High-Frequency Rhythmicity in a Mixed Siliciclastic-Carbonate Shelf (Late Miocene, Guadix Basin, Spain): A Model of Interplay Between Climatic Oscillations, Subsidence, and Sediment Dispersal

Abstract

Rhythmites in pelagic sediments can include information on paleoclimate and with orbital cycles. This paper documents and interprets an unusual rhythmic succession from a cool-water shallow-marine shelf that includes features of Mediterranean-type ramps and open-ocean-type ramps. In the subsiding southwestern margin of the Guadix Basin (southern Spain, Betic Cordillera), during the late Tortonian, a 640-m-thick succession was deposited over a short period (7.8-7.2 Ma). This succession contains 30 sedimentary packages or rhythmites, each defined by two facies associations: a mixed crossstratified siliciclastic-skeletal sandstone and a homogeneous marl rich in planktonic foraminifera. Sandstones ranging in thickness from 3 m to 20 m contain coralline algae, bivalves, bryozoans, benthic foraminifera, echinoids, and brachiopods (typical temperate-water shelf biofacies). These units exhibit cross-strata sets up to four meters high, interpreted to have been produced by strong unidirectional currents. The marly deposits range in thickness from 2 to 17 m and contain an association of cold-water planktonic foraminifera as well as thin sandstone layers that exhibit normal grading corresponding to typical incomplete Bouma sequences or a lower division with planar lamination and an upper division of very fine-to fine-grained sandstone with hummocky and swaly cross-stratification. On the basis of the sedimentary structures, the sandstone layers are interpreted as sporadic turbidity flows and storm ebb-surge deposits.On the basis of the sedimentary structures, the hydrodynamic conditions during deposition of the mixed siliciclasticcarbonate interval were high-energy. Based on sedimentary and biogenic features of the rhythmites and their temporal durations (ca. 20 ka), rhythmicity is interpreted to reflect alternating cool-wet and cold-dry climate episodes driven by precession orbital cycles. This occurrence of alternating mixed carbonate-siliciclastic sedimentation and pelagic sediments represents a unique occurrence in the geologic record.

Micromammal biostratigraphy of the Upper Miocene to lowest Pleistocene continental deposits of the Guadix basin, southern Spain

“…1998). The two lower units (Units I and II) were deposited in a phase of marine sedimentation during the Tortonian, and the third one (Unit III) includes shallow marine sediments, deposited during the sea retreat from the central sector of the Betic Cordillera at the end of the Tortonian (García‐García et al. 2009).…”

Sedimentary features and their controls in a mixed siliciclastic–carbonate system in a shallow lake area: An example from the BZ‐X block in the Huanghekou Sag, Bohai Bay Basin, Eastern China

“…In such a model, the algal/bioclastic‐rich intervals could correspond to episodes of a dry climate (Figures and ; García‐García, Soria, Viseras, & Fernandez, ; Korngreen & Bialik, ), as reflected in (a) less siliciclastic supply due to a decrease in precipitation and the consequent inactivity of the feeding systems in the source area (Pujalte, Robador, Payros, & Samsó, ); (b) relatively warm temperature that favoured the formation of carbonate sedimentation (e.g., Wright & Burchette, ). In contrast, the siliciclastic‐dominated interval could correspond to a wet climate stage, as suggested by increasing supply of coarse sediments due to intense precipitation in the source area, which give the unlikelihood of tectonic influence (García‐García et al, ; Pujalte et al, ). Accordingly, the alternation of the couplets of heterolithic laminae represents a record of different hydrodynamic cycles, possibly reflecting high‐frequency changes in climate.…”

“…The alternations of the mixed silici–bioclastic strata in marine setting has been reported, which can be attributed to a result of tidal or wave actions (Longhitano, ; Tomkins, Nielsen, & Hughes, ). The cases about high‐frequency cycles controlled by climatic oscillations in a marine was proved to be associated with orbital cycles (García‐García et al, ; Zhao, Li, Huang, & Yu, ). The driving mechanism for dry–wet climate cycles in this study needs to be further investigated, however, the effects of climate for such a strata mixing should be focused in lacustrine settings.…”

‘Hummocky cross‐stratification‐like structures in deep‐sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France)’ by Mulder et al. (2009), Sedimentology, 56, 997–1015: Discussion

“…However, Granularia and Helminthopsis are known in shallow‐marine deposits (Buatois et al. , 1998; García‐García et al. , 2009); the former is a junior synonym of Ophiomorpha (Uchman, 2009).…”