Precessional and half-precessional climate forcing of Mid-Devonian monsoon-like dynamics

Abstract

Abstract.A Devonian magnetic susceptibility (MS) record obtained on limestones ranging from the Uppermost-Eifelian to the Lower-Givetian and located on the southern border of the Dinant Synclinorium in Belgium was selected for timeseries analysis. In these carbonate ramp and platform deposits, spectral analyses highlight persistent, high-frequency cycles in both the MS-signal and the microfacies curve, reflecting environmental and climate changes. These metrescale variations in the MS-signal are interpreted as changes in the flux of magnetic minerals towards the marine system, most likely controlled by monsoon rainfall-intensity. By combining chrono-and biostratigraphic information with theoretical knowledge of sedimentation rates in different depositional environments, these cycles are interpreted as astronomically driven and dominated by precession. It is hypothesized that during precession minima (longitude of the perihelion ≈270 • ) the trans-equatorial pressure gradient reaches a maximum and intensifies the northeasterly monsoonal circulation. The consequent increase in moisture transport towards the continent leads to enhanced precipitation and runoff, which, in turn, induces a higher flux of detrital material -including magnetic minerals responsible for the MS-signal -towards the marine system. Moreover, this unique high-resolution climate signal reveals halfprecessional cycles. These cycles suggest that during precession maxima (longitude of the perihelion ≈90 • ) southeasterly monsoonal circulation strengthened due to an increased inter-hemispheric pressure gradient.

Low-latitude climate variability in the Heinrich frequency band of the Late Cretaceous greenhouse world

“…It is this cycle that is responsible for the observed triple-peak signature of the most prominent precession-related cycles in the short intervals. Similar ∼ 7 kyr sub-Milankovitch cycles have been observed in deeptime successions (e.g., De Vleeschouwer et al, 2012;Boulila et al, 2010).…”

“…Such cycles have indeed been described from Pliocene lignite-bearing lacustrine successions of northern Greece (Steenbrink et al, 2003) and platform carbonates of the Great Bahama Bank (Reuning et al, 2006). Sub-Milankovitch cycles have further been described in Upper Jurassic marls (Rodríguez-Tovar and Pardo-Igúzquiza, 2003;Boulila et al, 2010), Triassic marine sections (Zühlke et al, 2003;Wu et al, 2012) and Devonian carbonates (De Vleeschouwer et al, 2012). They have further been found in fluvial floodplain successions in the Eocene Willwood Formation in North America (Abdul Aziz et al, 2008), although the latter may equally well be associated with autogenic processes acting on the floodplain (Bown and Kraus, 1992).…”

The astronomical calibration of the Givetian (Middle Devonian) timescale (Dinant Synclinorium, Belgium)

“…This section has been subjected to detailed sedimentological and cyclostratigraphic studies and provides good knowledge of facies, environmental and sealevel variations (Mabille & Boulvain 2007;De Vleeschouwer et al 2012a). The 'Monts de Baileux' section (50802 ′ 25 ′′ N, 4823 ′ 37 ′′ E) exposes a succession of strata from the Hanonet Fm to the base of the Mont d'Haurs Fm, and also encompasses the Eifelian -Givetian boundary (Mabille & Boulvain 2008).…”

The global monsoon across timescales: coherent variability of regional monsoons

“…For the early Paleozoic, for example, the late Ordovician monsoon climate has been inferred from geological evidence of ITCZ migrations (Armstrong et al, 2009). Aspects of the Silurian monsoon have been inferred from paleoceanographic reconstructions (Wilde et al, 1991), and the variability of the middle Devoian monsoon climate has been reconstructed using magnetic susceptibility records (De Vleeschouwer et al, 2012). For the late Mesozoic, the monsoon-driven reversal of surface tropical currents in the Cretaceous Tethys Seaway has been simulated in models (Bush, 1997), and middle Cretaceous limestone-marlstone couplets have been interpreted as arising from precessionforced variability in monsoon precipitation (Floegel et al, 2005).…”

“…A mounting body of evidence indicates that precession and eccentricity cycles were manifested in P. X. Wang et al: The global monsoon across timescales paleomonsoon archives throughout the Phanerozoic. For example, the magnetic susceptibility record has been used to indicate the precession and semi-precession cycles of monsoon precipitation in Devonian limestone (De Vleeschouwer et al, 2012); geochemical and lithological analyses of clay lake deposits reveal precession, obliquity and eccentricity cycles in Triassic monsoon precipitation (Vollmer et al, 2008); and Cretaceous limestone and marlstone couplets have been shown to indicate precessional rhythms of monsoon-related hydrological cycling (Floegel et al, 2005). Although a global vision of the Pre-Quaternary paleomonsoon is hampered in most cases by a scarcity of data, the orbital forcing in monsoon variations is widely documented.…”