The Oxfordian stable isotope record (δ18O, δ13C) of belemnites, brachiopods, and oysters from the Kachchh Basin (western India) and its potential for palaeoecologic, palaeoclimatic, and palaeogeographic reconstructions
The Oxfordian stable isotope record (δ18O, δ13C) of belemnites, brachiopods, and oysters from the Kachchh Basin (western India) and its potential for palaeoecologic, palaeoclimatic, and palaeogeographic reconstructions
复制标题
DOI：
10.1016/j.palaeo.2012.05.018
复制
发表时间：
2012-08-01
影响因子：
3
通讯作者：
Pandey, Dhirendra K.
中科院分区：
文献类型：
--
作者：
Alberti, Matthias;Fuersich, Franz T.;Pandey, Dhirendra K.
这项研究结合了稳定同位素（三角洲C-13，三角洲O-18）分析的结果，从中到上侏罗纪（上卡洛夫纪到Kimmeridgian）的印度西部的Kachchh盆地的187 belemnites，腕足动物和牡蛎。一般来说，与底栖动物相比，箭石显示出较低的三角洲C-13和较高的三角洲O-18比值。有人提出，这种差异是由两个群体的不同生活栖息地造成的，箭石的大部分生活在Kachchh盆地以外的深水中，偶尔进入浅水区（例如，在季节性迁移到产卵场）。一种像许多现代乌贼物种一样快速游动的游泳捕食者的生活模式似乎是合理的。该研究强调，稳定同位素分析的结果应单独评估每个化石组。除了成岩蚀变、风化、盐度变化和海平面波动的影响外，还必须考虑所分析的化石分类群的生态学。从三角洲O-18比率计算出的温度表明，中晚侏罗世过渡期周围的温度相对较暖，没有证据表明该边界存在冰期。一个明显的温度下降，观察到在中牛津达到最低限度，在早期晚牛津。人们很容易将这一事件与冈瓦纳大陆的分裂联系起来，导致特提斯西北部的上升流更强，或者是跨冈瓦纳海道的开放导致极地水的涌入。然而，如果没有进一步的数据，最好是来自马达加斯加湾南部地区的数据，就无法核实这种联系（例如，马达加斯加）和年轻的地平线（Kimmeridgian-Tithonian）。(C)2012爱思唯尔有限公司版权所有。
The study combines the results of stable isotope (delta C-13, delta O-18) analyses of 187 belemnites, brachiopods, and oysters from the Middle to Upper Jurassic (Upper Callovian to Kimmeridgian) of the Kachchh Basin in western India. Generally, belemnites show lower delta C-13 and higher delta O-18 ratios than the benthic fauna. It is proposed that this discrepancy is caused by different life habitats of both groups with belemnites spending major parts of their life in deeper water outside the Kachchh Basin and entering shallow areas only occasionally (e.g., during seasonal migrations to spawning grounds). A mode of life as fast-swimming, nektonic predators similar to many modern squid species seems plausible. The study emphasises that results of stable isotope analyses should be evaluated separately for each fossil group. In addition to the influence of diagenetic alteration, weathering, salinity changes, and sea-level fluctuations, the ecology of the analysed fossil taxa has to be considered. Temperatures calculated from delta O-18 ratios point to relatively warm conditions around the Middle to Late Jurassic transition with no evidence for a glacial phase which had been proposed for this boundary. A distinct fall in temperatures is observed during the Middle Oxfordian reaching a minimum in the early Late Oxfordian. It is tempting to connect this event with the break-up of Gondwana causing stronger upwelling in the northwestern Tethys or alternatively the influx of polar water by the opening of the Transgondwanan Seaway. However, such connections cannot be verified without further data, preferably from localities in the southern Malagasy Gulf (e.g., Madagascar) and from younger horizons (Kimmeridgian-Tithonian). (C) 2012 Elsevier B.V. All rights reserved.