Lagoonal Facies Research Articles

Latest Pleistocene-Holocene sedimentary evolution from sediment records of the Tam Giang-Cau Hai coastal lagoon system, central Vietnam

The latest Pleistocene-Holocene sedimentary evolution was reconstructed from two boreholes collected in the Tam Giang-Cau Hai coastal lagoon region of central Vietnam. This research was based on analyzing radiocarbon dating, grain size, sedimentary structure, petrological components, and diatom assemblages. Besides, some high-resolution seismic data from the lagoon water body were interpreted to estimate Holocene sediment thickness. Sedimentary records of two boreholes revealed various sedimentary facies under the sea-level change since the Last Glacial Maximum (LGM): Fluvial channel facies, fluvial-lagoonal transition facies, lagoon facies, lagoonal-to-fluvial facies, and flood plain facies. Radiocarbon dating indicated that the coastal lagoon system possibly initiated around 8.8–8.5 cal kyr BP, corresponding to the meltwater pulse 1 C when saltwater intruded into the lagoon system. The borehole-sediment data combined with the high-resolution seismic data shows the thickness of Holocene sediments is approximately 20–35 m in the lagoon region. The study also suggested that the sandy barrier complex along the coast between the lagoon system and the open sea has been likely built during the transgression since 10–8.8 cal kyr BP. Additionally, five ecological zones were identified based on diatom assemblages in borehole HK02 indicating variations in marine and fluvial influence in the coastal lagoon system during the past 8.8 kyr: Dia-HK02–1 indicates a low presence of diatoms, suggesting a weak marine influence in the coastal lagoon system; Dia-HK02–02 shows the strongest marine influence and stable ecological conditions in the coastal lagoon system; Dia-HK02–03 demonstrates a partial decrease in marine influence; Dia-HK02–4 shows an increasing fluvial influence; and Dia-HK02–5 developed under completely dominated fluvial conditions on land.

Microfacies Analysis of the Mishrif Formation (Mid-Cretaceous) at the Tuba and Zubair Oilfields, Southern Iraq

The Cenomanian-Early Turonian Mishrif Formation, which has been studied in selected Oilfields of Tuba Well (TU-5, TU-24, TU-40) and Zubair Well (ZB-41, ZB-42, and ZB-46), which are located in the Mesopotamian basin, southern Iraq, and considered major carbonate reservoir in Iraq and the Arabian Gulf. Seven microfacies types are identified showing that Mishrif formation deposited in five sedimentary facies: 1. Basin Facies Associations; 2. Deep Marine Facies Associations: Bioclast pelagic foram mudstone-wackestone; 3. Shallow Open Marine Facies Associations: Foraminiferal bioclastic wackestone-packstones; 4. Rudisted Reef Facies Associations; 5. Shoal Facies Associations: Peloidal packstone-grainstone; 6.aBack-shoal Facies Association: a. Foraminiferal-bioclastic wackestone-packstone, b. Rudisted-foraminiferal wackestone-packstone; 7. Lagoon Facies Associations: a. Fossiliferous mudstone-wackestone, b. Bioclast foraminiferal wackestone, c. Benthic foraminiferal wackestone.

Nonmatrix pores form high-permeability zones in carbonate layers: The Furna Feia cave in the Potiguar Basin, Brazil

Studying nonmatrix porosity in reservoirs is challenging, especially between core samples and seismic scales. To fill this gap, this work studied a karst system as an analog for a nonmatrix carbonate reservoir. We used a multidisciplinary approach, analyzing host rock data (petrography, petrophysics, and tectonic history) and porosity geometry (terrestrial laser scanner, ground penetrating radar, and field analysis). The karst system occurs in Cretaceous carbonates of the Jandaíra Formation along a regional subaerial unconformity that forms the boundary between lagoonal facies (bed package II) and tidal bar facies (BP-III). BP-I (tidal bar 1) is observed at the base of the cave, while BP-II is in the middle of the cave walls, and BP-III (tidal bar 2) occurs at the ceiling. We find that matrix pores are more pervasive in BP-I. Nonmatrix pores predominate in BP-II and BP-III but mostly in the boundary between them. Horizontal dissolution (decametric-cavernous pores) is more intense along the subaerial unconformity. Metric nonmatrix pores, such as gigapores (pockets) and cavernous pores (cupolas), occur within dolomitic lagoonal facies but predominate in tidal bar facies at the cave ceiling. Most of these metric pores are elongated, and their principal axes are preferentially oriented along NW–SE-striking fractures, indicating tectonic control of the Poço Verde Fault Zone. In this way, we conclude that nonmatrix porosity follows tectonic features below a subaerial unconformity, forming high-permeability zones in carbonate layers. Dolomitization guides the fractures intensity, leading to their consequent enlargement. The features studied here led to cave evolution. These findings can guide karst reservoir prediction.

Petrophysical properties and their influencing factors of carbonates in the fourth member of Sinian Dengying Formation, Sichuan Basin, SW China

Based on the measurements of petrological, petrophysical and elastic properties of the samples of different sedimentary facies in the fourth member of Sinian Dengying Formation (Deng 4 Member) in the Sichuan Basin, the diagenetic processes of reservoirs of different sedimentary facies and their controls on the petrophysical properties were discussed. The results show that cracks and mineral composition jointly control the petrophysical properties, and both are significantly influenced by sedimentary environment and diagenesis. The microbial dolomite of mound-shoal facies mainly experienced multi-stage dolomitization, penecontemporaneous dissolution, tectonic rupture and hydrothermal/organic acid dissolution processes, giving rise to cracks and dissolved pores. The grannular dolomite of inter-mound-shoal bottomland or dolomitic lagoon facies mainly underwent mechanical compaction, burial dolomitization and tectonic-hydrothermal action, creating cracks and intercrystalline pores. The diagenesis related to crack development increases the pressure- and saturation-dependent effects of samples, leading to significant decrease in the compressional wave impedance and Poisson’s ratio. Dolomitization changes the properties of mineral particles, resulting in a Poisson’s ratio close to dolomite. The muddy, siliceous and calcareous sediments in the low-energy environment lead to the decrease of impedance and the differential change of Poisson’s ratio (significantly increased or decreased). The samples with both cracks and dissolved pores show high P-wave velocity dispersion characteristics, and the P-wave velocity dispersion of samples with only fractures or pores is the lowest.

Lacustrine and palustrine carbonates in a Brigantian (late Dinantian) intrashelf basin in the Derbyshire carbonate platform

The Brigantian (late Dinantian) Headstone Laminite provides a record of freshwater carbonate deposition in an intrashelf basin when the surrounding Derbyshire carbonate platform was emergent. The laminated grainstone/carbonate mudstone facies contains calcified plant material, peloids, ostracods and lenses of calcite tufa deposited in a lake margin and sublittoral part of a freshwater lake in a humid palaeoclimate. Precipitation of tufa may have taken place along water courses or resurgences fed by meteoric run‐off and seepage from the karsted carbonate platform. The fenestral carbonate mudstone with calcrete and fenestrae represent deposition in well‐drained parts of the lake margin. A shift to more arid conditions is represented by the laminated dolomudstone facies with an allochem assemblage of calcified plants and micropeloidal dolomicrospar grains and occasional alginite in restricted a lake basin setting. Gypsum crystals and desiccation curls are also present in evaporitic lake margin settings. A return to more humid conditions is indicated by deposition of the laminated grainstone/carbonate mudstone facies with organic‐rich mudstone with thin coal seams and carbonized roots deposited in a poorly drained lake margin setting. This may be a reflection of a gradual transgression after emergence. The eastern margin of the intrashelf basin may have been formed by the Edensor Anticline; however, it is not known if a further complex of lacustrine, palustrine and lagoonal facies was present to the east. Deposition of graded beds containing lithoclasts derived from lacustrine facies were associated with slumping generated by reactivation of structures controlling the intrashelf basin margins.

Back-reef and lagoonal communities, Givetian (Middle Devonian) in Guangdong, South China: Their role in global Devonian reef development

Back-reef and lagoonal communities played an important role in the construction of global reef ecosystems and shallow water carbonate factories during the Devonian Period, but their reef-building significance is not fully understood. This study describes a previously undocumented Givetian stromatoporoid biostromal sequence, 12 m thick and comprising 7 biostromes, in the Tangjiawan Formation of Yaozhai, Guangdong Province, Southeast China. Large bulbous or columnar stromatoporoid Actinostroma and delicate dendroid stromatoporoid Amphipora are abundant, with a comparatively smaller presence of tabulate corals, rugose corals, brachiopods, gastropods, calcimicrobes, and tubeworms. The dominant Actinostroma-Amphipora assemblage, together with leperditicopid ostracods, parathuramminid foraminifers, and calcispheres, indicates a shallow, low-energy back-reef to lagoonal setting. Taphonomic analysis shows a common occurrence of overturned skeletons, and the deposit is interpreted as a parabiostrome constructed in a low-energy environment and affected by episodic high-energy events. Statistical data of similar global assemblages from the Lochkovian to the Famennian based on 153 localities show a relatively rare occurrence of back-reef and lagoonal communities from the Lochkovian to the Eifelian, peaking during the Givetian and Frasnian together with metazoan reefs then declining sharply in the Famennian after the Kellwasser Event. Although autobiostromes have rarely been documented, the densely packed reworked bulbous/domical and dendroid stromatoporoids justify the existence of low-diversity but highly abundant metazoan ecosystems in back-reef to lagoonal settings. This study thus highlights our understanding of the back-reef and lagoonal facies and the important role they played in the expansion of large-scale carbonate factories and reef ecosystems during the Middle to Late Devonian.

Petroleum geology of marl in Triassic Leikoupo Formation and discovery significance of Well Chongtan1 in central Sichuan Basin, SW China

In 2022, the risk exploration well Chongtan1 (CT1) in the Sichuan Basin revealed commercial oil and gas flow during test in a new zone – the marl of the second submember of the third member of Leikoupo Formation (Lei-32) of Middle Triassic, recording a significant discovery. However, the hydrocarbon accumulation in marl remains unclear, which restricts the selection and deployment of exploration area. Focusing on Well CT1, the hydrocarbon accumulation characteristics of Lei-32 marl are analyzed to clarify the potential zones for exploration. The following findings are obtained. First, according to the geochemical analysis of petroleum and source rocks, oil and gas in the Lei-32 marl of Well CT1 are originated from the same marl. The marl acts as both source rock and reservoir rock. Second, the Lei-32 marl in central Sichuan Basin is of lagoonal facies, with a thickness of 40–130 m, an area of about 40 000 km2, a hydrocarbon generation intensity of (4–12)×108 m3/km2, and an estimated quantity of generated hydrocarbons of 25×1012 m3. Third, the lagoonal marl reservoirs are widely distributed in central Sichuan Basin. Typically, in Xichong–Yilong, Ziyang–Jianyang and Moxi South, the reservoirs are 20–60 m thick and cover an area of 7500 km2. Fourth, hydrocarbons in the lagoonal marl are generated and stored in the Lei-32 marl, which means that marl serves as both source rock and reservoir rock. They represent a new type of unconventional resource, which is worthy of exploring. Fifth, based on the interpretation of 2D and 3D seismic data from central Sichuan Basin, Xichong and Suining are defined as favorable prospects with estimated resources of (2000–3000)×108 m3.

Self-Sourced Unconventional Tight Marlstone Reservoir Potential from Evaporative Lagoon of Triassic Leikoupo Formation in the Central Sichuan Basin

A breakthrough was made in tight marlstone reservoirs from an evaporative lagoon in the second sub-member of the third member of the Leikoupo Formation (Lei3-2) in the Central Sichuan Basin. The source rock characteristics, reservoir characteristics of the marlstone and geochemical parameters of the oil and natural gas were investigated to evaluate the unconventional hydrocarbon exploration potential of the tight marlstone from the evaporative lagoon. The results revealed that the source rocks were deposited in evaporative lagoon environments, and the average total organic carbon (TOC) content value for the samples was 0.75 wt%. The thermal maturity of the organic matter was relatively high, with a calculated vitrinite reflectance (Rc) of 1.7%. The characteristics of marlstones suggest that the potential source rocks had fair to good hydrocarbon generative potential. The condensate samples had low densities, low viscosities and high thermal maturity, with a Rc value of 1.7%. For the natural gas, the dry coefficient was around 0.90, and the carbon isotopic compositions of methane and ethane was −41.3‰ and −28.4‰, respectively. According to the carbon isotopic compositions, thermal maturity and geological background, the oil and natural gas from Lei3-2 are comparable with the marlstone of Lei3-2. Thus, the oil and natural gas is self-sourced and originates from the marlstone in the Lei3-2. Micropores and microfractures are often detected in the marlstone from Lei3-2, and a gypsum layer is conducive to the hydrocarbon preservation. These results suggest that the evaporative lagoon facies in Lei3-2 have large, self-sourced, unconventional, tight marlstone reservoir potential. This study also enhances the prospects for further oil and gas exploration of evaporative lagoon facies in other basins.

Emphasizing Lithostratigraphic Rules In Distinction Of Formal Units: Sinjar Vs Khurmala Formations, Case Study

Recognition, identification, and correlation of formal lithostratigraphic units should always follow the rules of the definition of lithostratigraphic units established in the Stratigraphic Code of Nomenclature, set by the International Stratigraphic Commission. This case study is attempting at elaborating on this argument by discussing the identification and differentiation between the Sinjar and Khurmala formations in outcrop and well sections. Stratigraphic data for this study were compiled basin-wide, with nearly fifty localities of both formations from the Zagros foreland basin of Kurdistan in NE Iraq. Examinations include a review of microfacies documentation, Facies reinterpretation as well as sequence analysis. The Sinjar and Khurmala formations are carbonate units developed during the final filling stage of the Zagros foreland basin of northeast Iraq. The Sinjar Formation is characterized by shallow marine coralgal-foraminiferal limestone of reefal, lagoonal, shoal, and overall ramp setting. Other lithologies such as dolomitic limestone or marly limestone are minor and secondary. The Khurmala Formation, on the other hand, is dominated by thick beds of dolostone with secondary lithologies including recrystallized limestone and dolomitic limestone and marly limestone. Microfacies analysis of the Khurmala Formation reveals that it represents a lagoonal lithofacies equivalent to the lagoonal facies of the Sinjar Formation but intensively dolomitized at specific areas of the basin. This close relationship between the two formations, leading in some cases to mixing between both lithologies or rather confusion and misidentification. The best way of differentiating between the two units is by adhering to the lithostratigraphic rules and principles of the formal stratigraphic description, which emphasize the formal lithostratigraphic description of each formation.

Stratigraphic Analysis and Depositional Environment of the Newly Recorded Umm Er Rhadhuma Formation (Paleocene) from the Borehole K.H12/7, South Anah City, Western Iraq

The Paleocene benthic foraminiferal zonation of the Umm Er Rhadhuma Formation from the borehole (K.H 12/7), South Anah City (Western Iraq), has been re-studied and re-analyzed precisely based on the large benthic foraminifera (LBF). They are represented by two biozone Rotorbinella hensoni Partial Range Zone, recorded from the Lower and middle parts of the Umm Er Rhadhuma Formation and Lockhartia praehaimei Partial Range Zone determined Uppermost of this unit, and dated to be the Selandian – Thanetian stage. Almost all the biogenic (micro and macro) and non-biogenic constituents, including large benthic foraminifera, Algae, Echinoderm, Bryozoans, Oyster, Gastropod fragments, and peloids, in addition to lithofacies types, indicate that this succession belongs to the Umm Er Rhadhuma Formation. Furthermore, the Paleocene shallowing upwards succession is recognized from seven identified microfacies (MF1 to MF7), which suggests three significant facies associations. A broad inner ramp represents them and is warm shallow open normal marine water (FA1). In contrast, the second facies association represents by the predominated bioclastic sand shoal facies association (FA2) and finally reaches the semi-restricted lagoon facies associations (FA3). The interaction between the local tectonic disturbance along Rutba high and eustatic sea level mainly controls the development of two sequence boundaries of Type-1 (SB1) that occurred respectively at the Cretaceous /Palaeogene K- Pg boundary and Paleocene /Eocene boundary. The Paleocene depositional system starts with major transgression during the Selandian above a sequence boundary of type one (SB.1), that separates the Late Cretaceous (Maastrichtian) successions of the Tayarat Formation from the overlying Paleocene succession with a significant gap, covering the whole Danian age (That is the top of Tectonic Megasequence AP. 9). The predominance of retrogradation staking tract indicated the transgressive system tract during the late Selandian and early Thanetian as a result of an increase in the sea level rise and expanded accommodation space. The highstand system tracts show aggradational and then change to a progradational stacking pattern by the end of the Thanetian and mark significant sea level drawdown with a new sequence boundary of type one between them.

Integration of geoscience data to delineate quality of the Asmari reservoir, Iranian part of the Persian Gulf basin

The Hendijan Field is an asymmetric structure located in the northwestern Persian Gulf and consists of several oil and gas-bearing intervals. Oligocene to Miocene successions in the field host large volumes of hydrocarbons. The Asmari Formation comprises the mixed siliciclastic and carbonate members formed in a shallow marine carbonate ramp depositional environment. The siliciclastic part displays the best reservoir quality within the Asmari Formation. Through petrophysical, sedimentological, and geophysical analysis, this study divides the Asmari Formation into six, third-order depositional sequences. By doing so, it clarifies the relationships between depositional sequences and reservoir characteristics, particularly porosity and water saturation. Detailed petrographical analysis, core description, well log analysis, and seismic interpretation distinguish eight microfacies, two petrofacies, and six third-order sequences within the Asmari Formation. 3D reservoir-property models are developed that incorporate elements of the sequence stratigraphical framework. Within the six identified sequences, high reservoir quality zones are associated with AS-4 and AS-5, which comprise mostly grain-supported lithologies associated with shoal facies. The supratidal, intertidal, and lagoonal facies of AS-2, which are often associated with the occurrence of anhydrite and mud-supported fabrics, reflect lower reservoir quality. Hydraulic flow units (HFU) are delineated to assist in characterizing reservoir heterogeneity and porosity/permeability prediction. Five HFU were identified by applying the flow-zone-indicator method to evaluate reservoir quality. Both the transgressive system tract (TST) of AS-2 and early TST plus late highstand system tract (HST) of AS-6 contain elements of HFU-A. The most productive units of AS-4 and AS-5 belong to HFU-E.

Facies Architectuer and Stratigraphic Evolution of Campanian Succession in Balad, East Baghdad and Kifl Oil Fields

The sediments of the Hartha Formation were deposited during the Upper Campanian- Maastrichtian cycle. Due to the importance of this sequence in terms of stratification and economics in the oil industry, it has been focused on in this study. The present study includes three oil fields in central of Iraq within the Mesopotaminan Zone, East Baghdad, Balad and Kifl oil fields. This study was accomplished by describing 190 thin sections and interpreting the response of the available well logging data. Seven major microfacies were diagnosed in the Hartha succession at studied oil fields, they are; Orbitoidal wackestone - packstone, Orbitoidal and miliolids wackestone, Rotaliidae and Siderolites with echinodermata wackestone - packstone, Peloidal - echinoderm packstone - grainestone, Pellets - echinodermata packstone - grainestone, Planktonic foraminifera wackstone - packstone and Evaporitic mudstone microfacies. These microfacies were deposited in lagoon, restricted, shallow open marine, shoal, mid ramp and outer ramp. The Hartha Formation in the studied oil fields represents one cycle third order with three cycles fourth order (A1, A2 and A3). These cycles are asymmetrical and starts with cycle A where the open marine facies in the Lower Hartha represents the TST underly the HST, which bounded below by a TS which coinside with the unconformable surface (SB1) with the underlying Sadi Formation. The highstand systems tract of cycle A1 is reflected by the open marine facies of the Hartha Formation, A2 is reflected by the open marine and mid ramp facies represent thick TST and then appear the HST which reflected by the open marine facies bounded by a transgressive surface (TS) reflected mid ramp and outer rampfacies in the TST which represents A3. The second cycle A2 is disappeared in Kifl Oil Field with appeared evaporitic lagoon facies.

Reconstruction of the proto-type basin and tectono-paleographical evolution of Tarim in the Cenozoic

The Tarim Basin is the largest sedimentary basin in China, and it has experienced a complex tectonic evolutionary history. Reconstruction of the proto-type basin and tectono-paleogeography is helpful to understand the different stages of evolution of the sedimentary basin and basin-mountain relationship. It is significant to combine the basin with the regional tectonic background to discuss the process of basin-mountain coupling and the tectonic evolution of the peripheral orogenic belts. With a reliable residual thickness map and lithofacies map of the Tarim Basin in the Cenozoic, based on the amount of shortening we quantified from previous works and 81 balanced cross-sections, we restored the original range and compiled the proto-type basin map of Tarim Basin. From a compilation of previous studies on the lithofacies of peripheral blocks, the tectono-paleogeography of the Tarim Basin in Cenozoic has been reconstructed. The Indian Plate collided with the Eurasian continent at ∼45–40 Ma. The remote effect of the collision led to the resurrection and reactivation of the Kunlun and Tianshan Mountains. The Southwest Tarim and Kuqa rejuvenated foreland basins separately developed along the north front of the Kunlun Mountains and the south front of the Tianshan Mountains. The tectonic evolution process of the Tarim Basin in the Cenozoic was divided into two stages: 1) in the Paleogene, the Neo-Tethys Ocean retreated stepwise westward from the Southwest of the Tarim Basin, and the sedimentary lithofacies of the Southwest Tarim Depression were bay lagoon facies and lake facies; 2) the Neo-Tethys Ocean retreat finally occurred in the Tarim Basin during the Late Oligocene to Early Miocene, and it became an almost closed terrestrial basin, with the deposition of fluvial facies and lacustrine facies. The Cenozoic tectono-paleogeography of the Tarim Basin is closely related to the closure of the Neo-Tethys Ocean and the reactivation of the Kunlun and Tianshan Mountains.

Sedimentary and stratigraphic characteristics of the Maastrichtian Dukamaje formation of southern Iullemmeden Basin: Implications for the paleogeography of the Upper Cretaceous trans-Saharan seaway

The Maastrichtian Dukamaje Formation is a fossiliferous, shale- and marl-dominated unit, albeit with contentious paleodepositional environment, of the Rima Group, southern Iullemmeden Basin (northwestern Nigeria). The Basin holds records of the global sea-level highs of the Late Cretaceous - Paleocene. Hence, an improved understanding of the associated sedimentary infill will provide opportunity for an improved reconstruction of paleogeography and ancient stratigraphic sequences. Two different models (a low-energy, hypersaline lagoon and marsh based on predominance of fine grains with gypsum and preserved vertebrate fossils, or high energy/inshore, shallow marine environment supported with Libycoceras ammonite fossil) have been proposed by different workers who studied the same outcrop sections. The discrepancy in these previous models is partly due to inherent depositional complexities and the need to invoke deductive interpretations for epicontinental basins. Here, we used a systematic facies analysis (for the first time and with particular attention to stratigraphic relationships and correlation of some of the outcrop sections) integrated with previous biostratigraphic data in order to reconstruct the paleogeography of the Dukamaje Formation. The objectives are to describe the facies characteristics and provide a well-constrained interpretation for the depositional setting of the Dukamaje Formation. Results: two alternating, low-energy facies associations (marsh and lagoonal and restricted?/nearshore marine) were identified. The marsh and lagoonal facies association is characterised by fossiliferous and gypsiferous shale enriched in arenaceous foraminifera. The restricted marine facies association comprises highly fossiliferous nodular marls. The facies associations form a coastal sabkha facies succession, deposited in a marginal marine environment with likely brackish influence, under a warm tropical climate. The coastal sabkha facies succession is interpreted as a retrogradational system, which suggests that the Dukamaje Formation is a product of marine transgression of a low-lying, embayed, partially restricted, stable coast. By implication, the hypothesised Upper Cretaceous epicontinental sea (“trans-Saharan seaway”) across the North to West Africa was, rather than fully open, restricted in some places. Restrictions were related to presence of embayments in which hypersaline conditions developed due to low circulation. This model is largely consistent with the view of a partially restricted shallow marine for the Upper Cretaceous of the southern Iullemmeden Basin.

Discrimination Reef and Non-Reef Environments, Using REE Geochemistry

This research aims to distinguish the reef environment from the non-reef environment. The Oligocene-Miocene-succussion in western Iraq was selected as a case study, represented by the reefal limestone facies of the Anah Formation (Late Oligocene) deposited in reef-back reef environments, dolomitic limestone of the Euphrates Formation (Early Miocene) deposited in open sea environments, and gypsiferous marly limestone of the Fatha Formation (Middle Miocene) deposited in a lagoonal environment. The content of the rare earth elements (REEs) (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Ho, Tm, Yb, Lu, and Y) in reef facies appear to be much lower than of those in the non-reef facies. The open sea facies have a low content of REEs due to being a transitional phase. The facies investigated have ƩREEs lower than the PAAS. The lagoonal facies shows an average ƩREEs higher than the Global Standard of Carbonate Rocks (GSCR), whereas reefal and open sea facies contain lower. The Y/Ho, Y/Dy, and Er/Nd were used as distinctive indicators of facies diagnosis; reefal facies have a high value of Y/Ho, Y/Dy, and Er/Nd as compared to PAAS are higher than1. In contrast, non-reef facies (lagoonal) have a lower value of Y/Ho, and Y/Dy as compared to PAAS is lower than 1, but Er/Nd is higher than 1. While in open sea facies the Y/Ho and Y/Dy have moderate values as compared to PAAS are close to 1, but a high value of Er/Nd as compared to PAAS higher than 1.

MESOZOIC DELTAIC SYSTEM AND SEQUENCE STRATIGRAPHIC MODEL OF THE LOWER JURASSIC DATTA FORMATION ALONG THE WESTERN SALT RANGE, PAKISTAN

In this research, the Early Jurassic Datta Formation from three outcrop sections of the western Salt Range has been extensively studied to elucidate facies architecture, sedimentary features, diagenetic features, sequence stratigraphy, and depositional model. Datta Formation is well exposed with massive thickness in the western Salt Range and the Trans Indus Ranges, while tapering in the central Salt Range further eastward, it dies out. Its mainly dominated by variegated sandstone, siltstone, shale, fire clays, laterites, and carbonates. Seven lithofacies has been identified and interpreted in the Datta Formation, i.e., (i). Fluvial Meandering Lithofacies (JDL-01), (ii). Braided Fluvial Lithofacies (JDL-02), (iii). Lateritic Lithofacies (JDL-03), (iv). Flood Plain Lithofacies (JDL-04), (v). Siliciclastic Lagoon Lithofacies (JDL-05), (vi). Carbonates dominant Lagoon Lithofacies (JDL-06), (vii). Swamps related Deltaic Lithofacies (JDL-07). Sequence stratigraphic analysis is primarily based on recognizing sequence surfaces, finning-coarsening upward trends, and types of facies. Two transgressive-regressive cycles are identified in the south-eastern section (Kassan Nala and Kaowali sections), while four sequences are identified in the Nammal Gorge section. These sequences are started with the underlying sequence boundary of LST and ended with the sequence bounding surface after HST. Datta Formation is possibly deposited in fluvial to deltaic environments in the study area, revealing a prograding delta with a shoreline oriented in the SW-NE direction and the siliciclastic detritus fed the fluvial system running over the Indian cratonic basement in the direction of N-NW. The lower part of the formation is deposited in fluvial settings, probably in the incised valley. The point bar sequences result from meandering channel facies and show association with overlying flood plain/overbank facies. Moreover, the lagoonal facies mainly covered the upper part of the formation and displayed mixed lithologies of delta plain to delta front setting. However, the repetition of these lithofacies in the study area at several points indicates the recurrence of depositional phases. The carbonaceous shales and coal streaks are evident by the presence of swamp or marshy lands. These conditions meet the criteria of deltaic settings. Furthermore, several laterites and fire clay horizons are also argue periodic sub-aerial exposure of the depositional area. Thus it is concluded that the depositional area lies in a fluvial to deltaic setting with major distributary channels and their flood plain in the adjoining delta plain to delta front part.

Geochemical Criteria for Discriminating Shallow and Deep Environments in Oligocene-Miocene Succession, Western Iraq

The geochemical study of the Oligocene-Miocene succession Anah, Euphrates, and Fatha formations, western Iraq, was carried out to discriminate their depositional environments. Different major and trace patterns were observed between these formations. The major elements (Ca, Mg, Fe, Mn, K, and Na) and trace elements (Li, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Cs, Ba, Hf, W, Pb, Th, and U) are a function of the setting of the depositional environments. The reefal facies have lower concentrations of MgO, Li, Cr, Co, Ni, Ga, Rb, Zr, and Ba than marine and lagoonal facies but have higher concentrations of CaO, V, and Sr than it. Whereas dolomitic limestone facies are enriched V, and U while depletion in Li, Cr, Ni, Ga, Rb, Sr, Zr, Ba, and Pb Conversely, the lagoonal facies are rich in clay minerals and associated trace elements Li, V, Cr, Co, Ni, Cu, Ga, Rb, Zr, Ba, and Pb.

Geology of recently recognized lithologies inside the Red Bed Series in the Chwarta-Mawat area, Kurdistan Region, NE-Iraq

The sequence of the coastal siliciclastic facies of the Paleocene-Eocene Zagros Foreland Basin is well exposed in the Chwarta-Mawat area, north of Sulaimani Governorate, northeastern Iraq. According to previous studies, this sequence is designated as Red Beds Series (RBS), consisting of more than 2000 m of fine and coarse red and grey clastics. The present study found recently recognized lithologies (RRLs) about 100 thick inside the series and encompassed green marlstone with subsidiary detrital limestone which has significant tectonic and paleogeographic results. The petrography, biostratigraphy, and boundary conditions studies are applied to uncover their origin. The new lithologies are deposited in the subsiding basin in the Imbricate Zone during the Middle Eocene. During this age, the Tertiary Foreland Basin was separated by a paleohigh into two basins, (northern and southern basins). In the northern basin, the RRLs have deposited as deep facies of the Naopurdan Formation while in the southern basin the Pila Spi Formation was deposited as lagoonal facies. The former formation was deposited as reefal facies in the shelf area of the northern basin to the northeast Chawrta and Mawat Towns. The RRLs, units one and two of the series (in the Thrust Zone) are correlated respectively with Pila Spi, Sinjar and Gercus formations in the High Folded Zone. These correlations are shown on the stratigraphic columns and paleogeographic models with the aid of nannofossil and benthonic foraminiferal studies. This study is the most important step for solving the tectonic and paleogeographic setting of northeastern Iraq and for a better understanding of the Zagros Collisional belt.

Biostratigraphyand Paleoenvironments of Benthic Foraminifera From Lower Part of the Damlouk Member, Western Desert, Iraq

Age and paleoenvironment of part of the Damlouk Member, Ratga Formation from a surface section in the Iraqi Western Desert are investigated. Twenty-nine species of Larger Benthic Foraminifera (LBF) belonging to 13 genera are recognized from the studied section. The LBF assemblage is dominated by the following groups, Nummulites, Alveolina, Rotalia, and Lockhartia. Two species of corals with fragments of bryozoan, red algae and mollusca had also been identified. The palaeontological investigation aimed at identification of LBF assemblages to evaluate their abundance and distribution with respect to sedimentary environment and to determine its age. Based on the recognized Larger Benthic Foraminifera of the studied part of the Damlouk Member, it is subdivided into two biozones: Nummulites gizhensis -Nummulites moculatus Assemblage Zone and Assilina spira- Lokharatia hunti Concurrent Range Zone. Both biozones suggest a Middle - Late Lutetian to Early Bartonian age. The LBF are concentrated around shallow marine carbonate bank-controlled limestone unit and the associated ramp facies. Two basic environmentally significant assemblages were recognized based on the vertical distribution and the relative abundance of the LBF. The Nummulite bank assemblage is characterized by lensoidal and robust Nummulites of different species. The other group is the fore-bank assemblage which shows relatively higher diversity, including flat LBF such as: Nummulite, Assilina, Lockhartia, Heterostigina and Operculina. The third back-bank assemblage is not well presented in the studied section, shows the limited distribution, and is considered part of the back-bank lagoon facies. This group is characterized by the occurrence of Alveolina and other imperforated forams. The recognized assemblages represent the transition from inner to middle ramp facies with a water depth not exceeding 50m in relatively low energy conditions.

Unraveling an alkaline lake and a climate change in Northeastern Brazil during the Late Aptian

The Codó Formation is an Aptian marine-influenced lacustrine depositional system in the Parnaíba Basin (Brazil). This unit is an important sedimentary succession because of the high organic matter content and for being an ancient analog for the depositional systems of the Brazilian Pre-salt interval. However, mineralogical and lithogeochemical studies have not been sufficiently carried out on the Codó Formation, which hinders detailed sedimentological knowledge. We report new mineralogical and lithogeochemical data that allow a better understanding of the environmental, climatic, and provenance evolution of the Codó deposits. Mineralogical and lithogeochemical studies were performed on 50 lutite samples collected from the 1-UN-32-PI core and 13 outcrop lutite samples obtained from sites close to the Grajaú and Imperatriz regions. A magnesium-sulfate-rich shallow alkaline hypersaline lake was identified in the lower Codó Formation based on the identification of a clay mineral assemblage composed of authigenic saponite and detrital illite. Hydrothermal processes were interpreted as the magnesium source of this alkaline lake. A salinity-alteration event was identified at the upper limit of the alkaline lake and was interpreted as the first marine ingression in the Codó Formation. This event changed the lake's pH from alkaline to acid, inhibiting the formation of Mg-smectites, and changing its hydrochemical conditions, originating a marine-influenced sulfate-rich acid saline/hypersaline sabkha. This facies succession coincides with a clay mineral assemblage composed of detrital montmorillonite, illite and kaolinite. A regional paleoclimate humidification process was identified from the sabkha to a lagoon facies succession in the upper Codó Formation. This last succession reveals the marine-dominated interval of the Codó Formation and coincides with a clay mineral assemblage composed of detrital kaolinite, montmorillonite and illite. Based on lithogeochemical data, a common post-Archean intermediate source area was also interpreted for these three environments.