High-resolution Sequence Stratigraphy In The Application Of The Quaternary Aquifer Division And Correlation

Heterogeneity and anisotropy of the aquifer is currently the core issues plaguing the hydrogeologists.The roots are lack of study on the deposition phase transition and its spatial and temporal distribution of aquifer,and the lack of high-precision stratigraphic framework.To this end,a case study of quaternary fluvial aquifer structure is carried out at Hutuo River Piedmont Plain in Hebei Province,and sendimentary theory and high-resolution sequence stratigraphy analysis method are applied.Based on the datum of drill core,grain size and OSL age,detailed analysis of the single drilling sedimentary facies is done.Through identifying the sequence boundary and base-level cycles of the boreholes at the study area,we will correlate the stratum of boreholes based on the high-resolution sequence stratigraphy.Thereby the quaternary sequence stratigraphic framework of the typical section at Hutuo River Piedmont Plain is established.On the basis,the distribution of quaternary alluvial-fluvial sand body is clarified,and the aquifer of the study area is divided reasonably.By conducting different space scale fluvial facies strata division and comparison,the applicability of high-resolution sequence stratigraphy applying to the quaternary aquifer division is discussed.The results will provide reference for the further scientific division of regional aquifer groups,and provide foundation work for scientific management and sustainable utilization of groundwater resources.The main results are as follows:(1)Based on the comprehensive analysis of stratigraphic lithology,age data and sporopollen data,the quaternary stratigraphic framework of the key borehole ZD08-1 of Hutuo River Piedmont Plain is established.The bottom of Holocene series is buried at the depth of 5.49 m.The bottom of Upper Pleistocene series is buried at the depth of 32.68 m.The bottom of Middle Pleistocene series is buried at the depth of 66.08 m.The bottom of Lower Pleistocene series is buried at the depth of 157.04 m.Two types of sedimentary facies of alluvial fan and braided rivers are mainly deposited at the borehole since the quaternary period.(2)Through recognition of different levels of base-level cycle of the core section,quaternary stratigraphic sequence of borehole ZD08-1is established.20 super short-term cycles,6 short-term base level cycles,2 mid-term base level cycles and a long-term base level cycle are identified in Quaternary series of this borehole section.Among them,the sequence interface of the long-term base-level cycle is the bottom of Quaternary series,and the sequence interface between two mid-term base-level cycles is the bottom of Middle Pleistocene series.The phase transformation from rise to fall of long-term base level cycle is at the position of alluvial fan turn to braided river.(3)Based on stratigraphic correlation between different levels of base level cycle,the quaternary high resolution sequence stratigraphy framework along the river section at Hutuo River Piedmont Plain is established.Throughout the quaternary period,the sedimentary strata of study area is in the control of a long-term base level cycle(LSC1).The overall thickness of the cycle from piedmont to plain is changed from thin to thick.By the influence of tectonic uplift of Taihang Mountains and active faults of NNE,the long-term base level is given priority to rise in the quaternary period of the study area.The sedimentary strata of rising period is continuous about 2.1 million years.Since Middle Pleistocen,the long-term base level began to drop until today.Inside the long-term base level cycle framework,the mid-term and short-term base level cycles of borehole sections can be compared one by one.(4)In the quaternary high resolution sequence stratigraphy framework along the river section,the spatial distribution of sand body since the quaternary period is discussed.The development degree and permeability of sand body is very well near the phase transformation from fall to rise of short-term base level cycles.Moreover,the sand body development degree is well at the rising half cycle and relatively poor at the falling half cycle of mid-term base level.The sedimentary environment of sand body changed from west to east along the river section.MSC1 changed from alluvial fan to braided river channel.Early MSC2 changed from alluvial fan to braided river channel,and then to meandering river channel.Late MSC2 changed from braided river channel to meandering river channel.(5)Quaternary series of Hutuo river piedmont plain can be divided into five aquifers.They are aquifer??aquifer??aquifer??aquifer? and aquifer? from top to bottom ordinally.Among them,aquifer ?and ? can be corresponding to aquifer groups ? from previous studies.Aquifer ? can be corresponding to aquifer groups ? from previous studies.Aquifer ?and ? can be corresponding to aquifer groups ? from previous studies.However,aquifer groups ? from previous studies should belong to Pliocene according to this study.There are two reasons of different division.One is that we have different understanding to the continuity of fine grained sediment from falling half cycle of SSC1.The other is that Quaternary bottom is defined deeper than the actual because of lacking of standard borehole section at piedmont plain.(6)The applicability of high resolution sequence stratigraphy theory applied to the division of the quaternary aquifer.By identifying the different levels of base level cycle and sequence interface,different spatial scale analysis of the stratigraphic correlation and aquifer structure can be carried out.High-precision stratigraphic study based on super short-term cycle correlation can be carried out at field scale area.In the same sedimentary system of secondary tectonic units,short-term base level cycle correlation can be carried out inside the stratigraphic framework of mid-term base-level cycle.For a large area of the whole basin or plain,the comparison of mid-term base level cycle can be tried out inside the stratigraphic framework of long-term base level cycle.