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Article

What Do Fossil charophytes Whisper to Us? Palaeoecological and Palaeoenvironmental Reports from Pleistocene Continental Deposits of Umbria (Central Italy)

by
Angela Baldanza
1,2,*,
Paola Angelini
3,
Anna Maria De Santis
4,
Isabella Nalli
5 and
Roberto Bizzarri
1,6
1
Department of Physics and Geology, University of Perugia, Via Pascoli, 06123 Perugia, Italy
2
Museo dei Cicli Geologici di Allerona-Il Golfo dei Cetacei, Via Roma, 05011 Allerona, Italy
3
Department of Chemistry, Biology and Biotechnology, University of Perugia, Via del Giochetto, 06123 Perugia, Italy
4
Dr in Biology, Independent Researcher, Via G. Pontano, 73, 06049 Spoleto, Italy
5
Dr in Biology, Independent Researcher, Via Orchi 5, 06034 Foligno, Italy
6
PhD Freelance Researcher, Via A. Capitini 8, 06055 Marsciano, Italy
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(10), 392; https://doi.org/10.3390/geosciences15100392 (registering DOI)
Submission received: 1 August 2025 / Revised: 29 September 2025 / Accepted: 8 October 2025 / Published: 10 October 2025
(This article belongs to the Section Climate and Environment)
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Abstract

The Early Pleistocene continental deposits of the Tiberino Basin (Central Italy) host exceptionally preserved fossil charophyte assemblages that provide critical insights into palaeoenvironmental and palaeoclimatic dynamics during a key phase of the Mediterranean evolution. Integrated micropalaeontological and sedimentological investigations at three reference sections reveal distinct charophyte communities characterized by Chara cf. hispida (Hartman) Wood, 1962, Chara cf. vulgaris Linnaeus, 1753, Nitellopsis obtusa (Desvaux in Loiseleur) Groves, 1919, and Lychnothamnus barbatus (Meyen, 1827) von Leonhardi 1863, not reported until now. These assemblages reflect a mosaic of stable lacustrine, ephemeral swamp, and palustrine environments shaped by increasing climatic oscillations approaching the Early–Middle Pleistocene transition. Comparative data from Mediterranean basins, such as Laguna de Gallocanta, Lake Afourgagh, and Ilgin Palaeolake (Türkiye), highlight the role of charophytes as sensitive indicators of hydrological and climatic variability. This study strengthens the palaeolimnological and palaeoenvironmental significance of charophyte fossils and proposes new avenues for multidisciplinary research into Quaternary environmental evolution in Mediterranean continental basins.

1. Introduction

Characeae (Charophyceae, Charales) are a group of aquatic plants that colonize shallow freshwater and brackish or even saline waters, often thriving where other aquatic plants are limited by ecological constraints [1]. Their reproductive calcified fructifications (gyrogonites) form a robust and widespread fossil record extending from the Silurian (~420 million years ago) to the present [2,3]. Due to their strict ecological requirements, sensitivity to hydrochemical conditions, and rapid evolutionary turnover, charophytes are widely recognized as valuable proxies for reconstructing ancient aquatic environments [4,5].
In Central Italy, the Early Pleistocene continental deposits of the Tiberino Basin (Figure 1A) provide an exceptional archive of palaeoecological and palaeoenvironmental evolution. Fossil charophyte assemblages used as palaeoenvironmental and palaeoecological proxies, associated with mollusk and ostracod faunas, reveal dynamic shifts in freshwater ecosystems responding to climatic oscillations during the Quaternary. Through integrated micropalaeontological and sedimentological investigations in three selected sites (the Arquata Quarry, near Bevagna, a borehole at Acquasparta, and the ex Quasar section at Ellera di Corciano: Figure 1B), this study aims to reconstruct the palaeohydrological conditions and to explore broader Mediterranean palaeoclimatic trends during the same time range.

2. Geological Setting

The Tiberino Basin [6,7,8,9,10,11,12,13] is a major Plio-Pleistocene depression located between the Apennine ridges in Central Italy (Figure 1A). It exhibits an inverted Y-shaped morphology, extending southward from Città di Castello and Perugia towards Spoleto and Terni (Figure 1B). Its formation was driven by the Miocene to recent extensional tectonics related to the northeastwards migration of the Apennine Chain and the opening of the Tyrrhenian Basin during the Neogene–Quaternary transition. Presumably characterized by endorheic drainage in its first phases, through time, the basin encompassed several stages, from residual marine to lacustrine, palustrine, and alluvial/fluvial environments [9,11]. Nonetheless, each sector of the basin had its own, although similar, evolution, with structured sequences dominating the sedimentary record [9,10,11], also intercalated by travertines associated with groundwater resurgence and high carbonate saturation [6,9,14].
South of Perugia, the main part of the Tiberino Basin divided into two branches (Figure 1B): the eastern branch, descending to Spoleto, and the western branch that reached Terni (to the south).
Excluding the northern sector, whose evolution started later [10], the outcropping successions are Late Pliocene to Early Pleistocene in age. These successions primarily consist of clay, silty-clay, and sand deposits, with interposed lignite horizons and calcareous beds. The three reference sections considered in this research, pertaining to three different sectors of the basin, are almost coeval and all record the occurrence of charophyte gyrogonites.

2.1. The Eastern Branch and the Arquata Quarry Section

The eastern branch, named Valle Umbra, was a Plio-Pleistocene intermountain depression placed in the eastern Umbria Region (Figure 1). From the Pliocene to the present day, this part of the Tiberino Basin followed a peculiar sedimentary evolution, which significantly differed from the southwestern and northern areas [7,8,13]. The area evolved through time, still maintaining its organization as an endorheic basin until historical time [12,13]. This probably reflects repeated transitions between freshwater lake phases during wetter climatic intervals and marsh or swamp development during drier periods, closely modulated by global glacio-eustatic oscillations [8,12]. The main available succession of sediments in the northern part of the eastern branch, representative of the latest sedimentary evolution of the Basin (Early Pleistocene, approaching the transition to the Middle Pleistocene [8,11]), crops out inside the Arquata quarry, near Bevagna, where a nearly 70 m thick stratigraphic profile was measured (Figure 1 and Figure 2). The deposits are mainly silty clays and sands with lignite horizons. Throughout the stratigraphic succession, three main facies associations, attributed to a shallow-water lake, alluvial plain with distal fluvial supplies, and marsh/pond, respectively, have been recognized [8,13].

2.2. The Western Branch and the Acquasparta Borehole

The western branch of the Tiberino Basin (corresponding to the present day south Tiber Valley) contains several outcrops of continental deposits, and a long and articulated composite succession, representative of the sedimentary evolution of this area, was proposed [6,9,11]. The Pliocene–Pleistocene succession ends with deposits attributed to the Acquasparta Unit [6,9], from which the samples containing charophyte come. The unit is made of calcareous silts with travertine debris, alternated to large banks of travertine, with local clay intervals of varying thickness. The deposits are indicative of a lacustrine or palustrine environment, sometimes with clear evidence of subaerial exposure (palaeosols). The age has been classically referred to as the transition between the Early and Middle Pleistocene [9,11]. Near the historical center of Acquasparta town (Palazzo Cesi: Figure 3), this unit was drilled to over 40 m in 2019, revealing the presence of older, presumably Early Pleistocene, continental to transitional deposits.

2.3. The Minor Ellera Basin and Its Sedimentary Succession

The area of Ellera di Corciano (a few kilometers west from Perugia city) pertains to a continental sedimentary basin, generated by synsedimentary extensional tectonic during the Early Pleistocene as a “satellite basin” of the larger Tiberino Basin (Figure 1B, Figure 4 and Figure 5). The Ellera section is representative of its sedimentary evolution. The integrated sedimentological and micropalaeontological analyses allow us to identify two different sedimentary palaeoenvironments: (1) a periodically flooded alluvial plain with swamps and ponds where clay, silts, sandy clays, and palaeosol deposits accumulated, and (2) a lake/swamp environment with CaCO3 precipitation and formation of calcareous tufa/travertines [14].

3. Materials and Methods

Field sampling was conducted over several years at three key sites: Arquata Quarry, Acquasparta borehole, and Ellera di Corciano. Fine-grained sediments were collected, and 200 g of each sample was processed using 10% hydrogen peroxide and water to disaggregate the matrix without damaging delicate fossil structures. Wet sieving at 63 µm isolated gyrogonites and plant fragments, which were then air-dried and hand-picked under a stereomicroscope (Nissho optical TZ-240). Study sections were closely sampled (about 20–50 cm intervals on average) during past campaigns: unfortunately, sixteen samples returned charophytes, with a limited number of taxa (four) and their relative abundances identified (Table 1 and Table 2).
We do not have 30 complete gyrogonites for each taxon and cannot fulfill the standard request of regular measurements. It was only possible to measure ten gyrogonites (Table 3). However, they provide useful information. Charophyte remains were identified following the specialized literature [5,15,16,17]. Selected specimens, metallized with graphite, were analyzed using a Scanning Electron Microscope (COXEM-CX 200 plus) to document diagnostic morphological features. Abundance and diversity metrics were calculated based on standardized aliquots, supporting palaeoecological reconstructions. All the analyses were performed at the Dept. of Physics and Geology, University of Perugia (Italy).

4. Results

Table 1 summarizes the charophyte taxa identified in the three sites, with the different palaeoecological meanings and the preferred environmental conditions, while Table 2 illustrates the assemblages with the relative abundances of species. In all the study sections (Figure 5), the presence of charophyte is discontinuous and often limited to selected beds. Four different taxa were found.

4.1. Charophyte Assemblages at the Arquata Quarry (Bevagna)

The charophyte assemblages recovered at the Arquata Quarry site were rich and taxonomically diverse (Table 2 and Table 3). The samples with charophyte (Figure 5) come prevalently from the lower section and are associated with lignite levels and clay–silty–sandy sediments. The assemblages include Chara cf. hispida (Hartman) Wood, 1962, Chara cf. vulgaris Linnaeus, 1753, Nitellopsis obtusa (Desvaux in Loiseleur) Groves, 1919, and Lychnothamnus barbatus (Meyen, 1827) von Leonhardi. The preservation states of gyrogonites were excellent, with many specimens showing intact oospores, minimal abrasion, and an absence of transport-induced damage, suggesting rapid burial within low-energy depositional environments.

4.2. Charophyte Assemblages at Ellera—Ex Quasar Section

The Ellera assemblage, coming from a unique sample represented by a travertine/carbonate level, was less diverse and characterized by Lichnothamnus barbatus and Chara cf. vulgaris (Figure 5, Table 2 and Table 3).
Gyrogonites at this site were very rare, more fragile, and often incomplete (several specimens are germinated, with the apical or basal structure destroyed). The gyrogonites and many stems and branches are totally encrusted with calcium carbonate (Figure 6B,C). Several gyrogonites have microperforations that are circular in shape (Figure 6A,B), produced by predation activity and comparable to those found in ostracods of Early Pleistocene Tiberino Basin lacustrine deposits [19]. This is the first report of predation activity on gyrogonites.

4.3. Charophyte Assemblages at Acquasparta Borehole

The Acquasparta borehole section, with ten samples containing gyrogonites, is the site with the highest number of fruiting samples. The charophyte remains are concentrated in precise levels (Figure 5, Table 2). The species Chara cf. hispida, Chara cf. vulgaris, and Lichnotamnus barbatus, often associated with calcareous silt layers and minor travertine-like beds, characterize the assemblages.

5. The Charophytes and Their Fossil Record

Charophytes, particularly those within the family Characeae, are fundamental components of both extant and fossil freshwater ecosystems. Their calcified reproductive structures, gyrogonites, serve as resilient biological markers for reconstructing past environmental conditions [15].
The fossil assemblages from the Tiberino Basin include representatives of the genera Chara, Nitellopsis, and Lychnothamnus (Table 1, Table 2 and Table 3, Figure 7) [8,14]). Each taxon exhibits distinctive gyrogonite morphologies, which, coupled with their known ecological preferences, allow for refined palaeoecological interpretations.

5.1. Genus Chara Linnaeus, 1753

Chara cf. hispida (Hartman) Wood, 1962 (Figure 7A–C)
Materials: The gyrogonites were found at Arquata Quarry (a total of 55 specimens in three samples: 4, 22, 29) and in seven samples from the Acquasparta borehole (over 120 specimens: samples 5–9, 15, 20, 40). The population is rich in both sites, and most specimens are germinated. The preservation state is good. Ten gyrogonites were measured to obtain morphometric data (height, width, and isopolarity index (ISI)).
Description: Gyrogonites are variable in size: the specimens (Table 2 and Table 3) measure 820–720 μm (mean average 766 μm) in height and 680–560 μm (mean average 626 μm) in width. The ISI value is variable, from 113 to 136. Eleven to eight (frequently nine) convolutions are visible in lateral view (Figure 7C). Spiral cells, non-ornamented, are flat to convex and 80 μm in height. The apex is psilocharoid-type (according to the taxonomy of [16]). A prominent apex formed by spiral cells that swell in the central part is typical of this taxon (Figure 7A). The tapering base of gyrogonite possesses a basal pore within the star-shaped pentagonal funnel (Figure 7B).
Fossil record: Chara hispida has frequently been found in Quaternary Lake deposits of Europe, Africa, and South America ([18,20] and references therein). In Türkiye, this species has been reported in deposits of the Early Pleistocene (Calabrian) in Western Anatolia [21] and of the Early Pleistocene at Ilgin Basin [18].
Ecology/Palaeoecology: The cosmopolitan species Chara hispida grows in alkaline, well-oxygenated, and mesotrophic permanent lakes and shows a preference for phreatic water [22]. This species thrives in waters with a pH ranging from 7.3 to 8.4 and hard waters with values of 50–200 mg/L of dissolved calcium. C. hispida develops at depths up to 15 m and forms thick meadows between 0.5 and 7 m in depth [23]. The plants growing in deeper waters are perennial and reproduce vegetatively [24]; on the contrary, plants grown at shallower depths fructify, producing gyrogonites when the water temperature exceeds 20 °C [25]. The species prefers fresh, oligotrophic waters and can grow at depths up to 9 m, commonly between 1 and 7 m [26,27]. It is found in shallow freshwater ecosystems, often under ice cover, and in environments containing gyttja and peat–limestone sediments [22].
Chara cf. vulgaris Linnaeus, 1753 (Figure 7D–F)
Materials: The gyrogonites were found in all the samples of the Arquata quarry section and in three samples (2, 14, 17) from the Acquasparta borehole. The population is rich, and most specimens are germinated. The preservation state is good. Ten gyrogonites were measured to obtain morphometric data (height, width, and isopolarity index (ISI)).
Description: The size of the gyrogonites is variable; the specimens (Table 2 and Table 3) measure 820–760 μm (mean average 762.5 μm) in height and 700–520 μm (mean average 618 μm) in width. They are prolate in shape with an isopolarity index varying from 107 to 146. Seven to eleven (frequently seven) convolutions are visible in lateral view (Figure 7F). The spiral cells are concave, with sharp sutures and without ornamentation. The height of a spiral cell is 76 μm. The apex is of the psilocharoid type (Figure 7D). The base of the gyrogonite is generally pointed and shows a basal pentagonal pore (Figure 7B).
Fossil record: C. vulgaris populations have been found in Chad, Algeria, Mali, and Sudan in lacustrine deposits of the Pleistocene and Holocene [28,29]. In addition, populations of C. vulgaris been found in Quaternary deposits in Romania [30], while [24] signaled the presence of C. vulgaris in Early Pleistocene deposits in Western Anatolia (Türkiye) and [18] reported gyrogonites of C. vulgaris in Early Pleistocene deposits at the Ilgin Basin (Türkiye).
Ecology/Palaeoecology: C. vulgaris is a worldwide pioneer species that thrives in shallow freshwater environments [22] in a wide array of shallow, temporary, or permanent freshwater habitats, including slow-flowing streams and semi-permanent springs. It favors mesotrophic to eutrophic clear waters on calcareous, gypseous, or sandy substrates. Its altitudinal distribution spans from lowlands to subalpine zones [18]. C. vulgaris develops in temporary ponds or permanent lakes from a few centimeters to 19 m in depth [31]. The development of oospores and gyrogonites occurs in temporary water bodies, and, according to [25], gyrogonites are only formed at salinities below 3‰. The vegetative propagation predominates in permanent waters.

5.2. Genera Nitellopsis and Lychnothamnus

Nitellopsis obtusa (Desvaux in Loiseleur) Groves, 1919 (Figure 7G–I)
Materials: The gyrogonites of N. obtusa were found in samples 4, 8, 22, and 29 from Arquata quarry. The population is rich, and most specimens are germinated. The preservation state is good. Ten gyrogonites were measured to obtain morphometric data (height, width, and isopolarity index (ISI)).
Description: The gyrogonites are very large; the height is variable, from 1120 to 840 µm (mean average 1014 µm), and the width varies from 920 to 800 µm (mean average 850 µm). Prolate spheroidal to subprolate in shape, with an isopolarity index that varies from 105 to 128. The number of convolutions visible in lateral view varies from 7 to 5 (frequently 6) (Figure 7I). The spiral cells are concave and measure 160 µm in height and 71 µm in thickness. The prominent apex of gyrogonite is of the nitellopsidoid type and has well-developed apical nodules (Figure 7G). The base displays a rounded profile and shows a large basal pore (80 µm in diameter) within a pentagonal or star-shaped funnel (Figure 7H). Many specimens show a taped pentagonal pore (Figure 7H). The population of the Arquata quarry samples is the richest, with one hundred seventy specimens, which, upon initial analysis, appear to be of the same size. Many of the specimens have germinated, resulting in the loss of the basal or apical part of the gyrogonites.
Fossil record: Fossil gyrogonites of Nitellopsis obtusa have been found in lacustrine deposits (Pleistocene to subrecent) in France, Germany, the UK, Romania, North Africa, and Türkiye [20,32]. Other Early Pleistocene localities include the Po Basin (Italy), Poland [33,34], and western Türkiye (Söke) [21]. Furthermore, the taxon was first documented in Central Anatolia in the Early Pleistocene deposit of the Ilgın Basin [18].
Ecology/Palaeoecology: This is a boreal species with a widespread distribution in Asia and Europe. It prefers cold, alkaline, oligotrophic lakes with depths of 4–12 m, where plants may attain lengths of up to 2 m. It occupies neutral-to-basic, moderately calcareous waters with sandy or silty substrates containing slightly organic content [35,36].
Lychnothamnus barbatus (Meyen, 1827) von Leonhardi 1863 (Figure 7J–L)
Materials: The gyrogonites of L. barbatus were found in all three sections (Table 2 and Table 3), with the maximum of specimens not exceeding 25 units, and most specimens are germinated. The preservation state is moderate. Ten gyrogonites were measured to obtain morphometric data (height, width and isopolarity index (ISI)).
Description: Gyrogonites are medium in size: the specimens measure 820 to 760 μm (mean average 784 μm) in height and 730 to 600 μm (mean average 784 μm) in width. The specimens are poorly prolate in shape, with an isopolarity index varying from 106 to 136. Seven to nine convolutions are visible laterally. Spiral cells are concave to flat and vary between 111 and 100 μm in height. The apex is flat and without periapical modification (Figure 7J). Gyrogonites own large basal pores within a star shaped funnel (Figure 7L).
Fossil record: Populations of L. barbatus are limited to a few localities in India, Australia, Egypt, Mali, Albania and Poland ([37] with references). Few specimens of Lichnothamnus barbatus var. antiquus Soulié-Märsche 1989, were reported in Early Pleistocene deposits of the Ilgin Basin (Türkiye) [15].
The finding of this taxon (even if very rare) in the Tiberino Basin sections enlarge the knowledge on its distribution ([8]; this work).
Ecology/Palaeoecology: Lychnothamnus barbatus at present thrives in permanent lakes of Northern Europe, forming dense meadows at depths between 2 and 8 m (14 m maximum) [22]. This species grows in cold, oligo-mesotrophic lakes frequently associated with phreatic water sources ([23,38] and references therein), favoring clear, flowing waters at depths of 50–130 cm [39].

5.3. Comparison of Tiberino Basin and Coeval Ilgin Basin Morphometric Data (Türkiye)

The morphometric data of the gyrogonites, including height, width, ISI value, and number of convolutions, were compared with the population from the Early Pleistocene of Türkiye (Table 3). The measurements of the gyrogonites of C. cf. hispida are comparable to those indicated by [18], although our forms mainly appear to fall within the smaller dimensional ranges (Table 3). L. barbatus shows smaller morphometric values. In contrast, the dimensions of C. cf. vulgaris are larger and exceed those of the compared species, and N. obtusa has dimensions that fall within the dimensional ranges indicated by [18].
The limited number of complete specimens measured prevents us from formulating hypotheses about the dimensional variations of the specimens in the Tiberino Basin. These dimensional variations could either fall within the range of intraspecific variability or be linked to variations in palaeoecological factors (i.e., water and/or air temperature, low levels of Ca) that induce stress in the plants. The collection of a greater number of specimens will likely help us to understand the reasons for these variations.

6. Discussion

6.1. Environmental Interpretations Supported by Charophyte Assemblages

Through its long and complex evolution, from the Early Pliocene to recent, the Tiberino Basin encompassed several different palaeoenvironments [6,7,8,9,10,11,12,13,14]. Figure 8 tentatively proposes a simplified palaeoenvironmental reconstruction for the three different situations described in this work, during almost the same time interval (i.e., the late Early Pleistocene). Local conditions guided a sectorized evolution, as expected from a wide and articulated continental basin. Nonetheless, the distribution of charophyte assemblages (among other taxa [8,13,14]) underlines sedimentary, ecological, and climatic variations in these environments.
The integrated micropalaeontological data from the three study sections reveal a diverse array of Early Pleistocene freshwater environments within the Tiberino Basin.
In the Arquata Quarry section, the abundant presence of Nitellopsis obtusa, a species typically associated with cold, oligotrophic, and stable lacustrine environments, indicates the persistence of a relatively deep, clear freshwater lake [8,40]. Lychnothamnus barbatus, known for its preference for undisturbed cold aquatic settings with low turbidity, corroborates the interpretation of relatively stable hydrological conditions [41]. The presence of C. cf. hispida confirms the existence of shallow, oligotrophic-to-mesotrophic lacustrine systems characterized by clear and cold waters, stable low-energy conditions, and limited salinity fluctuations. A relatively prolonged period of hydrological stability, favoring the development of stratified, persistent lakes [8], alternating with alluvial/palustrine palaeoenvironments is highlighted by the Charophyte assemblages.
In the Acquasparta borehole section, the presence of C.cf. vulgaris, a pioneer species tolerant of variable water chemistry and depths, points towards a palustrine environment with intermittent groundwater-fed aquatic phases [42]. The occurrence of pioneer species C. cf. vulgaris in the basal sample (sample#2) and in sample #14 evidences the formation of temporary ponds.
The presence of common C. cf. hispida, a species that prefers hard and cold waters (50–200 mg/L of calcium), with a negative correlation in relation to L. barbatus suggests periods of stable water levels [43] with a possible decrease in depth. Travertine/carbonate deposition (Figure 5) suggests episodes of carbonate supersaturation related to spring activity, possibly linked to semi-arid climatic conditions interspersed with wetter intervals. The Charophyte assemblages at Acquasparta thus record groundwater resurgence phases and localized hydrological stability within an otherwise fluctuating continental basin.
In the Ellera basin, the rarity of charophyte remains, alongside intermittent travertine formation, suggest a palustrine environment with periodic groundwater resurgence. The depositional settings were characterized by seasonal water level changes, rapid sedimentation, and episodic desiccation. The ecological signal suggests a dynamic, short-lived aquatic habitat rich in dissolved calcium carbonate, strongly influenced by seasonal rainfall patterns and evaporation. The formation of temporary ponds is supported by the occurrence of the pioneer species C. cf. vulgaris. This setting would have experienced alternating subaerial exposure and shallow flooding with ephemeral lacustrine episodes, compatible with semi-arid climatic intervals punctuated by wetter phases [14].
The palaeoecological signals recorded by the charophyte assemblages mirror the dynamic hydrological history of the Tiberino Basin during the Early Pleistocene.
The basin underwent recurrent alternations between stable lacustrine phases, favored by wetter climatic conditions and high positions of the groundwater table, and ephemeral swamp development during drier intervals. These palaeoenvironmental shifts were driven by regional climatic oscillations approaching the Early–Middle Pleistocene transition (~1.4 Ma), which marked the intensification of glacial–interglacial cycles across the Mediterranean [8].
Charophytes, due to their ecological specificity, captured these rapid environmental responses with remarkable fidelity, allowing fine-scale reconstruction of palaeohydrological conditions. Assemblages dominated by Nitellopsis obtusa and Lychnothamnus barbatus reflect humid climatic phases with well-developed lakes [44]. Thus, the Tiberino Basin can be interpreted as a sensitive recorder of Early Quaternary climatic dynamics in the Mediterranean region.

6.2. Charophytes as Palaeoenvironmental Proxies

Charophyte gyrogonites are among the most reliable indicators of past aquatic environments, thanks to their sensitivity to ecological parameters such as water depth, salinity, trophic status, and hydroperiod variability.
In the Tiberino Basin, the taxonomic composition and distribution of charophyte assemblages reconstruct a mosaic of freshwater habitats (Table 4) shaped by climatic oscillations during the late Early Pleistocene.
These findings align with previous palaeolimnological studies (e.g., [5,47]), which underscore the value of charophytes as high-resolution proxies for palaeohydrological reconstructions, particularly in response to fluctuations in hydrochemistry and water permanence. Reconstructions from Lake Tigalmamine (Morocco [47]) and other Mediterranean sites [45,48] further validate the gyrogonites’ ability to record subtle environmental changes.
The Early Pleistocene successions in the Tiberino Basin capture key transitions associated with the intensification of glacial–interglacial cycles around 1.4 Ma [8,49]. Phases dominated by Nitellopsis obtusa and Lychnothamnus barbatus indicate humid intervals with stable, shallow lacustrine conditions, mainly in the eastern branch (Arquata Quarry section, Valle Umbra [8,13]).
At Acquasparta (western branch, Valle Tiberina), the phases with C.cf. vulgaris alternated with those dominated by C. hispida and L. barbatus, clearly revealing that water levels were variable when transitioning from lacustrine to palustrine environments.
In contrast, in the Ellera basin, the incidence of L. barbatus, accompanied by the pioneer species C. cf. vulgaris—highly tolerable to environment degradation—points to low-stand phases characterized by hydrological instability, evaporation-driven salinity, and ephemeral swamp formation [14]. These alternating regimes reflect regional climatic trends, particularly increasing seasonality and the expansion of semi-arid belts in Southern Europe approaching the Early–Middle Pleistocene transition.

6.3. Insights from Comparative Palaeolimnology

Comparative records (Table 4) from Mediterranean basins support the interpretations derived from the Tiberino charophyte data. At Laguna de Gallocanta (Spain) [45], shifts from persistent lakes to seasonal basins mirror similar transitions in the Tiberino Basin, while Lake Afourgagh (Morocco) [46] documents charophyte assemblages indicative of alternating water levels in response to Holocene climate variability. The Early Pleistocene charophyte assemblages reported in the Ilgin Basin (Türkiye) [18] indicate that the lake was oligohaline and its conditions changed from very shallow and eutrophic to stable, oligotrophic, and relatively deep (up to 15 m). Ref. [18] related this lacustrine transgression to water availability ruled by climatic fluctuations during the Günz glaciation.
These parallels emphasize common climatic control across Mediterranean latitudes, likely orbitally forced, and reinforce the applicability of charophyte assemblages as palaeoclimate proxies in diverse geological settings.

7. Conclusions

The finding of charophyte gyrogonites in the Early Pleistocene deposits of the Tiberino Basin represent a milestone for palaeoenvironmental reconstructions.
The integrated micropalaeontological and sedimentological analysis of continental deposits of the Arquata, Ellera, and Acquasparta sites has allowed us to reveal a detailed picture of palaeohydrological and palaeoclimatic evolution in Central Italy.
This first report of charophyte fossil gyrogonites represents an initial step in the study of the lower Pleistocene population. Our study, in fact, does not include statistical analyses on the morphological parameters of gyrogonites, which necessitate a larger number of specimens than we currently possess.
Future research directions will include the following:
(1)
Laboratory preparation of additional samples from the three sites with the aim of increasing the number of specimens. This approach will facilitate the collection of more data on morphological parameters and potential variations in relation to hydrological/climatic changes.
(2)
High-resolution stable isotope analyses of charophyte calcifications.
(3)
Palynological studies (at Acquasparta and Ellera sites) to reconstruct associated terrestrial vegetation.
These approaches will enhance our understanding of Quaternary climate dynamics in Mediterranean continental basins and reinforce the palaeoenvironmental utility of charophyte fossils. Finally, we hope that our new data can be an important “bridge” connecting the associations of the Eastern, Southern, and Western Mediterranean.

Author Contributions

Conceptualization, A.B., P.A., R.B., I.N. and A.M.D.S.; investigation, A.B., A.M.D.S. and I.N.; writing—original draft preparation, A.B., P.A., R.B., I.N. and A.M.D.S.; writing—review and editing, A.B., P.A., R.B. and I.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data is contained within the article and the specimens of fossil gyrogonites are available for comparison at the Department of Physics and Geology of the University of Perugia.

Acknowledgments

We acknowledge the technician Luca Bartolucci (Department of Physics and Geology, University of Perugia) for assistance during the SEM analysis and three anonymous reviewers for their useful and stimulating suggestions.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Figure 1. (A) Simplified structural scheme and distribution of main Neogene–Quaternary basins in Central Italy. (B) Tiberino Basin profile showing the positions of the studied sections. After [6] (redrawn and modified).
Figure 1. (A) Simplified structural scheme and distribution of main Neogene–Quaternary basins in Central Italy. (B) Tiberino Basin profile showing the positions of the studied sections. After [6] (redrawn and modified).
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Figure 2. Schematic geological map (A) and location of the Arquata quarry; (B) aerial view of the quarry, distribution of sedimentary units, and anthropic reorganization of the clay deposits for brick production; (C) panoramic view of the measured and sampled succession (modified after [8]).
Figure 2. Schematic geological map (A) and location of the Arquata quarry; (B) aerial view of the quarry, distribution of sedimentary units, and anthropic reorganization of the clay deposits for brick production; (C) panoramic view of the measured and sampled succession (modified after [8]).
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Figure 3. (A) Location of the Acquasparta borehole (red arrow) near the historical Palazzo Cesi and (B) sediments of the lowermost interval with charophyte gyrogonites (from −40 to −30 m).
Figure 3. (A) Location of the Acquasparta borehole (red arrow) near the historical Palazzo Cesi and (B) sediments of the lowermost interval with charophyte gyrogonites (from −40 to −30 m).
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Figure 4. Outcrop of the Ellera section (Ellera di Corciano); the position of the sample with charophyte is shown (red arrow). The thickness of the outcrop is about five meters.
Figure 4. Outcrop of the Ellera section (Ellera di Corciano); the position of the sample with charophyte is shown (red arrow). The thickness of the outcrop is about five meters.
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Figure 5. Simplified stratigraphic/sedimentological column for the three studied sections (redrawn and simplified after [8,14]). The numbers refer to the samples and the charophyte species/assemblages in Table 1 and Table 2.
Figure 5. Simplified stratigraphic/sedimentological column for the three studied sections (redrawn and simplified after [8,14]). The numbers refer to the samples and the charophyte species/assemblages in Table 1 and Table 2.
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Figure 6. (A,B) Specimens of Chara sp., in transverse basal and lateral views, affected by microperforations; (C) detail of branch with two encrusted gyrogonites (Ellera section). SEM microphotos.
Figure 6. (A,B) Specimens of Chara sp., in transverse basal and lateral views, affected by microperforations; (C) detail of branch with two encrusted gyrogonites (Ellera section). SEM microphotos.
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Figure 7. Gyrogonites of Tiberino Basin: (A–C) Chara cf. hispida: apical, basal, and lateral views, Acquasparta sample 7; (D–F) Chara cf. vulgaris: apical, basal, and lateral views, Arquata sample 22; (G–I) Nitellopsis obtusa: apical, basal, and lateral views, Arquata sample 8; (J–L) Lichnothamnus barbatus: apical, basal, and lateral views, Acquasparta sample 2.
Figure 7. Gyrogonites of Tiberino Basin: (A–C) Chara cf. hispida: apical, basal, and lateral views, Acquasparta sample 7; (D–F) Chara cf. vulgaris: apical, basal, and lateral views, Arquata sample 22; (G–I) Nitellopsis obtusa: apical, basal, and lateral views, Arquata sample 8; (J–L) Lichnothamnus barbatus: apical, basal, and lateral views, Acquasparta sample 2.
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Figure 8. Simplified palaeoenvironmental restoration for the three study sections, according to the literature [8,13,14] and original data. The distribution of charophytes (indicated by numbers) refers to Figure 5 and Table 2.
Figure 8. Simplified palaeoenvironmental restoration for the three study sections, according to the literature [8,13,14] and original data. The distribution of charophytes (indicated by numbers) refers to Figure 5 and Table 2.
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Table 1. Summary of charophyte taxa identified in the Tiberino Basin and their associated palaeoenvironmental interpretations.
Table 1. Summary of charophyte taxa identified in the Tiberino Basin and their associated palaeoenvironmental interpretations.
TaxaPreferred Environmental
Conditions		Palaeoecological Meaning
Nitellopsis obtusaDeep, cold, stable, oligotrophic lakesStable low-energy lake
Lychnothamnus barbatusOligo- to mesotrophic lakes, low nutrient and energy levels, cold, phreatic watersStable lacustrine conditions
Chara cf. hispidaOligo- to mesotrophic lakes, cold Moderate trophic levels, decrease in water depth
Chara cf. vulgarisVariable freshwater habitats, temporary pondsResilience to environmental change
Table 2. Charophyte taxa abundances (specimen numbers) in the three sections.
Table 2. Charophyte taxa abundances (specimen numbers) in the three sections.
Tiberino Basin SitesArquata QuarryEllera Acquasparta Borehole
Taxa\Samples481122296256791415172040
Chara cf. hispida10--2025--2752936-1-15
Chara cf. vulgaris6421016104----28-1--
Nitellopsis obtusa250-12010-----------
Lychnothamnus barbatus1-61051225-84-10---13
Table 3. Morphometric data comparison of Tiberino Basin and Ilgin Basin specimens (Türkiye [18]).
Table 3. Morphometric data comparison of Tiberino Basin and Ilgin Basin specimens (Türkiye [18]).
TaxaHeight/WidthISIConvolutions
Chara cf. vulgaris (this paper)
Chara vulgaris [18]		800–760/700–520107–1467–11
746–414/465–256115–2096–15
Chara cf. hispida (this paper)
Chara hispida [18]		820–720/680–560113–1368–11
1143–721/707–432126–1978–14
Nitellopsis obtusa (this paper)
Nitellopsis obtusa [18]		1120–840/920–800105–1285–7
1198–836/1015–645101–1406–10
Lichnothamnus barbatus (this paper)
Lichnothamnus barbatus [18]		820–760/730–600106–1337–9
912–854/671–650130–13711
Table 4. Comparative palaeoenvironmental interpretations based on charophyte assemblages from the Tiberino Basin (east and west branches) and selected Mediterranean basins [8,14,18,45,46].
Table 4. Comparative palaeoenvironmental interpretations based on charophyte assemblages from the Tiberino Basin (east and west branches) and selected Mediterranean basins [8,14,18,45,46].
SiteDominant TaxaInferred EnvironmentClimatic Implications
Tiberino Basin
(Arquata Quarry)		Nitellopsis obtusa, Lychnothamnus barbatus, Chara cf. hispida, Chara cf. vulgarisStable freshwater lakesHumid cold phases
Tiberino Basin
(Acquasparta borehole)		Chara cf. hispida, Chara cf. vulgaris, Lychnothamnus barbatusTemporary ponds alternated with stable water level lakeIncreased aridity
Ellera “satellite” BasinLichnothamnus barbatus, Chara cf. vulgarisEphemeral lakesIncreased aridity
Laguna de Gallocanta [45]Chara vulgaris, Lamprothamnium papulosumEphemeral lakesSemi-arid oscillations
Lake Afourgagh (Morocco) [46]Chara aspera, Chara hispida, Chara globularisAlternating lake water levelsHolocene climatic variability
Ilgin Basin (Türkiye)
[18]		Chara vulgaris, Chara globularis (palustrine interval); Chara hispida, Nitellopsis obtusa (lake interval) Very shallow eutrophic lake evolved to a shallow, stable, oligotrophic, alkaline, and oligohaline lakeClimatic oscillation
during the Günz
glaciation
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Baldanza, A.; Angelini, P.; De Santis, A.M.; Nalli, I.; Bizzarri, R. What Do Fossil charophytes Whisper to Us? Palaeoecological and Palaeoenvironmental Reports from Pleistocene Continental Deposits of Umbria (Central Italy). Geosciences 2025, 15, 392. https://doi.org/10.3390/geosciences15100392

AMA Style

Baldanza A, Angelini P, De Santis AM, Nalli I, Bizzarri R. What Do Fossil charophytes Whisper to Us? Palaeoecological and Palaeoenvironmental Reports from Pleistocene Continental Deposits of Umbria (Central Italy). Geosciences. 2025; 15(10):392. https://doi.org/10.3390/geosciences15100392

Chicago/Turabian Style

Baldanza, Angela, Paola Angelini, Anna Maria De Santis, Isabella Nalli, and Roberto Bizzarri. 2025. "What Do Fossil charophytes Whisper to Us? Palaeoecological and Palaeoenvironmental Reports from Pleistocene Continental Deposits of Umbria (Central Italy)" Geosciences 15, no. 10: 392. https://doi.org/10.3390/geosciences15100392

APA Style

Baldanza, A., Angelini, P., De Santis, A. M., Nalli, I., & Bizzarri, R. (2025). What Do Fossil charophytes Whisper to Us? Palaeoecological and Palaeoenvironmental Reports from Pleistocene Continental Deposits of Umbria (Central Italy). Geosciences, 15(10), 392. https://doi.org/10.3390/geosciences15100392

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