Phytolith Assemblages Record Vegetation History During the Middle Miocene Climatic Optimum in the Coastal Santa Cruz Formation, Patagonia, Argentina.
Abstract
The Middle Miocene Climatic Optimum (MMCO; ca. 17-14.5 Ma) was characterized by high temperature and pCO2, thought to promote warm and wet climates at high latitudes. The Santa Cruz Formation (SCF; ca. 17.8-16.6 Ma) of coastal Patagonia (47-52°S) represents the southernmost sedimentary record in the world spanning the onset of the MMCO. SCF fossiliferous horizons yielded one of the most species rich and well preserved Cenozoic vertebrate assemblages known. Plant macrofossils, and well-preserved phytolith assemblages also occur in the SCF within the same strata as the faunas. These linked fossil records allow us to, for the first time, compare in detail animal and plant paleoecology, vegetation structure, and local climate through the MMCO global warming event in southern South America.
Here, we present results from analysis of phytolith assemblage composition (% plant functional types) from the SCF Atlantic coastal localities of southern Argentina, documenting vegetation change during the onset of the MMCO, which we interpret in light of current climatic reconstructions based on isotopic and faunal data. Overall, phytolith assemblages are more or less dominated by forest indicators, including palms; grass phytoliths are more abundant in the oldest assemblages ( 40-60%) compared to in the upper strata ( 10-40%). In addition to this temporal pattern, there is also variation in the overall assemblage composition laterally along individual strata, with different forest indicators dominating different assemblages, and varying forest indicator: open habitat indicator ratio. This pattern points to important spatial heterogeneity in vegetation throughout the onset of the MMCO. Grass phytolith assemblages consist mainly of morphotypes from C3 pooid grasses throughout the section, although we observe changes through time in the specific pooid phytolith morphotypes that dominate these assemblages. These results are consistent with isotopic data indicating dominantly C3 vegetation and a shift toward a more arid climate characterized by decreased MAP as well as increased MAT during the onset of the MMCO, but suggest that this drying resulted in the expansion of a dry-adapted woody vegetation rather than open-habitat grasses.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP44B..05C
- Keywords:
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- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 1620 Climate dynamics;
- GLOBAL CHANGEDE: 4936 Interglacial;
- PALEOCEANOGRAPHY