CARBONATE MUD MOUNDS OF THE EARLY CARBONIFEROUS: EVALUATING TEMPORAL AND GEOCHEMICAL RELATIONSHIPS BETWEEN THE TICE AND WAULSORTIAN-LIKE MUD MOUNDS

The Late Paleozoic Ice Age (LPIA) represents one of the longest and most extensive icehouse intervals in Earth history. However, the interplay between life and environmental forcings for the initiation of LPIA-related cooling have yet to be fully realized. Of particular note is the mid-Tournasian positive carbon isotope excursion (TICE), globally documented ~352 Ma, that is among the largest magnitude carbon isotope excursions of the Phanerozoic (~7‰). The TICE represents a significant δ¹³C excursion hypothesized to be the result of extensive organic matter burial, likely contributing to early LPIA-related cooling. Recent studies also indicate the development of anoxic conditions affecting up to 30% of the seafloor at the initiation of the TICE. Another notable feature of this time is the emergence of large-scale (~10s of meters) Waulsortian or Waulsortian-like carbonate mud mound buildups. These structures appear temporally constrained to the interval surrounding the TICE and are globally documented in deep marine strata. The Waulsortian-like mounds signify a shift in reef communities and carbonate factories, favoring the formation of massive mound structures devoid of reef framework builders. However, the broader environmental context of these mounds remains ambiguous, particularly concerning the geochemical implications surrounding their growth and their timing in relation to the TICE event.

Here, we present stable carbon isotopic records from strata that contain Waulsortian-like mounds in an attempt to better decipher the relationship between the mounds and the TICE event. The Bat Mountain study locality, within the Funeral Mountain Range of California, offers the opportunity to study both mound fabrics and background sea water contained in strata lateral to and onlapping onto the mound. We hypothesize that the mounds either represent a response to geochemical change associated with the TICE (e.g. anoxia) or the opening of a unique carbonate factory that may have provided an additional carbon sink, enhancing the sequestration of atmospheric CO₂ leading up to the LPIA. Establishing a more detailed correlation between the geochemistry preserved in the surrounding strata and the mound fabric is paramount to understanding the balance between biological adaptation and geochemical cycling during turbulent environmental tipping points in Earth history.