Pliocene mammals and climatic reconstruction in the Western Mediterranean area
AGUILAR, J.-P., LEGENDRE, S., MICHAUX, J. and MONTUIRE, S. 1999. Pliocene mammals and climatic reconstruction in the Western Mediterranean area. In J. H. Wrenn, J.-P. Suc and S. A. G. Leroy (eds). The Pliocene: Time of change. American Association of Stratigraphic Palynologists Foundation, Dallas, pp. 109-120.
The specffic diversity of extant mammalian faunas, the body weight distribution of component species (as expressed by... more
The specffic diversity of extant mammalian faunas, the body weight distribution of component species (as expressed by cenograms), and the specific richness of some taxonomic groups change with the climate. Using these parameters, we attempt to estimate the climatic conditions of earlier times and to estimate past temperatures and precipitation.
Cenogram analysis shows that there is a contrast between rather closed and warm environments at the beginning of Pliocene times, and more open and cooler environments during the Pleistocene, and also that the Iberian Peninsula, as compared to southern France, was characterized by more open environments. The specific diversity of Murinae in Western Europe shows that the climate was warm with high precipitation (mean annual temperature = 21°C and mean annual rainfall = ca. 1100 mm) at the end of the Lower Pliocene (-4.0 to -3.5 My). The drop in diversity in Murinae that can be seen in Spain and in France is probably related to a deterioration of the climate towards coolness and dryness between -3.2 My and -2.0 My. About 1 My ago, the climate became dryer, with estimates of about 13°C and 700 mm. The first glacial phases are thus characterized by rather mild temperatures.
Rodents and climate: A new model for estimating past temperatures
LEGENDRE, S., MONTUIRE, S., MARIDET, O. and ESCARGUEL, G. 2005. Rodents and climate: A new model for estimating past temperatures. Earth and Planetary Science Letters, 235, 408-420.
Based on the high correlation between species richness in sigmodontine rodents and temperatures, we propose a new... more
Based on the high correlation between species richness in sigmodontine rodents and temperatures, we propose a new model in order to quantify past climates. Because of the close phylogenetic relationship and the tooth morphological similarity between extant New World cricetids (Sigmodontinae) and fossil European cricetids (Cricetinae s.l.), extant New World sigmodontines are taken as analogues for Old World fossil cricetines. Sigmodontine species richness has been compiled for 282 extant local faunas from North, Central and South America, with corresponding climatic data (temperatures and precipitations). There is almost no correlation between areas covered by local faunas (ranging from 1 km2 up to 46,000 km2) and numbers of sigmodontine species in localities (R2=0.027). Number of sigmodontine species in local faunas and mean annual daily temperatures are highly correlated (R2=0.88). The relationships of species richness and precipitation is low (R2=0.19 for mean annual precipitation).
The method is exemplified for Old World cricetines using well documented Miocene rodent faunas located in the Lyon area (France MN4-5 to MN10).
Paleotemperature and paleosalinity inferences and chemostratigraphy across the Aptian/Albian boundary in the subtropical North Atlantic
Paleoceanography, 26, PA4221, doi:10.1029/2011PA002178
Geochemical analyses of extraordinarily well preserved late Aptian–early Albian foraminifera from Blake Nose (Ocean... more Geochemical analyses of extraordinarily well preserved late Aptian–early Albian foraminifera from Blake Nose (Ocean Drilling Program Site 1049) reveal rapid shifts of δ18O, δ13C, and 87Sr/88Sr in the subtropical North Atlantic that may be linked to a major planktic foraminifer extinction event across the Aptian/Albian boundary. The abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0.8–1.4 million years at the boundary contact, but the values before and after the hiatus indicate that major oceanographic changes occurred at this time. 87Sr/88Sr increase by ~0.000 200, δ13C values decrease by 1.5‰ to 2.2‰, and δ18O values decrease by ~1.0‰ (planktics) to 0.5‰ (benthics) across the hiatus. Further, both 87Sr/88Sr ratios and δ18O values during the Albian are anomalously high. The 87Sr/88Sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter-basin differences in seawater 87Sr/88Sr during the Albian or revision of the seawater curve. For δ18O, planktic values in some Aptian samples likely reflect a diagenetic overprint, but preservation is excellent in the rest of the section. In well preserved material, benthic foraminiferal values are largely between 0.5 and 0.0‰ and planktic samples are largely between 0.0‰ to –1.0‰, with a brief excursion to –2.0‰ during OAE 1b. Using standard assumptions for Cretaceous isotopic paleotemperature calculations, the δ18O values suggest bottom water temperatures (at ~1000–1500 m) of 8–10°C and surface temperatures of 10–14°C, which are 4–6°C and 10–16°C cooler, respectively, than present day conditions at the same latitude. The cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid-Cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present. Because of their exquisite preservation, whole scale alteration of the analyzed foraminifera is an untenable explanation. Our proposed solution is a high evaporative fractionation factor in the early Albian North Atlantic that resulted in surface waters with higher δ18O values at elevated salinities than commonly cited in Cretaceous studies. A high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and, like the Sr isotopes, implies limited connectivity among the individual basins of the Early Cretaceous proto-Atlantic ocean.
45 views
Seen by:
