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1.
Quaternary sediment deposits are well exposed along the eastern coastal margin of Sri Lanka. Systematic trace fossil studies along with sediment characteristics have been carried out for the first time to interpret the paleoenvironment that prevailed during Quaternary sedimentation in eastern Sri Lanka. The trace fossils Thalassinoides, Skolithos and Polykladichnus have been recognized about 5m above the present mean sea level. Features of the major trace fossil, Thalassinoides, indicate that it was formed by Thalassinidean shrimp Calianassa. Isolated, vertical to steeply inclined, cylindrical to sub cylindrical tubes with thin internal wall lining and inner wall striations of Skolithos and Polykladichnus show that they were formed by polychaetes. The typical characteristic of Polykladichnus isY-shaped branching with slight enlargement at junctions. Morphology and association of burrows as well as mineralogy, grain size and roundness of sediments indicate that the environment prevailed was marine soft grounds of the intertidal zone. Presence of preserved fine-scale features of burrows indicate that the bioturbated sandy tidal flat was suddenly exposed to the tropical environment due to sea level regression in Quaternary periods. Due to the microbial activities of wall linings, burrows were preserved and it was supported by other microbial activities that produced secondary iron bearing minerals that suffered subsequent oxidation. The bio-origination of red sediments of eastern coastal area of the present study can be used to interpret the debatable origin of the red beds found in northwestern and southeastern coastal areas of the island.  相似文献   

2.
At Siwa Oasis, the carbonate-rich Middle Miocene Marmarica Formation includes several firmground discontinuity surfaces, characterized by extensive burrow systems. These surfaces are confined to the boundary between the Oasis and Siwa Escarpment members in addition to several intraformational marine firmground discontinuities at several horizons within these two members. The marine trace fossils from all these discontinuities are represented mainly by the ichnogenus Thalassinoides. In all occurrences, Thalassinoides are characterized by a sharp erosional lower contact and grades upward into fossiliferous argillaceous limestone facies. Three Thalassinoides ichnospecies have been reported, including: Th. horizontalis Myrow, 1995, Th. suevicus (Rieth, 1932) and Th. paradoxicus (Woodward, 1830). They are mostly recorded as hypichnial/endichnial forms at the sole of fossiliferous argillaceous limestone facies. Rare exichnial occurrences are also recorded. Thalassinoides ichnospecies displayed considerable variations in their stratigraphic distribution, in addition to remarkable variations in their complexity and dimension. These variations are mostly reflecting environmental conditions prevailed during the trace-maker life. Paleoenvironmental interpretation of these burrows confirmed a well-oxygenated shallow marine environment with extremely slow or nearly nil rate of sedimentation.  相似文献   

3.
The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia. Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated muddy bottom with a low rate of sedimentation is envisaged. An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia.  相似文献   

4.
Trace fossils namely, Planolites, Planolites montanus, Thalassinoides and stuff burrows belonging to the Lameta Formation of Central India are reported for the first time from two new localities, i.e., Salbardi and Belkher area. Both the exposures are well represented by the typical marker lithounits as of Jabalpur, Nand-Dongargaon area of central India, i.e., greenish yellow sandstone, clays of various shades, chertified and brecciated limestones, etc. These successions are devoid of megaforal remains, therefore, these biogenic structures play a significant role in the interpretation of palaeoenvironment and palaeoecology during the deposition of the Lameta sediments. The trace fossils assemblage shows that the benthonic community was mainly polychaetes and crustaceans.  相似文献   

5.
In the first ever systematic study of trace fossils from the Badhaura Formation, the authors described a nesting burrow, which they ascribed to a stomatopod. The purpose of this paper is two-fold: primarily, to document ichnofauna from (post-glacial marine late Palaeozoic rocks of peninsular India) the Badhaura Formation (Sterlitmakian) representing marine rocks deposited following the Late Palaeozoic glaciation and secondly to contribute to the data on post-glacial ichnofauna from constituent continents of the Gondwanaland. Trace fossils described here are from the Harbans Bed, the topmost lithounit of the Badhaura Formation. The ichnofauna includes Arenicolites tenuis, Beaconites isp., Curvolithus isp., Cylindrichnus concentricus, Didymaulichnus lyelli, Ophiomorpha isp., Palaeophycus tubularis, Planolites beverleyensis, P. montanus, Rosselia chonoides, R. socialis, Skolithos linearis, Taenidium cameronensis, Thalassinoides paradoxicus, Thalassinoides isp. and a flask-shaped brood chamber assigned to a stomatopod crustacean. This mixed assemblage is assigned to distal Skolithos ichnofacies and is suggestive of a period of relatively quiet, shallow water conditions of deposition. The ichnofauna, when viewed in context of peri-gondwanic ichnofaunas, mainly consisting of simple tracks and trails, from late Palaeozoic post-glacial deposits of other Gondwanan continents, is interesting due to dominance of domichnia. Profusion of brood chambers along with Thalassinoides in the Badhaura Formation validates the concept of pre-Mesozoic Thalassinoides being non-decapod in origin and suggestive of adaptive convergence.  相似文献   

6.
Dhosa Oolite Member of the Jumara Formation comprises alternating bands of oolitic limestones and shales, exposed in Jhura dome of Mainland Kachchh, Western India. This sequence is highly bioturbated and exhibits a moderate diversity and behaviourally complex assemblage of ichnospecies. The rhythmically bedded sequence shows three different levels of preservation of traces. Epichnial tiering consists of moderately bioturbated oolitic limestone exhibiting horizontal or low-angle protrusive/retrusive biogenic laminae, commonly dominated by feeding structures like Rhizocorallium jenense, R. irregulare, Zoophycos brianteus and Zoophycos isp. The endichnial structures within the oolitic limestone can be separated into two different preservational trace fossil suites. The endichnial shallow suites consist chiefly of deposit feeders like Chondrites intricatus, C. targionii, Planolites beverleyensis, Taenidium cameronensis, Thalassinoides isp., Z. brianteus, Z. cf circinnatus and Zoophycos isp. and few suspension feeder forms like Palaeophycus tubularis; while endichnial deep suites consist of Chondrites intricatus, Skolithos linearis and Zoophycos isp. Hypichnial structures consists abundant, cylindrical, branched, horizontal, large-sized three dimensional feeding burrows of Thalassinoides isp. and somewhat irregular, obtuse angle ramification burrows of Phycodes isp., which are attached to the lower surface of the casting medium. The trace fossil association indicates Cruziana ichnofacies and abundance of Zoophycus species below the fair weather wave base level is largely a preservational artifact. The preservational processes of the trace fossils indicate soft substrate and diversity and their abundance reflects the other palaeoecological parameters of the open shallow marine environments.  相似文献   

7.
New lithological, ichnological, and isotope data are given for the rhythm from the section of the Middle Cenomanian rhythmic sequence at Mount Selbukhra. The intense rock bioturbation has distinct multistage structure that is typical of writing chalk sections and corresponds to the Cruziana ichnofacies that are characteristic of the soft grounds of the open shelf. The values of the ??13C and ??18O ratios in ichnofossils contradicts the model of the farming structures for the Chondrites and Zoophycos and indicate the passive infilling of Thalassinoides burrows by sediments. It was established that organic-rich marlstones accumulated under higher bioproductivity and the bottom anoxia were augmented by dissolution cycles. Based on our data, it is not possible to relate the rhythmicity to the precession cycles with confidence.  相似文献   

8.
In Jabalpur area about 18 m to 45 m thick Lameta Formation is stratigraphically divisible into five lithounits namely, Green Sandstone, Lower Limestone, Mottled Nodular Beds, Upper Limestone and Upper Sandstone. Having differentiated lithofacies constitution and here grouped as facies associations, these units are intensively burrowed and sparingly fossiliferous. Ichnogenera including Arenicolites, Calycraterion, Fucusopsis, Laevicyclus, Macanopsis, Ophiomorpha, Paleomeandron, Rhizocorallium, Stipsellus, Thalassinoides and Zoophycos are recovered from the Lower Limestone, Mottled Nodular Beds and Upper Limestone associations of the Lameta Formation of Jabalpur area.Among these, Arenicolites, Calycraterion, Laevicyclus, Ophiomorpha, Rhizocorallium, Stipsellus and Thalassinoides belong to mixed Skolithos and Cruziana ichnofacies and indicate sandy backshore to sublittoral condition of deposition. Additionally rhyzocretes, some times chertified, are also present in different parts of the Lameta Formation. Ichnofacies assemblage supported by sedimentological information suggests that the Lameta Formation of Jabalpur area was deposited in coastal marine settings where sediments were subaerially exposed intermittently.  相似文献   

9.
The arrangement of sediment couplets preserved in Thalassinoides shafts suggests that tides regulated the passive filling of these trace fossils and, thus, represent tubular tidalites. The thickness variation in individual layers and couplets implies a mixed diurnal, semi‐diurnal tidal signature where packages of either thick‐layered or thin‐layered couplets alternate. Calcarenitic sediment accumulated when tidal current velocity was too high to allow deposition of mud, whereas a marly mud layer is interpreted to have formed during more tranquil times of a tidal cycle (in particular, low‐tide slack water). The tidal record within the burrows covers a few weeks and the corresponding spring–neap cycles. The fill of the Thalassinoides shafts is the only known record to decipher the tidal signature from otherwise totally bioturbated sediments. These deposits accumulated in a lower‐shoreface to upper‐offshore setting during the late Miocene on a shallow shelf extending from the Atlantic Ocean to the west into northern Patagonia. The fill of all investigated burrows started around spring tide and, thus, the behaviour of the burrow producers – probably crustaceans – is speculated to have been affected by tides or the high water level because all studied burrows became abandoned around the same period of a tidal cycle.  相似文献   

10.
Trace fossils provide detailed palaeoenvironmental and palaeoecological information of both ancient and modern sedimentary systems. During middle Miocene times the Aures Massif located in the northeastern part of Algeria, was affected by, at least, one marine transgression. The latter led to the installation of a carbonate platform, which is placed, for the first time, in a Mediterranean context. In the Rhassira basin, the Middle Miocene marine succession is characterised by carbonate platform deposits dominated by rhodolith beds, typical of those known throughout the Mediterranean area. This succession can be divided into many units separated by discontinuities interpreted here as omission surfaces. The Djebel Arhane section shows two omission surfaces characterised by a pre-omission suite (firmground) represented by Balanoglossites burrows for the first surface and Gastrochaenolites ornatus burrows/borings for the second one, and an omission suite (hardground) as evidenced by the bioerosive structures Trypanites and Caulostrepsis, in both surfaces, respectively. Gastrochaenolites ornatus traces were formed and preserved in firm, compact, semi-lithified and fine-grained substrates (firm- to hardground), indicating the Glossifungites ichnofacies. They show bioglyphs which have been formed during contraction of the posterior adductor muscles. These suggest that their tracemakers were represented by suspension-feeding bivalves, most probably Pholadidae or Mytilidae, which rotated during penetration. The fill of these traces is composed of marine deposits related to a transgressive lag. The omission suite is divided into two ichnocoenoses: (i) pre-lithification burrows/borings, and (ii) post-lithification borings. This is the first report of the ichnotaxon G. ornatus from Algeria.  相似文献   

11.
Well preserved ichnofossils were found in Kulakkalnattam sandstone exposed at Kulakkalnattam stream in Ariyalur area, Cauvery Basin. It consists of infaunal structures of both suspension and deposit feeders. Five ichnofossils are present in a fine to coarse grain sandstone which includes Ophiomorpha, Palaeophycus, Planolites Skolithos, and Thalassinoides. The study infers that ichnofossils Skolithos and Ophiomorpha are infaunal colonization of the suspension feeders in high energy condition in shifting substrate, whereas Thalassinoides and Planolites-Palaeophycus ichnofossils indicate infaunal deposit feeders living at the sediment-sediment interface in low to moderate energy conditions. Furthermore, the abundance and diversity of the trace fossils indicates there was alternatively fluctuations in energy conditions which lead to development of Skolithos and Cruziana ichnofacies type condition during the deposition of Kulkkallanattam sandstone in foreshore-shoreface environments.  相似文献   

12.
The ichnofossil Rhizocorallium—an oblique to horizontal U-shaped spreiten burrow—has been recognized in a broad range of Phanerozoic continental, marginal marine, and shallow to deep marine facies. Nonetheless, occurrences of this ichnotaxon in Cretaceous estuarine deposits are rarely described. Herein we document Rhizocorallium in the Ingersoll shale, a carbonaceous clay lens within an estuarine succession contained in the Upper Cretaceous (Santonian) Eutaw Formation exposed in the eastern U.S. Gulf coastal plain. The Ingersoll Rhizocorallium specimens, assigned to R. commune var. irregulare based on their basic morphology, horizontal disposition, dimensions, and actively filled spreiten, record a change in depositional conditions and substrate consistency linked to transgression. The Ingersoll shale accumulated rapidly in a restricted tidal channel in a bayhead delta setting and hosts an impoverished resident ichnofauna reflecting soupground conditions. In contrast, attributes of Rhizocorallium (e.g., burrow wall bioglyphs) and associated Thalassinoides in the upper part of the Ingersoll shale reflect firm substrates (i.e., Glossifungites ichnofacies). Firmground development and colonization reflect burial dewatering and subsequent exhumation by bay-shoreline ravinement of clays and the concomitant shift to estuarine central bay deposition. The biological affinity of the Rhizocorallium trace makers cannot be confidently established. However, based on relatively straight and seemingly current-aligned axes, passive burrow fills, lack of associated fecal pellets, and emplacement in firm clay, these structures were likely produced by suspension-feeding organisms—either crustaceans or worms—that took advantage of wave- or tide-induced currents in shallow areas near the estuary head.  相似文献   

13.
Reported ancient bottom current deposits in deep marine settings are scarce and most of them remain contentious. This study describes sedimentological, ichnological and petrographical characteristics of a drill core that covers ca 10 Myr of Upper Cretaceous stratigraphy at Hold with Hope, north-east Greenland. The core is divided into four facies associations, which are interpreted to reflect deposition from bottom currents, turbidity flows and hemipelagic settling in slope and/or near slope environments. The evidence for bottom current influence is three-fold. Firstly, pervasive indications of winnowing such as marine bioclast-rich lags and outsized clasts on ‘mud on mud’ contacts are suggestive of low-sediment concentration flows capable of transporting up to pebble-sized clasts. Common Mn–Fe–Mg rich carbonate matrix cements and various types of hiatal chemogenic lag deposits showing glauconite, apatite and carbonate clasts also point to condensation, prolonged exposure at the sediment–water interface and recurrent phases of sea-floor erosion. Secondly, such deposits can show indicators for tidal processes such as double mud-drapes, tangential bottom sets in dune-scale cross-bedding and cyclic rhythmites. Thirdly, inverse to normal grading at various scales is common in fully marine, commonly seafloor-derived sediments. Ichnological data indicate considerable taxonomic variability in the bottom current deposits, but recurrent fabrics are characteristically dominated by morphologically simple burrows such as Thalassinoides and Planolites, with secondary Phycosiphon, Nereites, Zoophycos and/or Chondrites. In general, opportunistic taxa are common whereas mature composite ichnofabrics are rare. The omission surfaces are locally burrowed with stiffground to firmground trace fossil suites. The results contribute to establishing sedimentological, ichnological and mineralogical criteria for recognition of bottom current deposits as well as to the understanding of the Late Cretaceous palaeoenvironmental evolution of the Arctic region.  相似文献   

14.
Facies analyses and a sequence stratigraphical framework with regional correlation of the upper Campanian phosphate province are presented, based on three main sections located in Egypt (Gebel Duwi and Abu Tartur sections) and north Jordan (Umm Qais section). Fifteen facies types were grouped into: phosphate (FT1–5), carbonate (FT6–11) and siliciclastic (FT12–15) facies associations. The main component of phosphate rocks is pellets in situ and common reworked biogenic debris, especially in the upper phosphate beds (e.g. fish teeth and bones), which along with abundant Thalassinoides burrows suggests that the skeletal material was the main source for phosphates in Egypt; in contrast the common authigenic phosphatic grains (pristine) in Jordan reflect an upwelling regime. Based on age assignment as well as stratigraphical position, the phosphorite beds show great similarity that may suggests a similar origin and proximity during the period of deposition of the Duwi Formation of the Red Sea coast of Egypt and its equivalent, the Al-Hisa Phosphorite Formation in Jordan, which represents an early transgressive system tract of a depositional sequence. On the Abu Tartur plateau, the presence of sandy pyritic phosphatic grainstone (FT1) and glauconitic quartz arenite (FT12) in the middle part of the studied section, along with the absence of chert facies (FT14), reflects a more shallow marine depositional environment with increased fluvial sediment supply compared to those along the Red Sea coast and north Jordan.  相似文献   

15.
Sediments of Manaveli Formation (Palaeocene) are studied from the Thondaimanattam quarry section and Manaveli section of the Pondicherry area, which comprises of bioturbated arenaceous limestone-shale and shaly-sandstone sequences respectively. These sediments consist of high density and low diversity trace fossil genera which includes Lanicodichnus, Ophiomorpha, Planolites, Palaeophycus, Skolithos, Thalassinoides, and Polychaetes tubes. The abundance of horizontal structures of the Thondaimanattam quarry section indicate low to moderate wave and current energy in fully marine subtidal environments while the presences of vertical structures of the Manaveli section indicate moderate to high wave and current energy in the marginal marine environment of deposition for the Palaeocene sediments of the Pondicherry area.  相似文献   

16.
The C and N stable isotope compositions of some flora of East Africa from coastal Tanzania and Amboseli National Park (Kenya) are used to assess if they can be used as a terrestrial end member during the estimation of terrestrial fraction in coastal marine sediments. The results of C isotope composition of various tree leaves, which average −29.3 ± 1.4%, indicate that these tropical higher land plant species follow a Calvin-Benson or non-Kranz (C3) type of metabolism. The results for grass species, which average −13.2 ± 2.4%, indicate that most of them follow a Hatch-Slack or Kranz (C4) type of metabolism. However, some of the succulent plants from the Amboseli National Park have δ13C values that average −14.7%, an indication that they follow a CAM (Crassulacean Acid Metabolism) type of metabolism. The N isotope values are relatively higher than expected for the terrestrial organic material. The average δ15N values for both tree and grass samples are higher than 5% and fall within the range normally considered to be marine. The high enrichment in 15N may be related to the environmental conditions in which plants thrive. Plants growing in sandy, dry and overgrazed environments are expected to be enriched in 15N owing to full utilisation of all available N species, regardless of their isotopic compositions. Other processes which may cause an enrichment in 15N include adsorption by various types of clay minerals, supply of 15N-enriched nitrate through sea-spray, and local denitrification, especially in swampy and lake margins where the input of organic matter may be higher than the rate of decomposition.The stable isotopic composition of organic C and N for surficial organic matter for the coastal marine sediments averages −17.0 ± 0.9% and 5.4 ± 1.1%, respectively. These values indicate a substantial contribution of C4 plants and sea grasses. However, contribution of C4 relative to that of sea grasses can not be evaluated owing to the fact that there is no significant difference in the isotopic compositions between the two groups.In the savannah environment, where a contribution from the C4 types of plants might be substantial, the δ13C value for a terrestrial end member needs to be established prior to evaluation of the terrestrially derived organic matter in the marine environment. Owing to a significant contribution of sea grasses to the total organic matter preserved in coastal marine sediments, the stable isotopes of organic C seem to have a limited applicability as source indicators in the East African coastal waters. Furthermore, the results indicate that N stable isotopes seem to have a limited applicability as source indicators in coastal waters of East Africa. However, more work needs to be conducted to determine the terrestrial and sea grass end member values for the coastal areas.  相似文献   

17.
In the locality of Rambla de los Gavilanes (Betic Chain Murcia, Spain), six new outcrops with dinosaur footprints are reported from an uppermost Cretaceous succession of coastal marine deposits. Four of these sites are found in the upper part of the lower Maastrichtian and the other two in the upper Maastrichtian, these latter located only a few meters below the Cretaceous-Paleocene boundary (K/Pg). Traces appear as impressions or as natural casts, on tabular limestone beds consisting of micritic carbonate facies, these deposited in coastal marine areas that include a variety of environments (coastal lakes, tidal flats, salt marshes, and shallow coastal lakes). Two main types of traces have been recognized, respectively attributed to sauropod footprints and large ornithopod footprints with remarkable pointed hoof marks. The Maastrichtian sites with large ornithopod footprints in Europe are reported from Spain, Poland and Romania. Sauropod (titanosaurian), theropod (Irenesauripus and other undetermined theropods), and ornithopod footprints have been found at sites located up to 20 m below the K/Pg boundary. The Spanish dinosaur ichnites known closest to the K/Pg boundary are in the Pyrenean upper Maastrichtian, and are tridactyl, theropod and ornithopod (Hadrosauropodus and Amblydactylus) footprints. In this work, the assignation of the Rambla de los Gavilanes ornithopod footprints has been made following the recommended synthesis in several recent papers which reduce the large ornithopod ichnogenus to four.  相似文献   

18.
Two types of ‘pseudobreccia’, one with grey and the other with brown mottle fabrics, occur in shoaling‐upward cycles of the Urswick Limestone Formation of Asbian (Late Dinantian, Carboniferous) age in the southern Lake District, UK. The grey mottle pseudobreccia occurs in cycle‐base packstones and developed after backfilling and abandonment of Thalassinoides burrow systems. Burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence. Mottling formed when an early diagenetic ‘aerobic decay clock’ operating on buried organic material was stopped, and sediment entered the sulphate reduction zone. This probably occurred during progradation of grainstone shoal facies, after which there was initial exposure to meteoric water. Microspar calcites then formed rapidly as a result of aragonite stabilization. The precipitation of the main meteoric cements and aragonite bioclast dissolution post‐date this stabilisation event. The brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete, which developed beneath palaeokarstic surfaces capping cycle‐top grainstones and post‐date all depositional fabrics, although they may also follow primary depositional heterogeneities such as burrows. They consist of coarse, inclusion‐rich, microspar calcites that are always very dull to non‐luminescent under cathodoluminescence, sometimes with some thin bright zones. These are interpreted as capillary rise and pedogenic calcrete precipitates. The δ18O values (?5‰ to ?8‰, PDB) and the δ13C values (+2‰ to ?3‰, PDB) of the ‘pseudobreccias’ are lower than the estimated δ18O values (?3‰ to ?1‰ PDB) and δ13C values of (+2‰ to +4‰ PDB) of normal marine calcite precipitated from Late Dinantian sea water, reflecting the influence of meteoric waters and the input of organic carbon.  相似文献   

19.
Sedimentological, ichnological and paleontological analyses of the Early Miocene uppermost Monte León Formation and the lower part of the Santa Cruz Formation were carried out in Rincón del Buque (RDB), a fossiliferous locality north of Río Coyle in Santa Cruz Province, Patagonia, Argentina. This locality is of special importance because it contains the basal contact between the Monte Léon (MLF) and the Santa Cruz (SCF) formations and because it preserves a rich fossil assemblage of marine invertebrates and marine trace fossils, and terrestrial vertebrates and plants, which has not been extensively studied. A ∼90 m-thick section of the MLF and the SCF that crops out at RDB was selected for this study. Eleven facies associations (FA) are described, which are, from base to top: subtidal–intertidal deposits with Crassotrea orbignyi and bioturbation of the Skolithos-Cruziana ichnofacies (FA1); tidal creek deposits with terrestrial fossil mammals and Ophiomorpha isp. burrows (FA2); tidal flat deposits with Glossifungites ichnofacies (FA3); deposits of tidal channels (FA4) and tidal sand flats (FA5) both with and impoverish Skolithos ichnofacies associated; marsh deposits (FA6); tidal point bar deposits recording a depauperate mixture of both the Skolithos and Cruziana ichnofacies (FA7); fluvial channel deposits (FA8); fluvial point bar deposits (FA9); floodplain deposits (FA10); and pyroclastic and volcaniclastic deposits of the floodplain where terrestrial fossil mammal remains occur (FA11).The transition of the MLF–SCF at RDB reflects a changing depositional environment from the outer part of an estuary (FA1) through the central (FA2–6) to inner part of a tide-dominated estuary (FA7). Finally a fluvial system occurs with single channels of relatively low energy and low sinuosity enclosed by a broad, low-energy floodplain dominated by partially edaphized ash-fall, sheet-flood, and overbank deposits (FA8–11). Pyroclastic and volcaniclastic materials throughout the succession must have been deposited as ash-fall distal facies in a fluvial setting and also were carried by fluvial streams and redeposited in both estuarine and fluvial settings. These materials preserve most of the analyzed terrestrial fossil mammals that characterize the Santacrucian age of the RDB's succession. Episodic sedimentation under volcanic influence, high sedimentation rates and a relatively warm and seasonal climate are inferred for the MLF and SCF section.Lateral continuity of the marker horizons at RDB serve for correlation with other coastal localities such as the lower part of the coastal SCF south of Río Coyle (∼17.6–17.4 Ma) belonging to the Estancia La Costa Member of the SCF.  相似文献   

20.
13C- and 1H-NMR spectra were obtained for humic substances isolated from a coastal marine environment and also for the intracellular and extracellular extracts of a marine diatom. Phaeodactylum tricornutum Bohlin. Highly branched alkyl chains constitute a large proportion of the structure of the marine humic material, whereas aromatic components are less important. Carbohydrate-type materials, possibly uronic acids, are also present in appreciable amounts. Furans (derived from carbohydrates). pyrroles and nitriles (derived from proteins, nucleic acids and/or tetrapyrroles) and phenols and methylphenols (non-lignin derived) are pyrolysis products derived from pyrolysis-gas chromatography-mass spectrometry of the extracts. The results indicate the similarities in chemical structure of P. tricornutum exudate and dissolved marine humic material.  相似文献   

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