EXCEPTIONALLY LARGE FOSSIL BURROWS FROM CRETACEOUS DEPOSITS OF THE SOUTHERN FERGANA BASIN (SW KYRGYZSTAN) AND THEIR PALEOENVIRONMENTAL IMPLICATIONS

In the Southern Fergana Basin (southwestern Kyrgyzstan), strikingly red siliciclastic Cretaceous strata contrast sharply with surrounding lithologies, including older Triassic to Jurassic terrestrial, and younger Paleogene marine sediments within the Madygen Geopark area (Trubin et al., 2025). These Cretaceous deposits are associated with marginal marine settings, reflecting the marine transition of this complex and long-lived basin and its connection to the Peritethys (Getman et al., 2015).

These Cretaceous deposits lack body fossils and diagnostic sedimentary structures, hindering precise stratigraphic and paleoenvironmental interpretations. However, previously undescribed, exceptionally large ichnofossils, interpreted as burrows, offer rare insights into the Cretaceous of the Southern Fergana Basin. At three sites within the Madygen Geopark area, these structures are remarkable in size, density, and abundance, making them the only known evidence of macrobiotic activity from this time in the region. Despite the absence of body fossils, the burrows preserve sufficient morphological detail to suggest functional significance and potential tracemakers.

Their presence provides a valuable proxy for reconstructing local paleoenvironmental conditions during the Cretaceous and help interpret the extent of the shifting habitat. Moreover, the ichnofossils contribute to the broader understanding of large fossil burrows—an ichnological group often difficult to interpret due to the lack of modern analogs (Bromley et al., 1975). To support further analysis, the ichnofossils were documented using photogrammetry, and selected samples were examined via scanning electron microscopy (SEM). We suggest that the burrows have been produced by crustaceans, as they show strong similarity to the ichnogenus Camborygma (Hasiotis and Mitchell, 1993).