Early diagenetic alteration of chlorophyll-a and bacteriochlorophyll-a in a contemporaneous marl ecosystem; Florida Bay

This report covers the analyses of tetrapyrrole pigments in sediments and numerous source biota from northern central Florida Bay. Sediment cores were all carbonate marls and 'bedrock' (Pleistocene limestones) was typically at 0.6-1.2 m bsf. (below sea floor). Extraction of the sediments was performed using tetrahydrofuran, shown to be 3-7 times as effective as more common solvents. Surficial sediments were found to contain a pigment distribution indicating a diatomaceous-cyanobacterial biofilm/mat underlain with purple sulfur bacteria as the microphytobenthos. Downhole trends in pigment diagenesis revealed differences due to paleoenvironment. That is, when bacteriochlorophyll-a (BCHLa) plus derivatives were elevated, indicating strong syn-depositional anoxia, the pheophytins-a (PTINsa) were the major chlorophyll-a (CHLa) derivatives. Conversely, when BCHL-a plus derivatives were low, indicating oxic to dys-oxic syn-depositional conditions, then pyropheophorbide-a (pPBIDa) and 13(2), 17(2)-cyclopheophorbide-a (CYCLO) were strongly dominant. The generation of cyclopheophorbide in carbonate marls with weakly anoxic to dysoxic syndepositional conditions may yield an oil-source paleoenvironmental marker for bitumen containing compounds such as bicycloalkanoporphyrins (BiCAPs). Downhole conversions were observed for the following diagenetic steps; CHLa to pheophytin-a (PTINa), PTINa to pyropheophytin-a (pPTINa), pPBIDa to CYCLO, BCHLa to bacteriopheophytin-a (BPLTINa), and BPTINa to bacteriopyropheophytin-a (BpPTINa). (C) 2000 Elsevier Science Ltd. All rights reserved.