The delta rocks in which these fossils are found are commonly red due to oxidized iron minerals, indicating that the deltas formed in a climate that had alternate wet and dry periods.

　　词汇解析：

　　delta: an area of low land where a river spreads into many smaller rivers near the sea

　　oxidized: to combine with oxygen, or make something combine with oxygen, especially in a way that causes rust.

　　mineral: a substance that is formed naturally in the earth, such as coal, salt, or stone. minerals can be dug out of the ground and used

　　alternate: two alternate things are placed one after the other in a regular pattern

　　结构分析：

　　复合句。带有in which 引导的定语从句和that 引导的宾语从句，随后又有第二个that引导的定语从句。

　　句子分析：

　　The delta rocks in which these fossils are found are commonly red due to oxidized iron minerals,主句中，the delta rocks 是主语，后接in which 引导的定语从句，which指代的是delta rocks, 在从句中，these fossils 是主语， are found 是谓语。接下来回到主句，are commonly red 是系表结构作谓语部分，due to oxidized iron minerals, 原因状语。本部分意思是：化石常在这些三角洲的岩石中发现，而这些岩石由于氧化铁矿物，通常都是红色的。

　　indicating 作为定语。 that the deltas formed in a climate that had alternate wet and dry periods. 第一个that引导的宾语从句中，the deltas 是主语，formed 谓语，in a climate 时间状语。第二个that引导的定语从句中，that指代climate， 作为主语， had 谓语，alternate wet and dry periods， 宾语。本部分意思是：表明三角洲形成于干湿交替时期。

　　参考翻译：

　　化石常在这些三角洲的岩石中发现，而这些岩石由于氧化铁矿物，通常都是红色的，表明三角洲形成于干湿交替时期。

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