Geol 3000 Name Geologic Maps Score 12 Lab 8A Surficial Geology of Pope County Minnesota Refer to the Pope County Atlas C 15 Part A Plate 3 to answer the following questions 1 What is the age difference between Holocene and Pleistocene sediments 2 What are the three main geologic Pleistocene map unit groups in Pope County from oldest to youngest 3 The thick blue lines on the map represent the outer margin of the ice lobe at a particular stand still stage see Fig 3 Goose River Group sediments tend to be confined inside SW of what number ice margin 4 What ice margin position developed an earthen dam moraine of till which created Glacial Lake Benson as the ice retreated 5 Note that in the correlation of map units diagram the units are grouped by the environment in which the sediments were deposited glacial sediments till river sediments outwash and lake sediments For each of these groups describe their most common attributes in terms of sediment size sorting and bedding Understand that the term loam indicates a mix of sand silt and clay if it is very rich in the clay component it is termed clay loam if it also contains gravel pebble and cobble sized particles the modifiers gravelly pebbly and cobbly are often used Glacial sediments Sediment sizes Sorting Bedding River sediments Sediment sizes Sorting Bedding Lake sediments Sediment sizes Sorting Bedding 6 How are tunnel valleys interpreted to form 7 Identify at least 5 lakes that are mantled by tunnel valley walls describe their orientation e g NE N ESE and identify the ice margin number that marks their eastern termination 1 Orientation Ice Margin 2 Orientation Ice Margin 3 Orientation Ice Margin 4 Orientation Ice Margin 5 Orientation Ice Margin 8 Consider the sediments and landforms in T124N R37W See that the tunnel valley mantling Swenoda Lake is eroded out of unit gp and ends at ice margin 3 Then northeast of ice margin 3 the sediment is a mix of ogp ogr ogo and gcc What depositional environment do you think these mixed sediments represent 9 What sediment type do the longer esker landforms tend to develop on and is this consistent with how eskers are thought to form 10 Unit hs is described as holocene rubble How does this type of recent sediment form 11 Assuming prevailing winds from the west from what unit s was the silt that makes up the loess deposits derived 12 Note that the map units are defined by the sediment type not the interpreted origin of the sediment the interpretation of each unit is shown in italics at the end of each map unit description This is very different from the Washington County map Which way of classifying map units genetic or non genetic do you think is preferable and why