Table 3- 1 Division and correlation of Cretaceous strata in northwest Zhejiang
(1) Early Cretaceous strata-Jiande Group K 1J (Laocun Group K 1l, Huangjian Group K 1h, Shou Chang Group K 1s).
A member of Jiande Group originated from the "Jiande School" founded by Liu and Zhao Yaceng (1927), and its primitive age was the Late Cretaceous. After the field meeting on Stratigraphy in West Zhejiang 1959, researchers gradually divided the Jiande Series into Jiande Series (J22? —J3), purple sandstone shale (K 1) and Zhejiang rhyolite (K 1) or renamed Wuyi group (Jiande group and Zhejiang rhyolite group). 1965, the stratigraphic system still in use was gradually established, and Jiande Group was divided into Laocun Formation, Huangjian Formation, Shouchang Formation (lower, middle and upper members) and Hengshan Formation from bottom to top. These four groups are the most basic lithostratigraphic units, which can be independently used for geological mapping, description and clarification of regional geological characteristics. Therefore, it seems that we can give up a Jiande Group, but considering that Jiande Group has been widely used and has a high reputation since its establishment; At the same time, the first three groups of fossils of Jiande Group belong to the same biota, which is obviously different from Yongkang biota. Keeping the name of this group is beneficial to regional stratigraphic correlation and biota analysis and comparison.
The Stratigraphic Guide of China pointed out that "Stratigraphic groups can be composed of two or more adjacent or related stratigraphic groups with common lithologic (or lithologic combination) characteristics". Accordingly, Laocun Formation to Shouchang Formation belong to the onshore volcanic eruption sedimentary assemblage, which constitutes a complete volcanic activity cycle and has similar paleontological fossils, so it is appropriate to classify them into one group. Hengshan Formation is mainly composed of purplish red clastic sedimentary rocks with huge thickness (up to 1 400 m). Ostracoda and Ostracoda fossils found in the bottom or lower part are different from similar fossils in the underlying strata. A sporopollen assemblage different from Shouchang Formation was found in the middle and upper strata. In recent years, dinosaur eggs have been found in Muwu, Duntou, Lanxi. Near Shangmukeng and Yujie at the eastern end of Duntou Basin, there is basalt porphyrite at the bottom of Hengshan Formation, with a porosity of 20 ~100 m. Judging from the sequence, fossils and regional stratigraphic correlation, Hengshan Formation seems to be roughly equivalent to Guantou Formation and Chaochuan Formation in southeastern Zhejiang. Therefore, as far as lithology and fossils are concerned, it will be dominated by red beds, with single lithology and huge thickness. It seems inappropriate that the Hengshan Formation in the dinosaur egg belongs to Jiande Group. This book suggests that Jiande Group be defined as a set of onshore volcanic eruption and sedimentary assemblage, including Laocun Formation, Huangjian Formation and Shouchang Formation. Its unconformity covers the Middle Jurassic or older strata, and its conformity or overlapping unconformity covers Hengshan Formation, resulting in a unique multi-class fossil assemblage, which belongs to the early Early Cretaceous. This definition is not only conducive to the comparison of large-scale regional stratigraphy and paleontology, but also in harmony with geological facts.
1. Laocun Formation (K 1l)
The Laocun Formation was founded by Zhejiang Regional Geological Survey Brigade (1965) and named after Laocun, Datong, jiande city. The original time was the late Jurassic, which has been widely used since its establishment.
Laocun Formation in the northwest of Zhejiang Province is developed in a basin with intermittent distribution in the northeast direction, mainly exposed in the old village of Jiande-Meicheng, the south and north sides of Pujiang Basin, Yang Jiawu, Lin 'an and Anji in Tonglu, and sporadic exposed in Xukou, Deng Xin and Chun 'an in Fuyang.
The lithology of this formation is mainly purplish red sand and mudstone mixed with acidic pyroclastic rocks of river and lake facies, with ordinary conglomerate at the bottom, calcium and calcium nodules in some areas, and a small amount of marl lenses. The thickness varies greatly, generally 526 ~ 1 3 18m, and the maximum thickness can reach more than 2,000 meters. Generally, it is not integrated and covered on the middle Jurassic Yushanjian Formation or older strata. The typical lithology of Laocun Formation is red beds containing volcanic rocks, but in the east of Jiande Meicheng-Shoufeng Mountains, the volcanic rocks increase sharply, which almost constitutes the main body of the formation, while the purple clastic sedimentary rocks only appear in the form of interlayer. According to the lithology and lithofacies characteristics of Laocun Formation, volcanic rocks gradually increase from west to east and from south to north in space, while purple clastic rocks decrease and become thinner. From the time point of view, volcanic rocks gradually developed from bottom to top, and sedimentary rocks decreased correspondingly, reflecting the intermittent weak eruption of volcanic activity from scratch and from weak to strong, showing the initial stage of large-scale volcanic eruption in Cretaceous.
The biological fossils of Laocun Formation mainly include plants, gastropods, bivalves, ostracods, insects, ostracods and fish.
According to the collection and summary of Cretaceous isotopic age values in Zhejiang by Yu et al. (1999), it is pointed out that the age value of Laocun Formation is between 135 ~ 127 Ma. In addition, the isotopic age of the Laocun Formation in Tonglu is 124 Ma by Ar-Ar method.
2. Huangjian Formation (K 1h)
Huangjian Formation was first proposed by Gu Zhiwei and Zou Zuoxin in 1962, and was first reported by Zou Zuoxin (1964). The named road section is located in Huangjianshan, 4 kilometers south of Shouchang Town, jiande city, and has been in use ever since its completion. The primitive age is the late Jurassic.
The distribution range of Huangjian Formation is basically the same as that of Laocun Formation, in which Jiande Niaolong Mountain-Fuyang Xingmeijian and Tianmu Mountain are the most developed. The lithology of this formation is a set of acidic volcanic lava or acidic pyroclastic rocks, mixed with neutral lava and occasionally mixed with a small amount of tuffaceous sandstone, which is the product of Cretaceous volcanic activity in this area. The thickness of Jianzu section changes greatly, and the thickness of Zaoyuan section from the north 175 m is only 1 55 1 m, and the general trend is to thicken from southwest to northeast. For example, the thickness of Wangjiashan in Shaoxing is 65438+.
The bottom of the formation is covered with neutral or acidic volcanic lava and pyroclastic rocks in an integrated relationship on the sedimentary rocks of Laocun Formation, and the top is covered with acidic pyroclastic rocks in an integrated relationship under the sedimentary rocks of Shouchang Formation, so the top-bottom boundary is clear and easy to identify in the field.
The sedimentary interbeds of Huangjian Formation are few and thin, rich in tuff, with few fossils and poor preservation. Only a few plants and sporopollen fossils were found.
The isotopic age values of this group (Yudeng, 1999) are all between 130 ~ 140 Ma, which is similar to the isotopic age of the underlying Laocun Formation.
3. Shouchang Formation (K 1s)
Gu Zhiwei (1959) founded a member of Shouchang Formation in Shou Chang, jiande city. From 1962 to 1964, Gu Zhiwei, Zou Zuoxin and others merged the middle and upper parts of the Shouchang Formation, formerly known as the Cailanggang Formation, into the Shouchang Formation, thus expanding the Shouchang Formation. The former Zhejiang Bureau of Geology and Mineral Resources (1996) revised the top boundary of Shouchang Formation, and classified the acidic tuff at the bottom of the original Hengshan Formation as Shouchang Formation, and the top boundary of this tuff was bounded by the purplish red medium-layered gravelly siltstone at the bottom of the overlying Hengshan Formation. This book follows this division.
Shouchang Formation is mainly distributed in Shou Chang Basin in Shou Chang-Linpu area, the edge of Duntou Basin in Lanxi, Nverkeng, Yangshan, Hangkouping and Zhuji in Pujiang Basin. Shouchang Formation in Chun 'an-Lin 'an area is undeveloped and sporadic. The lithology of this formation is a set of gray-green, yellow-green, purple-red sandstone and shale, and there is an acid volcanic rock with unstable thickness in the middle and top. The Shouchang Formation in Shou Chang Basin is dominated by lacustrine sediments, with a small proportion of volcanic rocks. The volcanic rocks of this group have increased obviously in Duntou, Lanxi, Pujiang and Zhuji in east longitude, with the thickness of volcanic rocks in Shou Chang basin only 65 m, Pujiang basin nearly 467 m and Zhuji basin 736 m.
The thickness of this formation varies from tens of meters to1200m, and it is in integral or overlapping unconformity contact with the underlying Huangjian Formation and the overlying Hengshan Formation. The lithologic boundary is clear and easy to identify in the field. It is worth mentioning that Shouchang Formation in Pingshan Basin of Lin 'an is a fluvial volcanic sedimentary rock, which contains a lot of volcanic glass. Under the constant action of sodium-alkaline water, a large-scale calcium-sodium bentonite deposit has been formed.
Shouchang Formation is famous for its rich fossils, including plants, Charophytes, Sporopollen, Gastropoda, Bivalves, Ostracoda, Insects, Ostracoda and Fish.
Isotopic age data of Shouchang Formation are between124 ~124 ~117ma (et al., 1999).
(2) Late Early Cretaceous to Early Late Cretaceous-Hengshan Formation (K 1-2h)
See Figure 3-2 for the stratum distribution from late Early Cretaceous to late Cretaceous in Zhejiang Province.
There is only one stratigraphic unit-Hengshan Formation in the upper part of Lower Cretaceous in this area. Zhejiang Regional Geological Survey Brigade (1965) discovered a section of Hengshan Formation in Shouchang Town, jiande city, with the original age of Early Cretaceous. Jian Formation profile has not peaked yet, revealing thickness "2 14m. Hengshan Formation in Duntou Basin of Lanxi is well developed, with a thickness of about1400 m..
Hengshan Formation is mainly developed in Jiande Shou Chang Basin and Lanxi Duntou Basin, and also exposed in Chun 'an-Lin 'an area. The lithology of Hengshan Formation in Shou Chang Basin is mainly purplish red argillaceous siltstone and silty mudstone mixed with sandstone, and the thickness is more than 2 14 m, and the lithology is obviously thicker at the edge of the basin, with purplish red conglomerate, gravel and fine sandstone interbedded with thin tuff, and the thickness is thinner. Hengshan Formation in Duntou Basin is well developed, with a clear top-bottom boundary and a thickness of 1400 m. The upper part is fluvial purplish red calcareous siltstone, fine sandstone, conglomerate and glutenite. The middle part is lakeside grayish purple calcareous siltstone mixed with calcareous medium-fine grained sandstone and tuffaceous coarse sandstone; The lower part is shallow lake purple thick calcareous and argillaceous siltstone mixed with purple gray tuffaceous sandstone. Near Shangmukeng and Yujie at the eastern end of the basin, the bottom of this formation is sandwiched with 20 ~ 100 m porous basalt.
The thickness of this formation is 82 ~1400 m, which is in a continuous transitional relationship with the acidic pyroclastic rocks at the top of the underlying Shouchang formation. However, at the edge of the basin, there is a layer of dark gray purple conglomerate at the bottom of Hengshan Formation, which seems to be an overlapping unconformity contact relationship. This stratum can also overlap with Huangjian Formation, Laocun Formation or older strata. Relationship with overlying strata: In Duntou Basin, Lanxi, it is in integral contact with conglomerate in the lower member of Zhongdai Formation.
The fossils of Hengshan Formation are mostly collected from the bottom or lower part of Hengshan Formation in Shou Chang Basin, including plants, gastropods, bivalves and ostracods. Only sporopollen fossils were found in Duntou Basin. In 2003, dinosaur eggs were found in the upper or near the top of the stratum. This new discovery is of great significance and provides reliable fossil evidence for the age attribution of Hengshan Formation.
Figure 3-2 Schematic Diagram of Strata Distribution from Late Early Cretaceous to Late Cretaceous in Zhejiang Province (redrawn according to Zhejiang Bureau of Geology and Mineral Resources 1996)
(3) Qujiang Group (K2Q) in the middle and late Late Cretaceous (K2z of Zhongdai Formation, K2j of Jinhua Formation and K2q of Quxian Formation).
A member of Qujiang Group originated from "Qujiang Red Sandstone" created by Liu and Zhao Yaceng (1927), and its primitive age is Neogene. Since 1960, Zhejiang Regional Geological Survey Brigade and Zhejiang Petroleum Geological Brigade have done a lot of geological work in Jinqu Basin (Jinhua-Quzhou) for many times, and have put forward various opinions on the subdivision of Qujiang Group, which has gradually evolved from five lithologic sections to three rock groups. So far, there are two main division schemes: Zhejiang Petroleum Exploration Office (1993) divides Qujiang Group into Fangyan Formation, Lanxi Formation and Quxian Formation, and also divides Tongxiang Group covered by Quaternary in Hangzhou (Zhou) into Qujiang Group; Gui (1989) and Zhejiang Bureau of Geology and Mineral Resources (1996) divided Qujiang Group into three groups: Zhongdai Formation, Jinhua Formation and Quxian Formation. This book uses the latter to divide views.
Definition of this book: Qujiang Group refers to the clastic sedimentary strata in the northwest of Zhejiang Province, which are integrated on Hengshan Formation or overlapped on Qianhengshan Formation, and consist of piedmont accumulation facies-fluvial facies-lacustrine facies-fluvial facies, including Zhongdai Formation, Jinhua Formation and Quxian Formation, with no roof on it. Now it is described by composition as follows.
1. Central Belt Group (K2z)
Gui (198 1), a middle belt formation, is produced in the middle belt area of Jinhua City, Zhejiang Province, and its primitive age is Late Cretaceous.
The Zhongdai Formation is mainly developed in Jinqu basin, extending eastward to Yiwu, Dongyang and Pujiang basins, with sporadic outcrops in Si 'an-Jiaxing area. The lithology of this formation can be divided into two sections: the lower section is piedmont facies accumulation, mainly composed of purple massive conglomerate and glutenite, with gravel sandstone and siltstone, and occasionally volcanic rocks; The upper member is fluvial deposit, the lower part is sandwiched by purple-gray conglomerate and brick-red gravelly siltstone, the upper part is medium-grained sandstone and siltstone, occasionally medium-coarse gravelly sandstone, and the top part is purple-red calcareous and silty mudstone mixed with calcareous siltstone.
The thickness of this formation is 247- 1500m. Lanxi Duntou Basin is in contact with the underlying Hengshan Formation as a whole, Pujiang Basin is in superimposed unconformity contact with Shouchang Formation, and most of them are in superimposed unconformity contact with different horizons of Moshishan Formation.
This group of fossils is rare, including plants, Charophytes, Ostracoda and Gyllenhax.
K-Ar method was used to determine the isotopic age of olivine basalt collected from the upper weitou of Longyou, and the age value was 105 Ma (Zhang Limin, 1997).
2. Jinhua Formation (K2j)
Jinhua Formation was founded by Zou Heying (1964) and introduced by Gu Zhiwei (1980). It is named after Jinhua City, Zhejiang Province. The original geological age is Late Cretaceous, and the stratigraphic type is in Gaoxiantang section of Longyou, Zhejiang Province (Zhejiang Regional Geological Survey Brigade 1993).
Jinhua Formation is mainly developed in Jinqu Basin. The lithology of this formation is light grayish purple thin silty mudstone, argillaceous siltstone, siltstone, fine sandstone and grayish green, light gray and grayish black mudstone, which belongs to lake sediments. The lithology at both ends of Jinqu Basin becomes coarse, with dark mudstone and silty mudstone in the north, and marl, gypsum-bearing mudstone, dolomite and dolomite mudstone occasionally seen. Its thickness is 469. The thickness of Shendian in Lanxi is 27m, while the thickness of Longyou area in the south of the basin becomes thinner, about 263m, and the maximum thickness is 2 125m. It has a continuous transition with the underlying middle belt formation, and the lithologic boundary is not obvious, which is a gradual transition from river facies to lake environment.
Jinhua Formation is rich in fossils, including plants, Charophytes, Gastropoda, Bivalves, Insects, Ostracoda and so on.
3. Quxian Formation (K2q)
Li Longtong and Zhen Jinsheng of Quxian Formation (198 1) were founded in Quxian County, Zhejiang Province. The original definition means that Zhejiang Petroleum Geological Brigade (1979) divided the fifth member of Qujiang Group in Jinqu Basin, followed by Qiu (198 1). The stratum type of Quxian Formation is Caolong-Liucun section in Xiaonanhai, Longyou, Zhejiang (Zhejiang Regional Geological Survey Brigade, 1993).
Quxian Formation is fluvial deposit, mainly exposed in Jinqu Basin. According to drilling data, there seems to be Quxian Formation in Hangjiahu area. Its lithology is mainly composed of brown and reddish brown, medium-thick layer, thick layer to massive sandstone, siltstone, gravel sandstone, glutenite and conglomerate. The eastern and western parts of Jinqu Basin are relatively coarse in lithology, mainly composed of brownish red and light brownish red thick layers to massive siltstone and fine sandstone, with grayish white thick layered sandstone, gravel sandstone and glutenite lens. Common irregular cross bedding and large plate cross bedding.
The thickness of Quxian Formation is generally above 1 000 m, the thickness of Longyou Hengshan area is above 1 562 m, and the thickness of Lanxi Shendian area is above 236 1 m ... It has an overall gradual relationship with the underlying Jinhua Formation, and the surface profile has not yet peaked. This group of fossils is rich in ostracods and charophytes, and dinosaur teeth, broken bones and dinosaur eggs have also been found.
(4) Late Cretaceous strata-Tongxiang Formation (K2t)
The first member of Tongxiang Formation was founded by Zhejiang Petroleum Exploration Office (1988), which is a stratigraphic unit based on drilling data. It was named in the drilling profile (Hang31well) of Baimamiao Shuangqiao, Tongxiang County, Zhejiang Province, and its primitive age was late Cretaceous.
Tongxiang Formation is only distributed in Tongxiang sag, and there is no outcrop on the surface. This layer has been discovered successively in Well Hang31,Well Hang33, Well Hang34 and Well Hang38, and its lithology can be summarized into three parts: the lower part is grayish purple, light brown mudstone, siltstone, fine sandstone, gravelly sandstone, glutenite and fine conglomerate, and the general trend is thick at the bottom and thin at the top, with a thickness of 287. 4. The middle part is interbedded with light brown and grayish purple argillaceous siltstone, fine sandstone, gravelly sandstone, glutenite, mudstone or silty mudstone, mainly coarse clastic rock, with a thickness of178 ~ 235.5m; The upper part is dominated by light brown and pink argillaceous siltstone, siltstone and fine sandstone, with grayish purple mudstone and silty mudstone, and the bottom is conglomerate or glutenite. In a word, it is mainly composed of fine clastic rocks, with a thickness of about100 m. The contact relationship between Xiaxia Formation and Quxian Formation is not completely clear, so it is presumed to be false conformity contact (? ) 。
Tongxiang Formation is rich in microfossils such as ostracods, charophytes and sporopollen.