Mediterranean contributions to cyclostratigraphy and astrochronology

Abstract

In 1895, G.K. Gilbert suggested that rhythmical repetition of patterns in the sequences of strata correspond to orbital variations and could provide a chronology for Earth history. This suggestion remained a heuristic hypothesis in need of testing; in this, the Mediterranean region latterly played a crucial role. Its extended sequences of pelagic and lacustrine-paludal strata provide long time series of hierarchical rhythmic variations tied directly to biostratigraphy and to magnetic reversals. The latter provide historical control and links to astronomically calculated curves that have been extended progressively into the past. These comparisons verify the orbital origins of the major sedimentary rhythms and are serving to reduce the age uncertainties of the significant time stratigraphic levels (biostratigraphic and magnetostratigraphic zones) from an order of ca 500 kyr toward the precessional (20 kyr) level. This refinement has essentially been reached for the last 14 Myr of Earth history in the Mediterranean, and beyond in the Pacific Ocean. The cyclic structure of shallow-water platform carbonates is also hierarchical but here the identification with specific orbital cycles has been equivocal and complicated by conflicts with radiometric data. In the gap-riddled shallow-water successions showing hierarchical 'sequences', the identification of some third-order, fourth-order and fifth-order 'sequences' or 'parasequences' with orbital forcing is being explored but remains inferential. Beyond chronology, the orbital variations constitute an endless series of experiments: similar variations in insolation, which resulted in sedimentary patterns formed by a chain of responses extending through atmospheric and hydrospheric dynamics to geological processes and the dynamics of the biotic systems. The emerging patterns offer glimpses into the past, to reveal previously unexpected phenomena such as systematic oscillations in deep-water aeration and unexpected oscillations in composition of upper-water plankton: patterns that pose new challenges to the understanding of Earth history.

Milankovitch and sub‐Milankovitch forcing of the Oxfordian (Late Jurassic) Terres Noires Formation (SE France) and global implications

“…3) or significant palaeoclimatic cycles (e.g. Park et al , 1993; McIntyre & Molfino, 1996; Ortiz et al , 1999; Reuning et al , 2006; Sun & Huang, 2006; Fischer et al , 2009). Close examination of the C6 and C7 cycles confirm that these high‐frequency components are not artefacts, but are actual variations in the MS data.…”

A well‐established Early–Middle Pleistocene marine sequence on south‐east Zakynthos island, western Greece: Magneto‐biostratigraphic constraints and palaeoclimatic implications

“… Offshore and onshore Mediterranean sequences (from Hilgen, 1991; Massari et al ., 2002; Fischer et al ., 2009) compared with the Zakynthos onshore sequence (this study). Nannofossil biozones are from Rio et al .…”

The role of the Mediterranean region in the development of sedimentary geology: a historical overview

“…These rocks have, therefore, been interpreted as products of the summer‐perihelion phase during times of high eccentricity, when monsoons are strongest. Further elaboration of these cycles is given in a section below and in Fischer et al. (2009).…”

“…As noted by Fischer et al. (2009), the Scot James Croll (1875) had viewed the effects of trans‐annual orbital variations of the Earth on the patterns of insolation as the pacemakers for the Pleistocene glacial advances and Gilbert (1895) suggested that they drove sedimentary cyclicity.…”

“…It was not only continuity of deposition that allowed Tethys and its small successor, the Mediterranean Sea, to play this role: the pelagic record in both was exceptionally sensitive to orbital forcing, in having provided a double variation that offers new insight into the Earth response. One variation is a precessional ( ca 20 ky) oscillation in coccolith productivity, seemingly positively correlated with moderate seasonality that finds expression in the alternation of a more carbonate‐rich and a more clay‐rich bed, in settings in which deposition in aerated waters was succeeded by anaerobic diagenesis producing the ‘meta‐aerobic aeration facies’ (one of several ‘aeration facies’ proposed and elaborated on by Fischer et al. (2009).…”