ichnodiversity penetration depth bioturbation index burrow diameter ichnofabric principal component analysis tiering demarcation surfaces ethology ichnofabric variables stratigraphic surfaces Earth Science Geology Glossifungites Kutai Basin Mahakam Delta Miocene Paleoecology RPD (redox potential discontinuity) behavior bioturbation brackish burial colonization window delta type diameter diversity environmental conditions erosional firmground fluktuasi temperatur fluvial discharge ichnofossil diameter ichnotaxa iknologi kecepatan relatif kondisi lingkungan pengendapan konsistensi substrat number of behaviors number of behaviour number of behaviours number of tiers oscillatory curves softground substrate consistency substrate stability tranquil woodground