The magnitude and rapidity of the climate change marking the end of the Pleistocene in the mid-latitudes of South America

A.C. Ashworth; J.W. Hoganson

doi:10.1016/0031-0182(93)90018-e

Home/Archive/USGS

USGS · 70018311

The magnitude and rapidity of the climate change marking the end of the Pleistocene in the mid-latitudes of South America

A.C. Ashworth·J.W. Hoganson

View original source ↗Export metadata ↓

Abstract

The chi-squared test of independence and cluster analysis of Otsuka similarity coefficients of fossil beetle assemblages from the Chilean Lake Region in the mid-latitudes of South America support the following conclusions: (1) the mean summer temperature of the glacial climate was 4-5??C lower than today's climate; (2) the climatic change from glacial to interglacial mode was in a single step centered on about 14,000 yr B.P.; (3) the climatic change was rapid, and within 1500 years the biota of a moorland had been completely replaced by a biota of a rain forest; (4) by 12,500 yr B.P., the low elevation beetle fauna of the Chilean Lake Region was similar in composition to that of the present day; and (5) no reversal in the postglacial warming trend, equivalent in age to the Younger Dryas Stade, was detected.

Explore related subjects

Palaeogeography, Palaeoclimatology, Palaeoecology Article

Source-reported bounding extent: -40.741320377357766° to -33.79189864452927° latitude; -74.29096675825205° to -71.5696905220094° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

A.C. Ashworth, J.W. Hoganson. 1993. The magnitude and rapidity of the climate change marking the end of the Pleistocene in the mid-latitudes of South America. https://doi.org/10.1016/0031-0182(93)90018-e

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

A diatom-based quantitative sea-ice proxy for the Bering and Chukchi seas

Sea ice affects Earth's climate system on both regional and global scales. Its incorporation into climate can be used to achieve more accurate predictions of future climate. However, instrumental records of sea-ice concentration do not extend earlier than 1978. In an effort to extend this record, we constructed a proxy using the generalized additive model based on relative abundances of five easy-to-identify diatom species found in sediment samples across the Bering and Chukchi seas. Here we present the first quantitative diatom-based sea-ice proxy developed for Beringia. The developed proxy has been applied to two sediment cores in the Bering Sea ranging from 0 to 25.7 ka (HLY0204 51JPC) and 369 to 430 ka (IODP Exp 323 Site U1345) and one in the Chukchi Sea ranging from 2.7 to 10 ka (HLY0204 24JPC). The obtained reconstructions of sea-ice concentrations are similar, but not identical to previously published qualitative and nearby records based on other proxies. Because our results are quantitative, they can be incorporated into regional climate models. The proxy is publicly available as an R Shiny application (app) and can be applied to any diatom count from marine sediments in the region.

Bering Sea, Chukchi Sea↗

USGS2026

Miocene evolution of the Humboldt Current

Diatom records from the East Pisco Basin (EPB) of southern Peru and offshore Ocean Drilling Program (ODP) Hole 682 A reveal stepwise increases in the primary productivity of the Humboldt Current during the middle and late Miocene. Although diatoms are present back through the late middle Eocene, successively enhanced diatom production occurs during the Miocene in four steps. The first step between 14.2 and 13.8 Ma marks the onset of diatom deposition in the Pisco-0 sequence. A second step at ∼12.9 Ma coincides with a major drop in global sea level during which diatom deposition ceased in the EPB but continued in ODP 682 A as well as in Chile, Ecuador, and Colombia. Beginning at 10.4 to 10.0 Ma, a major increase in diatom sedimentation rates in both the EPB and in ODP 682 A signals an abrupt intensification of the Humboldt Current productivity, which may be related to the closure of the Central American Seaway to deeper water circulation. A fourth step coincides with the transgressive deposition of the diatom-rich Pisco-2 sequence at 8.4 Ma and is enhanced by the onset of the global Late Miocene Biogenic Bloom (8.0–4.5 Ma). Between 7 and 6 Ma, common subtropical diatoms in ODP 682 A contrast with high diatom deposition rates in the EPB, suggesting variable El Niño-La Niña conditions. During this time, fossil vegetation evidence from southern Peru supports the presence of seasonal periods of enhanced rainfall typical of El Niño conditions. The Miocene trend of increasing sea mammal diversity in the EPB parallels these steps, further supporting stepwise enhancement of primary productivity in the Humboldt Current during the Miocene.

Humboldt Current↗

USGS2026

Constraining the onset of carboniferous cyclicity in the Arkoma Basin of the Midcontinent, North America: Implications for calibrating a globally significant latest Bashkirian transgression

Cyclothems are defined by the repeat juxtaposition of littoral and open marine successions over short stratigraphic distances (meters to 10's of meters) and are interpreted to be driven by glacioeustatic forcing of sea level during the late Paleozoic Ice Age. The concept of cyclothems was defined in the Midcontinent region of the United States. However, correlating the Midcontinent region to other cyclic successions is difficult, which is the result of no geochronologic control for the Midcontinent biostratigraphic framework. We present the first high-resolution U Pb zircon CA-ID-TIMS and feldspar 40 Ar/ 39 Ar age control for the onset of Midcontinent cyclothem deposition in the Arkoma Basin, Arkansas USA. Geochronologic control is obtained from a volcaniclastic unit preserved in the newly recovered Dare Creek #1 core. We integrate these data with biostratigraphic, lithostratigraphic and trace element analyses to investigate the timing, stratigraphic and geochemical response to late Paleozoic climate forcing. The lowermost Atoka Formation is associated with the onset of five high frequency transgressive-regressive cycles, which are defined by nearshore sandstones juxtaposed on top of offshore marine mudstones and are associated with changes in salinity and redox conditions. The Trace Creek Member of the lower Atoka Formation hosts a thick, organic-rich black shale, which defines the last and maximum transgression of the lower Atoka Formation in the Arkoma Basin, in the latest Bashkirian. Base-level records from time equivalent stratigraphic successions from Arrow Canyon, Nevada, U.S.A. and the Donets Basin, Ukraine also record a maximum transgression in the latest Bashkirian. The synchroneity of maximum flooding events from multiple basins which span the low latitudes in the latest Bashkirian support that cyclothem deposition was controlled by allostratigraphic forcing mechanisms, likely glacioeustatic forcing resulting from dynamic glaciation in high-latitude Gondwana.

Arkansas, Oklahoma↗