Algal Limestones Research Articles

Lithological types and characteristics of carbonate open platform in pre-Caspian basin

The Carboniferous KT-II carbonate formation in N Oilfield at the eastern edge of pre-Caspian Basin has been developed in open marine carbonate platform. The present work aims to make an evaluation on the physical properties of limestone reservoirs, in order to identify the causes for strong heterogeneity. In the study area, limestone rocks are dominant and diverse that can be divided into fifteen types based on the grain contents: algal limestone, foraminifera limestone, fusulinid limestone, bioclast limestone, algal skeletal limestone, and oolitic limestone, etc. The oolitic limestone, algal limestone and algal skeleton limestone have the best physical properties and constitute the most favourable reservoirs in KT-II formation.

Lower Moscovian Limestones of the Bogdashan Range (NW China) as an Indicator of Cessation of Arc Magmatism in the Junggar Region

The field revision of the Carboniferous and Lower Permian stratigraphy of the northern Bogdashan (South Junggar, Northwest China) shows that the Lower to Middle Carboniferous island arc volcanic rocks, widely developed in this region, are overlapped everywhere by carbonate and terrigenous-carbonate sediments, containing occasional lava flows and overlain up the section by thick terrigenous series practically devoid of volcanic rocks. The deposition of limestone occurred at the stage of dying off of a volcanic arc, and the question of their age is of fundamental importance for dating this event. Carbonates are represented by facies of lagoons, shoals, and bioherms that formed on the leveled surface of the arc and on the slopes of the last active volcanoes. Bioherms are Waulsortian mounds and are mainly composed of algal limestones and carbonate mud. There are no framestones composed of corals and sponges (chaetetids) typical of the tropical zone. The facies of shallow crinoid-fusulinid limestones typical of the adjacent territories of the Southern Tien Shan and Tarim are poorly represented. Paleogeographically, the position of bioherms corresponds to the northern boundary of the realm of Pennsylvanian reefs. On the basis of foraminifers, brachiopods, and corals, the age of carbonates is early Moscovian (ca. 315–310 Ma). Cessation of island-arc volcanism, followed by the accumulation of limestone in Bogdashan, occurred sub-synchronously with formation of the West Junggar (Bayingou) suture and may reflect docking of the Bogdashan arc to the Yili active margin of the Kazakhstan continent. Further subsidence of Bogdashan and adjacent regions of the Junggar and Turfan basins, which was somewhat slower at the end of the Carboniferous and more intense in the Early and Middle Permian, may reflect the development of the foreland basin that formed along the northern flank of the Tien Shan orogen. Marine facies were locally preserved in this basin until the Artinskian (ca. 285 Ma), and later the Junggar and Turfan basins lost connection to the ocean and developed in continental environments.

NOVÉ POZNATKY O MIOCENNÍ PALEONTOLOGICKÉ LOKALITĚ TALIÁNSKÁ SKÁLA U KELČIC (KARPATSKÁ PŘEDHLUBEŇ, ČESKÁ REPUBLIKA)

The Taliánská skála locality is situated near Prostějov within the Vranovice-Kelčice cadastral area, about 1 km se. of Kelčice (Fig. 1). It is an old abandoned quarry in Miocene (Lower Badenian) sediments of the Carpathian Foredeep belonging to the formation with algal limestones. In 2014–2016, a new detailed study of this locality has been carried out as a part of a bachelor thesis at the Department of Biology, Faculty of Education, Palacky University in Olomouc (Zapletal 2016). By macroscopic study of the rocks at the locality it has been ascertained that they are represented by sandy limestones to calcareous sandstones, also microscopic study of two thin-sections confirmed that these rocks can be classified more likely as calcareous sandstones than as typical algal limestones. The new research confirmed this locality to be relatively rich in fossils, namely with regard to both their amount and number of species. The following species were found: the worm Ditrupa cornea (Linnaeus), bivalves Aequipecten macrotis (Sowerby in Smith), Corbula cf. gibba (Olivi), Panopea (Panopea) menardi (Deshayes), Tellina sp. and ?Ervilia sp.; additionally, there were the gastropods Turritella cf. badensis Sacco and Turritella sp., one undeterminable bryozoan and the ichnofossil Ophiomorpha isp. In the thin-sections from the rocks collected at the locality there were ascertained foraminifers, ostracods, echinoderms (echinoids) and worms. The presence of red algae has not been proved either macroscopically or microscopically.

NON-TRADITIONAL OIL AND GAS-PERSPECTIVE RESERVOIRS OF THE INTER-SALT COMPLEX OF THE PRIPYAT TROUGH

Lower Famenian inter-salt deposits (Belarus) have been studied comprehensively. The microlithofacies are as follows: laminated organic-carbonate-silica rock; massive limestone; radiolarite; algal limestone; massive dolomite; porous dolomite; dolomite of indistinct lumpy texture. Rocks contain pores of dissolved radiolarians, cracks of fluid auto-fracturing and weakened zones encountered in the secondary transformations. Rocks of Domanic type in the Central oil area of the Pripyat can be oil-bearing and oil-generating ones.

The occurrence and origin of celestite in the Abolfares region, Iran: Implications for Sr-mineralization in Zagros fold belt (ZFB)

The major celestite deposits in Zagros Fold belt are associated with coastal marine carbonate and evaporate sediments of Oligo-Miocene Asmari and Lower Miocene Ghachsaran Formations. In the Abolfares region, celestite mineralization is extended in the western limb of Bangestan anticline in the carbonates of Early Miocene (middle part of Asmari Formation), underlying by dolomitic carbonates of Burdigalian. From bottom to top three main types of mineralization can be distinguished in the study area: (1) layer texture resulting from replacement of algal limestone by celestite minerals with some parts showing idiomorphic crystals (geodes) along the walls of the cavities, (2) celestite occurrence as irregular massive shape interconnected small crystals and nodules, and (3) celestite mineralization associated with steeply dipping veins and open space fracture fillings, resulting from late-stage epigenetic processes. Highlightly, the ore-hosting carbonate rocks were deposited in an intertidal – supratidal protected setting with hypersaline conditions, in accordance with other celestite deposits of the Zagros Fold belt. The abundance of diagenetic crystallization rhythmites, carbonate and anhydrite inclusions as confirmed by Laser Raman spectroscopy analysis, high Sr/Ba values (average; 8726.1) and strong negative correlations between SO3 vs CaO (R2 = 0.98), SrO vs CaO (R2 = 0.96) with positive correlations between Ba vs SrO (R2 = 0.54) and SO3 vs SrO (R2 = 0.98) highlight the role of high Sr late-diagenetic brines in replacement of carbonates with celestite minerals. It seems that the inception of compressional folding during or soon after the deposition of the Asmari Formation in the carbonate platform at the margin of NW-trending basin in the foreland of the Zagros orogenic belt lead to the upward refluxing of penetrated high-Sr diagenetic brines and celestite mineralization.

Microfacies of a Permian calcisponge reef in Lichuan, western Hubei, South China

The Lichuan Jiantianba reef is located at the platform margin between the carbonate platform and the marine trough in western Hubei, China. The water depth of this area became shallow in the late Permian Changhsingian Age, and a huge aggradation-progradation platform marginal reef developed. Based on precise field measurements and microscopic observation, this paper describes the petrological characteristics and biological assemblages of the reef in detail and distinguishes 10 microfacies: small echinoderm wackestone, sponge floatstone, bound sponge bioliestone, bound sponge framestone, large echinoderm wackestone, red algal limestone, bioclastic grainstone, dasycladales wackestone, shelly wackestone, and microbialites. Sponge floatstone and bound sponge bioliestone are defined as toppled sponge limestone. Comparisons of the petrological characteristics and biotic association of toppled sponge limestone, bound sponge framestone and bioclastic wackestone and grainstone revealed that the toppled sponge limestone and the bound sponge framestone are similar in sponge content in terms of the types and contents of reef-dwellers, except that the sponge content is slightly lower, and the preservation state is mainly toppled for the former and upright or inclined for the latter. The toppled sponge limestone is dominated by tabular calcite, and the bound sponge framestone is dominated by fibrous calcite. The bioclastic wackestone and grainstone do not contain reef-building sponge organisms, and the bioclast content is very high and often dominated by a certain class, such as echinoderms, foraminifers, green algae or shells. The toppled sponge limestone below the framework, which was classified as fore-reef breccia or bioherm bafflestone-bindstone in previous studies, should be defined as reef-core sponge limestone deposited in situ that experienced serious post-karstification. The vertical evolution of the sedimentary facies of the reef is analyzed based on the microfacies and sedimentary environment. The toppled sponge limestone and the bound sponge framestone should be classified as reef core, which is the only subfacies of the reef facies. The underlying small echinoderm wackestone should be classified as the shelf facies, whereas the overlying bioclastic wackestone and grainstone should be classified as the open platform facies. These classifications represent a modification of the sedimentary facies subdivision of the Jiantianba reef in Lichuan, Hubei Province, South China, and provide a new reference model for the subdivision of the Permian calcisponge reefs on platform margin.

Intense hurricane transports sand onshore: Example from the Pliocene Malbusca section on Santa Maria Island (Azores, Portugal)

Southern cliffs on Santa Maria Island in the Azores archipelago (North Atlantic Ocean) feature submarine volcanic sequences inter-bedded with Pliocene coralline algal limestone, shelly coquinas, and mixed volcaniclastic-calcarenite sandstone. Within the 20-m sedimentary succession at Malbusca, a singular, 5-m sandstone bed is distinguished by dark and light laminae dominated alternately by heavy minerals and carbonate detritus. Carbonate grain-size varies between that of coarse silt and very fine sand. The basal part shows coarser and more poorly sorted sand in an upward transition to increasingly finer carbonates. Accessible over a lateral space of 34m, the big bed is shouldered against and overlaps the remnants of a drowned rocky shore with a paleorelief of 4m that preserves intertidal to shallow subtidal biotas. Extrapolated from the big bed's rock face (1830m2) and the width of the eroded shelf on which it resides (8m), calculations yield a projected volume of 14,500m3. Unique to the island, the big bed is interpreted as a major hurricane deposit that moved sand from an offshore bar in an onshore path. Such an event fits the context of the Pliocene Warm Period, during which global El Niño conditions were more intense than today.

Porosity-Permeability Relationships in the Early Oligocene Algal Limestone Member of Wadi Al Buwayrat, Tansolukh Area, Al Jabal Al Akhdar, NE Libya

Porosity-Permeability Relationships in the Early Oligocene Algal Limestone Member of Wadi Al Buwayrat, Tansolukh Area, Al Jabal Al Akhdar, NE Libya

Analysis on the Construction of Huayuan MVT Lead - Zinc Ore Field in Zhangjiajie of the Western Hunan, China

Huayuan lead-zinc ore field in Zhangjiajie of western Hunan, is a large-sized, and the ore bodies algal limestones the margin of the shallow platform in the lower part of the Early Cambrian Qingxudong Formation. The authors expounded the ore-hosting lithology, sedimentary environment and petrographic evolution of Huayuan lead-zinc ore field. According to the metallogenic characteristics of the Huayuan lead-zinc ore field, the formation and evolution of the ore field is divided into the First construction (geological processes), the secondary construction (lithofacies characteristics) and the third-level construction (basic rock unit).

UPPER CRETACEOUS-TERTIARY GEOLOGY/STRATIGRAPHY OF PERTEK AND ITS VICINITY (TUNCELİ, TURKEY)

The basement units of the study area are Paleozoic-Mesozoic Keban metamorphics and Late Cretaceous Elazig magmatics. As a result of tectonic events caused by final collision in Middle Maastrichtian, all these basement units were juxtaposed, uplifted, eroded and acted as a source area for the Maastrichtian-Paleogene basins. Upper Cretaceous Paleogene deposits were systematically sampled in order to determine their ages and lithologies. Due to new age findings and stratigraphical positions the marine units were identified as; Harami, Seske and Kirkgecit formations. Late Oligocene-Early Miocene Alibonca formation and Pliocene Karabakir formation are the other units of the study area. Maastrichtian-Thanetian Harami formation is formed by grainstone intercalated with sandstone at the bottom and white limestone at the top. Early Lutetian Seske formation consists of conglomerate at the bottom and much nummulitic, carbonate cemented sandstone with ophiolitic fragments at the top. Kirkgecit formation consists of sandstone-siltstone-limestone intercalation, and it is early Bartonian early Chattian. Late Chattian-middle Burdigalian Alibonca formation consists of conglomerate at the bottom, reefal limestone in the middle and clayey limestone intercalated with algal limestone at the top. Pliocene Karabakir formation is formed by conglomerate-mudstone and locally by intercalations of pyroclastics and lavas. Pertek Andesite and Basalt Members are both vertically and laterally transitional with sedimentary lithologies of the Karabakir formation. There is no data to date the lithology; however, it was assumed that it had been Pliocene in age according to the lithostratigraphical succession. In the study area, macrotectonic events were experienced in Late Cretaceous, Early Eocene, middle-late Lutetian, Middle?-Late Miocene and in the Latest Pliocene. During the last tectonic phase, the Anatolian plate bounded by the East Anatolian Fault (EAF) in E-SE began to move westward, and the right lateral strike slip Pertek Fault activated in the study area.

A Preliminary Documentation of the Coral Reefs from Libya

Corals studies in Libya are very limited, although they play an important role in the oil exploration as they form excellent reservoirs of coral reef buildups at some oil fields of Sirt Basin (e.g. Intisar “Idris” and Sahabi Fields). Both fields are produced from Paleocene coral reefs. Meanwhile, in Cyrenaica, corals are of less importance as they are not reported in subsurface tertiary rocks, which probably in the environmental settings of these sediments out of the core of reef as occurred in the surface. Meanwhile, corals are reported from older (Jurassic) subsurface successions as in Concession NC-152, but the cementation diagenesis leads to blocking and destroying the porosity. This study presents the first surface documentation work of eight scleractinian coral species from the exposed sediments in northern Libya, where sixtaxa is reported from Al Jabal al Akhdar region, these include a) an association of huge colonies of Caulastrea sp. and Stylophora sp., from the Middle Eocene Darnah Formation at West Darnah road cut section. Theco-existence of the fastCaulastrea sp. with the slow Stylophora sp. is due to the competition strategy; b) Antiguastrea sp. which is reported from the Oligocene Algal Limestone of Al Bayda Formation at Daryanah-Abyar Roadcut section; c) Cyphastrea sp. andAleveopora sp. from Oligo-Miocene Al Faidiyah Formation at Al Fatayah cement quarry and d) Tarbellastraea sp. From Middle Miocene Benghazi Formation at Benghazi Cement Quarry. In addition, two species Astraeaopora sp. and Actinacis paroraiare reported from the Upper Miocene sediments of formation “M” in As Sahabi area.

The characteristics of dolomite reservoir in saline lacustrine Basin, Qaidam, China

Qaidam is a plateau saline lacustrine basin in China. The Eocene in western Qaidam mainly consists of lacustrine carbonate, and the sedimentary rocks mainly include micrite, bioclastic limestone, algal limestone, dolomicrite, algal dolomite and so on. Among these rocks, dolomite is the most important petroleum reservoir rock, which mainly includes algal dolomite and dolomicrite. The pores of carbonate are mainly the intercrystalline pores, and there are dissolution pores locally. The analysis based on electronic probe energy spectrum scanning instrument shows that the enrichment region of element Mg in the algal dolomite is highly consistent with the distribution of algal laminas, which means the algal dolomite is a biogenic primary dolomite, because the microbial activities can overcome the kinetic obstacles and create a favorable microenvironment for the formation of dolomite. The analysis based on X-ray diffraction instrument shows that most dolomicrite includes clastic particles and argillaceous components because of the combined sedimentation of clastic materials brought from the peripheral fan delta deposit. The rock composition analysis based on the electronic probe shows that the average content of FeO in the dolomicrite is 0.942 %, and that of MnO is 0.052 %, which are obviously lower than the average contents of Fe and Mn in the hydrothermal dolomite. Meanwhile, due to the high contents of SiO2 and Al2O3, it is considered that the dolomicrite has a penecontemporaneous metasomatic formation mechanism. This type of dolomicrite generated a lot of disseminated intercrystalline pores during the metasomatism. The pore radius is small and the pore number is enormous, which are the main cause of relatively high porosity and relatively low permeability. The type of dolomicrite is a good petroleum reservoir in the study area, so adequate attention shall be given to the dolomicrite during the oil and gas exploration in the carbonate rock reservoir of Eocene in Qaidam Basin.

Petrography and stable isotopic variations in Dalmiapuram Formation of Cauvery Basin, South India: implication on OAE1d

Petrography, carbon and oxygen isotopic study was carried out to interpret isotopic variations on the predominant carbonate sequence of the Dalmiapuram Formation of the Cauvery Basin, South India. The common petrographic types identified in the Dalmiapuram Formation range from wackestone to boundstone. The gray shale and limestone members show large variations in δ13C and δ18O values (Gray shale member: +1.44 to +2.40 ‰ VPDB, −3.05 to −5.92 ‰ VPDB, respectively; Limestone member: −6.07 to +2.93 ‰ VPDB; −7.08 to −0.39 ‰ VPDB; respectively). In the present study, the carbon and oxygen values are not correlated, which supports the fact that these limestones retain their primary isotopic signatures. In carbon isotope curve, one negative shift is identified in the gray shale member and a positive isotopic excursion is detected in the coral algal limestone (CAL). The observed positive isotopic excursion in the lower part of the CAL correlates with OAE1d and suggests the global nature of the late Albian OAE1d in the Cauvery Basin.

Cretaceous-Tertiary (K-T) boundary evaporites in the Malatya Basin, eastern Turkey

The Malatya basin is situated on the Anatolid-Torid plate of the Neo-Tethys Sea. Evaporites were deposited in the northwestern part of the Malatya basin, which is referred to as the Hekimhan sub-basin. Although the Gunduzbey sub-basin in the southeastern Malatya basin has coeval deposits, it contains no evaporate deposits. The evaporite is most likely the result of the last transgressive–regressive cycle of the Late Cretaceous Sea. The pre-evaporitic unit is represented by the carbonate platform deposit of the Loftusia banks, which partly underwent dolomitization and overlies the deep marine sediments. Celestite-bearing algal limestone was deposited directly below the gypsum-dominated evaporate unit in association with the organic-rich mudstone. Evaporite sedimentation took place in various types of environments, such as marginal shallow subaqueous with the association of sabkha–coastal lagoon and deeper subaqueous. It is assumed that the tectonic evolution of the basin margin, which occurred during the latest stage of the Cretaceous regression, was responsible for the environmental restriction leading to evaporate sedimentation under arid/semiarid climatic conditions. The 87Sr/86Sr ratios obtained from 38 samples of the gypsum and celestite-bearing limestones (11 samples) range between 0.707817 and 0.707980 and between 0.707783 and 0.707864, respectively. The δ34S values range from +19.5 to +22.4 ‰, and the δ18O values range from +9.6 to +12.7 ‰. These isotopic signatures correspond to that of Late Cretaceous/Early Paleocene (Cretaceous-Tertiary boundary) marine water. However, celestite exhibit(s) relatively higher δ34S and 87Sr/86Sr values than expected marine values, which could be a result of contribution of diagenetic fluid into the celestite-precipitated environment.

Identification of Neogene mixed lacustrine carbonate in western Qaidam basin

Compared with marine carbonate, lacustrine carbonate is limited in distribution globally; moreover, as an unconventional kind of carbonate, it cannot be evaluated and identified with conventional methods, so less attention has been paid and fewer studies have been made on it. However, according to exploration experiences all over the world, lacustrine carbonate can be an important source rock and reservoir rock in some cases. Qaidam basin, a large salt-water lake basin, had the lacustrine mixed deposition setting to form complex carbonate reservoirs. The recently found Neogene lacustrine algal limestone is an exploration target worthy of attention. The author has used drilling and well logging data to identify lacustrine algal limestone. The method is of great significance for the exploration and development of lacustrine carbonate in other areas.

Petroleum Source Rock Assessments of the Upper Permian Strata in the Central Taurus Region of Turkey

This study presents the hydrocarbon source rock potential and organic maturity of the Upper Permian Tozara Formation in the Gazipaşa-Sugözü area in the central Taurus region. The Tozara Formation deposited oxic to dysoxic shelf conditions consists of algal limestone and organic matter-rich shales. In order to assess the hydrocarbon source rock potential of the Upper Permian lithologies, two different stratigraphic sections described and sampled for organic geochemical analyses and determination of mineralogical composition.

The role of microalgae and their carbonic anhydrase on the biological dissolution of limestone

This study aims to investigate the effect of microalgae and their carbonic anhydrase (CAex) on limestone dissolution. The dynamics of Ca2+ and Mg2+ release, the model for the amount of Mg2+ released and biological cumulative effect time by the microalgae Chlamydomonas reinhardtii (CR) and Chlorella pyrenoedosa (CP), and the algal stable carbon isotopic composition (δ13C) in the presence and absence of the membrane-impermeable CAex inhibitor acetazolamide (AZ) were compared in a medium containing limestone. The amount of Mg2+ released from the limestone in the treatment without AZ was more than that with AZ during the logarithmic phase. The amounts of Mg2+ release unit algal biomass and unit time in CR and CP were 3.37 × 10−4 and 2.44 × 10−4 mg/μg days in the treatment without AZ, respectively, and only 1.99 × 10−4 and 2.19 × 10−4 mg/μg days in the treatment with AZ, respectively. The biological dissolution of the algae increased with increasing algal CAex activity. The variation of Ca2+ was influenced by reprecipitation, and the algal limestone dissolution cannot be shown distinctly. The CAex of the microalgae may be beneficial for CaCO3 reprecipitation, and the δ13C values of the algal cells with AZ were lower than those without AZ. Therefore, AZ not only can inhibit limestone dissolution by inhibiting microalgal growth, but also can reduce limestone dissolution by decreasing CAex catalysis. The results suggest the important influence of microalgae and their CAex on the biokarst process.

Lacustrine algal limestone reservoir in western Qaidam Basin, China

Compared to marine carbonate around the world, lacustrine carbonate is relatively scarce. Much less attention has been paid to it. Lacustrine carbonate, a product of mixed deposition of continental clastics and carbonate under special conditions, can be both important source rocks, and oil and gas reservoir rocks. Qaidam Basin is a large salt lake basin on the Tibetan Plateau where oil and gas flow has recently been discovered in lacustrine algal limestone. Study of the algal limestone is a potentially valuable target of exploration, and is of great significance to the exploration and development of mixed carbonate formations.

Stratigraphic status, age, and paleobathymetry of the Grey shale Member, Dalmiapuram Formation, Cauvery Basin, India

Grey shale Member of the Dalmiapuram Formation, Ariyalur Group, Cauvery Basin, India was studied for its stratigraphic position, age, and paleobathymetry with a re-look into the lithological relationship and foraminifer assemblages in the deepened limestone mine excavations at M/s Dalmia Cements, Dalmiapuram. Twenty grey shale samples from Kovandankurchchi (pit-4) and Kallakkudi mines yielded diversified calcareous, benthic, and rare index planktic foraminifera. The foraminiferal assemblages suggest a latest Albian age and middle neritic depositional conditions. The abundance of kaolinite and smectite clay minerals relate to warm/humid climate which corroborate with rising relative sea level during grey shale deposition. The grey shale occurs in patches within the marl bedded limestone member which exhibits cyclic deposition of limestone and marl. The limestone mine sections demonstrate that the grey shale forms part of basal marl bedded limestone, directly overlying the coral algal limestone. The present study demonstrates that the grey shale outcrops in Dalmiapuram Formation should be placed stratigraphically as part of marl bedded limestone. The member status for grey shale which is current usage stands discounted.

New Late Eocene genus Gaziryina (Foraminifera) from the Al Bayda Formation (ShahhatMarl Member), Al Jabal al Akhdar, Northern Cyrenaica, Libya

The foraminifers of the Shahhat Member of the Al Bayda Formation exposed in three sections (at theWadi Az Zad quarry, and the Wadi Al Kuf and Al Hamamah road cuts) in the region of Jabal Al Akhdar in Libya have been investigated. The rock unit consists of marly limestone grading intomarl in places and is assigned a Late Eocene age according to the presence of forms suggesting the Nummulites fabianii Biozone, and suggesting also the Early Oligocene age, to which the Shahhat Member has been generally assigned in most previous publications should be revised. Nummulites ruetimeyeri de la Harpe 1883 and Chapmanina gassinensis (Silvestri 1904) has been recovered in association with Nummulites fabianii (Prever in Fabiani 1905). Gaziryina pulchellus (Hantken 1883) n. gen. in de la Harpe (1883) has also been retrieved in associationwith a Nonion-Uvigerina assemblage suggesting relatively deep marine conditions in the lower intervals of the investigated Late Eocene marly sequence. Nummulites gizehensis (Forskal) is found in the underlying Darnah Formation (Middle Eocene, Lutetian), and the overlying algal limestone of the remaining of the Al Bayda Formation includes species suggesting the Nummulites fichteli Biozone of Early Oligocene age.