Lipid biomarker analyses of sedimentary organic matter from a marine Triassic-Jurassic (T-J) section at Queen Charlotte
Islands, British Columbia reveal significant bacterial activity and microbial community changes that coincide with faunal
extinctions across the T-J boundary. Bacterial activity is indicated by the 25-norhopane biodegradation index
(25-norhopanes / 25-norhopanes+regular hopanes). Microbial community changes is revealed by variations in relative
abundance of 2-methylhopane which is mainly generated from cyanobacteria. The 2-methylhopane index (2-methyl
hopane/ C<sub>30</sub> hopane + C<sub>29</sub> 25-norhopane) increases above the radiolarian based T-J boundary, and coincides with changes
in the 25-norhopane index. The data reveal a complex microbial event involving both autotrophic and heteorotrophic
bacteria responding to variations in allochthonous organic matter and nutrient supply.