Late Quaternary climatic history of NW Romania: results from Th/U dating of speleothems

Transcription

1 Late Quaternary climatic history of NW Romania: results from Th/U dating of speleothems Tudor Tamas 1 Bogdan P. Onac 2,1 1 Universitatea Babes-Bolyai & 2 University of South Florida

2 Outline Facts U-series dating Speleothems & time Romanian speleothem database Case studies: o V11 Cave o Lithophagus Cave o Bears & Poleva caves o Vartop Cave

3 Facts Speleothem: a general term for secondary deposits precipitated in caves, e.g., stalactites, stalagmites, or flowstones. U-series dating: is a radiometric dating technique commonly used to determine the age of calcium carbonate materials such as speleothems or corals.

4 Speleothems as paleoclimate archives Carbonate speleothems = U-series dating = absolute chronologies Oxygen & carbon isotope profiles Speleothem fabric Luminescence Trace elements geochemistry Growth lamina analysis Quaternary climate Vegetation changes

5 Radioactive decay U/Th dating has an upper age limit of ~600 ka; 230 Th half-life: 75 ka

6 Speleothems and time

7 Geochemical constraints 1. Stable mineral phase: preferably macro-crystalline with sufficient U content (0.01 to 300 ppm); 2. The system must be closed after co-precipitation of U and calcite in speleothems; - internal corrosion; - high porosity; - re-crystallization; 3. No 230 Th be deposited in the initial calcite ( 230 Th/ 232 Th >20); 4. Ages in stratigraphic order

8 Chemistry U and Th separation through anion exchange α-spectrometry; TIMS; MC ICP-MS

9 tudied sites Piatra Rea Magurici Schneider Lithophagus, Ponoras, Rotarides, P. Negrului, Vantului, Vadu Crisului, Galaseni Humpleu, Piatra Altarului, Scarisoara, Vartop, V11, P. Rece, P. Ursilor Herculane Topolnita P. Liliecilor Limanu

10 number of dates U-Th dates distributed on growth intervals MIS Time intervals > No of dates time intervals (ky)

11 V11 Cave - Three stalagmites and two flowstone sequences dated - 48 ages on the stalagmites, 11 U-Th tests on flowstones

12 V11 Cave flowstones V succession of three calcitic layers deposited on top of a lacustrine sediment sequence (alternances of silt/clay deposits) - U-Th analyzes all suggest ages > 600 ka; - palaeomagnetism data have shown the detrital deposits are >800 ka (Matuyama epoch) V11 33a-b - separate flowstone layers with high U content (3 14 ppm) showing speleothem growth at 365 ka (MIS 11), ka (MIS 12), ka (MIS 13) and 630 ka (~MIS 15) - the oldest U/Th ages on speleothems from Romania

13 V11 Cave stalagmites V11 22, dates on two stalagmites with 6 growth intervals from MIS 6/5 to MIS 1 Tamas & Causse, 2001

14 V11 Cave stalagmites (Onac & Lauritzen 1996) NW Europe (Baker et al. 1993) (Martinson et al. 1987) V11-22 V growth intervals

15 Lithophagus Cave LFG2 = 39.5 cm stalagmite Lauritzen & Onac, 1999, J. Cave Karst Studies 61:

16 Lithophagus Cave

17 Bears Cave a Holocene record Dendritic fabric; N+, x40 Onac et al., 2002 JQS, 17: Columnar fabric; N+, x40

18 Bears Cave

19 Ursilor vs Poleva ~3.5 cm/kyr Mild & humid ~3.7 cm/kyr Temperate, sub-mediterranean Onac et al., 2002 JQS, 17: ; Constantin et al., 2007, 243:

20 Ursilor vs Poleva Difference in modelled solar output From 90 ka average (%) d 13 C in PP9 vs. PU2 d 13 C t u tp u o r la o s d le e d o m in e c n re ife d ) (% e g ra e v a k 0 9 m fro PP9 d 13 C signal solar output model C4 ) ry (d 4 C dry -9.0 present-day d 13 C PU2 d 13 C signal C3 t) e (w 3 C wet age (ka)

21 Ursilor vs Poleva - Positive relationship between 18 O and temperature - Spikes of depleted 18 O values reflect cool conditions - No 8.2 ka event in PP9 - Growth rates almost similar --> no major changes in drip rate - 13 C shows poor correlation to the solar output curve --> i.e., changes in temperature alone cannot explain the major shift of 13 C - for PP9 the 13 C indicates a major change in the vegetal association (from 10 to 6.5 ) triggered probably by a drier, meridional climate in SE Europe (e.g., Sahara Aridity at 6.9 ka)

22 Vartop Cave 1.6 cm ~ 1.5 m 2 22 cm length 10.6 cm width 146 cm tall Onac et al., 2005 QSR, 24:

23 Stratigraphy of moonmilk and U-series ages 11 U/Th ages (7 to construct the isochron) The prehistoric man stepped on the cave floor some time between ~97 and 64 kyr. Stalagmite started to grow on top of less porous moonmilk layer (C) at 63.7 kyr Thin layer of moonmilk covered footprint at 22.4 kyr ± 29 kyr Soda straws embedded in moonmilk Soda straw dated at 19.9 kyr fell onto moonmilk surface First layer filling the footprint Original moonmilk surface at the time the footprint was made Uppermost layer containing cast of footprint Moonmilk samples ( ) used to calculate the isochron age of 96.6 kyr for layer A and B

24 Facts Lower part of the moonmilk deposited during OIS 5; During OIS 4 (cold/dry conditions) moonmilk transformed into calctufa; Climate ameliorated ~64 kyr, stalagmite begun its growth; The newest calc-tufa layer deposited ~22 kyr other paleoclimate evidences are available What was the cave man looking for?shelter? Ritual place? The footprint cannot be anatomically assigned to a Neanderthal, but -The stratigraphic position of the footprint, -The U-series ages of the moonmilk & stalagmite, support the idea that the Vartop footprint belong to a Homo sapiens neanderthalensis who visited the cave some time between ~96 and ~64 kyr ago.

25 Thank you!

26