Occurrence of Cordaitales from lower Gondwana sediments of Ib-River Coalfield, Orissa, India: An Indian scenario

The Ib-River Coalfield in Orissa State is a part of Mahanadi Master Basin. Recent extensive investigations were conducted in this Coalfield to locate fossiliferous beds in the Lower Gondwana deposits and as a result a large cache of plant fossils were recovered from Lower Permian sediments (Barakar Formation) exposed in Jurabaga and Lajkura Collieries. The complete flora includes 23 genera representing nine orders viz., Lycopodiales, Equisetales, Sphenophyllales, Filicales, Cordaitales, Coniferales, Ginkgoales, Cycadales and Glossopteridales. Only the Cordaitales, represented by four genera i.e., Noeggerathiopsis, Cordaites, Euryphyllum and Kawizophyllum are discussed in this paper. Cordaitalean leaves are described for the first time from this coalfield; the remaining plant groups will be considered in a subsequent publication. Cordaitalean leaves attributable to Noeggerathiopsis hislopii, Noeggerathiopsis minor, Euryphyllum whittianum, Euryphyllum maithyi, Kawizophyllum dunpathriensis and Cordaites sp. constitute about 13.90% (111 specimens) of the total plant assemblage collected from this Coalfield. Of the cordaitaleans, N. hislopii is most abundant (47.75%; 53 specimens) followed by E. whittianum (40.54%; 45 specimens). A summary of the distribution of Cordaitales throughout the Indian Gondwana is also presented. Floristic composition varies stratigraphically at the two Barakar exposures (Lajkura and Jurabaga Collieries). Cordaitales are preserved only in the lowermost (4th) horizon (lower floral zone). Strata in these collieries have been assigned to the lower and upper Barakar Formation based on floristic content and an Early Permian (Artinskian) age is assigned.     

Floral biodiversity and geology of the Talcher Basin,Orissa, India during the Permian–Triassic interval

The review paper provides an updated account of the previous and recently published records concerning the palaeobiology and the geology of the Talcher Basin of Orissa State, India. We conclude that fossil floral species in this basin originated in the earliest Permian Talchir Formation and evolved and diversified through the Karharbari Fm., Barakar Fm., Barren Measures Fm. and the uppermost Kamthi Fm. (Late Permian–Triassic). The megaflora and the palynology of the different formations of the basin are also discussed briefly. The geological setting of the basin along with the status of different formations (especially the Kamthi Formation) has been redefined. The post‐Barakar Fm. rocks, earlier retained in the Raniganj/Kamthi, Panchet and Mahadeva formations in this basin, have been critically assessed and redefined as the Lower and Upper Kamthi formations of Late Permian and Triassic ages, respectively. Accordingly, the geological map of the basin has been modified. Permian deposits (particularly the Barakar and the lower Kamthi formations) not only have the best preserved flora but also possess the highest diversity, whereas the upper Kamthi Triassic sediments have a meagre number of taxa. The plant diversity of the basin has been discussed in detail to interpret the development of the flora, evolutionary trends and palaeoenvironments of the basin. The patchy Gangamopteris vegetation of the Talchir glacial phase has ultimately evolved and diversified through time (Karharbari Fm. to Lower Kamthi Fm.) and gave rise to the thick dense swampy forests consisting of large Glossopteris trees and other shade‐loving under‐storied pteridophytes. Several groups of plants including spores and pollen have disappeared in a ladder pattern during the Permian–Triassic interval (Lower Kamthi–Upper Kamthi Fm.) and, similarly, in steps, many new fore‐runners appeared in the Upper Kamthi Formation. Records of marine acritarchs and ichnofossils in this basin at various Permian–Triassic levels demonstrate that there were marine influences. These features suggest a paralic (coastal marine to deltaic) mode of origin of the coal beds and associated sediments in the basin. The present study also advocates the continued survival of plants, rather than a mass extinction near the vicinity of the Permian–Triassic (P–T) boundary in this basin. Copyright © 2012 John Wiley & Sons, Ltd.     

Morphological and stratigraphical significance of lower Gondwana plant fossils of Mohpani Coalfield, Satpura Gondwana Basin, Madhya Pradesh

Plant fossils from the coal bearing Barakar Formation exposed in Gottitoria open cast mine of Mohpani Coalfield, Satpura Gondwana Basin are described for the first time. The assemblage is represented by Glossopteris communis, G. indica, G. stenoneura, Gangamopteris angustifolia, G. cyclopteroides, G. karharbariensis, G. major, seeds of Cordaicarpus zeilleri and equisetaceous stems. The dominance of the species of Gangamopteris over the species of Glossopteris and absence of Noeggerathiopsis indicate the floral affinity with the flora of Lower Barakar Formation of Lower Gondwana.     

Palaeoecology and taxonomy of Pentoxylales from the Albian of Antarctica

Reproductive pentoxylalean material from the Albian Triton Point Formation, Fossil Bluff Group of Alexander Island, Antarctica is the youngest record of this group globally. Leaves are referred to Taeniopteris daintreei McCoy, ovulate reproductive organs to Carnoconites cranwelli Harris, and stem material to Pentoxylon sp. Occurring in leaf litter layers on palaeosol surfaces the sedimentology suggests that pentoxylalean plants grew upon areas of the floodplain distal to the river channel, where they covered the forest floor in a similar habit to modern brambles. The forest floor was shared with Equisetales and liverworts, an abundance of ferns [Cladophlebis Brongniart, Gleichenites Goeppert, Phyllopteroides Medwell, Sphenopteris (Brongniart) Sternberg], as well as angiosperms. Bennettitales, Ginkgoites Seward and Nilssonia Brongniart were rare within these communities, as were coniferous trees.     

陶枣矿区太原组成煤植物群落及其意义

陶枣矿区太原组煤层中赋存大量黄铁质和钙质煤核，其植物组成包括高等植物科达类，石松类，辉木类，楔叶类等和低等生物藻类及菌类。由这些植物构成的太原组成煤植物群落在垂直结构上分为三个层次，第一层次为群落主要层，以科达类和鳞木类等高大乔木为主；第二层次是楔叶类为代表的林下植物，第三层次是水体中大量存在的藻类和菌类，植物群落的层次结构和生态环境与现代落羽杉森林沼泽相似，明显的菌藻类低等生物贡献是华北太原组成     

Biostratigraphy and floristic evolution of coal swamp floras of a part of Talcher Basin,India: a window on a Permian temperate ecosystem

The present megafloral assemblage recorded from the Barakar sediments of Dholpahar section along Singda rivulet near Gopal Prasad Village in Talcher Basin comprises of equisetaceous stems, Gangamopteris buriadica, Palaeovittaria kurzii and 19 species of the genus Glossopteris. Record of Gangamopteris, Palaeovittaria and many narrow mesh forms of Glosspteris viz., G. angustifolia, G. churiensis, G. communis, G. recurva, G. spatulata, G. stenoneura, G. tenuifolia, G. vulgaris and G. zeilleri from two older fossiliferous horizons demonstrates that these fossils were preserved during Lower Barakar sedimentation. The report of middle and broad mesh forms of Glossopteris viz., G. barakarensis, G. browniana, G. indica, G. intermittens, G. karharbariensis, G. nakkarea, G. oldhamii, G. taeniensis and G. retifera in the youngest fossiliferous horizons reveals that these fossils were preserved during the deposition of Upper Barakar sediments. The continuation of some of the Karharbari plant fossils in the early phase of Barakar Formation and their disappearance in the flora of Late Barakar suggests a shift in the climatic setup. Palaeoclimate and palaeovegetation of this area are also summarised in this study. Moreover, the fossil assemblages of different fossiliferous beds of Dholpahar section demonstrate the evolution of midrib and meshes in different reticulate leaves.     

Permian macro- and miofloral diversity,palynodating and palaeoclimate implications deduced from the coal-bearing sequences of Singrauli coalfield,Son–Mahanadi Basin,central India

The coal-bearing sequences of Barakar and Raniganj formations exposed in Bina and Jhingurdah open-cast collieries, respectively, are analysed for their macro- and miofloral content. The sediment successions primarily comprise of sandstones, shales, claystones and coal seams. In addition to the diverse glossopterid assemblage, four palynoassemblage zones, namely Zones I and II in Bina Colliery and Zones III and IV in Jhingurdah Colliery, have also been recorded in the present study. The megafossil assemblage from the Barakar strata of Bina Colliery comprises of three genera, namely Gangamopteris, Glossopteris and cf. Noeggerathiopsis. Palynoassemblage-I is characterised by the dominance of non-striate bisaccate pollen genus Scheuringipollenites and subdominance of striate bisaccate Faunipollenites and infers these strata to be of Early Permian (Artinskian) age (Lower Barakar Formation). The palynoassemblage has also yielded a large number of naked fossil spore tetrads, which is the first record of spore tetrads from any Artinskian strata in the world and has a significant bearing on the climatic conditions. The palynoassemblage-II is characterised with the dominance of Faunipollenites over Scheuringipollenites and is indicative of Kungurian age (Upper Barakar Formation). The megafossil assemblage from the Raniganj Formation of Jhingurdah Colliery comprises of five genera with 26 species representing four orders, viz., Equisetales, Cordaitales, Cycadales and Glossopteridales. The order Glossopteridales is highly diversified with 23 taxa and the genus Glossopteris, with 22 species, dominates the flora. The mioflora of this colliery is represented by two distinct palynoassemblages. The palynoassemblage-III is correlatable with the palynoflora of Early Permian (Artinskian) Lower Barakar Formation. The assemblage suggests the continuity of older biozones into the younger ones. The palynoassemblage-IV equates the beds with composition V: Striatopodocarpites–Faunipollenites–Gondisporites assemblage zone of Tiwari and Tripathi (1992) of Late Permian (Lopingian) Raniganj Formation in Damodar Basin. The FAD’s of Alisporites, Klausipollenites, Falcisporites, Arcuatipollenites pellucidus and Playfordiaspora cancellosa palynotaxa in this assemblage enhance the end Permian level of the Jhingurdah Top seam, as these elements are the key species to mark the transition of Permian into the Lower Triassic.     

Early Maastrichtian larger foraminifera of the Qahlah Formation, United Arab Emirates and Sultanate of Oman border region

The Early Maastrichtian (Late Cretaceous) Qahlah Formation is the oldest stratigraphical unit lying upon the eroded top of the obducted Semail Ophiolite, of Santonian–Campanian age, in the Northern Oman Mountains. It crops out as a series of low hills on the western flank of the mountains, which are located along the boundary between the United Arab Emirates and the Sultanate of Oman. This paper presents the results of an investigation into the bio- and lithofacies of the Qahlah Formation in the Jabal Huwayyah section (at the boundary between the Al Ain area of the United Arab Emirates and the Buraimi area of Oman). The data collected were used to determine the age and depositional environment of the rock unit studied. In addition, the section is lithostratigraphically correlated with other sections in the study area. Microfossils from Jabal Huwayyah are represented mainly by the larger benthic foraminifera Loftusia elongata, L. morgani, Pseudorbitolina marthae, Orbitoides media, Omphalocyclus macroporus and Lepidorbitoides minor. These foraminifera are reported for the first time from this section. The diversity and abundance of fauna, particularly within the calcareous siltstone bed near the top of the formation (unique to the Huwayyah area), reflect a shallow marine depositional environment.     

Upper Permian plant fossil assemblage of Bijori Formation: A case study of Glossopteris flora beyond the limit of Raniganj Formation

Plant fossils collected from the Bijori Formation of Satpura Gondwana Basin are described in detail from the type locality as well as from other exposures. The assemblage is dominated by glossopterid remains with few specimens of pteridophyte of Glossopteris flora viz. Santhalea bansloiensis, Neomariopteris sp., Trizygia speciosa and 20 species of Glossopteris viz., G. angustifolia, G. searsoliensis, G. tenuifolia, G. surangei, G. kamthiensis, G. utkalensis, G. syaldiensis, G. sp. cf G. zeilleri, G. stricta, G. bosei, G. intermittens, G. stenoneura, G. gopadensis, G. wilkinsonii, G. retifera, G. conspicua, G. mohudaensis, G. browniana, G. communis, G. indica, Vertebraria indica, dispersed seeds of Cordaicarpustype and equisetalean axes with or without nodes and internodes.     

滇中川街盆地中侏罗世弓鲛(软骨鱼类)化石新材料

云南禄丰县川街盆地中侏罗统产出弓鲛鱼类化石后甸弓鲛(Hybodus houtienensis Young)、新庄弓鲛(新种)(Hybodus xinzhuangensis Sun)、川街弓鲛(新种)(Hybodus chuanjieensis Sun)。后甸弓鲛(Hybodus houtienensis Young)是中国发现最早的弓鲛鱼类之一,正型标本为破碎的鳍棘,副型标本为一枚牙齿齿冠。依据在川街盆地相同层位发现的新化石材料,对后甸弓鲛副型标本进行了增补,补充了描述,建立了2个弓鲛新种:新庄弓鲛与川街弓鲛,丰富了"后甸弓鲛带"弓鲛类群,并讨论了弓鲛属的生物地层、生活的古环境和地理分布特征。     

云南临沧晚中新世一种水龙骨科植物化石的修订及其生物学意义

云南现代真蕨类植物资源丰富,蕨类植物多样性的地史起源,必须从化石记录入手。在云南临沧上中新统邦卖组植物化石采集中发现了槲蕨属1块不育叶和2块腐殖叶的新材料,这些标本为修订Drynaria propinqua Wen et al.,2013,以及揭示该种不育叶和腐殖叶的特征提供了新的材料。通过与槲蕨属国内外报道的化石种和现生种的详细比较,将其重新定名为Drynaria cf.propinqua。Drynaria cf.propinqua的发现,表明云南临沧晚中新世的气候与现今中国西南地区温暖湿润的气候类似,这些附生植物的生活习性表明,临沧地区复杂分层的森林生态系统至少在晚中新世已经确立。     

Early Permian Palaeoenvironment in Damodar Valley Coalfields, India: an Overview

In the Damodar Valley Basin, coalfields containing coal bearing Barakar Formation are Raniganj, Jharia, Bokaro, Ramgarh, and Karanpura. The Barakar Formation is composed of conglomerate, sandstone, siltstone, shale, fireclay, and coal. The lower part of Barakar Formation represents a braided channel deposit, and also in few places glacio-fluvial deposit which changes to meandering channel system with the formation of some ox-bow lake, and cut-off channel in the middle part. In a few places deltaic/brackish water condition possibly existed along with this meandering channel system. In the upper part of Barakar Formation, marine signatures are more prominant. Marine signatures/influences have been reported from Barakar Formation of Ramgarh, South Karanpura, and West Bokaro coalfields on the basis of trace fossil assemblage, sedimentation character, and trace element content. Although, definite marine signatures have not been observed from Jharia, and Raniganj coalfields, high concentration of boron, vanadium, and chromium, and presence of skolithos, and thalassinoides burrows possibly suggest a brackish water condition. The upper part clearly suggest that the sediments were deposited in a geographic setting very close to the sea or at the edge of the sea possibly in a peritidal setting where storm activity played a vital role during sedimentation which in turn suggests the presence of a broad shallow sea (epeiric/epicontinental sea) that develop during times of high sea level. The sea water possibly entered from the northeastern side as vast seaways or as embayment through the Damodar Valley which acted as a channel.     

Palynological dating and correlation of surface and subsurface sediments from Wardha valley coalfield,Maharashtra

42 genera of palynomorphs have been reported from the qualitative and quantitative analysis of the palynoflora from both open cast mine and bore holes viz., Ballarpur open cast mine, Durgapur open cast mine and Bore hole CMWNM-57 on barrier between Kawadi/Majri open cast and Hindustan Lalpeth Colliery from the Wardha valley coalfield of Wardha basin. Two palynoassemblages have been recorded i.e., an Upper Karharbari palynoassemblage comprising dominance of radial monosaccate genus Parasaccites and subdominance of nonstriate disaccate genus Scheuringipollenites and a Lower Barakar palynoassemblage consisting of dominance of Scheuringipollenites and subdominance of striate disaccates chiefly Faunipollenites, suggesting an Early Permian age (Late Sakmarian to Early Artinskian) to the sediments. It is further authenticated by the occurrence of palynotaxa viz., Crucisaccites, Caheniasaccites, Indotriradites and Tiwariasporis. Upper Karharbari Formation has been demarcated for the first time in lithologically designated Barakar Formations in Ballarpur, Durgapur, Majri and Hindustan Lalpeth Colliery while the sample 57/2 of bore hole CMWNM from Kawadi area may belong to the Kamthi Formation on the basis of pinkish yellowish coarse grained to medium grained sandstone. An attempt has been made to correlate these palynoassemblages with other Lower Gondwana basins of Early Permian affinity.     

Bird and dinosaur footprints in the Woodbine Formation (Cenomanian), Texas

The ichnofauna of the Woodbine Formation (Cenomanian), Denton County, Texas includes bird and dinosaur tracks. A new bird trackway,Magnoavipes loweiichnogen. et ichnosp. nov., appears to represent the largest bird tracks known from the Mesozoic. A theropod trackway,Fuscinapedis woodbinensisichnogen. et ichnosp. nov., is characterized by long digits of uniform width and pointed small claws. Six hadrosaurid trackways,Caririchnium protohadrosaurichnosichnosp. nov., are the oldest hadrosaurid tracks associated with skeletal elements. They include one isolated small footprint, a medium sized quadrupedal, and five large bipedal hadrosaurid trackways.     

Revision of the conchostracan genus Estherites from the Upper Cretaceous Nenjiang Formation of the Songliao Basin and its biogeographic significance in China

The diagnosis of Estherites corrugatus from the basal part of the Coniacian Second Member of the Nenjiang Formation in Nenjiang County, north-east China is revised following the application of a new preparation technique to some of the carapaces and an examination of specimens under a scanning electron microscope, both of which revealed morphological features on the carapace that had not been recognized previously. Restudy of the type species of the two subgenera Estherites (Euestherites) and Estherites (Parestherites) also revealed details of carapace features not seen hitherto. These indicate that they should be separated from Estherites. As a result, Euestherites is upgraded to genus level and Parestherites is placed in synonymy. The importance of Estherites and Euestherites is considered in the context of Late Cretaceous assemblages of these crustaceans and the three conchostracan provinces (South-West, South-East and North China) that are recognized to have been present in China during the Turonian–Santonian period.     

The oldest barnacle from the Caribbean is a rudist bivalve (Maastrichtian, Jamaica)

Four new specimens of Euscalpellum? coatesi Donovan and Davis-Strickland from the Maastrichtian of Jamaica are described; two of these occur in association with the right valve of the rudistid bivalve Chiapasella radiolitiformis (Trechmann). This demonstrates that E.? coatesi is not a barnacle, but rather represents an unusual preservational state of the left valve of C. radiolitiformis retaining only the cellular inner part of the shell.     

Early Cretaceous planktonic foraminifera from the Tethys: the large, many-chambered representatives of the genus Globigerinelloides

This paper deals with the taxonomic revision of the Early Cretaceous large, many-chambered planispiral planktonic foraminifera, historically assigned to the genus Globigerinelloides or alternatively assigned in the 1990s to the genera Globigerinelloides Cushman and ten Dam, Biglobigerinella Lalicker, Blowiella Krechmar and Gorbachik and Alanlordella BouDagher-Fadel. In a previous paper we demonstrated that the morphological and microstructural features used in the literature for distinguishing Blowiella from Globigerinelloides have value only at species level, and the former genus was thus invalidated (being the junior synonym). Moreover, the Late Aptian specimens assigned to Biglobigerinella by some authors, based on the presence of twin last chamber(s), are also included in Globigerinelloides because individuals sharing the same features (number of chambers, growth rate, size of umbilicus, and a finely perforate wall) may or may not possess twin last chamber(s). Meanwhile, Moullade et al. questioned the taxonomic value of Alanlordella, erected by BouDagher-Fadel to accommodate planispiral taxa possessing a macroperforate wall. All the species analysed here possess a finely perforate wall and consequently cannot be assigned to this taxon.The large species of Globigerinelloides retained here, with six or more chambers in the outer whorl, are G. algerianus Cushman and ten Dam, G. aptiensis Longoria, G. barri (Bolli, Loeblich and Tappan) and G. ferreolensis (Moullade).In the sections studied, Globigerinelloides aptiensis was first found close to the Barremian/Aptian boundary, even though this species was recorded in Spain (Rio Argos) in the mid Upper Barremian; very rare, small, seven-chambered individuals here assigned to Globigerinelloides ferreolensis are recorded in the Lower Aptian (just below and within the Selli Level, OAE1a), while a few specimens belonging to Globigerinelloides barri occur in the Globigerinelloides ferreolensis Zone (Upper Aptian). Globigerinelloides aptiensis and G. ferreolensis range up to the Ticinella bejaouaensis Zone while Globigerinelloides barri disappears at the top of the Globigerinelloides algerianus Zone; finally, Globigerinelloides algerianus obviously spans the eponymous total range zone.From an evolutionary point of view, two lineages within the many-chambered Globigerinelloides have been recognized. In the first, already known in the literature, Globigerinelloides aptiensis gave rise to G. ferreolensis, which evolved into G. algerianus; the latter in turn gave rise to Pseudoplanomalina cheniourensis as the final evolutionary member. In the second lineage Globigerinelloides barri originated from G. blowi.     

Palynochronology of Lower Cretaceous volcano-sedimentary succession of the Rajmahal Formation in the Rajmahal Basin, India

In the Rajmahal Basin Lower Cretaceous rocks are classified under the Rajmahal Formation. It includes a series of volcanic basalt flows and associated sedimentary intertrappean beds. Up to 15 basalt flows have been recorded in this basin. The intertrappean beds comprise sandstone, shale, siltstone, and clay deposits which are rich in spores and pollen. The palynoflora recovered from intertrappean beds shows definite pattern of evolution and diversification. On the basis of its overall composition, distribution pattern of age marker taxa and the First Appearance Datum of key taxa, four palynological assemblages have been identified. The chronology of these assemblages in ascending order is (1) Ruffordiaspora australiensis, (2) Foraminisporis wonthaggiensis, (3) Foraminisporis asymmetricus, and (4) Coptospora verrucosa. These assemblages ascertain the age of the volcano-sedimentary sequence of the Rajmahal Formation in the Rajmahal Basin as Berriasian to Aptian. The palynochronology of the intertrappean beds enables their correlation in the Rajmahal Basin. In different areas of the basin, the palynological dating of the lowermost intertrappean bed within the Rajmahal Formation which overlies the Dubrajpur Formation, has provided a Berriasian to Aptian age. The palynological assemblage indicating the Berriasian age is inferred as the time of the initiation of volcanic activity which continued up to the Aptian in the Rajmahal Basin.     

Taxonomy and affinity of Early Mesoproterozoic megascopic helically coiled and related fossils from the Rohtas Formation, the Vindhyan Supergroup, India

A well preserved assemblage of compressed, straight, circular to sinuously coiled megascopic and helical carbonaceous fossils and other varied megascopic morphoforms are known from the Early Mesoproterozoic Rohtas Formation, Semri Group within Vindhyan Supergroup exposed in Katni district of central India. These megascopic remains are preserved as impressions, compressions, partially mineralized remains, and/or epi-relief. Some of the forms are typical filamentous empty sheaths and others are trichomes, with cell like entities under various stages of degradation. This study, based on fresh collections and also of the topotype material of the helically coiled megascopic fossils, straight forms and related fossilized remains occurring as epi-relief from Katni indicate that the two morphotaxa are distinct entities and possibly appear to be prokaryotes. Grypania spiralis and Katnia singhii are most likely of cyanobacterial origin. Spirally coiled and circular fossils, with epi-relief, and which probably represents a tissue grade organism, are considered as Spiroichnus beerii Mathur, 1983. Linear sheet-like carbonaceous solitary form has been placed in the morphotaxon Proterotainia and described as P. katniensis n. sp. Certain rare circular, carbonaceous forms are considered as Chuaria sp. A few circular disc-like forms found in the assemblage are treated as dubiofossils.     

柴达木盆地昆特依地区晚更新世正构烷烃分布特征及其环境变迁

为探讨柴达木盆地晚更新世的环境变迁,同时为青藏高原隆升对气候变化的影响提供基础资料,对柴达木盆地昆特依地区ZK1404钻孔沉积物中的正构烷烃分布特征以及ASM~(14)C测年数据进行了分析。结果显示,昆特依地区晚更新世沉积物的正构烷烃总体上呈现以高碳数为主的分布特征,多数样品以nC_(27)、nC_(29)为主峰,部分以nC_(31)为主峰,呈现出显著的奇碳优势。少数样品中低于nC_(21)的短链正构烷烃相对丰度较高,主要以nC_(17)、nC_(20)为主峰碳数,无明显的奇偶优势。根据正构烷烃分布特征、AMS~(14)C测年数据、区域地质调查资料及沉积环境判断,柴达木盆地昆特依地区晚更新世(33600～26370a B.P.)气候环境以温凉干旱与温凉干旱偏湿交替出现为特征,与现代大陆性干旱荒漠气候截然不同。