Monday, 12 May 2014

Pollen and Spores from the Early Cretaceous Damoguaihe formation in eastern Mongolia.

The Damouguaihe formation is found in the Hailar Basin in Inner Mongolia, where it has been accessed from a number of coal mines (it never naturally outcrops at the surface). More recently it has also been found in the Tamutsag Basin of Mongolia, where it has been accessed by exploration wells sunk by oil companies. The formation comprises grey lacustrine siltstones and mudstones (i.e. siltstones and mudstones that were originally laid down in a lake environment) and is quite rich in fossils, having produced Bivalves, Estherians (Branchiopod Crustaceans), Ostracods and Macro-plant fossils, as well as an abundant supply of pores and pollen. 

Dating the formation has proved to be problematic, as the sediments contain no volcanically derived sediments that can be used to date is using isotope methods (some minerals formed in volcanic eruptions contain unstable, radioactive isotopes, which decay over time; since the speed at which this occurs is known, such isotopes can be used to date these minerals) and most of the larger fossils are of endemic lake species, not found in other deposits elsewhere and therefore not very useful in dating the Damouguaihe Formation. Pollen and Spores, on the other hand, are wind-blown microfossils produced by plants, which are typically scattered over very wide areas, with many forms having global distribution.

Previous studies of pollen and spores from coal mines in Inner Mongolia have suggested the formation to be Valanginian-Barremian in age (139.8-129.4 million years old), due to the presence of Angiosperm (Flowering Plant) pollen, while studies based upon oil-well data from Inner Mongolia have failed to find such pollen, and instead date the Damouguaihe Formation to the Valanginian-Hauterivian (139.8-132.9). While it has not been possible to date the Damougaihe Formation isotopicly, it has been possible to date some strata above and below it, indicating that the formation is less than 145-149 million years old and more than 127.1 million years old.

In a paper published in the journal Acta Geologica Sinica in February 2014, Wang Liyan of the College of Geosciences at Jilin University, Wan Chuanbiao of the Research Center of Paleontology and Stratigraphy at Jilin University and the Exploration and Development Research Institute of Daqing Oilfield Company Limited, and Sun Yuewu, also of the Research Center of Paleontology and Stratigraphy at Jilin University, describe the results of a study of pollen and spores from the Damougaihe Formation obtained from oil well drillings in the Ta’nan Sag and Bayin Gobi Sag, both parts of the Tamutsag Basin in Mongolia.

The assemblage was dominated by Gymnosperm (Conifers, Cycads etc.) Pollen, which comprised 46.35-65.57% of the material found, and Fern Spores, comprising 34.43-52.58% of the material. Angiosperm pollen was present, but rare, comprising 0-1.07% of the material.

Nine species of the Fern Spore Cicatricosisporites were found in the Damougaihe Formation in the Mongolian well drillings. Cicatricosisporites minutaestriatus, which forms 0.42-1.64% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, and Cicatricosisporites minor, which forms 0-2.14%, have previously been found in the Damougaihe Formation in the Hailer Basin of Inner Mongolia as well as the Da Hinggan Mountains, which run across a large area of northeast China, where it was also found in the overlying Yimin Formation. The two spore species are known from the middle and late Early Cretaceous of Siberia, the Russian Far East, Argentina and Australia and the late Early Cretaceous of Canada. Cicatricosisporites minor is also known from the Shahai and Fuxin Formations of western Liaoning Province and Berriasian deposits (145.0-139.8 million years old) in India. Cicatricosisporites minutaestriatus is also known from the Chengzehi Formation of eastern Heilongjiang Province.

Cicatricosisporites minutaestriatus. Wang et al. (2014).

Cicatricosisporites australiensis, which forms 0-1.64% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, is known from the Hauterivian-Albian of the Purbeck Formation in England (132.9-100.5 million years old), as well as the Early Cretaceous of Russia, Kazakhstan, Japan, Canada, the United States and Australia, and the Shahezi Formation of the Songliao Basin (also northeast China) and Berriasian-Barremian deposits in Tibet (145.0-125.0 million years old). 

Cicatricosisporites delicatulus, which forms 0-0.13% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has previously been described from Barremian-Albian deposits elsewhere (129.4-100.5 million years old).

The known distribution of spores of the genus Cicatrcosisporites. Wang et al. (2014).

Fern spores of the genus Appendicisporites first appear in the middle-to-late Early Cretaceous and persist to the Late Cretaceous. Five species of Appendicisporites have been found in the Damoguahi Formation. 

Appendicisporites crimensis, which forms 0-0.27% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has been found in the Hauterivian-Albian (129.4-100.5 million years old) of Siberia, the Russian Far East and Canada, as well as the Yimin Formation in the Da Hinggan Mountains, the Damoguahi and Yimin Formations of the Hailar Basin in Inner Mongolia, Chengzehi Formation of eastern Heilongjiang Province, the Dalazi Formation of eastern Jilin Province and the Fuxin Formation of western Lioaning Province. 

Appendicisporites crimensis. Wang et al. (2014).

Appendicisporites tricornitatus, which forms 0-0.85% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has previously been recorded from the Berriasian-Cenomanian (145.0-93.9 million years old) of Canada, the United States, the Netherlands, Germany, Siberia and northern China.

Appendicisporites tricornitatus. Wang et al. (2014).

Five species of the Fern spore Aequitriradies were found in the Mongolian well drillings of the Damoguaihe Formation. These spores first appear elsewhere in the Berriasian (145.0-139.8 million years ago) and persist to the Maastrichtian (72.1-66.0 million years ago). 

Aequitriradies verrucosus, which forms 0.13-0.85% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has been recorded from the Early Cretaceous of Lebanon, the Hauterivian of Egypt (132.9-129.4 million years old), the Aptian of the United States (125.0-113.0 million years old), the Early Cretaceous of India, the Neocomian-Albian of eastern Australia (145.0-100.5 million years old), in the Wealden Supergroup in northern Germany, the Neocomian-Senonian (145.0-65.5 million years old) of the Vilyuisk Basin in Siberia and the Early Cretaceous of Argentina. It has also been found in the Chengzehi Formation of eastern Heilongjiang Province, the Changeai Formation in the Yanbian area of eastern Jilin Province, the Damoguaihe Formation in the Da Hinggan Mountains, the Yimin Formation in the Hailar Basin of Inner Mongolia, the Saihantala Formation in the Eren Basin of Inner Mongolia, the Yantouya Formation in northern Shanxi Province and the Qinshila and Tujingzi Fromations in Hebei Province.

Aequitriradies verrucosus. Wang et al. (2014).

Aequitriradies spinulosus, which forms 0.13-0.78% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has been found in the Neocomian (145.0-129.4 million years ago) and Aptian-Albian (125.0-100.5 milliom years ago) in North America, and the Albian (113.0-100.5 million years ago) of the Wealden Supergroup in Europe, the Early Cretaceous of South Americ, the Berriasian of India (145.0-139.8 million years ago), and the Late Mesozoic of Australia. It is known from the Purbeck Formation in England, the Hauterivian-Aptian in southwest France (132.9-113.0 million years old) and the late Neocomian and Hauterivian-Aptian in Egypt (132.9-113.0 million years old). It has also been found in the Damoguaihe and Yimin Formations in the Da Hinggan Mountains, the Chengzehi Formation of eastern Heilongjiang Province, and the Naizishan and Wulin Formations of the Jiaohe Basin in eastern Jilin Province.

Aequitriradies spinulosus. Wang et al. (2014).

The known distribution of spores of the genus Aequitriradies. Wang et al. (2014).

The Fern spore Leptolepidites verrucatus, which forms 0-1.07% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, is known from the Chengzehi and Muling Formations of eastern Heilongjiang Province, Damoguaihe and Yimin Formations in the Da Hinggan Mountains, the Yimin Formation in the Hailar Basin and Lishangou Formation of the Guynag Basin in Inner Mongolia, the Saihantala Formation in the Eren Basin of Inner Mongolia, the Qiqusi Formation of Hechuan District in Sichuan Province, the Baihedong and Shanshui Formations of the Shaunshui Basin in Guangdong Province.

Leptolepidites verrucatus. Wang et al. (2014).

Leptolepidites major, which forms 0-0.13% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, is known from the Bayanhua Group of the Eren Basin in Inner Mongolia, the Tandonggou Formation of the Yaojie area in Gansu Province, the Yan’an and Anding Formations of the Yan’an area in Shaanxi Province, and in the Wulong Formation of the Yichang area in Hubei Province. Leptolepidites psarosus is known from the Naijaihe Formation in the Liupanshan Mountains in Ningxia Province, the Xie’ersu Formation in the Horqin Left Wing Rear Banner of Inner Mongolia, the Juifutang Formation in the Fuxin Basin of western Liaoning Province and in the Damoguaihe Formation in the Da Hinggan Mountains.

The Fern Spores Pilosisporites trichopapilosus and Pilosisporites versus are mainly found in the Hauterivian-Barremian (132.9-125.0 million years old), Kuylisporites lunaris is known from the Barremian-Albian (129.4-100.5 million years old), Triporoletes reticulates is known from the Barremian-Cenomanian (129.4-93.9 million years old), Triporoletes rilobosporites bernissartensis is known from the Berriasian-Albian (129.4-100.5 million years old) and Crybelosporites striatus is known from the Aptian-Albian (125.0-100.5 million years old). 

(1) Pilosisporites versus, (2) Kuylisporites lunaris, (4) Pilosisporites trichopapilosus, (19) Triporoletes reticulates and (22) Crybelosporites striatus. Wang et al. (2014).

Among the Gymnosperm pollen, Paleoconifers appeared in before the start of the Jurassic and persisted till the Late Cretaceous. The dominant species of Paleoconifer Pollen in the Damoguahi in the Hailar Basin of Inner Mongolia is Protoconiferus, forming 9.68% of the total assemblage. 

Protoconiferus funarius. Wang et al. (2014).

This remains constant in the Tamutsag Basin of Mongolia, but the rest of the Paleoconifer assemblage is more diverse here, with a variety of pollen associated with the Early-Middle Cretaceous. 

The genus Classopollis is known from the Late Triassic till the end of the Cretaceous. In the Minghe Basin in Shaanxi Province it forms 55-76% of the pollen assemblage in the Late Jurassic and 30-40% in the Early Cretaceous. In the Jiande area of Zhejiang Province it forms 72-79% of the pollen assemblage in the Late Jurassic and 31.1-34.6% in the Early Cretaceous. In the Wuchan Basin of Inner Mongolia it forms 33.0-76.9% of the pollen assemblage in the Late Jurassic and 13-24% in the Early Cretaceous.

Classopollis annulatus, which forms 0-0.82% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has previously been found in the Shahezi Formation in the Songliao Basin of northerrn China, the Chengzehi and Muling Formations of eastern Heilongjiang Province, and the Damoguaihe Formation in the Hailar Basin of Inner Mongolia.

Angiosperm (Flowering Plant) pollen is found at very low levels in the Damoguaihe Formation in the Tamutsag Basin of Mongolia, though this is typical of the earliest Angiosperms. 

Clavatipollenites, which forms 0-0.80% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, is considered to be one of the oldest known Angiosperm pollens. This first appears in the Barremian of southern England (129.4-125.0 million years ago), in the upper marls of the Wealden Group, and becomes abundant in the lower Part of the Green Sand Formation. It has also been recorded from the Barremian of Argentina, Russia and Northern France. Clavatipollenites has been recorded in the Fuxin and Qingshila Formations of the Jehol Group in western Liaoning Province, the Chengzehi Formation of eastern Heilongjiang Province, the Denglouku Formation in the Songliao Basin of northern China, the Changcai Formation in eastern Jilin Province, the Bayanhua and Guyang Formations of Inner Mongolia, the upper Hekou Formation and upper Miaogou Group in Gansu Province, the Lianmuqin Formation in the Junggar Basin and Gecun Formation in the Jurong Basin in Jiangsu Province. 

In drill core samples from the Hailar Basin of Inner Mongolia Clavatipollenites has been found in the Yimin Formation, and associated chips thought to be from the Damoguaihe; though it was not actually found in the core samples from the Damoguaihe, so this claim cannot be asserted with confidence. The Yimin Formation core samples also contained the Anigiosperm pollen Asteropollis, which was not found in the chip samples, and which is believed to have originated later than Clavatipollenites. The presence of Clavatipollenites in the Damoguaihe of the Tamutsag Basin lends support to this theory.

Clavatipollenites sp. Wang et al. (2014).

Songipollis, which forms 0-0.27% of the total pollen and spore assemblage in well samples of the Damoguaihe Formation in the Tamutsag Basin of Mongolia, has previously been reported from the middle-late Early Cretaceous of northern China, the eastern United States and western Canada.

Based upon this pollen and spore assemblage Wang et al. conclude that the Damoguaihe Formation in the Tamutsag Basin of Mongolia is most likely Hauterivian-Barremian in age (i.e. 139.2-125.0 million years old). The plant assemblage was also used to reconstruct the climate of the region, suggesting that the Tamutsag Basin had a semi-humid to humid, warm subtropical climate in the Early Cretaceous. This is very different from the cold, dry, climate of eastern Mongolia today, but is in line with expectations for the greenhouse world of the Early Cretaceous.

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