首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 500 毫秒
1.
 Cold-seep communities have relatively low diversity, are dominated by one or two taxa present in high density and high biomass in comparison with the surrounding fauna, and are restricted to aphotic habitats. Their associated heterotrophic fauna are usually distinctive from the fauna of their surroundings. In contrast, a more commonplace chemoautotrophically based community occurs in shallow photic habitats. The associated heterotrophic fauna includes many of the species typical of the surrounding communities and typically dominates abundance, whereas the species with chemoautotrophic symbionts dominate biomass. All modern seep assemblages are deeper than 550 m. Many fossil seep assemblages occurred in water as shallow as the mid-shelf (<200 m). In contrast, communities where species with chemoautotrophic symbionts are biomass dominants, but not numerical dominants, are common in shallow waters at present but rarely reported in the geological record. We suggest that the absence of cold-seep communities on the continental shelf presently is due to a combination of predation and competitive exclusion by primary consumers limiting the presence of species dependent on chemoautotrophic symbionts. We suggest that cold-seep assemblages are more common at shelf depths in the fossil record for two reasons: (a) The biases of preservation have accentuated their distribution by transforming communities where species with chemoautotrophic symbionts dominate by biomass, but not numerically, into cold-seep-appearing assemblages. (b) The importance of predation pressure and oligotrophy has varied, with decreased predation pressure accompanying increased oligotrophy favoring cold-seep communities. We suggest that the paucity of shallow-water assemblages with species harboring chemoautotrophic symbionts as biomass dominants in the fossil record is based on the reliance of paleoecological analysis on numerical abundance data when energy flow analyses are required to identify these assemblages. The distinctiveness of the fossil seep assemblage is intensified by taphonomic processes that bias the assemblage against small individuals and epifaunal species, so that diversity declines, the small heterotrophic component of the assemblage is significantly reduced, and the epifaunal component is minimized. The final assemblage is usually dominated by the better-preserved large infaunal clams which perchance are also the species with chemoautotrophic symbionts. In contrast, preservation does not enhance the distinctiveness of these chemoautotroph-harboring species in shallow water. Received: 16 April 1998 / Accepted: 29 June 1999  相似文献   

2.
To study the quantitative relationship between surface sedimentary diatoms and water depth, 67 surface samples were collected for diatom analysis on eight profiles with water depth variation from the muddy intertidal zone to the shallow sea area in North-Central Bohai Bay, China. The results showed that the distribution of diatoms changed significantly in response to the change in water depth. Furthermore, the quantitative relationship between the distribution of dominant diatom species, their a...  相似文献   

3.
Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths.  相似文献   

4.
朱明善 《沉积学报》1988,6(3):78-88
本文据东海五口探井的559个碎屑矿物样资料,用主要重矿物的含量及其组合特征编绘了含量变化图,试图进行分层比较。位于西湖凹陷的平湖一井和玉泉1井重矿组合特征可比性较好;龙井2井三潭组以下与上两井缺少可比特点;灵峰1井除东海群外,其余地层与上列3井相比,差异是大的。  相似文献   

5.
Hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for As-enrichment in part of the Gangetic plain (Barasat, West Bengal, India). Analysis of water samples from shallow tubewells (depth 24.3–48.5 m) and piezometer wells (depth 12.2–79.2 m) demonstrate that the groundwater is mostly the Ca-HCO3 type and anoxic in nature (mean EhSHE = 34 mV). Arsenic concentrations ranged from <10–538 μg/L, with high concentrations only present in the shallow to medium depth (30–50 m) of the aquifer along with high Fe (0.07–9.8 mg/L) and relatively low Mn (0.15–3.38 mg/L) as also evidenced in core sediments. Most groundwater samples contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V), exhibiting the reducing condition. Results show lower concentrations of NO3, SO4 and NO2 along with higher values of DOC and HCO3, indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of As from sediments into groundwater. Positive correlations of As with Fe and DOC were also observed. The presence of DOC may actively drive the redox processes. This study revealed that reduction processes of FeOOH was the dominant mechanism for the release of As into the groundwater in this part of the Ganges Delta plain.  相似文献   

6.
Well-preserved and abundant Jurassic–Early Cretaceous palynomorph assemblages were recorded from the Kabrit-1 well, north Eastern Desert, Egypt. Thirty-one rock-cutting samples were analyzed and six rock units were differentiated. Seventy-one palynomorph species were identified from the productive samples. Six palynozones were differentiated, and they covered all the studied succession except for a palynomorph barren interval present in the uppermost part. These palynozones arranged in ascending order are as follows: two palynozones were recorded from the Middle-Upper Jurassic (Gonyaulacysta jurassica – Lithodinia jurassica Assemblage Zone and Klukisporites pseudoreticulatus- Systematophora penicillata – Escharisphaeridia pocockii Assemblage Zone) and the other four palynozones characterize the Lower Cretaceous deposits (Pilosisporites trichopapillosus – Cribroperidinium orthoceras Assemblage Zone; Dicheiropollis etruscus Interval Zone; Murospora florida – Afropollis operculatus Assemblage Zone and Afropollis jardinus Range Zone). We infer open marine conditions during deposition of the lower part of the Khalig El Ayoun Formation (Oxfordian-Kimmeridgian) and within the Kharita Formation (Albian), and shallow marine or coastal environments during deposition of the remainder of the studied succession. Paleobiogeographically, Late Jurassic index terrestrial palynomorph species documented here are in common with those previously recorded from North Africa, while marine dinocyst species are common to those documented from the West European and North American province. During the Early Cretaceous, the recorded terrestrial microfloral species were similar to those previously recorded from the West African-South American Province, while the marine dinocyst species were still related to the West European and North American marine palynofloral province.  相似文献   

7.
The southern Kattegat is characterized by a strong halocline at a water depth of 10–20 m. Samples were collected within and below the halocline at 12–58 m. A Q-mode factor analysis identified three major and three minor foraminiferal assemblages, each characterized by one diagnostic species. Linear regression analyses showed that the distribution of assemblages and their diagnostic species is associated with substrate and hydrography. The Bulimina marginata assemblage is connected with fine-grained, organic-rich sediments below the halocline. The Elphidium excavalum and the Eggerelloides scabrus assemblages show weak correlations with substrate and are presumably connected with the halocline. Minor assemblages of Cibicides lobatulus and Textularia bocki are associated with coarse-grained sediments. The Stainforthia fusiformis assemblage has only weak correlation with substrate and hydrography.  相似文献   

8.
The biofacies analysis of benthic foraminifers in sediments of the Sea of Okhotsk paleobasin revealed the presence of typical abyssal species in their Oligocene-Miocene assemblages that are missing in the Pliocene and Pleistocene section. The development of the abyssal fauna in the Sea of Okhotsk was determined by its relatively large depths (>2000 m) and intense water exchange with the Pacific Ocean. The Sakhalin folding phase at the Neogene-Quaternary transition resulted in the uplifting of the Japan-Kurile cordillera and separation of deep basins of the Japan and Okhotsk seas from the ocean, which was responsible for the formation of unfavorable conditions for migration and existence of the Pacific abyssal fauna. The taxonomic similarity and general tendencies in the development of the Neogene benthic foraminifers common for the Japan and Okhotsk seas imply the lack of narrow and shallow thresholds between these basins similar to the present-day Nevel’skoi, La Pérouse, and Sangar straits. Such bottom topography stimulated the intense northward water flow, which determined the similarity between the benthic foraminiferal assemblages of the Japanese and Okhotsk paleobasins.  相似文献   

9.
Quantitative analyses of palynomorph assemblages, particulate organic matter (kerogen), and total organic carbon (TOC) have been made on samples of the Albian–Cenomanian Kharita and Bahariya formations encountered in the Abu Gharadig-5 well, Western Desert, Egypt. Two assemblage palynozones are defined: Assemblage Zone A (Kharita Formation) of late Albian–early Cenomanian age and Assemblage Zone B (Bahariya Formation) of early–middle Cenomanian age. Palynofacies of the Kharita Formation suggest that sedimentation of these strata took place in a warm, shallow, nearshore-marine environment. The deposition of the lower Bahariya Formation took place initially in similar conditions but subsequently further offshore in somewhat deeper water of the inner shelf. The relatively high percentage of Ephedripites, Afropollis and elaterate pollen in both formations indicates an arid climate. The Kharita Formation yields kerogen types III and IV whereas the assemblages recovered from the Bahariya Formation contain types II and III. The TOC is generally between 0.42 and 0.65% in the Kharita Formation, while it ranges between 0.42 and 0.80% in samples of the Bahariya Formation. The spores and pollen grains are pale in colour; hence little source potential for hydrocarbons is indicated.  相似文献   

10.
A previously reported porphyry Cu + Mo deposit in an Eocene pluton within the South Shetland Island magmatic arc has been re-interpreted as three distinct hydrothermal assemblages. The oldest assemblage (1) exsolved under confinement from the deep (～6 km?) cooling magma whereas assemblages (2) and (3) formed during tectonic ± magmatic episodes at depths of < 1.5 km in the late Cenozoic. The three assemblages occur over the 5 × 11 km mapped in Barnard Point tonalite pluton. Assemblage (1) comprises shallowly dipping sheets of aplite, biotite + tourmaline pegmatite, massive ‘grey’ quartz, and quartz + tourmaline + bornite + chalcopyrite + molybdenite veins. Magnetite + tourmaline + chalcopyrite breccias have associated biotite, K-feldspar and muscovite alteration. Fluid inclusions indicate formation from hot (～600°C), saline (40 equivalent weight % NaCl + CaCl2) aqueous-carbonic fluids that exsolved from the partly consolidated magma. The primary control on solution chemistry and nature of fracturing was the depth of pluton emplacement. Assemblage (2) consists of steep, vuggy veins and country-rock breccias, with thick propylitic alteration selvages, cemented by microcrystalline quartz, complex inter-growths of FeMg carbonate, bladed barite and trace amounts of bornite and chalcopyrite. These rocks, previously described as breccia (sensu ‘pebble’) dykes in the porphyry complex, are reinterpreted as an influx of moderately hot (175–330°C), weak to moderately saline (2–21 EWP NaCl), aqueous-carbonic fluids that underwent isobaric boiling at 0.8 to 1.3 km depth. Assemblage (3) consists of thin, hematitic fault infillings formed during a second episode of brittle faulting.  相似文献   

11.
A Late Eocene foraminiferal fauna of free specimens is recorded from Cascade Seamount, a feature of volcanic origin, whose age and fauna were previously studied only in thin section. The fauna is of Late Eocene (P15) age because of the presence of Globigerapsis index, Globigerapsis rubriformis, Subbotina linaperta, Subbotina angiporoides and Chiloguembelina cubensis. Many typical Eocene indicators, such as Hantkenina, Pseudohastigerina and key globorotaliids, are absent. The age is a little older than that estimated for previous samples from the seamount. The fauna is dominated (78%) by benthic species, especially species of Cibicides that have greater affinities with New Zealand faunas than with coeval southern Australian faunas. The sediment and its fauna accumulated near the lower limits of wave activity, off the coast of a volcano that probably stood at least 400 m above sea level. The location has subsided nearly 1000 m over the past 40 million years to its present water depth of 1000 m, suggesting that the entire East Tasman Plateau was approximately 1000 m above its current depth at the time. Conditions were cool temperate and the fauna lacks any warm water indices, consistent with a palaeolatitude of 55–60°S, but also with cool waters at a time of oscillating conditions in southern Australia and also in Antarctica. There is essentially no infauna and the waters were highly oxygenated in the turbulent zone.  相似文献   

12.
于俊杰  胡飞  杨祝良  张宗言  蒋仁  柯学  劳金秀 《地质通报》2014,33(10):1609-1620
对江苏省南通市四甲镇CSJA6钻孔上部近43m的沉积物岩心进行了沉积学、年代学研究和有孔虫鉴定及组合划分,发现41属77种(含8个未定种)有孔虫。根据有孔虫动物群的垂直分布特征与AMS14C年龄,初步建立了时间被部分标定的全新世有孔虫化石组合,自上而下为Ammonia beccarii vars.-Cribrononion subincertum Asano组合、Ammonia beccarii vars.-Globigerinira glutinata组合和Ammonia beccarii vars.-Elphidium magellanicum组合。组合2、3带的时间界线约为8.1ka cal BP,组合3带的下界至少是10ka cal BP。这3个组合带的特征与以珠海、上海地区为代表的中国东部沿海平原全新世有孔虫组合相似。若将前人全新世海侵的14C年龄做进一步的校正,并结合本文钻孔研究成果可初步推测,在8.5~8ka cal BP时长江三角洲地区达到最大海侵,形成以镇江、扬州为顶点的长江巨大河口湾。  相似文献   

13.
The Triassic?Jurassic (Tr?J) boundary marks a major extinction event, which (~200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr?J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key-species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites?Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites?Pinuspollenites Assemblage, and the Sinemurian Perinopollenites?Cycadopites Assemblage. The Tr?J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio?Ferganoconcha and Waagenoperna?Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio?Ferganoconcha and Waagenoperna?Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine?littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian.  相似文献   

14.
Benthonic foraminifera indicate that part of the Middle Miocene Brasso Formation, central Trinidad (planktonic foraminiferal Zones N11–N12), was deposited during a regression. A stratigraphic sequence of five foraminiferal assemblages reflects changes in paleodepth and dissolved oxygen concentration and indicates that the relative fall in sea level brought the seabed into contact with an oxygen minimum zone (OMZ): (1) Assemblage 1 (Uvigerina quesqueyana, Siphonina pulchra) lived in upper bathyal, moderately oxygenated water beneath the OMZ; (2) Assemblage 2 (S. pulchra, Cassidulina laevigata, lesser Globocassidulina subglobosa) lived in outer neritic, moderately oxygenated water below the OMZ; (3) Assemblage 3 (U. subperegrina) occupied the outer neritic, lower margin of the OMZ; (4) Assemblage 4 (Brizalina subaenariensis, U. subperegrina) lived at the core of the OMZ and rates the lowest on the Benthonic Foraminiferal Oxygen Index; and (5) Assemblage 5 (middle-neritic species with few Uvigerina spp. and Brizalina spp.) lived in well-oxygenated water above the OMZ. The onset of the severest oxygen depletion was abrupt and occurred shortly after the N11–N12 boundary. Previous work on the Brasso Formation has reported a similar sequence of benthonic assemblages in planktonic foraminiferal Zones N8–N10. These assemblages may be useful for local correlation of the Brasso Formation.  相似文献   

15.
Recent collecting in exposures of the lowermost Burgersdorp Formation (Beaufort Group), of the Karoo Basin of South Africa, has revealed a previously unknown fish fauna from the Early Triassic (Scythian), lowermost Cynognathus Assemblage Zone (CAZ), which forms an important component of the total vertebrate assemblage. The newly discovered fish material includes lungfish, saurichthyids, and a large microfauna that includes numerous isolated chondrichthyan teeth, two fin spine fragments, and actinopterygian scales and teeth. The latest fish finds, together with the lowermost Cynognathus Assemblage Zone vertebrate faunas, make this Karoo Basin Assemblage Zone one of the most diverse Early Triassic faunal assemblages, comparable in faunal diversity to those from the Czatkowice Formation (Poland) and the Arcadia Formation (Australia). The presence of the lungfish Ptychoceratodus phillipsi in the early Middle Triassic Cynognathus Assemblage Zone (Subzone B), and in the underlying latest Early Triassic Cynognathus Assemblage Zone (Subzone A), indicates that these lungfish could serve as range index fossils within the CAZ, and thus are potentially useful biostratigraphic markers across the Early-Middle Triassic boundary. Furthermore the ‘new’ fish fauna provides a vital marine realm link in particular with the faunas of Madagascar and Australia, that is unavailable using the tetrapod faunal elements of the lower CAZ.  相似文献   

16.
平凉安国镇六盘山群介形类   总被引：4，自引：0，他引：4  
李祖望 《甘肃地质》1995,4(2):10-21,T003
平凉安国镇六盘山群的介形类化石采自和尚堡组、李洼峡组与马东山组，计１０属２２种（含６新种、１新亚种、３未定种）。自下而上可分为：Ｃｙｐｒｉｄｅａ（Ｕｌｗｅｌｌｉａ）－Ｄａｍｏｎｅｌｌａ组合，时代属中上凡兰吟期；Ｃｙｐｒｉｄｅａ（Ｃｙｐｒｉｄｅａ）－Ｚｉｚｉｐｈｏｃｙｐｒｉｓ组合，时代属豪特里维一巴列姆期及Ｃｙｐｒｉｄｅａ－Ｌｉｕｐａｎｓｈａｎｉａ组合，时代属阿普第期。  相似文献   

17.
The varved sediments of the Santa Barbara Basin off southern California, offer a unique opportunity to study the changes in oceanographic conditions of this nearshore area during the last 8000 yr. Quantitative analysis of Radiolaria found in recent surface sediment samples from the eastern North Pacific allows the identification of four “assemblages” which can be related to the physical oceanography of the California Current. Two assemblages are associated with the southerly flowing California Current, one with the main stream of the current (California Current Assemblage) and the other with the offshore flow along northern California (Central Assemblage). The two other assemblages are associated with the subtropical region of the eastern North Pacific (Subtropical Assemblage) and one found mostly off the coast of Baja California (Baja Assemblage). Analysis of the Radiolaria found in the varved sediments of a core from the Santa Barbara Basin give an 8000-yr continuous record of these four assemblages. The California and Baja Assemblages show only minor fluctuations in their importance in the sediments of the Santa Barbara Basin. The California Assemblage, however, shows a steady increase during this time period. Prior to 5400 yr B.P. the Radiolaria were predominately subtropical in character, whereas after 5400 yr B.P. the Central Assemblage becomes more important. Since 5400 yr B.P. most of the changes in the radiolarian fauna consist of fluctuations in the importance of these two assemblages. Past sea-surface temperatures for the month of February were calculated using the transfer function technique of J. Imbrie and N. G. Kipp (1971, In “The Late Cenozore Glacial Ages” L. K. Turekian, Ed.), (Chap. 5, Yale Univ. Press, New Haven, Conn.). The time series of paleotemperature estimates show major changes in the average February temperature of Santa Barbara Basin waters. The range of estimated temperatures (12°C) exceeds that of the historical observations of February temperatures in the Santa Barbara Basin but does not exceed the observed range for the California Current region. The intervals from 800 to 1800 yr B.P. 3600 to 3800 yr B.P. and 5400 to the end of the record appear to have been generally warmer than today. Comparison of the Holocene record of alpine glacial advances with the radiolarian assemblage and paleotemperature time series shows that the initiations of advances was coincident with a decrease in sea-surface temperatures and an increase in the importance of the Central Assemblage in the Santa Barbara Basin. The terminations of these advances were not marked by any consistent characteristic in the Santa Barbara Basin time series.  相似文献   

18.
The Paleocene/Eocene boundary intervals were studied in three outcrops along the Nile Valley: Gabal Taramsa, Gabal Qreiya, and Gabal Nag El Quda in Qena and Esna regions. The planktonic and benthic foraminifera have been examined. The qualitative study of planktonic foraminifera distinguishes eight planktonic biozones from (P4 and P5) Paleocene age to (E1, E2, E3, E4, E5, and E6) Early Eocene age. The analysis of quantitative distribution patterns of benthic foraminifera allows the reconstruction of the paleoenvironmental settings in the studied area. The disappearance or scarce appearance of deeper-water benthic foraminifera (Angulogavelinella avnimelechi and Gavelinella rubiginosus) and increasing dominance of shallow-marine taxa (Buliminides, Loxostomoides applinae) indicate deposition in shallow water environments. The benthic foraminiferal assemblages which dominated by Loxostomoides applinae, Buliminids, and Lenticulina indicate Dysoxic conditions and maximum food levels. The species of mid-way type fauna dominate the assemblages of the studied area; the species of Velasco-type fauna are very rare.  相似文献   

19.
经过对青海同仁县古浪堤组实测剖面的17块样品做孢粉分析, 在6个层位样品中见有孢粉化石30属41种, 据此在该剖面自下而上划分2个孢粉组合:Dictyophyllidites-Di-saccus组合和Verrucosisporites-Di-saccus组合.上述孢粉组合中的孢粉的优势属为Dictyophyllidites, Cyathidites, Verrucosisporites和Chasmatosporites, Protopicea, Pinuspollenites.其中, Dictyophyllidites频繁出现于欧亚、北美、大洋州的晚三叠世和早侏罗世组合, Aratrisporites在南半球大量发育于中三叠世, Asseretospora在澳大利亚的分布时期是中三叠世-早侏罗世.前人于黄南的阿龙江上游及柴陇沟北, 古浪堤组产卡尼期的菊石Protrachycerassp.及双壳类Eumorphotis (Asoella) cf.illyrica.综合而言, 该地区古浪堤组时代厘定为中-晚三叠世, 古植物群生长于暖温带-亚热带河控三角洲环境.   相似文献   

20.
Forty-seven samples from Upper Cretaceous sections penetrated by the Kachi-1 and Inga-1 wells in the South Yellow Sea Basin have been analysed for their spore and pollen content. Thirty-five species of 18 spore genera and 54 species of 28 pollen genera are documented. One new monotypic genus, Diporocolpopollenites, and its type species, D. kachiensis sp. nov., are erected, and Dilwynites Harris, 1965, and its type species, D. granulatus Harris, 1965, are emended. There are also three new combinations: Ephedripites eocaenicus (Selling, 1944), E. praeclarus (Chlonova, 1961), and Retitricolpites anguloluminosus (Anderson, 1960). Two palynological zones are erected: anAquilapollenites attenuatus Assemblage Zone, which encompasses deposits that are considered to be latest Campanian–Early Maastrichtian in age, and an Aquilapollenites eurypteronus Assemblage Zone for sections that have been dated as Late Maastrichtian. The assemblages are typical of the Yenisey-Amur Subprovince of the Aquilapollenites (floral) Province. Lowland floodplain to shallow, commonly mesotrophic, lacustrine environments of deposition are indicated. The climate was probably wet subtropical, with rainfall being somewhat higher during the Late Maastrichtian than through the latest Campanian–Early Maastrichtian.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号