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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Sedimentological and carbonate data evidence for lake level variations during the past 3700 years from a southern Indian lake
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Sedimentological and carbonate data evidence for lake level variations during the past 3700 years from a southern Indian lake

机译：沉积和碳酸盐数据证明了过去3700年间印度南部湖泊的湖面变化

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Over the years, several proxies have been developed to reconstruct rainfall variability. However, most rely on indirect approaches to provide qualitative paleorainfall estimate. In an attempt to obtain a more direct measure of paleorainfall, Shankar et al. (2006) explored the rock magnetic properties of lake sediments from Thimmannanayakanakere (TK) in tropical southern India. They proposed the use of magnetic susceptibility as a proxy for rainfall in the tropics. Warrier and Shankar (2009) provided geochemical evidence in support of this proposition. Here, sedimentological and carbonate data is provided as further evidence to bolster Shankar et al.'s (2006) proposition. High (low) values of χlf indicate high (low) rainfall in the region of TK during the past 3700 years. Particle size variations suggest that the sand % was high (low) during arid (humid) periods, when the TK lake level was low (high). Hence, a negative correlation is documented between sand % and χlf along with other rock magnetic parameters. HIRM (an indicator of magnetically "hard" minerals like haematite and goethite) is suggestive of a relatively arid climate; the high (low) HIRM values in TK sediments indicate arid (humid) conditions. For this reason, sand % is positively correlated with HIRM. By contrast, fine silt and clay contents are low during low-rainfall periods and vice versa. Thus, both fine silt and clay contents are positively correlated with χlf and other rock magnetic parameters, but negatively correlated with HIRM. Magnetic minerals reside principally in the fine silt fraction of TK sediments as evidenced from the positive correlation between fine silt content and magnetic susceptibility. Carbonate content too is indicative of paleorainfall conditions, being high (low) during arid (humid) climatic conditions. Based on the χlf, sand % and carbonate % data, we have inferred lake level variations in TK during the past 3700 years.
机译：多年来，已经开发了几种代理来重建降雨的可变性。然而，大多数依靠间接方法来提供定性的古降雨估计。为了获得一个更直接的古雨量度，Shankar等人。 （2006年）探索了印度南部热带地区Thimmannanayakanakere（TK）的湖泊沉积物的岩石磁性。他们提议使用磁化率来替代热带地区的降雨。 Warrier和Shankar（2009）提供了地球化学证据来支持这一观点。这里，沉积学和碳酸盐数据提供了进一步的证据，以支持Shankar等人（2006年）的主张。 χlf的高（低）值表示过去3700年内TK地区的高（低）降雨量。粒度变化表明，在TK（低）湖水位低（高）的干旱（潮湿）时期，沙含量高（低）。因此，砂％和χlf以及其他岩石磁参数之间存在负相关关系。 HIRM（指示赤铁矿和针铁矿等磁性“硬”矿物质的指标）表明气候相对干旱。 TK沉积物中的高（低）HIRM值表明干旱（潮湿）条件。因此，砂％与HIRM正相关。相反，在低雨期，细粉质和粘土含量较低，反之亦然。因此，细粉质和粘土含量均与χlf和其他岩石磁参数正相关，而与HIRM负相关。磁性矿物主要存在于TK沉积物的细粉质中，这从细粉质含量和磁化率之间的正相关关系可以看出。碳酸盐含量也表示古降雨情况，在干旱（潮湿）气候条件下较高（较低）。根据χlf，沙％和碳酸盐％的数据，我们推断出过去3700年中TK的湖泊水位变化。

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