Karstic Lakes in the Iberian Range: Late Holocene sedimentological - - PowerPoint PPT Presentation

Karstic Lakes in the Iberian Range: Late Holocene sedimentological evolution and environmental and climatic implications

Fernando Barreiro-Lostres * Ana Moreno Santiago Giralt Pilar Mata Blas Valero-Garcés

Instituto Pirenaico de Ecología (IPE)-CSIC

Instituto Pirenaico de Ecología (IPE) CSIC

Introduction

 Large carbonate areas afected by endo- and exokarstic processes with … circular funnel-shaped depressions … travertine –damned lakes  If this depressions intercept the regional aquifer, relative deep lakes occur.

On the Iberian Range

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Introduction

KARST IMPERMEABLE LAKE SEDIMENTS

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Introduction

 These systems are very sensitive to regional hydrological balances.  In response to climatic changes, they present large variations on water properties (water table levels, chemistry, biota, etc.)  So, climatic, environmental changes and the possible human impact are recorded in the sediments

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Introduction

Lacustrine sediments → Excepcional records

• f the environmental evolution of an area. We

can study:

• Clastic input: Human impact in the

watershed during the last millennia has provoked an increase in sediment delivery to many lakes in Spain... but Increase run-off cause by climate factors can also be identified as short-term flooding events.

• Evolution of redox stages at the lake

bottom: Fe/Mn, Fe/S and Fe/Ti ratios can be used to unravel the evolution of the pH/Eh conditions during the sedimentation and early diagenesis stages.

• Endogenic calcite formation: preservation
• f calcite varve in discrete intervals

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Introduction

We present here the sedimentary sequence

• f 3 karstic lakes

Location and Geological settings

1) Taravilla 3) El Tobar 2) La Parra

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Introduction Taravilla

1) Taravilla

Taravilla lake

Upper Tagus River Valley (Guadalajara)

Location and Geological settings

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Taravilla lake

Inlet Outlet

Geology dominated by Jurassic and Cretaceous Limestones 1100 m asl. 2 ha surface area 11m max depth Inlets: 1 permanent spring at E. Outlets: 1 at SE (non functional on dry periods). Associated with tufa growths Water: freshwater, similar to River Tagus Mediterranean climate with strong continental influence (700 mm av rainfall)

Introduction Taravilla Location and Geological settings

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Taravilla lake

Composite sequence from 2 cores retrieved in 2004 (Kullemberg piston) – Last 1700 yr

• Sediment record is composed of

dm-bedded, massive to faintly laminated, brownish-gray, carbonte sediments with variable amounts of Organic remains and several intercalated sandy layers.

• 5 main sedimentary facies were

identified.

Introduction Taravilla Location and Geological settings

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Taravilla lake

Facies Description Depositional environment 1: Massive, dark grey silty-sand to coarse sand Cm- to dm-thick beds, massive to faintly laminated; abundant plant macrorest. Intense flood deposits reaching the inner areas of the lake. 2: Massive to light grey carbonate silt Cm- to dm-thick layers, massive, variable amount of carbonate and OM Deposition in the middle of the lake during open water circulation periods 3: Massive to faintly laminated, dark grey carbonate silt and mud Cm to dm-thick layers, faintly laminated, relatively higher organic matter and lower carbonate content. Relatively high magnetic susceptibility. Deposition in the middle of the lake during periods of more restricted water circulation. 4: Gastropod and charophyte-rich coarse silt and mud Cm- thick layers with abundant fossils and calcified Chara remains. Organic rich layers associated with flood events 5: Laminated light gray-yellowish silt Cm-thick layers, laminated, dominant carbonate

• composition. Relatively low

magnetic susceptibility. Middle of the lake, low energy dominant oxic bottom conditions

Introduction Taravilla Location and Geological settings

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Taravilla lake

Introduction Taravilla Location and Geological settings

Flood facies (1-4) Flood facies (1-4) dominate dominate during LIA during LIA Low energy-oxic Low energy-oxic facies (5) facies (5) L L I I A A MP MP & RA & RA

HIATUS HIATUS

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Taravilla lake

To underline:

• Facies variability
• Several allochthonous terrigenous layers in

the sediment sequence have been identified deposited during the LIA (wetter and colder period) Main sedimentary processes: Flood layers as consequence of period of intense precipitation (with minor local anthropogenic impacts -deforestation-).

Introduction Taravilla Location and Geological settings

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2) La Parra

La Parra lake

Cañada del Hoyo doline complex (“Torcas” de Cuenca)

Introduction Taravilla Location and Geological settings La Parra

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Geology dominated by Cretaceous Dolostones 1000 m asl. 1 ha area 17 m depth Holomictic Inlets: Mainly groundwater and runoff water. Outlets: Irrigation wells Water: Magnesium - bicarbonated  500 mm av. precipitation

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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La Parra lake

11 sedimentary facies!! (3 main Units) from

• ne core retrieved in 2010 (UWITEC platform)

– Last 1600 yr A) Detritical

Facies A Facies B Facies C Facies F Facies D Facies E Facies G Facies H Facies I Facies J

1) Silts 2) Sands 3) Gravels B) Laminated

Introduction Taravilla Location and Geological settings La Parra

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Unit III: 1st lacustrine deposits → Increase

• f water table
• Laminated

facies changing to coarser silts:

• Fast water

table levels changes;

• Litoral and

shallower environment deposit .

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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Unit II: High Ti content and fine facies:

 Increase of fine siliciclastic inputs  Implies:

• Higher lake

levels

• Higher local

anthrogenic impacts (erosion).

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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Bottom Unit I: Maintained decrease in Ti content + coarser facies:

 Deposited during the

• nset of the

MWP (900 yr cal BP)

1 1

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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Medium Unit I: Fine and Laminated facies

 Higher lake levels.  Laminated facies: as trends to anoxia at lake bottom  Corresponds with the LIA (similar pattern than nearby La Cruz lake)

2 2

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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Top Unit I: Dominancy of fine massive silts

 Laminated facies disappear  Relative drop of lake levels during recent times

3 3

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

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To underline:

• Sedimentray record is mainly composed by

clastic carbonated deposits.

• High facies variability...
• … controlled by changes in detritic inputs.

Main sedimentological aspects:

• Detritic inputs more intense than expected

(possible anthropogenic impacts during MWP)

• Laminated facies restricted to some periods

(wet and cold, favours meromixis, LIA) Large hydrological fluctuations during the last 1600 yr.

La Parra lake

Introduction Taravilla Location and Geological settings La Parra

As consequence of

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3) El Tobar

El Tobar

Cuenca Mountains (Cuenca)

Introduction La Parra Taravilla El Tobar

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Developed on carbonated and evaporitic Triassic formations 1250 m asl. 2 sub-basins:

El Tobar

Inlets: Recent connection with nearby reservoir (“La Tosca”, S shore), saline groundwater (diffuse) and freshwater springs (NE shore). Outlets: 1 surface outlet on the W shore

Holomictic

• Holomictic: shallower (12 m depth)
• Meromictic: funnel-shaped (20 m) → Has a

permanent saline anoxic monimolimnion below 12 m due to groundwater seepage.

Introduction Taravilla Location and Geological settings La Parra El Tobar Meromictic

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El Tobar

• 6 long cores were recovered in both sub-

basins (Kullemberg corer).

• They consist of 3 main facies, giving a

finely-laminated to banded aspect to the sediment: 1- Cm-thick beds of massive dark carbonatic mud with diatoms. 2- Cm-thick beds

• f

coarse grey carbonatic-silty mud with Qz. 3- Cm-thick beds of medium-fine brown carbonatic mud with Qz.

Introduction Taravilla Location and Geological settings La Parra El Tobar

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El Tobar

Introduction Taravilla Location and Geological settings La Parra El Tobar

• Several short cores (gravity corer) were

also recovered in both sub-basins.

• Dating is in progress, but 137Cs suggest

high sedimentation rates (1cm/yr)

• This

yellow clay can serve as chronological marker, as we consider it was deposited immediately after the

• pening of the connection between La

Tosca reservoir and the lake (mid 1960).

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El Tobar

Introduction Taravilla Location and Geological settings La Parra El Tobar

To underline: The work is preliminary yet, but:

• Sedimentray record is mainly composed by

3 facies of carbonatic mud (with 2 crystal sizes) with Qz, finely laminated in the mayor part of the core. Main sedimentological aspects:

• Lake

combines mero and holomixis (carbonates precipitation as laminaes) in a small karstic basin with a strong human impact since 1960.

• La Tosca channel modified the hydrology,
• pening it to new sediment imputs (new fine

detritic layers -yellow clays- and eutrophism).

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El Tejo karstic lake

Introduction Taravilla Location and Geological settings La Parra El Tobar

• Deeper than La Parra lake (28 m depth),

trends to development of meromixis.

• Presents laminated sediments, probably

varves in origin, but bad preserved in time.

• High detritic influence on first 60 cm and

some other detritic episodes intercalated at depth between lamination.

New Horizonts

Belongs to the Doline Cuenca complex (“Torcas”), as La Parra lake. Geology dominated by Cretaceous Dolostones

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• 1. Why each sedimentary

sequence is so different?

Introduction Taravilla Location and Geological settings La Parra El Tobar

• Karstic lake origin on this area is similar
• Climatic context is similar

So? a) A high unexpected detrital influence has affected all lakes. b) Depth of lakes: Laminated facies only in deeper lakes (El Tobar, El Tejo, La Cruz). c) Calcite varve preservation is limited in time (El Tobar, El Tejo, La Cruz). d) Differential local human impact (grazing, fires, irrigation).

New Horizonts General Conclusions

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• 2. Depositional Evolution

Introduction Taravilla Location and Geological settings La Parra El Tobar

a) Higher run off and sediment delivery during the LIA (Taravilla, La Parra, also in La Cruz) b) Lower lake levels during the MWP (La Parra, not so clear on Taravilla) c) The “Torcas” (Cuenca doline complex) were dry prior to 1600 yr

New Horizonts General Conclusions

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That's All!

Introduction Taravilla Location and Geological settings La Parra El Tobar

Thanks for your attention

New Horizonts General Conclusions

The study is funded by GLOBALKARST and GRACCIE CONSOLIDER-INGENIO projects (Spanish Government) Core Platform at El Tejo lake. Sometimes, logistics are not so easy!

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References

Introduction Taravilla Location and Geological settings La Parra El Tobar

• 1. Barreiro-Lostres et al, “Facies sedimentarias de la laguna kárstica de La Parra

(Cuenca) durante los últimos 1600 años”. Geogaceta, in press.

• 2. Moreno et al., “Flood response to rainfall variability during the last 2000 years

inferred from the Taravilla Lake record (Central Iberian Range, Spain),” Journal of Paleolimnology 40, no. 3 (April 2008): 943-961.

• 3. García-Gil et al., “Vertical distribution of photosynthetic sulphur bacteria linked to

saline gradients in Lake El Tobar (Cuenca,Spain),” Aquatic Microbial Ecology 20 (1999): 299-303.

• 4. Valero Garces et al., “The Taravilla lake and tufa deposits (Central Iberian Range,

Spain) as palaeohydrological and palaeoclimatic indicators,” Palaeogeography, Palaeoclimatology, Palaeoecology 259, no. 2-3 (2008): 136–156.

• 5. Valero Garcés et al., “Una visión paleolimnológica de tres lagos kársticos (Zoñar,

Estanya y Taravilla): evolución sedimentaria y paleohidrológica, clima e impacto humano e implicaciones para la gestión y conservación,” Boletín Geológico y Minero 120, no. 3 (2009): 479-496.

• 6. Romero-Viana et al., “Climate Signal in Varve Thickness: Lake La Cruz (spain), a

Case Study,” Journal of Paleolimnology 40, no. 2 (February 2008): 703-714.

• 7. Romero-Viana et al., “Meromixis origin and recent trophic evolution in the Spanish

mountain lake La Cruz,” AQUATIC SCIENCES 60, no. 4 (1998): 279-299.

• 8. Romero-Viana et al., “Climate Signal in Varve Thickness: Lake La Cruz (spain), a

Case Study,” Journal of Paleolimnology 40, no. 2 (February 2008): 703-714.

New Horizonts General Conclusions