Origin of rhythmic Albian black shales (Piobbico core, central Italy): Calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions

Abstract

[1] The mid-Cretaceous ($120-90 Ma) was a time of excess atmospheric CO 2 , greenhouse climate, and widespread O 2 deficiency in the ocean. The Albian is punctuated by brief, intermittent episodes of anoxia/ dysoxia, recorded as cyclic black shales in the western Tethys and Atlantic oceans. The Albian section of the Piobbico core (central Italy) contains 30 m ($10 Ma) of rhythmic black shales that were sampled at a high resolution and examined for calcareous nannofossil assemblages and C and O stable isotopes. Unlike oceanic anoxic events, productivity was not the primary factor controlling the deposition of Albian rhythmic black shales. It is suggested that during warm humid climatic cycles, higher temperatures and/or increased precipitation and runoff produced density stratification at a regional scale. Recurrent lowered salinity in the early Albian and warming in the late Albian are credited with causing development of a pycnocline, resulting in slower rates of deep-water renewal and consequent anoxia.

Onset and demise of Cretaceous oceanic anoxic events: The coupling of surface and bottom oceanic processes in two pelagic basins of the western Tethys

“…The 20 m thick section at Le Brecce (Figure ) is located inside a gorge, at 3 km west from the Piobbico village. The studied outcrop is at the km 34 of the state road 257‐Apecchiese, close to the Piobbico drill site [ Tiraboschi et al, ]. The 90 m thick section at Monte Petrano (Figure ) is about 2 km east of the Moria village [ Giorgioni et al, ].…”

Palynology of Aptian and upper Albian (Lower Cretaceous) amber-bearing outcrops of the southern margin of the Basque-Cantabrian basin (northern Spain)

“…those controlling the record of OAE1b-d) is attractive, the lack of pertinent age determination involving marine faunal and/or floral markers with a broader distribution and a consistent record will probably prevent any further fine calibration. Recent studies (Tiraboschi et al, 2009;Trabucho-Alexandre et al, 2011) suggest that the depositional settings of 'black shales' are much more varied than previously thought and may have been the result of several processes acting on a local rather than global scale. In this context, the further study and correlation between coeval amber-bearing terrestrial and marine successions of the Basque-Cantabrian basin may help to clarify the relative role of local and global palaeoenvironmental forcing in the origin of these deposits.…”

“…Various hypotheses have been proposed, including abrupt changes in temperature, local salt resurgence, fires, damage inflicted by megaherbivores, insects or pathogens and storage of unwanted metabolic substances (Martínez-Delcl os et al, 2004;Najarro et al, 2009). Tiraboschi et al (2009) suggested that high temperatures and drastic and repeated changes in the precipitation regime were key factors in the deposition of lower and upper Albian black shales from the eastern part of the Tethys. The production of resin by certain conifers from coastal associations may also have been a response to such unusual, widespread, palaeoclimatological conditions, and may represent the terrestrial counterpart of the black shales associated with Albian oceanic anoxic events.…”

“…During this period, the Iberian Peninsula was situated at low latitudes, under prevalent megathermal climatic conditions characterised by orbitally-paced climate episodes (Chumakov et al, 1995;Tiraboschi et al, 2009;Rodríguez-Lop ez et al, 2012). Located between the European and African plates, the Iberian plate was an authentic centre of biotic interchange between the Gondwanan and Boreal realms (Heimhofer et al, 2007;Villanueva-Amadoz et al, 2010).…”

Environmental consequences of Ontong Java Plateau and Kerguelen Plateau volcanism

“…Sample lithologies vary from carbonates (chalks and limestones) to marlstones, cherts, siltstones, and black shales (DSDP and ODP Scientifi c Results volumes for Sites 167, 463, and 866; Erba et al, 1999;Premoli Silva et al, 1989a;Tiraboschi et al, 2009). Bulk samples (2 cm 3 each) were fi rst crushed and powdered using an agate mortar and pestle, then ~50 mg of powder were dissolved with HF, HNO 3 , and HCl in a CEM Corporation MARS 5 microwave digester.…”