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1.
Suman Sarkar 《Journal of the Geological Society of India》2016,88(3):281-294
Early Eocene carbonate sediments of the Umlatdoh Limestone (Meghalaya, N-E India) represent a shallow marine shelf environment. The major biotic components characterizing these carbonates are calcareous green algae and small to larger benthic foraminifera. Based on the biogenic associations and general sedimentological features, five major facies types (MFTs) are distinguished. They are dominated by poor to moderately sorted grainstones followed by packstones, rudstones and wackestones. Considerable abundance of Halimeda, scarcity of z-corals and poor to moderate occurrence of filter-feeding organisms imply mesotrophic to a slightly oligotrophic nutrient regime. Rare occurrence of geniculate coralline algae is probably due to the lack of suitable substrate and environmental conditions. High incidence of grainstones and packstones, fairly preserved microfossils and few reworked specimens indicate a parautochthonous mode of deposition. Preponderance of Alveolina and Nummulites indicate the possible advent of larger foraminiferal turnover (LFT) in the east Tethys during or even before early Eocene. A conceptual palaeoenvironmental model for the studied succession is provided to showcase various facies gradients, bathymetry levels and shelf zones pertinent to the Umlatdoh Limestone. 相似文献
2.
The southwestern part of south Shillong plateau (Meghalaya, N-E India), designated as Sylhet Limestone Group is sub-divided into three lithounits i.e., Lakadong, Umlatdoh and Prang formations in ascending order. The Prang Formation is the youngest lithostratigraphic unit of the Sylhet Limestone Group and has been dated as Middle to early Upper Eocene based on the benthic foraminifera studies. Thin section analysis of carbonate rocks from Prang Formation, exposed in the Bholaganj limestone quarry yielded a rich assemblage of calcareous algae. The coralline algal assemblage comprises both non-geniculate and geniculate forms. The green algae are represented by species of Halimeda belonging to the family Halimedaceae. Palaeoecological interpretation based on diversity, growth-form analysis and taphonomic aspects of the algal assemblage indicate that in all probabilities the deposition of Prang Formation occurred in shallow, warm, shelf environment of normal salinity within the transgressive phase. 相似文献
3.
P. K. Misra A. K. Jauhri R. P. Tiwari S. Kishore Ajay Pratap Singh S. K. Singh 《Journal of the Geological Society of India》2011,78(4):355-364
The present paper records nine species of coralline algae from the Prang Formation of middle-late Eocene age from the Jaintia
Hills, Meghalaya. The algae are associated with the larger foraminifera including Nummulites, Alveolina and Discocyclina throughout the succession. The temporal distribution of algal species indicates that seven species are known from the Eocene.
Of the remaining two, one ranges from the Palaeocene to Eocene and the other is Palaeocene in age. The coralline algae and
larger foraminifers are differentiated into two associations, the lower one indicating inner-ramp environment of high energy
and the upper one showing deposition in relatively calm waters of deeper ramp environment. 相似文献
4.
The Eocene Nummulitic Limestone of the Dauphinois domain in the Argentina Valley (Maritime Alps, Liguria, Italy) is characterized by the local presence of carbonate ramp facies rich in acervulinid macroids, rhodoliths and larger foraminifera. The development of these particular facies is mainly controlled by palaeomorphology of the substratum, tectonics, type and amount of terrigenous supply and global sea level changes.
The Upper Cretaceous to Eocene succession outcropping in the Argentina Valley shows differences in facies and age if compared to the typical succession of the Maritime Alps:
The Eocene tectonostratigraphic evolution can be summarized as follow: (1) synsedimentary tectonic activity that causes the development of a carbonate ramp with an adjacent structural trough where ramp-derived bioclastic material is deposited (late Lutetian); (2) interruption of the tectonic activity and uniform deposition of deep circalittoral sediments, characterized by deepening upward trend (late Lutetian?); (3) regression indicated by an abrupt shallowing of the depositional setting (Bartonian); and (4) deepening of the depositional setting, ending with the drowning of the carbonate ramp (late Bartonian).The evolution of the Eocene Argentina Valley succession is strongly influenced by tectonics related to the Alpine foreland basin development, but locally, and during definite time intervals, the global sea level changes could be recorded by the sediments during periods of stasis in tectonic activity. The regressive events recognized in the studied succession could be related to the sea level fall reported in the global sea level curve during the Bartonian. 相似文献
- the Cretaceous substratum is younger (early Maastrichtian) and is followed by an unconformity that is interpreted as a submarine discontinuity surface;
- the first Eocene carbonate deposits are older (late Lutetian);
- the Nummulitic Limestone is characterized by the development of carbonate facies deposited in a deep infralittoral-circalittoral setting of a carbonate ramp, sheltered from terrigenous input; in these facies encrusting foraminifera (Solenomeris) replace calcareous red algae in nodules similar to rhodoliths (acervulinid macroids);
- the Nummulitic Limestone is thicker than usual, reaching 110–160 m of thickness.
5.
6.
The Eocene represents the last greenhouse interval before Present. The maximum warming during the early Eocene was followed by a long-term cooling trend culminating in the Antarctica glaciation at the base of the Oligocene. Superimposed on this long-term cooling trend there is a prominent transient warming event known as the middle Eocene climatic optimum (MECO) occurring during the early Bartonian. The carbonate ramp succession cropping out in the Argentina Valley (Maritime Alps) offers new insights on the evolution of shallow water realms during this time interval. This ramp displays two main facies belts, middle and outer ramp. The middle ramp is recorded by larger benthic foraminifer floatstone to rudstone, passing to Solenomeris branches and nodule floatstone to rudstone evolving to branching coralline algal floatstone. The outer ramp is dominated by bioturbated marly wackestone to packstone alternating with larger benthic foraminifer floatstone with a silty matrix. The investigated ramp was affected by continuous dispersion and reworking of the skeletal components as other Tethyan Eocene ramps. During the Eocene, the Alpine foreland was influenced by fine terrigenous input controlling the trophic conditions and promoting seawater stratification and the development of a strong pycnocline, for which many perturbations could propagate as internal waves. The reworking of skeletal components of the ramp has been ascribed to the action of internal waves. The switch of carbonate production from a carbonate factory dominated by larger benthic foraminifera to a factory in which the encrusting foraminifer Solenomeris was the main carbonate producer biota, is indicative of a radical change in palaeoenvironmental conditions affecting the early Bartonian. The acme of Solenomeris often coincided with the crisis of carbonate producers during intervals of an evident deterioration of environmental conditions. In this case the acme is probably related to the adverse conditions linked to the (MECO) warming event. Finally, the drowning of the nummulitic ramp has been caused by light reduction for the photo-dependent biota due to progressively increasing depth linked to flexural subsidence of the foreland plate, and minor efficiency of the aphotic carbonate factory. 相似文献
7.
Sruthi P Sreenivasan Melinda Kumar Bera Arpita Samanta Ravikant Vadlamani 《Journal of Earth System Science》2018,127(8):105
The exact magnitude of the carbon isotopic excursion (CIE) for the Palaeocene–Eocene Thermal Maximum (PETM) is essential for our understanding of the carbon cycle perturbation. Global compilation of the PETM CIE magnitudes indicates that the shallow-marine inorganic carbonate could be a potential candidate to decipher the actual CIE magnitude. The present study, therefore, made an attempt to explore the thick Palaeogene shallow-marine carbonate sequence of the Sylhet Limestone exposed in the Jaintia Hills of northeast (NE) India, in terms of the preservation and magnitude of the PETM CIE. Exploratory sampling carried out across the Sylhet Limestone suggests that this sequence was deposited during the Late Palaeocene and Early Eocene, as evident from the age-diagnostic foraminifera. The observed \({\sim }3.4\permille \) CIE at the top of the Lakadong Limestone, resting above the Miscellanea miscella and Ranikothalia nuttalli foraminifera-bearing horizon, can, therefore, be correlated with the PETM CIE. Although the magnitude of the CIE from our limited data set agrees well with the global compilation, the absence of a stepped profile questions the preservation of the CIE reported elsewhere from the Tethyan sequence. Further work is needed for a better understanding of the PETM interval in NE India. 相似文献
8.
Middle Eocene Fulra Limestone and Oligocene Maniyara Fort Formation represent platform carbonate deposits of Kutch at the north-western margin of India. These carbonates contain larger benthic foraminifera, including Alveolina, Assilina, Discocyclina, Lepidocyclina, Miogypsina, Nummulites and Spiroclypeus. This study presents paleodepositional and paleobathymetric interpretations for both formations using benthic foraminifera in combination with lithological association, sedimentary structures and early diagenetic features. The six carbonate facies comprising the Fulra Limestone indicate a depositional spectrum ranging from bar-lagoon to mid-ramp depositional conditions. It records several shallowing upward cycles, leading to emergence and formation of paleokarst. The four carbonate facies of the Maniyara Fort Formation represents deposition within the inner ramp setting in bar-lagoon and patch-reef environment, while intervening fine siliciclastics correspond to episodes of relative sea level fall. Nummulitic accumulations form low-relief bars within the fair weather wave base in both the formations. The depositional setting of the Paleogene carbonate in Kutch broadly resembles Eocene platformal deposits in the circum-Tethys belt. 相似文献
9.
Utkarsh Misra S. Kishore S. K. Singh P. K. Misra A. K. Jauhri 《Journal of the Geological Society of India》2016,87(3):308-316
The present paper examines the coralline algal assemblage recovered from the Holocene sediments of Agatti Island, Lakshadweep, India. The assemblage comprises nine species of coralline algae which include Amphiroa fragilisma, Lithophyllum nitorum, Lithophyllum incrustans, Lithoporella melobesioids, Spongites sp., Porolithon craspedium, Aethesolithon problematicum, Clathromorphum parcum, Melobesoideae gen. et spec. indet. Clathromorphum parcumis an endophytic coralline alga reported for the first time from the Indian subcontinent. Out of these, seven species belong to the family Corallinaceae and the two represent the family Hapalidiaceae of the class Rhodophyceae. Coralline algal association of this area is dominated by Lithophylloideae, Melobesioideae and Mastophoroideae which include encrusting to fragmented growth forms. The associated branching corals are well developed and adapted to shallow, warm water, low turbid, protected lagoonal environment. 相似文献
10.
The Paleogene sections of Kutch are the reference for the regional chronostratigraphic units of India. The ages of these dominantly shallow marine carbonates are mainly based on larger benthic foraminifera (LBF). The taxonomic revisions of the LBF and the progressively refined shallow benthic zonations (SBZ) have necessitated the present study on updating the stratigraphy of the area. The sedimentation in Kutch commenced with the deposition of volcaniclastics in terrestrial environments in the Paleocene. The marine transgression in SBZ 5/6 deposited finer clastics and carbonates, designated as Naredi Formation, in early Eocene. There is no evidence of marine Paleocene in Kutch. A major hiatus spanning SBZ 12 to SBZ 16 was followed by the development of a carbonate platform and deposition of Harudi Formation – Fulra Limestone during the Bartonian, SBZ 17. The hiatus corresponds to a widespread stratigraphic break in Pakistan and India to Australia, referred as the ‘Lutetian Gap.’ The Maniyara Fort Formation is assigned to SBZ 22 B and SBZ 23, and its age is revised to Chattian. Climate played a major role in building up of the Paleogene stratigraphic succession of Kutch, the carbonates formed during the warming intervals and the stratigraphic gaps were in the intervening cooling periods. 相似文献
11.
Several sections from the uppermost Eocene and Oligocene of northern Slovenia have been investigated with respect to sedimentary facies, foraminiferal assemblages, stable isotopes, carbonate microfacies, and palynology. The main objective was to reconstruct the paleoenvironmental history of the Paleogene Paratethys in this region of the eastern Alpine realm. The sediments exhibit a transgressive succession beginning with conglomerates, sandstones, and mudstones of fluvial and lacustrine origin followed by carbonates and muddy marls indicating marine conditions. The foraminiferal faunal changes from brackish to shallow marine to deeper marine assemblages and the distribution of the palynofloras corroborate the sedimentological results. Microfacies analysis of the limestones shows a wide variation of shallow water, generally mud-rich facies dominated by coralline algae, foraminifera, and corals. Microfaunas adapted to low-oxygen conditions indicate temporal sluggish bottom-water circulation which can be associated with high fresh-water fluxes. These results are discussed as reflecting both the global sea-level rise during the Early Oligocene and the regional tectonic and climatic evolution. 相似文献
12.
P. Kundal Milind P. Kundal S. K. Humane 《Journal of the Geological Society of India》2016,88(1):39-46
The present paper reports five nongeniculate coralline algal species, viz., Lithothamnion valens Foslie, Mesophyllum roveretoi Conti, Phymatolithon calcareum (Pallas) Adey and Mckibbin, Melobesioideae gen. et spec. indet. and Lithoporella melobesioides Foslie form the early middle Miocene Chhasra Formation of Offshore Sequence of Kachchh basin, western India. The present day depth distribution of Lithothamnion and Mesophyllum and growth forms of five nongeniculate coralline algal species points that the two cores belonging to the Chhasra Formation of offshore sequence of Kachchh basin were deposited in inner shelf environment at 60-100m depth in moderate-energy conditions. 相似文献
13.
The Jahrum Formation (Upper Paleocene to Middle Eocene) is composed of carbonate and dolomitic carbonate rocks in the Zagros Basin. The Zagros is located at the boundary between the Arabian and Eurasian lithosphere plates and represent the orogenic response to a collision between Eurasia and advancing Arabia during the Cenozoic. The study area is located in the northern part of Kuh-E-Tudej, ~175 km southeast of Shiraz in the Folded Zagros Zone. The Jahrum Formation at Kuh-E-Tudej, with a thickness of 190 m, consists of medium to massive bedded limestone. The following foraminiferal index species are identified in the studied section: Fallotella alavensis, Kathina sp., Miscellanea sp., Lockhartia sp.,Orbitolites shirazeinsis, Nummulites sp., Opertorbitolites sp., Dictyoconus cf. egyptiensis, Orbitolites cf. complanatus, Dictyoconus sp., Coskinolina sp., Somalina stefaninii, Discocyclina sp., Praerhapydionina sp., Coskinolina cf. liburnica, Nummulites cf. globulus, Nummulites cf. aturicus, and Alveolina sp. The age of the studied sediments ranges from Upper Paleocene to Middle Eocene. The microbiostratigraphic studies revealed four biozones based on the foraminifers identified in the studied section. 相似文献
14.
The early Paleogene experienced the most pronounced long-term warming trend of the Cenozoic, superimposed by transient warming events such as the Paleocene–Eocene Thermal Maximum (PETM). The consequences of climatic perturbations and associated changes on the evolution of carbonate platforms are relatively unexplored. Today, modern carbonate platforms, especially coral reefs are highly sensitive to environmental and climatic change, which raises the question how (sub)tropical reef systems of the early Paleogene reacted to gradual and sudden global warming, eutrophication of shelf areas, enhanced CO2 levels in an ocean with low Mg/Ca ratios. The answer to this question may help to investigate the fate of modern coral reef systems in times of global warming and rising CO2 levels.Here we present a synthesis of Tethyan carbonate platform evolution in the early Paleogene (~ 59–55 Ma) concentrating on coral reefs and larger foraminifera, two important organism groups during this time interval. We discuss and evaluate the importance of the intrinsic and extrinsic factors leading to the dissimilar evolution of both groups during the early Paleogene. Detailed analyses of two carbonate platform areas at low (Egypt) and middle (Spain) paleolatitudes and comparison with faunal patterns of coeval platforms retrieved from the literature led to the distinction of three evolutionary stages in the late Paleocene to early Eocene Tethys: Stage I, late Paleocene coralgal-dominated platforms at low to middle paleolatitudes; stage II, a transitional latest Paleocene platform stage with coralgal reefs dominating at middle paleolatitudes and larger foraminifera-dominated (Miscellanea, Ranikothalia, Assilina) platforms at low paleolatitudes; and stage III, early Eocene larger foraminifera-dominated (Alveolina, Orbitolites, Nummulites) platforms at low to middle paleolatitudes. The onset of the latter prominent larger foraminifera-dominated platform correlates with the Paleocene/Eocene Thermal Maximum.The causes for the change from coral-dominated platforms to larger foraminifera-dominated platforms are multilayered. The decline of coralgal reefs in low latitudes during platform stage II is related to overall warming, leading to sea-surface temperatures in the tropics beyond the maximum temperature range of corals. The overall low occurrence of coral reefs in the Paleogene might be related to the presence of a calcite sea. At the same time larger foraminifera started to flourish after their near extinction at the Cretaceous/Paleogene boundary. The demise of coralgal reefs at all studied paleolatitudes in platform stage III can be founded on the effects of the PETM, resulting in short-term warming, eutrophic conditions on the shelves and acidification of the oceans, hampering the growth of aragonitic corals, while calcitic larger foraminifera flourished. In the absence of other successful carbonate-producing organisms, larger foraminifera were able to take over the role as the dominant carbonate platform inhabitant, leading to a stepwise Tethyan platform stage evolution around the Paleocene/Eocene boundary. This szenario might be also effective for threatened coral reef sites. 相似文献
15.
Eocene cool-water carbonate and biosiliceous sedimentation dynamics, St Vincent Basin, South Australia 总被引：2，自引：0，他引：2
Middle and Upper Eocene biogenic sediments in the Willunga Embayment along the eastern margin of the St Vincent Basin are a series of warm‐temperate limestones, marls and spiculites. The Middle Eocene Tortachilla Limestone is a thin, coarse grained, quartzose, biofragmental, bryozoan–mollusc calcarenite of stacked metre‐scale depositional cycles with hardground caps. Lithification, aragonite dissolution and the filling of moulds by sediment and cement characterize early marine‐meteoric diagenesis. Further meteoric diagenesis at the end of Tortachilla deposition resulted in dissolution, Fe‐oxide precipitation and calcite cementation. The Upper Eocene Blanche Point Formation is composed of coccolith and spiculite marl and spiculite, all locally rich in glauconite, turritellid gastropods and sponges. Decimetre‐scale units, locally capped by firmgrounds, have fossiliferous lower parts and relatively barren upper parts. Carbonate diagenesis is minor, with much aragonite still present, but early silicification is extensive, except in the spiculite, which is still opal‐A. All depositional environments are interpreted as relatively shallow water: high energy during the Middle Eocene and low energy during the Upper Eocene, reflecting the variable importance of a basin‐entrance archipelago of carbonate highs. Marls and spiculites are interpreted to have formed under an overall estuarine circulation system in a humid climate. Basinal waters, although well mixed, were turbid and rich in land‐derived nutrients, yet subphotic near the sea floor. These low‐energy, inner‐shelf biosiliceous sediments occur in coeval environments across other parts of Australia and elsewhere in the rock record, suggesting that they are a recurring element of the cool‐water, carbonate shelf depositional system. Thus, spiculites and spiculitic carbonates in the rock record need be neither deep basinal nor polar in origin. The paradox of a shallow‐water carbonate–spiculite association may be more common in geological history than generally realized and may reflect a characteristic mid‐latitude, humid climate, temperate water, palaeoenvironmental association. 相似文献
16.
The plant fossil records from the Siwalik Group of Arunachal Pradesh, India are far from satisfactory due to remoteness and dense vegetation of the area. We report seven fossil woods of which three belong to the Middle Siwalik (Subansiri Formation), while the rest are from the Upper Siwalik (Kimin Formation). The modern analogues of the fossils from the Middle Siwalik are Lophopetalum littorale (Celastraceae), Afzelia-Intsia and Sindora siamensis (Fabaceae) and from the Upper Siwalik are Miliusa velutina (Annonaceae), Calophyllum tomentosum and Kayea (Calophyllaceae) and Diospyros melanoxylon (Ebenaceae). The dominance of diffuse porosity in the fossil woods indicates a tropical climate with low seasonality (little variation) in temperature, while a high proportion of large vessels and simple perforation plates in the assemblage infer high precipitation during the deposition of the sediments. The aforesaid inference is in strong agreement with the previous quantitative reconstruction based on fossil leaves. Several modern analogues of the fossil taxa are now growing in low latitudes possibly due to an increase in seasonality (increased variation) in temperature caused by the rising Himalaya. 相似文献
17.
Continental (fluvial) strata of the Pinjor Formation (Siwalik Group), northwestern Himalayas, India, contain an invertebrate trace fossil assemblage containing Planolites beverleyensis, Palaeophycus isp., Scoyenia gracilis, Taenidium barretti and other undifferentiated traces. The traces are found in an \(\sim \)26 m thick interval of alternating pinkish red siltstone, which is intercalated with mudstone, and thickly-bedded buff and greenish coloured sandstone. These sediments are interpreted as the deposits of floodplains and channel-bars of fluvial environments and low-energy overbank floodplain deposits. The trace fossils studied here are the first well documented ichnofossil assemblage from the vast, late Cenozoic Siwalik depositional system. They are not only of palaeoenvironmental significance, but they add to the growing ichnofossil database in facies of fluvial origin and should be an impetus to further ichnological studies of the Siwalik Group. 相似文献
18.
The Global Stratotype Section and Point for the Palaeocene/Eocene (P/E) boundary was defined at Dababiya Quarry (Egypt) at the base of the carbon isotope excursion (CIE). We present the first detailed analysis of Palaeocene–Eocene benthic foraminifera from Dababiya, in order to infer the palaeoenvironmental turnover across the P/E boundary. At Dababiya, the CIE coincides with a major turnover in foraminiferal assemblages; the last occurrence of Angulogavelinella avnimelechi, at the base of the CIE, may be correlated to the main phase of extinction of deep-sea benthic foraminifera. Benthic foraminifera indicate that stressful conditions such as oxygen deficiency, carbonate dissolution, and changes in food supply, persisted at the sea floor over most of the CIE interval. The main phase of recovery of benthic foraminifera is recorded c. 250 cm above the P/E boundary, and it may be linked to increased productivity and oxygenation at the sea floor. 相似文献
19.
The Kopet-Dagh sedimentary basin is located in northeast of Iran and southeast of Turkmenistan in the Middle East. The Khangiran formation represents the last marine deposition in the Kopet-Dagh sedimentary basin. The early Eocene planktonic and benthic foraminifera from the Khangiran formation which belongs to the lower 376 m thickness of this formation are identified and biostratigraphically evaluated. Due to rarity of Morozovella species, planktonic foraminiferal zonation was difficult to determine in this formation. The determination of upper part of the late Paleocene for the lower 124 m of this formation is according to the lowest occurrence of Acarinina sibaiyaensis species. From E5 to near middle of E7 biozone, increasing trend of Acarinina frequency and a peak in Morozovella species and decreasing trend of frequency of Subbotina and Pseudohastigerina species indicate the warm and oligotrophic condition of the seawater during sedimentation of the studied interval. Toward the Ypresian-Lutetian boundary, the increasing trend of Pseudohastigerina and Subbotina species and decreasing in frequency of Acarinina species suggest the low-oxygen level, eutrophic and intermediate condition of the seawater. In this formation, the high abundance of the epifaunal taxa such as Anomalinoides spp., Cibicidoides spp., Gyroidinoides spp., and Lenticulina spp. from the base (late Paleocene sediments) up to E6 biozone reflects oligotrophic and oxic shallow water conditions. The occurrence of several peaks in abundance of Bulimina and Uvigerina species at the Ypresian/Lutetian boundary suggests eutrophic condition. These paleoecological conditions could be correlated with fluctuations in the numbers of the planktonic foraminifera. 相似文献
20.
Facies characterization of Piacenzian （late Pliocene） carbonate sediments of the Guitar Formation in Car Nicobar Island,India and the subsequent integration of paleoecological data have been applied to interpret the paleoenvironment of the coralline algal-reef deposits.Thin-section analysis reveals that Amphiroa,Corallina and Jania are the dominant geniculate corallines,while Lithothamnion,Mesophyllum,Phymatolithon,Lithophyllum,Spongites and Lithoporella are the major non-geniculate corallines contributing to the sedimentary facies.Numerous small and larger benthic foraminifera also dominate the biogenic assemblages.Corals,barnacle shells,echinoid spines,fragments of bryozoans,mollusks and ostracodes are the subordinate constituents.Grainstones dominate the studied facies while packstones and boundstones （with wackestone elements） are the sub lithofacies showing a fair representation.Six carbonate facies presenting a complete reef complex have been distinguished that were deposited in shallow intertidal,back-reef shelf/lagoon,reef and deeper fore-reef shelf settings.Evidences of coralline algal and benthic foraminiferal assemblages,taphonomic signatures of abrasion and fragmentation,grain size,angularity and encrustation indicate a shallow to relatively deeper bathymetric horizon of approximately 10-60 m that corresponds to a regime of high to moderate hydrodynamic conditions. 相似文献