Orbitally Driven Cycles in Trace-Fossil Distribution from the Piobbico Core (Late Albian, Central Italy)
- P. L. de Boer2,
- D. G. Smith3
Published Online: 29 APR 2009
Copyright © 1994 The International Association of Sedimentologists
Orbital Forcing and Cyclic Sequences
How to Cite
Erba, E. and Premoli Silva, I. (2009) Orbitally Driven Cycles in Trace-Fossil Distribution from the Piobbico Core (Late Albian, Central Italy), in Orbital Forcing and Cyclic Sequences (eds P. L. de Boer and D. G. Smith), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304039.ch16
Utrecht, The Netherlands
- Published Online: 29 APR 2009
- Published Print: 28 JAN 1994
Print ISBN: 9780632037360
Online ISBN: 9781444304039
- orbitally driven cycles in trace-fossil distribution from Piobbico core - late Albian central Italy;
- Amadeus segment;
- density of bioturbation;
- planktonic forminiferal spectra;
- calcareous nannofossils
The Aptian–Albian Scisti a Fucoidi Formation from central Italy consists of a pelagic rhythmic varicoloured sequence of marls, marly clays, marly limestones and subordinate limestones. Black shale layers are abundant and cyclically modulated in several intervals.
A multidisciplinary study performed on the late Albian ‘Amadeus Segment’ of the Piobbico core (Marche) shows that the rhythmically alternating beds of grey to black marls and whitish limestones (marl–limestone bedding couplets) record the precession cycle, and grouping of these couplets into bundles records the short and long cycles in eccentricity.
In order to reconstruct the bottom-water palaeo-oxygenation history, a semiquantitative study of the trace-fossil distribution was performed from the ‘Amadeus Segment’. Based on absence/occurrence of laminations, absence/occurrence of bioturbation, type of trace fossils (ichnogenera), density of bioturbation, and maximum burrow diameter and penetration into sediments, three assemblages were recognized: (i) Chondrites-1 assemblage represented by intervals with only ‘small’ Chondrites; (ii) Chondrites-1/Chondrites-2 assemblage represented by intervals with ‘small’ and ‘large’ Chondrites; and (iii) Teichichnus/Zoophycos assemblage represented by intervals with ‘small’ and ‘large’ Chondrites along with Teichichnus and/or Zoophycos. The constructed palaeo-oxygenation curve shows that sedimentation occurred mainly under dysaerobic conditions. However, a trend was detected from a more oxygenated environment in the lower portion of the segment to overall less oxygenated conditions, which also alternate with real anoxia, followed by a reverse trend towards more oxygenated conditions again in the uppermost portion of the interval investigated.
Fast Fourier spectral analysis was performed on palaeo-oxygenation and bioturbation density using the Stratabase program. Regular and cumulative spectra of both parameters show two main peaks with periodicities around 100 and 41 ka, which are correlatable with the orbital eccentricity and obliquity frequencies. Spectral evidence for precession (19–23 ka) is weaker, though present in both palaeo-oxygenation curve and bioturbation density spectra, which show a double peak at 28 and 19 ka and at 26 and 20 ka, respectively. Weakness of precessional peak was previously recorded in calcium carbonate, light transmission and planktonic foraminiferal spectra from the same interval, and suggests the presence of distortions in all curves.
Cross-correlation of palaeo-oxygenation and carbonate-content curves shows that these two parameters oscillate with the same frequencies and are perfectly in phase. This means that the increased seasonality, leading to a better stirring of the oceans, is responsible for both the increase in carbonate primary productivity and the enhancement of bottom-water ventilation. The resulting sediments are intensively bioturbated whitish limestone. In contrast, during times of weak seasonality, primary productivity is lower and bottom waters are less oxygenated, as represented by the darker marls showing very slight bioturbation or being barren of trace fossils. The anoxic episodes were cyclic and were controlled by precession, modulated by eccentricity (both short and long) cycles, with a discrete influence of obliquity, at least at the palaeolatitude of the Piobbico core.