Preface

 This book contains four chapters dealing with the investigation of facies analysis and paleoecology, chemostratigraphy, and chronostratigraphy referring to paleoecological and facies analysis techniques and methodologies. The chapters pertain in particular to an Oligo-Miocene carbonate succession of the Persian Gulf (Asmari Formation), the chemostratigraphy of Paleozoic carbonates of Peninsular Malaysia through the integration of stratigraphic, sedimentologic, and geochemical data, and the chronostratigraphy of a small ice-dammed paleolake in Andorra (Spain), applying fast Fourier transform analysis, resulting in 6th-order stratigraphic cycles, which have outlined the occurrence of system tracts and unconformities controlled by glacio-eustasy. The chapters are separated into four main sections: (1) introduction; (2) facies analysis and paleoecology; (3) chemostratigraphy; and (4) chronostratigraphy. There is one chapter in the first section, introducing the stratigraphic setting of Paleozoic to Miocene deposits based on different stratigraphic methodologies, including facies analysis, paleoecology, chemostratigraphy, and chronostratigraphy. In the second section, there is one chapter dealing with the Oligocene-Miocene Asmari Formation, allowing for the recognition of several depositional environments based on sedimentological analysis, distribution of foraminifera, and micropaleontological study. In the third section, there is one chapter aimed at addressing research on the chemostratigraphy of cores, allowing for a significant increase in the stratigraphic knowledge existing on the Kinta Valley (Malaysia), coupled with extensive field work on Paleozoic carbonates. In the fourth section, there is a chapter dealing with the high-resolution chronostratigraphic setting of a paleolake located in Andorra (Spain) and the inference with the MIS2 isotopic stage of Atlantic and Mediterranean regions in the regional geological setting of the southeastern Pyrenees.

#### **Introductory chapter**

This chapter introduces the stratigraphic setting of Paleozoic to Miocene deposits based on different stratigraphic methodologies, including facies analysis, paleoecology, chemostratigraphy, and chronostratigraphy, applied in this book. Concepts and methods of facies analysis and paleoecology are discussed. Chemostratigraphy, a relatively young discipline in the field of stratigraphy, has been defined, coupled with recent attempts for its formalization in stratigraphy. The definitions of chronostratigraphy and geochronology, deeply revised in recent stratigraphic literature, are further clarified.

#### **Facies analysis and paleoecology**

The second chapter, "Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari Formation (Qeshm Island, SE Persian Gulf)" by Seyed Hadi Sajadi and Roya Fanati Rashidi, improves the geological knowledge of the Oligocene-Miocene Asmari Formation, allowing for the recognition of several depositional environments based on sedimentological analysis, distribution of foraminifera, and micropaleontological study.

## **Chemostratigraphy**

 The third chapter, "Chemostratigraphy of Paleozoic Carbonates in the Western Belt (Peninsular Malaysia): A Case Study on the Kinta Limestone" by Haylay Tsegab and Chow Weng Sum, takes the Kinta Valley (Malaysia) as an example, addressing stratigraphic research on the chemostratigraphy of cores, allowing for a significant increase in the stratigraphic knowledge existing in this area, coupled with extensive field work on Paleozoic carbonates.

### **Chronostratigraphy**

 The fourth chapter, "High Resolution Chronostratigraphy from an Ice-Dammed Palaeo-Lake in Andorra: MIS 2 Atlantic and Mediterranean Palaeo-Climate Inferences over the SE Pyrenees" by Turu Valenti, studies the high-resolution chronostratigraphic setting of a paleolake located in Andorra (Spain) and the inference with the MIS2 isotopic stage of Atlantic and Mediterranean regions in the regional geological setting of the southeastern Pyrenees.

I thank Mrs. Dolores Kuzelj, Author Service Manager of IntechOpen Science, Open Minds, who has contributed to this book on stratigraphy with competence and patience, following day after day the editorial activities and facilitating the publication of this book.

> **Dr. Gemma Aiello, PhD**  Full-Time Researcher, National Research Council of Italy (CNR), Institute of Marine Sciences (ISMAR), Section of Naples, Naples, Italy

Section 1 Introduction

**3**

**Chapter 1**

and Meanings

*Gemma Aiello*

**1. Introduction**

unconformities.

presented by Laursen et al., 2009 [11].

Introductory Chapter: An

Introduction to the Stratigraphic

Setting of Paleozoic to Miocene

Deposits Based on Paleoecology,

Facies Analysis, Chemostratigraphy,

and Chronostratigraphy - Concepts

This is the introductory chapter of the book "New insights into the stratigraphic

The topic of the Asmari Formation and its depositional environments has been deeply studied [1–12]. Referring to its biostratigraphy, it was earlier outlined in the 1960s based on unpublished reports [11]. The application of isotopic stratigraphy has later proved that the sediments ascribed to the Miocene "Aquitanian" are, in fact, Late Oligocene, Chattian in age. This was proved by the application of Sr-isotope stratigraphy to cored sections from 10 Iranian oil fields and 14 outcrop sections, within the framework of a high resolution sequence stratigraphy study down to fourth order cycles. The Chattian/Aquitanian boundary is marked by a major faunal turnover, with the general extinction of *Archaias species* and *Miogypsinoides complanatus*. The age interpretation of the early, unpublished zonations has needed a deep revision and the establishment of an updated biozonation. The new zonation and the stratigraphic ranges of selected key species have been

The isotopic stratigraphy based on strontium has constrained the stratigraphic setting of the Asmari Formation [8]. This formation, consisting of approximately 400 m of cyclic platform limestones and dolostones, with subordinate intervals of

setting of Paleozoic to Miocene deposits: case studies from the Persian Gulf, Peninsular Malaysia and south-eastern Pyrenees." In this chapter, the research themes studied in this book have been introduced referring to the paleoecological and facies analysis techniques and methodologies, pertaining, in particular, an Oligo-Miocene carbonate succession of the Persian Gulf (Asmari Formation), the chemostratigraphy of Paleozoic carbonates of Peninsular Malaysia through the integration of stratigraphic, sedimentologic, and geochemical data, and the chronostratigraphy of a small ice-dammed paleolake in Andorra, applying the FFT (Fast Fourier Transform) analysis, resulting in sixth-order stratigraphic cycles, which have outlined the occurrence of glacially controlled system tracts and

#### **Chapter 1**

Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene Deposits Based on Paleoecology, Facies Analysis, Chemostratigraphy, and Chronostratigraphy - Concepts and Meanings

*Gemma Aiello* 

#### **1. Introduction**

This is the introductory chapter of the book "New insights into the stratigraphic setting of Paleozoic to Miocene deposits: case studies from the Persian Gulf, Peninsular Malaysia and south-eastern Pyrenees." In this chapter, the research themes studied in this book have been introduced referring to the paleoecological and facies analysis techniques and methodologies, pertaining, in particular, an Oligo-Miocene carbonate succession of the Persian Gulf (Asmari Formation), the chemostratigraphy of Paleozoic carbonates of Peninsular Malaysia through the integration of stratigraphic, sedimentologic, and geochemical data, and the chronostratigraphy of a small ice-dammed paleolake in Andorra, applying the FFT (Fast Fourier Transform) analysis, resulting in sixth-order stratigraphic cycles, which have outlined the occurrence of glacially controlled system tracts and unconformities.

The topic of the Asmari Formation and its depositional environments has been deeply studied [1–12]. Referring to its biostratigraphy, it was earlier outlined in the 1960s based on unpublished reports [11]. The application of isotopic stratigraphy has later proved that the sediments ascribed to the Miocene "Aquitanian" are, in fact, Late Oligocene, Chattian in age. This was proved by the application of Sr-isotope stratigraphy to cored sections from 10 Iranian oil fields and 14 outcrop sections, within the framework of a high resolution sequence stratigraphy study down to fourth order cycles. The Chattian/Aquitanian boundary is marked by a major faunal turnover, with the general extinction of *Archaias species* and *Miogypsinoides complanatus*. The age interpretation of the early, unpublished zonations has needed a deep revision and the establishment of an updated biozonation. The new zonation and the stratigraphic ranges of selected key species have been presented by Laursen et al., 2009 [11].

The isotopic stratigraphy based on strontium has constrained the stratigraphic setting of the Asmari Formation [8]. This formation, consisting of approximately 400 m of cyclic platform limestones and dolostones, with subordinate intervals of sandstones and shales, has been studied in the subsurface at several oil fields and in an outcrop section. The methods of Sr-isotope stratigraphy is suitable for dating these strata because of the fast rate of marine strontium ratio during the depositional processes (roughly 32–18 My). The profiles of age against depth in the four areas have shown a decrease from higher accumulation rates in the lower Asmari to lower rates in the middle-upper part of the formation. These changes reflect the dynamics of platform progradation, from early deposition along relatively high accommodation margin to slope settings and then, to conditions of lower accommodation on the shelf top [8]. The ages of the sequence boundaries have been estimated from the age-depth profiles at each locality, providing a framework for stratigraphic correlation. The depositional sequences have an average duration of 1–3 My, whereas the component cycles represent average time intervals of 100–300 ky.

 On the other side, the Kinta limestones have been matter of previous studies, mainly referring to the depositional environments [13–16]. In the Kinta valley, they are composed of medium-to-dark gray, fine-grained, thinly bedded limestones, with preserved bedding planes and slump depositional features. The faunal content is quite scarce, except that some conodont faunas, while a high organic content is suggested from the dark color of the deposits. The sedimentological and facies analysis has suggested the occurrence of low energy, slope environment hosting the deposition of the Kinta limestones. The high organic content coupled with the lacking of benthic fauna has indicated a low-oxygen setting. On the other side, the Kinta limestones were dominated by mudstones interlayered with bedded cherts and perhaps were deposited in a slope environment with a significant contribution of pelagic deposits [13]. The geological evolution of the Kinta Valley has been recently outlined as characterized by both deposition and structural deformation [14]. During the Devonian, the deposition started, composed of alternating sandstones and mudstones, followed in the Carboniferous by fine-grained shales, which are, in turn, overlain by Permian limestones. During the Triassic-Early Jurassic, the intrusion of granites cut previously deposited carbonate deposits. The whole deposits are overlain by Quaternary alluvial deposits. An early compressional event and a late extensional event have been distinguished [14]. Folding and thrusting occurred during the compression, also controlling the granitic intrusion, which was fractured due to compressional deformation. The extensional tectonic event resulted from the individuation of normal faults, controlling the present-day drainage network evident from DEM analysis [14].

A high resolution biostratigraphy of the Kinta limestones has been later proposed based on conodonts sampled in three boreholes, composed of carbonate mudstones with shales and siltstones [15]. Nine diagnostic conodont genera and 28 age diagnostic conodont species have been identified. In particular, *Pseudopolygnathus triangulus triangulus* and *Declinognathodus noduliferus noduliferus*  have indicated that the successions, pertaining to the Kinta limestones, range in age from the Upper Devonian to the Upper Carboniferous. Moreover, these data have provided clues to the Paleo-Tethys paleogeographic reconstruction and paleo-depositional conditions [15]. Recently, the deformational styles and the structural history of the Paleozoic limestones of the Kinta Valley have been defined by using remote sensing mapping, outcrop samples, and hand specimens [16]. An early extensional event has been identified, as marked from normal faults, while a compressional event was indicated by a set of strike-slip faults. The geologic evolution has been interpreted as an intra-basinal extension during Permo-Triassic times, which was followed by a Late Miocene to Quaternary tectonic uplift [16].

The high resolution chronostratigraphy of the paleo-lakes is a main research topic, which has been deeply studied by several authors [17–27]. In particular, the Ibate paleolake has shown a distal lacustrine environment with low-oxygen conditions in its bottom waters [17].

#### *Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene… DOI: http://dx.doi.org/10.5772/intechopen.85516*

The occurrence of *Anacolosidites eosenonicus* sp. nov., combined with the lacking of *Steevesipollenites nativensis*, indicates a late Santonian age for the paleolake (ca. 84 Ma). This age is constrained by the occurrence of carbonized sclereids that are associated with the "Great Santonian Wildfire" recorded in coeval marine offshore strata of the Campos and Santos basins [17]. The palynological content, coupled with the occurrence of rhythmic deposits have indicated a Late Santonian age of these deposits. The age assignment is based on palynostratigraphic relationships established from a reliable biostratigraphic framework, based on integration of palynological and biostratigraphic data [17]. On the other side, the Qaidam lake represents an excellent example in order to study the interplay of climatic and tectonic controls on continental saline lakes [19]. Two main events of increase of salinity have been controlled by the climate during the Late Eocene since the Oligocene, while tectonic events have controlled the migration of the saline centers [19]. The accumulation of halites and their preservation were the result of a coupled control by active tectonism, in order to provide accommodation space and trigger a rapid subsidence.

 The Navamuno peatbog system, located in western Spain, has been deeply studied [21]. During the Late Pleistocene, it was dammed by the Cuerpo de Hombre glacier and was fed by lateral meltwaters. This depression was then filled by glaciolacustrine deposits. During the Holocene, its geologic evolution was controlled by a fluvial plain, controlling the episodes of shallow pond/peat bog sedimentation. An age model was constructed based on radiocarbon dating, allowing to interpret the environmental changes during the Late Glacial and the post-glacial [21]. Another representative paleolake is the Tangra Yumco, represented by a wide saline paleolake located on the Tibetan Plateau, which has been recently studied as a valuable example in order to reconstruct the climatic variations [23]. Micropaleontologic and sedimentologic data have been integrated with isotopic stratigraphy. Integrated stratigraphic information has allowed to reconstruct the geologic evolution of the paleolake during the last 17 ky [23]. The lake level was low at 17 ky BP, followed by a highstand phase at 8–9 ky BP. Since 2.5 ky, the paleolake remained stable regarding its level, with a short highstand-lowstand cycle around 2 ky [23]. These changes have been considered as good hints of paleo-climatic conditions in order to refine the paleo-climatic models in this area.

 In this book, different case studies have been presented, respectively, located in the Persian Gulf, in the Peninsular Malaysia, and in the Andorra. To this aim, it should be useful to clarify their geological structure to put the studied cases in a proper geological setting [28–30]. The Persian Gulf is represented by an enclosed sea, limited from the western Arabian platform to the south and by the Zagros fold and thrust belt to the north-east. These mountains define the zone of convergence between the Arabian plate and the Eurasian plate and represent, perhaps, a tectonically active area. Since the last glacial maximum (18 ky BP), the sea level fluctuations in the Persian Gulf have been predicted in order to show their variability [28]. The paleo-shoreline reconstructions of the gulf have been compared with the general models of glacio-hydro-isostatic effects. Starting from the peak of the glaciations (14 ky), the Persian Gulf is free from the marine influence. The present shoreline of the Persian Gulf was reached about 6 ky ago, also controlling the evolution of the deltas of the rivers Euphrates, Tigris, and Kan [28]. In the Persian Gulf, the present-day water depths do not exceed 100 m, while the average water depths are of 35 m, suggesting that it was above the sea level during glacial times.

The geological setting of the Persian Gulf and the Oman Gulf has been studied by Ross et al. [29]. During Mesozoic times, the Arabian platform was formed by the Arabian Peninsula, by the Persian Gulf, by the south-western Iran, and by the eastern Iraq [29]. Significant geological processes outlined in this region include the deformation of the Musandam Peninsula during the Late Cretaceous and the

Middle Tertiary and the corresponding subduction processes, the collision of the Arabian platform and of the Eurasian plate, controlling the formation of the Zagros fold and thrust belt. This orogenesis has reduced the former platform to the Persian Gulf. This reduction was also controlled by the tectonic uplift of the Arabian Peninsula during the opening of the Red Sea and by saline tectonism [29]. During recent times, tectonics is still active in this complex region at the northern edge of the Gulf of Oman. Here, the Arabian plate has undergone subduction, while the Arabian and Eurasian plates lie in a collisional setting.

As a general rule, the Persian Gulf Basin represents a foreland basin, lying between the western Zagros fold and thrust belt, whose formation was controlled by the collision between the Arabian and the Eurasian plates [30]. An interesting topic is that the name "Persian Gulf" refers not only to the Persian Gulf but also to the Gulf of Oman, to the Straits of Hormuz, and to various outlets which are genetically related to the Arabian Sea. During the Early Triassic, the thermal subsidence and the stretching of the Arabian Plate started, resulting in extensional faulting and rifting of Zagros, opening the neo-Tethys sea. During the Late Cretaceous, a new tectonic phase controlled the beginning of the Alpine orogeny, resulting in major uplift and erosion, in addition to the closure of the Neo-Tethys sea [30]. During the Tertiary tectonic phase, the Late Alpine orogeny verified, resulting from the collision of the Arabian and Eurasian plates, resulting in the formation of the Zagros fold and thrust belt and then, the individuation of the foreland Persian Basin. Another main geodynamic event is represented by the opening of the Red Sea, about 25 My ago, resulting in the separation of the African and Arabian plates [30].

In this book, another important research topic is represented by the Peninsular Malaysia [31–36]. Three main tectonostratigraphic belts characterize these regions, respectively, the Western Peninsular Malaysia, the central Peninsular Malaysia, and the eastern Peninsular Malaysia. The oldest rocks can be found at the northwestern portion of the peninsula, while relatively younger rocks can be found toward the southeast. In the Peninsular Malaysia, the Upper Paleozoic and Mesozoic sequences have been studied in detail, regarding the structural and stratigraphic setting [32]. In particular, the Upper Paleozoic sequences have revealed several phases of folding coupled with the regional metamorphism, perhaps suggesting the occurrence of two main compressional events affecting the Peninsular Malaysia (Late Permian and Middle-Late Cretaceous) [32]. The Late Permian compressional event has controlled the intrusions of major plutons, cropping out in the eastern range. Harbury et al. [32] have suggested that the Permo-Triassic granites of the eastern belt have been separated from the granites cropping out in the main range due to crustal attenuation and subsidence during the Triassic and the Jurassic. I have found very clear on the geology of Peninsular Malaysia the study of Metcalfe [34]. This author has suggested that the aforementioned three belts occur based on different stratigraphic and structural settings, coupled with magmatism, geophysical signatures, and geologic evolution. The Western Belt is composed of the Sibumasu Terrane, derived from the margin of Gondwana during the Permian. The central and the eastern belts are composed of the Sukhothai Arc, formed during the Late Carboniferous-Early Permian on the Indochina continental margin [34]. During the Early Triassic, the collision between the Sibumasu and Sukhothai Arcs started, allowing for the formation of a foredeep basin and of an accretion complex. Granitic intrusions have cut the Western Belt and the Bentong-Raub suture zone. A back-arc basin (Sukhothai) opened during the Early Permian, collapsing and closing during the Middle-Late Triassic. In the Malay Peninsula, the marine deposition ended during the Late Triassic and red beds formed a cover sequence during the Cretaceous. A main tectonic and thermal event occurred during the Late Cretaceous, coupled with individuation of faults and granitic intrusion [34].

#### *Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene… DOI: http://dx.doi.org/10.5772/intechopen.85516*

 The third research topic of this book is represented by the geology of the Andorra (Spain), put in the regional context of the south-eastern Pyrenees [37–42]. The Andorra region is located in the central Pyrenees (Spain). This region has been strongly folded during the rotation of the Iberian Peninsula on the European plate. The stratigraphy of the Andorra region is characterized by the occurrence of rocks ranging in age from the Cambrian to the Ordovician, composed of conglomerates, limestones, phyllites, quarzites, and slates [40]. Moreover, gneiss and schist crop out in the cores of anticlines located in the north-eastern sector of the country. The occurrence of antiforms and anticlines is linked with shear zones including thrusts of metamorphosed sediments. In the south-eastern Andorra region, the Mt. S. Louis-Andorra Batholith crops out, controlling the metamorphism on its western edge.

A classical paper dealing with the Andorra's geology is that of Hartevelt [41]. The study region includes part of the Axial Zone, the Nogueras Zone, and the related marginal throughs. The outcropping formations, mapped with detail, range in age from the Cambro-Ordovician to the Pliocene. The detailed lithostratigraphy of this formation has allowed for the stratigraphic correlation with other regions of the Pyrenees. In this zone, the Hercynian orogenesis has controlled the formation of geological structures controlled by N-S trending stresses. A first tectonic phase has formed wide folds of kilometric extension, while the second one has controlled the formation of different compressional structures [41]. The thrust sequences in the eastern Pyrenees have been deeply investigated [42]. In this region, the Alpine thrusts involve both the basement and the sedimentary cover. Balanced cross sections have been constructed in order to restore the geometry of the thrusts and the propagation sequence, so resulting in a piggy-back sequence [42]. A duplex has been reconstructed, whose sole thrust is represented by the Vallfogona thrust, while the roof thrust owes its roots in the Axial Zone. Small antiforms have also been reconstructed, occurring as wide folds involving the higher sequences [42]. Casas et al. [43] have discussed the role of the Hercynian and Alpine thrusts in the Upper Paleozoic rocks of the Central and Eastern Pyrenees. The geological structure of the pre-Hercynian rocks of the Central and Eastern Pyrenees, forming the antiformal stack of the so-called Axial Zone, is characterized by coeval folds and thrusts, both Alpine and Hercynian. These thrusts separate sheets, ranging in age from the Upper Paleozoic to the Devonian, showing a different lithostratigraphy and geological structure [43]. Some examples have been shown in order to discuss the role of the Hercynian and Alpine thrusts in controlling the geological setting of the Pyrenees [43].

#### **2. Facies analysis and paleoecology**

In this book, the sedimentary environments and the paleoecology of the Oligo-Miocene deposits of the Asmari Formation have been reconstructed based on biostratigraphy, microfacies analysis, and facies analysis (see Chapter 1). Moreover, in Chapter 2, the facies analysis of Paleozoic carbonates drilled by three boreholes located in the Western Belt has been carried out. Perhaps, it should be useful to clarify some concepts and methods of facies analysis and paleoecology.

The stratigraphic analysis is mainly based on the field geological survey, on the measurement of stratigraphic sections and on the lithologic and paleontologic descriptions, with the aim to reconstruct the depositional environments and to correlate the stratigraphic sequences. A basic paper on facies analysis is that of Flugel [44], showing that every facies in a depositional setting is characterized by petrographic, geognostic, and paleontological characters, clearly different from the same characters of other facies occurring in the same geological period. The facies analysis needs interdisciplinary studies, as stated by Amanz Gressly in 1838 [45], showing that in the facies

analysis, the sedimentologic, paleontologic, and geochemical data provide a basic information about the depositional environments, the lithogenesis, and the fossils.

 In particular, the concept of facies needs to be recalled. It is a rocky body having distinct lithological, physical, and biological characteristics, allowing for its distinction from the adjacent rocky bodies. The concept of facies is usually referred to the whole characteristics of a sedimentary unit, including, the lithology, the grain-size, the sedimentary structures, the color, the composition, and the biogenic content [46]. A single facies does not indicate a single environment, but one or more geological processes through which the sediments have been deposited [47]. Perhaps, the environmental interpretation may be derived by the concept of facies association and by the integration of the physical characters of the deposits with the paleoecological ones. The facies associations are composed of several facies, occurring in combination and representing one or more depositional environments or facies groups, which are genetically related one to each other. Their shape is the cycle or the sequence, which is not a random vertical succession of facies. The facies associations are controlled by the Walther law, one of the most basic principles of stratigraphy. On the other side, a facies model is a general summary of depositional systems, including many single examples from recent sediments and old rocks.

Main criteria of facies analysis are briefly recalled [46, 47]. They include: (i) the mineralogic and petrographic composition, which gives information mainly on the provenance (relief, climate, and lithology of the source area), but also on the transport and on the diagenesis; (ii) the textural analysis, giving information on the provenance (shape), but mainly on the dynamics of transport and deposition; (iii) the fossil content, allowing for the dating and the correlation of deposits and giving paleoecological information and on the reworking; (iv) direction data, consisting of paleo-currents and paleo-slope models and dispersal of sediments, deduced from current lineations and depositional geometries; (v) geometry of the sedimentary bodies, derived through the synthesis of previous data and giving information on the depositional environments; and (vi) vertical sequential analysis, allowing for the determination of the relative depth fluctuations, the shoreline migrations, the growth and retreat of depositional systems, and the evolution of the sedimentary basins (basin analysis).

The paleoecology is represented by the study of the interactions between the organisms and the environments across the geological time scales and is linked with other disciplines, including the paleontology, the ecology, the climatology, and the biology [48]. It was born as a branch of the paleontology through the examination of the fossil and the ancient life environments. The main paleoecological approaches include: (i) the classic paleoecology, which is based on the fossils allowing for the reconstruction of the ancient ecosystems and uses the fossil remnants, such as the shells, the teeth, the pollens, and the seeds. A final result will be a paleo-environmental reconstruction. (ii) The evolutionary paleoecology, based on the holistic approach and using both the fossils and the physical and the chemical changes in the atmosphere, lithosphere, and hydrosphere in order to study the vulnerability and the resilience of species and environments. (iii) The community paleoecology, based on statistical methods and making use of physical models and computer analyses [48].

A main aim of the paleoecology is to construct a detailed model of the environments of life of the fossils, using the archives (represented by sedimentary sequences), the proxies (providing evidence of the biota and the related physical environments), and the chronology, allowing for the dating of events in the archive. Important proxies to carry out these reconstructions include the charcoal and pollens, particularly applied in paleolakes and peats. Some main paleoecological studies have been carried out in the Persian Gulf [49, 50]. Abdolmaleki and Tavakoli [49] have

*Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene… DOI: http://dx.doi.org/10.5772/intechopen.85516* 

 stated as the Permo-Triassic boundary represents one of the most important mass extinctions during the history of the earth, marking for a strong decrease of the living taxa. Important changes of depositional processes also occurred, forming anachronistic facies in whole earth. Anachronistic facies have been reported in the Early Triassic deposits of the Persian Gulf, consisting of microbial facies, composed of stromatolitic boundstones, oncoidal facies, and thrombolytic facies. The formation of these facies has also been controlled by the fluctuations in the CaCO3 saturation level [49]. García-Ramos et al. [50] have evaluated the live-dead fidelity of the Mollusk assemblages in soft sediments of the carbonate tidal flats along the coasts of the Persian Gulf. Wide differences of this parameter have been controlled by the early cementation, lateral mixing, strong bioturbation, and low sedimentation rates. The obtained results have suggested that the average times in carbonate tidal flats are higher if compared with the times affecting the subtidal carbonate environments [50].

#### **3. Chemostratigraphy**

 In this book, the chemostratigraphy of Paleozoic carbonates of the Western Belt (Peninsular Malaysia) has been studied (see Chapter 2). Perhaps, it should be useful to recall the chemostratigraphy as a branch of the integrated stratigraphy. Different stratigraphic methods are included in the integrated stratigraphy, including the chemostratigraphy, the isotopic stratigraphy, the oxygen isotopes, the carbon isotopes, the strontium isotopes, the orbital cyclostratigraphy, the response of the climate system to the orbital forcing, the orbital forcing and the sedimentary environments, the identification of cyclical features, and the spectral analysis of time series. Particular attention must be given to the methods of absolute dating and to the geological time scale. The chemostratigraphy (chemical stratigraphy) is based on the study of the chemical variations in the sedimentary successions with the aim to reconstruct the stratigraphic relationships [51–55]. It is based on the principle that the chemical signatures may be used as fossil groups or lithological groups in order to establish the stratigraphic relationships between the rocky layers. The types of chemical variations may be summarized [51]. Colorimetric variations among the strata may be detected in some stratigraphic sequences, triggered by the content of metals of transition incorporated during the deposition. Other colorimetric variations may be controlled by variations in the content of organic carbon in the deposits. The development of new techniques of analysis, including the electronic microprobe and the X-ray fluorescence, has facilitated the chemical analysis of the deposits, coupled with the geochemistry of the stable isotopes. In particular, the variability of the oxygen in the carbonate shells of foraminifera represents a proxy for the temperatures of the ocean during the geological past [56–57]. Recently, there were some attempts to formalize the chemostratigraphy as a standard method of stratigraphy [54–55], but this discipline is too young and many efforts need to be made again.

#### **4. Chronostratigraphy**

In this book, a chronostratigraphic reconstruction of lacustrine deposits located in Spain has been carried out (see Chapter 3). For this reason, it is useful to recall some chronostratigraphic concepts. Recently, the definitions of chronostratigraphy and geochronology have been deeply revised [58]. The realignment of the two terms has been proposed, contemporaneously solving the problem if the Geological Time Scale must have single or double time units. This discussion must be carried out based on the use of the Geological Time Scale (GTS) reported in the International

Stratigraphic Chart of the International Commission of Stratigraphy and its units. It must be taken into account that the last version of the International Stratigraphic Chart has been published in 2018 [59]. The most used units are represented by the geological periods of the geochronology (Triassic, Jurassic, for instance) and the chronostratigraphic systems on which they are based. These systems are composed of series and stages, while the periods, epochs, and stages are referred to time intervals during which the deposition of strata occurred. Therefore, there is a double hierarchy of chronostratigraphic units (time/rocks), which have been used to indicate rocky strata contemporaneously deposited and time intervals (geochronologic) used to indicate intervals during which geological processes occurred, including the evolution, the extinction, the deformation, and the transgression/regression, for instance [58]. In the meaning of this paper, the geochronology indicates the timing and the age of main geological events of the earth's history (such as a glaciations or a mass extinction). Moreover, it refers to the methods of numerical dating.

 On the other side, the definition of chronostratigraphy is quite different. It includes the whole range of the stratigraphic disciplines, such as the magnetostratigraphy, the chemostratigraphy, the sequence stratigraphy, the cyclostratigraphy, and the radiometric dating [60–64]. The main aims of the chronostratigraphy include both the establishment of the time relations of regional successions and the definition of a GSSP (Global Boundary Stratotype Section and Point). In the realignment proposed by Zalasiewicz et al. [58], the chronostratigraphic (time/rock) and geochronologic (time) units have been, respectively, defined as it follows: (i) eonothem (Phanerozoic, for instance); (ii) erathem (Mesozoic, for instance); (iii) system (Cretaceous, for instance); (iv) series (Upper Cretaceous, for instance); (v) stage (Cenomanian, for instance); (vi) eon (Phanerozoic, for instance); (vii) era (Mesozoic, for instance); (viii) period (Cretaceous, for instance); (ix) epoch (Late Cretaceous, for instance); and (x) age (Cenomanian, for instance). The proposed method is to use the chronostratigraphic units in reference to layered rocks and to use the geochronologic units in reference to time and phenomena associated to the rocks [58].

#### **5. Outline of this book**

 This book examines different stratigraphic studies regarding the fields of facies analysis and paleoecology, chemostratigraphy, and chronostratigraphy focusing on several applications, including the paleoecology and the sedimentary environments of the Asmari Formation (south-eastern Persian Gulf), allowing for the recognition of two assemblage zones based on foraminifera, indicating an age ranging between the Chattian and the Aquitanian, while facies analysis has indicated a depositional environment of carbonate ramp, the chemostratigraphy of Paleozoic carbonates in the Western Belt through the integration of stratigraphic, sedimentological, and geochemical data on three boreholes, indicating that the variations of major elements is directly related to the lithofacies types in the study samples and finally the application of the chronostratigraphic chart through a Fast Fourier Transform (FFT) analysis on lacustrine deposits of Andorra (Spain), indicating the occurrence of 6th order stratigraphic cycles, genetically related to high frequency sea level fluctuations during the Late Pleistocene.

This book contains four chapters, as follows:

Chapter 1 [Introductory Chapter: An Introduction to the stratigraphic setting of Paleozoic to Miocene deposits based on paleoecology, facies analysis, chemostratigraphy, and chronostratigraphy: Concepts and Meanings].

Chapter 2 [Paleoecology and Sedimentary Environment of the Oligocene-Miocene (Asmari Formation) deposits, in Qeshm Island, SE Persian Gulf].

*Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene… DOI: http://dx.doi.org/10.5772/intechopen.85516* 

Chapter 3 [Chemostratigraphy of Paleozoic carbonates in the Western Belt, Peninsular Malaysia; case study from the Kinta Valley].

Chapter 4 [High-resolution chronostratigraphy from an ice-dammed paleolake in Andorra: MIS 2 Atlantic and Mediterranean paleoclimate inferences over the SE Pyrenees].

#### **Conflict of interest**

I declare that there is no conflict of interest.

### **Author details**

Gemma Aiello Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Napoli, Italy

\*Address all correspondence to: gemma.aiello@iamc.cnr.it

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Section 2

## Facies Analysis and Paleoecology

**19**

**Chapter 2**

**Abstract**

Persian Gulf)

Oligocene-Miocene, Qeshm Island

**1. Introduction**

Paleoecology and Sedimentary

Miocene Deposits of the Asmari

The Asmari Formation is composed of limestones, marly limestones, and marls, whose subsurface thickness in this region is about 148 m. Two assemblage zones have been recognized through the distribution of large foraminifera in the study area, indicating a Late Oligocene (Chattian)-Early Miocene (Aquitanian) age. The gradual facies changes and the lacking of turbiditic deposits show that the Asmari Formation was deposited in a carbonate ramp environment. Based on the depositional textures and petrographical studies, characterizing gradual shallowing upward trends of an open marine carbonate ramp, three distinct depositional settings have been recognized: lagoon, barrier, and open marine. MF1 was characterized by the occurrence of hyaline benthic and planktonic foraminifera representing distal middle ramp and below the storm wave base of other ramp. Paleolatitudinal reconstructions based on skeletal grains suggest that carbonate sedimentation of the Asmari Formation took place in tropical waters within the photic zone.

**Keywords:** Asmari Formation, microfacies, paleoecology, benthic foraminifera,

reservoirs in the world) [1], an Oligocene-Miocene carbonates succession cropping out in the south-eastern Zagros basin, southern Iran (**Figure 1**). At the type section outcropping in Tang-e Gel-e Tursh (Valley of Sour Earth), which is located on the south-western flank of the Kuh-e Asmari anticline, the Asmari Formation mainly consists of limestones, dolomitic limestones, and argillaceous limestones [3, 4], having an average thickness of 314 m. In the Qeshm Island, the Asmari shallow marine limestone is located in the subsurface and was deposited over the Pabdeh Formation with a gradational stratigraphic contact. The contact with the overlying Gachsaran Formation (i.e., evaporitic rocks) is conformable and gradual (**Figure 2**). This formation is present in the most part of the Zagros basin, and its lithology is characterized by limestones, dolomitic limestones, dolomites, and

This chapter deals with the Asmari Formation (one of the best known carbonate

Formation (Qeshm Island, SE

Environments of the Oligo-

*Seyed Hadi Sajadi and Roya Fanati Rashidi*

#### **Chapter 2**

## Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari Formation (Qeshm Island, SE Persian Gulf)

*Seyed Hadi Sajadi and Roya Fanati Rashidi* 

#### **Abstract**

The Asmari Formation is composed of limestones, marly limestones, and marls, whose subsurface thickness in this region is about 148 m. Two assemblage zones have been recognized through the distribution of large foraminifera in the study area, indicating a Late Oligocene (Chattian)-Early Miocene (Aquitanian) age. The gradual facies changes and the lacking of turbiditic deposits show that the Asmari Formation was deposited in a carbonate ramp environment. Based on the depositional textures and petrographical studies, characterizing gradual shallowing upward trends of an open marine carbonate ramp, three distinct depositional settings have been recognized: lagoon, barrier, and open marine. MF1 was characterized by the occurrence of hyaline benthic and planktonic foraminifera representing distal middle ramp and below the storm wave base of other ramp. Paleolatitudinal reconstructions based on skeletal grains suggest that carbonate sedimentation of the Asmari Formation took place in tropical waters within the photic zone.

**Keywords:** Asmari Formation, microfacies, paleoecology, benthic foraminifera, Oligocene-Miocene, Qeshm Island

#### **1. Introduction**

 This chapter deals with the Asmari Formation (one of the best known carbonate reservoirs in the world) [1], an Oligocene-Miocene carbonates succession cropping out in the south-eastern Zagros basin, southern Iran (**Figure 1**). At the type section outcropping in Tang-e Gel-e Tursh (Valley of Sour Earth), which is located on the south-western flank of the Kuh-e Asmari anticline, the Asmari Formation mainly consists of limestones, dolomitic limestones, and argillaceous limestones [3, 4], having an average thickness of 314 m. In the Qeshm Island, the Asmari shallow marine limestone is located in the subsurface and was deposited over the Pabdeh Formation with a gradational stratigraphic contact. The contact with the overlying Gachsaran Formation (i.e., evaporitic rocks) is conformable and gradual (**Figure 2**). This formation is present in the most part of the Zagros basin, and its lithology is characterized by limestones, dolomitic limestones, dolomites, and

**Figure 1.** 

*Cenozoic stratigraphic correlation chart of the Iranian sector of the Zagros Basin, after James and Wynd [2].* 

marly limestones. Some anhydrite (Kalhur Member) and lithic and limy sandstones (Ahwaz Member) also occur within the Asmari Formation [3, 4]. Previous studies have focused on biostratigraphy and lithostratigraphy of the Asmari Formation and were originally defined in primary works [5–8]. Later, other researchers have introduced the microfaunal characteristics and the assemblage zones for the Asmari Formation [2, 9, 10]. More recent studies of the Asmari Formation have been conducted on facies and sedimentary environment [8, 11–17]. Referring to the biostratigraphy of the Asmari Formation, it was earlier outlined in the 1960s based on unpublished reports [18]. The application of the isotopic stratigraphy has later proved that the sediments ascribed to the Miocene "Aquitanian" are in fact Late Oligocene, Chattian in age. This was proved by the application of Sr-isotope stratigraphy to cored sections from 10 Iranian oil fields and 14 outcrop sections, within the framework of a high-resolution sequence stratigraphic study down to fourth order cycles. The Chattian/Aquitanian boundary is marked by a major faunal turnover, with the general extinction of *Archaias* species and *Miogypsinoides complanatus*. Main insights on the stratigraphic setting of the Asmari Formation have been given from the strontium isotopic stratigraphy [19]. The Asmari Formation

#### **Figure 2.**

*Lithostratigraphy column, microfacies, benthic and planktonic foraminifers' distribution and biozonation of the Asmari Formation at Qeshm Island (well no. 2).* 

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

 has been studied in the subsurface at the Bibi Hakimeh, Marun, and Ahwaz oilfields and in an outcrop section from the Khaviz anticline. It consists of approximately 400 m of cyclic platform limestones and dolostones with subordinate intervals of sandstone and shale. The method of Sr-isotope stratigraphy is well suited for dating these strata because of the rapid rate of change of marine strontium ratio during Asmari deposition (roughly 32–18 Ma) and the common presence of well-preserved macrofossils. Profiles of age against depth in the four areas show a decrease from higher stratigraphic accumulation rates in the lower Asmari to lower rates in the middle to upper part of the formation. There is also a trend toward less open marine depositional conditions and increasing early dolomitization and anhydrite abundance above the lower part of the formation. These changes reflect the dynamics of platform progradation across the areas studied, from early deposition along relatively high accommodation margin to slope settings to later conditions of lower accommodation on the shelf top. Ages of sequence boundaries have been estimated from the age-depth profiles at each locality, providing a framework for stratigraphic correlation. The Asmari deposition began in early Rupelian time (34–33 Ma) in the Bibi Hakimeh area, when basinal marly facies accumulated in the north-western sector of the study areas. The depositional sequences have durations of 13 Ma, whereas the component cycles represent average time intervals of 100–300 Ky. This chapter reports on the subsurface sedimentological study of the Asmari Formation, whose results have been correlated and compared for a better geologic comprehension of the outcrops of the Asmari Formation in the adjacent areas. The objectives of this study are (1) a description of the facies and their distribution on the Oligocene-Miocene carbonate platform and (2) an interpretation of the paleoenvironmental features based on the assemblages of benthic hyaline and imperforate foraminifera.

#### **2. Geological setting**

 The Zagros Basin is the second largest basin in the Middle East and is defined by a 7–14-km thick succession of coverage sediments deposited over a region located along the north-northeast edge of the Arabian plate. This basin was part of the stable Gondwana supercontinent in the Paleozoic era and of a passive margin in the Mesozoic era, and it became a site of plate convergence and formation of thrust belts in the Cenozoic era [20]. The Zagros Fold-and-Thrust Belt of Iran is a result of the Alpine orogenic events [21, 22] in the Alpine-Himalayan mountain range. It extends in a NW-SE direction from eastern Turkey to the strait of Hormoz in southern Iran. The tectonic activity of this area was entirely due to the convergence of the Arabian and Eurasian continents. After the closure of the Neo-Tethys basin, during late Oligocene-early Miocene times, the Zagros basin was gradually narrowed and the Asmari Formation was deposited with a lithology including lithic sandstone (Ahwaz Member) and evaporites (Kalhur Member) [1, 23]. The maximum thickness of the Asmari Formation is found in the north-eastern corner of the Dezful Embayment. On the basis of the lateral facies variations, the Iranian Zagros fold-thrust belt is divided into different tectono-stratigraphic domains, which are from SE to NW: the Fars Province or eastern Zagros, the Khuzestan province or Central Zagros, and finally the Lurestan Province or Western Zagros [3, 4] (**Figure 3b**). Also, from south-west to north-east of the Zagros basin, there are the Zagros folded belt, folded and thrusted belt, and High Zagros and crush zone [25–28]. The Hormozgan Province is located in southern Iran and is part of Zagros Folded belt. This region is accompanied by NW-SE, W-E, and N-S trending simple anticlines and synclines with very great thickness of Fars Group deposits (Gachsaran, Mishan, Aghajari, and Bakhtiari Formations) and presence of 118 salt plugs. So, for these specific features, Motiei [3, 4] called this area as the"Bandar Abbas Hinterland" (**Figure 3**).

**Figure 3.**  *Geological location and geological map of the studied section, modified after geological map [24].* 

#### **3. Methods and study area**

 This study involves one stratigraphic subsurface section from the Asmari Formation. The study area is located at Qeshm Island, southern Iran (**Figure 3c**). The lithologies and the microfacies types were classified and described according to Dunham [29]. Some samples from the underlying Pabdeh and overlying Gachsaran Formations were also analyzed for boundaries distinction. A total of 60 thin sections of the cores and cuttings have been analyzed under the microscope for biostratigraphy and facies. Petrographic studies were carried out for facies analysis and paleoenvironmental reconstruction of the Asmari Formation. Facies have been determined for each paleoenvironment according to carbonate grain types, textures, and interpretation of functional morphology of small and larger foraminifers. Biostratigraphy has been determined based on the well-known benthic foraminifera biozones of Adams and Bourgeois [30].

#### **4. Result**

#### **4.1 Biostratigraphy**

Biostratigraphic criteria of the Asmari Formation were established by Wynd [10] and reviewed by Adams and Bourgeois [30] in unpublished reports only. Biozonation and age determinations in the study area are based on benthic foraminifera

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

 biozonation of Adams and Bourgeois [30]. From the base to the top, two foraminiferal assemblages have been recognized and were discussed as it follows:

*Assemblage I*. This assemblage corresponds to the *Eulepidina*-*Nephrolepidina*-*Nummulites* Assemblage Zone (3) [30]. The assemblage is considered to be Chattian in age. The most diagnostic species include Miliolids gen. et sp. Indet., *Peneroplis evolutus*, *Archaias* sp., *Peneroplis* sp., *Operculina* spp., *Peneroplis thomasi*, *Austrollina asmariensis*, *Reussella* sp., *Dendritina rangi*, *Elphidium*  sp. 1, *Spiroculina* sp., *Quinqueloculina* sp., *Asterigerina* sp., *Nummulites* spp., *Neorotalia viennoti*, Cibicidae gen. et sp. Indet, *Archaias kirkukensis*, *Hetererilina*  sp., *Glomospira* sp., *Textularia* sp., *Meandropsina anahensis*, *Ammonia* sp., *Discorbis* sp., *Pyrgo* sp. 1, *Valvulinid* sp. 1, *Spirolina* cf. *clyndracea*, *Lepidocyclina*  (*Nephrolepidina* spp.), *Nummulites intermedius*/*fichteli*, *Heterostegina* sp., *Schlombergerina* sp., *Triloculina trigonula*, *Eulepidina dilatata*, *Rotalia* sp., *Bolivina* sp., *Paragloborotalia mayeri*, and *Globigerina* spp.

*Assemblage II*. This assemblage corresponds to the *Miogypsinoides*-*Archaias*-*Valvulinid* sp. 1 Assemblage Zone (2) [30]. The assemblage is considered to be Aquitanian in age. The most important foraminifera in this assemblage are *Miliolids* gen. et sp. Indet., *Peneroplis evolutus*, *Archaias* sp., *Peneroplis*  sp., *Operculina* spp., *Peneroplis thomasi*, *Austrollina asmariensis*, *Reussella* sp., *Dendritina rangi*, *Elphidium* sp. 1, *Spiroculina* sp., *Quinqueloculina* sp., and *Archaias kirkukensis*.

#### **4.2 Microfacies analysis**

The microfacies analysis of the Asmari Formation in the study area has resulted in the definition of seven types of facies, which characterize the platform development. Each microfacies exhibits typical skeletal and non-skeletal components and related sedimentary textures. These facies are related to the three depositional settings (lagoon, barrier, and open marine) of inner, middle, and outer portions of a carbonate platform (**Figure 4**). Since the Asmari Formation overlies the Pabdeh Formation and conformably underlies the Gachsaran Formation, some samples from the Pabdeh and Gachsaran Formations have also been studied. The general environmental interpretation of the microfacies is discussed in the following paragraphs.

#### **Figure 4.**

*Depositional model for the carbonate platform of the Asmari Formation at the southeast of Zagros basin, Qeshm Island [31].* 

*New Insights into the Stratigraphic Setting of Paleozoic to Miocene Deposits...* 

#### *4.2.1 MF1 marl facies*

There are intercalations of marl across the section, but this facies mainly occurs in the lower part of the succession (**Figure 5A**–**D**). They are gray to green marl and contain benthic (miliolids, *Nummulites*, *Neorotalia*, *Elphidium*, *Operculina*, *Amphistegina*  and textularids) and planktonic (*Paragloborotalia mayeri* and *Globigerina* spp.) foraminifera. The planktonic foraminifera occur at the base of the succession, where the boundary between the Pabdeh and Asmari Formations is located [32].

#### *4.2.1.1 Interpretation*

 The features of benthic faunas and the stratigraphic relationships with the other microfacies suggest that the marly facies was deposited in an open lagoon

#### **Figure 5.**

*Microfacies types of the Asmari Formation. (A–D) MF1, Marl facies. (E–G) MF2, bioclastic Lepidocyclinidae, Nummulitidae, Neorotalia, Wackestone-packstone. (H and I) MF3, coral boundstone. (J and K) MF4, miliolids corallinacea bioclastic wackestone. (L and M) MF5, miliolids bioclastic wackestone. (N and O) MF6, imperforate foraminifera bioclast wackestone-packstone. (P) MF7, evaporite.* 

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

with a normal-salinity water, but the coexistence of planktonic and some benthic (Nummulitidae) foraminifera in the base of the Asmari marls and marly limestones has suggested that this facies was deposited in calm, low-energy hydrodynamic, and deep normal-salinity water, which indicates a deposition below the storm wave base [33–36].

#### *4.2.2 MF2 bioclastic wackestone-packstone with Lepidocyclinidae, Nummulitidae, and Neorotalia*

 This microfacies is composed of grain-supported texture with abundant large benthic foraminifera (**Figure 5E**–**G**). The foraminiferal assemblage is represented by numerous large benthic perforate foraminifera such as Lepidocyclinidae and Nummulitidae (*Nummulites* and *Operculina*). Other components such as *Astigerina* and red algae are rare. Due to changes in the type of fauna in some samples, the name of this facies changes to bioclastic wackestone-packstone with Lepidocyclinidae, Nummulitidae and Neorotalia. The biostratigraphic distribution and paleoenvironmental model of the Asmari Formation in this stratigraphic interval are most prominent in the lower parts of the Asmari Formation [37].

#### *4.2.2.1 Interpretation*

It consists of gray marly limestone beds. The combination of micritic matrix and abundance of typical open marine fauna including large Nummulitidae, Lepidocyclinidae and Neorotalia suggest a low-medium energy, open marine environment. Other bioclasts such as red algae and shell fragments are rare. This microfacies shows an environment between the storm wave base and fair-weather wave base (FWWB) [35, 36]. The presence of large *Nummulites* and lepidocyclinids suggests that this microfacies took place in relatively deep water and was formed in the lower photic/oligophotic zone in a distal middle ramp [22, 38–50].

#### *4.2.3 MF3 coral boundstone*

This facies is characterized by the abundance of scleractinian and massive coral colonies (**Figure 5H** and **I**).

#### *4.2.3.1 Interpretation*

 This microfacies is interpreted to be formed by in situ organisms as an organic reef (Bioherm) in margin of platform and was located above the fair-weather wave base (FWWB) [36].

#### *4.2.4 MF4 miliolids corallinacea bioclastic wackestone*

Miliolids, coralline red algae and coral are dominating components in this microfacies (**Figure 5J** and **K**). Other bioclasts are rare but include *Peneroplis* and dendritic fragments. The textures are wackestones.

#### *4.2.4.1 Interpretation*

The MF5 represent low- to medium-energy open lagoon shallow subtidal environments, but there is different from MF4 by their texture and grain composition.

Depositional textures, fauna and stratigraphic position took place in warm, euphotic and shallow water, with low to moderate energy conditions, in a semirestricted lagoon. This area is located within inner carbonate platform setting [32]. The presence of well-preserved coralline algae indicates a relatively quiet-water environment with a stable substrate and low sedimentation rates [51]. The associations of miliolids within this facies support the additional interpretation of a relatively protected environment, probably the inner part of a platform [52].

#### *4.2.5 MF5 miliolids bioclastic wackestone*

This facies is characterized by the dominant presence of small benthic foraminifera (miliolids) (**Figure 5L** and **M**). Other components such as *Peneroplis*, *Elphidium*, bryozoan and extraclasts are rare. The matrix is fine-grained micrite.

#### *4.2.5.1 Interpretation*

This facies is characterized by low diversity skeletal fauna and was deposited in a restricted low-energy lagoonal environment. There is a low biotic diversity of fauna, which shows a high-stressed habitat in very shallow restricted areas, where great fluctuations in salinity and temperature probably occurred [52].

#### *4.2.6 MF6 imperforate foraminifera bioclast wackestone-packstone*

The main elements of this microfacies are skeletal and non-skeletal components (**Figure 5N** and **O**). The skeletal components include a high diversity of imperforate foraminifera in grain-supported textures and several genera of benthic foraminifera (*Austrotrillina*, *Archaias*, *Peneroplis*, *Meandropsina*, *Elphidium*, *Dendritina* and miliolids). Peloids are rare, and other minor biota consists of particles of bryozoans and corals.

#### *4.2.6.1 Interpretation*

The occurrence of large number of porcelain imperforate foraminiferal tests may point to the depositional environment being slightly hypersaline [15]. These deposits include different textures ranging from wackestone to packstone. Some porcelain imperforate foraminifera (*Peneroplis* and *Archaias*) live in recent tropical and subtropical shallow water environments [53]. Textural characteristics and prolific porcelain foraminifera suggest that a medium-to-high energy portion of a restricted lagoon with a nearby tidal flat sedimentary environment prevailed [17]. Such an assemblage can be associated with an inner ramp environment [1, 17, 35, 36, 53, 54].

#### *4.2.7 MF7 evaporite*

Anhydrite and gypsum facies have been observed in the upper part of the Asmari Formation, which represents the beginning of the Gachsaran Formation (**Figure 5P**). The first anhydrite has been deposited above the marly limestones with a sharp contact.

#### *4.2.7.1 Interpretation*

Considering the deposition of anhydrite implies that the depositional environment became isolated from the open marine at that time, which has allowed for the concentration and submarine precipitation of salt. The thickness of the evaporate deposits indicates that they are submarine deposits formed in an isolated saline basin. A eustatic sea level fall is one of the most likely causes. This event took place around the early Miocene (Aquitanian), and its stratigraphic expression was recorded at the boundary of the Asmari and Gachsaran Formations. Based on Ehrenberg et al. [19], this

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

anhydrite is exposed at the top of the Asmari Formation and indicates the Oligocene-Miocene boundary. Ehrenberg et al. [19] noted that strontium dates got from anhydrite formed as an evaporate rather than as a later diagenetic product.

#### **5. Discussion**

#### **5.1 Sedimentary development of the Oligocene-Miocene Fars sub-basin**

Planktonic and benthic foraminifera and non-foraminifera distribution of the Oligocene deposits can represent the type of sedimentary environment, adopted from joint project of French and Iran Oil Company [55] (**Figure 6**). During the Paleogene, Pabdeh (basinal marls and argillaceous limestones) Formation was deposited in the middle and on both sides of the Zagros basinal axis [3] (**Figure 1**). The shallow marine limestones of the Asmari Formation were deposited above the Pabdeh Formation in the section of this study (**Figure 1**). During the Rupelian and early Chattian, outer ramp facies (Pabdeh

#### **Figure 6.**

*Foraminifera and non-foraminifera distribution of the Oligocene deposits, adopted from joint project of French and Iran Oil Company [55].* 

Formation) was predominant at the Qeshm section (well no. 3) (**Figure 2**). This is visible in the lower part of the Asmari Formation. So, the Chattian sediments of the Asmari Formation in this section gradationally overlie the Pabdeh Formation. Indeed, Chattian basin in this time restricted by shallow subtidal environments.

#### **5.2 Paleoecology**

 Large benthic foraminifera (such as Nummulitidae) produced great amount of carbonates during the Early and Middle Paleogene. In the Oligocene, euphotic conditions prevailed and carbonate production related to these foraminifers (especially *Nummulites*) declined [56]. Larger perforate forms are represented by *Amphistegina*, nummulitids and lepidocyclinids. Perforate foraminifera that live in shallow waters are characterized by hyaline walls and so protect themselves from ultraviolet light by producing very thick, lamellate test walls to prevent photo inhibition of symbiotic algae within the test in bright sunlight. These large forms are the most important indicators for constructing paleoenvironmental models in the warm, shallow marine environments [42]. The presence of these large and flat forms (Lepidocyclinidae and Nummulitidae) in the lower part of Asmari Formation, in comparison with analogues in the modern platform, allowed interpreting these sediments as having been deposited in the lower photic zone [41–45, 48]. In contrast, coralline red algae communities become dominant, as most phototrophic carbonate producers thrive in shallow marine environments [56], especially through Early Miocene to Tortonian [57]. Coralline red algae and large benthic foraminifera (*Nummulites*, *Operculina*, *Lepidocyclina*, *Archaias*, *Peneroplis*  and *Dendritina*) are the most significant and dominant biota in the Asmari Formation at the study area. Other components such as corals, bryozoan and echinoderms are present within the matrix. The distribution of larger foraminifera and coralline red algae are largely dependent on the salinity, depth, light, temperature and climate, nutrients, effect of hydrodynamic energy and flow substrate on the biostrate and dispersion of taxa [13, 58]. Small benthonic foraminifera are common locally and include porcellaneous (miliolids) and perforated (rotaliids) forms. Rotaliids are dominated by *Neorotalia viennoti* specimens. Larger foraminifera represented by the porcellaneous imperforate tests such as *Archaias* and *Peneroplis* may point to the depositional environment being within the photic zone in tropical carbonate platforms and slightly hypersaline [17, 35, 37, 54]. Flatter tests and thinner test walls with increasing water depth reflect decreased light levels at greater depths or perhaps poor water transparency in shallow waters [40]. These test shapes reflect adaptation to low hydrodynamic energy. Some biogenic components such as miliolids indicate stress conditions within restricted environments. Miliolids-dominated benthic foraminiferal assemblages reflect a decreased circulation and probably a reduced oxygen contents or euryhaline conditions. Miliolids are found in a variety of very shallow, hyposaline to hypersaline environments or are even common in the sand shoal environments of normal salinities [59, 60] and are generally taken as evidence of restricted lagoon [53].

#### **5.3 Depositional environments**

Three depositional environments have been identified in the Oligocene-Miocene succession of the Qeshm Island, on the basis of the biostratigraphic content and of the facies relationships (**Figure 6**). These include lagoon, barrier and open marine (**Figure 4**). These three environments are represented by seven microfacies types (MF1: distal middle ramp and below the storm wave base of other ramp,

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

 MF2: deeper fair water wave base of a middle ramp setting and MF 3–6: shallow water setting of an inner ramp influenced by wave and tide processes). Carbonate ramp environments are characterized by (1) the inner ramp, between the upper shore face and fair weather wave base, (2) the middle ramp, between fair weather wave base and storm wave base and (3) the outer ramp, below normal storm wave base down to the basin plain [61]. Inner ramp deposits represent marginal marine deposits indicative of open lagoon and protected lagoon. In the restricted lagoon environment, faunal diversity is low and normal marine faunae are lacking, except for imperforate benthic foraminifera such as miliolids and *Dendritina*, which indicate quite conditions. A large number of porcellaneous imperforates points to somewhat hypersaline waters [33, 52]. The presence of imperforate foraminifera that include *Archaias*, *Peneroplis*, *Dendritina*, *Meandropsina*, *Austrotrillina* and miliolids indicates a low-energy, upper photic, shallow lagoonal depositional environment. The large porcellaneous foraminifera types such as *Archaias*, *Peneroplis* and *Dendritina* are present in MF 6. The occurrence of *Archaias* and *Peneroplis* is typical of recent tropical and subtropical shallow water environments [46, 62] and are characteristics of the upper part of the upper photic zone (inner ramp). Furthermore, these large porcellaneous foraminifera are also common fossils in the Mesozoic and Cenozoic neritic sediments [57]. And also, inner ramp deposits represent a wider spectrum of marginal marine deposits, indicative of a highenergy reef (MF 3). The middle ramp setting is represented by the medium to fine grained foraminiferal bioclastic wackestones-packstones, dominated by assemblages of larger foraminifera with perforate walls such as *Amphistegina*, *Operculina*, and *Nummulites* (**Figure 5**). The faunal association suggests that the depositional environment was situated in the mesophotic to oligophotic zone [48, 63]. Open lagoon shallow subtidal environments are characterized by microfacies types that include mixed open marine bioclasts (such as red algae, echinoids and corals) and protected environment bioclasts (such as miliolids). The diversity association of skeletal components represents a shallow subtidal environment, with optimal conditions as regards salinity and water circulation. The change in larger foraminiferal fauna from porcellaneous imperforated to hyaline perforated forms points to a decrease in water transparency [38]. The microfacies 1 and 2 are subject to an open marine environment of a proximal outer ramp and middle ramp, respectively. More common components of the microfacies 1 is biota association, such as large benthic foraminifera (Lepidocyclinidae, *Nummulites* and *Operculina*), small benthic foraminifera (*Neorotalia*), coralline red algae, which is dominated in lower photic zone. Moreover, the red algae association with these larger foraminifera places the middle ramp in an oligophotic to mesophotic zone [48, 53, 57, 63, 64].

#### **6. Conclusions**

 The Oligo-Miocene Asmari Formation is a thick sequence of shallow water carbonates and is widespread in the Zagros basin. The subsurface section of the Asmari Formation in the south-eastern part of the Zagros and Qeshm Islands has allowed to recognize different depositional environments based on the sedimentological analysis, on the distribution of the foraminifera and on the microfacies studies. The occurrence of large foraminifera (*Nummulites*, *Operculina*, *Lepidocyclina*, *Archaias*, and *Peneroplis*), coralline red algae, coral debris and fragments of Echinoderms, Mollusks and Bryozoans has evidenced that a high nutrient stability in an oligothrophic to mesothrophic condition existed during the deposition of the Asmari Formation. Based on the occurrence of these fossils, two assemblage zones ( *ulepidina*-*Nephrolepidina*-*Nummulites* Assemblage Zone and

*New Insights into the Stratigraphic Setting of Paleozoic to Miocene Deposits...* 

*Miogypsinoides*-*Archaias*-*Valvulinid* sp. 1 Assemblage Zone) have been recognized, and the Asmari carbonate in the study area is Chattian-Aquitanian in age. Based on the occurrence of skeletal (large benthic foraminifera and coralline red algae) and non-skeletal components, the following environmental and palaeoecological implications have been defined for the Asmari depositional environment at the Qeshm Island, southern Bandar Abbas Hinterland. Based on components and texture, seven microfacies types have been recognised and grouped into three depositional environments, corresponding to inner, middle and outer carbonate ramp. The microfacies 1 and 2 were deposited in an open marine environment of a proximal outer ramp and middle ramp, respectively. The microfacies 3–6 belong to an inner ramp/platform environment. These assemblages of the Asmari Formation suggest that the carbonate sedimentation took place in tropical waters in oligotrophic to slightly mesotrophic conditions.

### **Acknowledgements**

The studies were supported by National Iranian Oil Company (NIOC). The authors wish to thank the Exploration Directorate (NIOC) for financial support and permission to publish this research.

### **Author details**

Seyed Hadi Sajadi1 \* and Roya Fanati Rashidi2 \*

1 Department of Geology, North Tehran Branch, Islamic Azad University, Tehran, Iran

2 Department of Geology, Science and Research Branch, Islamic Azad University, Tehran, Iran

\*Address all correspondence to: h.sajadi10@gmail.com and roya\_fanati@yahoo.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Paleoecology and Sedimentary Environments of the Oligo-Miocene Deposits of the Asmari… DOI: http://dx.doi.org/10.5772/intechopen.81402* 

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Section 3
