No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Carbonate Fades in Geologic History
Abstract
Most, though not all, carbonate sedimentation results basically from chemical or biochemical processes occurring in a special marine environment: one of clear, warm, shallow water. A world map (Fig. I-1) showing areas of modern carbonate deposition demonstrates clearly a positive correlation between such deposition and the equatorial belt and areas of warm ocean currents. Fairbridge (Chilingar et al., 1967, p. 404) presented a graph showing that neritic carbonates exist chiefly north and south of the equator below latitudes of 30 degrees. Furthermore, whereas the bottoms of deep ocean basins between 40 degress north and south latitudes contain much planktonic carbonate, those in higher latitudes do not, except in the north Atlantic along the Gulf stream. Invertebrates precipitate thicker calcite and aragonite shells in clear, warm waters, many more calcareous algae thrive there, and algal-dependent hermatypic or reef-building corals are restricted to such an environment. Cooler marine waters do support swarms of invertebrates whose tests and shells may form local accumulations of shelly lime sand (Lees, 1973; Chave, 1967), but other types of lime sediment, such as ooids, grapestones, peloids, reefy boundstone and lime mud accumulations, are confined to tropical and subtropical waters.
... As a result, the sedimentation environment of the Kahtepe Formation limestones is a carbonatedominated shelf environment. We can say that mudstone, wackestone, packstone, and grainstone microfacies developed in Wilson's (1975) ...
... The mudstone, wackestone, packstone, and grainstone microfacies of the Kahtepe Formation limestones occurred in Wilson's (1975) six (Winnowed edge sands), seven (Shelf lagoon: open circulation), and eith (Shelf and tidal plains: limited circulation) carbonate belt environments. ...
... The carbonate standard facies belt of Wilson (fromWilson, 1975). ...
... In addition, some non-carbonate components are frequent such as clay admixture, quartz, pyrite.Planktic Foraminiferal Wackestone Facies is equivalent to Wilson's [9] and Flugel's [10] Standard Microfacies 3 (SMF 3). It represents deposition at Facies Zone 2 (FZ 2) that is deep shelf figure (5). ...
... In addition, echinoid is present, which indicate nearness to open marine outer shelf environment figure (5). It can be correlated with SMF8 within FZ2 [10]. ...
... a). All the paleontological attributes impose an upper bathyal environment with water depth ranging between 200 -400 m and it is a mach to SMF3 within FZ1[10]. The microfacies occurs in the lower and middle parts of the Zt-4 section figure(5).Planktic Foraminiferal Wackestone/ PackstoneThis is the most common facies in the Serikagni Formation. ...
... 410 thin sections of carbonate rocks were collected at ~40 cm intervals for petrographic analysis, stained for dolomite identification using the Dickson (1965) method and classified according to Dunham's (1962) scheme. The depositional environment of each facies was determined using the standard microfacies classification by Wilson (1975) and Flügel (2010) (Table 1). We followed Lucia (1995,2007) for reservoir quality characterization (Table 2). ...
... On the other hand, anhydrite-filled pores caused an overall poor reservoir quality. This microfacies is comparable to SMF21 and RMF23 of Flügel (2010), facies belt 9A of Wilson (1975), and facies belt 1 (inner ramp-peritidal zone) of Buxton and Pedley (1989), respectively. ...
... F2: The precursor to this rock type was likely deposited in hypersaline subtidal to supratidal environments (Awaramik and Sprinkle, 1999). This microfacies is comparable to SMF21 and RMF23 (inner ramp-peritidal zone) of Flügel (2010), facies belts 8 and 9 of Wilson (1975), or facies belt 1 of Buxton and Pedley (1989). The reservoir quality is poor. ...
... Algal laminites. dismicrites, and limestones with well-rounded bioclasts from open marine fauna as well as feldspar-rich sandstones with layers of well-rounded pebbles (facies association L) were probably deposited in shoal or beach environments (Facies Belt 6 or 8 of Wilson (1975)). Their occurrence indicates that after deposition of the Multithecopora Limestone, lagoonal areas became shallower and were sporadically and locally cut off from open circulation. ...
... intercalated sandstones (Kastner & Siever 1979). These uppermost beds of facies association L were deposited in higher intertidal to supratical regimes (Facies Belt 8 of Wilson (1975) ), suggested by James ( 1984) to represent the uppermost part of a shallowing-upward sequence. Above the shoal deposits ostracods represent the dominating fauna: below, forams are more abun- dant. ...
... In conclusion. the microfacies of the Scheteligfjellet Member suggests stillwater conditions, the depositional environment being a shallow bay with lagoons along the coast protected by shoals or barriers from the open sea (Facies Belt 7 of Wilson (1975)). The bay was characterized by sea grass and a faunal association of forams. ...
The change from continental to marine conditions in the Middle Carboniferous on Brøggerhalvøya started at the end of the Bashkirian with short-term transgressive events at the top of the Brøggertinden Formation. Local basin subsidence was responsible for the pulsatory nature of the transgression. The establishment of a shallow marine carbonate-dominated environment is represented by the Moscovian Scheteligfjellet Member which overlies the post-Caledonian red beds of the Brøggertinden Formation. The Scheteligfjellet Member is the lowermost member of the Nordenskioldbreen Formation and shows distinct lateral facies variations. Three facies associations can be distinguished: lagoonal facies, shoal facies and open marine facies. The succeeding two members were deposited in subtidal areas of the carbonate platform. A basin subsidence event at the Carboniferous/Permian boundary was responsible for a short shift into deeper depositional environments during a time of worldwide regression. After this a continuous regression led to supratidal conditions at the top of the Nordenskioldbreen Formation.
... The dominant porosity is mainly of the moldic and vuggy type. Interpretation: Abundance of peloids and green algae in micrite with low diversity of fossils indicates deposition in restricted shallow subtidal (lagoonal) water as well as a slow sedimentation rate (Wilson, 1975; Flügel, 2010). The facies is very similar to those described by Wanas (2008) and Amel et al. (2015) for lagoon environments around the margin of carbonate shoals. ...
... Moreover, this facies lacks anhydrite, which it advantageous for reservoir quality. Interpretation: Lack of micrite and occurrence of ooids are indicative of high energy shoal environments (Wilson, 1975). The facies is similar to the RMF29 (shoal environment) of Flügel (2010) and displays moderate to good reservoir quality (Table 2). ...
... In the studied section, the inner ramp depositional environment includes tidal flat, lagoon and shoal facies belts (Fig. 6). This view is substantiated by the following observations: (I) the peritidal flat facies association (MF1 to MF4) is characterized by the lack of allochems, no significant facies change (mainly anhydrite and nodular dolomudstone), common sabkha facies, absence of clastics, occurrence of fenestral fabrics besides stromatolite facies and presence of rhombic dolomites, which are indicative of an inner carbonate ramp system developed under arid to semi-arid conditions (Wilson, 1975; Read, 1985; Burchette and Wright, 1992), (II) the lagoon facies association (MF5, MF6 and MF7) with specific lagoonal bioclasts such as green algae, benthic foraminifera, especially miliolids, textulariids and gastropods, and also abundant peloids, micritic matrix, and bioturbation is suggestive of sedimentation in a limited zone behind shoals (Brachert, 1992) or a windward shoal environment (lagoon-facing side), and (III) grain-dominated facies, lack of micrite, presence of graded bedding and cross-bedding, and allochems such as ooids, intraclasts , and to a lesser extent oncoids and green algae fragments deposited in a high-energy zone are among the characteristics of the shoal facies belt in an inner ramp setting (Read, 1985; Burchette and Wright, 1992), showing the highest reservoir quality (Table 2). The dolomitization process is generally pervasive. ...
This study aims to determine the depositional facies, diagenetic processes and sequence stratigraphic elements of the subsurface carbonate-evaporite succession of the Upper Jurassic (Kimmeridgian-Tithonian) Surmeh Formation of the Salman Oil Field (the Persian Gulf, Iran), in an attempt to explore their impacts on reservoir quality. The Surmeh Formation consists mainly of carbonate rocks, intercalated with evaporite layers. Petrographically, the Surmeh Formation consists of nine microfacies (MF1-MF9). These microfacies are grouped into three facies associations related to three depositional environments (peritidal flat, lagoon and high-energy shoal) sited on the inner part of a homoclinal carbonate ramp. The recorded diagenetic processes include dolomitization, anhydritization, compaction, micritization, neomorphism, dissolution and cementation. Vertical stacking patterns of the studied facies reveal the presence of three third-order depositional sequences, each of which consists of transgressive systems tract (TST) and highstand systems tract (HST). The TSTs comprise intertidal and lagoon facies whereas the HSTs include supratidal and shoal facies.
... Thin gypsum layers located in the red mudstones are interpreted as evaporite ponds (playa) that developed in the alluvial plain during arid climatic episodes (Warren, 2006; Varol and Atalar, 2016). Restricted platform (FZ 8) (Wilson, 1975; Flügel, 2004). Periodically open sea connection (Playford and Cockbain, 1976). ...
... Open platform (FZ 7) (Wilson, 1975; Flügel, 2004). ...
... Platform margin reef " algal mounds " (FZ 5) and slope (FZ 4) ( Wilson, 1975; Flügel, 2004). ...
The Sivas Cenozoic Basin and coeval Central Anatolian basins such as Cankırı and Tuz Golu are characterized by both marine and terrestrial sediments ranging in age from the Eocene to early Miocene. The evaporite regime here generally appeared during the late stage of Eocene transgression and persisted through the Oligocene time. However, marine-induced Oligocene evaporites are less known because of less paleontological evidence and regional tectonics and salt diapirism that mostly caused the destruction of their original stratigraphic positions. The Eğribucak area studied here, located about 25 km southeast of Sivas, provides a well-stratified key section to shed light on the depositional history of the Oligocene marine evaporite (coastal lagoon or sabkha complex) and other associated carbonate and siliciclastic units. The Eğribucak succession has a thickness of approximately 400 m and rests on thick fluviatile sediments commencing with red beds (mudstone, sandstone, and gravelly sandstone), and upwards, terrestrial gypsums are present within the red units as thin beds that are overlain by thick marine gypsum beds with rhythmical alternations of gray and green colored sandstonemarly limestone and limestone. The limestones alternating with the thick gypsum beds are rich in benthic foraminifers yielding a Rupelian-Chattian age. At the top of the section evaporites disappeared and lagoon-type limestone turned into thick platform carbonate dated as Oligocene-early Miocene. The Eğribucak succession shows a wide variety of depositional environments ranging from terrestrial to restricted marine to open marine from bottom to top. The short periods of the lithological alternations from siliciclastic to carbonate and evaporite indicate that the evaporite environment was not consistent through the Oligocene period. This would be formed as a marginal evaporite environment, presumably a coastal lagoon/sabkha affected by seasonal variations with arid and humid periods as well as eustatic sea-level changes. The Oligocene transgression culminated in the area with the deposition of platform-type carbonates and it continued during the early Miocene.
... This MF have been deposited in a low energy deep environment under quiet water. It can be compared with the Standard Microfacies No.3 (SMF.3) of Wilson (1975), also comparable with Ramp Microfacies No.5 (RMF.5) of Flugel (2004) belonging to the open marine facies zone ( Fig. 2-1). ...
... This microfacies includes dolomitized mudstone without any bioclast and fossils. This type can be comparable with the SMF.19 of Wilson (1975) and RMF.22 of Flugel (2004) belonging to the intertidal environment of inner ramp (Fig. 2-10). ...
... By comparing the observations and results with those of modern carbonate depositional setting like the Persian Gulf, also considering the standard depositional setting previously proposed by the famous geologists (Wilson, 1975;Read, 1985;Burchette and Wright, 1992;Flugel, 2004), a carbonate ramp model which likely can be a low gradient homoclinal ramp is suggested for the Asmari formation in the Karanj oil field. ...
The Asmari formatin contains the most important and perimier oil reservoir of the Zagros foreland basin. This formation in subsurface section of the study area consists of 354m limestone, dolostone and anhydrite layers in some depths. Microscopic investigations of the core samples and drilling cuttings of the mentioned deposits have led to recognition of 12 microfacies types. Vertical analysis of these microfacies and their depositional texture and fauna, represented fife facies belts including supratidal, intertidal, open lagoon, shallow open marine and deep open marine or basin. Interpretation of the microfacies and depositional subenvironments and comparing with standard models of carbonate deposition demonstrates that the Asmari formation in studied section was deposited in a carbonate ramp. Sequence stratigraphic study based on the T-R methodology caused to detection of three 3 rd order T-R sequences and three maximum flooding surfaces (MFS) as the lowest sequence gradationally has been deposited over the Pabdeh formation with conformable boundary (MRS) and the upper sequence has been formed with an unconformable boundary under the Gachsaran formation.
... This MF have been deposited in a low energy deep environment under quiet water. It can be compared with the Standard Microfacies No.3 (SMF.3) of Wilson (1975), also comparable with Ramp Microfacies No.5 (RMF.5) of Flugel (2004) belonging to the open marine facies zone ( Fig. 2-1). ...
... This microfacies includes dolomitized mudstone without any bioclast and fossils. This type can be comparable with the SMF.19 of Wilson (1975) and RMF.22 of Flugel (2004) belonging to the intertidal environment of inner ramp (Fig. 2-10). ...
... By comparing the observations and results with those of modern carbonate depositional setting like the Persian Gulf, also considering the standard depositional setting previously proposed by the famous geologists (Wilson, 1975;Read, 1985;Burchette and Wright, 1992;Flugel, 2004), a carbonate ramp model which likely can be a low gradient homoclinal ramp is suggested for the Asmari formation in the Karanj oil field. ...
The Asmari formatin contains the most important and perimier oil reservoir of the Zagros foreland basin. This formation in subsurface section of the study area consists of 354m limestone, dolostone and anhydrite layers in some depths. Microscopic investigations of the core samples and drilling cuttings of the mentioned deposits have led to recognition of 12 microfacies types. Vertical analysis of these microfacies and their depositional texture and fauna, represented fife facies belts including supratidal, intertidal, open lagoon, shallow open marine and deep open marine or basin. Interpretation of the microfacies and depositional subenvironments and comparing with standard models of carbonate deposition demonstrates that the Asmari formation in studied section was deposited in a carbonate ramp. Sequence stratigraphic study based on the T-R methodology caused to detection of three 3 rd order T-R sequences and three maximum flooding surfaces (MFS) as the lowest sequence gradationally has been deposited over the Pabdeh formation with conformable boundary (MRS) and the upper sequence has been formed with an unconformable boundary under the Gachsaran formation.
... The major facies types that were distinguished within the current study were based on the main characteristics of the sedimentary textures and the relative abundance of the biotic components. Therefore, four major microfacies types (Mudstone, wackestone, wackestone to packstone, and packstone) and nine submicrofacies were identified based on Dunham's (1962), classification and taking the Wilson (1975) and Flugel's (2010) standard microfacies and facies belts in consideration. The main submicrofacies, which are recognized within this study represent: ...
... Some chambers of the planktonic foraminifera were filled with dark pyrite minerals, ( Figure 10A). The high amounts of lime mud, lack of mechanical sedimentary structures, and bearing of planktonic foraminifera recommend that these facies were deposited in low-energy conditions with normal salinity (Wilson, 1975) and corresponding to RMF 2 of mid to outer ramp setting, Flugel (2010). ...
المستخلص
تهدف هذه الدراسة الى تحديد العمر النسبي والسحنات الدقيقة لتكوين مودود في بيئر مسيب 1، وسط العراق. تم
تشخيص ست وثلاثون نوعا من الفورامنيفيرا القاعية تعود الى اثنان وعشرون جنسا. وقد تم تسجيل ثلاث أنطقة حياتية
المعتمدة على الفورامنيفيرا القاعية لعمر البيان المتأخر سينومانين المبكر وهى من الأقدم الى الأحدث: -
1-Mesorbitolina texana - Orbitolina qatarica Concurrent Range Zone
2- Orbitolina sefini Total Range Zone
3- Orbtolina concava Total R. Zone
و من ثم تم مقارنة الأنطقة المشخصة في هذه الدرا سة مع الأنطقة الأخرى لدراسات سابقة داخل وخارج العراق. بناءً
على التحليلات البتروغرافية، وعليه تم تحديد أربعة سحنات دقيقة أساسية مع تسع سحنات فرعية ) Mudstone ،
wackestone ، wackestone to packstone and packstone (. ان تكوين مودود قد ترسب في بيئة بحرية تحتوي
على البيئات الفرعية الثلاث التالية:
... The major facies types that were distinguished within the current study were based on the main characteristics of the sedimentary textures and the relative abundance of the biotic components. Therefore, four major microfacies types (Mudstone, wackestone, wackestone to packstone, and packstone) and nine submicrofacies were identified based on Dunham's (1962), classification and taking the Wilson (1975) and Flugel's (2010) standard microfacies and facies belts in consideration. The main submicrofacies, which are recognized within this study represent: ...
... Some chambers of the planktonic foraminifera were filled with dark pyrite minerals, ( Figure 10A). The high amounts of lime mud, lack of mechanical sedimentary structures, and bearing of planktonic foraminifera recommend that these facies were deposited in low-energy conditions with normal salinity (Wilson, 1975) and corresponding to RMF 2 of mid to outer ramp setting, Flugel (2010). ...
Upper Albian and Lower Cenomanian biostratigraphy and microfacies types of the Mauddud Formation from Musaiyib well No.1, Central Iraq are described and examined, which consists of thick to medium bedded limestone, marly limestone rich in argillaceous material, green shale, and dolomitic limestone beds. Thirty-six species from twenty-two genera of benthic foraminifera in addition to calcareous algae, coral, bivalves, gastropods, rudist fragments, brachiopods, bryozoan, and echinoid fragments are recognized from the Mauddud Formation of the studied well. On the basis of the recognized benthic foraminifera three biozones were determined: Mesorbitolina texana-Orbitolina qatarica Concurrent Range zone-Orbitolina sefini-Total R. Zone and Orbtolina concava Total R. Zone. Both suggest the Late Albian-Early Cenomanian age. The results of this study are compared with the work of others inside and outside Iraq. Based on the petrographical analyses, four major microfacies (Mudstone, wackestone, wackestone to packstone, and packstone), and nine sub-microfacies were identified. The Mauddud Formation was formed in a marine environment that was composed of the following three sub-environments: the inner ramp and the middle to the outer ramp.
... This formation consists mainly of crystalline limestone and dolomitic limestone. There are three main microfacies within two standard microfacies of Wilson's (1975) [3] and Flügel's (2010) [4] in studied succession: ...
... This formation consists mainly of crystalline limestone and dolomitic limestone. There are three main microfacies within two standard microfacies of Wilson's (1975) [3] and Flügel's (2010) [4] in studied succession: ...
The present study is focused upon the sedimentology and basin development of the Jeribe and Fatha Formations by using the field observations and microfacies analysis. The area of study situated in the Zurbatiyah area to the south of the Shur sharin valley about 21 km northeast of Badrah city to the southeast of Baghdad. This area lies within the Zagros foreland basin, and located between the Zagros mountains at the northeastern and the Arabian shield at the southeastern. The studied succession which including the Jeribe and Fatha Formations were deposited within four associated facies for the Jeribe Formation and three for the Fatha Formation, as shown below:-Jeribe Formation includes dolomitized mudstone-wackstone (semi restricted); Milliolid wackestone-packstone (shallow open marine), Dolomitic packstone (lagoon). Fatha Formation includes pelecypods bioclastic wackestone-packestone (lagoon); peloidal bioclastic packstone (lagoon); massive gypsum (evaporitic lagoon); laminated gypsum (supratidal and evaporitic lagoon) The facies analysis for the studied succession showing two stages of deposition:-The first stage is represented the final transgression stage in the studied area. The fall sea level gradationally appeared by shallowing upward and more dolomitized upward from the middle part of the Jeribe Formation. The second stage the deposition was started when the first beds gypsum and anhydrite is appeared for the Fatha Formation refer to the restricted and supratidal environment. The uplifted of the eastern and northeastern parts of Iraq generate a tectonic depositional ridge to the west and northwestern resulted in the formation of restricted basins and regional regression in the Arabian plate. 1410 تكويني المتضمن المدروس التتابع ترسب يبي جر و الفتحة في ثالث ية صخر سحنات لتكوين يبي جر و بعة ار لتكوين الفتحة أدناه مبين ىو كما ، : تكوين يبي جر ؛ (بيئة اكي الو و الطيني الجيري الحجر سحنة يتضمن محجوز شبو ة الجيري الحجر سحنة و) المتدلمت المرصوص الجيري الحجر و المفتوح) الضحل البحر (بيئة الميميوليدي المرصوص و اكي الو (الغون). بينما يتضمن تكوين الفتحة سحنة المرصوص و اكي الو الجيري الحجر بطنيات ات لمكسر الحامل ية تبخر (بيئة الكتمي الجبس و (الغون) المرصوص البمويدي الجيري الحجر سحنة و ة) محجوز (بيئة القدم ية). التبخير المدية فوق (بيئة قق المتر الجبس ضحمة)و لمترسيب احل مر ثالث اظير المدروس التتابع سحنات تحميل ان :-مرحمة تمثل األولى المرحمة البحري التقدم المدروسة. المنطقة في النيائي حيث ظير السحنات تتابع ت ية الجير الصخور بتدلمت وخصوصا ، االعمى نحو تضحل النخفاض كمؤشر بشكل البحر سطح مستوى يجي تدر يبي. الجر من االول النصف بعد الثانية المرحمة في الترسيب من يت األنييدر و الجبس من طبقة أول ظيور عند لتكوين الفت حة التي و تشير البيئة إلى المدية فوق و ة المحجوز. تفاع ار ان و اق العر شرق وشمال شرق تكون الى ادت التي من اجز حو بي الغر الشمال و الغرب إلى التكتونية اسب الرو سبب في لمبحر اقميمي اجع تر و محجوز حوض تشكل الى ادى بية العر الصفيحة. Introduction The latest Eocene-Recent Megasequence is associated with collision of Neo-Tethyan terrains along the north and east sides of the Arabian plate, and the opening of the Gulf of Aden and red sea on the south and west sides of the plate. The opening of the red sea and Gulf of Aden was associated with thermal uplift, flood basalt, and rifting. The opening of Gulf of Aden was end first in Oligocene time followed by the Red Sea opening in the early Miocene (Makris and Henke,1992 and Hughes and beydoun,1992 in [1]. The north and northeast drift of Arabia and the closure of the Neo-Tethys resulted in folding and thrusting of the neo-Tethyan terranes along the new margin of the Arabian plate [1]. This Megasequence is subdivided in to three sequences of latest Eocene-Oligocene, Early-Middle Miocene including the Ghar, Euphrates, Serikagni and Dhiban formations, and the Late Miocene-recent age is including the Jeribe and Fatha formations (Figure-1) [2]. The latest two subdivisions are the more important in the present study, because of the expected succession in the studied area is within these cycles. The area of study situated in the Zurbatiyah area to the north of studied area at N33°23'55.99" E45°58'22.23" about 31 km northeast of Badrah city to the southeast of Baghdad (Figure-2). This area lies within the Zagros foreland basin, bordered on the northeast by the Zagros mountains and on the southeast by the Arabian shield, and consists of linear and high-amplitude folds that trend in a northwest-southeast direction. The aim of the present study is the sedimentology and basin development of the Jeribe and Fatha Formations by using the field observations and microfacies analysis.
... Moreover, bioclastic grains are commonly occurred. These features can be compared with Wilson's (1975) standard facies belt-4 which suggested accumulated on the foreslope environment. Lithoclastic-bioclastic packstone also indicates that the sediments accumulated on the foreslope of the shelf platform. ...
... These sediments accumulated at the top of slope carbonate producing shelf from material derived from the shelf. These features can be compared with Wilson's (1975) standard facies belt-3 which suggested accumulated on the basin margin. The strata in basin margin facies association are chiefly thin, well segregated carbonate mud with minor interbeds and some siliceous materials (Win Naing, 1989). ...
... Hallock & Glenn (1986) showed that large foraminifera can be used as depositional environment based on their research in the northwest of Palawan Island, Philippines on 1985. This method based on the test morphology and distribution of large foraminifera which refers to carbonate facies classification by Wilson (1975). ...
... Porosity calculation shows poor to very good classification, with value ranging from 5 to 25% (Figure 10 4. Based on petrographic thin section analysis, the porosity of the sample shows poor to very good classification (ranging from 5% to 25%). Wilson (1975) by Hallock and Glenn (1986) based on the foraminifera. ...
Bulu Formation is part of North East Java Basin that has widespread distribution especially in the North Rembang Anticlinorium. This formation composed of larger foraminifera limestone and fossiliferous sandy limestone which was deposited during Middle Miocene to Early Late Miocene time (N13-N15). This paper focuses on heterogeneity of large foram organisms and their porosity, implication for determining depositional facies. This study uses outcrop data and petrography analysis to determine the species of large foraminifera as well as calculating visible porosity. Large foram is clustered into three groups based on shell test character, the first group consists of Amphistegina and Miogypsina, the second group consists of Cycloclypeus, Lepidocyclina, Operculina, Heterostegina, and plankton, whereas the third group consists of Alveolinella, Flosculinella, Calcarina and Amphistegina. Porosity calculation shows poor to very good classification, with value ranging from 5 to 25%. Large Foram is used to analyze the depositional environments based on the shell shape, genus and quantity. The analysis showed that the Formation of Bulu in the research area is deposited in open-shelf facies and toe-of-slope facies. Open-shelf facies is characterized by genus Amphistegina, Cyclolypeus, Miogypsina, and Lepidocyclina. Toe-of-slope facies is characterized by genus that is similar to open-shelf facies but dominated with Cycloclypeus genus. The abundance of the certain organisms could be an indication of depositional environment of the organism.
... hetrohelix reussi and rugoglobigerina rugosa (Figure 3‐1), as well as; milliolids, Gastropoda, Ostracoda and Echinoderms. The last one refer to marine environment of 30‐40% salinity (Figure 3‐2) (Wilson, 1975) the non‐skeletal grains were: pellets and cortoid which graded from high energy area to low energy area (Fluegel, 2010). The presence of deep water planktonic foraminifera with the shallow marine cortoids refers to the interaction between these two environment continuously (Greiner, 1970) the important minerals of this bed are rhombic dolomite scattered at the micrite matrix and also presence of pyrite at the foramineferal chamber (Figure 3‐3) mentioned chamber represents suitable authigenic environment for the pyrite mineral deposition due to the available of organic matter which make alkaline and reducing environment to form the best condition of pyrite recrystallization (Siesser, 1967). ...
... mm (Figure 4‐4). Crystal size coarsening upward refers to more intensive digenetic processes (Wilson, 1975) and high porosity resulted from late dolomitization processes under supratidel environment due to fossil disappear. ...
Mauddud formation has been studied petrographically Southern Iraq in Ansab well KH‐6. A total of 90 thin
sections of mineral composition and fossils content were studied. Rock units of this formation were subdivided
into 5 beds. The main digenec processes were recrystallizaon, fossil chambers filled by cement and
dolomitization process.
Keywords: Mauddud Formation, Subsurface, Sedimentology, Iraq.
... These microfacies have been interpreted as formed in dominantly shallow subtidal lagoon setting with open to moderate circulation and locally developed intertidal/supratidal environments. Most microfacies are comparable with Wilson's (1975) Standard Microfacies Types (SMFT) and/or with Givetian microfacies described from the eastern part of the Moesian Platform, as well as with other shallow-marine Devonian successions from Europe. Andreeva, P. 2016. ...
... Most of the identified microfacies types were compared with the classical microfacies scheme created by Wilson (1975), and expanded by Flügel (2004), and/or with Givetian microfacies described from the eastern part of the Moesian Platform, as well as with other shallow-marine Devonian successions from Europe. ...
Seven carbonate microfacies types (MFT 1–7) have been distinguished and described in the Givetian dolomite formation from the Totleben-2 well (Moesian Platform, central North Bulgaria). They have been grouped in three microfacies associations: 1) shallow subtidal microfacies with open circulation (MFT 1, coral-stromatoporoid floatstone/rudstone; and MFT 2, brachiopod floatstone/rudstone); 2) protected shallow subtidal microfacies (MFT 3, intraclastic-ooidal packstone/grainstone; MFT 4, palaeosiphonoclad wacke-stone/packstone; and MFT 5, bioclastic-peloidal packstone/grainstone); 3) intertidal-supratidal microfacies (MFT 6, fenestral microbial bindstone; and MFT 7, mudstone to packstone with Palaeomicrocodium). These microfacies have been interpreted as formed in dominantly shallow subtidal lagoon setting with open to moderate circulation and locally developed intertidal/supratidal environments. Most microfacies are comparable with Wilson's (1975) Standard Microfacies Types (SMFT) and/or with Givetian microfacies described from the eastern part of the Moesian Platform, as well as with other shallow-marine Devonian successions from Europe. Andreeva, P. 2016. Givetian carbonate microfacies from the Totleben-2 well (Moesian Platform, central North Bulgaria). Geologica Balcanica 45, 21–31.
... The Lower Carboniferous carbonate-dominated strata of the Western Canada Sedimentary Basin (WCSB) were deposited on carbonate ramps and poorly differentiated carbonate platforms (Fig. 9). Following Richards et al. (1993Richards et al. ( , 1994), the concept of a carbonate ramp used here is basically that of Wilson (1975), who derived his model largely from that of Ahr (1973). Ahr considered a ramp to be a two-dimensional surface, whereas Wilson interpreted it as a body of carbonate strata. ...
... Carbonate platforms are large buildups that have a more or less horizontal top (shelf) and relatively abrupt shelf margins, where sediment deposited in high-energy environments occurs (Wilson, 1975). On platforms, the shelf margin is separated from the main shoreline by a broad, relatively low-energy, protected-shelf environment, where carbonates are deposited in the neritic and intertidal zones. ...
... Most of these bioclasts were underwent a recrystallization that distorted their original structure. The presence of the various kinds of fossils, glauconite and very fine quartz grains indicate a subtidal marine environment below the wave base (Wilson, 1975 andHottinger, 1997). ...
... The bioclasts are belonging to different types of organisms. The oolites need warm conditions and shallow depths to be formed (Wilson, 1975 andFlugel, 1982). The presence of oolites with rounded bioclasts at the end of shallowing upward cycles may suggest high agitation of water. ...
The Turonian sediments at Wadi Askhar (south eastern part of the Northern Galala Plateau) are represented by Wata Formation. Lithologically, the Wata Formation consists of marl, marly limestone and dolomitic limestone with occasional sandstone and shale interbeds. The petrographic studies of the different rock types of the Turonian Wata Formation revealed that the limestone comprise lime-mudstone; sandy wackestone, bioclastic packestone and sandy oolitic grainstone. Dolostones are composed of dolomicrite and dolosparite. The sandstones are represented by quartz arenite. The most common diagenitic features are; cementation, recrystallization, dolomitization and dedolomitization. Dolomitization represents the most important diagenetic process affecting the different studied rock types. On the basis of petrographic investigation; geochemical analysis and isotopic detection of δO 18 and δC 13 the dolomites were formed under mixed (marine-meteoric) waters. The depositional pattern of the Turonian (Wata Formation) lithofacies had revealed a deposition in a shallow water (intertidal to subtidal) environment. INTRODUCTION Wadi Askhar located in the northeastern side of Wadi Araba (south of the Northern Galala) on the western side of the Gulf of Suez between Lat. 29 o 02 \-29 o 15 \ N and Long. 31 o 40 \-31 o 53 \ E (Fig. 1). Generally, the Turonian sediments in the north Eastern Desert and in the western side of the Gulf of Suez are conformably underlain by the Cenomanian Galala Formation and overerlain by the Senonian Matulla Formation. They are represented by two distinct formations, the Abu Qada Formation at the base and the Wata Formation at the top (Said, 1990). Moreover, the facies of the Wata Formation changes northwards at Gabal Ataqa where it consists essentially of dolostone and named "Maghra El-Hadida" Formation (El-Akkad and Abdallah, 1971). Also, the Turonian sediments are represented in neighboring areas in Sinai by three distinct formations; Abu Qada, Buttum, and Wata formations (Issawi et al., 1999). The Wata Formation measures about 90 m thick at the studied area. It is exclusive1y composed of limestone and dolostone with shale and sandstone intercalations in the middle part. The age assignment of the Wata Formation was dated back and fixed to Turonian age according to Ghorab (1961); Cherif et al., (1989) and Orabi (1992).
... Interpretation: these facies associations indicate a reefal carbonate shelf setting that includes lagoonal back reef, inner platform, reefal area (including reef flanks and/or slope apron), reef core and forereef environments (Schlager, 2005;Wilson, 1975). This is supported by microfacies analysis which also indicates a reefal environment. ...
Collision between Australia and SE Asia began in Sulawesi, the world’s eleventh‐largest island, in the Early Miocene and subsequently Neogene sediments were deposited largely in coastal to shelf environments throughout the island. These sediments have been assigned to the Celebes Molasse, previously considered as a single post‐orogenic unit deposited unconformably on pre‐Neogene sedimentary, metamorphic and ophiolitic rocks. The most complete and extensive sequences of Neogene sediments are in the Kendari Basin, situated at the southern end of the SE Arm of Sulawesi, where an outcrop‐based sedimentological study was undertaken to interpret depositional environments, palaeogeography and stratigraphy. The oldest Neogene sediments are shallow marine carbonates and deltaic siliciclastics of the Bungku Formation. They are unconformably overlain by the Upper Miocene Pandua Formation which consists of sediments deposited in a variety of environments including braided river channels, fluvio‐tidal channels, tidal flats, mouth bar complex and shoreface deposits. A Mio‐Pliocene subaerial unconformity separates the marginal marine serpentinite‐rich sediments of the Pandua Formation from the overlying fluviatile quartz‐rich Langkowala Formation. The sediments of the lower part of the Langkowala Formation include conglomeratic channel fill, whilst the sediments of the upper part are transgressive deposits decreasing in maximum grain‐size, marked by a reduction in channel/overbank ratio and increasing tidal influence. The transgressive Pliocene Eemoiko Formation is characterised by transgressive lags or onlap shell beds and deposits of a landwards‐backstepping carbonate platform. The improved understanding of the Kendari Basin will aid the interpretation of the sedimentation history of frontier basins surrounding SE Sulawesi, many of which have not yet been drilled.
... Fossils chamber filled by cement or micrite (plate 2-3) and sometimes by pyrite (plate 2-d). Carbonate mudstone characterized by the lack of fossils due to the high amount of clay materials which prevents production of organic carbonate (Wilson, 1975). This facies similar to the standard facies (S. ...
Microfacies Analysis of Shiranish Formation
At Hijran Section- NE Iraq
Saadi K. Jan*, Aqeel A. Al- Zubaidi*, Salam I. Al- Dulaimi**
*Natural History Research Centre and Museum, University of Baghdad.
**Department of Geology, College of Science, University of Baghdad.
Abstract:
Shiranish Formation (Late Campanian- Maastrichtian) that cropping out north east Iraq, is studied by microfacies analysis of 52 thin section collected from Hijran Section, about 10 km west Shaqlawa Town, Governorate of Erbil. According to petrography, mineralogy and organic contents, rocks are subdivided to crystalline carbonate and microfacies units (biowackstone, packstone, and mudstone facies). Biowackstone facies have high ratio of the rock components, while the other facies have low ratio. Microfacies analysis led to relatively quiet deep marine environment.
Key words: Shiranish, microfacies, deep marine, environment, NE Iraq.
السحنات الدقيقة لتكوين شيرانش مقطع حجران
شمال شرق العراق
سعدي خان جان* ، عقيل عباس الزبيدي* ، سلام اسماعيل الدليمي**
*مركز بحوث ومتحف التاريخ الطبيعي ، جامعة بغداد .
** قسم علم الارض ، كلية العلوم ، جامعة بغداد .
المستخلص:
درس تكوين شيرانش ( كامبانيان متأخر- ماسترختيان ) الذي تنكشف صخوره في شمال شرق العراق ، بطريقة تحليل السحنات الدقيقة بعد تحضير 52 شريحة صخرية ، جمعت من مقطع حجران الذي يبعد 10 كم عن مدينة شقلاوة في محافظة اربيل . استناداً الى الصخارية ، والمعدنية ، والمحتوى الحياتي قسمت طبقات صخور التكوين الى صخور جيرية متبلورة و سحنات دقيقة ( سحنة الحجر الجيري الواكي الحياتي ، وسحنة الحجر الجيري المرزوم، وسحنة الحجر الجيري الوحلي )؛ واشار تحليل السحنات المجهرية الدقيقة للتكوين الى انه ترسب في بيئة بحرية عميقة هادئة نسبياً.
... Micro porosity is most common in the mud-dominated facies, such as the burrowed wackestone and the algal wackestone (Wilson, 1975;Moshier, 1987Moshier, , 1989aBudd, 1989). ...
The present study deals with the computerized well logging analysis for Raha Formation, using eight wells scattered in Ras Budran Field in the Gulf of Suez. This study was done utilizing different types of open-hole well logs such as: gamma-ray, density, and resistivity. The considered wells don't produce from the Raha Formation although it has suitable amount of oil with good values of the different petrophysical parameters. This is related to the absent of effective porosity which is considered in this paper through the discrimination of effective from ineffective porosity by using resistivity logs. These logs are considered as the most useful and helpful tool in detecting high effective porosity zones.
... This Pleistocene formation serves as a reference example for comparison to Holocene sand units in the Bahamas, and more importantly, subsurface examples in the geological record. Continued interest in modern and outcrop analogues for carbonate sand reservoirs is warranted based on the substantial number of carbonate reservoirs that produce from grainstones and packstones, for example reservoirs described by Wilson (1975), Harris (1984), Roehl & Choquette (1985), Keith & Zuppann (1993) and Harris & Weber (2006). The spatial variability of depositional environments and early diagenetic overprint that potentially create reservoir heterogeneity within a carbonate sand system can be observed in outcrops of the Miami oolite. ...
Exposures of the Pleistocene Miami oolite in South Florida provide excellent examples of preserved primary sedimentary features and subsequent diagenetic changes of a ‘fossilized’ ooid sand body that has been subaerially exposed in a tropical climate since its deposition during the last interglacial highstand – Marine Isotope Stage 5e. Using a robust airborne LiDAR (light detection and ranging) digital terrain model and select outcrops, a detailed analysis of the morphologies and dimensions of the different portions of the Miami oolite was conducted. The sand body, extending 95 km north to south and approximately 15 km wide, consists of shoals (or bars) separated by tidal channels and is partly bounded on the ocean-facing side by a prograding barrier bar that collectively cover an area of approximately 1000 sq. km. Results of the quantitative interrogation of the Miami oolite are compared with those of Harris et al. (2011) from modern sand bodies on Great Bahama Bank including the Exumas, Schooners Cays and Tongue of the Ocean. Digital terrain models developed for these modern sand bodies on the Great Bahama Bank and the ancient Miami oolite were used as the basis for the definition of shoals, shoal crests (peaks) and channels which were examined with respect to their size, shape and orientation. The Exumas sand body is the best morphometric match when analysing the bars and the channels, and the Joulter Cays area is an analogue for the formation of the barrier bar and for burrow reworking of cross-bedding within stabilized sand shoals. The Exumas is a particularly compelling analogue for the Miami oolite with respect to length and overall visual comparison between the morphologies of the sand bodies, shoal (or bar) shape, number of tidal channels, channel length and width, and high areas parallel to the strike trend of the sand body (islands in the Exumas and possible islands as part of the Miami oolite barrier bar). Despite ca 115 kyr of subaerial exposure and meteoric diagenesis including karst, the morphology of the Miami oolite is still relatively intact to the point where it can be easily analyzed and meaningful comparisons to modern systems can be made. The Miami oolite serves as a key reference example for comparison to Holocene sand units in the Bahamas – it validates the concept of comparative sedimentology and in particular emphasizes how results from the modern can improve the interpretation of a fossilized example. This article is protected by copyright. All rights reserved.
... These waves are among one of the mechanisms which are responsible for supplying abundant siliciclastic materials to the sea, mixed with the deposition of carbonate (Koeshidayatullah et al., 2016 ). Another mechanism that contributes to the existence of clastic content is coastal dunes and beach sands reworked in the foreshore environment (Wilson, 1975; Al-Ramadan, 2014). Several authors have investigated modern foraminifera from different parts of the Arabian shallow shelf. ...
Four outcrops along a west to east transect in the Al Lidam escarpment of Saudi Arabia were investigated to understand the vertical and lateral distribution of foraminiferal assemblages for paleoenvironmental reconstruction. The samples were processed using the standard acetic acid method, which extracts foraminifera from llithified carbonate rockswithout destroying the fossil content. The foraminiferal assemblages fromthe DamFormation are dominated by calcareous porcelaneous Miliolina (Quinqueloculina, Peneroplis, Triloculina, Cornuspira, Sigmoilinita, Coscinospira, Spirolina, Pyrgo, Borelis), followed by hyaline genera (Elphidiumsp., Ammonia, Cibicides, Discorbinella) and a minor percentage of agglutinated forms, e.g., Textularina.
The high percentage of calcareous porcelaneous taxa and the absence of planktonic foraminifera indicate that the DamFormation was deposited in a restricted carbonate platform environment, very shallow hypersaline shallow marine, gently sloping ramp (inner ramp to mid ramp) which ranges from supratidal to subtidal with local reef patches towards the basin. The formation was deposited in an arid subtropical climatic environment with water temperatures ranging from20 to 35 °C. Based on the observed assemblage composition, the present day Arabian Gulf can be considered as a modern analogue for the Dam Formation during Miocene times.
... To the south and west of our study area, the Hartselle Sandstone is a quartzarenite up to 50 m thick (Raymond et al., 1988 ) that was likely deposited as a series of northwest oriented, shallowmarine barrier island complexes (Thomas and Mack, 2013). , Pray, 1961; Wilson, 1975; Lees and Miller, 1995 ), Chesterian organosedimentary structures are comparatively rare in shallow marine regions surrounding the Black Warrior basin (Thomas, 1972; Andronaco 1986). Previous work by Merkel and Haywick (2001) identified only 10 small mounds across all the outcrops they examined in the Bangor Limestone, the largest a coral-microbial biohermal complex near Moulton, Alabama (Fig. 1 ). ...
Chesterian (Mississippian) strata in northern Alabama comprise a mixture of shallow marine carbonate and siliciclastic units. Monteagle Limestone consists primarily of medium-to thick-bedded skeletal grainstone consisting of oolitic intervals and thin len-ticular layers of green-gray calcareous shale. The Hartselle Sandstone is mostly quartzarenite in north-central Alabama, but toward the northeast, near its stratigraphic terminus 30 km east of Huntsville, Alabama, Hartselle-equivalent strata consist primarily of shale with thin skeletal limestone and calcareous sandstone interbeds. We studied four sections along U.S. Highway 72 that cut through the Monteagle-Hartselle interval in this region in order to resolve the petrography and faunal characteristics of these strata. Monteagle Limestone is dominated by skeletal grainstone enriched in echinoderm and bryozoan debris. Some allochems are oolitically coated. Parallel-laminated to low-angle cross-laminated oolites occur locally. Two intervals are marked by prominent color variation and lenses of green-gray calcareous shale. Dolomitized intervals, some pervasive, are found in all of the outcrops. Portions of the Monteagle contain well-sorted sub-rounded dolomite clasts, which likely originated from erosion of dolostone during synsedimentary subaerial exposure. The Hartselle-equivalent interval consists of tan/ brown to gray-black bituminous and fossiliferous silty shale with interbedded lenticular to channelized skeletal grainstone beds. Brachiopods and crinoids are common in both rock types, but limestone strata also contain bryozoans (including Archimedes and rare rugose corals. Microbial colonies coat many of the skeletal allochems and form one small buildup atop limestone at the base of the Hartselle-equivalent interval. Two smaller mounds were found within dolostone intervals in the Monteagle. Lithofacies relationships between the four sections suggest that the Monteagle Limestone was deposited as a series of carbonate shoals and that calcareous shale might have formed in slightly deeper water intershoal areas. Hartselle-equivalent shale was deposited in shallow water in advance of a prograding siliciclastic wedge derived from the southwest, but interdigita-tion with carbonate lithofacies was common. Shallow marine carbonate sedimentation (Bangor Limestone) resumed domination on the platform soon after deposition of the Hartselle.
... Anticlines are considered to belong to oil and gas traps and the majority of oil and gas stores are located in these oil traps (Wilson, 1975). Accordingly, identification of oil traps is crucial the growth strata analysis is effective in identifying these oil traps (Soleimany and Sabat, 2010). ...
The growth strata in the Middle-Late Cretaceous deposits including Kazhdumi, Sarvak and Ilam formations and Lafan Shale in the Well 1 located between Qatar-Iran height and Hormuz Strait in Persian Gulf was studied. The present work is based on the lithostratigraphic analysis and distribution of microfossils. Based on the microfossils content, the age of studied successions is Albian to Campanian. Comparison of seismic points, lithostratigraphic analysis and distribution of microfossils show that growth and generation of anticlines are occurred in the Middle-Late Cretaceous. As of results, the Kazhdumi, Sarvak and Ilam formations and Lafan Shale have potential reservoir and oil trap.
... nated forms (orbitolinids, Nezzazata, Charentia, Praechrysalidina and Marssonella) are representative of relatively low turbulent water and circulation and abundant carbonate mud in a partially protected lagoon (Wilson 1975; Geel 2000; Sudar et al. 2008; Flügel 2010). The dominance of miliolids (Figure 4) suggests limited circulation and probably euryhaline conditions or decreased oxygen level in a shelf lagoon setting (Brandano et al. 2009; Sadeghi et al. 2011). ...
This study is focused on the depositional model and paleoenvironmental distribution patterns of orbitolinids-rich microfacies in an Upper Cretaceous carbonate succession in the Kuh-e Mazar anticline in Kerman Province, Central Iran. Twelve microfacies indicating a tidal flat (including intertidal and supratidal) and an inner ramp (consisting of subtidal lagoon and orbitolinid–rudist barrier shoal) belonging to a shallow-water ramp-type carbonate platform were recognised. Generally, the orbitolinid associations in the carbonate ramp are indicative of shallow warm waters with normal salinity. The occurrence and abundance of thick or conical orbitolinids in both shoal and lagoon show that such associations were well adapted to different environmental conditions including different depth, substrate stability and water energy. The slightly discoidal, almost discoidal and discoidal forms were only present in the deeper depths of the environment including the lagoon with muddy and more stable substrates and lower water energy. However, the orbitolinids in the inner part of the carbonate ramp were scarce or almost absent in the deep inner to middle lagoon due to the deep restricted environmental conditions unfavourable for benthic marine life.
... During the Early Mississippian, epicontinental seas covered the entirety of Kansas, but the transition into the Late Mississippian records that epicontinental seas inundated only the western and southern portions of the state. During this period, an amalgamation of factors such as global paleoclimate, sea level change, and geochemical factors, along with optimal regional paleogeographic and tectonic conditions, resulted in extensive deposition of marine oolitic limestones across the continent of North America (Qi, et al., 2007; Wilson, 1975; Wilkinson et al., 1985; Handford, 1988; Ettensohn, 1993; Keith and Zuppann, 1993). These oolitic limestones make excellent reservoir facies, resulting in numerous producing fields across the Mid-Continent region. ...
... Reef-building organisms are generally preserved in situ and form primary reef frameworks that were filled and cemented by bioclasts and micritic matrix. Amphipora floatstone/packstone microfacies is the fourth microfacies identified and, represents a restricted back-reef depositional setting (Wilson, 1975). This microfacies indicates a progradational back-reef deposition seaward as the reef ceases to grow upwardly when the sea level is too high for reef development. ...
... Reef-building organisms are generally preserved in situ and form primary reef frameworks that were filled and cemented by bioclasts and micritic matrix. Amphipora floatstone/packstone microfacies is the fourth microfacies identified and, represents a restricted back-reef depositional setting (Wilson, 1975). This microfacies indicates a progradational back-reef deposition seaward as the reef ceases to grow upwardly when the sea level is too high for reef development. ...
Interior Fars region is an important geological province of Zagros basin due to historical events. The present paper focused on the time span of the Asmari deposition (Oligo-Lower Miocene) in Fars area bounded by Kazerun and Nezamabad faults. The studied samples of Asmari Formation were collected from 3 different stratigraphic sections A, B and C. The area is discussed in view of microfacies variation, sequence stratigraphy and environmental factors such as diagenetic processes and sea level changes. Microscopic studies led to identification 13 carbonate facies in this area. The results showed that the Asmari Formation has been deposited in a carbonate shelf in 5 sedimentary sub-environments including open sea, bar, lagoon, shoal and tidal flat. Basin changes were also compared with global sea level changes. Sequential stratigraphic evidence showed that the Asmari Formation consists of two sedimentary sequences of third order. The unconformity in the lower boundary of Asmari Formation with Jahrom Formation in sections-B and C can be ascribed to the result of Pyrenean orogenic phase activity in this area. The Asmari Formation in this area has been undergone extensively by diagenetic processes. Micriticization, dolomitization, cementation, hematitization, stylolitization, neomorphism and dissolution are among the important and noteworthy of diagenetic processes. The intensity of each process is a function of facies characteristics (fabric control). Microfacies data and sea level changes curve in local (the area), regional and global scales revealed that these facies are more correlated to the local sea level variation than others. The present study resulted to new main points related to the Fars basin evolution. Reactivation of faults (such as Kazerun and Nezamabad), regional sea level changes and Alpine orogenic phases impact (i.e., Pyrenean phase) have involved a major role in sedimentary facies distribution and basin evolution.
The Late Devonian‐Early Carboniferous deposits of the Anarak section in northeastern Isfahan, Central Iran, evaluated based on conodont biostratigraphy, sedimentary environment and sequence stratigraphy. According to the field observations, five lithological units were identified. Investigating the conodont fauna of the Late Devonian‐Carboniferous (Mississippian‐Pennsylvanian) deposits of Bahram, Shishtu, and Qaleh (Sardar 1) formations in Anarak section led to the identification of 67 species of 18 conodont genera, and accordingly 22 conodont biozones were differentiated. The correlation of sea‐level change curves, regarding to the conodont biofacies with the global sea‐level curve, demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins. The microfacies analysis led to the identification of 12 microfacies related to the open sea, bioclastic barrier, lagoon and tidal flat sub‐sedimentary environments in a homoclinal carbonate ramp environment. Based on sequence stratigraphy studies, three 3 rd order sequences were identified. The first sequence, which is of the Late Devonian (upper part of the Bahram Formation, 32.5 m), the second sequence (12.5 m) is the Late Devonian (uppermost part of the Bahram Formation), and the third sequence (68 m) is the Early Carboniferous (the Shishtu I Formation).
A late Kasimovian (Pennsylvanian) coral reef is reported in the Yanbanzhai (YBZ) area, southern Guizhou Province, South China. The YBZ coral reef, with a thickness of approximately 5.5 m and a lateral exposure of nearly 50 m, is primarily composed of the colonial rugose coral Fomichevella. The fusulinids collected from the reef indicates a late Kasimovian age. Five microfacies types have been identified, including coated bioclastic grainstone, coral (Fomichevella) framestone, bioclastic wackestone, bioclastic grainstone, and peloidal grainstone. The vertical evolution of the microfacies in the YBZ coral reef indicates major sedimentary environmental changes associated with relative sea-level changes. The growth of the reef-builder Fomichevella was controlled by the transgression and regression. Deep water promoted the upward expansion of Fomichevella, while shallow water inhibited its growth. Published records of atmospheric pCO2 estimation and sea-surface temperatures, combined with geochemical proxies, confirm a warm climatic period during the late Kasimovian. This is an interglacial period conducive to the growth of the coral reef. Sea-level and climate changes associated with the Late Palaeozoic ice age (LPIA) are interpreted as significant controls of the development of the YBZ coral reef. This research of the YBZ coral reef in South China provides practical palaeobiological evidence for global sea-level rising during the late Kasimovian period caused by the highlatitude Gondwana delaciation.
Detailed taxonomy and biostratigraphy of the limestone, shale‐rich Cretaceous Goru Formation within the western Sulaiman Range refer to diverse and well‐preserved planktonic foraminifera. The age‐diagnostic planktonic foraminifera encountered are; Biticinella breggiensis (middle Albian), Rotalipora ticinensis (late Albian), Rotalipora appenninica (latest Albian), Rotalipora brotzeni (early Cenomanian), Rotalipora cushmani (late Cenomanian), Whiteinella archeocretacea (latest Cenomanian–Earliest Turonian), Helvetoglobotruncana helvetica (early to middle Turonian), and Marginotruncana sigali (late middle to late Turonian). Based on the recovered planktonic foraminifera a middle Albian–late Turonian age has been assigned to the studied formation. The Rotalipora reicheli (middle Cenomanian) Zone was not identified as the First Appearance Datum of the nominal taxa present within the Rotalipora cushmani Zone. The planktonic foraminiferal assemblage characteristics suggest that the bioprovince of the Cretaceous Goru Formation belongs to the subtropical, warm water environment belonging to the Cretaceous Tethyan Realm and the palaeobiogeographic reconstruction suggests that the Neotethys was well‐connected during the Albian–Turonian time interval. This study focuses on the detailed taxonomy, biostratigraphy, correlation, and paleobiogeography of the Goru Formation in the middle Indus Basin of Pakistan. Based on the encountered planktonic foraminifera, the middle Albian‐late Turonian age is assigned to the Formation. The paleobiogeographic reconstruction suggests that the Neotethys was well‐connected.
The Hagen-Balve Reef Complex of the northern Rhenish Massif, Germany, is one of the best examples for the globally widespread Givetian to Frasnian reefs. At its eastern end, in the Hönne Valley, it reaches up to 1000 metres in thickness. In general, there is limited knowledge concerning the faunas and palaeoecology of Rhenish initial reef phases. A unique section at Binolen exposes the sharp boundary between the underlying, siliciclastic Upper Honsel Formation and the lower part of the reefal Hagen-Balve Formation. A ca. 14 m thick succession is assigned to the new Binolen Member and investigated in terms of carbonate microfacies, micro-, and macrofaunas. Seven Microfacies types (MF) characterise a crinoidal coral-stromatoporoid garden setting (MF-2 to MF-6) or allobiostrome of an initial open platform turning upsection into a coral parabiostrome (MF-7/8). The base of the Asbeck Member is locally defined by the appearance of back-reef facies types, such as fenestral limestones (MF9), which indicate the transformation into a bioherm. Low-diversity conodont faunas prove an influx of open shelf organisms for the Binolen Member and suggest a lower Givetian age (probably Polygnathus timorensis Zone). There are two new Givetian conodont biofacies types characteristic for open biostrome settings, the Bipennatus Biofacies and a Simple Cone Biofacies. Thin sections reveal over 40 different reef builders (rugose and tabulate corals, stromatoporoids, and chaetetid sponges). Around 4200 microfossils from conodont residues consist of agglutinating foraminifers, calcareous sponge spicules (e.g. Heteractinida), scolecodonts, echinoderms (mostly crinoid ossicles and holothurian sclerites), pyritised benthic ostracods, assumed calcified moulds of chitinozoans, subordinate microvertebrates, and other groups. They were analysed quantitatively in order to document changing distribution patterns and environments through time. We distinguish six microfossil-based biofacies types (BF), namely the Ostracoda Biofacies (BF-O), Foraminifera Biofacies (BF-F), Scolecodont Biofacies (BF-S), Chitinozoa Biofacies (BF-C), Porifera-Scolecodont Biofacies (BF-PS), and Porifera-Echinodermata Biofacies (BF-PE). Microfacies and microfossil assemblages led to a reconstruction of the local facies development, consisting of seven successive depophases with further subdivisions. At the base, the sudden termination of siliciclastic influx enabled a proliferation of reef builders and microfaunas (Depophase I), followed by a longer deepening phase characterised by exclusive bioclastic wackestones (Depophase II).
Depophase III is a short regressive phase with crinoidal coral-stromatoporoid floatstones. Depophase IV is characterised by fluctuations in facies and relative sea-level, which results in three subphases. Depophase V resembles Depophase III, but with argillaceous interbeds and more abundant scolecodonts. It is followed by an interval with coral-stromatoporoid rudstones, which grade into coral-dominated bafflestones of an (auto)parabiostrome (both Depophase VI). Depophase VII represent the back-reef
facies, including fenestral pack-bindstones of the basal Asbeck Member. The systematic analysis of reefal microfaunas represents pioneer work that should be tested and expanded to other reefs of the Rhenish Massif and beyond.
p>The provenance of coarse-grained detritus from the Upper Jurassic Corallian Group and Lydite Beds and Lower Cretaceous Purbeck Formation, Spilsby Sandstone Formation, Wealden Group, Claxby Ironstone Formation, Lower Greensand Group and Gault Clay Formation of southern Britain and Normandy (northern France) has been studied. The coarse-grained detrital suites contain extrabasinal phenoclasts derived from Palaeozoic and Precambrian massifs, and Jurassic and Cretaceous clasts from intrabasinal highs. The former assemblage is dominated by chert derived from Carboniferous limestones and quartz. Sandstones, radiolarian cherts and tourmalinites are locally abundant. The intrabasinal detritus is composed principally of chert, phosphorite and ironstone.Progressive changes in phenoclast suites provide a means for studying both local variations associated with uplift of intrabasinal structures and regional variations associated with basin development.Local variations in the intrabasinal pebble suites of Dorset provide evidence of major fault-associated uplift of the South Dorset High during earliest Cretaceous times. Post-faulting subsidence resulted in marine onlap and further erosion of the structure. The South Dorset High is structurally similar to other fault-associated highs in the Wessex and Paris Basins, and it is probable that they have all undergone extensive Early Cretaceous uplift in conjunction with basin rifting.The Upper Jurassic and Lower Cretaceous phenoclast suites of southern Britain and Normandy are separable into three stratigraphical assemblages. The oldest assemblage, Oxfordian to Early Berriasian in age, is dominated by chert derived from Carboniferous limestones. The two younger assemblages (Late Berriasian to Barremian and Aptian to Middle Albian) are distinguished by a generally higher proportion of quartz. The Aptian to Middle Albian phenoclast assemblage is separable into two subassemblages (Aptian and Lower Middle Albian) and the latter shows lateral changes which enable it to be divided into three geographical provinces and five subprovinces. In the Wessex Basin, a change from chert-dominated to quartz-dominated phenoclast suites occurred at the beginning of the Cretaceous System. This resulted from uplift and erosion of the marginal massifs adjacent to the rifting basin. On the East Midlands Shelf, however, modifications in the detrital suites did not occur until mid-Cretaceous times. The delayed change was caused by limited uplift of the adjacent massifs during Early Cretaceous times and reworking of slightly older pebble beds on the shelf. The marginal highs were then uplifted and eroded during the mid-Cretaceous phase of thermal subsidence in the Southern North Sea Basin.</p
The Upper Cretaceous Ilam Formation in southwest Iran was studied in order to provide a better understanding of the palaeoenvironments that lead to the deposition of heterogeneous carbonate rocks. This formation is an important hydrocarbon reservoir of the Bangestan Group in the Zagros Basin and the Abadan Plain. The Ilam Formation is comprised mainly of carbonate rocks and was studied from three subsurface sections (100, 74, and 100 m thick). Petrographic investigation reveals that the Ilam Formation consists of 12 microfacies and a shale petrofacies that were deposited in lagoonal, shoal, and open marine facies belts of a carbonate ramp. Two third–order depositional sequences are recognised. Comparison of Ni/Co reveals that the limestones of the Ilam Formation formed under oxic to anoxic conditions. The main diagenetic features of the Ilam Formation include compaction, dissolution, dolomitization and cementation that occurred in marine, meteoric and burial diagenetic environments. We document for the first time the relationship between facies and geochemistry in the carbonate rocks of the Ilam Formation. These findings provide a more comprehensive understanding of the palaeoenvironments that lead to the deposition of heterogeneous carbonate rocks and their relationship with geochemistry and reservoir characteristics.
The present study deals with the depositional facies, diagenetic processes, and sequence stratigraphy of the shallow marine carbonates of the Samanasuk Formation, Kohat Basin, to elucidate its reservoir quality. The Samanasuk Formation consists of thin to thick‐bedded, oolitic, bioclastic, dolomitic, and fractured limestone. Based on the integration of outcrop, petrographic, and biofacies analyses, the unit is thought to be deposited on a gentle homoclinal ramp in peritidal, lagoonal, and carbonate shoals settings. Frequent variations in microfacies based sea‐level curve have revealed seven Transgressive Systems Tracts (TSTs) and six Regressive Systems Tracts (RSTs). The unit has undergone various stages of diagenetic processes including mechanical and chemical compaction, cementation, micritization, dissolution, and dolomitization. The petrographic analyses show the evolution of porosity in various depositional and diagenetic phases. The fenestral porosity was mainly developed in peritidal carbonates during deposition while the burial dissolution and diagenetic dolomitization have greatly enhanced the reservoir potential of the rock unit that is further confirmed by the plug porosity and permeability analyses. The porosities and permeabilities were higher in shoal facies deposited in TSTs as compared to lagoonal and peritidal facies except for the dolomite in mudstone, deposited during RSTs. Hence good, moderate, and poor reservoir potential is suggested for shoals, lagoonal, and peritidal facies respectively.
Upper Devonian carbonates deposited through the Frasnian/Famennian (F/F) stage boundary in the Xom Nha Formation, Central Vietnam, were studied. The section is mainly composed of fossiliferous, brecciated, and laminated limestone beds, while shale beds occur in a subordinate number. Microfacies generally suggests a hemipelagic setting on an outer shelf environment with low sedimentation rates. A sediment accumulation rate of 0.217 cm/kyrs for this section is calculated. The Xom Nha section does not exhibit characteristic black shales or black limestones through the F/F boundary, but instead shows a similar lithology in comparison to other F/F sections in Southeast Asia. The carbonates yielded abundant conodonts, which represent mainly cosmopolitan species but the section differs from most sections in Europe in showing relatively high numbers of Palmatolepis linguiformis species. Deposition through the F/F boundary interval reported here for the Xom Nha section appears to have occurred during a~1.2 Ma, and shows well-defined climate cyclicity.
Two stratigraphic sections (Arjooieh and Firoozabad) of the Mymand anticline located in the Interior Fars sub‐basin of the Zagros mountains were measured and sampled in order to document sedimentological characteristics, microfacies types, and paleo‐seagrasses indicators of the Oligocene succession (Asmari Fm.). Planktonic and benthic foraminifera and coralline red algae are the principal fossils from these strata. Foraminifera are represented by the following families: Soritidae, Peneroplidae, Austrotrillinidae, Alveolinidae, Planorbulinidae, Discorbidae, Lepidocyclinidae, Amphisteginidae, Rotaliidae, Nummulitidae, and Globigerinidae. Nine microfacies types were recognized, namely planktonic foraminiferal‐peloidal packstone (MF1), bioclast nummulitid/Nerorotalia/Amphistegina packstone‐grainstone‐rudstone‐floatstone(MF2), Neorotalia‐echinoid coralline red algae packstone‐grainstone (MF3), coral boundstone (MF4), coral/coralline red algae rudstone‐floatstone‐packstone‐grainstone (MF5), diverse imperforate foraminifera bioclast packstone‐grainstone (MF6), pelloid wackestone‐packstone‐grainstone (MF7), fenestrated mudstone and microbial mats (MF8), and anhydrite (MF9). MF1 indicates on outer ramp, MFs 2–4 represent middle ramp, and MFs 5–9 are interpreted as inner ramp environment. Paleo‐seagrass indicators are consisting of foraminifera, hooked and tabular forms of coralline red algae, and corals. They were determined in MFs 5 and 6 reflecting the presence of vegetated environments within the middle‐inner ramp setting. The Mymand anticline was dominated by the outer ramp environment at the start of the Rupelian. Middle to inner ramp environments prevailed during the Rupelian. The Chattian was correspond to the spread of inner ramp setting over the Mymand anticline.
The Sarvak Formation is a carbonate sequence of the Late Albian‐Early Turonian age in Zagros Basin in Iran. In this investigation, the Sarvak Formation at the Pyun Anticline section (Izeh Zone) has been studied. It consists of limestone of 797m thick which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at Pyun Anticline. A very rich fossil association (85 genera and 132species) characterizes the Pyun section. Based on the stratigraphic distribution of diagnosed foraminifers, five biozones are established:1‐Muricohedbergella‐ Globigerinelloides sp. assemblage zone (Late Albian) 2‐Praealveolina iberica‐ Chrysalidina gradata interval zone (Early Cenomanian) 3‐Chrysalidina gradata‐ Cisalveolina fraasi (fallax) and C. lehneri interval zone (Middle Cenomanian)4‐C. fraasi (fallax) and C. lehneri ‐ Praetaberina bingistani assemlage zone (Late Cenomanian) 5‐Nezzazatinella picardi‐ Mangashtia‐ Dicyclina assemblage zone (Early Turonian). Based on the petrographic and sedimentology analyses, some 13 carbonate microfacies were identified. The investigated microfacies confirm ramp‐type paleoenvironment. These microfacies from distal to proximal environments consist of: MF1:Planktonic foraminifera wackestone–packstone, MF2:Oligostegina planktonic foraminifera wackestone to packstone, MF3:Planktonic‐benthic foraminifers sponge spicules wackestone‐packstone, MF4:Rudist floatstone, MF5:Rudist rudstone, MF6:Bioclast intraclast grainstone, MF7:Peloid intraclast grainstone, MF8:Benthic foraminifers rudist grainstone‐packstone, MF9:Peloid bioclast grainstone‐packstone, MF10:Bioclast (benthic foraminifers) wackestone‐packstone, MF11:Peloid bioclast packstone, MF12:Dacycladacea benthic foraminifera packstone‐wackestone, MF13:Miliolids wackestone‐packstone.
Shallow carbonate deposits (Tarbur Formation) were formed in the Zagros foreland basin with dynamic tectonics during the Maastrichtian age. From the viewpoint of reconstruction of depositional conditions in these deposits, studies of biostratigraphy, microfacies, microtaphofacies, and sequence stratigraphy were performed in a single area at Tang‐e Shabi Khoon, northwest of Zagros. Based on the identification of two assemblage zones consisting of benthic foraminifera in these strata, the formation was deposited during the middle to late Maastrichtian. The number of cycles in test size and type of coiling in Loftusia decreased from the study area toward the northwest of the Neotethys basin. The input of clastic sediments affected the distribution of Loftusia and rudists in the study area. Nine microfacies, six microtaphofacies, and one terrigenous facies (shale) were identified based on the sedimentary features. These deposits of the middle‐late Maastrichtian were deposited on a homoclinal carbonate ramp. The platform can be divided into restricted and semi‐restricted lagoon, shoal, and open marine environments. In the study area, the deposits of the Tarbur Formation were deposited during four third‐order depositional sequences. Local fault activities affected the formation of depositional sequences in the study area.
Two stratigraphic sections (Arjooieh and Firoozabad) of the Mymand anticline located in the Interior Fars sub‐basin of the Zagros Mountains were measured and sampled in order to document sedimentological characteristics, microfacies types, and paleo‐seagrasses indicators of the Oligocene succession (Asmari Fm.). Planktonic and benthic foraminifera and coralline red algae are the principal fossils from these strata. Foraminifera are represented by the following families: Soritidae, Peneroplidae, Austrotrillinidae, Alveolinidae, Planorbulinidae, Discorbidae, Lepidocyclinidae, Amphisteginidae, Rotaliidae, Nummulitidae, and Globigerinidae. Nine microfacies types were recognized, namely planktonic foraminiferal‐peloidal packstone (MF1), bioclast nummulitid/Nerorotalia/Amphistegina packstone‐grainstone‐rudstone‐floatstone(MF2), Neorotalia‐echinoid coralline red algae packstone‐grainstone (MF3), coral boundstone (MF4), coral/coralline red algae rudstone‐floatstone‐packstone‐grainstone (MF5), diverse imperforate foraminifera bioclast packstone‐grainstone (MF6), pelloid wackestone‐packstone‐grainstone (MF7), fenestrated mudstone and microbial mats (MF8), and anhydrite (MF9). MF1 indicates on outer ramp, MFs 2–4 represent middle ramp, and MFs 5–9 are interpreted as inner ramp environment. Paleo‐seagrass indicators are consisting of foraminifera, hooked and tabular forms of coralline red algae, and corals. They were determined in MFs 5 and 6 reflecting the presence of vegetated environments within the middle‐inner ramp setting. The Mymand anticline was dominated by the outer ramp environment at the start of the Rupelian. Middle to inner ramp environments prevailed during the Rupelian. The Chattian was correspond to the spread of inner ramp setting over the Mymand anticline.
The Middle Triassic succession of the Sichuan Basin contains key information about the early Indosinian Movement, during which it has changed from extensional to compressional. In order to clarify the relationship between the evolution of the Sichuan Basin during the Indosinian Movement, the Middle Triassic tectonostratigraphic environment should be determined. Detailed stratigraphy and facies analysis integrated with structural and basin analysis, allowing a full reconstruction of the tectonic and depositional environments for the Middle Triassic strata of the Sichuan Basin. Six facies associations from two rock systems of: (1) carbonate–evaporite system and (2) a mixed carbonate–siliciclastic system, were characterized. Four depositional stages highlighted by the lithostratigraphic members were divided: (1) stable subsidence and deposition of the Lei-1/Ba-1 Member, leading to an embryonic “uplifts and sags” configuration; (2) inherited deposition of the Lei-2/Ba-2 Member, with the platform margin belt extended; (3) rapid deposition of the Lei-3/Ba-3 Member, characterized by an eastward shift of the depositional center and formation of the central anhydrite-rich lagoon; and (4) intensification of cratonic tectono-sedimentary differentiation during the Lei-4/Ba-4 deposition, resulted in a subaerial exposure along the Luzhou–Kaijiang uplift zone and a hydrodynamically restricted depression along the western platform. The Middle Triassic tectonic framework of the Sichuan Basin was dominated by compression in the east and extension in the west. The western margin was a passive continental margin, inheriting an early rifting event, while the eastern area within the craton showed an “uplift-sag” pattern, which is a response to intracontinental tectonic movement of the Xuefengshan uplift belt. The basin evolved from incipient low-relief uplifts and sags within the intracratonic depression to subsequent isolated foreland and restricted depression during the Middle Triassic.
Prediction of carbonate distributions at a global scale through geological time represents a challenging scientific issue, which is critical for carbonate reservoir studies and the understanding of past and future climate changes. Such prediction is even more challenging because no numerical spatial model allows for the prediction of shallow-water marine carbonates in the Modern. This study proposes to fill this gap by providing for the first time a global quantitative model based on the identification of carbonate factories and associated environmental affinities. The relationships among the four carbonate factories, i.e., “biochemical”, “photozoan-T”, “photo-C” and “heterozoan-C” factories, and sea-surface
oceanographic parameters (i.e., temperature, salinity and marine primary productivity) is first studied using spatial analysis. The sea-surface temperature seasonality is shown to be the dominant steering parameter discriminating the carbonate factories. Then, spatial analysis is used to calibrate different carbonate factory functions that predict oceanic zones favorable to specific carbonate factories. Our model allows the mapping of the global distribution of modern carbonate factories with an 82% accuracy. This modeling framework represents a powerful tool that can be adapted and coupled to general circulation models to predict the spatial distribution of past and future shallow-water marine carbonates.
Facies and microfacies of the Tithonian-Berriasian ramp from the Neuquén basin (Vaca Muerta Formation) in the Loncoche creek sect- ion - Malargüe, Mendoza. Facies association of the Tithonian-Berriasian Vaca Muerta Formation from the Loncoche creek sec- tion, Neuquén Basin, west central Argentina, allow the distinction and definition of 12 lithofacies and 8 microfacies, which are dominated by molluscs, echinoderms, foraminifera, brachiopods, serpulids and radiolarians. The Vaca Muerta Formation con- sists of a rhythmical alternation of black shales, grey shales, marls and siltstones, with bioclastic mudstones, wackestones, packs- tones, floatstones and rudstones. Facies associations corresponding to four types of depositional settings were distinguished: basin, outer ramp (distal and proximal), and middle ramp. The Nassellaria/Spumellaria ratio was used for bathymetrical inter- pretation and allows an estimation minor than 200 m depth. The strata pattern and vertical facies distribution show three depo- sitional sequences between a tithonian homoclinal ramp and a berriasian steep homoclinal ramp system. The depositional sequence 1 consists of basin and distal outer ramp facies and it is characterized by a retrogradational pattern. It reaches 124 m in thickness, and may be assigned to the Virgatosphinctes mendozanus Zone up to the base of Corongoceras alternans Zone. Depositional sequences 2 and 3 consist of outer ramp and middle ramp facies. They are characterized by agradational and pro- gradational patterns. The thickness of the sequences 2 is 66 m and is assigned to Corongoceras alternans Zone, meanwhile sequen- ce 3 reachs 78 m and corresponds to Substeueroceras koeneni and Spiticeras damesi zones.
Abstract
Microfossils from an outcrop of the Garagu Formation at Gara Mountain, Duhok Governorate, Kurdistan Region, Northern Iraq,
indicate a shallow marinewith normal to hypersaline conditions, shelf lagoonal environment, and open platform. Twenty samples
were collected from unbroken succession of the Garagu Formation. The thickness of the succession is 90mand it consists mainly
of different colored limestone beds with different fauna contents. The lower boundary with a gradational and conformable nature
is with Chia Gara Formation (Tithonian-Berriasian) and the upper boundary is gradational with Sarmord Formation (Valanginian-
Aptian). The microbiota associations are mostly composed of species of foraminifera, ostracods, calcareous algae, and coral, with
dissociated elements and skeletal fragments of gastropods, pelecypods, bryozoans, sponge spicules, crinoid debris, and
echinodermata spines. Sixty species are recorded in this study; the combined stratigraphic ranges of the microfossil species
identified from the studied section of the Garagu Formation support an age determination of the Late Valanginian-Barremian.
Keywords Microfossils . Garagu formation . Early Cretaceous . Systematic description . Duhok . Kurdistan . Iraq
The lowermost carbonate beds of the Cerro San Pedro (San Pedro de la Cueva, Sonora State, Mexico) previously assigned to the Mississippian, belong in fact to the lower Ordovician. The limestone of this succession is often dolomitized and chertified, and displays gastropods, pelmatozoans, sponges, and trilobites as major bioclastic components. The different microfacies show that high-energy grainstones, proximal tempestites, and distal tempestites dominated the sedimentation. The paleoenvironments of deposition correspond to an inner ramp, a mid-ramp, and perhaps the upper part of an outer ramp. The strata are characterized by the incertae sedis cyanobacteria Nuia sibirica. A taxonomic revision and discussion of these cyanobacteria, often confused with ooidic grains, is emphasized. Some data are presented on other microfossils, such as primitive, monothalamous foraminifers: Rauserina sp., Vicinesphaera sp., and Neoarchaesphaera sp., leperditicopida and their endolithic microperforations, and primitive chaetetids. Compared to the contemporaneous deposits of the USA, some paleobiological components, e.g., the lithistid siliceous sponges Archaeoscyphia, stromatoporoids? Pulchrilamina, and receptaculacean algae Calathium, are quite rare in the studied section of Sonora, but the predominance of tempestites in the carbonate succession shows that boundstones formed before were systematically eroded and resedimented. The paleogeographic implications are the following: (1) a lower Ordovician intertropical Nuia Province is newly defined in the western part of the lower Ordovician intertropical belt; (2) San Pedro de la Cueva constitutes one of the westernmost outcrops of this new Nuia Province; (3) from Sonora, Nuia extends eastward as far as South China; (4) due to its westernmost paleoposition, San Pedro de la Cueva was frequently affected by tropical storms; and (5) northern lower Ordovician terranes of Mexico (Sonora, Chihuahua, and Baja California) are entirely distinct from the southern ones (Oaxaca). The paleopositions and paleogeographic connections of these northern Mexican terranes with Laurentia, Avalonia, and peri-Gondwanan parts of South America, through the Iapetus and Rheic oceans, still remain disputable or unknown.
Microporosity in carbonate reservoirs is generated by the complex interplay between depositional and diagenetic processes. This petrographical, SEM, fluid-inclusion and isotopic study of a Lower Cretaceous carbonate reservoir, Abu Dhabi, UAE, revealed that: (1) micritization of ooids and skeletal fragments, which resulted in spheroidal (rounded) micrite, accounts for most microporosity in peloidal packstones and grainstones; and (2) transformation of spheroidal micrite into subhedral/euhedral micrite and microspar, known as aggrading neomorphism, could happen via precipitation of syntaxial calcite overgrowths around micrite (micro-overgrowths) and not only, as suggested previously in the literature, by recrystallization involving the dissolution (of micrite) and reprecipitation (of microspar). Precipitation of calcite cement around micrite (i.e. destruction of microporosity) is more extensive in the water zone than in the oil zone, which is possibly contributing to the lower porosity and permeability of the carbonate reservoir in the water zone. Similarity in bulk oxygen isotopic values of micritized packstones and grainstones in the water and oil zones (average δ 18OV-PDB = -7.2% and -7.8%, respectively) is attributed to: (1) a small difference in temperatures between the crest (oil zone) and the flanks (water zone); and (2) calcite precipitation around micrite occurred prior and subsequent to oil emplace¬ment. Bulk carbon and strontium isotopic compositions of micritized packstones and grainstones in the water and oil zones (average δ 13CV-PDB = +3.7% and average 87Sr/86Sr ratios = 0.707469) indicate that calcite cement was derived from marine porewaters and/or dissolution of the host limestones. The minimum formation temperatures of bulk micrite/microspar, which are inferred based on paragenetic relationships, fluid-inclusion microthermometry and oxygen isotope data, are around 58–78°C.
ResearchGate has not been able to resolve any references for this publication.