Preface

In this book, "Sedimentary Processes – Examples from Asia, Turkey, and Nigeria", the geological characteristics of different depositional environments have been singled out, particularly referring to deltas, beach systems, and coastal lacustrine environments. In this book, the other research topics are the riparian zone and the role of mangroves in controlling coastal sedimentation. The sedimentary processes represent one of the most important control factors influencing the facies distribution in a stratigraphic succession and are critical in coastal environments. In deltaic systems the vertical arrangement of depositional cycles is mainly controlled by the decrease of the gradients due to the progradation of the distributary channels. Exceptional events, including floods, storms, and earthquakes also influence the corresponding changes in the sedimentary patterns. The sedimentary processes are strictly related to the role of the sedimentary supply in controlling the stratigraphic architecture of the sedimentary sequences, depending on the availability of sediments, subsidence, and relative sea-level changes. In this framework, two situations may be distinguished, i.e. transgressive and regressive. In the transgressive situation, the subsidence and the sea-level rise are more important than the terrigenous supply and a sediment starvation occurs. Reworking, erosion, and diagenesis take place, coupled with an increase of chemically and biologically formed sediments. In the regressive situation, the subsidence and the sea level rise are less important than the terrigenous supply, resulting in progradation and increase of continental facies. Another important control factor acting on sedimentary processes is represented by the climate, due to the climate affecting the facies apart from temperature and rainfall, seasonal extremes, and sporadic fluctuations. Relative sea-level changes have been brought about by the sediment progradation, by the vertical movements, or by the tectonic tilting of the crustal blocks, by the changes in volume of the oceanic waters, or by the global tectonic changes, such as the variation in volume of the oceanic ridges. Delta models have individuated high constructive (tideinfluenced and wave-influenced) deltas and high destructive (lobate and elongate) deltas. Each delta type is distinguished from a characteristic morphology and facies pattern, which has been described including the vertical sequences, the facies associations, the facies distribution, and the geometry of the sandy bodies and reservoirs. The delta progradation produces a typical facies succession, consisting of prodelta facies, delta front, and delta plain facies. A coarsening upward succession of prodelta sediments to delta front sediments is overlain by a fining upward succession, composed of upper delta front sediments to delta plain sediments. The lacustrine deposits have a high potential of preservation and perhaps they represent excellent sedimentary archives in palaeo-climatic reconstructions. The sedimentary records of varves, annually laminated, provide high-resolution archives of palaeo-environmental conditions, so providing both chronological and geochemical information. Beach depositional systems and their changing morphology have been controlled by storm events, changing the coastal morphology, and triggering the formation of megacusp embayments. The impact of storms on the variation of the beach has been analyzed by combining the historical measurements of the beach profile surveys and the numerical modeling of storm-induced beach changes. The role of mangroves in controlling the coastal sedimentation is critical, since they

allocate more carbon below the ground, representing rich-carbon biomes, which facilitate the deposition of fine-grained sediments.

This book, made up of six chapters, examines different studies on the sedimentary processes, including the geologic characteristics. The first chapter introduces the sedimentary processes and related geological controls, examining the role of the deltas (Niger Delta), the coastal and lacustrine geo-archives, the beach systems and their morphological variations, and the geological role of mangroves. Using geophysical techniques for the analysis of the seismic attributes, in the second chapter it has been established that the N5.2 reservoir is a massive sandy unit, located in the Agbada Formation, representing a structural high, characterized by two main peaks. The correlation of well logs was performed, highlighting the occurrence of sandstones with traces of glauconites. In the third chapter, the coastal and lacustrine sedimentary archive of Lake Bafa was analyzed, individuating four main depositional stages, ranging in age from 4.5 ky B.P. to 0.8 ky B.P. The ecosystem characteristics of the basin have been controlled by hydroclimatic and geotectonic processes. The fourth chapter applied a fingerprinting technique to the sediment sources of the riparian zone, taking into account several depths of a tributary channel. The main sediment sources are represented by the topsoil above the riparian zone, by the sediments suspended by the Yangtze river, and by the sediment suspended by the Ruxi river. The fifth chapter has studied the long-term variations of the beach of the Kaike coast (Japan), starting from the analysis of aerial photographs and then producing a contour-line change model, which has considered the variations of sediment grain-size. In the sixth chapter, marker horizon techniques and surface elevation table (SET) tests have highlighted the spatial variability in the sedimentary patterns by examining several coastal sites, located in Malaysia and Thailand (south-eastern Asia).

I thank Mrs. Romina Skomersic, who has followed the publication process with competence and patience, allowing for the development of this book process.

> **Dr. Gemma Aiello, PhD** Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione Secondaria di Napoli, Napoli, Italy

> > **1**

**Chapter 1**

*Gemma Aiello*

**1. Introduction**

tary environments.

Introductory Chapter: An

Turkey, and Nigeria

Introduction to Sedimentary

Processes - Examples from Asia,

This is the introductory chapter of the book *Sedimentary Processes - Examples from Asia, Turkey and Nigeria*. In this book, different topics on the sedimentary processes have been treated, focusing, in particular, on the geological characteristics and production response of a sandstone reservoir located offshore the Niger Delta (Nigeria); on coastal lacustrine sedimentary archives with the example of Lake Bafa (Mediterranean Sea); on the riparian zone of the Three Gorges Reservoir (China), representing a transitional area located between aquatic and terrestrial environments; on the long-lasting changes of the beach environments along the Kaike coast (Japan); and, finally, on the role of the mangroves in coastal and estuarine sedimen-

The facies distribution and the corresponding changes are strongly influenced

by several control factors, including the sedimentary processes, the sediment supply, the climate, the tectonics, the sea level changes, the biological activity, the water chemistry, and the volcanism. In different depositional environments, these control factors are of variable importance, but the climate and the structural setting act on the whole sedimentary environments. On the other side, the sedimentary processes are critical in deltaic and fluvial environments. On the continental margins, relative sea level fluctuations involve the shallow seas and the shorelines, more than in the continental and deep marine environments, also if their effects are not negligible [1–4]. In a given depositional environment, the sedimentary processes, represented by the processes intrinsic to sedimentation, are responsible for the facies distribution and change. For instance, the progradation of the distributary channels of a delta controls a decrease of the gradient, so that the river has a short route, starting a new depositional cycle. Due to the nature itself of the depositional environments, these kinds of changes are inevitable, since the timing of these changes is controlled by unusual events, such as floods, storms, or earthquakes. These trigger causes must be distinguished from the fundamental causes represented by the delta progradation [5–7], by the river aggradation, and by the slope instability [8–10]. Sediment supply represents another important control factor. Its effect depends on the sediment availability, subsidence, and relative sea level changes. In this book, the main research topics are represented by the deltas, particularly referring to the Niger Delta; by the coastal and lacustrine sedimentary archives, particularly referring to the Lake Bafa; by the riparian zone; by the beach environments and their variations during the geological time; and, finally, by the
