1,721,016 research outputs found
High-resolution biostratigraphy and isotope stratigraphy in an Albian pelagic succession of Southern Italy.
No full textThe Lower Cretaceous pelagic succession of the Gargano promontory (Southern Italy): foraminiferal, calcareous nannofossils and geochemical data.
No full textForaminiferal, calcareous nannofossils and geochemical data in the Lower Cretaceous pelagic succession of the Gargano Promontory.
No full textBiotic and geochemical response to anoxic events: the Aptian pelagic succession of the Gargano Promontory (Southern Italy)
No full textMicrofossil distribution patterns and high-resolution δ13C and δ18O curves, calibrated against planktonic foraminiferal and calcareous nannofossil data, are provided for the Aptian pelagic Coppitella section of the Gargano Promontory (southern Italy). The succession consists of cyclically arranged couplets of bioturbated grey marlstones and off-white marly limestones, referable to the Marne a Fucoidi. In the lower portion of the section, two thin black shales were recognized. The high- resolution δ13C curve presented here correlates with those of other Alpine–Tethyan sections, albeit with lower absolute values. The onset of deposition of organic-rich sediments falls at the top of the interval of unchanging carbon-isotope values, whereas the upper black shale is documented from the interval of the main Aptian positive δ13C excursion. According to our biostratigraphic data, the deposition of organic matter in the Gargano Promontory persisted through Early/Late Aptian boundary time. Using a chemostratigraphic definition, only the lower black shale is referred to the Selli Level. As far as the biotic response is concerned, the onset of the ‘nannoconid crisis’ is recorded considerably below the lower black shale, whereas the ‘Globigerinelloides eclipse’ is recorded below and within the upper black shale. The distribution of meso-eutrophic indices (Zygodiscus spp., radiolaria) vs. moderate-fertility indices (Rhagodiscus asper and Lithraphidites carniolensis) testifies to a modest increase of surface- water fertility only throughout the stratigraphically higher black shale. The occurrence of a benthic foraminiferal fauna, albeit impoverished, in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor. Relative sea-level rise at the time of the Selli Event in the Gargano Promontory is documented by drowning and foundering of the Apulia platform margin, situated adjacent to the basin in which the Marne a Fucoidi accumulated
Biotic and geochemical response to anoxic events: the Aptian pelagic succession of the Gargano Promontory (Southern Italy).
No full textGeochemical and micropaleontological response to Lower Cretaceous anoxic eents in the Gargano Promontory succession (Southern Italy).
No full textAlbian high-resolution biostratigraphy and isotope stratigraphy: The Coppa della Nuvola pelagic succession of the Gargano Promontory (Southern Italy)
No full textHigh-resolution δ13C and δ180 curves, calibrated against planktonic foraminiferal and
calcareous nannofossil biostratigraphy, are provided for the upper Aptian–lower
Cenomanian pelagic succession of the Gargano Promontory (Coppa della Nuvola
section, southern Italy). The succession consists of two superimposed formations: the
Marne a Fucoidi and the Scaglia (lower portion only). According to our integrated
biostratigraphy, the entire succession spans the latest Aptian (planktonic foraminiferal
T. bejaouaensis and calcareous nannofossil R. angustus Zones) and early Cenomanian
stages (R. cushmani Zone CC9c). The Marne a Fucoidi–Scaglia transition
falls in the late Albian (R. ticinensis Zone; CC9a+b Subzones).
The high-resolution δ13C curve from the Coppa della Nuvola section can be subdivided
into characteristic segments. Four negative shifts of δ13C are recorded, followed
by increasing values in, respectively, the early Albian (C11, C12), the early
late Abian (C14, C 15), the late Albian (C16, C17), and the early Cenomanian (C22).
The late Albian carbon-isotope event, corresponding to the Oceanic Anoxic Event
(OAE) 1d or Breistroffer Event, is possibly missing in the Coppa della Nuvola section
as a result of condensation or erosion (C19–C20?). Even if, in the section studied,
carbon-rich levels are not recorded (though some stratigraphic intervals are covered
by Quaternary deposits in the lower portion), it is likely that the lower Albian (T.
primula; P. columnata Zones) and the upper Albian (T. praeticinensis Subzone–
R. subticinensis Zone; R. achlyostaurion Zone) positive δ13C peaks succeeding negative
trends in δ13C (C11–C12; C16–17) record the pattern of global carbon burial,
documented in other areas of the Gargano Promontory and elsewhere and connected
to the OAE1b and OAE1c. Some or all of the negative δ13C shifts may record the
introduction of isotopically light carbon into the ocean−atmosphere system from the
dissociation of gas hydrates.
The δ18O curve of the Coppa della Nuvola section shows a similar trend to that
of the δ13C curve. Although partly of diagenetic origin, the negative shifts in the early
Albian, late Albian and early Cenomanian may be interpreted as records of warming
events resulting from the introduction of methane and its oxidation product carbon
dioxide into the atmosphere.
The palaeoceanographic conditions inferred by the biotic and isotopic changes
suggest fluctuating meso-eutrophic conditions through the late-Aptian–early-middle
Albian and increasingly stable oligotrophic situation starting from the late Albian interval.
Two main possible episodes of increased eutrophy, suggested by pulses in radiolarian
abundance and marked drop in foraminiferal diversity, occurred during the
Albian and correlate with the above-mentioned positive carbon-isotope shifts and regional
and supraregional accumulation of organic matter (OAE1b and OAE1c)
Methane-release as possible forcing mechanism of rapid climate changes during the Albian Anoxic Events: geochemical and biotic evidences from the Apulian Platform margin (Southern Italy).
No full textAptian-Albian carbon burial episodes at the Apulian Platform Margin (Gargano promontory, Southern Italy): regional versus global-driven mechanisms.
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