tethys and Paratethys region.
This study reveals the development of a rhodalgal dominated carbonate factory during late Chattian in the southern Apulia platform. The Calcarenite overlies the Castro Limestone Formation (Lower Chattian).
The basal rhodolith-rich horizon is 4-m thick and 80-m wide. It consists of rhodolith rudstone with bioclastic grainstone-packstone matrix. Rhodoliths are ellipsoidal (68%) and subspherical (38%). Ellipsoidal rhodoliths major axis range from 3 to 9 cm and laminar (in some case boxwork) to columnar structure (RANGE?). The subspherical rhodoliths range 3 to 7 cm in diameter, the structure is laminar in the centre to columnar outward. Rhodoliths long axes parallel bedding (hydraulic stable orientation). Rhodolith structure is irregular, with large voids partially filled with bioclastic sediment. Nuclei generally consist of biogenic grains. Red algae association is dominated by melobesioids (Lithotamnion 1.24%, Lithothamion/Phymatolithon 48.55%), sporolithaceans (Sporolithon 32.6%) and subordinate mastophoroids (Spongites, 8.04%, Lithoporella 8.78%) and peyssonneliaceans (0.25%).
The overlying 20 meters of the succession are composed by 0.6-m to 3-m thick beds of alternating larger foraminiferal floatstone-rudstone and medium to coarse-grained bioclastic packstone-grainstone. Coralline red algae debris, small benthic (porcellanaceous, small rotalids, Neorotalia) larger benthic (Nephrolepidina, Eulepidina, Miogypsinoides, Heterostegina, Operuculina, Amphistegina) and encrusting foraminifera (Acervulina, Planorbulina), as well as bivalve fragments, bryozoans (Celleporids), and echinoderm plates are the main skeletal components.
These carbonates facies represent fully marine production within the photic zone. Red algae associations and foraminiferal assemblages suggest carbonate deposition took place in the oligophotic zone (lower infralittoral zone) in a tropical climate
Stratigraphic architecture of the Salento coast from Capo d'Otranto to S.Maria di Leuca (Apulia, southern Italy)
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