Regional-scale variability in the spread of grasslands in the late Miocene

Abstract

Highlights• C 3 and C 4 plant abundances are reconstructed using phytoliths and δ 13 C org values • Penecontemporaneous sites from the same region show different temporal patterns • Expansion of C 4 in the Northern Rocky Mts. does not match the global pattern • Elevation places a primary control on C 4 abundance Abstract A new paleovegetation reconstruction based on both phytolith and paleosol carbon isotopic data is presented for the middle-late Miocene (11.2-9.5 Ma) of southwestern Montana. Both sources of data indicate an open-habitat, C 3 grassland ecosystem with a small C 4 component (<10%).However, while a penecontemporaneous record from further south within the same region indicated significant spatial and temporal variability in C 4 abundance, the new record indicates relatively little change either in space or in time. Because paleoclimatic conditions reconstructed at these two sites are the same, we hypothesize that other ecological factors controlled C 4 abundance across the region. The relative abundance of C 3 and C 4 plants in the Miocene is the same as in modern environments at both sites, suggesting that their distribution was likely established by the middle-late Miocene. This is consistent with the idea that paleoelevation was also similar, which agrees with independent constraints on the regional tectonic history. TheMontana records indicate a more limited distribution of C 4 vegetation than is observed in the Great Plains and elsewhere globally, as well as variable timing in the shift to C 4 dominance in ecosystems. Taken together, this local, regional, and global variability during a time of little or no climate change suggests that C 4 distribution and expansion was driven by local, rather than global, environmental factors.

Multi‐century stasis in C3 and C4 grass distributions across the contiguous United States since the industrial revolution

“…Yet, δ 13 C values from such proxies have only rarely been compared directly to abundances of C 3 and C 4 source vegetation at the spatial resolution and extent of many biogeographical processes (e.g. C 4 range expansion; Chen, Smith, Sheldon, & Strömberg, ; Jenkins & Ricklefs, ; Powell, Yoo, & Still, ; Strömberg, ; Wynn et al., ). Similarly, applications that depend on δ 13 C data often fail to consider the spatial grain at which different δ 13 C proxies integrate C (Auerswald et al., ).…”

Pieces of the puzzle: Lack of significant C4 in the late Miocene of southern California

“…. Although abundant evidence indicates that there was a worldwide, rapid increase in C 4 ecosystems in the late Miocene, there have been several instances where the isotopic signature of C 4 plants has been found in paleosol carbonates and fossil teeth prior to the global C 4 expansion in the late Miocene (Morgan et al, 1994;Fox and Koch, 2003;Fox et al, 2012;;Cotton et al, 2012;Chen et al, 2015;Feranec and Pagnac, 2013;. This suggests an earlier regional spread of C 4 grasses, although the timing of such an event is not well constrained.…”

Early agriculture in Sri Lanka: New Archaeobotanical analyses and radiocarbon dates from the early historic sites of Kirinda and Kantharodai (Kandarodai)

“…(Table 9, S1). (Madella et al 2005) and beyond that utilising the phytolith reference collection at UCL and published references (Metcalfe, 1960, Kealhofer and Piperno, 1988, Chen et al, 2013, Weisskopf, 2014, de Albuquerque et al, 2015) (S3).…”