Analogue and Numerical Modelling of Sedimentary Systems: From Understanding to Prediction: 40 (International Association Of Sedimentologists Series) - Hardcover

Hardcover

ISBN 10: 1405189304 ISBN 13: 9781405189309

Publisher: Wiley-Blackwell, 2008

Synopsis

Understanding basin-fill evolution and the origin of stratal architectures has traditionally been based on studies of outcrops, well and seismic data, studies of and inferences on qualitative geological processes, and to a lesser extent based on quantitative observations of modern and ancient sedimentary environments. Insight gained on the basis of these studies can increasingly be tested and extended through the application of numerical and analogue forward models.

Present-day stratigraphic forward modelling follows two principle lines: 1) the deterministic process-based approach, ideally with resolution of the fundamental equations of fluid and sediment motion at all scales, and 2) the stochastic approach. The process-based approach leads to improved understanding of the dynamics (physics) of the system, increasing our predictive power of how systems evolve under various forcing conditions unless the system is highly non-linear and hence difficult or perhaps even impossible to predict. The stochastic approach is more direct, relatively simple, and useful for study of more complicated or less-well understood systems. Process-based models, more than stochastic ones, are directly limited by the diversity of temporal and spatial scales and the very incomplete knowledge of how processes operate and interact on the various scales.

The papers included in this book demonstrate how cross-fertilization between traditional field studies and analogue and numerical forward modelling expands our understanding of Earth-surface systems.

About this title

About the Author

Poppe de Boer and George Postma are the authors of Analogue and Numerical Modelling of Sedimentary Systems: From Understanding to Prediction, published by Wiley.

Present-day stratigraphic forward modelling follows two principle lines: 1) the deterministic process-based approach, ideally with resolution of the fundamental equations of fluid and sediment motion at all scales, and 2) the stochastic approach. The process-based approach leads to improved understanding of the dynamics (physics) of the system, increasing our predictive power of how systems evolve under various forcing conditions unless the system is highly non-linear and hence difficult or perhaps even impossible to predict. The stochastic approach is more direct, relatively simple, and useful for study of more complicated or less-well understood systems. Process-based models, more than stochastic ones, are directly limited by the diversity of temporal and spatial scales and the very incomplete knowledge of how processes operate and interact on the various scales.

The papers included in this book demonstrate how cross-fertilization between traditional field studies and analogue and numerical forward modelling expands our understanding of Earth-surface systems.

Present-day stratigraphic forward modelling follows two principle lines: 1) the deterministic process-based approach, ideally with resolution of the fundamental equations of fluid and sediment motion at all scales, and 2) the stochastic approach. The process-based approach leads to improved understanding of the dynamics (physics) of the system, increasing our predictive power of how systems evolve under various forcing conditions unless the system is highly non-linear and hence difficult or perhaps even impossible to predict. The stochastic approach is more direct, relatively simple, and useful for study of more complicated or less-well understood systems. Process-based models, more than stochastic ones, are directly limited by the diversity of temporal and spatial scales and the very incomplete knowledge of how processes operate and interact on the various scales.

The papers included in this book demonstrate how cross-fertilization between traditional field studies and analogue and numerical forward modelling expands our understanding of Earth-surface systems.

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Analogue and Numerical Modelling of Sedimentary Systems

From Understanding to Prediction (Special Publication 40 of the IAS)

John Wiley & Sons

Copyright © 2008 International Association of Sedimentologists
All right reserved.
ISBN: 978-1-4051-8930-9

Chapter One

Numerical simulation of the syn- to post-depositional history of a prograding carbonate platform: the Rosengarten, Middle Triassic, Dolomites, Italy

AXEL EMMERICH, ROBERT TSCHERNY, THILO BECHSTDT, CARSTEN BKER, ULLRICH A. GLASMACHER, RALF LITTKE and RAINER ZHLKE

ABSTRACT

A combination of thermal history, numerical basin-reverse and sequence-stratigraphic forward modelling is applied to the Mesozoic outcrop analogue of the Rosengarten carbonate platform area in the Dolomites of northern Italy. This integrated multidisciplinary approach of numerical simulation quantifies the thermal, subsidence, geometrical and subsequent facies evolution of the area. Calibration data during modelling were vitrinite reflectance (VR) and apatite fission-track (FT) analyses as well as detailed outcrop studies. Vitrinite reflectance values in strata underlying the carbonate platform vary between 0.5 and 0.8% [VR.sub.r]; apatites from these formations reveal cooling ages of around 165.6 Ma and track lengths of approximately 9.8 m. This low thermal maturity combined with the FT data in apatites indicates a relatively cool (<11C), protracted (between 250 and 30 Ma) and shallow burial (thickness of eroded strata overlying present-day topography is <1100 m), as well as a fast exhumation from the Middle Miocene onward. Maximum temperatures are reached during the Middle/Late Triassic, when the basal heat flow was elevated owing to regional volcanic and hydrothermal activity. Local anomalies in vitrinite reflectance of up to 1.1% [VR.sub.r] in the immediate surroundings of the Predazzo/Monzoni volcanic centre show that its thermal influence decreased rapidly with increasing distance. The geometrical evolution of the Middle Triassic (Anisian/Ladinian) Rosengarten platform is twofold: the first stage reveals aggradation, the second progradation of the platform margin. Basin-reverse modelling results indicate that these two intervals originate from a temporal change in tectonic subsidence. Spatial variations in flexural and tectonic subsidence along the 6 km transect are insignificant due to the rigidity of the basement (up to 2500 m of Late Permian ignimbrites). During the first stage of platform evolution, high pulse-like total subsidence rates of up to 820 m [Myr.sup.-1] led to aggradation, whereas the subsequent drop to 100 m [Myr.sup.-1] initiated platform progradation. The short-spanned subsidence peak was linked to block movements in a strike-slip tectonic setting (Cima Bocche Anticline-Stava Line approximately 10 km southeast of the study area). Stratigraphic forward modelling quantifies the sediment volumes involved in the geometrical evolution of the platform. In order to replicate platform architecture, constant carbonate accumulation rates between 900 and 1000 m [Myr.sup.-1] - increasing from periplatform environments to the slope - have to be assumed throughout the existence (approximately 5.8 Myr) of the Rosengarten. As the carbonate factory successfully keeps up with the modelled accommodation rates, it must have completely recovered from the Permian-Triassic biotic crisis during the onset of platform growth in latest Anisian times despite the low biotic diversity of the platform succession seen elsewhere in the Dolomites. Our forward modelling confirms that the main carbonate factory was situated on the slope at water depths from shallow subtidal to 300 m ('slope-shedding') and that it therefore switched on during all possible stages of accommodation change.

Keywords Basin analysis, numerical simulation, subsidence, thermal maturity, thermochronology, carbonate platform, aggradation, progradation, sedimentation rates, Triassic, Southern Alps, Dolomites.

INTRODUCTION

The Dolomites of northern Italy (Fig. 1) have long been a study area for carbonate platforms and their reef communities. Since Mojsisovics termed the word 'berguss-Schichtung' back in 1879 (i.e., clinostratification), many authors have worked on platform-to-basin transitions of carbonate build-ups in the Dolomites (Hummel, 1928, 1932; Pia, 1937; Leonardi, 1962, 1967; Bosellini, 1984, 1988). In particular, the Rosengarten has served as a reference model for progradational geometries (Bosellini & Stefani, 1991; Bosellini et al., 1996). However, assessing the evolution of carbonate platforms and their clinoforms has been mainly of a qualitative nature. Quantitative approaches of subsidence and carbonate accumulation of Middle Triassic platforms in the Dolomites have so far been scarce (Schlager, 1981; Doglioni & Goldhammer, 1988; Schlager et al., 1991; Maurer, 1999, 2000; Keim & Schlager, 2001) and lack unbiased numerical modelling techniques. The age of these platforms is usually constrained by coeval basinal sediments containing abundant biostratigraphic information (Buchenstein Fm; Brack & Rieber, 1993, 1994). Recently, age-diagnostic airborne tuff layers in basinal and lagoonal strata were used to synchronize bio-, cyclo- and chronostratigraphy (basinal Buchenstein Fm at Seceda/Geisler Group, western Dolomites: Mundil et al., 1996; lagoonal Schlern Dolomite Fm 1 at Latemar, western Dolomites: Mundil et al., 2003; for locations see Fig. 2) providing a high-resolution database for numerical simulation. The particular feature of the Rosengarten platform is that some of these dated tuff layers can be physically correlated to coeval slope deposits (Maurer, 1999, 2000).

The aim of this paper is the quantification of the development of the Rosengarten platform and the assessment of its primary controlling factors during platform growth. This is realized by an integrated approach of basin-reverse and stratigraphic-forward modelling combined with thermal basin modelling. Datasets for all modelling procedures are derived from existing studies and from new detailed analyses on allo-/sequence stratigraphy and facies architecture, thermal maturity and apatite fission tracks in strata underlying the platform body.

BASIN AND CARBONATE-PLATFORM DEVELOPMENT

The southwestern Dolomites (for location within the Alps, Fig. 1) are located on the Adriatic Plate between former Laurussia and Gondwana (Dercourt et al., 2000). Throughout the Triassic, this area represents the eastern margin of a highly differentiated passive continental margin with mixed siliciclastic-carbonate sedimentation (Blendinger, 1985; Doglioni, 1987). First, carbonate ramps (early Anisian/Aegean) and small reef mounds (early in the late Anisian/Pelsonian) developed in the Dolomites (Fois & Gaetani, 1984; Senowbari-Daryan et al., 1993) after the carbonate factory had eventually recovered from the severe faunal crisis at the close of the Permian. From the late Anisian into the late Ladinian, a considerable submarine relief with local subaerial highs prevailed in the western Dolomites. Middle Anisian transpressive-transtensive tectonics dismembered the continental shelf and created strong regional differences in facies (the so-called 'Facies Heteropie' sensu Bechstdt & Brandner, 1970; see also Zhlke, 2000). Deep marine, stagnant basins with fine-grained chert- and organic-matter-rich sediments (Anisian: Moena Fm and Anisian/Ladinian: Buchenstein Fm; Figs 2 and 3) existed alongside shallow marine subtidal carbonate ramps and platforms (Anisian: Contrin Fm and Anisian/Ladinian: Schlern Dolomite Fm 1; Figs 2 and 3). Structural highs of the dismembered carbonate ramp (Contrin Fm) represent the nuclei of the Schlern Dolomite Fm 1 platforms in the Late Anisian (Masetti & Neri, 1980; Gaetani et al., 1981; Bosellini, 1989). Evolution of the Ladinian carbonate platforms such as the Rosengarten/Schlern, Monte Agnello and possibly also the Latemar was terminated by the extrusion of the Longobardian Wengen Group volcanics (Mojsisovics, 1879; Viel, 1979a, 1979b; De Zanche et al., 1995; Fig. 3). The volcanic centre at Predazzo/Monzoni was nourished by a source linked to a deep-reaching fracture zone (Cima Bocche Anticline/Stava Line; Fig. 4; Blendinger, 1985). Tectonics also played a crucial role in platform development in the southwestern Dolomites as regional subsidence and accommodation development were controlled by downward movements along faults and upward movements through magmatic updoming (Doglioni, 1983, 1984, 1987).

Owing to its excellent, laterally continuous seismic and sub-seismic scale outcrop (Fig. 5a and b), the Rosengarten part of the Rosengarten/Schlern platform is ideally suited for a study on the geometric development of a carbonate platform and its accumulation rates. The platform top of the Rosengarten passes laterally into a platform slope interfingering with basinal sediments. The maximum north to south progradation of the Rosengarten slope was approximately 6 km. Lagoon, reef and slope facies of the build-up are all part of the Schlern Dolomite Formation 1, whereas coeval basinal sediments belong to the Buchenstein Formation. Bio- and chronostratigraphic data (Brack & Rieber, 1993, 1994; Mundil et al., 1996, 2003; Maurer, 1999, 2000; Fig. 4) indicate the onset of platform growth in the upper Reitzi-biozone (Anisian; Middle Triassic stages after Brack & Rieber, 1993, 1994). According to Maurer (1999, 2000), the slope of the Rosengarten records five ammonite biozones (Fig. 5b). During the first two - Reitzi and Secedensis - biozones of platform existence, aggradation occurred. This first stage of platform evolution was followed by a second stage of progradational clinoforms. The preserved record of carbonate sedimentation lasted at least until the basal Archelaus-zone (middle/late Ladinian; Maurer, 1999, 2000; Fig. 5b). The maximum thickness of the Rosengarten - and therefore also its growth mode - can be inferred only by projecting stratigraphical information from the Schlern platform (Bosellini & Stefani, 1991; Fig. 6). At Schlern, 850 m of cyclically arranged platform carbonates are partially covered by Wengen Group volcanics (Fig. 4) preserving the maximum thickness of the Schlern Dolomite Fm 1 (Fig. 3). Using all available biostratigraphic data, Maurer (1999, 2000) estimated compacted carbonate accumulation rates for the first aggradational phase of 200 m [Myr.sup.-1] increasing during the second progradational phase.

As the oldest rocks in the study area that have been preserved belong to the uppermost Ladinian, the geological evolution from Late Triassic times onward can be derived only by studying younger successions in other parts of the Dolomites (e.g. Sella platform, Fig. 2) and the Southern Alps (e.g. Trento platform). Late Triassic volcaniclastics and carbonates (Wengen Group; Mastandrea et al., 1997) filled the basins. An extensive carbonate platform developed with the onset of a period of tectonic quiescence. The so-called Trento platform comprises the entire central segment of the Southern Alps on the Adriatic Plate (Dolomia Principale Fm and Calcari Grigi Fm; Leonardi, 1967; Bosellini & Broglio Loriga, 1971; Bosellini & Hardie, 1985; Trevisani, 1991; Boomer et al., 2001). From Middle Jurassic times onward, the Trento platform started to subside and eventually drowned. A phase of deep marine sedimentation began (Ammonitico Rosso Fm; Winterer & Bosellini, 1981; Martire, 1996; Winterer, 1998) and lasted until Late Cretaceous times (Marne del Puez Fm; Claps et al., 1991; Antruilles Fm; Stock, 1996). Water depths decreased when the tectonic regime switched from extensional to compressional and the collision of the Adriatic plate with Europe began with Late Cretaceous subduction of oceanic crust (Hs, 1971; Smith, 1971; Trmpy, 1982; Laubscher & Bernoulli, 1982; 'eoalpine' sensu Doglioni & Bosellini, 1987; Hs, 1989). Towards the east, the Southern Alps were strongly involved in the Dinaric orogeny during the Late Eocene, but the compression front is thought to have extended even into the Dolomites (Doglioni & Bosellini, 1987). This interval of convergence was shortly interrupted by an Oligocene extensional phase recorded along the Periadriatic Line by plutonic intrusions (e.g. Adamello pluton) and dykes as well as by effusive basalts at the southwest termination of the Trento Plateau (Zattin et al., 2006). Upper Oligocene shallow-marine conglomerates (Monte Parei Fm) record uplifted source areas during ongoing or renewed continent collision in the eastern Dolomites (Cros, 1966; Mair et al., 1996). Although steady state or episodic exhumation of parts of the Alps remains debated (Bernet et al., 2001; Carrapa et al., 2003; Kuhlemann et al., 2006), there seems to be increasing consensus on the timing of exhumation. At least three stages of exhumation are observed: rapid exhumation before approximately 35 Ma, slower exhumation until ~15 Ma and very rapid exhumation to present-day positions from then onward (Carrapa et al., 2003; Zattin et al., 2003; Bertotti et al., 2006).

METHODS AND DATABASE

Sedimentological analyses

Detailed sedimentological analyses (logging, facies mapping, lateral tracing of physical surfaces, thin sections) have been carried out on the underlying strata of the Rosengarten platform (Fig. 6). Ten sections/sedimentological logs cover the entire basin fill from basement (Atesina Volcanic Complex, AVC) to the basal Schlern Dolomite Fm 1. Additional data on the upper Anisian succession and the Buchenstein Fm were taken from the literature (Bosellini & Stefani, 1991; Maurer, 1999; Zhlke, 2000). These analyses are necessary to obtain datasets on thicknesses, lithologies and palaeowater depths. The latter is based on the integration of all sedimentological evidence from the outcrops (channels, ripples, exposure surfaces, bioturbation, etc.) combined with microfacies analyses of the 283 thin-sections.

Stratigraphy and timescale

Within the past years, there has been some controversy about the duration of Schlern Dolomite Fm 1, informally known as the 'Latemar controversy' (Brack et al., 1997; Hardie & Hinnov, 1997). Several studies (Goldhammer & Harris, 1989; Hinnov & Goldhammer, 1991; Preto et al., 2001) proposed a specific type of orbital forcing for the cyclically arranged lagoonal interior of the Schlern Dolomite Fm 1. Subsequent studies (Brack & Rieber, 1993; Brack et al., 1996; Mundil et al., 1996) questioned this Milankovitch model because of its incompatibility with bio- and chronostratigraphic data. Radiometric age dating on detrital zircons in airborne tuff layers intercalated within the lagoonal sediments of the Latemar helped to solve the controversy (Mundil et al., 2003). Subsequent time-series analyses and numerical simulation based upon in situ bio- and chronostratigraphic data indicate a much higher frequency of the cycles and thus a much shorter duration of the entire cyclic succession (Zhlke et al., 2003; Zhlke, 2004; Emmerich et al., 2005a). This study follows the stratigraphic concept laid down in Emmerich et al. (2005a).

Upper Triassic formations were evaluated and thicknesses projected from the western and central Dolomites (Schlern, Sella and Gardenaccia platform), Jurassic strata from the Trento platform, and Cretaceous and Tertiary formations from the eastern Dolomites (Table 1). Lithology information was combined with published data on chronostratigraphy and palaeobathymetry. Initial Jurassic palaeowater depths were calculated with a subsidence curve for the Trento platform proposed by Winterer & Bosellini (1981) and Winterer (1998). If necessary, thickness of eroded stratigraphic units and palaeowater depth were adapted within a range of values provided by studies on the regional geology (Table 1) in order to fit the simulated time-temperature evolution.

(Continues...)

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Edition details

• Publisher: Wiley-Blackwell
• Publication date: 2008
• Language: English
• ISBN 10: 1405189304
• ISBN 13: 9781405189309
• Binding: Hardcover
• Edition number: 1
• Number of pages: 328
• Editor: De Boer Poppe, Postma George, Van Der Zwan Kees, Burgess Peter, Kukla Peter