Depositional Environments and Timing of Formation of the Lilesville Gravels, Anson County, NC

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Yankech, M. (2022). Depositional Environments and Timing of Formation of the Lilesville Gravels, Anson County, NC. Unc Charlotte Electronic Theses And Dissertations.
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Abstract

MATTHEW ROBERT YANKECH. Depositional Environments and Timing of Formation of the Lilesville Gravels, Anson County, NC (Under the direction of DR. JOHN DIEMER). Near Lilesville, North Carolina, on the western margin of the Fall Zone, there occur upland gravels containing unusually coarse-grained, imbricated pebbles and cobbles. These upland Lilesville gravels form an extensive plateau capping the hilltops at an elevation of ~135 meters above sea level (~100 meters above the current Pee Dee River). They unconformably overlie weathered Lilesville granite and locally cap Cretaceous sediments belonging to the Middendorf Formation. The origin and age of the Lilesville gravels and other upland gravel deposits have been debated for decades. This study was performed at the BV Hedrick Gravel and Sand quarry. Due to the quarry actively being mined, observation of outcrops in several locations with orientations at various trends are described. In these outcrops the Lilesville gravels contain the following facies: 1) massive to poorly bedded gravel; 2) trough cross-bedded gravel; 3) trough cross-bedded sand; 4) horizontally laminated sand; 5) massive sand; 6) ripple cross laminated sand, 7) laminated sand, silt and clay; and 8) organic rich silt and clay. Architectural elements include channel forms, point bars with lateral accretion surfaces, and crevasse splay complexes. The Lilesville gravels are assigned to the Neogene based on pollen, plant macrofossils and phytoliths derived from the organic rich (lignite) facies. The age of the Lilesville gravels may be further constrained to the mid-to-late Miocene (7-10 million years old), based on their elevation above the current position of the Pee Dee River. Soil profiles from quarry high walls suggest multiple periods of post-Miocene soil formation, indicating times of stable conditions alternating with periods of deposition by the ancient Pee Dee River. Lithofacies analysis and facies architectural elements suggest that the Lilesville gravels are the product of braided fluvial systems and record an interval of erosion followed by aggradation by the southerly-flowing ancestral Pee Dee River system as it migrated back and forth across the landscape. The deposition of the Lilesville gravels indicates that a combination of processes were involved in their formation: a "Miocene Rejuvenation" leading to epeirogenic uplift in the source area and a transition to a wetter paleoclimate during the late Miocene, creating the external conditions to mobilize large quantities of coarse-grained sediment.

Details
Author

Yankech, Matthew

Title

Depositional Environments and Timing of Formation of the Lilesville Gravels, Anson County, NC

Physical Description

1 online resource (189 pages) : PDF

Date

2022

Degree Granting Institution

University of North Carolina at Charlotte

Abstract

MATTHEW ROBERT YANKECH. Depositional Environments and Timing of Formation of the Lilesville Gravels, Anson County, NC (Under the direction of DR. JOHN DIEMER). Near Lilesville, North Carolina, on the western margin of the Fall Zone, there occur upland gravels containing unusually coarse-grained, imbricated pebbles and cobbles. These upland Lilesville gravels form an extensive plateau capping the hilltops at an elevation of ~135 meters above sea level (~100 meters above the current Pee Dee River). They unconformably overlie weathered Lilesville granite and locally cap Cretaceous sediments belonging to the Middendorf Formation. The origin and age of the Lilesville gravels and other upland gravel deposits have been debated for decades. This study was performed at the BV Hedrick Gravel and Sand quarry. Due to the quarry actively being mined, observation of outcrops in several locations with orientations at various trends are described. In these outcrops the Lilesville gravels contain the following facies: 1) massive to poorly bedded gravel; 2) trough cross-bedded gravel; 3) trough cross-bedded sand; 4) horizontally laminated sand; 5) massive sand; 6) ripple cross laminated sand, 7) laminated sand, silt and clay; and 8) organic rich silt and clay. Architectural elements include channel forms, point bars with lateral accretion surfaces, and crevasse splay complexes. The Lilesville gravels are assigned to the Neogene based on pollen, plant macrofossils and phytoliths derived from the organic rich (lignite) facies. The age of the Lilesville gravels may be further constrained to the mid-to-late Miocene (7-10 million years old), based on their elevation above the current position of the Pee Dee River. Soil profiles from quarry high walls suggest multiple periods of post-Miocene soil formation, indicating times of stable conditions alternating with periods of deposition by the ancient Pee Dee River. Lithofacies analysis and facies architectural elements suggest that the Lilesville gravels are the product of braided fluvial systems and record an interval of erosion followed by aggradation by the southerly-flowing ancestral Pee Dee River system as it migrated back and forth across the landscape. The deposition of the Lilesville gravels indicates that a combination of processes were involved in their formation: a "Miocene Rejuvenation" leading to epeirogenic uplift in the source area and a transition to a wetter paleoclimate during the late Miocene, creating the external conditions to mobilize large quantities of coarse-grained sediment.

Genre

masters theses

Subjects--Topics

Sedimentology

Degree

M.S.

Keywords

Lignite
Lilesville Gravels
Lilesville Lignite
Pollen
Upland Gravels

Subject Area

Earth Sciences

Advisor(s)

Diemer, John

Committee Members

Bobyarchick, Andy
Eppes, Martha

Degree Note

Thesis (M.S.)--University of North Carolina at Charlotte, 2022.

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Rights Holder Information

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Identifier

Yankech_uncc_0694N_13016

Permalink

http://hdl.handle.net/20.500.13093/etd:2958