Do Freshwater Foraminifera Disrupt Stromatolite Laminations?
Abstract
Microbialites are lithified microbial mats, with an extensive geological record spanning at least 3 billion years. Two of the three primary types of microbialites include stromatolites (laminated) and thrombolites (clotted), the latter of which emerged around 1.9 billion years ago. The cause for the decline in stromatolites during the Neoproterozoic (700 - 541 million years ago) remains a topic of debate. A popular hypothesis to explain the decline in stromatolites and rise in thrombolites is the growth in abundance of metazoan predators that may have inhabited and disrupted stromatolite fabric, though fossil evidence for this hypothesis is lacking. Marine "naked" foraminiferal species that lack mineralized shells, and thus do not easily fossilize, have been shown to disrupt marine stromatolite laminations in one experimental setting. Here, we aim to test the same hypothesis in an alkaline environment at Fayetteville Green Lake, NY (FGL), which has a prominent microbialite platform exhibiting laminations near the surface. The alkaline setting also allows FGL to be an analog for Proterozoic oceans. Three short cores of extant stromatolites were collected and scanned via microCT with a table-top Bruker SKYSCAN 1272. We then seeded each core with ~10 individual Haplomyxa saranae, a naked freshwater foraminifer. The seeded cores were left in a humid container and given adequate sunlight to simulate conditions at FGL. The water overlying each core was changed weekly with a filtered supply from FGL, which was collected at the time of sampling. Cores were re-scanned ~3.5 months later. The before (T0) and after (T1) scans were analyzed in the 3D.SUITE software package from SKYSCAN (CTVox, Data Viewer, and CTAn) to evaluate possible disturbance to laminations. ImageJ (NIH) was used to overlay corresponding 2D slices from T0 and T1 of each scan at various coronal sections throughout the cores. Preliminary results show limited disturbance to the relatively large-scale laminations, implying that fabric disruption by foraminifera may not be the leading cause of stromatolite decline. Ongoing textural analyses aim to quantify differences between the T0 and T1 microCT scans at finer scales that could be due to foraminiferal activities or microbial growth. Supported by NSF EAR 1561204 (WHOI) and 1561173 (UConn).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP013..04S
- Keywords:
-
- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL