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Date Permissions Signed

5-20-2020

Date of Award

Spring 2020

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Foreman, Brady

Second Advisor

Rice, Melissa S.

Third Advisor

Mitchell, Robert J. (Geologist)

Fourth Advisor

Dahl, Robyn

Abstract

Preserved fluvial and deltaic sedimentary deposits found within martian crater-fill basins are important evidence documenting past warmer, wetter climatic periods on Mars. The morphologic and stratigraphic patterns of these sedimentary deposits are commonly interpreted to record variably complex transgression and regression histories of crater-lake levels, driven by fluctuations in the prevailing hydroclimatic conditions. Yet this tendency for direct inversion of sedimentary characteristics to formative boundary conditions largely neglects large-scale autogenic processes operating in crater-fill basins. The goal of this research is to illustrate an idiosyncratic feature of these basin types, wherein attributes of the sediment source play an outsized role in dictating conditions of the sink that ultimately stores the sediment. This linkage is rarely a concern in sedimentary basins on Earth but appears to strongly influence martian stratigraphy. Here, we examine sequence stratigraphic patterns produced in an experimental sedimentary basin wherein an initially empty basin passively receives a constant sediment flux and water discharge until reaching a spill-point elevation. This experimental setup captures the simplest of all feasible crater-fill basin evolution histories, and we present data from five experiments that vary the initial basin size and sediment flux parameters. We used Computed Tomography (CT) scans to analyze internal deltaic stratigraphy and found that five main sequence stratigraphic phases are produced. These phases are spontaneously generated under constant boundary conditions, indicating they are autogenic and directly attributable to the consequences of mass balance. As sediment and water input volumes "compete" for accommodation in the crater they cause five major depositional phases: 1) an early fluvial progradational phase; 2) a transitional phase from fluvial to deltaic progradational deposition; 3) a retreat phase of retrogradation/aggradational back-stepping deltaic deposition; 4) an over-topping phase of late progradational delta deposition; and 5) a forced progradational phase when steady state base level is reached. This experimental sequence stratigraphic pattern compares favorably with well-studied martian crater-fill sedimentary packages such as the Eberswalde Delta, the Southwest Eberswalde Deposit and the Jezero Western Delta. Thus, we suggest our experiments constitute a alternative, but useful "starting" sequence stratigraphic framework for approaching crater-fills rather than a direct application of marine sequence stratigraphic models, which assume an infinitely large ocean basin.

Type

Text

Keywords

Deltaic, fluvial, martian, crater, stratigraphy, experiment, shoreline trajectory, autogenics

Publisher

Western Washington University

OCLC Number

1156241224

Subject – LCSH

Martian craters; Sediments (Geology); Geology, Strategraphic--Paleocene; Alluvium

Geographic Coverage

Mars (Planet)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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