Geologic Characterization of Ladon Valles, Mars and the Surrounding Area a Thesis Presented to the Faculty of the College Of

Home , Athabasca Valles, Ladon Valles, Maja Valles, Margaritifer Terra

Geologic Characterization of Ladon Valles, Mars and the Surrounding Area

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

Doug C. Wolfinger

May 2014

This thesis titled

Geologic Characterization of Ladon Valles, Mars and the Surrounding Area

DOUG C. WOLFINGER

has been approved for

the Department of Geological Sciences

and the College of Arts and Sciences by

Keith M. Milam

Associate Professor of Geological Sciences

Robert Frank

Dean, College of Arts and Sciences

Abstract

WOLFINGER, DOUG C., M.S., May 2014, Geological Sciences

Geologic Characterization of Ladon Valles, Mars and the Surrounding Area

Director of Thesis: Keith A. Milam

Ladon Valles and Ladon Basin, Mars (Ladon study area), are in the path of what is potentially the solar system’s longest fluvial system. In this study, the geology of the

Ladon study area is analyzed in an attempt to reconstruct the geologic record for the

Uzboi-Ladon-Morava drainage system and the Margaritifer Terra region of Mars. An integral part of this reconstruction has been to determine the geologic processes that formed Ladon Valles. Although previous workers have referred to Ladon Valles as an

“outflow channel system,” no formal geologic characterization has led to that determination. Only precursory discharge estimates have been produced for Ladon

Valles and there are discrepancies regarding the timing and duration of erosional and depositional events in the Ladon study area. High resolution orbital data (Mars Global

Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express), has been used to assess the types of channel that is Ladon Valles’s middle channel (main channel), as well as its outer channels, and their discharge as well as establish the timing and duration of events in the Ladon study area through crater retention dating. With these constraints, discharge rates have been estimated. Ladon Valles landforms are consistent with both glacially carved and outflow channels, with the exception of streamlined islands, which is indicative exclusively of outflow channels. With the exception of the final stage, maximum estimates of the discharge values through the main channel are all

4 at least 106 m3 s-1, placing them within the range for outflow channels. The final stage through the main channel was less powerful and is most accurately categorized with valley networks in terms of discharge magnitude. Discharge results for Ladon Valles’s anastomosing channels are considerably weaker, some falling within the range for valley networks, and others within that for outflow channels. Water flowed abundantly through the Early-to-Mid-Noachian and began tapering off in the Late Noachian. An Early

Hesperian flow was possible but fluvial action more likely came to an end by the Late

Noachian.

Acknowledgments

My sincere thanks and appreciation go to my advisor, Dr. Keith Milam, for his mentorship, and to my committee members, Dr. Doug Green, and Dr. Greg Springer, for their assistance in building this graduate thesis. I would also like to extend my gratitude to Dr. Caleb Fassett, of Mount Holyoke College, for his advice.

Table of Contents

Page

Abstract ...... 3

Acknowledgments...... 5

List of Tables ...... 7

List of Figures ...... 8

1: Introduction…………………………………………………………………………... 10 Geologic Setting………………………………………………………………… 10 Is Ladon Valles an Outflow System ...... 11 Timing and Duration of Events in Ladon Valles ...... 16

2: Questions ...... 19

3: Methods ...... 20 Is Ladon Valles an Outflow Channel? ...... 21 Estimating Discharge in Ladon Valles ...... 25 Timing and Duration of Flow in Ladon Valles ...... 31

4: Results ...... 35 Is Ladon and Outflow Channel ...... 35 Timing and Duration of Events...... 61

5: Discussion ...... 66 Landforms ...... 66 Discharge ...... 67 Timing and Duration of Events Outside Ladon Valles ...... 75 Timing and Duration of Ladon Valles Events ...... 77

6: Summary ...... 92

References ...... 93

Appendix A Images Corresponding to Unit Descriptions in Table 3...... 99 Images Corresponding to Unit Descriptions in Table 4...... 108 Appendix B Plan Views of Cross-sectional Profiles in Figure 15...... 117

List of Tables

Tables Page

1. Data Specifications…………………………………………………………….. 20

2. List of Geomorphic Features Found on Mars………………………………….. 24

3. Descriptions of the Geologic Units Outside the Main Channel……………….. 39

4. Descriptions of the Geologic Units Within the Main Channel…………….…... 45

5. Values for Sinuosity and Aspect Ratio………………………………………… 51

6. Discharge Estimates for Ladon Valles………………………………………… 55

7. Ages of Proposed Geologic Units Outside the Main Channel………………… 62

8. Ages of Formations of the Ladon Valles Group………………………………. 64

9. Floor Elevation Ranges of Ladon Valles’s Anastomosing Channels…………. 78

10. Comparisons of Mid-to-Early Noachian Main Channel Discharge Estimates.. 82

List of Figures

Figures Page

1. MOLA Elevation Map……………………………………………………...... 12

2. Schematic of Margaritifer Terra Flow Directions…………………………….. 13

3. Martian Terrain Mapped by Period of Formation…………………………….. 14

4. Comparison of Discharge Estimates………….……………………………….. 15

5. Timing of Major Events in the Ladon Study Area……………………………. 17

6. Example of a Profile Line Used in a Discharge Calculation………………….. 26

7. Floor of the Main Channel…………………………………………………….. 29

8. Martian Crater-count Isochron Diagram………………………………………. 33

9. Geologic Map of Ladon Valles and Vicinity………………………………….. 36

10. Geologic Map of Northern Ladon Valles…………. ………………………….. 37

11. Geologic Map of Southern Ladon Valles…….………………………………... 37

12. Stratigraphic Column of Ladon Valles and Vicinity……………………….….. 38

13. Cross-sectional Profiles of Various Martian Valleys………………………..…. 48

14. Profiles of the Channels of Ladon Valles……………………………………… 49

15. Cross-sectional Profile Showing V-shape of Main Channel Floor……………. 50

16. Aerial Views of Channels Analyzed for their Sinuosity……………………..... 51

17. Landforms of Ladon Valles………………………………………………...…. 53

18. Profiles Used to Produce Discharge Estimates in Ladon Valles……………… 54

19. Crater-counting curves for Units Outside the Main Channel…………………. 63

20. Ladon Valles Main Channel Crater Retention Data…………………………... 65

21. Comparison of Discharge Estimates Including My Results…………………... 68

22. Flow Velocity as a Function of Channel Floor Slope………………………...... 73

23. Crater-retention Data for All Four Anastomosing Channels……………….…. 79

24. Cross-section of Profile C2...... ………………………………………………... 85

25. Possible Evidence of the Extent of Ladon Valles…………………………….. 89

1. Introduction

1.1 Geologic Setting

Present-day Mars is a dry and dusty world where water is presently unstable on the surface (Carr, 2006; Carr and Head, 2010). Yet the planet features ancient landforms where water erosion or deposition is evident. Many were likely developed on early Mars when its atmosphere generally may have been denser and the surface was warmer (Carr and Head, 2010; Milliken and Bish, 2010; Grant et al, 2009a). Margaritifer Terra (Fig. 1) is home to many such landforms: valley networks, outflow channels, and depositional basins are dispersed throughout. Loire, Samara, and Panará Valles are its major valley networks. Uzboi, Ladon and Morava Valles comprised what Grant and Parker (2002) refer to as a “mesoscale outflow system”, while Ladon Basin, and Holden and

Eberswalde craters are Margaritifer Terra’s most notable depositional basins (Fig. 1). As part of the Uzboi- Ladon-Morava drainage system (Mangold et al., 2012 and Grant et al.,

2009a), Ladon Valles’s main channel (main channel) stretches ~150 km from Holden

Basin to Ladon Basin and is about 30 – 60 km wide, 700 – 1000 m deep, and 200 – 300 m in relief. Ladon Basin, which lies at the terminus of Ladon Valles, is thought to be a

Noachian impact structure (Lillis et al., 2008). The circular basin is ~440-450 km in diameter and its gradient is 0.00077 km/km (Grant and Parker, 2002) inside the rim.

The Ladon Valles area provides prime examples of landforms formed by erosional processes during the Late Noachian-Early Hesperian and serves as an integral link in the fluvial pathway extending from Argyre Planitia to Ares Valles (Fig. 1a).

Given the likelihood that the source of Argyre’s water supply was melting ice from the

11 south polar region, the pathway from source to ultimate destination may well be more than 8000 km in length, which would make it the most extensive drainage in the solar system (Carr, 2006).

Water may have flowed from Holden Basin into Ladon Valles in the Late

Noachian / Early Hesperian to form the observed erosional features (Grant and Parker,

2002). If that is the case, Holden crater may have blocked the flow of water from Uzboi

Vallis (Mangold et al., 2012). The magnitude and timing of this erosion are consistent with the high abundance of water in the area (Fig. 2) and the hypothesis that the

Noachian was the wettest martian period (Barlow, 2008; Carr and Head, 2010). They are also in keeping with the estimated Noachian age of the terrain in the Ladon Valles study area (Fig. 3).

1.2 Ladon Valles as an Outflow System?

Given its fluvial landforms (Grant and Parker, 2002) and associated minerals

(including phyllosilicates and chlorides (Milliken and Bish, 2010; Mangold et al., 2012;

Grant et al., 2009a)), the Ladon study area holds important clues to the aqueous evolution of the Margaritifer Terra region and Noachian-aged Mars. Despite its role in the larger drainage system, there has been little work characterizing the fluvial nature of Ladon

Valles. For instance, while Grant and Parker (2002) and Grant et al. (2009b and 2011a) refer to the Uzboi-Ladon-Morava (ULM) area as a “meso-scale outflow system” and

Grant et al. (2008) refer to the Uzboi-Ladon-Margaritifer area as an “outflow channel system,” neither group substantiated their basis for identifying Ladon Valles as an

Figure 1. a) MOLA 4 pixel per degree (ppd) elevation map with the Ladon study area highlighted (black box). b) Inset map, with MOLA 32 ppd data, from (a). The Ladon study area is boxed. Warmer and cooler colors denote areas of higher and lower elevations, respectively. Elevation scalebar from Fortezzo et al. (2009).

Figure 2. Schematic of Margaritifer Terra flow directions (Grant et al., 2002). Holden Basin is located between Ladon Valles and Holden Crater (Fig. 1b).

outflow channel. Does Ladon Valles have geomorphic features consistent with those of known outflows channel (with a characteristically high aspect ratio, low sinuosity, and anastomosing channel) or is it similar in nature to a valley network or a channel carved by glaciers? Grant and Parker (2002) characterized the ULM system in an effort to determine its hydrologic contribution to Ares Vallis drainage. The maximum discharge for Ladon Valles was estimated between 1.5-4.5 x105 m3 sec-1 (Grant and Parker 2002).

This range is approximately equal to maximum discharge estimates for martian valley networks (Figure 4), a notion inconsistent with the characterization of Ladon Valles as an

14 outflow channel. Maximum outflow channel estimates (Figure 4) are all at least one order of magnitude higher than that of Ladon Valles.

Figure 3. Martian terrain mapped by period of formation, from Scott et al. (1987) (NASA, 1987). Browns, grey and darker purple indicate Noachian terrain. Yellows, blues, and lighter purple indicate Hesperian. Greens indicate Amazonian (Scott et al, 1987). (1) - Holden Crater (arrow) has been dated to the Early Hesperian (~3.5 Ga) (Mangold et al., 2012).

Figure 4. Comparison of estimated discharge values between Ladon Valles, valley networks, and outflow channels. All values listed are considered maximum. Coordinates of Unnamed valley network at 12N, 43E, Unnamed valley network at 6S, 45E from Hoke et al. (2011). Hoke et al. (2011) do not specify where these coordinates are located within the respective valles. (1) – Grant and Parker (2002), (2) – Hoke et al. (2011), (3) – Komatsu and Baker (1997) (4) – Robinson and Tanaka (1990), (5) – Coleman et al. (2007), (6) – Ori and Mosangini (1998), (7) –De Hon and Pani (1993), (8) – Leask et al. (2006), (9) – O’Connor and Baker (1992), (10) – Komar (1979), (11) – Burr et al. (2002a, b); Head et al. (2003).

Therefore, Ladon Valles’s discharge, as calculated by Grant and Parker (2002) is unusually low in comparison to that of well-characterized outflow channels. This stands in stark contrast to the notion that Ladon Valles was part of the largest fluvial system in the solar system (Carr, 2006). In light of the uncertainties in Grant and Parker’s (2002) discharge estimates and the dissimilarity of Ladon Valles flow with discharge estimates of other outflow channels, additional work is required to constrain discharge.

1.3 Timing and Duration of Events in Ladon Valles

Discrete geologic units within the Ladon Valles study area can be analyzed to characterize the chronology of erosional and depositional events. This is an aspect of the geologic history of the study area that appears to have room for clarification due to previous findings that are either nebulous or conflicting.

Citing Grant and Parker (2002), Mangold et al. (2012) and Milliken and Bish

(2010), date Ladon Valles to the Late Noachian / Early Hesperian Epochs. This is at odds with the Mid- to Late-Hesperian estimate produced by Irwin and Grant (2009) and

Rotto and Tanaka (1995). While Milliken and Bish (2010) state that the relationship between Holden Crater and the timing of the events that formed Ladon Valles is uncertain, other workers (Grant and Parker (2002), Parker (1985), and Boothroyd (1983)) assert that the chaotic terrain northeast of Holden Crater’s rim is evidence of subsurface discharge.

Mangold et al. (2012) determined that Holden crater had formed at least 100 m.y. later than the latest possible date for a Holden Crater subsurface discharge (Figure 5), as determined by Grant and Parker (2002), Parker (1985), and Boothroyd (1983).

Therefore, determination of the age of the Holden impact event implicates the timing of

Ladon Valles’s late-stage formation.

Figure 5. Timing of major events in the southern Ladon study area (Mangold, et al., 2012). Note the appearance of Holden crater in the Late Hesperian. Bold dates are from Ivanov (2001) and italic dates are from Hartmann (2005).

Detailed stratigraphic analysis, coupled with crater age dating, of Ladon Basin and Ladon Valles could lead to a better understanding of the Ladon Valles study area’s

18 water budget, the hydrologic source that was required, the duration of its input, and requisite climatic conditions for early Mars. The majority of reports on the duration of erosion express with confidence that the Ladon Valles study area’s climate was arid to semi-arid starting Late Noachian (Barnhart et al., 2008; Milliken and Bish, 2010; and

Grant et al., 2011a). Results from previous literature, however, suggest that the volume of water that existed in the Ladon study area as fluvial action was occurring is poorly constrained. For instance, Milliken and Bish (2010) found evidence for a low water-to- rock ratio, while Irwin and Grant (2009) cite geomorphologic evidence for abundant deposition in Ladon Basin. In addition, Mangold et al. (2012) stress that more analysis is needed to determine the duration of fluvial activity in the Ladon Valles study area.

Age constraints of the formation of specific geologic units can be obtained through crater counting analysis (a.k.a. crater age dating). For instance, an event that formed a channel can be assigned a minimum age based on the density of the craters on the channel floor (Hartmann, 2005). Crater analysis can also lead to determination of cross-cutting relationships since impact ejecta are younger than terrain that they superpose.

2. Questions

This study builds on the minimal number of previous studies of the Ladon Valles study area and attempts to answer the following outstanding questions:

 Are the channels in Ladon Valles outflow channels that formed by cataclysmic

flooding?

 What were the discharge rates for Ladon Valles’ channels? How do they compare

with those presented in Grant and Parker (2002), with that of other outflow

channels on Mars and Earth, and with other types of channels?

 What was the timing and duration of flow through Ladon Valles in relation to

Holden crater and other features (e.g. Ladon Basin) in the region?

3. Methods

In an effort to determine what type of fluvial landform Ladon Valles represents and to estimate discharge and timing of fluvial activity in the Ladon study area, this study will utilize multiple orbital datasets from the Mars Global Surveyor (MGS), Mars

Odyssey (MO), and Mars Reconnaissance Orbiter (MRO). Data intended for use in this report’s analysis will be amassed from the High Resolution Imaging Science Experiment

(HiRISE) from MRO, Mars Orbiter Laser Altimeter (MOLA) from MGS, Mars Orbiter

Camera (MOC) from MGS, Thermal Emission Imaging Spectrometer (THEMIS) from

MO, Thermal Emission Spectrometer (TES) from MGS, and Context Camera (CTX) from MRO (Table 1).

Table 1. (1) – McEwen et al. (2007), (2) – NASA (2012), (3) - Bridges et al. (2010), (4) Christensen et al. (2004), (5) - Mellon et al. (2000). (6) – Malin et al. (2007) Spatial Resolution (m) Spectral Coverage (nm) HiRISE(1) 0.9, 3 pixels across an object 400 – 1100 1/128 deg/pixel = MOLA(2) ~400 – 700 ~463m/pixel MOC(3) 3-10 (horizontal), 2(vertical) ~400 – 700

(4) 18/pixel (VIS), 100/pixel THEMIS 420 – 860, 680 – 1490 (IR) TES(5) 3000/pixel 6000 – 50000 CTX(6) 6/pixel ~400 – 700

All datasets used in this study were rendered in the Java Mission-planning and Analysis for Remote Sensing (JMARS) software application, which is developed and maintained by the Arizona State University Mars Space Flight Facility (ASU). Crater counting and

21 geomorphologic, stratigraphic, and topographic inspection was performed by visualizing multiple datasets in JMARS. Stream profiles were analyzed in Microsoft Excel using

MOLA data downloaded from JMARS. Crater count curves were produced by counting craters and measuring their diameters using a measurement tool in JMARS. Esri’s

ArcMap was used in the classification of MOLA 128 ppd elevation data to find large buried craters. This enabled circular or quasi-circular structures to be distinguished from the surrounding terrain. Terrain area was measured using the JMARS polygonal area calculation function, which automatically calculates the area upon the completion of the drawing of the polygon.

3.1 Is Ladon Valles an Outflow Channel?

Data from HiRISE, MOLA, MOC and THEMIS, have enabled dimensional comparison of Ladon Valles with other types of fluvial landforms: outflow channels, valley networks, gullies, and glacially carved valleys (Carr, 2006). Outflow channels and glacially carved channels are distinguished from valley networks primarily by girth and depth. Outflow channels are typically tens to hundreds of kilometers wide (Carr, 2006),

100 - 3000 m deep (Baker, 2009; Mest et al., 1998), and are thought to develop from chaotic flooding (Carr, 2006). Valley networks are typically 50-200 m deep and 1-5 km wide (Baker, 2001; Carr, 2006), relatively flat (Howard, 1988; Baker et al., 1992), and are thought to develop from either a gradual erosion due to fluvial streams (Carr, 2006) or groundwater sapping (Squyres and Kasting, 1994). Gullies are steep, tens of meters in width and hundreds of meters long, and form most likely by relatively recent melting ice

22 and snow (Carr, 2006). They have theater-shaped alcoves near their headlands and grow narrower downward as their channels converge (Carr, 2006).

Landforms associated with each type of these fluvial systems can be used to characterize unknown fluvial systems. For instance, valley networks are characterized with many short stubby tributaries, but may form a dendritic pattern with many stream orders. Like outflow channels, they can be U-shaped in cross-section (Craddock and

Howard, 2002), but can also be V-shaped (Baker et al., 1992; and Craddock and Howard,

2002) and may be highly sinuous. Outflow channels typically branch out into short and stubby tributaries or lack them altogether and have low sinuosity (Carling et al., 2009a).

Sinuosity was estimated by tracing the distance from one end of the channel to the other, and dividing by the distance of a straight line between the same two endpoints. This provides a measure of maturity of a stream where a low sinuosity indicates a relatively short-lived stream that formed a straight channel, and high sinuosity indicates a mature stream that formed a meandering pattern.

Outflow channels, however, are not as easily distinguished from glacially carved channels. Lucchitta (2001) demonstrated that Antarctic glacially carved channels are similar in width and depth to outflow channels. Other features commonly associated with both kinds of channels are longitudinal grooves, hanging valleys, a U-shaped cross- section (Lucchitta, 2001), and grooved terraces (Baker et al., 1992).

Observations and measurements of associated landforms can help to discern the channel type of Ladon Valles and the geologic processes responsible for its formation.

Measurements used to produce stream profiles enable the assessment of the channel’s

23 shape. Table 2 provides a categorized list of morphological features that have been used to determine whether Ladon Valles is an outflow channel, a glacially carved channel, or a valley network.

Table 2. List of Geomorphic Features Found on Mars. Features are categorized according to their associated geological and geographical setting (modified from Baker et al., 1992). A search for these features has been conducted to assess the origin and history of Ladon Vallis. An upper case “X” denotes a strong relationship, and a lower case “x” denotes a weak relationship. Information from: (1) – Pacifici et al. (2009), (2) – Carr (2006), (3) - Hauber et al. (2008), (4) – Baker (2001), (5) – Baker et al. (1992), (6) – Carling et al. (2009b), (7) – Carling et al. (2009a), (8) – Lucchita (2001), (9) – Craddock and Howard (2002), (10) – Malin and Edgett (2000), (11) - Squyres (1989).

Outflow Valley Networks Gullies Glacial Channels Streamlined Islands X(1,2,3,4,5,6) (Broad Interfluves) Anastomosing channels X(5,6) x(2) X(5) Pendant Bars X(1,5) Giant Bars X(1,4,5,7) Grooved Terraces X(1,5) X(5) Longitudinal Grooves X(4,5,7) X(4,5) Cataract-like Features X(1,2,4,6) Headcuts X(8) Hanging Valleys X(4) X(4) X(8) U-shaped channels X(2,8) X(8) X(8) Table 2: continued V-shaped channels X(9) Theater-like Valley Heads X(4,9) Low Junction Angles X(4) Quasi-parallel Patterns X(4) Indistinct Terminal Areas X(4) Pingos, Kames, Eskers X(1) Thermokarst Depressions X(1) Patterned Grounds X(1) Polygonal Terrain X(1) Alcoves X(10) Lobate Debris Aprons X(3, 11) Plucked (Scour) Zones X(2,5,6) X(2)

3.2 Estimating Discharge of Ladon Valles

Discharge required to form Ladon Vallis has been determined by producing several latitudinal (perpendicular across stream) topographic profiles of Ladon Vallis from MOLA data. Each profile used in a discharge calculation (main profile) had ancillary profiles that are parallel and located nearby upstream and downstream (Figure

6). These ancillary profiles were drawn to establish the veracity of the identification of a terrace seen in the main profile. Terrace tops were used to establish the flow stage, which enabled the calculation of average depth of the flow. Since each terrace is assumed to represent a flow, they were also used as markers to delineate between flows.

Figure 6. (A) An example of a main profile line used in a discharge calculation (red line), along with its ancillary profiles (blue lines). (B) The four graphs of bench check profile lines help to confirm the terrace top seen in Profile C at ~-1950 m. Horizontal axis numbers each represent a ~463-meter MOLA cell.CTX image: P02_001890_1572_XN_22S028W

Measurements from the main profiles have been used in equations to calculate discharge. The Manning Equation is typically used for computing discharge Q in terrestrial rivers (Carr, 2006):

2/3 1/2 -1 Q = A*Rh *S *n (1) where A is the cross-sectional area, Rh is A divided by the wetted perimeter, which is twice the height of one channel wall plus the width of the channel floor, S is the floor gradient, and n is the bed-roughness coefficient (Strangeways, 2000). The basic martian version of this is (Carr, 2006):

4/3 2 1/2 Q = A(gm*S*R /ge*n ) (2) where the difference in gravitational acceleration, between Mars and Earth, gm and ge respectively, is corrected by including the ratio of gm and ge.

The first step in calculating discharge is to determine the mean flow velocity, U, for a specific flow with the Darcy-Weisbach equation (Wilson et al., 2004),

1/2 U = [(8*gm*d*S)/f] (3) where g = (9.8 * 0.38)m/s2, d is flow depth, S is the channel floor gradient, and f is the friction factor, which is a function of the overall roughness of the channel bed (ratio of flow depth over grain size distribution) (Hoke et al., 2011). Quantification of the friction factor depends on the hydraulic radius, R, of the channel and the grain size distribution on the channel floor (Wilson et al., 2009), where R is defined as:

R = A/(w + 2d) (4) which equates to the channel’s cross-sectional area divided by its wetted perimeter.

Friction factor is solved using the relationship:

1/2 0.02929 -0.1113 -0.1606 (8/fc) = 4.529*(R/D50) *S *σ (5) where D50 is the grain size distribution, equal to 0.1 m (Kleinhans, 2005), where 50% of the clasts are smaller than 0.1 m. Equation (5) is one of a variation of friction factor equations presented in Wilson et al. (2009) and is one of the preferred here because it is appropriate for channels with sand-dominated beds (Wilson et al., 2009), which is one of the two likely best characterizations of the main channel. Grains in the size range of silt to very fine sand are assumed to be a prominent component in the composition on the floor of the main channel where impact ejecta is absent, based on the thermal inertia values. The range of thermal inertia units (TIU) on the main channel floor (as have been measured in this study) correspond to a grain size of about 0.025 mm or medium silt

(Pelkey, 2001). Equation (5) is intended for lower regime flows (Wilson et al, 2009), which most likely match the conditions in Ladon Valles, based on analysis in of martian and terrestrial outflow channel bedforms (Burr et al, 2004). However, visible HiRISE data reveals that the main channel floor is also densely populated with boulders (Fig. 7).

Therefore, two friction factor equations were used. The friction factor for boulder- dominated streambeds is

1/2 (8/fc) = 5.62*log10[R/D84]+4 (6)

Where D84 stipulates that 84% of the clasts on the channel floor are smaller than 0.48 m.

Figure 7. Floor of the main channel, densely populated with boulders, showing as small bright knobs. HiRISE ID: ESP_016579_1575_RED (NASA/JPL/ASU)

Channel dimensions have been measured and values for each parameter have been used in (3) and (4). Discharge, Q, is computed as:

Q = UA (7) where A is the rectangular cross-sectional area (Komar, 1979). There are constraints that need to be taken into account due to limitations of martian data when calculating channel discharge. For instance, determination of cross-sectional area is difficult due to the difficulty of precisely estimating flow depths (Grant and Parker, 2002; Carr, 2006). This is largely due to the fact that well-defined terrace tops that are necessary for stage

30 determination are not commonly observed in channel walls. Additionally, the mass wasting covering part of the Ladon Vallis main channel along each profile crossing the channel necessitates that each estimated discharge be presented as a minimum.

Estimating a roughness coefficient is also uncertain (Carr, 2006). However, cross- sectional uncertainties can be mitigated by analyzing a large number of channel profiles

(Grant and Parker, 2002). Furthermore, terraces are more easily and accurately distinguishable in HiRISE imagery, due to its improved spatial resolution over MOC- narrow angle imagery used in previous studies (McEwen et al., 2007). Ubiquitous visible image data for the study area has also undergone a resolution upgrade with the CTX and

THEMIS daytime thermal inertia datasets. CTX, MOC and MOLA imagery have been used where HiRISE imagery is nonexistent. This has enabled a more accurate analysis of

Ladon Valles’s cross-sectional area, as compared to that of Grant and Parker (2002).

Terrace top elevations observed in CTX data were used to estimate average minimum stream depth. Together with the gradient, the width and average depth provide the channel’s geometry, which is necessary for use in Equation (4). Width was determined by measuring the distance in meters between the terrace top on one bank to the terrace top on the channel’s other side. If the terrace cliff on the other side had been eliminated as part of a cut bank, making the profile smooth on that side, the same elevation as the terrace top was used for the opposing side. The average stream depth of each flow was calculated with MOLA data contained in a stream cross-sectional profile.

The depth at each data point in the profile was calculated by subtracting the elevation at each data point along the main profile from the terrace top elevation. The data point

31 depths were summed and the stream’s average depth was obtained by dividing the sum by the total number of data points (tens of points on average) plus one to include the depth at stage.

Depth was measured with respect to bankfull conditions where the elevation of the terrace top represents that of the stage, and the lowest elevation of the channel floor represents that of the flow’s bottom depth. Maximum discharge results include 100% of the measured depth. A range of discharge values was produced for each stream profile by decreasing the flow depth value by 25%, 50%, 75% and 90%. Where 100% of the measured depth represents bankfull flow conditions, the lesser depth increments account for the possibility that bankfull conditions were never sustained for a significant amount of time.

Stream gradient was measured as meters of vertical elevation difference divided by horizontal distance in meters. To compute the vertical elevation difference, the elevation at the profile line was subtracted from the elevation at a point that marked a location in the channel where either the channel begins, or its slope dramatically changes.

3.3 Timing and Duration of Flow in Ladon Valles

Timing constraints of the flooding events are crucial to reconstructing the Ladon study area’s geochronology. Age estimates for flow through Ladon Valles were obtained by conducting a crater count of each defined geologic unit, using THEMIS visible and thermal inertia, HiRISE, CTX and MOC imagery. Crater retention dating as per

Hartmann (2005) was performed on defined geologic units within Ladon Basin and

Ladon Valles, along with units defined in the surrounding area. Contacts that delineate

32 geologic units were drawn where distinguishing characteristics (e.g. textures, landforms, apparent crater densities) indicated a distinct surfacing history (Michael and Neukum,

2010). Characteristics used to distinguish geologic units included their THEMIS thermal inertia, a cursory comparison of apparent crater density, and geologic description. Each unit’s geologic description includes an assessment of its morphology and topographic characteristics. Specifically, the descriptions are composed of: apparent smoothness, steepness and consistency of slope and elevation, surficial tone brightness as seen in visible data, miscellaneous distinguishing features, and its elevation relative to adjacent units. A unit’s topography played a major role in contact delineation since, for instance, a change in slope could mark a change in geologic units. Crater counts of each delineated terrain were plotted against estimated age isochrons for Mars (Fig. 8). Each crater included in the count was added to a specific bin, each of which represents a diameter range (0.063 – 0.125 km, 0.125 – 0.25 km, 0.25 – 0.5 km, 0.5 – 1.0 km, 1.0 – 2.0 km, 2.0

– 4.0 km, 4.0 – 8.0 km, 8.0 – 16.0 km, 16.0 – 32.0 km, 32.0 – 64.0 km, 64.0 – 128 km,

128 – 256 km) and is delineated on the isochron chart’s x-axis. The number of craters in each bin was divided by the terrain’s area in km2. Periods are divided into the Noachian,

Hesperian and Amazonian, which begin at ~4.1, ~3.5, ~3.0 Ga, respectively (Hartmann,

2005). The Noachian is subdivided into Early, which begins ~4.1 Ga, Middle (~4.0) and

Late(~3.8) (Hartmann, 2005) . The Hesperian is divided into Early and Late, the border of which is ~3.3 Ga (Hartmann, 2005).

Figure 8. Martian crater-count isochron diagram (Hartmann, 2005). Solid black above 4 Gy represents crater density saturation. Short solid black lines represent divisions between periods. Short grey lines represent divisions between epochs (e.g. Mid-Late Noachian). The Hesperian Period has only one subdivision.

This analysis has the potential to improve on accuracy of previous age estimates for terrain in the Ladon Valles area (Grant and Parker, 2002; Irwin and Grant, 2009) due to the usage of higher-resolution data sets and updated crater retention dating isochrons

(Hartmann 2005). Age determinations produced from these data enabled the establishment of the relative timing relationships and duration of surficial fluvial erosion.

Stratigraphic relationships have aided in this analysis, the end result of which is a map depicting the age relationships of the Ladon Valles study area’s geologic units (as defined by this study). Uncertainty is quantified by a factor of ~2 (Hartmann, 2005). The area

(in km2) of each delineated geologic unit was measured using projected MOLA data in

JMARS. Large craters that are buried to degree that they are nearly indistinguishable from the surrounding terrain—referred to as quasi-circular depressions (QCD’s) (Frey et al., 1999)—were identified in ArcMap by stretching their MOLA data.

Unit thicknesses presented in the stratigraphic column were measured in JMARS using MOLA 128ppd data by subtracting the elevation of the lower contact from the upper one. This method provides only minimum estimated apparent thicknesses for some units since upper contacts may be representative of eroded surfaces, lower contacts may not always be exposed, and regional dips are assumed to be minimal

4. Results

Results in this work are presented with respect to the Ladon study area’s geologic units, which are mapped in Figures 9, 10 and 11 and presented in Figure 12. Geologic units are described in Tables 3 and 4. Unit plan views are shown in Appendix A.

4.1 Is Ladon Vallis an Outflow Channel?

4.1.1 Channel Geometry

Cross-sectional profiles are shown in Figure 13 comparing the main channel’s shape and aspect ratio to that of other outflow channels and valley networks.

Corresponding plan views are shown in Appendix B. Cross-sectional profiles for the four anastomosing channels and the main channel are shown with their associated plan views in Figure 14. The same is shown for the main channel with a larger scale in Figure 15.

Sinuosity is demonstrated in aerial views of various channels in Figure 16.

Values for sinuosity and aspect ratio are listed in Table 5.

Figure 9. Geologic map of Ladon Valles, Mars, and vicinity. Geologic units in legend are those for the study area outside of the black inset boxes.

Figure 10. Part of northern Ladon Valles.

Figure 11. Part of southern Ladon Valles.

Figure 12. Stratigraphic column of Ladon Valles, Mars, and vicinity. The range of values associated with each unit represents its range of apparent minimum thickness in meters. The Ladon Valles Main Channel Group (Figures 10 and 11) is separated from the rest of the Ladon study area (Figure 9)because some main channel formations are disproportionately thin (and difficult to view in Figure 9) in comparison to outside units.

Table 3. Descriptions of the Geologic Units Outside the Main Channel. THEMIS Nighttime Thermal Inertia Age (b.y.) (J/km2s1/2) Terrain Description Range Average Holden Variably rocky and smooth. with 3.5 – 3.7 60 – 160 120 Crater Rim a downhill gradient away from (Nhcr) crater center of about 1/30. Tone varies from medium to light. Typically 100 – 500 m higher than Holden Basin. Moderately cratered.

Holden Smooth with a downhill gradient 3.5 – 3.8 Interior: 70 – Interior: Crater (Nhc) away from crater center of about 180 135 1/1000. Medium toned. Rim: 50 – Rim: 170 Typically 100 – 200 m lower than 240 Holden Crater Rim. Tranverse dunes seen in western half of image, with slopefaces facing south. Southern half of floor is moderately fractured. Occasional knobs up to a few kilometers wide. Outside of study area: fans at base of wall with distributaries. Moderately cratered.

Eberswalde Flat with low relief. Etched 3.6 – 3.7 70 – 210 160 Crater (Nec) topography. Light to medium tone. Common alluvial fans with distributaries. Occasional landforms shaped similar to eskers where adjacent to Nlhu. Abundant light-toned layers on crater floor and locally on wall. Abundant fans at base of wall. Heavily cratered.

Shambe/Singli Smooth and very flat terrain, 3.6 – 3.75 Interior: 80 – Interior: Craters (Nsc) with a slight incline from 220 160 center to northwest rim. Rim: 100 – Rim: 135 Medium tone. Heavily 170 fractured. Smooth, inconspicuous rim that appears to be fluvially altered in the northwest.

Table 3 (Continued) Morava Chaotic u-shaped channel with 3.6 – 3.75 100 – 230 160 Vallis (Nmv) abundant large knobs that are nonuniform in size, and occasional buttes near channel mouth. Knobs decrease in size and angularity shortly downstream, while becoming uniform in size. Medium tone. Three brief grooved terraces downstream. Buttes become more common downstream where knob density decreases.

Margaritifer Hummocky terrain with low 3.65 – 3.75 80 – 150 100 Southeast relief. Light tone. Up to 100 (Nms) m lower than Nlhp. Features resembling giant hoodoos extend from the contact with Nlhp. Occasional wide stream valleys with common broad alcoves. Moderately cratered.

Holden Basin Etched terrain near the head 3.6 – 3.8 75 – 225 165 (Nhb) of Ladon Valles. Lightly to heavily rubble-filled throughout with abundant

equally spaced and similarly sized knobs.

Steeper slopes than Nlv10 latitudinal to direction of flow.

Ladon Basin Smooth and featureless unit 3.65 – 3.8 100 – 160 125 (Nlb) with a low gradient. Medium tone. Common fractures~1 km wide, 10’s km long. Occasional QCD’s. ~400 m cliff on the west side. Moderately cratered.

Table 3 (Continued) Ladon Uplands Heavily incised and etched 3.65 – 4.0 85 – 180 120 (Nlu) terrain with abundant high relief mountains in an eastern cliff adjacent to Ladon Basin Plains. Smoother, with a gradual ascent north and west toward Ladon Basin Rim. Hummocky and heavily incised and etched. Light to medium tone. Streams systems of moderate sinuosity commonly limited to one Strahler order, rarely two orders. Alcoves are seen in the walls of some valleys. Terrain becomes smoother and elevation ascends north and west away from Ladon Basin. Local light-tone layered deposits in southwest portion.

Table 3 (Continued) Ladon Outer Four prominent smooth 3.7 – 3.9 Individual Channels Valleys (Nlov) anastomosing channels. W = Western, Medium tone. Typically 300 MW = Middle Western, to 1000 m below Nlvh. ME = Middle Eastern, E = Eastern

W: 30 - 130 W: 85 MW: 55 – 120 MW: 95 ME: 90 - 190 ME: 50 E: 90 – 180 E: 45

Margaritifer Smooth and flat unit with 3.7 – 4.0 100 - 140 120 North (Nmn) exception of occasional ejecta aprons. Light to medium toned. Gradual incline with distance from Ladon Basin Rim. 200 – 300 m higher than Ladon Uplands, 300 – 1000 m lower than Rim Material (Nrm). Moderately cratered.

Table 3 (Continued) Arda Valles Very hummocky terrain with a 3.8 – 80 – 210 140 (Nav) moderate slope that trends 3.95 toward Ladon Valles. Light- toned outside of valleys, dark- toned on canyon floors. Abundant valleys—u-shaped, braided low- sinuosity systems up to four Strahler orders with abundant alcoves in canyon walls, sinuosity ~1.048 (Class 1). Other valleys do not exceed one Strahler order. Class 2 valleys are u-shaped, contain no alcoves, are not braided, and feature a sinuosity ~1.040. THEMIS NIR is very dark in Class 2 valleys and moderately bright on the surrounding surface. Braided systems morph to unbraided Class 2 with tributaries merging downstream. THEMIS Nighttime TIR is moderately bright in Class 1 valleys and very bright on the surrounding surface. Lineated tear-drop shaped that form a group of lineations in a radial pattern. Heavily cratered.

Margaritifer Moderately hummocky and 3.8 – 4.1 80 – 140 100 East (Nme) somewhat flat terrain. Occasional rounded knobs in the east. Moderately incised with one valley network in the western portion with up to 2 stream orders. Valleys are slightly sinuous. Common light- tone floor deposits. Dark wind streaks trend various directions. Heavily cratered.

Table 3 (Continued) Ladon Valles Slightly hummocky with low 3.8 – 4.1 60 – 130 100 Highlands relief. Typically ~300 m below (Nlvh) Nlhp. Less hummocky than Nlhp. Light to medium tone. Bright streaks trend N10E extending from small craters. Four streamlined islands, each with at least one terrace. Moderately cratered.

Ladon High Slightly hummocky, low 3.9 – 4.1 100 – 160 135 Plains (Nlhp) relief, featureless. High elevation in the south and southeast, sloping down toward Holden Crater in the southwest, east of Ladon Valles. No evidence of drainage. Dark dunes are seen in THEMIS Day TIR in the south, east of Ladon Vallis. Similarly smooth, flat and featureless west of Ladon Valles with lineated tear- drop shaped pits, interpreted to be secondary craters from Holden Crater, that form a group of lineations in a radial pattern. Arcuate wind streaks trending east/west, and long, thin grooves trending ~NNE/SSW, extending at least 1 kilometer, and up to 0.5 km in width in the western member. Heavily cratered.

Table 3 (Continued) Ladon Hummocky unit with 4.0 – 4.1 100 – 160 120 Hummocks moderately steep slope that (Nlh) trends toward Ladon Vallis to the southeast. Medium tone. Common stream valleys that are limited to one order. Rare braided systems up to two orders. No alcoves in canyon walls. Heavily cratered. Lineated tear-drop shaped pits that form a group of lineations, interpreted to be secondary craters from Holden Crater, in a radial pattern.

Rim Material Steep cliffs and high relief with 4.0 – 4.1 20 – 200 110 (Nrm) common jagged nonstratified ridges. Light toned. Hundreds to over 2000 m higher than adjacent terrains. Common colluvium, occasional alluvial fans. Forms an arcuate shape around the north, west, and south of Ladon Basin. Heavily cratered.

Table 4. Descriptions of the Formations Within the Main Channel. Terrain Description Age (b.y.) THEMIS Nighttime Thermal Inertia (J/km2s1/2) Range Average Ladon Hummocky ejecta apron surrounding 2.8 – 3.7 Ejecta: Ejecta: Valles crater predominantly to the northwest 75 – 125 100 Crater 2 southeast. Smooth crater floor. Light Rim: Rim: 40 (Hlc2) toned throughout. 10 – 40 meters 130 – 150 higher than Nlv2, 10 – 20 meters higher than Nlv5.

Ladon Hummocky ejecta apron surrounding 3.2 – 3.5 Ejecta: Ejecta: Valles crater predominantly to the north, west 105 – 180 140 Crater 1 and south. Smooth crater floor. Varies Rim: Rim: 240 (Hlc1) from medium to light toned. THEMIS 230 – 250 NIR reveals 2 thin bright rings from the floor to the top of the rim. 100 - 200 meters lower than Nlv9, 0 – 15 meters lower than Nlv7, 30 – 40 meters lower than Nlvh, 0 – 30 meters lower than Nlhe.

Ladon Smooth with a slope facing toward the 3.5 – 3.7 50 -120 90 Valles middle of the main channel at a Eolian gradient of 1/10 to 1/100. 10 – 100 m (Nlve) above adjacent units. Medium tone. Moderately cratered.

Ladon Smooth, gradually sloping terrain at 3.5 – 3.7 100 – 250 170 Valles 10 Ladon Valles’ head. Steep 0 - ~80 km (Nlv10) east of Holden Crater Rim. Becomes moderately flat east of this area. Medium tone. Heavily rubble-filled downstream from head with abundant equally spaced and similarly sized knobs. Steep incline begins, approaching Gori Crater. Porcelaneous surface in the two downstream members. 10 – 100 m lower than Nhb, 0 – 50 m lower than Nlhe, 30 – 100 m lower than Nlvh.

Table 4 (Continued) Ladon Chaotic with abundant large angular 3.5 – 3.7 0 – 200 120 Valles 9 light-tone knobs, most of which are on (Nlv9) channel floor. Other knobs sit on top of terrace. Erratic topography. Knobs and surface are medium tone. Typically ~300 m lower than Ladon Basin, and up to ~200 m higher than Nlv7. Moderately cratered.

Gori Hummocky ejecta apron surrounding 3.6 – 3.7 Ejecta: 95 Ejecta: Crater crater. THEMIS NIR reveals 2 bright – 210 145 (Ngc) rings between crater floor and top of Rim: 230 Rim: 245 rim. Rim exterior is medium-toned in – 250 THEMIS NIR. Ejecta is medium-toned throughout. 90 – 190 155 Ladon Smooth with a pronounced slope facing 3.7 – 3.8 Valles 8 latitudinal to direction of flow at a (Nlv8) gradient of about 1/100. Medium tone. Typically 0 – 100 m higher than Nlv3 in elevation. Moderately cratered.

Ladon Southern member: Moderately 3.7 – 3.9 100 – 190 145 Valles 7 hummocky and longitudinally flat (Nlv7) slope. Light tone. Typically 60 – 80 m higher than Nlv8 in elevation. Lower in elevation than Nlv2 by ~50 – 100 m, lower in elevation than Nlv5 ~100 – 150 m. One possible short stubby tributary (Fig. 8). Moderately cratered. Northern member: Smooth, very flat, typically gently inclined toward the east, down sloping toward the north. Black dunes trending longitudinally over the northern half. Fractured.

Table 4 (Continued) Ladon Southern member: Smooth, flat, gently 3.7 – 3.9 100 – 180 140 Valles 6 downsloping going north. Medium (Nlv6) tone. Typically 50 – 150 m lower in elevation than Arda Valles. Trough created by an apparent ~4 km-wide fault trending N80W. Lightly cratered. Middle member: Slightly hummocky. Higher in elevation than Nlv2 by 10 – 40 m. Hummock depressions are 10’s to 100’s m wide and contain latitudinal dunes. Northern member: Moderately hummocky. 50 – 80 m higher in elevation than Nlv2. ~100 m lower than Nlhp. Generally sloping downward going north until reaching the rim of Shambe/Singli Craters. Erractic topography near the Shambe/Singli rim.

Ladon Southern member: Smooth to slightly 3.7 – 3.9 90 – 150 125 Valles 5 hummocky. Moderate to light tone. (Nlv5) Typically ~40 m above Nlv7. Northern member: Smooth to slightly hummocky. Minimally light- to light- toned surface. Fractured. Trough created by an apparent ~4 km-wide fault bearing roughly N80W. Typically ~100 – 150 m higher than Nlv6. ~100 meters lower than Nlvh.

Ladon Smooth and flat terrain. An 3.7 – 125 – 150 140 Valles 4 approximately 15-meter incision that oversaturated (Nlv4) cuts Nlv10. 3.7 – 4.0 100 – 165 120 Ladon Smooth with occasional knobs in Valles 3 southern member, varying in size from (Nlv3) small to over 1 km. 20 meters lower in elevation than Nlv8. Marked by incision into Nhb in southern member. Consistently higher elevation than Nlv10.

Table 4 (Continued) Ladon Very smooth unit from southern border, 3.9 – 4.0 75 – 125 135 Valles 2 north for ~100 km, where terrain (Nlv2) transitions to slightly hummocky. Black dunes extend to this transition, but not beyond. Polygonal terrain in extreme southern portion. Flat with gradual downslope northward. Consistently higher in elevation than Hlc2. Typically lower in elevation than Nlv6. Drastic slope changes near the Ladon Valles mouth starting -2050 on the west contact and -2000 on the east contact distinguish this formation from Nlb.

Ladon Smooth and flat. Occasional 3.9 – 4.1 80 – 180 125 Valles 1 moderately sorted knobs. Smooth and (Nlv1) slightly inclined going downstream. Dark to medium tone. Occasional moderately sorted knobs, interpreted as colluvium from the adjacent Cliffside in Nlh. Typically ~30 meters above Nlv10. Heavily cratered.

Figure 13. Cross-sectional profiles of various martian valleys. No vertical exaggeration. All profiles display a u-shape, while the valley networks are distinguished by a lower aspect ratio and shallower and narrower dimensions. Profile plan views are found in Appendix B.

Figure 14. Profiles of the anastomosing channels and main channel of Ladon Valles. All channels feature a u-shape. VE = 5X. Base data: CTX images: P12_005569_1581_XI_21S029W, G04_019770_1553_XN_24S027W, B03_010777_1587_XN_21S028W, P02_001890_1572_XN_22S028W, G16_024583_1573_XN_22S028W, P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

Figure 15. Cross-sectional profile showing a v-shape of the main channel bed. Horizontal axis numbers each represent a ~463 meter MOLA cell. Base data: CTX image: P02_001890_1572_XN_22S028W

Figure 16. Aerial views of channels analyzed for their sinuosity. (a) Daga Vallis (~1.00). (b) Ladon Valles’ main. channel (~1.55). (c) Ares Vallis (~1.10). (d) Arda Valles (~1.04). Arrow points to the stream used in the measurement. Base images are all from THEMIS Day IR 100 m Global Mosaic (NASA/JPL/ASU)

Table 5. Values for Sinuosity and Aspect Ratio of Outflow Channels, Valley Networks and the Main Channel. Aspect Sinuosity Ratio From Coords To Coords Main Channel 1.55 87:1 331.4E, 22.5S 331.5E, 22.5S Ares Vallis 1.10 54:1 339.1E, 7.1N 339.2E, 7.3N Arda Valles 1.04 14:1 327.57E, 20.10S 327.59, 20.12S Nirgal Vallis 1.08 12:1 319.81E, 28.13S 319.86E, 28.05S 43E, 12N 1.05 22:1 42.67E, 12.02N 42.7E, 12.03N

4.1.2 Landforms

A Distinguishable landforms present in Ladon Vallis’ main channel include grooved terraces (Fig. 17a), an apparent locally confined polygonal terrain (Fig. 17b), and a possible short stubby tributary (Fig. 17c). Streamlined islands (labeled ‘S’ in Figure

17c) and their associated anastomosing channels (Fig. 14) are observed on either side of the main channel. Islands range in height from 100 to 1200 m, with the tallest positioned as the western-most island and the shortest the eastern-most island.

Figure 17. (A) Landforms of Ladon Valles. AC = anastomosing channels, S = streamlined islands, GT = grooved terraces, MC = main channel. (B) P = possible polygonal terrain. P13_006136_1582_XN_21S029W, B03_010777_1587_XN_21S028W, P02_001890_1572_XN_22S028W, P12_005569_1581_XI_21S029W (NASA/JPL/ASU) CTX data (a and c): P17_007784_1597_XN_20S028W G04_019770_1553_XN_24S027W, B03_010777_1587_XN_21S028W, P02_001890_1572_XN_22S028W, G16_024583_1573_XN_22S028W, P12_005569_1581_XI_21S029W,

4.1.3 Discharge

Ladon Valles discharges were calculated across 12 profiles (Fig. 18). Table 6 shows the measurements comprising channel discharge calculations and their resulting estimates.

Figure 18. Profiles used to produce discharge estimates in Ladon Valles. Profile line markers (white vertical lines) indicate the start and end points of their corresponding discharge estimate listed in Table 3. Note five and possibly six terraces on the streamlined island that flanks the main channel on the west. Base image from the THEMIS Day IR 100 m Global Mosaic (NASA/JPL/ASU)

Table 6. Discharge Estimates for Ladon Valles with the parameters used in their calculations. Discharge (Q) and velocity (V) are estimated to fall within a range bounded by the result obtained assuming a sand-dominated channel bed and the result obtained assuming a boulder-dominated channel bed. The range of estimates for each profile includes values obtained from depth estimates of 100% (bankfull), 75%, 50%, 25%, and 10% of the measured average depths. Q (sand) Width Average Slope V (boulder) Q (boulder) (x 106 m3 s- Profile (m) Depth (m) (km/km) (m s-1) V (sand) (m s-1) (x 106 m3 s-1) 1) A1a 2510 44.7 0.03621 195 37.8 21.8 4.24

2510 33.5 0.03621 154 32.2 12.9 2.71

2510 22.4 0.03621 109 25.7 6.12 1.44

2510 11.2 0.03621 58.1 17.4 1.65 0.489

2510 4.5 0.03621 24.4 10.4 0.274 0.117

A2a 2060 24.4 0.00368 37.4 14.3 1.88 0.718

2060 18.3 0.00368 29.2 12.2 1.10 0.459

2060 12.2 0.00368 20.4 9.71 0.511 0.244

2060 6.1 0.00368 10.6 6.59 0.133 0.829

2060 2.44 0.00368 4.10 3.95 0.0206 0.020

B1a 3531 63.1 0.01067 31.2 32.5 31.2 7.27

3531 47.3 0.01067 18.6 27.7 18.6 4.64

3531 31.6 0.01067 8.85 22.1 8.85 2.47

Table 6: continued 3531 15.8 0.01067 2.44 15.0 2.44 0.839

3531 6.31 0.01067 0.416 9.02 0.416 0.201

B2a 2160 20.2 0.00218 24.5 11.1 1.07 0.486

2160 15.2 0.00218 19.1 9.48 0.624 0.310

2160 10.1 0.00218 13.2 7.56 0.288 0.165

2160 5.05 0.00218 6.79 5.14 0.074 0.560

2160 2.02 0.00218 2.55 3.08 0.011 0.013

D1a 5310 55.4 0.01786 164 35.0 48.2 10.3

5310 41.6 0.01786 130 29.8 28.6 6.58

5310 27.7 0.01786 92.3 23.8 13.6 3.50

5310 13.9 0.01786 50.4 16.2 3.71 1.19

5310 5.54 0.01786 21.3 9.68 0.627 0.285

D2a 3930 27.9 0.006429 55.6 18.0 6.10 1.97

3930 20.9 0.006429 43.5 15.3 3.58 1.26

3930 14.0 0.006429 30.4 12.2 1.67 0.669

3930 6.98 0.006429 16.0 8.30 0.438 0.227

Table 6: continued 3930 2.79 0.006429 6.28 4.97 0.069 0.055

E1a 4980 40.8 0.04000 191 36.9 38.8 7.50

4980 30.6 0.04000 150 31.4 22.9 4.79

4980 20.4 0.04000 106 25.1 10.8 2.55

4980 10.2 0.04000 57.1 17.0 2.90 0.865

4980 4.08 0.04000 23.4 10.2 0.476 0.207

E2a 3600 20.2 0.002857 28.1 16.6 2.04 1.21

3600 15.2 0.002857 21.8 10.2 1.19 0.557

3600 10.1 0.002857 15.1 8.15 0.550 0.296

3600 5.05 0.002857 7.77 5.53 0.141 0.101

3600 2.02 0.002857 2.92 3.32 0.021 0.024

C1a 10400 87.8 0.00155 70.0 23.0 63.9 27.0

10400 65.9 0.00155 55.7 19.6 38.1 17.0

10400 43.9 0.00155 40.1 15.6 18.3 8.79

10400 22.0 0.00155 22.3 10.6 5.10 2.86

10400 8.78 0.00155 9.79 6.36 0.894 0.647

Table 6: continued C2a 10798 531 0.00027 113 38.5 645 221

10798 173 0.04113 91.5 32.8 394 141

10798 115 0.04113 68.0 26.2 195 75.2

10798 57.6 0.04113 40.3 17.8 57.7 25.6

10798 23.0 0.04113 19.5 10.7 11.2 6.13

C3a 15905 191 0.02418 504 76.0 1530 231

15905 143 0.02418 405 64.8 923 148

15905 95.5 0.02418 296 51.6 449 78.4

15905 47.8 0.02418 170 35.1 129 26.6

15905 19.1 0.02418 78.1 21.0 23.7 6.39

C3b 10911 150 0.00731 230 47.7 379 78.0

10911 52.5 0.00731 184 40.6 226 49.8

10911 35 0.00731 134 32.4 110 26.5

10911 17.5 0.00731 76.3 22.0 31.2 9.00

10911 7 0.00731 34.7 13.2 5.68 2.16

C3c 9229 216 0.00125 125 35.8 250 71.3

Table 6: continued 9229 162 0.00125 101 30.5 151 45.6

9229 108 0.00125 73.9 24.3 73.7 24.2

9229 54 0.00125 42.6 16.5 21.2 8.24

9229 21.6 0.00125 19.8 9.91 3.94 1.98

C3d 5161 22.9 0.00088 17.4 9.28 2.06 1.10

5161 17.2 0.00088 13.5 7.90 1.20 0.700

5161 11.5 0.00088 9.41 6.30 0.556 0.372

5161 5.73 0.00088 4.88 4.28 0.144 0.126

5161 2.29 0.00088 1.87 2.56 0.022 0.0030

C4a 14094 126 0.00685 195 42.5 347 75.4

14094 94.5 0.00685 156 36.2 208 48.2

14094 63 0.00685 113 28.9 100 25.6

14094 31.5 0.00685 63.9 19.6 28.4 8.70

14094 12.6 0.00685 28.7 11.7 5.10 2.09

C4b 9731 124 0.00134 85.0 26.8 103 32.3

9731 93 0.00134 68.0 23.0 61.5 20.6

Table 6: continued 9731 62 0.00134 49.3 18.2 29.7 11.0

9731 31 0.00134 27.8 12.3 8.40 3.73

9731 12.4 0.00134 12.5 7.40 1.51 0.893

C4c 5520 73.8 0.00083 92.1 26.3 37.5 10.7

5520 55.4 0.00083 73.1 22.4 22.3 6.83

5520 36.9 0.00083 52.5 17.9 10.7 3.64

5520 18.5 0.00083 29.1 12.1 2.96 1.24

5520 7.38 0.00083 12.6 7.27 0.512 0.296

4.2 Timing and Duration of Events

Results from crater counts reveal that proposed geologic units inside and outside the main channel range between Early to Late Noachian in age (Tables 7,8 and Figs. 19,

20).

Table 7. Crater Retention Ages of Proposed Geologic Units Outside the Main Channel.

Crater Retention Age Unit Label Terrain (Ga) Hhcr Holden Crater Rim 3.5 – 3.7 Hhc Holden Crater 3.5 – 3.8 Nec Eberswalde Crater 3.6 – 3.7 Nsc Shambe/Singli Craters 3.6 – 3.75 Nmv Morava Vallis 3.6 – 3.75 Nms Margaritifer Southeast 3.6 – 3.8 Nhb Holden Basin 3.8 – 3.9 Nlb Ladon Basin 3.65 – 3.8 Nlu Ladon Uplands 3.65 - 4.0 Nlov Ladon Outer Valleys 3.7 – 3.9 Nmn Margaritifer North 3.7 – 4.0 Nav Arda Valles 3.8 – 3.95 Nme Margaritifer East 3.8 – 4.1 Nlvh Ladon Valles Highlands 3.8 – 4.1 Nlhp Ladon High Plains 3.9 – 4.1 Nlh Ladon Hummocks 4.0 – 4.1 Nrm Rim Material 4.0 – 4.1

Fluvially incised units such as Arda Valles and Ladon Hummocks, and units lacking signs of fluvial activity, such as Ladon High Plains and Margaritifer North, are dated to the Noachian. One or more chaotic flood(s) originating from Nlb’s northeast corner occurred as late as the Late Noachian to form Nmv.

It is interesting to note that larger diameter crater density bins (generally 16-32- to

128-256 km) often plotted as oversaturated on crater retention graphs (Figures 19 and

20). This is perplexing since, in most cases, there appears to be room for more of the same-size craters in the units in question without saturation occurring. A source of this discrepancy could be the area limitation imposed by the bounds of the study area, as units were not analyzed outside the bounds. The problem this presents is that the oversaturated datapoints skew the consistency of the crater density curves in which they are located.

Regardless the cause of the problem, the larger crater densities were not used to assign final crater retention ages because the geologic units with respect to larger diameter craters obviously do not represent a saturated surface.

Figure 19. Crater counting curves for proposed geologic units outside the main channel. Oversaturation is commonly observed for the 16- to 32-, 32- to 64-, 64-to 128-, and 128- to 256-km bins. Dashed black, green and red lines represent (adapted from Hartmann (2005)): Early/Mid Noachian, Mid/Late Noachian and Early/Late Hesperian subdivisions respectively.

The only units outside the main channel that approach the Noachian/Hesperian boundary are Holden Crater (Nhc) and Holden Crater Rim (Nhcr). In contrast, the main channel (Fig. 20 and Table 8) has several units that date around the Noachian/Hesperian boundary and younger.

Table 8. Crater Retention Ages of Formations of the Ladon Valles Group.

Unit Label Ladon Valles Formation Age Hlvc2 Ladon Valles Crater 2 2.8 – 3.7 Hlvc1 Ladon Valles Crater 1 3.2 – 3.5 Nlve Ladon Valles Eolian 3.5 – 3.7 Nlv10 Ladon Valles 10 3.5 – 3.7 Nlv9 Ladon Valles 9 3.5 – 3.7 Ngc Gori Crater 3.6 – 3.7 Nlv8 Ladon Valles 8 3.7 – 3.8 Nlv7 Ladon Valles 7 3.7 – 3.9 Nlv6 Ladon Valles 6 3.7 – 3.9 Nlv5 Ladon Valles 5 3.7 – 3.9 Nlv4 Ladon Valles 4 3.7 - Oversaturated Nlv3 Ladon Valles 3 3.8 – 3.9 Nlv2 Ladon Valles 2 3.9 – 4.0 Nlv1 Ladon Valles 1 3.9 – 4.1

Figure 20. Ladon Valles main channel crater retention data. Dashed black, green and red lines represent (adapted from Hartmann (2005)): Early/Mid Noachian, Mid/Late Noachian and Early/Late Hesperian subdivisions respectively.

5. Discussion

5.1 Landforms

The main channel is part of an outflow system that initially formed, along with the adjacent anastomosing channels, from overland flow from Holden Basin. Its aspect ratio of 87:1 (Fig. 13, Table 5) and cascading grooved terraces (Fig. 17a), distinguish it from valley networks, while the system’s streamlined islands and anastomosing channels distinguish it from glacially carved channels. Polygonal terrain observed in Figure 15b indicates the former presence of a locally extensive ice sheet. Eskers and pingos that are often formed by the movement of glaciers were not observed associated with this terrain.

However, the main channel may well have been formed by more than one type of erosional and depositional process. It is possible, for instance, that polygonal terrain, eskers, pingos, and longitudinal grooves were initially formed by glacial erosion, and later removed by later fluvial events. The main channel is also distinguished from a gully by its longitudinal extent, and lack of internal lobate debris aprons.

It is also noteworthy that the main channel’s sinuosity (Fig. 16, Table 5) of 1.55 is anomalously high for martian channels, regardless of their type. This high value could be due to tectonic activity—perhaps resulting from uplift of the Tharsis Plateau— imposing structural control over the Ladon study area. Evidence for tectonic activity is seen in a right-lateral oblique-slip fault, located at about 23S to 24S latitude, and another that resembles a normal fault with its north side dropped down, at about 21S latitude

(Figs. 9 and 11). The main channel’s highly sinuous bend was likely influenced by the

67 southern portion of Ladon Basin’s rim (Rim Material (Nrm), Appendix A) directing the channel’s flow toward the northwest.

Despite its high sinuosity, analysis of the main channel’s landforms indicates it formed as part of an outflow system. This is based on the presence of cascading grooved terraces in the main channel, streamlined islands, and anastomosing channels outside of it, as well as its U-shape and dimensions.

5.2 Discharge

The maximum discharge (1.10 m3 s-1) calculated for the final flow of Ladon

Valles, represented by profile C3d, is within the range for that of lesser outflow channels.

Estimates for all channel discharge measurements for boulder-dominated streams are within the range of estimated discharges for typical martian outflow channels (Fig. 21 and Table 6). All but two maximum estimates for discharge based on a sand-dominated streambed are within the range of magnitude for outflow channels. Minimum estimates, marked by the vertical white line in each bar in Figure 21, are within valley network range for later-stage main channel profiles, and for all anastomosing channels. The discharge result for C4d, for instance, is comparable only to relatively weak values for valley networks when computed with a depth value that is reduced by 90%. For this profile and the anastomosing channels, all other depth increments (75%, 50% and 25%) lead to discharge estimates of varying magnitudes within the range for valley networks.

Figure 21. Comparison of estimated discharge values between Ladon Valles, valley networks, and outflow channels. All values listed are considered maximum. Vertical white lines represent the value obtained by decreasing the flow stage by 90%. My Ladon Valles discharge results listed here are minimum estimates. Coordinates are provided in place of names for the two unnamed valley networks—12N, 43E and 6S, 45E (Hoke et al., 2011). Hoke et al. (2011) do not specify where these coordinates are located within the respective valleys. (1) – Grant and Parker (2002), (2) – Hoke et al. (2011), (3) – Komatsu and Baker (1997) (4) – Robinson and Tanaka (1990), (5) – Coleman et al. (2007), (6) – Ori and Mosangini (1998), (7) –De Hon and Pani (1993), (8) – Leask et al. (2006), (9) – O’Connor and Baker (1992), (10) – Komar (1979), (11) – Burr et al. (2002a, b); Head et al. (2003).

The main channel exhibits evidence for at least five different flows, each of which is marked by a terrace (Fig. 17a), and delineated in Figure 18. There may have been another early flow that predated these five flows, as evidenced by a possible terrace in the southwestern portion that is a step up from the other terraces of the streamlined island that flanks the main channel on the west (Fig. 18). However, for consistency in this discussion, the number of flows through the main channel is established at five.

Although the anastomosing channels were carved contemporaneously with the main channel’s initial flows, the discharge of the flows through those channels was typically less by at least an order of magnitude. The main channel’s dimensions are greater than those of the anastomosing channels, with the exception of the slope.

Although, slope plays a major role in the calculation of flow velocity, the resulting larger hydraulic radius leads to generally higher velocity and discharge (Table 6).

The first of the five flows through the main channel is recorded by a terrace on the streamlined island that borders the main channel on the west. The widest measured profile--C3a--represents part of the second flow involved in forming the main channel.

The boulder discharge estimate of this profile, on the order of 109 m3s-1, is larger by an order of magnitude than the next largest Ladon Valles discharges, and comparable to the discharge measured for Kasei Valles (Fig. 21, Table 6). This profile’s result could be considered an outlier, however, and unrealistic given its velocity values, the maximum of which exceeds 500 m s-1. C3a’s sand estimate, however, includes far more realistic velocity, and a discharge of almost an order of magnitude less. The same was true along other profiles as estimates resulting from assumptions of a sand-dominated streambed

70 consistently produced more realistic velocities compared to boulder-dominated streambed calculations.

C4a is of a width that is similar to that of C3a but is categorized with the main channel’s third stage because its western edge is defined by the terrace top that is a step down from the western terrace top of C3a (Fig. 18). C3b is also associated with the third flow, and yields discharge estimates slightly greater than that of C4a. Main channel width became steadily narrower with each flow that produced incision. Depth, however, varied greatly among C3b, C3c and C3d, with the depth in C3c measuring about 30% greater than that in C3b, and about ten times as much as C3d. Average depth of the main channel produced by the final stage, and represented in profiles C3d and C4c, is comparable to the lower end of the measurements of the anastomosing channels, while their width is generally greater than that of the anastomosing channels. Accordingly, the discharge estimates for C3d and C4c are comparable to that of the same anastomosing channel profiles.

Maximum discharge estimates along main channel profiles are within the range for that of outflow channels (Fig. 21 and Table 6) and range from 106 to 109 m3s-1. The maximum discharge estimates for all Ladon Valles anastomosing channels range from valley network to mid-range outflow channel magnitudes, as they compute to at least 105 m3s-1. Main channel discharge estimates (e.g., C2a and C3a) of early flows were comparable to those of maximum estimated discharges for large outflow channels. The latter two stages of Ladon Valles flows were weaker, but were nevertheless at least 106 m3s-1 and therefore within the range for outflow channels. Of the two main channel

71 profiles that represent the final stage, the discharge estimate corresponding to profile C3d evokes the most confidence. This is because the stage’s average depth is more trusted since there is less Ladon Valles 8 (Nlv8) colluvium (Appendix A and Table 4) obscuring the channel floor along Profile C3d than there is along C4c. For comparison to discharge estimates in previous literature, the main channel maximum estimate in Grant and Parker

(2002), at 4.0 105 m3s-1, is about half an order of magnitude less than the weakest maximum estimates in this report. This is not necessarily a direct comparison, however, since their estimate refers to a small subchannel well upstream from the focus of discharge estimates in the main channel in Figure 18. The use of the subchannel to estimate discharge through Ladon Valles is consistent with advice in Wilson et al. (2009), who recommend against relying on bankfull conditions for maximum discharge calculations. This is because the equation for discharge flux (F):

F = wdu (8) where w is width, d is depth, and u is velocity, shows that F would have to increase with time to maintain bankfull conditions until the final floor depth was reached. However,

Wilson et al. (2009) assert that F decreases with time after an initial burst and brief increase. Based on this analysis, the use of subchannels in discharge estimations would appear to be meritorious. However, this method that may enhance the feasibility of the flow’s estimated discharge is also not without potential error since modern sedimentary deposits can greatly obscure the true depth of the flow that formed the subchannel.

Furthermore, the assumption of bankfull conditions is more useful in my analysis since I used the discharge estimates to constrain a generalized qualitative estimate of the volume

72 of water that moved through Ladon Valles in order to assess its contribution to the flowpath that extends from Argyer Planitia. This assumption produces discharges that are consistent with Komatsu and Baker’s (1997) discharge estimate of Ares Vallis—a prominent channel downstream from Ladon Valles in the same flowpath--since they also assumed bankfull conditions in their analysis.

However, based on the validity of the analysis of bankfull feasibility presented in

Wilson et al. (2009), the method of calculating discharge based on incremental depth assumptions enabled consideration of other perhaps more likely scenarios involving

Ladon Valles flows. The feasibility of what the true discharge of the flow being studied might have been further analyzed with the model of outflow channel velocity as a function of flow depth and streambed slope presented in Wilson et al. (2009) (Fig. 22).

Velocity decreases linearly with F and ranges from 3 – 10 m s-1 in a channel of depth <=

50 m, and up to 15 m s-1 in channels with a stage of <=100 m (Wilson et al., 2009).

Figure 22. Flow velocity as a function of channel floor slope and flow depth (Wilson et al., 2009). This model is valid for sand- and boulder-dominated beds since it is based on grain size distributions of D50 = 0.1m, D84=0.48m and D90=0.90 m.

Although the majority of the slope measurements for the main and anastomosing channels are greater than those featured in the Figure 22 chart, it can be used as a feasibility guide for velocity measurements featuring a comparable slope.

The only main channel discharge measurements with a slope and depth that both fall within the chart’s parameters are C3d and C4d. C3d’s sand velocity of 9.28 m s-1 is 2 to 3 times the corresponding velocity modeled in Figure 22, and C4d’s is greater than the

74 modeled result by a factor of about 4. For C3d, a 50% decrease in velocity would result in a discharge that is comparable to Grant and Parker’s (2002) maximum estimate and within the range for valley networks.

The waning magnitude included in this trend of flow strength demonstrated in this group of discharge estimates is consistent with Mars’s Noachian to Hesperian drying trend as presented in Carr and Head (2010), and Barlow (2008) since waning water supply would, over time, cause outflow channel discharge to dissipate. This waning supply may have begun to alter the Ladon Valles’s main channel type as seen in C3d’s discharge estimates (Fig. 21 and Table 8) and given the v-shape profile shown Figure 15.

Discharge through the individual anastomosing channels did not approach that through the main channel, save for the main channel’s final stage. Combined discharge results for the anastomosing channels amount to only ~50% of the magnitude of the C3b estimate.

Based on the discharges (Fig. 21 and Table 6) and the crater retention ages of their associated units (Fig 23), it is apparent that water volume began to decline in the Late

Noachian.

With respect to feasibility of the discharge results, those with depth components of 100% are probably not realistic, based on the bankfull stream analysis presented in

Wilson et al. (2009). Discharge estimates with outlandish velocity results (> ~40 m s-1) based on the model in Figure 22 are also not realistic. This includes, in particular, the results for C2a. The boulder-dominated calculations tend to result in outlandish velocities much more frequently than sand-dominated calculations. However, the presence of the grooved terraces, anastomosing channels and streamlined islands, as well

75 as the dimensions of the channels, indicate the flooding must have been at a high magnitude at least in the early to middle stages. Therefore, discharge results (Fig. 22 and

Table 6) from sand-dominated calculations with depth values that are from 25% to 75% of their respective maximum average depth invoke the most confidence.

5.3 Timing and Duration of Events Outside of Ladon Valles

5.3.1 Early- to Mid-Noachian Period (4.1 to 3.8 Ga)

Crater counts reveal generally Early to Mid Noachian geologic units in the southern portion of the Ladon study area, while the northern geologic units date as Late

Noachian. With the exception of Ladon Hummocks (Nlh) (Appendix A), units with landforms associated with fluvial activity (Arda Valles [Nav], Holden Basin [Nhb],

Margaritifer East [Nme] and Margaritifer Southeast [Nms]) (Appendix A) are younger than units devoid of such evidence. Incised terrain within and outside of Ladon Valles records evidence of numerous flow events in the Noachian Period. Valley networks to the west of Ladon Valles, in Nlh, record fluvial activity in the Early Noachian when precipitation might well have been the predominant source of flowing surface water

(Craddock and Howard, 2002 and Carr and Head, 2010), often producing overland flow.

Flow also originated from south of the study area, flowing in the Early-to Mid-Noachian through Uzboi Vallis (Grant and Parker, 2002) and Holden Basin (Grant and Parker,

2002, and this study). The timing of the occurrence of these flows is consistent with the

Early- through Mid-Noachian Epochs obtained for the formation of the anastomosing channels in Ladon Outer Valleys (Nlov) (Appendix A) outside the main channel. Smaller scale fluvial activity was also common during the epochs, as is evidenced by developed

76 drainage patterns in the Nlh, Nav, Nhb, Nme, Nms and Nlov geologic units. To the north of western Ladon High Plains (Nlhp) (Appendix A), fluvial action in Arda Valles

(Nav) (Appendix A) persisted through the Early-through-Mid-Noachian, resulting in deposition in Ladon Basin (Nlb) (Appendix A). In addition to Nav’s crater density, this age range is constrained by a cross-cutting relationship between Nav and Shambe and

Singli Craters (Nsc), which are dated to 3.6 – 3.75 Ga.

As water continued flowing over Holden Basin, and into Ladon Valles Highlands, what later became Ladon Valles’s main channel (Figs. 10, 11) may have experienced greater discharge (supported by the discharge estimates listed in Table 6 and Fig. 20), due in part to stream piracy, than the other four valleys, causing greater erosion and downcutting through the Middle to Late Noachian. This led to a greater downcutting in

Ladon Valles’s main channel, making its geometry distinct from that of the valleys of

Ladon Outer Valleys (Nlov).

Eberswalde Crater (Nec) (Appendix A) was formed near the end of the Mid-

Noachian and is important as a possible source of water for Holden Crater (Hhc)

(Appendix A), which formed in the earliest Late Noachian (Fig. 18 and Table 7). There is no evidence, however, for drainage flowing from Nec directly into Ladon Valles.

5.3.2 Late Noachian Period (3.8 to 3.5 Ga)

Further north, and into the Late Noachian, Ladon Uplands (Nlu) (Appendix A) delivered water to Ladon Basin (Nlb) from the rim (Nrm) (Appendix A) of the Ladon

Basin impact. There is little evidence for flooding into Nlb from the east or southeast, save for a low-density valley network to the southeast in Margaritifer East (Nme)

(Appendix A). Regardless of the source, the volume of water in Nlb was enough to eventually produce a flood in its northeast corner and form Morava Vallis (Nmv)

(Appendix A).

Margaritifer Southeast (Nms) shows abundant evidence of valley networks that were active in this period. On the other hand, Margaritifer North (Nmn) (Appendix A), a contemporary unit to Nms in the North and West areas of the Ladon study area, is absent any evidence of drainage. This suggests that drainage apparently was mainly constrained to southward and eastward flow from Ladon Basin’s Rim Material (Nrm) through Nlu or differential erosion of less resistant units. Another possibility is that resurfacing events may have erased evidence for drainage in Nmn that may have been produced. However, there is likewise no evidence for what may have been the source of resurfacing, such as lava flows or significant eolian activity.

5.4 Timing and Duration of Ladon Valles Events

5.4.1 Early- through Mid-Noachian Period (4.1 to 3.8 Ga)

Crater retention ages of the Main Channel Group formations indicate that fluvial activity began as overland flow directed toward Ladon Valles as early as 4.1 Ga, through the Noachian (e.g. Nlv1) (Appendix A). Flooding persisted through Holden Basin (Grant and Parker, 2002, and others) as overland flow, eroding much of the landscape and forming the anastomosing channels of Ladon Outer Valleys (Nlov) (Appendix A), which are flanked by the streamlined islands (Fig. 17a) of Ladon Valles Highlands (Nlvh).

The main channel may have become a preferential conduit for flooding starting in the Early- through Mid-Noachian Period (3.8 – 4.1 Ga). At this time, fluvial activity

78 began downcutting through the main channel and anastomosing channels, lowering the elevation of the channel floors of Nlov relative to the adjacent Nlvh. The main channel’s first two flows produced two terrace tops, the second represented by Profile C3a (Fig.

18), both of which appear to have formed penecontemporaneously with the anastomosing channels. This timing relationship is established by the fact that the main channel’s oldest unit, Nlv1 (Fig. 11), is stratigraphically lower than the second terrace. Therefore, these flows are likely to have occurred prior to 3.9 Ga, which is the youngest possible age for Nlv1, and it can be assumed that the Early Noachian to early Mid-Noachian was the most fluvially active time period for the channels in Ladon Valles. However, a comparison of crater densities (Fig. 23) between each adjacent anastomosing channel

(Figure 14) and geologic units in the main channel is necessary to determine when each channel ceased its fluvial activity. Elevation ranges for each anastomosing channel and the early stages of the main channel are shown in Table 9.

Table 9. Floor Elevation Ranges of Ladon Valles’s Anastomosing Channels. The depth range for the main channel was measured from the adjacent streamlined island ledges to C3c and C3c’ (Fig. 19), excluding the final main channel stage. Elevation range (estimated, in Approximate depth range Channel meters below zero datum) (meters) Main -1300 to -1700 900 – 1000

AC1 -1350 to -1850 300 – 500 AC2 -1200 to -2000 300 – 700 AC3 -1000 to -1350 400 – 500 AC4 -1300 to -1450 200 – 300

Figure 23. Crater densities and the associated age ranges for all four anastomosing channels. AC2 is considered slightly oversaturated due to its 0.25 – 0.50 bin datapoint (obscured by other datapoints) residing above, but close to, the saturation line.

Elevation ranges listed in Table 9 imply that significantly more downcutting took place in AC1 and AC2 than in AC3 and AC4. AC3, whose channel bed elevation range is at the highest elevation of the anastomosing channels, is the only one that has a profoundly oversaturated crater density (Fig. 23).

Additionally, AC3 is cross-cut by AC4 (Fig. 14), indicating the latter must be younger than the former. The anomalous elevation of AC3’s channel bed could be due to local preferential uplift. However, a preponderance of evidence suggests the final significant flow through AC3 occurred early in the Early Noachian and may have ceased penecontemporaneously with that of the second main channel flow, which is represented by profile C3a. The initial stages, however, through what are now AC3 and AC4 formed one channel without a streamlined island. This is evidenced by the fact that the eastern- most streamlined island (Fig. 17a) is at an elevation that is 300 – 600 m lower than the elevation of both the adjacent ledge of streamlined island that borders AC3 on the west, and the eastern ledge bordering AC4 on the east. Therefore, formation of AC4 began later than the other streamlined islands, the tops of which are at an elevation that is consistent with ledges that overlook their adjoining anastomosing channels.

Crater retention age ranges for AC1 and AC2 suggest the possibility that they were fluvially active at least through the entire Noachian Period. If the younger ends of the ranges are accurate, (3.1 and 3.5 Ga, respectively) AC2’s final stage would be penecontemporaneous with that of the main channel and AC1’s final stage would be considerably younger. It is worth mentioning that, since the area of the anastomosing channels is small and their respective crater retention age ranges are relatively large, confidence of the accuracy of the age ranges is low. However, a cursory look at each anastomosing channel’s crater density confirms the general determination that AC1 and

AC2 are significantly younger than AC3 and AC4.

In an effort to relate the timing of the flow represented by profile C3b, along with analysis of the crater density data, it is helpful to use a discharge and depth comparison between the main channel flows and those that formed the anastomosing channels (Table

10).

Table 10. Comparisons of Noachian Main Channel Discharge Estimates With Totals for Anastomosing Channels. All discharge estimates in this table were calculated using the friction factor formula for lower regime sand-dominated channel beds. The second and third columns each feature a main channel discharge. Each of the four right columns features a sum of anastomosing channel discharges. Q = discharge.

Main Channel Profiles Profiles A1a, Profiles A2a, Profiles A1a, C3a C3b C3c C3d B1a, D1a, E1a B2a, D2a, E2a B1a, E1a Q (m3s-1) 231.0x106 78.0x106 71.3x106 1.10x106 36.0x106 4.38x106 25.7x106

Depth (m) 191 150 216 22.9 204 92.7 149

Cross- 3.03x106 1.64x106 2.00x106 .0182x106 0.842 x106 0.729 x106 0.732 x106 sectional Area (m2)

Profile C3a’s (representing the main channel’s second flow) maximum discharge estimate is many times that of the sum of the estimates for the upstream anastomosing channel profiles, Ala, B1a, D1a and E1a, (upstream profiles) and the sum of the estimates for the downstream anastomosing channel profiles, A2a, B2a, D2a and E2a (downstream profiles). Profile C3b’s and C3c’s discharge estimates are each roughly twice the sum of the estimates for the upstream profiles, and many times the sum of the estimates for the downstream profiles. This comparison was also performed without D1a and D2a estimates included in the anastomosing channel discharge sums since it is a strong possibility that flow through AC3 ceased prior to that of the other anastomosing channels.

A depth comparison follows a similar pattern with the exception that C3a’s depth falls just short of that of the sum of the depths of the upstream profiles. The main channel profiles, C3a, C3b, and C3c, feature geometric dimensions that easily eclipse those of the sums of the upstream and downstream profiles.

Clearly the main channel was always the dominant channel in the Ladon Valles system. For all flooding events, it accommodated a volume of water that was greater than that which was contemporaneously flowing through the combined anastomosing channels when the flow represented by Profile C3a, which formed Ladon Valles 5 (Nlv5)

(Appendix A) 3.7 – 3.9 Ga, was active. The next two flows through the main channel were of much smaller magnitude than that of C3a, but still at least about twice that of the sum of the anastomosing channel’s discharge measurements and far greater when compared individually (Fig. 21 and Table 6). At widths of 15.9 and 10.1 km, for profiles

C3a and C3b, respectively, these main channel profiles are much wider than any of the

84 profiles of anastomosing channels, and their depths far are greater. This may be indicative of at least a comparable duration for the C3a and C3b flows.

C3c’s (representing the main channel’s fourth flow) discharge estimate suggests similar flow activity to the previous flow since the two discharges are fairly equal.

However, C3c’s depth and cross-sectional area are each ~25% greater than that of C3b’s depth. This indicates that abandonment of the anastomosing channels may well have begun sometime as the main channel’s fourth flow was occurring. The flow measured in

C3c, which formed Ladon Valles 7 (Nlv7) (Appendix A) (also 3.7 – 3.9 Ga (Fig. 18)), may have occurred when little or no water was flowing through the adjacent anastomosing channels. This does not suggest, however, that Ladon Valles’s volume of water had begun waning. Given the geometric comparison and the discharge of the two profiles, the fourth main channel flow was at least comparable to the third. Moreover, this is indicative that the source of the main channel’s fourth flow was likely the same as that for the previous flows through the main and anastomosing channels. The flow measured in profile C3d (the main channel’s fifth flow) was less by an order of magnitude than the summed discharges of the anastomosing channels (Table 10), indicating a waning flow volume. An age determination of the flow is hampered by the fact that the member it formed, the northern member of Ladon Valles 3 (Nlv3) (Appendix

A), was exhumed as determined by its aberrantly high crater density. However, elsewhere in the main channel, the floor unit Ladon Valles 10 (Nlv10) (Appendix A) is dated to 3.5 – 3.7 Ga. It is reasonable to assume this range as a tentative age range for the flows of C3d, and its downstream contemporary C4c.

It is notable that profile C2a yields an anomalously high discharge, is located upstream from profile C3d, and its measurement includes the floor of the main channel.

Its discharge that is two orders of magnitude greater than C3d’s seems to contradict

C3d’s discharge estimate since both profiles include a bottom depth that reaches the channel floor. However, the perfect U-shape of profile C2’s cross-section (Fig. 24) indicates that any lower level terraces that may have existed at one time were later removed. There is a similar discrepancy regarding the discharge estimate within C1a

Figure 24. Cross-section of Profile C2. Note the U-shape and that there is only one visible terrace. The profile line is shown in Figure 14. VE = 7X.

since its terrace tops, with the exception of that used in the measurement of C1a, also seem to have been destroyed. In this case, the culprit appears to be stream piracy, the

86 evidence of which can be seen in Figures 11 and 18. For these reasons, the discharge estimates of C1a and C2a are regarded with relatively low confidence.

Generally speaking, it is apparent that the majority of the flow through Ladon

Valles had occurred by 3.7 Ga near the beginning of the Late Noachian. There is so little chronological age separation between the Mid-Noachian geologic units of the main channel of Ladon Valles however, that it is difficult to date the individual stages to a resolution greater than 200 m.y.

5.4.2 Late Noachian Period (3.8 to 3.5 Ga)

The terraces formed by this fluvial activity indicate a more episodic pattern of erosion in the main channel in contrast to the fluvial activity that formed in the anastomosing channels of Ladon Outer Valleys (Nlov), each of which features no more than one terrace. Given the five terraces shown in Figure 17a, there were likely at least five different stages through the main channel. Formation ages do not perfectly conform to the main channel group’s stratigraphic sequence. For example, Ladon Valles 5 (Nlv5)

(Appendix A), which is slightly older than Ladon Valles 7 (Nlv7) (Appendix A), is one terrace above Nlv7. Nlv7, in turn, is two terraces above Nlv3 (Figs. 10, 11), which is significantly older. This is why exhumation of the northern member of Nlv3 seems a strong possibility, which makes it impossible to provide an accurate date (from crater counts) of when the flow that formed it occurred. While the crater retention age range of

3.5 – 3.7 Ga (Fig. 20 and Table 8) obtained for Ladon Valles 10 (Nlv10) (Appendix A) seems reliable, the discrepancy with Nlv3 would seem to impair efforts to constrain the final stages of flow through Ladon Valles.

However, crater retention dates of individual craters within the main channel (Fig.

20 and Table 8) provide the basis for key cross-cutting relationships with the surrounding

Ladon Valles strata. For instance, Gori Crater (Ngc) (Appendix A), boasts a relatively fresh and seemingly unmodified rim and ejecta that are bright in THEMIS Nighttime IR

(Table 4). Since its crater retention date range is 3.6 – 3.7 Ga (Fig. 20 and Table 8), this would suggest that flow ceased in the main channel and within Nlv10, south of Ngc midway through the Late Noachian. North of Ngc, however, Nlv10 was stripped due to downcutting through the surface, exposing Nlv3.

Ladon Valles Crater 2 (Hlc2) (Appendix A) is north of Nlv3, and marks the northern end of the northern Nlv10 member (Figs. 10, 11). Hlc2 also appears relatively unmodified based on its relatively high thermal inertia values (Table 4), making it unlikely that the crater was exposed to much flow. Unfortunately, its crater retention age

(2.8 – 3.7 Ga) is not well-constrained. There is, however, a cross-cutting relationship between Hlc2 and AC2 (within Nlov), which appears to incise the crater’s western ejecta.

This incision can be observed in Figure 10. Since the youngest end of the range of AC2 is 3.5 Ga, Hlc2 may well be of Late Noachian age, which is within the older portion of its crater retention date range listed in Figure 20 and Table 8. This is further evidence that

Nlv10 is at least 3.5 Ga since Hlc2 superimposes it. The same is true for Ladon Valles 9

(Nlv9) (Appendix A), which is also superimposed by Hlc2 (Fig. 10). Since the terrain north of Hlc2 is drastically different from Nlv10 it seems plausible that later main channel flows ceased at, or south of, the location of Hlc2. This could have been due to waning

88 water supply, or perhaps to backfill from previous flows raising the channel floor’s elevation, or a combination.

Ladon Valles Crater 1 (Hlc1) (Appendix A) obscures part of the extreme southern portion of Nlv2, which is also an exhumed formation, suggesting an age range greater than 3.2 - 3.5 Ga. Hlc1 has a particularly high thermal inertia (Table 4), suggesting a relatively unmodified history. The localized polygonal terrain surrounding the crater, however, indicates possible glacial activity occurred. If an ice sheet produced the polygonal terrain, it likely did so prior to Hlc1’s impact, based on its cross-cutting relationship between Hlc1 and the surrounding terrain. This is consistent with the assumption that Ladon Valles 2 (Nlv2) (Appendix A) is an exhumed formation.

Regarding the possibility of glaciation in Nlv2, it is notable that the longitudinal grooves, often seen as evidence associated with movement of an ice sheet, are not observed. An alternative to glaciation as a source of the polygonal terrain in Nlv2, is that its fractures could have formed due to local faulting. The extent to which Nlv2 continues north toward

Ladon Basin (Nlb) is another peculiarity since the sediment that would have been transported in the excavation of Nlv2’s surface is not observed anywhere nearby in Nlb.

However, THEMIS Nighttime IR, CTX visible data and MOLA elevation data (Fig. 25), show possible evidence for the extension of Nlv2 onto what was once likely southern

Ladon Basin (Nlb).

Figure 25. Possible evidence of extent of mouth of Ladon Valles. (a) THEMIS Nighttime TIR showing a distinctive bright band that seems to indicate the continuation of Ladon Valles. Location of Profile 1 (c) is marked with the white line. (b) Possible lobate deposits (arrows) indicating deposition from a current flowing north. Image data: CTX P16_007204_1631_XN_16S030W (c) Profile 1 showing the u-shape of an apparent streambed contained within Nlv2. Numbers on the x-axis represent MOLA cells.

If the data shown in Figure 25 resulted from Ladon Valles’ main channel cross- cutting Nlb, a maximum age of Late Noachian could be assigned to the final flow through

Nlv2. Note, however, that the contact delineating the mouth of the main channel from

Nlb is dashed since evidence for the northernmost contact presented in Figure 26 is not considered to be robust.

1’ 90

Nlv10, which incises Middle to Late Noachian Holden Basin (Nhb) to the east of

Holden Crater (Nhc) (Appendix A), is the lone indication of significant fluvial action in the Ladon study area south of Morava Vallis (Nmv) and Ladon Uplands (Nlu). The source of the flow that formed Nlv10 is an enigma since there is no evidence that water breached the eastern Holden Crater Rim (Nhcr) (Appendix A) and subsurface discharge in unlikely since Nhc’s water level did not reach the elevation of the western Nlv10 incisions. Additionally, secondary craters from the Holden Crater impact are observed 1 cross-cutting Ladon Valles (Mangold et al., 2012). Therefore, Grant and Parker (2002) may have slightly misestimated the timing involved in Ladon Valles’ final flooding event, since their estimate for Ladon Valles’s last flow was the Early Hesperian.

The timing of the formation of Ladon Valles presented in this research is consistent with previous work that has analyzed the entire ULM system. Irwin and Grant

(2009), for instance, assert that discharge was active through Uzboi, Ladon and Morava simultaneously. My age ranges for Morava indicate that it formed possibly as early as

Nlv5, Ladon Valles 6 (Nlv6) (Appendix A), and Nlv7 formed, and perhaps contemporaneously with Nlv9 (Nlv8 is not included in this list because it is composed of colluvium and eolian sediment and was not formed by a flow), and Nlv10. Uzboi Vallis’s last discharge occurred after the Holden Crater impact (Irwin and Grant, 2009).

However, as stated earlier, there is no strong evidence for a breach of Holden Crater.

Since Holden Crater is dated to the Late Noachian (this work and Scott and Tanaka,

1986) it seems reasonable to conclude that flow through Ladon Valles ceased before the start of the Hesperian Period.

Ladon Valles discharge estimates in this work are consistent with previous estimates of discharge upstream and downstream in the ULM system. Although there is no calculated discharge for Uzboi Vallis, Grant et al. (2011a) estimated its final flow to have produced a discharge that was anywhere from 105 to 106 m3s-1 based on channel floor landforms. If it was on the order of 106 m3s-1, it would have been of the same order of magnitude as the maximum estimate of Ladon Valles’s final flow as represented in profile C3d, and would be similarly consistent with the timing of Mars’s waning water supply. Grant and Parker (2002) estimated Morava Vallis’s discharge at approximately

0.36x106 m3s-1 and 1.6x106 m3s-1 for two separate profiles, respectively. Along with occurring contemporaneously with Ladon Valles’s final flow, the higher of the two discharges value is of the same order of magnitude.

Summary

Evidence from Ladon Valles’s landforms, dimensions and discharge estimates indicates that it is an outflow system and served as a fluvial connection between Holden

Basin and Ladon Basin during the Noachian Period. Ladon Valles formed as water flowed from Uzboi Vallis through Holden Basin. Ladon Basin filled, and water eventually overtopped its northeastern corner to form Morava Vallis. While the discharge to form Uzboi and Morava Valles may have been high enough to classify them as outflow channels, flows through Ladon Valles must have been particularly intense given the many anastomosing channels, and relatively persistent through the Noachian as evidenced by the main channel’s five terraces. Flow magnitude waned in the Late

Noachian to a level that is typical of valley networks. However, as floods carved Ladon

Valles channels with discharge magnitudes approaching that of Ares Vallis, it would have been an integral link in what may have been the solar system’s longest fluvial system. It is a strong possibility that the water volume required to supply the flow path extending from the south polar region to Chryse Planitia was present, at least in the

Ladon study area.

Constraints concerning fluvial activity in the Ladon study area are consistent with the general hypothesis on Mars’s paleoclimate that the planet was relatively wet through the Early-to-Mid-Noachian Epochs, and became semi-arid to arid in the Late Noachian /

Early Hesperian. Based on the findings in this study, the water supply started waning in the Late Noachian. Fluvial activity likely came to an end in the Late Noachian ~3.5 to

3.6 Ga.

References

Baker, V. R., Carr, M. H., Gullick, V. C., Williams, C. R., and Marley, M. S.,1992. Channels and valley networks, in Mars, ed. Kieffer, H. H., Jakosky, B. M., Snyder, C. W., Matthews, M. S., The University of Arizona Press, p. 493-522.

Baker, V. R., 2001, Water and the martian landscape, Nature, v. 212, p. 228-236.

Baker, V. R., 2009, The Channeled Scabland: A Retrospective, Annu. Rev. Earth Planet. Sci. 2009., v. 37, p. 393–411, doi:10.1146/annurev.earth.061008.134726.

Barlow, N. G., 2008, Mars: An Introduction to its Interior, Surface and Atmosphere, Cambridge Planetary Science, pp. 264.

Barnhart, C. J., Howard, A. D., and Moore, J. M., 2008, Long-term precipitation and late- stage valley network formation: Landform simulations of Parana Basin, Mars, Journal of Geophysical Research, v. 114, E01003, doi:10.1029/2008JE003122.

Boothroyd, J. C., 1983, Fluvial drainage systems in the Ladon Basin area: Margaritifer Sinus area, Mars, Geological Society of America Abstract Programs, 15, 530.

Bridges, N. T., Seelos, F. P., Hook, S. J., Baldridge, A. M., and Thomson, B. J., 2010, Simulating CRISM and HiRISE data using airborne hyperspectral imagery; lessons learned from ground truth, in Proceedings, 41st Lunar and Planetary Science Conference; Abstract 1887.

Burr, D. M., McEwen, A. S., and Sakimoto, S. E. H., 2002a, Recent aqueous floods from the Cerberus Fossae, Geophysical Research Letters, v. 29, no. 1, doi:10.1029/2001GL013345.

Burr, D. M., Grier, J. A., McEwen, A. S., and Keszthelyi, L. P, 2002b, Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant, deep groundwater on Mars, Icarus, v. 155, p. 53 – 73.

Burr, D. M., Carling, P. A., Beyer, R. A., and Lancaster, N., 2004, Flood-formed dunes in Athabasca Valles, Mars: morphology, modeling, and implications, Icarus, v. 171, p. 68 – 83.

Carling, P. A., Burr, D. M., Johnsen, T. F., Brennan, T. A., 2009a, A review of open- channel megaflood depositional landforms on Earth and Mars, in Megaflooding on Earth and Mars, ed. Burr, D. M., Carling P. A., and Baker, V. R., Cambridge, p. 33 - 49.

Carling, P. A., Herget, J., Lanz, J. K., Richardson, K., Pacifici, A., 2009b, Channel-scale erosional bedforms in bedrock and in loose granular material: character, processes and implications, in Megaflooding on Earth and Mars, ed. Burr, D. M., Carling P. A., and Baker, V. R., Cambridge, p. 13 – 32.

Carr, M., 2006, The Surface of Mars, Cambridge Planetary Science, 307 p.

Carr, M., and Head, J. W., 2010, Geologic History of Mars, Earth and Planetary Science Letters, v. 294, p. 185-203.

Christensen, P. R., Jakosky, B. M., Kieffer, H. H., Malin, M. C., McSween Jr., H. Y., Nealson, K., Mehall, G. L., Silverman, S. H., Ferry, S., Caplinger, M., and Ravine, M., 2004, The Thermal Emission Imaging System (THEMIS) for the Mars 2001 Odyssey Mission, Space Science Reviews, v. 110, p. 85—130.

Coleman, N. M., Dinwiddie, C. L., and Baker, V. R., 2007, Evidence that floodwaters filled and overflowed Capri Chasma, Mars, Geophysical Research Letters, v. 34, L07201, p. 1-5, doi:10.1029/2006GL028872.

Craddock, R. A., and Howard, A. D., 2002, The case for rainfall on a warm, wet early Mars, Journal of Geophysical Research, v. 107, no. E11, 5111, doi:10.1029/2001JE001505.

De Hon, R. A., and Pani, E. A, 1993, Duration and raters of discharge: Maja Valles, Mars, Journal of Geophysical Research, v. 98, E5, p. 9128 – 9138.

Fortezzo, C. M., Williams, K. K., and Grant J. A., 2009, Mapping Margaritifer Terra: MTMS -15017, -20002, -20007, 020017, 020022, 025002, 025007.

Frey, H., Sakimoto, S. E. H., Roark, J. H., 1999, Discovery of a 450-diameter, multi-ring basin on Mars through analysis of MOLA topographic data, Geophysical Research Letters, v. 26, no. 12, p. 1657-1660.

Grant, J. A., and Parker, T. J., 2002, Drainage evolution in the Margaritifer Sinus region, Mars, Journal of Geophysical Research, v. 107, no. E9, 5066, doi:10.1029/2001JE001678.

Grant, J. A., Irwin, R. P., Grotzinger, J. P., Milliken, R. E., Tornabene, L. L., McEwen, A. S., Weitz, C. M., Squyres, S. W., Glotch, T. D., and Thomson, B. J., 2008, HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars, Geology, v. 36, no. 3, p. 195-198.

Grant, J. A., Irwin III, R. P., and Wilson, S. A., 2009a, Geologic mapping of Holden Crater and the Uzboi-Ladon-Morava outflow system, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution.

Grant, J. A., Wilson, S. A., Fortezzo, C. M., and Clark, D. A., 2009b, Geologic Map of MTM -20012 and -25012 Quadrangles, Margaritifer Terra Region of Mars, Scientific Investigations Map 3041.

Grant, J. A., Irwin, R. P. III, Wilson, S. A., Buczkowski, D., Siebach, K., 2011a, A lake in Uzboi Vallis and implications for Late Noachian–Early Hesperian climate on Mars, Icarus, v. 212, p. 110-122.

Grant, J. A., Golombek, M. P., Grotzinger, J. P., Wilson, S. A., Watkins, M. M., Vasavada, A. R., Griffes, J. L., Parker, T. J., 2011b, The science process for selecting the landing site for the 2011 Mars Science Laboratory, Planetary and Space Science, v. 59, p. 1114-1127.

Hauber, E., van Gasselt, S., Chapman, M. G., and Neukum, G., 2008, Geomorphic evidence for former lobate debris aprons at low latitudes on mars: Indicators of the Martian paleoclimate, Journal of Geophysical Research, v. 113, E02007, doi:101029/2007JE002897.

Hartmann, W.K., 2005. Martian Cratering 8: Isochron refinement and the chronology of Mars. Icarus 174, 294–320. http://dx.doi.org/10.1016/j.icarus.2004.11.023.

Head, J. W., Wilson, L., and Mitchell, K. L., 2003, Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release, Geophysical Research Letters, v. 30, no. 111, 1577, p. 1 – 4, doi:10.1029/2003gL017135.

Hoke, M. R. T., Hynek, B. M., and Tucker, G. E., 2011, Formation timescales of large Martian valley networks, Earth and Planetary Science Letters, v. 312, p. 1-12.

Howard, A.D., 1988, Groundwater sapping experiments and modeling: in Sapping Features of the Colorado Plateau, ed. A.D. Howard, R. C. Kochel, and H. R. Holt, NASA SP-491, p. 71-83.

Ivanov, B. A., 2001, Mars/Moon cratering rate estimates. Space Science Review, v. 96, p. 87-104.

Kleinhans, M. G., 2005, Flow discharge and sediment transport models for estimating a minimum timescale of hydrological activity and channel and delta formation on Mars, Journal of Geophysical Research, v. 110, E12003, doi:10.1029/2005JE002521. Water Flows in Martian Outflow Komar, P. D., 1979, Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on Earth, Icarus, v. 37, p. 156 – 181.

Komatsu, G., and Baker, V. R., 1997, Paleohydrology and flood geomorphology of Ares Vallis, Journal of Geophysical Research, v. 102, E2, p. 4151 – 4160.

Leask, H. J., Wilson, L., Mitchell, K. L, 2006, Formation of Ravi Vallis outflow channel, Mars: Morphological development, water discharge, and duration estimates, Journal of Geophysical Research, v. 111, E08070, doi:10.1029/2005JE002550.

Lillis, R. J., Frey, H. V., Manga, M., Mitchell, D. L., Lin, R. P., Acuñ, M. H., Bougher, S. W., 2008, An improved crustal magnetic field map of Mars from electron reflectometry: Highland volcano magmatic history and the end of the martian dynamo, Icarus, v. 194, p. 575-596.

Lucchitta, B. A., 2001, Antarctic Ice Streams and Outflow Channels on Mars, Journal of Geophysical Research Letters, v. 28, no. 3, p. 403 – 406.

Mangold, N., Kite, E. S., Kleinhans, M. G., Newsom, H., Ansan, V., Hauber, E., Kraal, E., Quantin, C., and Tanaka, K., 2012, The origin and timing of fluvial activity at Eberswalde crater, mars, Icarus, v. 220, p. 530-551.

Malin, M. C., and Edgett, K. S., 2000, Evidence for recent groundwater seepage and surface runoff on Mars, Science, v. 288, 2330.

Malin, M. C., Bell, J. F. III, Cantor, B. A., Caplinger, M. A., Calvin, W. M., Clancy, R. T., Edgett, K. S., Edwards, L., Haberle, R. M., James, P. B., Lee, S. W., Ravine, M. A., Thomas, P. C., Wolff, M. J., 2007, Context Camera Investigation on board the Mars Reconnaissance Orbiter, Journal of Geophysical Research, v. 112, E05S04, doi:10.1029/2006JE002808.

McEwen, A. S., Eliason, E. M., Bergstrom, J. M., Bridges, N. T., Hansen, C. J., Delamere, A. W., Grant, J. A., Gulick, V. C., Herkenhoff, K. E., Keszthelyi, L., Kirk, R.

L., Mellon, M. T., Squyres, S. W., Thomas, N., Weitz, C. M., 2007, Mars Reconnaissance Orbiter’s High Resolution Imaging Science Experiment (HiRISE), Journal of Geophysical Research, v. 112, E05S02, doi:10.1029/2005JE002605.

Mellon, M.T., Jakosky, B. J., Kieffer, H. H., and Christensen, P. R., 2000, High- Resolution Thermal Inertia Mapping from the Mars Global Surveyor Thermal Emission Spectrometer, Icarus, v. 148, p. 437 – 455, doi:10.1006/icar.2000.6503.

Mest, S. C., Crown, D. A., Craddock, R. A., Zimbelman, J. R., 1998, Topographic characteristics of outflow channels in the martian southern highlands, Lunar and planetary science XXIX; Proceedings of the 29th Lunar and Planetary Science Conference.

Milliken, R. E., and Bish, D. L., 2010, Sources and sinks of clay minerals on Mars, Philosophical Magazine, v. 90 no. 17/18, p. 2293-2308, doi: 10.1080/14786430903575132.

O’Connor, J. E., and Baker, V. R., 1992, Magnitudes and implications of peak discharges from glacial Lake Missoula, Geological Society of America Bulletin, v. 104, no. 3, p. 267 – 279.

Ori, G. G., and Mosangini, C., 1998, Complex depositional systems in Hydraotes Chaos, Mars: and example of sedimentary process interactions in the Martian hydrological cycle, Journal of Geophysical Research, v. 103, E10, p. 22,713 – 22,723.

Pacifici, A., Komatsu, G., Pondrelli, M., 2009, Geological evolution of Ares Vallis on Mars: Formation by multiple events of catastrophic flooding, glacial and periglacial processes, Icarus v. 202 p. 60–77, DOI:10.1016/J.ICARUS.2009.02.029.

Parker, T. J., 1985, Geomorphology and geology of the southwestern Margaritifer Sinus- Northern Argyre region of Mars, Master’s thesis, California State University, Los Angeles.

Pelkey, S. M., Jakosky, B. M., and Mellon, M. T., 2001, Thermal inertia of crater-related wind streaks on Mars, Journal of Geophysical Research, v. 106, no. E10, p. 23909 – 23920.

Robinson, M. S., and Tanaka, K. L, 1990, Magnitude of a catastrophic flood event at Kasei Valles, Mars, Geology, v. 18, p. 902 – 905.

Rotto, S., and Tanaka, K. L., 1995, Geologic geomorphic map of the Chryse Planitia region of Mars, 1:5M, U. S. Geological Survey Misc. Invest. Ser. Map I-2441.

Scott, D.H., Tanaka, K.L, Greely, Ronald, and Guest, J.H., 1987, Geologic Maps of the Western Equatorial, Eastern Equatorial, and Polar Regions of Mars, United States Geological Survey Atlas of Mars, 1:15,000,000 Geologic Series, Maps I-1802-A, I-1802- B, and I-1802-C.

Squyres, S., 1989, Urey Prize Lecture – Water on Mars, Icarus, v. 79, p. 229-288.

Squyres, S.W., and Kasting, J. F., 1994, How warm and how wet?, Science, v. 265, no. 5173, p. 744—749.

Strangeways, I., 2000, Measuring the Natural Environment, Cambridge University Press, 365 p.

Wilson, L., Gil, J. G., Head, J. W., Mitchell, K. L., 2004, Mars outflow channels: A reappraisal of the estimation of water flow velocities from water depths, regional slopes, and channel floor properties, Journal of Geophysical Research, v. 109, E09003, doi:10.1029/2004JE002281.

Wilson, L., Bargery, A. S., and Burr, D. M., 2009, Dynamics of fluid flow in Martian outflow channels, in Megaflooding on Earth and Mars, ed. Burr, D. M., Carling P. A., and Baker, V. R., Cambridge, p. 290 - 311.

Appendix A, A.1. Images Corresponding to Unit Descriptions in Table 3

North is up in all images.

Holden Crater Rim. (Hhcr) CTX images P16_007270_1546_XI_25S033W, G03_019335_1542_XN_25S033W (NASA/JPL/ASU)

Holden Crater (Hcr). CTX images: B02_010408_1548_XI_25S033W, G03_019335_1542_XN_25S033W, G04_019757_1542_XN_25S033W , B22_018333_1548_XI_25S033W (NASA/JPL/ASU)

100

Shambe/Singli Craters (Nsc). CTX images: D05_029238_1595_XN_20S030W, P05_003090_1578_XI_22S030W, P02_001956_1601_XI_19S030W , P15_007059_1606_XN_19S031W B05_011621_1592_XI_20S030W (NASA/JPL/ASU)

Margaritifer North (Nmn). CTX images: G14_023871_1648_XN_15S032W, B17016289_15S032W (NASA/JPL/ASU)

101

Morava Vallis (Nmv). CTX images: P13_006149_1635_XN_16S025W, P17_007863_1630_XN_17S025W (NASA/JPL/ASU)

102

Margaritifer Southeast (Nme). CTX images: G16_024596_1573_XN_22S024W, G18_025163_1588_XN_21S024W P12_005582_1561_XI_23S024W, G18_025374_1564_XN_23S024W (NASA/JPL/ASU)

Ladon Basin (Nlb). CTX images: P18_008140_1623_XI_17S029W, P18_007995_1635_XN_16S030W, P16_007349_1637_XN_16S030W (NASA/JPL/ASU)

103

Ladon Uplands (Nlu). P16_007349_1637_XN_16S030W, P20_008786_1639_XN_16S030W and P16_007204_1631_XN_16S030W

Ladon Outer Valleys (Nlov). CTX images: P12_005569_1581_XI_21S029W, P02_001890_1572_XN_22S028W P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

104

Holden Basin (Nhb). CTX images: G01_018478_1557_XI_24S032W, B05_011687_1567_XI_23S032W B01_010197_1545_XI_25S032W (NASA/JPL/ASU)

Nlhp Arda Valles (Nav). CTX images: P15_007059_1606_XN_19S031W, P13_006202_1607_XN_19S032W, D07_030082_1611_XN_18S033W, P12_005635_1605_XN_19S031W, D05_029304_1599_XN_20S032W, D04_028882_1597_XN_20S032W, B19_017067_1596_XN_20S032W (NASA/JPL/ASU)

105

Margaritifer East (Nme). CTX images: P13_006215_1601_XN_19S027W, G03_019348_1574_XN_22S027W (NASA/JPL/ASU)

Ladon Valles Highlands (Nlvh). CTX images: P20_008852_1550_XN_25S031W, B05_011687_1567_XI_23S032W, B01_010197_1545_XI_25S032W (NASA/JPL/ASU)

106

Ladon High Plains (Nlhp). CTX images: G14_023673_1573_XN_22S025W , G19_025796_1572_XN_22S025W, G23_027207_1562_XN_23S025W (NASA/JPL/ASU)

Ladon Hummocks (Nlh). CTX images: P16_007428_1571_XN_22S026W, G03_019348_1574_XN_22S027W, B11_013757_1589_XN_21S027W, P15_006927_1583_XN_21S027W (NASA/JPL/ASU)

107

Rim Material (Nrm). CTX images: P18_007916_1636_XN_16S033W, B19_016922_1628_XN_17S033W, D08_030161_1611_XN_18S033W, B20_017489_1635_XN_16S033W (NASA/JPL/ASU )

108

A.2. Images Corresponding to Unit Descriptions in Table 4

Ladon Valles Crater 2 (Hlc2). P15_006993_1576_XN_22S029W, P11_005358_1608_XN_19S029W (NASA/JPL/ASU)

Ladon Valles Crater 1 (Hlc1). P02_001890_1572_XN_22S028W, P15_006993_1576_XN_22S029W, P11_005358_1608_XN_19S029W (NASA/JPL/ASU)

109

Eolian (Nlve). B03_010777_1587_XN_21S028W, P15_006993_1576_XN_22S029W, P02_001890_1572_XN_22S028W (NASA/JPL/ASU )

110

Ladon Valles 10 Nlv10. B03_010777_1587_XN_21S028W, P15_006993_1576_XN_22S029W, P02_001890_1572_XN_22S028W (NASA/JPL/ASU)

Ladon Valles 9 Nlv9. P02_001890_1572_XN_22S028W, P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

111

Gori Crater Ngc. P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

Ladon Valles 8 Nlv8. P02_001890_1572_XN_22S028W, P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

112

Ladon Valles 7 Nlv7. B03_010777_1587_XN_21S028W, P15_006993_1576_XN_22S029W, P02_001890_1572_XN_22S028W (NASA/JPL/ASU )

Ladon Valles 6 (Nlv6). P13_006136_1582_XN_21S029W, P12_005569_1581_XI_21S029W, P15_006993_1576_XN_22S029W (NASA/JPL/ASU)

113

Ladon Valles 5 (Nlv5). B03_010777_1587_XN_21S028W, P15_006993_1576_XN_22S029W P02_001890_1572_XN_22S028W (NASA/JPL/ASU )

114

Ladon Valles 4 (Nlv4). P11_005213_1549_XN_25S029W B07_012544_1540_XN_26S029W, P13_006136_1582_XN_21S029W (NASA/JPL/ASU)

115

Ladon Valles 3 (Nlv3). P02_001890_1572_XN_22S028W (NASA/JPL/ASU)

Ladon Valles 2 (Nlv2). P17_007850_1583_XN_21S030W, P05_003090_1578_XI_22S030W, G06_020759_1595_XN_20S030W, P13_006136_1582_XN_21S029W, P15_006993_1576_XN_22S029W, P12_005569_1581_XI_21S029W (NASA/JPL/ASU)

116

Ladon Valles 1 (Nlv1). P02_001890_1572_XN_22S028W, P15_006993_1576_XN_22S029W, P12_005569_1581_XI_21S029W (NASA/JPL/ASU )

117

Appendix B. Plan Views of Cross-sectional Profiles in Figure 15

118

Plan views of profiles displaying u-shaped outflow channels and valley networks. Aspect ratio was measured along profile lines LV2, AV and ArV. CTX images: LV1 - P13_006136_1582_XN_21S029W, LV2 - P02_001890_1572_XN_22S028W, AV - P18_008021_1875_XI_07N023W, P14_006518_1903_XN_10N023W, DV - P16_007389_1687_XI_11S043W, B09_013151_1696_XN_10S043W, ArV - B19_017067_1596_XN_20S032W, EV - B09_013083_1674_XN_12S346W, NV - P17_007534_1517_XN_28S040W

! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

Thesis and Dissertation Services ! !