北京延庆地质公园
北京延庆地质公园位于华北平原地区与内蒙古高原之间的过渡区。这是一个以著名的燕山命名的造山运动，它像一颗璀璨的明珠，镶嵌在雄伟的燕山山脉南坡。整个地质公园占地381.48平方公里，包括四个相连接的景区，西边是龙庆峡景区、古崖居景区，东边是千家店景区，南侧是八达岭景区。延庆地质公园以寒武纪海相碳酸盐岩为物质基础，以中生代燕山运动为代表，是一个综合性的地质公园，地质遗迹以结合构造、沉积、古生物化石等为主，与华北地区的岩浆式喀斯特地貌结合在一起。
1.5亿年前的北京延庆地质公园
在全球范围内，侏罗纪是地球上生物大发展时期之一，属于“恐龙时代”。与大量的植食性恐龙相匹配的，是这一时期的植物种类繁多，生长茂盛，森林密布。那个时期延庆地区气候温暖湿润，雨量充沛，原始森林郁郁葱葱，森林下方生长着各种蕨类植物，在湖泊、河流、盆地附近密布着苏铁、银杏及松柏，形成了一个完美的生态系统。根据在同时期地层中保留下来的大量恐龙足迹化石判断，本地区在上侏罗纪晚期生态环境非常好，适合各类动植物繁衍生息，是一个生命的乐园。
硅化木景区
硅化木景区位于延庆地质公园千家店景区的东北部，面积20.5平方公里，一共有57株硅化木裸露在地表，其中多数属于松柏类的宽孔异木和延庆苏格兰木，是华北地区最大的原地埋藏硅化木化石群，保存在约1.5亿年前的上侏罗纪地层中。千家店景区的硅化木化石表面一般是灰色、灰白色或浅黄褐色，大多数垂直于地面，少部分是倾斜或平卧状。
什么是硅化木
硅化木是木化石的一种。远古时期的树木因为各种原因被深埋在地下，树干周围的地下水中所含有的二氧化硅、硫化铁、碳酸钙等物质在合适的条件下逐渐替换掉了树木木质成分，但保留了树木的形态，再经过石化作用，就形成了木化石。如果替换物质的主要成分是二氧化硅（玻璃的主要成分），所形成的木化石就被称为硅化木。而这种替换作用如果是以等分子的速度进行，那么所形成的硅化木化石不仅可以保留树木的外部形态，而且还可以精确地保存树木的内部构造，甚至连年轮和细胞都清晰可见。硅化木化石可以为科学家研究古植物、地质环境和构造、气候变化提供重要线索。
延庆硅化木化石的形成
距今1.5亿年前的上侏罗纪晚期，延庆地区是一片茂密的原始森林。之后由于河流发育，树木在原地被周期性的洪水所携带的审计物质迅速掩埋压实，地下水中所含有的二氧化硅分子开始慢慢地替换树木中原有的木质成分，但保留下来树木的形态和内部结构，再经过石化作用后在地下深处形成了硅化木化石，因此景区内的大部分硅化木化石都保持着直立的原始生长状态。在之后的燕山构造运动中，本地区以垂直抬升为主，原本埋藏在地下深处的硅化木化石随着上覆层地层被逐渐剥蚀殆尽，最终暴露出地表，成为现在能看到的硅化木化石。
你的任务：
为了登记这个地理宝藏，你必须进入硅化木景区参观，门票30元人民币，学生减半。你可以先log，然后将以下三个问题的答案发到我的邮箱里，以确保您的log是真实有效的。如果在两个星期内没有收到你的邮件，我将会删除您的log。
1.硅化木的形成需要很多条件，其中它对地下水有什么样的PH要求？本地区是怎么到达这个PH值的？
2.在Q0048点，这株硅化木周边的地层和泥土有什么特点？
3.在Q0040点，你能准确地测量出最高的硅化木的高度吗？
请不要将问题答案写在您的log里，但是你可以上传和硅化木在一起的照片。
这里有一个停车场，注意来往车辆！
Yanqing Global Geopark of Beijing
Yanqing Global Geopark of Beijing is located at a transitional zone between North China plain and Inner Mongolian plateau. It is one of the famous naming places of Yanshanian movement, liking a shining pearl embedded on the south slope of magnificent Yanshan Mountains. Covering an area of 381.48km²。This Geopark comprises four connecting scenic areas, the west is Longqingxia Scenic Area, Guyaju Scenic Area ， the east is Qianjiadian Scenic Area，and the south is Badaling Scenic Area . Yanqing Geopark, taking the Precambrian marine carbonates as its material basis, dominated by the Mesozoic Yanshanian movementrelated geoheritage, is a comprehensive geopark by integrating the tectonic, sedimentary, paleontologic, magmatic geoheritage and North-China-type karst landforms into a whole.
Yanqing Global Geopark in 150 million years ago
Globally，the Jurassic period is one of the extremely developed periods of diverse organisms in the Earth’s history，it’s “dinosaur age”。Matched up with the large amount of plant－eating dinosaur，the plants and forest were flourishing everywhere。In that time the climate in this area was warm，humid and abundant rainfall。The forest was dense with various ferns，while the cycas，gingko tree and conifers were very prosperous distributed in the basins and basin edges。In addition，the rivers and lakes were quite developed and widely distributed，forming a perfect ecosystem。Judged from the numerous dinosaur footprints of at least three types of dinosaurs preserved in the strata of same age，there was a paradise for wildlife during the lake Jurassic。
About the silicified wood－protected area
The silicified wood－protected area is located in northeast of Qianjiadian Scenic Area of Yanqing Global Geopark，covering an area of 20.5km²。There are 57 silicified wood－protected exposed in here and it is the largest in situ preserved silicified wood group in north China。In there mostly belonging to Xenoxylon latiporosum Gothan and Scotoxylon yanqingense conifers，occurred in Upper Jurassic about 150 million years ago。Most of silicified wood are grey，grayish white or lightly yellowish brown，vertical to the bedding surface，only a few inclined or horizontal to bedding surface。
What is a silicified wood
silicified wood is one of petrified woods。Due to different causes，trees or other plants would be deeply buried，surrounded by the mineral charged underground water，the major minerals include SiO₂，FeS ，CaCO₃ and others。These mineral could replace the fibrous component of trees or plants and the petrified woods would be finally formed through the petrification。If the tree or plant was replaced by SiO₂，it would be transformed into the silicified wood。However，if the replacement would carry out at an equal rate on the molecular level，the silicified wood could preserve its trunk shape，annual rings and cell structure。In fact，the silicified wood can provide the detailed clues on paleobotanic，paleoenvironmental and climatic information to scientists。
The silicified wood formed in Yanqing Global Geopark
During the Upper Jurassic about 150 million years ago，this area was covered by lush primeval forest。Because of the fluvial development，the trees were rapidly in situ buried by the sediment carried by the periodic large scale flooding and these trees were surrounded by the underground SiO₂ water，the SiO₂ started to replace their fibrous components，so the silicified wood with trunk shape and internal structures have final been created through the petrification in the deep crust。So we can see silicified wood in this Geopark are still occurred in their life position。After then，under the effect of yanshan tectonic movement，this area was dominated by the vertical uplift，the deeply buried silicified woods were finally exposed out of the surface after the overlying strata were totally eroded away。
Your task：
In order to log this Earth Cache you must visit the silicified wood area，there is an entrance fee of around $30 CNY and half for student。You can immediately log and then send the answers of the following three questions to my email or message to make sure your log is valid. If I did not receive the mail or message within two weeks, I will delete your log。
1.The formation of the silicified wood needs a lot of conditions, in which it has what kind of PH requirements? How does this area arrive at this pH value?
2.In Q0048，what are the characteristics of the surrounding strata and soil of this area‘s silicified wood?
3.In Q0040，can you accurately determine height of the highest silicified wood?
Please do not share your answers in your log but you can put on a photo with silicified wood.
A park in there and be careful traffic!