Nowadays, fungal remains studies along with spores/pollen provide significant records for palaeoenvironmental interpretations. Their diversity and frequency pattern help in deciphering the sequential history of changes which occurred in palaeoclimate and palaeo habitat of the area.

The term “Subathu” was initially coined by Medlicott in 1864. It represents the oldest sequence of the Palaeogene succession of Himalayan Foreland Basin succession. It has wide geographic distribution and attains its maximum thickness in N-W direction while pinches out in S-E direction. In Northwestern Himalaya, its thickness varies from about 400 m in Himachal Pradesh to about 175 m in Jammu and Kashmir and about 60 m in Uttarakhand. This succession marks the beginning of the flexural depression of Himalayan Foreland basin resulted from the collision of Indian-Eurasian plates and subsequent closure of Tethys.

Although geological studies on the Subathu lithounit in Garhwal Syncline have been chiefly done by [1] - [8]. [4] studied in detail the Subathu Formation exposed in the Singtali, Nilkanth, Dhamand, Bidasini, and Dogadda area and recognised five major zones (Zone A-Zone E) in stratigraphic order and assigned Upper Paleocene to Early Eocene age to them. [5] gave detailed lithostratigraphy of Subathu Group exposed in Morni, Garkhal, Subathu, Kulra, Arki, Nilkanth and Dogadda blocks. Also considerable micropalaeontological work has been done on the Subathu sediments from the various regions of Uttarakhand by various workers. [9] recorded Nummulitescf.mamilla,Operculina patalensis, N.atacicus,Assilna granulosa chhumbiensis,Globorotalia sp. from the Subathu Formation of Dogadda, Garhwal Himalaya and assigned an Upper Paleocene to Lower Eocene age. [10] recorded lamellibranch genera Perna, Cardiocardita, Astarte from the Dogadda Formation in Garhwal Synform at Golikhet, Garhwal, U.P. On the basis of fossil records, the Subathu formation is considered to range in age from Upper Palaeocene to middle Eocene and the deposition of the lithounit in marine conditions.

Although, these workers deal with the foraminiferas and vertebrates, the fungal spores and their fruiting bodies seem to have been received no attention. Therefore, the present study is focused on the fungal remains from the Subathu sediments of the Dogadda area located in the Uttarakhand (Figure 1) because of its relevance in palaeoenvironmental considerations.

Tectonically, Subathu Formation has thrusted contact with the crystalline rocks of Bijni tectonic unit to the northwest [11] and to the south, it is delimited by Krol Thrust. Lithologically, the entire Subathu succession of the area is comprised of splintery carbonaceous shale, ooidal ironstone, grey, red and green shales, limestone and sandstone. The litholog of the study area is given in (Figure 2).

The basal part of Subathu Formation is comprised of dark grey, non-calcareous & poorly consolidated carbonaceous shale with coaly bands & ooidal iron stone. The berthierine rich ooidal iron stone has sharp lower contact with sediments of Kakara Formation. The ooidal iron stone is overlain by the grey shale, siltstone with minor bands of green & red shales with packstone containing foraminiferas. The top most part of the section is comprised of thick sandstone. The tectonic succession of the present study area is given in (Table 1).

The present investigation has been carried out on 17 representative samples

collected from 64m thick lithosection of Subathu Formation of present area for processing using the standard maceration technique. For this qualitative approach, each sample was taken and crushed into pea size with the help of mortar and pestle. 10 - 15 gm of each sample was taken and treated with HCl (40%) followed by HF (40%) in order to remove carbonates and silicates, respectively. The residue left was sieved using 40 mesh size sieve to eliminate the remaining clay particles. Now the residue was treated with conc. HNO₃ in order to oxidize the humic material. After digestion process, permanent slides were made using polyvinyl alcohol and Canada Balsam for palynomorph identification. Prepared slides were examined in transmitted light using Olympus light microscope and photographed.

The fungal remains recovered from the Subathu Formation exposed along Dogadda-Kotdwar road section in Dogadda, Uttarakhand comprised of 13 species belonging to 10 form genera. Of these, 7 genera and 9 species of fungal fruiting bodies belong to mycrothyriaceaea, one diporicellaesporites species to phragmosporae, cleistothecium type, one inapertisporites species to amerosporae and fungal spore type-I have been recovered. The check list of the fungal remains is given in (Table 2).

The lithology of the Subathu Formation is shown in field photographs (Figure 3).

Systematic Description

CleistotheciumType

(Pl. I, Figure 4(k))

Remarks: It is globular and completely closed cleistothecium containing ascocarps. Fruiting body is provided with some hyphae septate appendages, dark in color.

Dimensions: Size 30 μm, hyphae length 40 - 60 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Amerosporae.

Genus: CallimothalusDilcher, 1965 ex Jansonius & Hills, 1977.

Type species: Callimothaluspertusus Dilcher, 1965.

Callimothalus senii (Venkatachala & Kar 1969) Kalgutkar & Jansonius 2000.

(Pl. I, Figure 4(f))

Remarks: Perithecium subcircular, dark brown in colour, central part of perithecium darker than neighbouring regions, hyphae radially arranged, pseudoparenchymatous, outer layer thickened and minutely setose, Asci not seen.

Dimensions: Size 100 - 140 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: DiporicellaesporitesElsik, 1968.

Type species: Diporicellaesporitesstacyi Elsik, 1968.

Diporicellaesporitessp.

(Pl. I, Figure 4(m))

Remarks: Spore dark brown in color, 6-celled, fusiformis, central cells comparatively larger in diameter than terminal cells, diporate, one pore at each end, tranverse septa fairly thick, psilateSpore dark.

Dimensions: Size 35 × 15 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Phragmosporae

Genus: Haplopeltis

Type species: Haplopeltis

Haplopeltismucoris Dilcher, 1965

(Pl. I, Figure 4(b))

Remarks: Fungal body is circular to sub-circular in shape, non-radiating, ostiolate present, ostiolate is prominent, central in position, round and surrounded by small cells, no free hyphae present, margins non-radiating and complete.

Dimensions: Diameter 80 μm, ostiole 10 μm in diameter.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Haplopeltissp.1

(PL. I, Figure 4(d))

Remarks: Fungal body is circular to sub-circular in shape, ostiolate rounds, elevated, dark brown in color, centric, bordered by small cells, fruiting body having non-radiating cells, margin entire, composed of flattened cells.

Dimensions: Diameter 85 μm, ostiole 10 μm in diameter.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: InapertisporitesVan der Hammen, 1954 emend Sheffy & Dilcher, 1971

Type species: Inapertisporitesvariabilis van der Hammen, 1954

Inapertisporites sp.

(Pl. I, Figure 4(g))

Remarks: Fungal spore having oval shape, unicellate, spore wall thick and laevigate.

Dimensions: Size 90 × 40 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Amerosporae.

Genus: ParmathyritesJain & Gupta, 1970.

Type species: Parmathyritesindicus Jain & Gupta, 1970.

Parmathyritessp.

(Pl. I, Figure 4(c))

Remarks: Ascomata circular in shape, non-ostiolate, hyphae interconnected arranged radially forming pseudoparenchymatous non-porate cells. Central and marginal cells are rectangular in shape, peripheral cells are developed into spine like unequal processes, spines are pointed at apex and broader at the base. Ascospores unknown.

Dimensions: Diameter 80 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: PhragmothyritesEdwards, 1922 emend. Kar & Saxena, 1976.

Type species: Phragmothyriteseocaenica Edwards, 1922 emend. Kar & Saxena, 1976.

Phragmothyriteseocenicus Edwards, 1922 emend. Kar & Saxena, 1976.

(Pl. I, Figure 4(a))

Remarks: Ascomata circular to sub-circular in shape, non-ostiolate, hyphae radially arranged and interconnected forming one-celled thick pseudoparenchymatous cells. Marginal cells are more elongated then the middle region cells. Marginal cells are more darker, central region bears a single pore.

Dimensions: Diameter 70 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: PlochmopeltinitesCookson, 1947

Type species: Plochmopeltinitesmasonii Cookson, 1947

Plochmopeltinitessp.

(Pl. I, Figure 4(h))

Remarks: Epiphyllous fungi is rounded to rounded irregular in shape, discoid, brown to reddish brown, ostiolate, ostiole centric, dense border with 2 - 3 cell layers.

Dimensions: Size 102 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: SpinosporonitesSaxena & Khare, 1992

Type species: Spinosporonitesindicus Saxena & Khare, 1992

Spinosporonitessaxenae Saxena & Khare, 1992

(Pl. I, Figure 4(i))

Remarks: Fungal spore is circular to subcircular in shape, inaperturate, multicellate, each cell giving rise to a robustly built rounded spine, wall very thin, less than 0 - 5 µm, smooth, spines are broader at base.

Dimensions: Size 50 - 60 in diameter, cells are 5 - 7 wide at the base.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Spinosporonitesangularis Saxena & Khare, 1992

(Pl. I, Figure 4(j))

Remarks: Fungal spore is spherical in shape, inaperturate, multicellate, each cell having angular tip and broader base, wall 0 - 5 µm thick and smooth.

Dimensions: Size 44 × 60 in diameter.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Genus: Trichothyrites

Type species: Trichothyrites

Trichothyrites padappakkarensis

(Pl. I, Figure 4(e))

Remarks: Ascostromata is circular-subcircular in shape, ostiolate, ostiole surrounded by wall of few cells, hyphae radially arranged but donot anastomose to form distinct pseudoparenchymatous cells.

Dimensions: Diameter 70 μm.

Occurrence: Subathu Formation, Dogadda-Kotdwar section, Dogadda, Uttarakhand.

Affinity: Ascomycetes, Microthyriaceae.

Dominant retrieval of multiple forms of epiphyllous fungi i.e., Callimothalussenii,Haplopeltis mucoris,Haplopeltis sp.,Parmathyrites sp.,Phragmothyrites eocaenicus,Plochmopeltinites sp.,Spinosporonites saxenae,Spinosporonites angularis andTrichothyrites padappakkarensis inmajority provides authentic evidence for the prevalence of high humidity coupled with high temperature for the luxuriant growth of this group of plants. Although, modern microthyriaceous fungi infect both coniferous as well as angiospermous leaves. Also, the fossil taxa related to these fungi have been discovered on coniferous as well as angiospermous leaves [12] [13] [14] [15]. But, no coniferous remains have been recorded from the Subathus of Dogadda while angiospermic remains in the form of pollen grains are known abundantly from this lithounit. This obviously indicates that the microthyriaceous fungi recorded from the studied area are entirely depended on the angiosperm foliage only.

During Tertiary period, the distribution of microthyriaceous fungi shows globally appearance as evidenced by their occurrence in Scotland, Sicily, Sumatra, Siberia, Germany, Australia, USA, Western Canada, South Africa and India. At present, these fungal found in abundance in humid tropical to sub-tropical areas of the world with high rainfall. While, some of the members like Plochmopeltinies have enjoyed wider distribution during the tertiary period in comparison to present day distribution [13]. The occurrence of microthyriaceous fungi and their germlings in the deposits is a good indicator of moist tropical type of vegetation [16]. Microthyriaceous taxa are usually coorelated with humid, warm temperate to tropical climate [16] - [20]. The presence of microthyriaceous taxa supports swampy habitat during the deposition. Occurrence of Inapertisporitessp. and Dicellaesporitessp. indicates humid, tropical type of climate. The plate showing representative photographs of assemblage recovered is shown in (Figure 4). Based on the occurence of the Callimothalussenii (Late Paleocene - Miocene),Haplopeltis mucoris (Early Eocene),Phragmothyrites eocenicus (Late Paleocene - Middle Miocene),Spinosporonites saxenae (Late Paleocene - Middle Miocene),Spinosporonites angularis (Late Paleocene - Middle Miocene) in the present fungal assemblage, Late Palaeocene-Middle Eocene age is assigned to this horizon of Dogadda-Kotdwar section, Dogadda area, Pauri-Garhwal district, Uttarakhand.

1) The present paper records assemblage constituting 13 species assignable to 10 form genera of fungal remains from the Subathu Formation of Dogadda area, Uttarakhand.

2) The assemblage suggests that the region experienced warm and humid climate during the course of sediment accumulation with thick vegetation providing suitable substrates for the growth and proliferation of fungi.

3) The assemblage indicates moist tropical type of vegetation based on the dominance of microthyriaceous fungal assemblage.

4) The present fungal assemblage depends on the broad leaf angiosperm foliage.

5) The present horizon reported Late Palaeocene-Middle Eocene age diagnostic palynotaxa (Callimothalussenii, Haplopeltismucoris,Phragmothyrites eocenicus,Spinosporonites saxenae,Spinosporonites angularis), Late Palaeocene-Middle Eocene age is assigned to the present horizon.

Authors are grateful to the Chairman, Department of Geology, Kurukshetra University, Kurukshetra for providing necessary lab facilities for accomplishment of the research work.

The authors declare no conflicts of interest regarding the publication of this paper.

Panwar, R., Thakur, O.P. and Dogra, N.N. (2020) Fungal Remains from the Subathu Formation of Dogadda, Uttarakhand, India. Open Journal of Geology, 10, 1198-1209. https://doi.org/10.4236/ojg.2020.1012059