The Late Tremadocian(Ordovician)Graptolite Kiaerograptus from Central Hunan,China:Taxonomy and Biostratigraphy

Well-preserved graptolites of the genus Kiaerograptus are first reported from the upper Tremadocian Yinchupu Formation in the Nanba section,Yiyang,Hunan Province,South China,including four species,i.e.,Kiaerograptus lauzonensis(Erdtmann,1966),Kiaerograptus stoermeri(Erdtmann,1965),Kiaerograptus cf.supremus?Lindholm,1991,and Kiaerograptus sp.,which are robust in form.Based on these new specimens,the Kiaerograptus biozone is established for the first time in South China,increasing the late Tremadoc graptolite biozones in South China from four to five,in ascending order as follows:the Adelograptus tenellus biozone,the Aorograptus victoriae biozone,the Kiaerograptus biozone,the Sagenograptus murrayi biozone,and the Hunnegraptus copiosus biozone.A review of the occurrence records for robust Kiaerograptus species worldwide reveals that the distribution is restricted to the Aorograptus victoriae biozone and Kiaerograptus biozone in the late Tremadocian.This limited stratigraphical distribution makes Kiaerograptus a valuable taxon for precise biostratigraphical correlation at both the regional and global scales.

Biostratigraphy, Palynofacies and Organic Geochemical Characterization of Three Wells, Western Offshore Niger Delta Nigeria

Ditch samples from AP-4, ER-51 and UK-2 offshore Niger Delta were subjected to biostratigraphic and organic geochemical analyses which entail foraminiferal, palynological, Spore Colour Index (SCI), Rock-Eval Pyrolysis and Fourier Transform Infrared Spectroscopy (FTIR) analyses. The results have established N19 and N17;N17, N16 and N15;and N9 and N8 biozones;and P600 and P700 palynological zones. The dominance of palynomaceral (PM) I and II suggests Type III kerogen. PM III and IV (Type II and IV) were recorded. SCI ranges from 3/4 to 5/6 suggesting an early to mature liquid hydrocarbon generation phase. Rock-Eval Pyrolysis shows that the Total Organic Carbon (TOC), Hydrogen Index (HI), Pyrolysis temperature (Tmax), and Vitrinite Reflectance (VRo) range from 2.48 wt% - 6.37 wt%, 78 - 258, 411°C - 431°C and 0.26% - 0.69% respectively suggesting high TOC of Type II/III kerogen. FTIR indices show Type I kerogen in all the wells. VRo results range from 0.4 - 0.5 indicating an immature source. High concentrations of aliphatic saturates in identified functional groups indicate a low biodegradation. The abundance and diversity of recovered assemblages and dominance of PM I and II suggest shallow depositional environments with an age range of late Miocene to early Pliocene. Palynomaceral, SCI, and Rock-Eval inference contradict FTIR kerogen type suggesting that IR spectroscopy might not be suitable for kerogen typing and origin. The geochemical and biostratigraphical inferences must be corroborated for a successful evaluation. However, the source rock in the study area has adequate organic matter with the prospect to generate both oil and gas at appropriate maturity.

泥河湾盆地第四纪哺乳动物群概览及若干新认识

泥河湾盆地最初以其广泛分布的含化石河湖相地层而受关注,并以其丰富的哺乳动物化石而著称于世,而今,泥河湾盆地已成为世界著名旧石器考古重地和研究第四纪地质古生物的重要场所。狭义泥河湾动物群(或下沙沟动物群)是我国北方早更新世的标准动物群,其古地磁年龄是2.2-1.7 MaBP。随着地层古生物工作的深入开展,盆地内也发现了若干中-晚更新世化石点;丁家堡水库全新统中发现的象颊齿,之前被鉴定为亚洲象,新的测年数据表明其时代大于5万年,依据牙齿测量数据和形态特征,本研究将其归入诺氏古菱齿象。目前已在泥河湾盆地发现百余个化石地点,鉴定出236种(包括未定属种)哺乳动物,分属于8目、32科和121属,其中38个属种(包括亚种)最初是以泥河湾化石材料而建立。总而言之,泥河湾盆地哺乳动物化石以早更新世者居多,并且化石材料保存完好;有些属种在欧亚大陆古北区第四纪哺乳动物群形成过程中发挥过重要作用,例如早期猛犸象、披毛犀、野牛及真枝角鹿等,还有直隶狼、貉及各种真马。泥河湾盆地由于河流和断层切割以及沉积相变等原因,导致各个化石点及史前考古遗址地层难以直接对比,更难全窥盆地内动物群演化的整体脉络;新的生物地层对比研究表明,桑干河南岸的岑家湾台地周缘的早更新世化石点,其主化石层位与下沙沟地区经典泥河湾动物群的层位大致相当。泥河湾盆地哺乳动物化石主要产自细砂、粉砂及黏土地层;化石成堆产出或者呈条带状及凸镜状分布的特点,多数与水流搬运有关。除过1枚豪猪牙齿和少量麂类化石之外,泥河湾盆地第四纪哺乳动物群中几乎不含东洋界动物,总体反映了干冷草原为主的古环境背景。

Fossil Equidae in the Linxia Basin with Biostratigraphic and Paleozoogeographic Significance

The Linxia Basin is characterized by an abundance of Cenozoic sediments,that contain exceptionally rich fossil resources.Equids are abundant in the Linxia Basin,the fossil record of equids in this region including 16 species that represent 10 genera.In comparison to other classic late Cenozoic areas in China,the Linxia Basin stands out,because the fauna and chronological data accompanying Linxia equids render them remarkably useful for biostratigraphy.The anchitheriines in the region,such as Anchitherium and Sinohippus,represent early equids that appeared in the late stages of the middle and late Miocene,respectively.Among the equines,most species of Chinese hipparions have been identified in the Linxia Basin and some species of the genera Hipparion and Hippotherium have FAD records for China.Furthermore,Equus eisenmannae is one of the earliest known species of Equus in the Old World and is well-represented at the Longdan locality.Some species with precise geohistorical distributions can serve as standards for high-resolution chronological units within this framework.Located at the eastern margin of the Tibetan Plateau and subject to considerable uplift,the Linxia Basin has served as a biogeographic transition area for equids throughout the late Cenozoic.

论羌塘含油气盆地关键地层划分对比问题

羌塘含油气盆地勘探程度相对较低,一些关键地层的时代归属与划分对比尚存较大的争议,这制约了盆地石油地质条件评价与含油气系统分析。基于近年来在羌塘盆地获得的生物地层、年代地层、沉积层序、盆地演化等方面的最新资料,结合前人的研究基础,重点对制约含油气盆地分析的关键地层时代归属问题开展了综合分析与客观评述。取得的主要认识包括:(1)新的同位素年代学资料证实,羌塘盆地存在前寒武系变质岩结晶基底,古生界基底埋深可达7~15 km,中生界沉积超覆在古生界褶皱系之上;(2)那底岗日组时代归属为晚三叠世,而不是早—中侏罗世;(3)南羌塘古油藏白云岩属于上三叠统,古油藏白云岩很可能“异地无根”,与布曲组为构造断裂接触;(4)南羌塘毕洛错油页岩时代归属为早侏罗世;(5)雀莫错组原定义为中侏罗统,研究证实其时代归属为早—中侏罗世;(6)胜利河—长蛇山油页岩Re-Os同位素定年及生物化石资料证明其为下白垩统海相地层;(7)同位素年代学及野外露头剖面资料证实,康托组与唢呐湖组为同期异相地层。羌塘盆地地层学研究新进展为完善盆地地层划分对比方案,乃至盆地含油气系统分析与盆地资源潜力评价提供了新的依据。

Permian and Triassic Radiolarian Biostratigraphy in South and Southwest China

The study of Permian radiolarias in South and Southwest China has been advanced in recent years . A well-preserved radiolarian fauna of Triassic is recently found in Southwest China . Eight radiolarian assemblage zones are recognized as follows in ascending order: Pseudoalbaillella rhombothoracata assemblage zone (Qixian ), Pseudoalbaillella fusiformis assemblage zone (early-middle Maokouan ), Follicucullus assemblage zone (late Maokouan-Wujiapingian ), Cangyuanella assemblage zone (early-middle Changxingian ), Clavata assemblage zone (latest Permian), Triassocampe yini assemblage zone (early Early Triassic ), Pseudoeucyrtis liui assemblage zone (late Early Triassic )and Triassocampe dew even assemblage zone (Middle Triassic ). The Permo -Triassic boundary in chert mono -facial sequence of the Muyinhe Formation is discussed .

Event Stratigraphy, Biostratigraphy and Sequence Stratigraphy of Neoproterozoic in North China

The aim of this study is to discuss the chronostratigraphy, catastrophic event stratigraphy, biostratigraphy and sequence stratigraphy of Neoproterozoic. In the eastern part of the North China, the Neoproterozoic consists of Qingbaikou System (1 000-800 Ma) and Sinian System (800-600 Ma). The Qingbaikou System is widely distributed over the whole area and the Sinian System only in the eastern and southern parts of the plate. In this paper, we discuss the age limit of the formations, and try to establish the Neoproterozoic chronostratigraphic frame, the ages of which are partly based on recently obtained carbonate whole rock Pb Pb isotope. Based on the event records of ancient earthquake, which are well developed in Sinian carbonates, “a vibrational liquefaction seismic sequence” in carbonate rocks is established. We propose a time correlation for the Sinian formation in eastern North China, on the bases of event records of earthquake in combination with biostratigraphy, and thus revise the traditional correlation scheme that has been used for nearly 30 years. Some biostratigraphic results were obtained in fossil microplants, megafossils and metazoans in North China. A large amount of big double layered and complex ornamented acritarchs are found in Qingbaikou and Sinian systems. On the basis of the correlation by earthquake events, the Huainan fauna is regarded as Late Sinian, probably between 700 Ma and 600 Ma. Altogether 16 depositional sequences are distinguished in the Neoproterozoic, with an average time interval of about 15-16 Ma.

Uppermost Permian Radiolarian Biostratigraphy ofSouthern Guizhou, Southwest China

With abundant deep-water upper Permian sediments, Guizhou is an ideal place for the research of radiolarian biostratigraphy of Upper Permian. The sections of Sidazhai and Lekang in southern Guizhou Province are studied. Lithology and biostratigraphy of the siliceous rock sequence of uppermost Permian in the two sections are introduced. Radiolarian assemblage zones, Neoalbaillella optima assemblage zone and Klaengspongus spinosus assemblage zone in ascending order are established for the topmost Permian of southern Guizhou. The Klaengspongus spinosus zone has been the topmost radiolarian assemblage zone of Permian, which is also correlated with former ones in a considerable depth.

Reexamination of Radiolarian Biostratigraphy in Permian in Pelagic Chert Sequences at Dachongling Section, South China

Permian radiolarian biostratigraphy was reexamined in the bedded chertsection in Qinzhou area of southeast Guangxi Zhuang Autonomous Region, South China. On the basis ofthe analyses of characteristic radiolarian composition, six radiolarian zones are recognized,namely, Pseudoalbaillella longtanensis Zone, Pseudoalbaillella globosa Zone, Follicucullusmonacanthus Zone, Follicucullus scholasticus Zone, Follicucullus charveti Zone and Neoalbaillellaornithoformis Zone, in ascending order. Correlation of these radiolarian zones with those in Japanis presented. The Neoalbaillella ornithoformis Zone was firstly discovered in Dachongling Section,which may indicate that pelagic chert of the late Permian existed there, according to theco-occurring conodonts.

Cenozoic Calcareous Nannofossil Biostratigraphy of Sediments from Lingfeng Well in East China Sea

A biostratigraphic study of calcareous nannofossils of sediments from Lingfeng No.1 well in the East China Sea was carried out to provide more detailed nannofossil data and a stratigraphic correlation among offshore wells located in the East China Sea.14 Paleocene to Pleistocene calcareous nannofossil zones were recognized based on a detailed examination. According to these nannofossil data, the Paleocene/Eocene and Pliocene/Pleistocene boundaries, as well as the Miocene base were determined.Oligocene NP23 and Miocene NN1 zones are firstly recognized by this study. The existence of Miocene NN1 at this well suggests that the Miocene transgression began in the Early Miocene in this area. The records of NP23 indicate that the marine Oligocene sediments exist in the series of Lingfeng wells, but probably as very thin layers.

Biostratigraphy and Paleoecology of Maastrichtian Sediments in the Zagros Basin, Iran

To enable the lithostratigraphic and biostratigraphie study of the Gurpi Formation, within the ＇Dezak＇ or Globigerina Marl, a stratigraphic section at Booraki, located to the NNW of Shiraz, SW Iran, through the late Cretaceous was examined. The formation consists of shale and greenish-gray marls interbedded with cream limestone, brown sandstones and siltstones with an exposed thickness of 160 m in the studied section. Samples were taken at regular intervals in all yielding 14 genera and 16 different species of benthic and planktic foraminifera that allowed determination of the age of the beds as Maastrichtian. To examine the paleoecology of the formation, some important ecological factors including water level, salinity, and oxygen regime change during the depositional courses of the formation were analyzed. The density of foraminiferans decreases from the base to top of the Gurpi Formation whereas the ratio of planktic to benthic Foraminifera （i.e., P/B） and proportion of shallow-water fauna increase. These foraminiferal changes indicate an increase and decrease in depth, temperature, salinity and oxygen, respectively, at the base and top of the Formation.

The Maastrichtian-Danian in the SW Zagros Fold-Thrust Belt(S. Iran):An Integration of Planktonic Foraminiferal Biostratigraphy and Gamma-Ray Spectrometry

In this study, the Maastrichtian-Danian boundary was measured and sampled in two stratigraphic sections, the north and south flanks of the Dehnow anticline in Coastal Fars, Southern Iran. This boundary was also investigated in the drilled exploratory well-1 in the same region. The lithology of the Maastrichtian-Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozones are the Gansserina gansseri Interval Zone, and the Contusotruncana contusa Interval Zone, which indicates latest Campanian to middle Maastrichtian age for the upper part of the Gurpi Formation. In addition, the Eoglobigerina edita(P1) Partial Range Zone, Praemurica uncinata(P2) Lowest Occurrence Zone, Morozovella angulata(P3) Lowest Occurrence Zone and Globanomalina psudomenardii(P4) Taxon Range Zone represent a Danian to Thanetian age for the lower part of the Pabdeh Formation. From the absence of the Abathomphalus mayaroensis Interval Zone, Pseudoguembelina hariaensis Interval Zone, Pseudotextularia elegans Interval Zone, Plummerita hantkeninoides Interval Zone, Guembelitria cretacea(P0) Partial Range Zone and Parvularugoglobigerina eugubina(Pα) Total Range Zone, it can be deduced that there is a paraconformity across the Maastrichtian–Danian boundary in the studied area, this hiatus encompassing the late Maastrichtian and the earliest Danian. Danian deposits from the study area contain reworked glauconitized macrofossils, planktonic and benthic foraminifera of the Cretaceous. The obtained surface gamma-ray spectrometry logs resemble the exploratory well-1 gamma-ray wireline log.

A New Mid Early Pleistocene Mammalian FaunaDiscovered in Choukoutien，China and Its Application in Biostratigraphy

This paper deals with a new Early Pleistocene micromammalian fauna found in Choukonden (Zhoukoudian) and its application in biostratigraphy.The new locality (east cave ), discovered in 1985,is located on the north slope of the Taipingshan Hill, about 2 km northeast of the Loc.1 in Choukoutien and is about 140-150m in altitude. At this locality,abundant fossil mammals are found in thick cave-fissure deposit. This fauna comprises 30mammalian taxa. Based on the comparison of the fauna, as Well as the sporo-pollen, climate events and paleomagnetic polarity section with those in other areas,we come to the conclusion that the sediments (Taipingshan Formation) in east cave were formed during the Period about from 1.67 Ma B. P. to 0.97 Ma B. P., and the fauna is about 1.20 Ma B. P. in ags.

Larger Foraminiferal Biostratigraphy and Facies Analysis of the Oligocene–Miocene Asmari Formation in the Western Fars Sub-basin, Zagros Mountains, Iran

The Oligocene–Miocene carbonate record of the Zagros Mountains, known as the Asmari Formation, constitutes an important hydrocarbon reservoir in southern Iran. This marine carbonate succession, which developed under tropical conditions, is explored in terms of larger foraminiferal biostratigraphy, facies analysis and sequence stratigraphy in a new section at Papoon cropping out in the western Fars sub-basin, in the south-east of the Zagros belt. Facies analysis shows evidence of re-working and transport of skeletal components throughout the depositional system, interpreted here as a carbonate ramp. The foraminifera-based biozones identified include the Globigerina–Turborotalia cerroazulensis–Hantkenina Zone and Nummulites vascus–Nummulites fichteli Zone, both of Rupelian age, the Archaias asmaricus–Archaias hensoni–Miogypsinoides complanatus Zone of Chattian age and the ‘Indeterminate’ Zone of Aquitanian age. The vertical sedimentary evolution of the formation exhibits a progressive shallowing of the facies belts and thus the succession is interpreted as a high-rank low-order regressive systems tract. This long-lasting Rupelian–Aquitanian regressive event is in accordance with accepted global long-term eustatic curves. Accordingly, long-term eustatic trends would have been a factor controlling accommodation during the deposition of the Asmari Formation studied in the western Fars sub-basin.

Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province,China

The demarcation of the Lower-Middle Triassic boundary is a disputed problem in global stratigraphic research. Lower-Middle Triassic strata of different types, from platform to basin facies,are well developed in Southwest China. This is favorable for the study of the Olenekian-Anisian boundary and establishing a stratotype for the Qingyan Stage. Based on research at the Ganheqiao section in Wangmo county and the Qingyan section in Guiyang city, Guizhou province, six conodont zones have been recognized, which can be correlated with those in other regions, in ascending order as follows： 1, Neospathodus cristagalli Interval-Zone; 2, Neospathodus pakistanensis Interval-Zone; 3,Neospathodus waageni Interval-Zone; 4, Neospathodus homeri-N, triangularis Assemblage-Zone; 5,Chiosella timorensis Interval-Zone; and 6, Neogongdolella regalis Range-Zone. An evolutionary series of the Early-Middle Triassic conodont genera Neospathodus-Chiosella-Neogongdolella discovered in the Ganheqiao and Qingyan sections has an intermediate type named Neospathodus qingyanensis that appears between Neospathodus homeri and Chiosella timorensis in the upper part of the Neospathodus homeri-N, triangularis Zone, showing an excellent evolutionary relationship of conodonts near the Lower-Middle Triassic boundary. The Lower-Middle Triassic boundary is located at 1.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Qingyan section,whereas this boundary is located 0.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Ganheqiao section. There exists one nearly 6-m thick vitric tuff bed at the bottom of the Xinyuan Formation in the Ganheqiao section, which is usually regarded as a lithologic symbol of the Lower-Middle Triassic boundary in South China. Based on the analysis of high -precision and high-sensitivity Secondary Ion Mass Spectrum data ,the zircon age of this tuff has a weighted mean 206Pb/238U age of 239.0±2.9 Ma （2σ）, which is a directly measured zircon U-Pb age of the Lower-Middle Triassic boundary. The Ganheqiao section in Wangmo county can therefore provide an excellent section through the Lower-Middle Triassic because it is continuous, the evolution of the conodonts is distinctive and the regionally stable distributed vitric tuff near the Lower-Middle Triassic boundary can be regarded as a regional key isochronal layer. This section can be regarded not only as a standard section for the establishment of the Qingyan Stage in China, but also as a reference section for the GSSP of the Lower-Middle Triassic boundary.

Calcareous Nannoplankton Biostratigraphy of the Bartin Province,Western Black Sea,Turkey

Calcareous nannoplankton biostratigraphy has been performed on five sedimentary sections through the marine Akveren Formation from the Bartin region of northern Turkey, on the southern Black Sea coast. This new biostratigraphy provides an age for the formation of the Early Campanian （nannofossil zone UC15aTp） to Early Selandian （nannofossil zone NPS）, and highlights the presence of the Campanian/Maastrichtian, Cretaceous/Tertiary （K/T）, and Danian/Selandian boundaries in this intermediate palaeolatitude location. Micula murus was identified below the K/T boundary, but Micula prinsii and Nephrolithus frequens were not, which implies that the K/T boundary interval is not complete in the study area. These dates are in agreement with previous micropaleontological studies.

Late Cretaceous-Early Paleogene Foraminiferal Biostratigraphy in Xishan,Gamba,Southern Tibet,China

1 Introduction The Cretaceous/Tertiary(Paleogene)extinction event was a mass extinction event occurring at about 65 million years ago between the Mesozoic Cretaceous and Cenozoic Tertiary,which is the one closest to today among the five major extinction events in the the geological history period(Renne et al.,2013).At the end of the Cretaceous,the proportion of species declined gradually.

Biostratigraphy and Sequence Stratigraphy of the Tarbur Formation(Maastrichtian)from Iranian Zagros Foreland Basin,Southwest of Iran

Shallow carbonate deposits(Tarbur Formation)were formed in the Zagros foreland basin with dynamic tectonics during the Maastrichtian age.From the viewpoint of reconstruction of depositional conditions in these deposits,studies of biostratigraphy,microfacies,microtaphofacies,and sequence stratigraphy were performed in a single area at Tang-e Shabi Khoon,northwest of Zagros.Based on the identification of two assemblage zones consisting of benthic foraminifera in these strata,the formation was deposited during the middle to late Maastrichtian.The number of cycles in test size and type of coiling in Loftusia decreased from the study area toward the northwest of the Neotethys basin.The input of clastic sediments affected the distribution of Loftusia and rudists in the study area.Nine microfacies,six microtaphofacies,and one terrigenous facies(shale)were identified based on the sedimentary features.These deposits of the middle-late Maastrichtian were deposited on a homoclinal carbonate ramp.The platform can be divided into restricted and semi-restricted lagoon,shoal,and open marine environments.In the study area,the deposits of the Tarbur Formation were deposited during four third-order depositional sequences.Local fault activities affected the formation of depositional sequences in the study area.

Late Cretaceous non-avian dinosaurs from the James Ross Basin,Antarctica:description of new material,updated synthesis,biostratigraphy,and paleobiogeography

Although the fossil record of non-avian dinosaurs from the Cretaceous of Antarctica is the poorest of any continent,fossils representing at least five major taxonomic groups(Ankylosauria,early-diverging Ornithopoda,Hadrosauridae,Titanosauria,and Theropoda)have been recovered.All come from Upper Cretaceous(Coniacian–Maastrichtian)marine and nearshore deposits belonging to the Gustav and Marambio groups of the James Ross Basin at the northern tip of the Antarctic Peninsula.The majority of these finds have come from the Campanian–Maastrichtian Snow Hill Island and López de Bertodano formations of James Ross and Vega islands.Given the rarity of Antarctic Cretaceous non-avian dinosaurs,discoveries of any fossils of these archosaurs,no matter how meager,are of significance.Here we describe fragmentary new ornithischian(ankylosaur and ornithopod)material from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation and the Maastrichtian Sandwich Bluff Member of the López de Bertodano Formation.One of these specimens is considered to probably pertain to the holotypic individual of the early-diverging ornithopod Morrosaurus antarcticus.We also provide an up-to-date synthesis of the Late Cretaceous non-avian dinosaur record of the James Ross Basin and analyze the biostratigraphic occurrences of the various finds,demonstrating that most(including all named taxa and all reasonably complete skeletons discovered to date)occur within a relatively condensed temporal interval of the late Campanian to early Maastrichtian.Most or all James Ross Basin dinosaurs share close affinities with penecontemporaneous taxa from Patagonia,indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the final stages of the Mesozoic.

Biostratigraphy and Paleoecological Study of Pabdeh Formation in Interior Fars, Zagros Basin, Iran

The Zagros basin, which trends NW-SE, is covered by a sea during the Paleogene, resulting in deposition of the Pabdeh Formation in the deeper parts of the basin. The thickness of the Pabdeh Formation in Tang-e-Abolhayat is about 221 m and it consists of purple shale at the base, gray shale, marl and marly limestone with a few horizons of nodular limestone toward the top. Seventy-two samples were collected and processed for nannofossil studies. Based on the identified nannofossil zones the age of the formation in Tang-e-Abolhayat is Late Paleocene-Late Oligocene (NP9-NP24). Changes in the abundance of different genera over the studied interval have resulted in identification of three ecozones: Ecozone 1 is characterized by oligotrophic conditions with an abundance of warm water taxa;Ecozone 2 marks when conditions became more eutrophic and the abundance of temperate taxa increased;Ecozone 3 represents a return to oligotrophic conditions with an increase in warm water taxa.