Emiliano Mutti

Comparing Examples of Modern and Ancient Turbidite Systems: Problems and Concepts

A useful comparison of modern and ancient submarine fans can be based only on well-understood and thoroughly mapped systems. In addition, the examples selected for comparison must represent depositional systems similar in such characteristics as type of basin, size of sediment source, physical and temporal scales, and stage of development. Many fan sedimentation models presently in use do not meet these criteria.

Turbidite Systems and Their Relations to Depositional Sequences

Long-term global sea level variations and local tectonic control form the basic framework within which turbidite sediments develop as a response to breaks in the equilibrium between shelfal and basinal sedimentation. An understanding of the interaction of these processes and resulting types of turbidite deposition is still in its infancy and requires, as a preliminary approach, the precise framing of turbidite sediments within well defined depositional sequences.

An Integrated Approach to the Study of Turbidite Systems

Meaningful comparisons of modern and ancient turbidite systems must include consideration of the physical and temporal scales of the deposits as well as the limitations presented by the widely varying techniques used to map and describe the deposits. To facilitate such comparisons, we describe five basic elements of turbidite systems that, with appropriate types of field observations, can be recognized in both ancient and modern systems (i.e., in marine geologic, outcrop, or seismic-stratigraphie studies). The primary elements discussed are (1) major erosional features (other than channels), (2) channels, (3) overbank deposits, (4) lobes, and (5) channel-lobe-transition deposits. The determination of time-equivalent elements within any given turbidite system is necessary for deciphering depositional processes and sequence stratigraphy as well as for comparison with different systems to develop reliable, predictive sedimentation models for both modern and ancient submarine fans and other types of turbidite systems. This chapter is primarily intended to help stratigraphers and explorationists avoid being misled by the application of existing models. These models generally have not adequately taken into account either the complex interaction of the many factors that control turbi-dite deposition or the different stages of growth that many types of turbidite systems undergo with time during their evolution.

Turbidite systems: State of the art and future directions

The study of turbidite systems covering a wide range of physical scales has led to confusion regarding the use of certain key terms and hence a breakdown in communication between workers involved in turbidite research. There are three fundamentally different scales and types of observations derived from the study of outcrop data (ancient systems), high-resolution seismic reflection and side scan sonar data (modern systems), and multichannel seismic reflection data (modern and older buried systems). Despite the variability of scale the same terms are used to describe features that may have little in common. Consequently, turbidite system terminology has become imprecise and even misleading in some cases, thus providing impediments to developing useful predictive models for processes, depositional environments, and lateral and vertical distribution of sand bodies within turbidite systems. To address this concern, we review the principal elements critical to deepwater systems: slump scars, submarine canyons, channels, channel fill deposits, overbank deposits, and lobes and discuss some of their recognition criteria with each different type of data base. Local and regional tectonic setting, relative sea level variations, and bottom current activity are probably the main factors that control size, external geometry, internal stratal configuration, and facies characteristics of both modern and ancient turbidite systems. These factors ultimately control the timing and bounding characteristics between stages of growth of deepwater systems. If comparison of elements from different turbidite deposits using various data types is carried out at similar physical and temporal scales, predictive models eventually may be improved.

An introduction to the analysis of ancient turbidite basins from an outcrop perspective

Basin Studies Field Methods and Studies Sandstones and Clastics Sequence Stratigraphy. Turbidite sedimentation of ancient orogenic belts are considered as closely related to that of marginal flood-dominated fluvio-deltaic systems. Many conclusions are new and far from conventional. These notes represent a need for fresh air from the area of outcrop studies.

Seismoturbidites: a new group of resedimented deposits

Abstract Turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep-water basins. These beds, which may reach individual volumes in excess of 100 km3, are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins, most commonly elongate “flysch” troughs. Turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry, internal structures, and composition, and are termed herein seismoturbidites. Characteristically, these sediments lack time-persistent features of deep-sea fans such as channels and lobes. Seismoturbidites may occur as scattered intercalations diluted within otherwise “normal” turbidite sequences, thus forming generally excellent markers for basin-wide correlations, or as closely spaced, repetitive units comprising the bulk of the sedimentary fill of certain flysch basins. In both cases, they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space.

The Hecho Eocene Submarine Fan System, South-Central Pyrenees, Spain

The Eocene Hecho Group submarine-fan and basin-plain turbidites fill an elongate basin in the south-central Pyrenees that was tectonically active during deposition. The total volume of these sediments is about 21,000 to 26,000 km3. The bulk of the sand by-passed the fan-channel zone and was deposited in the lobe and fan-fringe environments. The stratigraphically lower part of the Hecho submarine fan was deposited during relative lowering of sea level.

Cengio Turbidite System, Italy

The Cengio sandstone member of the Tertiary Piedmont Basin in northwestern Italy has a conservatively estimated volume of 2.5 to 3 km3 (length: 6.4 km; width: 4.8 km; thickness: 170 m). It is interpreted as a sandstonerich submarine fan deposit. The Cengio member consists of eight tabular depositional sandstone lobes that are 5- to 25-m thick. These lobes filled a submarine structural depression and onlap and/or pinch-out against bounding slope mudstones. The stacking of the lobe units was related to synsedimentary tectonism.

The Specchio Unit (Northern Apennines, Italy): An Ancient Mass Transport Complex Originated from Near-Coastal Areas in an Intra-Slope Setting

Within the Eocene-Oligocene syn-orogenic deposits of the Epiligurian succession (Northern Apennines of Italy), a field-based study of the Specchio Unit (lower Rupelian) reveals that this complex is made up of three distinct but amalgamated mass-transport deposits (MTDs), the largest of which reaches a maximum volume of ca. 150 km3. These bodies were deposited inside the complex system of intraslope basin systems, developed atop the submerged Ligurian accretionary prism at the collision with the Adria continental plate. The MTDs originated from catastrophic retrogressive collapses starting from the upper slope and involving progressively shallow-water environments, from distal shelfal pro-delta and delta-front sediments up to proximal coastal fan-delta deposits. These recurrent and close in time, catastrophic slope failures were probably caused by tectonic and climatic triggers, such as the enhanced tectonic activity due to incipient Apenninic continental collision and the onset of harsh climatic conditions, as suggested by oxygen isotopic maxima (e.g., Oi-1a event). Although the wedge toe/foredeep systems are generally considered the principal loci of such, usually located in deep-water settings, here we stress the importance of catastrophic mass transport events also atop the wedge, in shallow-water depositional domains. Mass transport processes also have a fundamental role in reshaping the upper physiographic profile of an evolving accretionary wedge. The correct interpretation of such mass transport processes has also important implications for geohazard forecasting in modern active continental margins, for example in terms of tsunamigenic potential.

The Cengio submarine turbidite system of the Tertiary Piedmont Basin, Northwestern Italy

The Cengio sandstone member of the Tertiary Piedmont Basin in northwestern Italy has a conservatively estimated volume of 2.5 to 3 km3 (length: 6.4 km; width: 4.8 km; thickness: 170 m). It is interpreted as a sandstone-rich submarine fan deposit. The Cengio member consists of eight tabular depositional sandstone lobes that are 5- to 25-m thick. These lobes filled a submarine structural depression and onlap and/or pinch-out against bounding slope mudstones. The stacking of the lobe units was related to synsedimentary tectonism.