Cretaceous, Dakota Formation, Terra Cotta Member South Side of I-70, Salina County, Kansas

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1 Cretaceous, Dakota Formation, Terra Cotta Member South Side of I-70, Salina County, Kansas Written By: Steven D.J. Baumann G A Outcrop looking southeast Photo taken by: Steven Baumann on

2 Cretaceous, Dakota Formation, Terra Cotta Member, South Side I-70, Salina County Kansas Location: This outcrop is about 200 feet long and is exposed on the south side of the of Interstate 70, northeast of Salina about three miles in Salina County Kansas. It is about 1/2 mile northeast of the Saline River. GPS location is North by West (see Figure 1A and 1B). The bottom of the gully at the base of the exposed outcrop is approximately 1272 feet above mean sea level (MSL). The outcrop is exposed, at the base at the GPS location, and the to east about 150 feet and to the west about 50 feet. The outcrop runs east-northeast along the south side of the road, with an engineered drainage gully about 3 feet deep separating it from I-70. Significance: The outcrop is good location to understanding how the Cretaceous affects the local topography. The Cretaceous rocks in the area tend to form rolling hills with 10 to 50 feet of relief. They are underlain by the softer Permian Sumner Group which is not known to crop out in the area but is just at the base of most of the rolling Cretaceous hills. The local stream and river valleys produce very flat modern stream deposited land. Almost the entire town of Salina sits on these modern stream deposits. The Cretaceous rocks show striking color variation within (Figure 2). The shales are often white (kaolinite and gypsum), to gray and blues (illites), often green (glauconite and possibly sericite), yellow (limonite), and orange to red (iron rich minerals such as siderite). Within the array of multi-colored shales are diverse minerals. Siderite, limonite, pyrite, gypsum, sulfur, and possibly green sericite, nodules are common. Since the Terra Cotta Member of the Dakota Formation is mostly floodplain stream deposits, the diverse minerals are confined to local lenses and thin beds (Figure 3). There is an interesting subunit within Unit 4. In about the middle of the unit there is a red iron rich layer that grades east into a hard gray shale coated with an olive green mineral and occasionally with bright yellow sulfur (Figure 3F). The subunit is relatively thin (less than 0.8 feet). The olive green mineral is believed to be sericite, based on appearance and the fact that the deposit is not of marine origin. If this is the case it is difficult to explain why this unit contains iron to the west and then sericite and sulfur to the east over such a short area. One possible explanation is that Unit 4 was actually deposited in a mineral enriched, long existing, closed off, freshwater lake that may have been locally large. Although these sediments were deposited during the Lower Cretaceous during the days of the dinosaurs (100 to 112 million years ago), and floodplain deposits preserve fossils well, no dinosaurs have been found around Salina and the Terra Cotta is generally fossil poor. That doesn t mean that no dinosaur fossils exist in the area, they just haven t been discovered. The study of these rocks is economically important. Oil has been discovered and actively mined around the Salina area, mostly in Cretaceous rocks. 1

FIGURE 1A ZOOM IN South Side I-70, Salina County SITE LOCATION AND BASIC GEOLOGIC MAP Date Studied: 10/20/2010 Location: South side of I-70, about 3 miles northnortheast of Salina city limits GPS

3 FIGURE 1A ZOOM IN South Side I-70, Salina County SITE LOCATION AND BASIC GEOLOGIC MAP Date Studied: 10/20/2010 Location: South side of I-70, about 3 miles northnortheast of Salina city limits GPS location (Road Level): N: W: Elevation of Outcrop Base: 1272 feet above MSL N Contour Interval = 10 feet = 1200 feet = Outcrop Location = Geologic Contact Note: Geologic contacts are adapted from the Kansas Geological Survey s 2008 Surficial Geology of Kansas Map M-118 Kdt Kdt Kkc Kkc Ps Kkc Ps Qal Qal Kdt Kkc Ps Quaternary: (Undivided): Light soft sands and dark clays, derived from local Cretaceous deposits. Modern stream and floodplain deposits. Cretaceous: Dakota Formation, Terra Cotta Member: Soft dark gray to green gray, shale, with thick beds of white and yellow limonite rich shale, thin beds of evaporite coated pyrite and iron nodules common. Stream, alluvial, and possibly lake deposits. Cretaceous: Kiowa and Cheyenne Formations, (Undivided): Soft dark shales and limestones of the Kiowa intertongue with the thick beds of Cheyenne Sandstone. Locally the Kiowa dominates. Near shore to shallow marine deposits. Permian: Sumner Group: (Undivided) Light to red to pale yellow, soft shales with evaporates and limestones. Terrestrial and freshwater lake deposits. 2

4 FIGURE 1B ZOOM OUT South Side of I-70 Salina County SITE LOCATION MAP N Contour Interval = 10 meters (~33.3 feet) Date Studied: 10/20/2010 Location: South side of I-70, about 3 miles northnortheast of Salina city limits GPS location (Road Level): N: W: Elevation of Outcrop Base: 1272 feet above MSL = 2 miles = Outcrop Location SALINA 3

FIGURE 2: Lithology of Outcrop on south side of I-70, Salina County, Kansas UNIT 6 Covered UNIT 5 UNIT 4 UNIT 3 UNIT 2 UNIT 2A UNIT 2 UNIT 1 Outcrop of the Terra Cotta Member of the Dakota Formation

5 FIGURE 2: Lithology of Outcrop on south side of I-70, Salina County, Kansas UNIT 6 Covered UNIT 5 UNIT 4 UNIT 3 UNIT 2 UNIT 2A UNIT 2 UNIT 1 Outcrop of the Terra Cotta Member of the Dakota Formation Photo shows the entire outcrop with units labeled. DESCRIPTIONS OF UNITS UNIT 6 UNIT 5 UNIT 4 UNIT 3 UNIT 2A UNIT 2 Fissle gray to dark gray laminated shale capped with a 3-4 ledge of moderately hard yellow limonite coated siderite. Unit is 3 feet thick. Fissile, pale gray shale with a thin soft yellow orange bed at top. Unit is 3 feet thick. Fissile, blocky, gray shale. Upper 2 feet contains large iron concretions with a thin evaporate coated pyrite layer at base of upper part. Unit is 5.5 feet thick. Very soft yellow orange limonite rich shale that weathers almost white. Contains lenses and concretions of red and orange siderite nodules. Unit is 2.5 feet thick. Hard, white evaporate coated, pyrite nodules with a bumpy appearance. Unit is 0.2 to 0.3 feet thick. Soft, gray, laminated shale, with hard flat orange siderite concretions. Unit is 4.5 feet thick. UNIT 1 Fissile, blocky, dark gray laminated shale, with orange partings. Unit is >1.5 feet thick (base concealed). 4

FIGURE 3: Close-up Lithologies at Outcrop on south side of I-70,

layer at right) with the orange siderite concretions common in Unit 2.

6 FIGURE 3: Close-up Lithologies at Outcrop on south side of I-70, Salina County, Kansas 3A: Close-up of Unit 1 Photo shows the laminated nature of Unit 1. 3B: Close-up of Unit 2 and 2A Looking East Photo shows Unit 2A (white layer at right) with the orange siderite concretions common in Unit 2. 3C: Close-up of Unit 3 Photo shows the yellow orange laminated color of Unit 3 along with the almost white weathering pattern. 5

FIGURE 3 (Continued): Close-up Lithologies at Outcrop on south side of I-70,

large siderite iron concretion in Unit 2.

7 FIGURE 3 (Continued): Close-up Lithologies at Outcrop on south side of I-70, Salina County, Kansas 3D: Close-up of Unit 2: Siderite Concretion Photo shows a large siderite iron concretion in Unit 2. Quarter for scale 3E: Close-up of top of Unit 6 Photo shows the limonite coated siderite nodules at the top of Unit 6. 3F: Close-up of green lens in Unit 4 Photo shows the olive green coated rounded shale and siderite lens in about the middle of Unit 4. Occasionally coated with yellow sulfur. 6

8 References: Mesozoic Rocks, unlisted authors, Digital Version of KSGS Bulletin North American Stratigraphic Code, various authors, 2005, AAPG Bulletin v.89 no.11 p Regional Stratigraphy of the Dakota Formation, Kiowa Formation, and Cheyenne Sanstone in Kansas, P. A. Macfarlane, 1998, KSGS Annual Report, FY89 Surficial Geology of Kansas, various authors, 2008, KSGS Map M-118 Credits: Written by: Steven Baumann Field Work by: Steven Baumann Edited by: Melody Penne Photographs by: Steven Baumann 7

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