Reconstructing the Climate Variability During the Last 5000 Years From the Banni Plains, Kachchh, Western India

The climatic conditions during the beginning of the last 5,000 years have been discussed, debated, and documented from various parts of the Indian subcontinent, due to the human–climate interrelationship. In the present study, we report a multi-proxy dataset encompassing the widely used ∼ geochemical and mineral magnetic proxies supported by radiocarbon and optical chronologies from the Banni Plains of the Rann of Kachchh, western India. Our results support the earlier observations of the prolonged wetter climatic condition synchronous with the mature phase of Harappan era which witnessed a short and intense arid condition at the terminal part of the mature Harappan phase. The climate system dramatically fluctuated during the last five millennia from pulsating between relatively arid (4,800–4,400 years BP, 3,300–3,000 years BP, and at 2,400 years BP) and relatively humid phases (>4,800 years BP, 4,000–3,300 years BP, 1900–1,400 years BP, and 900–550 years BP). The multi-proxy dataset shows a gradual strengthening of the monsoonal conditions from the Banni Plains during the late Harappan phase. Apart from this, the high sedimentation rate (>1 mm/yr) recorded from the Banni Plains suggests it can be tapped as a robust archive to reconstruct multi-decadal to centennial climatic events spanning the Holocene epoch.

Significance of the Ukrainian loess-palaeosol sequences for Pleistocene climate reconstructions: rock magnetic, palaeosol and pollen proxies

Variations of rock magnetic parameters in loess-palaeosol sequences, related to climatic and environmental conditions during their formation, are a powerful tool for palaeoclimate reconstruction. Combined enviromagnetic study of loess deposits in Ukraine and its assessment for the palaeoreconstruction purposes are carried out in the framework of the National Research Foundation of Ukraine project 2020.02/0406 ‘Magnetic proxies of palaeoclimatic changes in the loess-palaeosol sequences of Ukraine’. Environmental/climatic reconstructions of the past are fulfilled using a significant number of palaeoindicators: morphology and lithological properties of palaeosols and loesses, their pollen assemblages and a wide range of magnetic characteristics. In this paper, we present a multi-proxy approach to palaeoenvironmental reconstructions, and introduce preliminary results obtained from magnetic susceptibility of loess-palaeosol sequences in the northern (at Vyazivok), central (Stari Kaydaky) and southern (Roksolany) parts of the Ukrainian loess belt. The amplitudes of palaeoclimate change established using magnetic proxies are well correlated with the lithological, palaeopedological and palynological patterns of the sites, and with the global oxygen-isotope scale (MIS). Ongoing studies of the Stari Kaydaky section confirm the correlation of the Upper Zavadivka (S3) soil unit and Lower Zavadivka (S4) soil unit with MIS 9 and MIS 11, respectively (this was proved earlier at the Vyazivok and Roksolany sites). The underlying Lubny (S5) pedocomplex likely corresponds to MIS 13, and the Martonosha (S6) pedocomplex to MIS 15. Palaeomagnetic investigations at Stari Kaydaky have not so far reached the Lower Shyrokyne unit, in which the Matuyama—Brunhes boundary has been detected at Roksolany and Vyazivok. The Upper Shyrokyne (S7S1) palaeosol unit has normal polarity and is preliminarily correlated with MIS 17.

Testing lake-level reconstructions based on rock magnetic proxies for the sediment record of Laguna Cháltel (Patagonia, Argentina)

This study was carried out on sediment cores collected with a gravity corer from Laguna Cháltel, an almost circular crater lake located in Patagonia, Argentina (49.9°S, 71°W). The main magnetic carrier was Ti-magnetite in the pseudo–single domain range. A model using magnetic grain size and concentration, previously applied to Laguna Potrok Aike to infer lake-level changes, was used for Laguna Cháltel. The main requirement to apply the model is uniform magnetic mineralogy, which is the case for Laguna Cháltel. After magnetic data were compared with previously studied lake levels, it was found that the magnetic proxies that best follow hydrologic changes are ARM/SIRM (anhysteretic remanent magnetisation/saturation of isothermal remanent magnetisation) and ARM. The concentration proxy (ARM measured with a 100 mT alternating field and 0.05 mT direct field) was also used as wind indicator. High wind strength was found at around 3650 cal yr BP, and low wind strength for the last century. ARM/SIRM and ARM were used to infer the strength of fluvial runoff into the lake for a core collected close to the shore and near a tributary. The results show that the magnetic model is promising for inferring lake-level variations, particularly in Patagonian lakes.

Stratigraphy, plankton communities, and magnetic proxies at the Jurassic/Cretaceous boundary in the Pieniny Klippen Belt (Western Carpathians, Slovakia)

A well preserved Upper Tithonian–Lower Berriasian Strapkova sequence of hemipelagic limestones improves our understanding of environmental changes occurring at the Jurassic/Cretaceous boundary in the Western Carpathians. Three dinoflagellate and four calpionellid zones have been recognized in the section. The onset of the Alpina Subzone of the standard Calpionella Zone, used as a marker of the Jurassic/Cretaceous boundary is defined by morphological change of Calpionella alpina tests. Calpionellids and calcified radiolarians numerically dominate in microplankton assemblages. The first occurrence of Nannoconus wintereri indicates the beginning of the nannofossil zone NJT 17b Subzone. The FO of Nannoconus steinmannii minor was documented in the lowermost part of the Alpina Subzone. This co-occurrence of calpionellid and nannoplankton events along the J/K boundary transition is typical of other Tethyan sections. Correlation of calcareous microplankton, of stable isotopes (C, O), and TOC/CaCO3 data distribution was used in the characterization of the J/K boundary interval. δ13C values (from +1.09 to 1.44 ‰ VPDB) do not show any temporal trends and thus show a relatively balanced carbon-cycle regime in sea water across the Jurassic/Cretaceous boundary. The presence of radiolarian laminites, interpreted as contourites, and relatively high levels of bioturbation in the Berriasian prove oxygenation events of bottom waters. The lower part of the Crassicolaria Zone (up to the middle part of the Intermedia Subzone) correlates with the M19r magnetozone. The M19n magnetozone includes not only the upper part of the Crassicollaria Zone and lower part of the Alpina Subzone but also the FO of Nannoconus wintereri and Nannoconus steinmannii minor. The reverse Brodno magnetosubzone (M19n1r) was identified in the uppermost part of M19n. The top of M18r and M18n magnetozones are located in the upper part of the Alpina Subzone and in the middle part of the Ferasini Subzone, respectively. The Ferasini/Elliptica subzonal boundary is located in the lowermost part of the M17r magnetozone. A little bit higher in the M17r magnetozone the FO of Nannoconus steinmannii steinmannii was identified.