Marchantiopsid colonization mats from the Upper Aptian–Lower Albian of the Escucha Formation (Oliete Sub-Basin, Iberian Ranges, eastern Spain)

Abstract

In the Oliete Sub-Basin, the Escucha Formation has been divided into three different lithologic intervals, from base to top: E1 (heterolithic with coal), E2 (mainly sandstones), and E3 (claystones). At the upper part of the interval E2, a grey-silty lithosome has been recognized, corresponding to a low-energy sedimentary environment related to a sandy shoal. In this lithosome, marchantiopsid-rich beds extending up to tens of square metres have been preserved. The plant association consists of well-developed mature gametophytes of complex thallose liverworts with thalli radial, dichotomous branched, rosette forming, prostrate and, in most cases, with gemmae cups located on their dorsal surface. The occurrence of scattered individuals forming distinct rosettes that, in many cases, are interlocked or interwoven and the loose arrangement of the association, along with sedimentological characteristics, allows us to interpret these liverworts-rich beds as monospecific colonization mats at early stages of colonization, in which marchantiopsids played the role of pioneers. In addition, the high proportion of gemmiferous individuals provides significant information on the environmental conditions and the effectiveness of colonization by asexual diaspores. Specimens have been assigned to family Marchantiaceae owing to their morphological features. Although liverworts colonization mats have been mentioned from the Albian of Antarctica, no fossil record of these existed at lower palaeolatitudes or in the Upper Aptian–Lower Albian. In addition, no previous record of clonal communities of plants derived from gemmae exists. Due to the latter, the occurrence of the studied colonization mats becomes of prime importance