A multi-proxy study of deeper-water carbonates (Upper Jurassic, southern Germany): combining sedimentology, chemostratigraphy and palynofacies

Abstract

A multi-proxy study of deeper-water carbonates (Upper Jurassic, southern Germany): combining sedimentology, chemostratigraphy and palynofacies Abstract Deeper shelf carbonates are often composed of relatively monotonous successions with few diagnostic sedimentological characteristics. The Upper Jurassic of southern Germany provides a classical example for deeper ramp carbonate environments, dominated by limestone/marl sequences including conspicuous sponge/microbial bioherms. Sedimentological analysis was integrated with stable isotope (O, C) and palynofacies analysis in an attempt to reconstruct the dominant depositional controls (sea level, climate, nutrients) as well as to delineate genetic sequences and their stacking patterns. Small-scale (3-10 m thick), medium-scale (5-25 m thick) and large-scale (45-60 m thick) sequences could be recognised, which all share similar patterns and trends. Oxygen isotopes from bulk rock carbonate samples were interpreted as records of temperature trends which were related to climatically induced sea level fluctuations. A positive oxygen isotope trend (i.e., cooling and associated relative sea-level fall) in combination with increasing absolute palynoclast abundances (increasing proximality) are inferred to mark regressive hemi-sequences. Negative trends in oxygen isotopes (i.e., warming and associated relative sea-level rise) and a decrease in absolute palynoclast abundances (increasing distality) are interpreted to indicate transgressive hemi-sequences. In contrast to the smallscale sequences, the medium-scale sequences could be

Delineating Sequence Stratigraphic Patterns in Deeper Ramp Carbonates: Quantitative Palynofacies Data from the Upper Jurassic (Kimmeridgian) of Southwest Germany

“…This observation is in accordance with the view that the isotopic composition of carbonates deposited in the Swabian Marl Basin records the changes in paleoenvironmental conditions on the adjacent shallow Helvetic Platform (Bartolini et al 2003). Moreover, cross-plots of d 18 O and d 13 C bulk carbonate measurements from various sections in the Oxfordian and Kimmeridgian of the Swabian Marl Basin have revealed no significant correlations, therefore corroborating the view that diagenesis has not strongly affected the isotopic composition (Ruf et al 2005b). Hence, although diagenetic overprints have to be taken into account, we conclude that the original trends in our d 18 O records have been preserved.…”

“…Here, the dip of strata is so low that already a relatively minor change in sea level causes significant shifts in shoreline position. Based on a dip of 0.002u, a value realized in numerous carbonate ramps (e.g., Shaw 1964;Irwin 1965; Burchette and Wright 1998), a sea-level change of 2 m causes a shoreline displacement of 57 km (compare Ruf et al 2005b). Hence, the observed differences in absolute abundances of terrigenous debris between situations of sea-level high and sea-level low are compatible with a minor sea-level change.…”

“…In a previous contribution, we focused on the development of the sedimentary facies and sequences of selected locations through the early and middle Upper Jurassic of SW Germany with a particular emphasis on reefal cycles (Ruf et al 2005a). In a more regional approach, the hierarchy of sequences and their correlation with other European basins has been studied by Ruf et al (2005b), relying on sedimentological data from more than 90 sections across the Upper Jurassic of SW Germany and northern Switzerland that were partially corroborated by stable-isotope and palynofacies information. In the present study, we focus on the palynofacies expression of sequence stratigraphic patterns in the Kimmeridgian of SW Germany.…”

Astronomical time scale for the Middle Oxfordian to Late Kimmeridgian in the Swiss and French Jura Mountains

“…Some of the estimated durations are in good agreement with the values given by Hardenbol et al (1998), others are quite different. For the Middle Oxfordian to Middle Kimmeridgian interval in southern Germany, Ruf et al (2005) defined medium-scale (400-kyr) sequences based on a chemostratigraphic and palynofacies analysis of deeper ramp carbonates. The durations of the corresponding ammonite zones are in the same order as those defined in the present study (Fig.…”

Palynofacies analysis for interpreting paleoenvironment and hydrocarbon potential of Triassic–Jurassic strata in the Sichuan Basin, China

“…Eccentricity cycles, especially the long cycles, are considered to act on relative sea level and terrestrial environment by periodic climate variations (Waterhouse, 1999;Bonis et al, 2010;G€ otz et al, 2008). High-resolution sequence stratigraphic and cyclostratigraphic studies suggested that, 400 kyr eccentricity cycle controls major depositional sequences via climatically-induced sea-level changes (Strasser et al, 2000;Ruf et al, 2005).…”