Palynoflora from an Upper Cretaceous freshwater paleolake in central India: paleoecological implications

Abstract

An Upper Cretaceous paleolake near Jamsavli in the Mandla Lobe of central India has provided a unique opportunity to understand paleoecological conditions during Deccan volcanism. The sedimentary deposits of this paleolake are dominated by freshwater aquatic and semiaquatic flora, such as algae (Pediastrum, Lecaniella), dinocysts (Pierceites deccanensis), diatoms (Aulacoseira), aquatic ferns of Salviniaceae (Azolla), Marsileaceae (Crybelosporites), and pollen grains of Sparganiaceae/Typhaceae (Sparganiaceaepollenites). Such paleolakes, representing a few hundred years of lake history with only aquatic and semiaquatic biota, have rarely been documented from the Deccan volcanic province.

An overview of aquatic and semiaquatic flora from the infratrappean and intertrappean beds associated with the Deccan volcanic province across the Cretaceous-Paleogene shows that the floral communities include algal remains of Botryococcaceae, Chlorophyceae, Chlorellaceae, Cyanophyceae, Hydrodictyaceae, Oedogoniaceae, Ulotrichaceae, Zygnemataceae, dinocysts, and diatoms. Bryophytes are scarce, whereas aquatic ferns of Salviniaceae (Azolla) and Marsileaceae (Marsilea and Regnellidium) are the dominating groups in the intertrappean deposits. Aquatic and semiaquatic angiosperms show less taxonomic diversity and are represented by only five families, namely Nymphaeaceae, Typhaceae, Liliaceae, Acanthaceae, and Pontederiaceae. The ubiquitous presence of macrophytes and microfloral fossil remains of Zygnemataceae (Ovoidites), Salviniaceae (Azolla), Marsileaceae (Crybelosporites and Gabonisporis), and palms, along with paleosol, indicate frost-free, warm, humid tropical to subtropical climates with intermittent dry and wet semi-arid conditions across the Late Cretaceous–early Paleocene.

Introduction

Freshwater terrestrial ecosystems, which include lakes, rivers, ponds, and swamps, have unique floral and faunal communities, and they are excellent archives of terrestrial environmental and climatic changes. The limited ability of aquatic flora to disperse with changing environmental conditions, and their sensitivity to water temperature are two important factors that make aquatic flora important for assessing prevailing ecological conditions (Woodward et al., 2010).

An examination of the global record of aquatic and semiaquatic biota reveals that a definite fossil record of free-floating algae is from the Precambrian (Martín-Closas, 2003; Becker and Marin, 2009), bryophytes from the Middle Devonian (Hernick et al., 2008), pteridophytes e.g., Isoetes from the Triassic (Collinson, 1988), and aquatic angiosperms from the Early Cretaceous (Zippi, 1998; Friis et al., 2011; Friss and Pedersen, 2011). A variety of Upper Cretaceous-lower Paleocene freshwater flora are reported from northern hemisphere, especially from North America and northeast Asia (Stockey et al., 2007; Krassilov et al., 2009; Samylina, 1974; Herman and Lebedev, 1991; Golovneva, 1994, 2000). Recent new data on aquatic flora from the Upper Cretaceous (Maastrichtian) deposits of Patagonia, have filled major knowledge gap in understanding of the aquatic floral diversity of the southern hemisphere (Gandolfo and Cu´neo, 2005; Zamaloa and Tell, 2005; Cu´neo et al., 2013; Hermsen et al., 2013; Cu´neo et al., 2013, Cu´neo et al., 2014; Vallati et al., 2017). Till now, the Western Interior Seaway (WIS) in North America (Nichols and Johnson, 2008; Braman, 2018) and Sangoli Lake in China (Wang et al., 2013) are the best studied Upper Cretaceous-lower Paleocene terrestrial freshwater ecosystems. Additional data on Late Cretaceous to early Paleocene terrestrial aquatic flora and paleoecological conditions are available from the Indian infratrappean (Lameta Formation) and intertrappean sedimentary beds (summarised in Khosla and Verma, 2015; Samant and Mohabey, 2014; Smith et al., 2015).

The Deccan volcanic associated fluvio-lacustrine infratrappean deposits occur in six geographically separated inland basins in central and western India (Mohabey, 1996; Mankar and Srivastava, 2015), whereas the intertrappean sedimentary beds occur between the lava flows in fringe areas of the Deccan volcanic province where small lakes/ponds formed during pauses in volcanic activity. The intertrappean lake deposits are generally 2–5 m thick, (rarely 10–15 m) and mostly represent a few hundred to a few thousand years of sedimentation.

Considerable data are available on the fossil megaflora of intertrappean localities across India (Kapgate, 2005; Bonde, 2008; Smith et al., 2015; Wheeler et al., 2017), but aquatic macrophytes and microbiota are scarcely described from these deposits. Here we present results of a microfloral study from an intertrappean locality, Jamsavli, in Chhindwara district, in the Mandla Lobe of the Eastern Deccan volcanic province in central India. In addition, we present a review of the literature on aquatic and semiaquatic floral communities from intertrappean sites that existed during the Deccan volcanic eruptions. This overview has helped in understanding the biodiversity of aquatic plants, reconstructing their communities, and assessing the paleoecological and paleoclimatic conditions of paleolakes during volcanism.