Tephrostratigraphy in the Woranso-Mille Study Area

TEPHROSTRATIGRAPHY IN THE WORANSO-MILLE STUDY AREA

IN THE AFAR REGION OF ETHIOPIA

JOSHUA D. ANGELINI

Submitted in partial fulfillment of the requirements

For the Degree of Master of Science

Thesis Advisor: Dr. Beverly Saylor

Department of Geological Sciences

CASE WESTERN RESERVE UNIVERSITY

May 2009 CASE WESTERN RESERVE UNIVERSITY

SCHOOL OF GRADUATE STUDIES

We hereby approve the thesis/dissertation of

______

candidate for the ______degree *.

(signed)______(chair of the committee)

______

(date) ______

*We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents Page Introduction………………………………………………………………………...... 8 Geologic and Paleontologic Setting of the Western Mille area………………….……... 11 Stratigraphy and Structure of the Western Mille area.…………………………………. 14 Waki-Mille Confluence…………………………………………………….…… 17 Mesgid Dora………………………………………………………………...….. 18 Makah Mera…………………………………………………………………….. 20 Aralee Issie……………………………………………………………………… 20 Korsi Dora…………………………………………………...…………………. 21 Correlations…………………………………………………...………………... 23 Field Methods………………………...………………………………………………… 26 Sample Preparation…………………………………………………………………...… 29 Microprobe Analysis……...……………………………………………………….……. 29 Data Analysis and Correlations……………………………………………………...…. 31 Time-dependent Intensity Variation: Corrections…..……………………………….…. 34 Geochemical Results…………..…………………………………………………….….. 37 Intra-basinal Correlations…………………………………………………………….…. 41 Inter-basinal Correlations…………………………………………………………...…... 50 Implications…………. …………………...………………………………………….…. 57 Future Work………………………...…………………………………………………... 62 Conclusion……………………………………………………………………………… 63 Appendices Appendix 1. Mesgid Dora Sections…………………………………………….. 64 Appendix 2. Sample Locations: GPS Coordinates……………………………... 65 Appendix 3. Corrected EMPA Data………………………...………………….. 66 References……………………………………………………………………………… 74

List of Figures

Figure page

1 Location map of WORMIL and other project areas…………....………….…… 9

2 Composite regional stratigraphic column……………………………………… 14

3 Detail map of the Western Mille area………………………………………….. 16

4 Stratigraphic sections from the Waki-Mille confluence and Mesgid Dora…..... 19

5 Photograph of a tuffaceous sandstone channel cutting through the Basalt-Rhyolite

tuff at Mesgid Dora…………………………………………………………..... 19

6 Photograph of ripple cross-stratification and planar laminations in the Kilaytoli

tuff at Korsi Dora……………………………………………………………… 22

7A Preliminary correlation of stratigraphy in the Western Mille area……..….….. 25

7B Revised correlation of stratigraphy in the Western Mille area……….…..…… 25

8 Stratigraphic locations of analyzed samples……………………....…………... 28

9 Example of linear and exponential fits to time-dependent Oxygen data…...... 36

10 Example of linear and exponential fits for time-dependent Sodium data……... 37

11 Example of linear fit for Iron data………………………………...…….…...... 37

12 Plot of Al2O3 v. Fe2O3 for all WORMIL samples……………………….……. 39

13 Plot of Al2O3 v. Fe2O3 for samples of the Kilaytoli tuff…………………….… 40

14 Plot of TiO2 v. MnO for both modes of the Kilaytoli tuff………………….…. 42

15 MgO v. CaO for all WORMIL tephra samples…..………………………….… 43

16 Fe2O3 v. SiO2 for all WORMIL tephra samples...…………………………...... 43

17 Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples

of the Kilaytoli and Waki tuffs…………………………………………...……. 45 3

18 Plot of O v. K2O for the Mille tuff and possible correlates…………....…….… 46

19A Plot of Al2O3 v. Fe2O3 for samples of the Mesgid Dora and Mille tuffs….….... 47

19B Plot of MgO v. CaO for samples of the Mesgid Dora and Mille tuffs……....… 47

20 Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples

of pumice-free and pumice-rich tuffs….………………………………………. 48

21 Illustration of positive chemical correlations………………………………….. 49

22 Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples

of the Kilaytoli tuff, average values for samples of the Lokochot tuff ….……. 53

23 Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples

of the Waki tuff, average values for samples of the Lomogol………………… 54

24 Plot of Fe2O3 v. Al2O3 for WORMIL tephra samples, average values for tephra

known elsewhere in the region………………………………………….….…. 57

25 Distribution of the Kilaytoli/Lokochot and Crystal tuffs…………...……….... 59

26 Schematic diagram of distribution of pyroclastic material…………………….60

List of Tables

Table page

1 Crystals, standards and count times for electron microprobe analysis………… 31

2 Comparison of different fits to time-dependent data………………………...... 36

3 Similarity coefficients for intra-basinal tephra comparisons………....………... 38

4 Similarity coefficients for inter-basinal tephra comparisons…………………... 51

5 Geochemical composition of Lokochot tuff and Kilaytoli tuff samples………. 52

Acknowledgements

Sincere thanks are due to my advisor, Beverly Saylor; Ralph Harvey and Peter

McCall, the other members of my committee; Yohannes Haile-Selassie, the director of the Woranso-Mille Paleontological Research Project; Stephanie Melillo for her Ethiopian and GIS expertise; all of the other members of the WORMIL team; John Fournelle of the

University of Wisconsin electron microprobe lab; my fellow graduate students for their suggestions and revisions throughout the thesis-writing process; and my friends and family, for their constant support and occasional, much-needed distractions.

Tephrostratigraphy in the Woranso-Mille study area

in the Afar region of Ethiopia

Abstract

JOSHUA D. ANGELINI

In the Woranso-Mille project area, near the western margin of the Afar depression

of Ethiopia, researchers find some of the few known fossiliferous sediments from ~3.5-

3.8 Ma – a transition period between hominid species – making paleontological finds crucial for filling in a gap in human evolution. Using microprobe analysis of major

elements in individual glass shards I have distinguished between tephra layers in the

Western Mille area. These include pumice-rich lapillistones and pumice-free tuffs, which

I have geochemically correlated between sites, confirming the correlation of the local

stratigraphy. I tested correlations of the fine-grained tuffs with widespread tuffs of similar

age in east Africa. The Kilaytoli tuff overlaps in age with and correlates geochemically

with the Lokochot tuff, found in the Turkana basin and deep sea cores in the region, and

may also correlate with the Crystal tuff, exposed ~500 km south of the Woranso-Mille

area. Additionally, the fine-grained Waki tuff is geochemically permissive of correlation

with the Lomogol tuff, often found along with the Lokochot.

Introduction

For the past several decades, the Afar region of Ethiopia has been known to hold a

wealth of information about the early stages of the evolution of our species. The fossil

remains of hominids – pre-human ancestors – have been found in this region and other parts of eastern Africa since the 1970s. The number of finds at well-researched locations has tapered off, but new locations have been discovered, and the remains that have been uncovered at these sites have filled in some of the gaps in our knowledge of human evolution. One such new area is the Woranso-Mille (WORMIL) study area, which has

only recently become the locus of active research (Haile-Selassie et al., 2007).

The Woranso-Mille Paleontological Research Project is one of the

paleoanthropological projects currently active in the Afar region, through which

researchers in the fields of geology, paleontology and anthropology work together to

discover the chronological, environmental and biological constraints and circumstances

surrounding the evolution of our species and its forebears. Led by Dr. Yohannes Haile-

Selassie of the Cleveland Museum of Natural History, the project has been active in the

region since 2003. The WORMIL study area is located in the central Afar region of

Ethiopia, approximately 360 km northeast of the Ethiopian capital, Addis Ababa (Haile-

Selassie et al., 2007), just north and west of the well-established fossiliferous areas of

Hadar, Gona, the Middle Awash Valley and Dikika (Figure 1). Located within the central

Afar rift valley of the Main Ethiopian Rift system, the study area lies near the western

margin of the Afar Depression (Figure 1).

Figure 1. Location of the Main Ethiopian rift, the WORMIL Paleontological Research Project (red rectangle) and other paleoanthropological research project areas in the vicinity: Gona, Hadar, Middle Awash, Dikika, Turkana.

Thus far, geologic and paleontologic work by the WORMIL project team has

focused on a small region, about 6 km by 6 km, in the north central part of the WORMIL

project area. This initial study area, which from here on will be referred to as the Western

Mille area, contains exposures of volcaniclastic-rich alluvial strata composed of

interbedded volcanic tephra and tuffaceous conglomerate, sandstone and mudstone,

which, based on biostratigraphic evidence and radiometric dates, range in age from ~3.5-

3.8 Million years (Ma). These are some of the only known fossiliferous strata from this

period of time (Haile-Selassie et al., 2007), during which the hominid species

Australopithecus anamensis (3.9-4.2 Ma) appears to have given rise to Australopithecus

afarensis (3.0-3.6 Ma) (White et al., 2006). This crucial transition has not been

extensively studied due to the lack of abundant remains from the time, but with continued

research in the Woranso-Mille study area, this transition will become increasingly well

understood.

An understanding of the geological provenance from which fossils are collected is

crucial for correctly interpreting changes in fossil assemblages over time, for the

following reasons. First, the age of the fossils is a necessary piece of information.

Second, in some cases it is important to know the relative ages of fossils at a finer

resolution than is achievable by radiometric dating, so a comprehensive understanding of the stratigraphic framework is advantageous. Finally, an understanding of the environmental context for fossil assemblages is essential to paleontological research. Not only is this important for an understanding of local depositional environments and their relation to taphonomical processes, but also in terms of regional climatic and tectonic changes, and their relation to macro-evolutionary trends, as evidenced in changes in fossil populations over time.

Each of the objectives mentioned above requires accurate correlation of stratigraphic layers across discontinuous and structurally faulted exposures. In order to constrain the absolute and relative ages of fossil layers, we have to be able to correlate radiometrically dated volcanic layers to undated fossiliferous beds and exposures. Since interpretations of depositional environments are based on the vertical and lateral distribution of sedimentary facies, as well as their relation to other paleogeographic features, such as active faults or volcanic centers, they are similarly reliant on correlation of stratigraphic layers.

In the case at hand, the presence of numerous volcanic tephra layers is ideal, as they provide outstanding marker horizons for correlating strata. Each tephra layer

delineates a time horizon, meaning that, though it may have been deposited over days or

weeks, or even as long as a year, within a geological context the deposition of a tephra

can be considered instantaneous. Thus, all sediments below a tephra layer will be older

than those above. In addition, tephra can be distinctive in terms of physical characteristics

and chemical compositions such that they can be uniquely identified and correlated

within a basin, and, for some, even over great distances – up to thousands of kilometers.

The objective of this thesis is to test hypotheses about and place constraints on

stratigraphic correlations, using major and minor element chemistry of volcanic tephra

layers in the WORMIL area. I describe the geologic and stratigraphic setting of the area,

and discuss the specific correlation hypotheses that have been proposed for the local

strata. Then I present the geochemical methods and data analysis techniques I have

employed. Finally, I describe the results of these analyses and the resultant correlations –

both intra-basinal and extra-basinal – and their implications for current and future work

in the area.

Geologic and Paleontologic Setting of the Western Mille Area

The WORMIL Paleontological Research Project, including the Western Mille

area is located within the central Afar rift valley of the Main Ethiopian rift system. The

study area lies near the western margin of the Afar Depression (Figure 1). The Main

Ethiopian Rift (MER) makes up one third of a rift-rift-rift triple junction, of which the

other two arms are the Gulf of Aden and the Red Sea. The MER appears to have been the

last arm of the junction to commence extension, which began ca. 11 Ma, approximately

20 My after flood basaltic magmatism began in the region (Wolfenden et al., 2004). The 11

rifting of the MER created rapidly subsiding basins, including grabens and half-grabens,

in which rapid accumulation of fluvial, deltaic and lacustrine sediments as well as

volcanic ejecta layers allowed for the quick burial and preservation of biological remains

(WoldeGabriel et al., 2000). Among the fossil remains preserved in sedimentary layers of

the Afar are Miocene- to Pleistocene-aged hominid populations which once lived in the

area, and have made this one of the most prolific paleoanthropological research areas in

the world today. 40Ar/39Ar dating of phenocrysts in interbedded volcanic tephras or the

groundmass in basaltic layers places absolute age constraints on the rock layers in which

hominid fossils and other associated fossil assemblages are preserved. Geochemical

correlation of tephra layers of east Africa and deep sea cores of the Gulf of Aden and the

Arabian Sea tie the terrestrial record of environmental change and biological evolution to the high resolution deep sea record of glacial-interglacial cycles (deMenocal and Brown,

1999; Brown et al., 1992; Feakins et al., 2007).

Paleoanthropological research in the Ethiopian rift system has been active since

the 1970s, when the International Afar Research Expedition discovered “Lucy”, a 40%

complete skeleton of an adult, female Australopithecus afarensis at Hadar (Johanson et

al., 1978). Since then, several additional research areas have been designated and

investigated, with a different team of scientists working in each of the areas. Many of

these research project areas are adjacent to one another (Figure 1), as fossiliferous strata

have been found to be widespread in the Afar. Despite the relatively dense coverage of

the area by research permits, there remain vast expanses of the region that have yet to be

thoroughly investigated. For example, the WORMIL area shares a border, the Mille-Bati

Road, with another research area known as Gona, directly to the south. Despite the

seeming continuity between the areas, we have yet to connect the two stratigraphically,

due to the vastness (>250 km2) and geological complexity of the areas in question. The

Western Mille area, where most of the geological and paleontological work has focused

so far, is in the northern part of the WORMIL area, more than 40 km from the border the

WORMIL project area shares with Gona.

Major Miocene to Pliocene geologic formations recognized in the

paleoanthropological research areas of the Afar include the Adu Asa, Sagantole, Hadar,

and Busidima formations (Figure 2). The Adu Asa Formation, exposed at Middle Awash

and Gona, consists of interlayered sedimentary deposits and lava flows and contains

fossils of Ardipithecus, the oldest yet recognized hominid genus, which date from 5.2 to

5.7 Ma (WoldeGabriel et al., 2001; Kleinsasser et al., 2008). The Sagantole Formation

(>4.6 to 4.2 Ma) consists of lacustrine, alluvial and volcaniclastic strata, plus basaltic

interlayers and distinctive tephra of bimodal basaltic-rhyolitic composition (Renne et al.,

1999). It is exposed in the Middle Awash project area (Renne et al., 1999) and in parts of

the Gona area (Quade et al., 2004); fossil remains of Ardipithecus ramidus (White et al.,

1994) and Australopithecus anamensis (White et al., 2006) are found in its strata. The

Hadar Formation (>3.5 to 2.9 Ma) is exposed in the Hadar, Dikika (Wynn et al., 2006)

and Gona areas (Quade et al., 2004; in press). The Basal Member of the Hadar Formation

at Dikika contains the 3.8 Ma Ikini tuff, but this member is poorly and only locally

exposed (Wynn et al., 2006). The lowest occurrences of hominid fossils in the Hadar

Formation are in the Sidi Hakoma Member, where specimens of Australopithecus

afarensis, such as “Lucy” have been found above and a few meters below the 3.4 Ma Sidi

Hakoma tuff (Wynn et al., 2006). Finally, the newly-designated Busidima Formation (2.7

to <0.2 Ma), the base of which is an angular unconformity with the Hadar Formation, is exposed in the Gona, Hadar and Dikika areas, where fossils of Homo erectus and some of the oldest known stone tools have been found (Quade et al., 2004). These formations have yielded a wealth of information about our species’ early evolution, but gaps in our knowledge remain. One of the larger gaps, as is evident in the ages of the aforementioned formations, spans a significant portion of the Pliocene epoch, from ~3.5-4.2 Ma. Therein lies the importance of the material in the Western Mille area – its potential to fill in this gap in our knowledge of human evolution.

Figure 2. Composite regional stratigraphic column, showing the approximate location for material found in the Western Mille area (in red).

Stratigraphy and Structure of the Western Mille Area

Several groups of fossil sites have been designated and named in the Western

Mille area, including Am-Ado, Aralee Issie, Mesgid Dora, Makah Mera and Korsi Dora

(Figure 2). Another area, the Waki-Mille confluence, is not a fossil site, but it is the

location of the project’s camp and it also has excellent exposures of the sedimentary

succession. These are the sites at which the most geological fieldwork has been done, and

for which stratigraphic correlations have been hypothesized. The fossiliferous strata at

these sites are predominantly fluvial and consist of volcanic tephra beds 5 cm to > 3 m

thick, interbedded with conglomerate, sandstone and siltstone, which is locally

volcaniclastic rich (Haile-Selassie et al., 2007). Conglomerate and sandstone beds

commonly are trough and tabular cross-stratified or planar stratified and form upward

fining packages that fill eroded channels. Rhizoliths are common in sandstone and

siltstone layers at the tops of channels. Tephra layers are predominantly air-fall pumice

lapillistones, though some were deposited in water and are reworked. Some of the tephra layers in the succession are fine-grained ash beds, which contrast sharply with the coarse

(lapilli-sized), pumice-rich layers that are more common. Fossiliferous horizons occur within local channel-fill sandstone, as well as within tephra beds and other layers.

These fossiliferous, volcaniclastic-rich strata overlie basalt at Am-Ado, Aralee

Issie and the Waki-Mille confluence; typically they are unconformably overlain by younger, Pleistocene conglomerates, which cap and are deeply incised into most of the sections in the area. Strata are offset by northwest-southeast striking, high angle normal faults, which form horst and graben structures (B. Saylor and M. Alene, unpublished data).

Figure 3. Detail map of the Western Mille area.

Previous published work on the Western Mille area has reported composite

measured stratigraphic sections for each of the above sites (e.g., Haile-Selassie et al.,

2007), identifying and naming tephra beds and proposing stratigraphic correlations

among sites. However, field relations documented during the 2008 and 2009 seasons

revised earlier proposed correlations and raised doubts about some other correlations.

These revised correlations and uncertainties are included in a paper in review by Deino et

al., which names additional tephra beds that were not previously recognized because they

were miscorrelated. The same paper provides 40Ar/39Ar dates for some of the Western

Mille tephra beds and for underlying basalt at some sites.

During the 2008 season I collected samples of tephra for glass shard geochemistry as a means to test stratigraphic correlations. These geochemical correlations, which are the foundation of this thesis, confirm the revised correlations of Deino et al. (in review).

However, some of the dated tuffs from Deino et al. (in review) are from structurally

isolated exposures and some uncertainties remain about the relationship of these tephra to

the intact stratigraphy. The type exposures of named tephra, the dated exposures of tephra

and basalt, and exposures of tuffs for which I have glass shard geochemical data in this

thesis, are described within structural and/or stratigraphic context. The description of the

tephra is followed by a summary of the initial and revised stratigraphic correlations. The

analyses have been useful for correlations with tephra from other locations in eastern

Africa as well as within the Western Mille area. Geochemical data from one of the fine-

grained tuffs (the Kilaytoli tuff) are included in the paper by Al Deino and other members

of the project, including myself. In this thesis I include the chemical results for all

samples analyzed, and present information beyond the scope of the objectives of the

Deino et al., article.

Waki-Mille Confluence

Basalt that underlies the section has been dated to 3.82 ± 0.18 Ma (Deino et al., in

review), which provides a lower limit for the age of material found in the area. This date

was obtained from a sample (WM-W-1) from the Waki-Mille confluence section, where two tephra beds have also been dated. About 10 m above the basalt, a ~25 cm thick air- fall pumice lapillistone has been dated to 3.76 ± 0.02 Ma (WM-W-2; Deino et al., in review). This is the lower of two similar tuffs, just above which there is a thicker (~2 m) pumice lapillistone tephra layer, here named the Mille tuff (but correlated with the Aralee

Issie tuff in Haile-Selassie et al., 2007). About 7 m stratigraphically above the lower dated tuff is the Basalt-Rhyolite tuff, so named due to its bimodal composition. It is ~35 cm thick, including both a lower, basaltic-rich part and an upper rhyolite-rich part; the

upper, rhyolitic part of this tuff at the Waki-Mille confluence has been dated to 3.78 ±

0.08 Ma. However, this date is based on a single phenocryst (Deino et al., in review). 1.5

m above the Basalt-Rhyolite tuff there is a ~50 cm thick, fine-grained, pumice-free tuff

layer named the Waki tuff (but originally correlated with the Kilaytoli tuff). About 2 m

above the Waki tuff is another pumice-rich air-fall tephra layer, ~1.5 m thick.

Mesgid Dora

Due to its distinctive appearance, the Basalt-Rhyolite tuff is one of the best

stratigraphic markers in the area. This marker horizon is also well developed at Mesgid

Dora, approximately 1.5 km northeast of the Waki-Mille confluence, where the Mille and

Waki tuffs are also recognized (Figure 3), though the underlying basalt is not exposed. A thin (~5-10 cm) tephra bed just above and likely co-eruptive with the bimodal tuff at this site has been dated to 3.77 ± 0.04 Ma. The highest pumice-rich lapillistone tephra at

Mesgid Dora, ~2 m above the Waki tuff, has been named the Mesgid Dora tuff. There are prominent tuffaceous sandstone channels at Mesgid Dora, which cut through the local stratigraphy and remove tephra, including the Basalt-Rhyolite tuff (Figure 4). These channels and a series of faults make the stratigraphy at this particular site rather complex.

However, the ease of recognizing some of the tephra layers found at the Waki-Mille confluence has aided progress in deciphering the stratigraphy of this complicated site.

Figure 4. Waki-Mille confluence and Mesgid Dora stratigraphic sections; vertical scale is meters; see Figure 2 for locations of sites; tephra abbreviations are BRT: Basalt-Rhyolite tuff, MLT: Mille tuff, WT: Waki tuff and MDT: Mesgid Dora tuff.

Figure 5. Tuffaceous sandstone channel cutting through the Basalt-Rhyolite tuff at Mesgid Dora; hammer pictured is 32.5 cm long.

Makah Mera

Just to the east of Mesgid Dora is another fossiliferous site, Makah Mera. The

stratigraphic succession at this site consists of a thick, pumice-rich lapillistone tephra

which makes up a resistant surface a few meters above the level of the Mille River, as

well as a fine-grained, pumice-free tephra layer ~5 m above the resistant plain. A

sandstone channel cuts down through the upper, fine-grained tuff, and through the

sediments between the two tuffs; it appears to be one of the sources of fossils found at

Makah Mera (Haile-Selassie et al., 2007). The section at this site is unconformably capped by younger conglomerates, as are most of the local sections in the Western Mille area.

Aralee Issie

To the west of Mesgid Dora is Aralee Issie, another fossiliferous site along the

Mille River. Here, a stratigraphic section of ~15 m is exposed, from the basal basalt up to a fine-grained, pumice-free tephra layer that exhibits planar laminations where exposed.

Between these two distinguished strata are several other tephra, most of them coarse- grained, pumice-rich deposits, though a pumice-free, fine-grained tephra is also present, a few meters below a thick pumiceous lapillistone tephra that makes up a resistant surface throughout most of the site. The other named tephra are found here, with the exception of the Basalt-Rhyolite tuff, which is absent from this section. The Aralee Issie tuff is a ~1 m thick air-fall lapillistone found on the upthrown side of a fault that runs to the east of the

Aralee Issie stratigraphic section. It exhibits trough cross-stratification, and rhizoliths are typically found along its upper reaches. This tephra bed, in which fossils have been found 20

in situ, has been dated to 3.72 ± 0.03 Ma (Deino et al., in review). It has since been

shown to be geologically isolated; that is, we cannot walk up section or down section

from exposures of this tephra layer to other tephra or distinguishable strata, and therefore

its stratigraphic relation to the rest of the section is unknown.

Korsi Dora

Finally, the section at Korsi Dora includes an isolated exposure of the Kilaytoli

tuff, which appears to have been offset from other strata at the site by faults. The

Kilaytoli tuff is named for exposures along the Kilaytoli River, which borders this site.

Along the river bed, the tephra is more than 3 m thick and fine-grained, lacking pumice

and consisting almost entirely of glass shards. It is thick and massively bedded at the

bottom, passing upward into well-laminated, low-angle cross-stratification, climbing

ripple cross-stratification and erosional stoss ripple cross-stratification (Figure 5). The

upper part of the tephra deposit consists of 5 cm-scale interbedded layers of volcanic

tephra, siltstone and very fine sandstone. Accretionary lapilli are also present locally. A

partial hominid skeleton was found at Korsi Dora, so its relation to the Kilaytoli tuff,

which has been dated, is an important focus for further fieldwork at this site.

Figure 6: Erosional stoss ripple cross-stratification and planar laminations in an exposure of the Kilaytoli tuff at Korsi Dora; scale is cm.

Samples of the Kilaytoli tuff from the Kilaytoli River exposures have been dated

to 3.57 ± 0.014 Ma (Deino et al., in review), but these exposures are geologically isolated

from other exposures at Korsi Dora by northwest-southeast trending normal faults. The

age of the Kilaytoli tuff is the same as that of a widespread tephra unit called the

Lokochot tuff, which has been sampled and analyzed from locations in the Turkana basin

of Kenya (Brown et al., 1992), as well as from deep sea cores from the Gulf of Aden

(Feakins et al., 2007) and the Arabian Sea (deMenocal and Brown, 1999). The Lokochot,

radiometrically dated to 3.596 ± 0.045 Ma (McDougall and Brown, 2008), and

independently assigned an orbitally-tuned age of 3.58 ± 0.01 Ma in a deep sea core

(deMenocal and Brown, 1999), provides the opportunity for region-wide correlation of

tephra in the WORMIL area with those from other study areas.

Correlations

Of the material that has thus far been dated in the Western Mille area, the two

youngest tephra were both sampled from locations which have since been shown to be

structurally isolated from the rest of the local stratigraphic succession. This fact presents

an additional impetus for correlation of the stratigraphy at each of these sites; given the

isolation of these strata, correlation is essential to understanding how they relate to one

another, and to the rest of the stratigraphic succession. Using the distinctive tephra layers

as stratigraphic markers, the sites in the Western Mille area were correlated prior to the

2008 field season as shown in Figure 6A (B. Saylor, pers. comm.; after Haile-Selassie et

al., 2007 Fig. 2), hanging all sections on what was believed to be a common factor, the

Aralee Issie tuff. However, observations made during the 2008 field season, such as the

recognition of two different fine-grained tuffs in the Aralee Issie stratigraphic section,

caused us to reinterpret the way the sites along the river are related to one another. The

higher tuff in the Aralee Issie section resembles exposures of the Kilaytoli tuff, named at

Korsi Dora, where it is exposed as a ~1-3 m-thick, fine-grained tuff with planar

laminations and low-angle and climbing-ripple cross-stratification locally (Figure 5). The lower fine-grained tuff in the Aralee Issie section, however, resembles a thinner fine- grained tuff exposed at the Waki-Mille confluence, where it is much thinner (< 0.5 m) and no sedimentary structures are evident, most importantly the seemingly-diagnostic planar laminations. This is also how the tuff typically outcrops at Mesgid Dora, though locally it expands to more than 1 m and exhibits planar laminations and a cherty consistency.

Due to the ambiguity of the previous correlation, we decided it was necessary to

test the previous hypothesis, and to propose a new correlation based on our field

observations. This was the task I set out to accomplish during the last two weeks of the

2008 field season, and it defined the goal of this thesis: to attempt to physically test the

new correlative hypothesis where possible, and to collect samples to otherwise assess its

validity. I had a hypothesis to test – namely, that there are two distinct fine-grained tephra

units in the area; I also wanted to try to follow one of the coarse-grained tephra layers

from Mesgid Dora into Makah Mera, to show which of them is present at the latter site.

The result of this work is the confirmation of the new correlation shown in Figure 6B.

The local tectonic setting and complex tectonic history can make stratigraphic

correlation, even at the scale of an individual site, very difficult. Due to high dissection

and erosion rates, high volcanic stochastic contribution, rapidly changing fluvial

conditions, and other factors, piecing together the puzzle of a single site’s original

stratigraphic succession can be challenging. This is why strata in the Western Mille area

were originally miscorrelated, and why geochemical correlation is necessary to verify the

new correlation.

Figure 7. Preliminary (A) and revised (B) correlations of the stratigraphy of sites in the Western Mille area; notice the difference in correlations of sections from the Waki-Mille confluence and Mesgid Dora; vertical scale is meters; see Figure 2 for locations of sites; tephra abbreviations and key same as Figure 3, with the addition of AT: Aralee Issie tuff and KT: Kilaytoli tuff.

What was called the Kilaytoli tuff has been shown to be two distinct tephra layers, with different stratigraphic positions. This realization has led us to name the thinner one, which often lacks laminations the Waki tuff. This is the tephra layer found between the

Basalt-Rhyolite and Mesgid Dora tuffs in sections at Mesgid Dora and the Waki-Mille

confluence. The thicker, younger tuff which is found at Korsi Dora and at the top of the

section at Aralee Issie will continue to be called the Kilaytoli tuff. In addition, the Aralee

Issie tuff has been shown to be geologically isolated, and thus cannot be correlated with

other tephra along the Mille River, as previously assumed. The tephra layer originally

correlated with the Aralee Issie tuff elsewhere is now shown to correlate with the Mesgid

Dora tuff, and the lowest lapillistone tephra in the Mesgid Dora and Waki-Mille

confluence sections is now called the Mille tuff (Figure 6B).

Field Methods

I conducted fieldwork in the spring of 2008 as a member of the WORMILPRP

team, led by Dr. Yohannes Haile-Selassie. Along with paleontologists, a photographer,

undergraduate students from CWRU, and field hands from the National Museum in

Addis Ababa, I spent six weeks in the west-central Afar region of Ethiopia, where we

worked with local Afar people who acted as guides, guards, and fossil collectors. I acted

as the resident geologist on the team until my advisor, Dr. Beverly Saylor and structural

geologist, Dr. Mulugeta Alene from Addis Ababa University arrived. During this time, I

measured stratigraphic sections at new sites, and attempted to correlate tephra layers and

basalts from one site to another by walking them out. At other times, when we visited a

site for which the stratigraphy was already well established, I attempted to determine the

provenance of fossiliferous horizons.

Toward the end of the field season, as my understanding of the local geological

setting was becoming more coherent, I narrowed my focus to a string of sites located

along the Mille River, in the northwestern part of the study area. This is one of the most 26

extensively-studied parts of the project area to date, due in part to the abundance of

fossils, but also to the presence of numerous volcanic tephra in the local stratigraphic

sequence. I returned to one of the sites along the river, Mesgid Dora, with the goal of

testing the internal stratigraphy which Saylor and the other geologists had been compiling

and revising over previous field seasons. I wanted to document the correlation of tephra layers across this site and into adjacent sites, such as Makah Mera and Aralee Issie, to test the most recent hypotheses about the stratigraphy of the area. To do so, I mapped the extent of tephra outcrops and took samples for subsequent chemical analysis.

Most of the mapping was done with a differential GPS setup, consisting of two

Thales ProMark 3 handheld units, one of which acted as a base station, and the other as a rover. For several days, I returned to the site, set up the base station, and walked the site with the rover, taking waypoints along the outcrops of tephra layers and other distinguishable units. Other, broader geological data – such as the nature of certain more

widespread outcrops – were recorded on satellite images in the field by all of the

geologists, and were added to the rest of the data. I later compiled all of the relevant data

in a visual format using ArcMap, a computer program from ESRI. I layered the geological data over georeferenced satellite images and aerial photos to create maps of

the area; an example is shown in Appendix 1. Other data, such as sample locations and

structural geological inferences made by M. Alene, were also added to the GIS database,

in order to make the information more accessible for visual interpretation.

In addition to the GPS mapping, I measured several stratigraphic sections at

Mesgid Dora to document the positions of various strata at different locations across the site (Appendix 1), which display the variability in the local stratigraphy. In addition, they

give a sense of the general site-wide trends, which provide information to be interpreted

along with inferred fault locations.

I also collected samples of tephra layers from Mesgid Dora and the other nearby

sites, in order to geochemically verify the correlative hypotheses which had been posited

based on stratigraphy. Whenever possible, I sampled from areas where I could verify the

identity of the sampled tephra layer stratigraphically, and was sure to mark the location at

which I collected each sample using the GPS units. Stratigraphic locations of samples are

shown in Figure 10 below, and GPS coordinates for each are provided in Appendix 2.

The interpretation of the stratigraphic sections, when considered alongside structural

inferences and the results of chemical analyses, has implications for the larger-scale

tectonic evolution of the local basin in which the study area is located.

Figure 8. Stratigraphic locations of samples; reference samples shown in red, others in black; vertical scale is meters; tephra abbreviations and key same as Figure 7.

Sample Preparation

When the samples I had collected returned from the field, I catalogued and

photographed each one, and disaggregated the majority of each using a mortar and pestle.

I then sieved them into five size fractions. Based on the abundance of identifiable glass shards, two of these, the 425-850 μm and 250-425 μm fractions, were most favorable for

analysis. I treated these fractions with 10% HCl for 30 s to remove carbonates, and for 15

s with 2-5% HF in an ultrasonic cleanser to remove adhering clay minerals (Brown and

Fuller, 2008). I then used a Frantz Isodynamic Magnetic Separator to isolate glass and

pumice fragments from other magnetic and paramagnetic materials. By trial and error, the

optimal settings for this separation were found to be: a magnet current of 1 A; a decline

of 30˚ down the length of separation; and dips of 8˚ into the magnet and 18˚ away from

the magnet, to isolate the least- and most-repelled fractions, respectively. These settings

were often effective, though some samples required some adjustment.

Microprobe Analysis

Electron microprobe analysis has been used in past studies to correlate tephra

layers by comparing the chemical composition of individual glass shards within samples of the various tephra. Since microprobe analysis is expensive and time-consuming, I could not analyze all of the samples I collected in the field. I therefore had to narrow my

focus to samples which would either support or refute my correlative hypotheses. This

being my goal, I decided to prepare one full set of the named tephra layers, from well-

known locations. With this set as a reference for correlation, I then prepared samples of

tephra exposures from other sites, which, if they correlated with the others, would verify 29

the new stratigraphic correlation we had posited in the field. I prepared all of the samples from Aralee Issie to test correlations of the sequence of tephra layers found low in the section at that site with the type exposures of the Mille, Waki and Mesgid Dora tephra at the Waki-Mille confluence and Mesgid Dora. I also wanted to test the correlation of the

Kilaytoli tuff at the top of the Aralee Issie section with the type exposure of the Kilaytoli

in the Kilaytoli Riverbed at Korsi Dora. In addition, I prepared samples of the coarse-

grained lapillistone at Makah Mera and of a tephra layer I believed to be the Kilaytoli

tuff, collected from an isolated exposure near the border between Mesgid Dora and

Makah Mera, in order to further test the new correlations of strata across exposures along

the Mille River. In all, I prepared fourteen samples for analysis (Figure 10), including

three samples of the Kilaytoli tuff collected at Korsi Dora by Al Deino, and one sample

of the Lokochot tuff collected by Francis Brown in the Turkana Basin of Kenya.

I mounted a small amount (<1 g) of the glass separates from each sample in resin,

then ground and polished each to expose the interior of individual glass shards for

electron microprobe analysis (EMPA). Analyses were conducted at the University of

Wisconsin on a Cameca SX-50 electron microprobe equipped with five wavelength-

dispersive spectrometers. The concentrations of twelve different major and minor

elements were measured using standards in Table 1. Analyses were conducted using an accelerating voltage of 15 KeV, a beam current of 10 nA, and a focused (10 μm) beam

diameter with an on-peak count time of 20 s for each element, which is consistent with

the work of other researchers on east African tephrostratigraphic correlations (e.g.,

Brown et al., 1992; Feakins et al., 2007; Roman at al., 2008). Element concentrations

were calculated using the Armstrong/Love Scott φ(ρz) algorithm (Armstrong, 1988), and

were converted to oxides computing all Fe as Fe2O3. Others have estimated H2O in glass

samples by adjusting stoichiometrically calculated O abundance for Cl and F abundances,

and then subtracting this value from the total measured O (Nash, 1992). Given the low F

concentrations of our samples (below detection limits; Table 1), I did not compute this

value, and measured O values closely approximate H2O concentrations.

Element Crystal Standard Count Time (s) Detection Limit (wt. %) Na TAP Lipari Obsidian 20 0.022 Mg TAP Kilbourne Olivine 20 0.015 O PC1 Lipari Obsidian 20 0.113 F PC1 F-Topaz 20 0.087 Cl PET Chlor-apatite 20 0.022 Ca PET Monash Andesine 20 0.021 K PET Lipari Obsidian 20 0.022 Si TAP Lipari Obsidian 20 0.021 Al TAP Lipari Obsidian 20 0.018 Ti LiF Rutile 20 0.052 Mn LiF Manganese Olivine 20 0.043 Fe LiF Fayalite 20 0.045

Table 1. Crystals, standards, count times and detection limits of EMP analysis.

Data Analysis and Correlations

The EMPA data were corrected for the effects of alkali mobility (Morgan and

London, 1996, 2005; Roman et al., 2008) upon bombardment by the electron beam, by

analyzing the raw, time-dependent intensity data for those elements that were measured

first on each spectrometer. Since only one element measured by each of the five

spectrometers could be analyzed for time-dependent intensity variability, careful consideration went into choosing Na, O, K, Si and Fe as the elements to be measured first, and therefore to be correctable. Though Al has been shown to migrate along with

the alkali elements (Kleinsasser et al., 2008), I was unable to correct for this element, due to its placement on the same spectrometer as Si, which varies in the same way, and to a

greater degree. Probe for Windows, the software which controls the microprobe itself,

contains algorithms for time-dependent data correction. Na, O and K were corrected

using an exponential fit of the time-dependent data, Si was corrected with a linear fit, and

Fe was corrected by an averaging method which doesn’t use a fit. The decision to apply

each of these corrections was based on determining which method best fit the data for

each element, or if a fit was necessary at all. After the corrections were applied, the data

were exported into simpler, data-organizing software to apply one final correction.

Since O and F were measured on the same spectrometer (Table 1), and only one

of the elements could be corrected for time-dependent intensity variability, the decision

had to be made to correct one or the other. Due to the low concentration of F in the

samples, we decided to correct O. However, without the correction for F, the weight

percents measured by the software – which compare the counts of each element to those

collected from standards of known composition – were returned as negative weight

percents. It seems the standard we used had too much F for comparison with such low-F

samples. This disconnect made it necessary to correct the total oxide percents – which

were being lowered by the negative F values – by calculating new totals given a F

concentration of 0 weight percent. This may have been avoided by using a standard with

lower F concentration, but we did not realize this in time to correct for our mistake.

To qualitatively compare the composition of each of the samples, I used the

criteria upon which others had based correlations of Miocene tephra in the Afar – I

plotted the various oxide concentrations on binary and tertiary diagrams. As shown by the

work of others in this field (e.g., Brown et al., 1992; Feakins et al., 2007), the oxides

Fe2O3 and Al2O3 are very useful in distinguishing these types of tephra from one another.

Thus I used comparisons based on these oxides as a starting point for qualitative comparison of the WORMIL tuff samples. For samples shown to be bimodal in Fe – namely the Kilaytoli and Lokochot tuff samples – I differentiated between ‘hi Fe’ and ‘lo

Fe’ modes using a cutoff value of 3.5 weight percent Fe2O3; those analyses yielding

values higher than 3.5 were grouped with the ‘hi Fe’ mode, and those below were

grouped as ‘lo Fe’.

I compared glass compositions quantitatively by calculating similarity

coefficients, using the following equation:

d (A,B) = Σ ( Ri * gi ) / Σ ( gi )

where d (A,B) is the similarity coefficient for comparison between sample A and sample B, i is the element number,

Ri = XiA / XiB if XiB ≥ XiA

Ri = XiB / XiA if XiA > XiB,

XiA and XiB are the concentrations of element i in samples A and B, respectively, and

2 2 gi = 1 – √ ( ( ( σiA / XiA) + ( σiB / XiB) ) / 0.33 )

where σiA and σiB are the standard deviations for concentrations XiA and XiB, respectively

(Borchardt et al., 1972). Following the methods of Borchardt et al. (1972), I changed

negative values of gi to zero, in order not to use elements with analytical error greater

than 33% in my calculations of d (A,B). This most often was the case with MgO, which is

present in many of our samples at a concentration at or near the detection limit of our

analyses.

Given the variability in the literature of methods for correcting for elemental

migration, I did not use the values obtained for Na, K and O concentrations in attempting to correlate the tephra in the Woranso-Mille study area with those from other regions.

This decision has also been reached by others attempting the same sort of correlations

(e.g., Roman et al., 2008). Some of the data from the literature also had to be de- normalized, as a common practice when O is not being directly measured is to normalize the weight percents of measured elements to total 100 percent (e.g., Walter and Aronson,

1993; Wynn et al., 2008; Roman et al., 2008). After these differences were accounted for,

I compared the compositions of the tephra in our study area to tephra from the same time

range (~3.5 - 4.0 Mya) found elsewhere. We acquired a sample of the Lokochot tuff

(#K80-295) collected in the Turkana basin by Francis Brown, and analyzed it along with the rest of the samples for which we collected compositional data.

Time-dependent Intensity Variation: Corrections

Several studies have shown that migration of alkali elements within the samples during analysis can alter element abundance data (Cerling et al., 1985; Morgan and

London, 1996). Na migration can be made negligible by analyzing with a current density less than 0.005 microAmps per micron squared (Morgan and London, 2005). I was unaware of this approach for minimizing element mobility when I conducted my EMPA analyses, and instead followed the methods of some other investigations of east African tephrostratigraphy and corrected the elemental abundances for time-dependent changes in intensity (Roman et al., 2008).

Using the Probe for Windows software, I had a choice of two algorithms – a ‘log-

linear (exponential)’ fit and a ‘log-quadratic (hyper-exponential)’ fit – which were at my

disposal in trying to correct these data. I also had the alternative of not applying a fit, and

simply averaging the time-dependent data. I determined which correction method to use for each element based on the quality of the fit each provided, or the need for a fit at all.

Table 2 shows the average value of each of the correctable oxides for each sample, using

each of the three available options for correction: linear, exponential, and no fit. The table

presents the variation between the values calculated by each correction method. The

choice of correction methods affects the abundance total for the sum of all oxides and the

ratios of oxides, but not the abundances of the other, uncorrected oxides.

I determined to use one correction method over the other for each element

qualitatively by comparing graphs of each of the fits to the time-dependent data. Figures

11 and 12 are examples of graphs of different fits for the same data. As can be seen,

depending on the behavior of a given element during analysis, one correction method is

typically more favorable than the other. By examining such graphs for each of the

samples, I determined to use the exponential fit for Na, O and K, the linear fit for Si, and

no fit for Fe (see Figure 13). Each of these decisions was also informed by the

conventions in the literature and the advice of experts (e.g., Fournelle, pers. comm.). All

data in their final, corrected form are presented in Appendix 3. Table 2 shows that the

effect of element mobility and the choice of correction method is large for Na, K and O.

Oxide (wt. %) Oxide (wt. %)

Sample Na2O O K2O SiO2 Fe2O3 Total Sample Na2O O K2O SiO2 Fe2O3 Total

Lin. 1.80 5.87 3.09 74.79 3.55 99.8 2.02 6.98 5.74 71.42 1.86 101.7

Exp. 3.70 4.71 3.62 74.24 3.55 100.6 2.89 5.54 6.14 70.86 1.96 101.1 K80-295 K80-295 None 0.73 5.63 1.81 76.29 3.66 98.8 MKM-08-1 1.02 7.30 4.04 72.85 1.90 100.7

Lin. 1.86 6.88 4.85 73.54 2.90 101.0 1.95 5.55 5.44 72.31 2.04 101.0

Exp. 3.02 4.97 4.96 72.83 2.88 99.6 2.93 4.16 6.02 71.39 2.00 100.3 MSD-08-5 MSD-08-5 None WM-KSD-1 0.76 7.20 3.16 75.15 2.99 100.1 0.98 5.95 3.88 73.55 2.13 100.1

Lin. 1.53 7.21 4.24 73.77 3.61 100.9 2.94 0.93 1.28 55.93 10.60 99.7

Exp. 2.89 5.56 4.54 72.95 3.43 99.9 3.03 0.65 1.34 55.91 10.60 99.5

None WM-KSD-3 0.52 6.93 2.31 75.46 3.74 99.4 MSD-08-3B 2.71 0.95 1.05 56.14 10.43 99.3

Lin. 1.47 7.56 4.62 73.41 3.42 101.2 1.95 7.48 5.40 73.46 1.86 102.1

Exp. 2.59 5.89 4.93 72.55 3.29 99.9 3.00 6.34 5.96 72.17 1.79 101.3 ARI-08-5 ARI-08-5 None 0.54 7.59 2.63 75.01 3.49 99.9 MSD-08-2 0.86 7.56 3.48 74.76 1.92 100.5

Lin. 1.11 8.22 4.33 73.24 4.20 101.2 2.18 7.04 5.18 73.29 1.95 101.7

Exp. 2.27 6.74 5.13 72.03 4.19 100.5 3.22 5.87 5.76 72.20 2.01 101.2

None ARI-08-2 0.38 7.92 2.10 74.90 4.29 99.7 ARI-08-3 0.97 7.35 3.42 74.39 1.97 100.1

Lin. 1.31 7.93 3.99 73.75 4.06 101.3 1.17 6.84 4.34 74.51 3.31 100.9

Exp. 3.17 6.45 4.74 72.71 3.95 101.3 2.39 5.21 5.02 73.48 3.34 100.2 WMC-08-4 WMC-08-4 None 0.45 7.72 1.98 75.25 4.12 99.7 MSD-08-13 0.43 6.55 2.33 75.90 3.30 99.2

Lin. 2.27 6.65 5.49 71.77 1.84 101.7 2.20 6.76 5.02 74.60 1.97 102.6

Exp. 3.10 5.11 5.38 70.73 1.77 99.8 3.24 5.20 4.98 73.68 1.87 101.1

None ARI-08-1 1.01 7.55 3.98 73.12 1.89 101.2 ARI-08-4 0.96 7.35 3.52 75.71 2.03 101.6 Table 2. Comparison of different fits to time-dependent data for each sample.

Figure 9. Examples of linear (left) and exponential (right) fits for time-dependent data for O; Notice the difference in y-intercepts (at time = 0s). 36

Figure 10. Examples of linear (left) and exponential (right) fits for time-dependent data for Na; Notice the difference in y-intercepts (at time = 0s).

Figure 11. An example of time-dependent data for Fe; Notice the ambiguity of linear fit slopes, and the variation in y-intercepts (at time = 0s).

Geochemical Results

The results of the chemical analyses provide the information necessary for correlating tephra with one another. Based on the work of others in this field, who have worked with tephra of similar age and from broadly the same region (e.g., Brown et al., 37

1992; Feakins et al., 2007), I have compared the composition of glass separates to

determine which of the samples are geochemically correlative. The most useful mode of

comparison has been the creation of binary plots of the abundance of the oxides Fe2O3 and Al2O3, though other oxides were useful for specific samples. I have also compared

the compositions of the WORMIL tephra quantitatively, using similarity coefficients

calculated with the average composition of each sample (Table 3). Because corrections

for element mobility are so large and because Na2O, K2O and O2 have not been included

in most previous studies of tephrostratigraphy, I did not include the abundances of these

oxides in my calculations of similarity coefficients.

Reference Sample Tephra Correlative Sample S. C. WM-KSD-3 Hi Fe KT Hi Fe ARI-08-5 Hi Fe 0.971 WM-KSD-3 Hi Fe KT Hi Fe MSD-08-13 Hi Fe 0.952 WM-KSD-3 Lo Fe KT Lo Fe ARI-08-5 Lo Fe 0.960 WM-KSD-3 Lo Fe KT Lo Fe MSD-08-13 Lo Fe 0.966 WMC-08-4 WT ARI-08-2 0.969 MSD-08-5 MDT ARI-08-1 0.966 MSD-08-5 MDT MKM-08-1 0.971 MSD-08-2 MLT ARI-08-3 0.981

Table 3. Similarity coefficients for tephra comparisons within the WORMIL study area; tephra abbreviations are: KT Hi/Lo Fe: modes of Kilaytoli tuff, WT: Waki tuff, MDT: Mesgid Dora tuff and MLT: Mille tuff.

On plots of Fe2O3 and Al2O3, it is possible to distinguish the majority of the

WORMIL samples from one another. This method has also revealed the bimodal nature of the Kilaytoli tuff (Figure 14), a characteristic it shares with the Lokochot tuff. It may also be argued that the Waki tuff exhibits bimodality, but further sampling and EMP analysis would be necessary to assess this claim. On the plot of these two oxides shown in Figure 14, the Kilaytoli and Waki tuffs appear different from the rest of the samples.

The data from samples of these two tephra cluster in a general band from the high-Fe, low-Al corner to the Low-Fe, High-Al corner of the region between Fe values of ~2.7-4.8 wt. % and Al values of ~9.3-11.0 wt. %. The other samples analyzed, the Mesgid Dora and Mille tephra, fall along a different band, exhibiting fairly consistent Fe content (~

1.5-2.5 wt. %). The difference between the two lies in their Al content; the Mille tuff values fall between ~ 11.0-12.0 wt. %, while the Mesgid Dora tuff values are slightly – though distinguishably – higher, ranging from ~ 12.5-13.5 wt. %.

Figure 12. Plot of Al2O3 v. Fe2O3 for all WORMIL samples, with the exception of the anomalous Basalt-Rhyolite tuff; notice the two general groupings of samples.

Figure 13. Plot of Al2O3 v. Fe2O3 for samples of the Kilaytoli tuff; notice the bimodal nature of the tuff with respect to these two oxides.

Some elemental abundances are more diagnostic in these comparisons than

others. Some are relatively constant across all samples analyzed, such as O, while others are too variable to be useful for correlation. An example of an element in the latter group

is Na, which, even after being corrected for element mobility, typically varies too much

to be useful for correlation; this is similar to the findings of others (e.g., Cerling et al.,

1985; Brown et al., 1992). However, the concentrations of most elements vary

consistently between samples, and are therefore useful for correlation. These diagnostic

elements are Fe and Al for all samples, with the addition of Mg and Ca, for distinguishing

the Mesgid Dora tuff from others; Si, to show the distinctiveness of the Mesgid Dora tuff and to distinguish between the Kilaytoli and Waki tuffs; Ti, to distinguish between the modes of the Kilaytoli tuff; and Mn, to distinguish between the Kilaytoli and Waki tuffs, as well as to differentiate between the modes of the Kilaytoli. Figure 14 above shows the

variability in Fe2O3 and Al2O3 across all of the samples analyzed; other figures in the

‘correlations’ sections show the variability in other oxides, between samples for which

this variation is useful for correlation.

Intra-basinal Correlations

For the Kilaytoli tuff, the reference sample – the one defined as the Kilaytoli, and

to which others are compared – is WM-KSD-3, which was collected by Al Deino from an

exposure along the Kilaytoli River at Korsi Dora. This exposure is separated by a fault from the rest of the exposures at Korsi Dora. Sample WM-KSD-1 is from a lateral equivalent of the same exposure. As mentioned before, the Kilaytoli exhibits bimodality in its chemical composition. What is referred to as the high-Fe mode typically has Fe2O3

content ~3.7-4.5 wt. %, along with Al content ~9.4-10.3 wt. %. The low-Fe mode, on the

other hand, has Fe content between ~2.7-3.3 wt. % and Al between ~10.5-11.0 wt. %.

The modes are also expressed in TiO2 content, but the differences are smaller (Figure 16).

MgO levels in the Kilaytoli tuff are extremely low, very near the detection limit of our

analyses, and thus are not useful for correlation of samples of this particular tephra.

Sample ARI-08-5, collected from the uppermost tephra in the Aralee Issie section, correlates with the Kilaytoli tuff, with similarity coefficients of 0.971 and 0.960 for the high- and low-Fe modes of the tephra. Likewise, sample MSD-08-13, collected from an

isolated exposure of a fine-grained, planar-laminated tephra just north of Mesgid Dora,

also correlates with the Kilaytoli tuff. The similarity coefficients for this correlation are

0.952 and 0.966 for the high- and low-Fe modes of the tephra, respectively.

Figure 14. Plot of TiO2 v. MnO for both modes of the Kilaytoli tuff.

The reference sample for the Mesgid Dora tuff is MSD-08-5, collected from the

upper, 2 m thick pumice lapillistone at Mesgid Dora. Two other samples, from Aralee

Issie and Makah Mera are here shown to correlate with this reference. These samples

exhibit similar geochemical composition, including relatively low Fe2O3 values (~1.5-2.2

wt. %) and high Al2O3 values (typically ~12.5-13.5 wt. %). Other elemental abundances

typical of these samples are high MgO and CaO values (typically ~0.13-0.21 and ~0.6-

0.9 wt. %, respectively) and low SiO2 abundance (~71-73 wt. %). Sample ARI-08-1, collected from an exposure that makes up a significant portion of the main resistant

surface at Aralee Issie, correlates with the Mesgid Dora tuff; the two samples have a

similarity coefficient of 0.966. Likewise, sample MKM-08-1, sampled from an exposure

along the Mille River between Mesgid Dora and Makah Mera, and believed to correlate

with the tephra layer that creates the main resistant surface at Makah Mera, also

correlates with the Mesgid Dora tuff. The similarity coefficient between these two samples is 0.971.

Figure 15. MgO v. CaO for all WORMIL tephra, except the Basalt-Rhyolite tuff; notice the high values for the Mesgid Dora tuff, for both oxides.

Figure 16. Fe2O3 v. SiO2 for all WORMIL tephra, except the Basalt-Rhyolite tuff; notice the low values for the Mesgid Dora tuff, for both oxides.

The reference sample for the Waki tuff is WMC-08-4, collected from the fine-

grained tephra bed between the Basalt-Rhyolite and Mesgid Dora tephra in the Waki-

Mille confluence section. One sample from Aralee Issie correlates with this reference.

Compared to the other tephra analyzed, the Waki has relatively high Fe content, though

there is a gradient of values for both Fe2O3 and Al2O3 values from samples of this tephra, as shown in Figure 19. The low-Fe values for the Waki tuff overlap with the values for the high-Fe mode of the Kilaytoli tuff (Figure 19). If it were not for the low-Fe mode of

the Kilaytoli tuff, the two might be difficult to distinguish. It may also be argued that the

Waki tuff exhibits bimodality, but in a different range than does the Kilaytoli tuff. As

seen in Figure 19, the data for the Waki tuff are spread out through Fe2O3 values of ~ 3.7-

4.8 wt. %, and Al2O3 values of ~ 9.3-10.4 wt. %, a greater range in each oxide than is

present in the high-Fe mode of the Kilaytoli. The two tephra are also distinguishable by

MnO content, which is generally higher in samples of the Waki tuff, and SiO2 content, which is generally lower in the Waki. Sample ARI-08-2, collected from a fine-grained,

pumice-free tephra layer below the Mesgid Dora tuff at Aralee Issie, correlates with the

Waki tuff, with a similarity coefficient of 0.969.

Figure 17. Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples of the Kilaytoli and Waki tuffs; notice the overlap between the two sets of data); dashed line is Mg detection limit.

The reference sample for the Mille tuff is MSD-08-2, collected from the lowest

tephra unit in the Mesgid Dora section. There, and similarly in the Waki-Mille

confluence section, it is a ~2-3 m thick pumice-rich air-fall lapillistone. Its physical

appearance is similar to those of the Aralee Issie and Mesgid Dora tuffs, which is part of

the reason for its later designation – it had previously been assumed to be correlative with

one of the other tephra layers already mentioned. Two other samples, both from Aralee

Issie, are here shown to have geochemical composition indistinguishable from that of this

reference; however, since they are from two different stratigraphic positions from the

same stratigraphic section, only one can correlate with the Mille tuff. These two lowest

tephra layers in the section at Aralee Issie are nearly geochemically indistinguishable

from eachother, using the oxides analyzed here. The only two elements to potentially

distinguish between the two are O and K, which are plotted in Figure 21 below. As

evident in the figure, sample ARI-08-3 appears to overlap more with the reference sample

than does sample ARI-08-4. With a similarity coefficient of 0.981, sample ARI-08-3 –

the stratigraphically higher of the two similar samples from Aralee Issie – most closely

resembles the Mille tuff geochemically.

Figure 18. Plot of O v. K2O for the Mille tuff and possible correlates, samples ARI-08-3 and ARI-08-4.

The Mille tuff is also relatively similar in composition to the Mesgid Dora tuff;

the two tephra have similar Fe concentrations (Figure 22A), which makes distinguishing

between the two potentially difficult. In this case, certain other oxides, such as MgO and

CaO, in addition to Al2O3, are shown in Figure 22B to be consistently different between

these two distinct tephra units. Outliers in the plots comparing the two tephra are likely

due to detrital glass fragments from the Mille tuff within fluvial deposits of the younger

Mesgid Dora tuff, or from aeolian reworking. While these two pumice-rich tephra are similar to each other, their chemical compositions are consistently different from those of the finer-grained, pumice-free Kilaytoli and Waki tuffs. The two groups of tephra vary significantly in their content of Cl, Ca, Al and Fe. These variations are evident in Figures

23 and 24 below.

Figure 19. Plots of Al2O3 v. Fe2O3 (A) and MgO v. CaO (B) for samples of the Mesgid Dora (solid symbols) and Mille (hollow symbols) tuffs.

Figure 20. Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples of pumice-free (Kilaytoli and Waki) and pumice-rich (Mesgid Dora and Mille) tuffs); dashed line is Mg detection limit.

The correlations of tephra within the Western Mille area verify the most recent

correlative hypotheses that we posited in the field (see Figure ###: colored lines between correlated samples, as in ppt). Since the Kilaytoli and Waki tuffs are chemically different and distinguishable from one another, we can be sure that there are indeed two fine- grained tephra in the area. This also explains the seeming duality which we had noticed in the outcrops of what we called the Kilaytoli tuff. Now we can distinguish between the thinly laminated, thicker Kilaytoli tuff and the thinner Waki tuff, which often lacks laminations and other sedimentary structures. Other correlations show that the Mesgid

Dora tuff outcrops at Makah Mera, and makes up the main resistant surface at Aralee

Issie. These geochemical data also support our correlations of the sub-Kilaytoli tephra at

Aralee Issie with the stratigraphic sections at Mesgid Dora and the Waki-Mille

confluence, with the exception of the absent Basalt-Rhyolite tuff.

Figure 21. Illustration of positive chemical correlations: Kilaytoli tuff (red line), Mesgid Dora tuff (yellow line), Waki tuff (green line) and Mille tuff (blue line).

The verification of the more recent stratigraphic correlation has important

implications for the age of material found near the top of the local sections. At Mesgid

Dora and the Waki-Mille confluence, the distinction between the Waki and Kilaytoli tuffs

means the Waki is no longer correlated with the dated samples of the Kilaytoli. Thus

material near the tops of these sections no longer must be younger than ~3.57 Ma; the

Kilaytoli tuff, to which this date applies, lies stratigraphically above this material, and is

therefore younger.

Inter-basinal Correlations

In addition to the internal correlations demonstrated above, two of the tephra from

the Woranso-Mille study area correlate with known tephra layers found at other locations in the region. Here I show that the Kilaytoli tuff correlates with the Lokochot tuff (Table

4), which has been sampled and analyzed from the Turkana basin of Kenya and in cores from the Gulf of Aden (Brown et al., 1992; Gathogo and Brown, 2006; Feakins et al.,

2007). Table 4 below displays the similarity coefficients for several different comparisons of samples of the Kilaytoli tuff and samples of the Lokochot tuff from elsewhere (Table 5).

The table also includes data we generated at the University of Wisconsin for sample K80-295, the sample of the Lokochot tuff from the Turkana basin. We obtained this sample from Francis Brown and analyzed it along with our other samples in order to provide a basis for interlab comparison (e.g., Brown et al., 1992). This overlap in data provides an opportunity for comparison of the results of our analyses and those made at a different EMP lab, at the University of Utah. Comparing the results of our analyses of this same sample, there are apparent differences. These are primarily in the weight percents of the alkali elements Na and K, as well as those in abundances near their detection limits, such as Mg, Ti and Mn. For each of these elements, the values we obtained are consistently greater than those obtained by Brown et al (1992). Since the

data to which I am comparing ours have not been normalized to 100 percent, this is not

the cause for any discrepancies. Likely, the differences are due to differing methods of correcting for element migration, and perhaps due to the use of different standards, as well. This is a difficult claim to verify, as these parameters and corrective measures are 50

not detailed in older publications about this sort of analysis (e.g., Brown et al., 1992).

Despite the differences, several of the oxides available for comparison agree between our analyses and those done at the University of Utah. Comparing Fe, Al, Si and Ca, the similarity coefficients between the analyses of high-Fe and low-Fe modes of the sample are 0.95 and 0.94, respectively.

Reference Sample Location Tuff WORMIL Sample S. C. Without Na, K, O IL02-194 (Hi Fe)1 Turkana B. Lokochot Hi Fe WM-KSD-3 Hi Fe 0.856 0.949 IL02-194 (Hi Fe)1 Turkana B. Lokochot Hi Fe ARI-08-5 Hi Fe 0.842 0.929 IL02-194 (Hi Fe)1 Turkana B. Lokochot Hi Fe MSD-08-13 Hi Fe 0.844 0.930 231-20-1 (20-30 cm) M32 G. of Aden Lokochot Hi Fe WM-KSD-3 Hi Fe 0.902 0.957 231-20-1 (20-30 cm) M32 G. of Aden Lokochot Hi Fe ARI-08-5 Hi Fe 0.913 0.947 231-20-1 (20-30 cm) M32 G. of Aden Lokochot Hi Fe MSD-08-13 Hi Fe 0.919 0.947 IL02-194 (Lo Fe)1 Turkana B. Lokochot Lo Fe WM-KSD-3 Lo Fe 0.838 0.904 IL02-194 (Lo Fe)1 Turkana B. Lokochot Lo Fe ARI-08-5 Lo Fe 0.845 0.919 IL02-194 (Lo Fe)1 Turkana B. Lokochot Lo Fe MSD-08-13 Lo Fe 0.84 0.916 231-20-1 (20-30 cm) M12 G. of Aden Lokochot Lo Fe WM-KSD-3 Lo Fe 0.895 0.951 231-20-1 (20-30 cm) M12 G. of Aden Lokochot Lo Fe ARI-08-5 Lo Fe 0.891 0.946 231-20-1 (20-30 cm) M12 G. of Aden Lokochot Lo Fe MSD-08-13 Lo Fe 0.896 0.957 231-20-1 (20-30 cm) M22 G. of Aden Lokochot Lo Fe WM-KSD-3 Lo Fe 0.933 0.948 231-20-1 (20-30 cm) M22 G. of Aden Lokochot Lo Fe ARI-08-5 Lo Fe 0.926 0.952 231-20-1 (20-30 cm) M22 G. of Aden Lokochot Lo Fe MSD-08-13 Lo Fe 0.926 0.949 232A1-53 G. of Aden Lomogol ARI-08-2 0.882 0.916 232A1-53 G. of Aden Lomogol WMC-08-4 0.917 0.934 K80-295 Hi Fe Turkana B. Lokochot Hi Fe WM-KSD-3 Hi Fe 0.926 0.976 K80-295 Hi Fe Turkana B. Lokochot Hi Fe ARI-08-5 Hi Fe 0.896 0.949 K80-295 Hi Fe Turkana B. Lokochot Hi Fe MSD-08-13 Hi Fe 0.9 0.947 K80-295 Lo Fe Turkana B. Lokochot Lo Fe WM-KSD-3 Lo Fe 0.903 0.936 K80-295 Lo Fe Turkana B. Lokochot Lo Fe ARI-08-5 Lo Fe 0.916 0.962 K80-295 Lo Fe Turkana B. Lokochot Lo Fe MSD-08-13 Lo Fe 0.894 0.943

Table 4: Similarity Coefficients for inter-basinal correlations; notice the difference between values calculated using all oxides (‘S.C.’) and those for which Na, K and O values were omitted; data sources: 1: Gathogo and Brown, 2006; 2: Feakins et al., 2007; 3: Sarna-Wojcicki et al., 1985.

Average analyses of glass shards by electron microprobe (wt %)

Tuff n Na2O MgO F Cl CaO K2O SiO2 Al2O3 TiO2 MnO Fe2O3 O†/H2O Total

Lokochot Tuff

K‐80‐295LoFe, U. of Utah1 16 3.45 0.03 n/a n/a 0.17 3.70 70.84 10.17 0.16 0.10 2.91 n/a 91.5

K‐80‐295HiFe, U. of Utah1 10 3.03 0.02 n/a n/a 0.18 3.41 69.94 9.37 0.19 0.14 4.12 n/a 90.4

K80‐293LoFe1 17 3.57 0.03 n/a n/a 0.18 4.31 72.06 10.37 0.16 0.09 2.94 n/a 93.7

K81‐532LoFe1 14 3.51 0.03 n/a n/a 0.16 2.99 72.00 10.43 0.16 0.09 2.95 n/a 92.3

K80‐293HiFe1 14 2.79 0.02 n/a n/a 0.19 3.33 71.04 9.48 0.20 0.14 4.19 n/a 91.4

K81‐532HiFe1 4 2.54 0.00 n/a n/a 0.17 2.29 70.88 9.57 0.21 0.13 4.20 n/a 90.0

232‐16‐4‐101 21 4.01 0.02 n/a n/a 0.17 4.67 71.34 10.40 0.18 0.08 2.86 n/a 93.5

IL02‐194 (Low Fe)2 9 3.12 0.03 0.19 0.15 0.20 1.56 76.28 10.87 0.23 0.10 2.80 3.98 99.6

IL02‐194 (High Fe)2 6 2.61 0.02 0.25 0.18 0.19 1.35 75.53 10.07 0.26 0.20 3.97 5.55 100.3

231‐20‐1 (20‐30 cm) M13 14 2.30 0.03 0.28 0.13 0.18 4.27 71.78 10.46 0.18 0.08 2.83 8.87 101.5

231‐20‐1 (20‐30 cm) M23 10 2.23 0.03 0.26 0.14 0.17 4.36 73.36 10.52 0.18 0.09 2.95 5.72 100.1

231‐20‐1 (20‐30 cm) M33 4 1.88 0.01 0.39 0.17 0.21 4.01 72.26 9.74 0.22 0.13 4.18 7.16 100.4

231‐20‐1 (20‐30 cm) M43 1 2.02 0.02 0.35 0.15 0.19 4.22 72.55 10.04 0.22 0.14 3.85 7.79 101.6

K‐80‐295LoFe, U. of Wisc. 5 4.26 0.03 * 0.13 0.18 4.12 77.33 10.83 0.19 0.12 3.03 2.39 102.6

1 σ 5 0.62 0.00 0.02 0.02 0.01 0.68 0.61 0.16 0.04 0.02 0.15 0.80 0.68

K‐80‐295HiFe, U. of Wisc. 5 3.12 0.03 * 0.17 0.19 3.12 76.00 9.88 0.26 0.12 4.27 4.93 102.1

1 σ 5 0.71 0.01 0.05 0.03 0.02 0.50 0.50 0.14 0.07 0.02 0.07 0.48 1.41

Kilaytoli Tuff

WM‐KSD‐1 14 3.01 0.04 * 0.13 0.18 4.96 75.34 10.70 0.18 0.07 2.98 3.87 101.4

1 σ 14 0.63 0.02 0.06 0.01 0.01 0.43 0.87 0.13 0.05 0.02 0.10 1.12 1.09

WM‐KSD‐3LoFe 9 2.88 0.02 * 0.13 0.18 4.52 75.92 10.51 0.15 0.09 3.08 4.33 101.8

1 σ 9 0.67 0.01 0.04 0.02 0.02 0.36 0.63 0.31 0.02 0.03 0.18 0.74 1.18

WM‐KSD‐3HiFe 11 2.89 0.03 * 0.17 0.20 4.56 75.49 9.96 0.26 0.14 4.26 4.26 102.2

1 σ 11 0.61 0.03 0.11 0.02 0.02 0.59 0.83 0.15 0.06 0.04 0.14 1.07 1.46

ARI‐08‐5LoFe 11 2.85 0.03 * 0.12 0.18 5.06 75.42 10.64 0.19 0.11 3.04 4.37 102.0

1 σ 11 0.68 0.01 0.08 0.02 0.02 0.63 0.50 0.09 0.07 0.02 0.08 1.14 0.77

ARI‐08‐5HiFe 7 2.16 0.03 * 0.15 0.20 4.73 74.75 9.95 0.25 0.14 4.18 5.23 101.8

1 σ 7 0.41 0.02 0.06 0.04 0.03 0.46 0.52 0.30 0.02 0.03 0.42 1.10 0.80

MSD‐08‐13LoFe 8 2.58 0.04 * 0.12 0.18 5.15 76.02 10.70 0.17 0.08 2.96 3.89 101.9

1 σ 8 0.42 0.02 0.08 0.01 0.01 0.60 0.84 0.16 0.05 0.03 0.14 0.98 0.70

MSD‐08‐13HiFe 3 1.86 0.04 * 0.18 0.18 4.70 76.07 9.63 0.20 0.14 4.19 4.80 102.0

1 σ 3 0.71 0.02 0.08 0.02 0.02 0.74 0.74 0.24 0.05 0.02 0.11 1.18 1.33

Table 5. Summary of compositional data for the Lokochot tuff and WORMIL samples of the Kilaytoli tuff; * denotes composition below detection limit; † excess O = measured O –

stoichiometric O; italicized values reported as H2O; for WORMIL samples, Hi Fe > 3.5 wt. % > Lo Fe.

Figure 22. Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples of the Kilaytoli tuff, average values for the Lokochot tuff, and sample K80-295 (Lokochot); dashed line is Mg detection limit.

Where the Lokochot is found, often another widely-recognized tephra layer, the

Lomogol tuff is also found. Slightly older than the Lokochot tuff (deMenocal and Brown,

1999), the Lomogol tuff is also found in various locations throughout the region (Haileab and Brown, 1992; deMenocal and Brown, 1999). Our two samples of the Waki tuff correlate with a sample of the Lomogol tuff from a core from the Gulf of Aden (Sarna-

Wojcicki et al., 1985), as shown in Figure 26. The similarity coefficients for these two comparisons, from which O and Cl were omitted due to a lack of data, are shown in

Table 4 above.

Figure 23. Plots of Al2O3 v. Fe2O3, SiO2 v. MnO, CaO v. TiO2 and MgO v. Cl for samples of the Waki tuff and average values for samples of the Lomogol tuff; dashed line is Mg detection limit.

Given the chemical correlations of the Kilaytoli and Waki tuffs to the Lokochot

and Lomogol tuffs, respectively, we ought to compare the dates obtained for each as a

verification of our results. deMenocal and Brown (1999) have assigned an orbitally-tuned

age of 3.58 ± 0.01 Ma to the Lokochot tuff; the tuff has also recently been radiometrically

dated to 3.596 ± 0.045 Ma, using a sample from the Turkana basin (McDougall and

Brown, 2008). Thus both ages determined for the Lokochot tuff – by different methods –

lie within error of the age of 3.57 ± 0.01 Ma obtained for the Kilaytoli tuff (Deino et al.,

in review).

The Lomogol tuff has been assigned an orbitally-tuned age of 3.62 ± 0.01

(deMenocal and Brown, 1999). We cannot compare this to that of the Waki tuff, since it

has not yet been directly dated. Thus the only constraints we can apply to the age of the 54

Waki tuff are those obtained for material above and below it stratigraphically. A thin,

unnamed tephra layer below it at Mesgid Dora has been dated to 3.77 ± 0.04 Ma, but the

only date we can stratigraphically place above the Waki is that for the Kilaytoli tuff.

These relatively broad constraints bracket the age of the Waki tuff to ~ 3.57-3.77 Ma.

This is not enough chronological evidence to correlate the Waki with the Lomogol tuff, but the age of the Lomogol is within the range for the Waki, and so the chemical correlation is possible.

In addition to these positive correlations, several other tephra from the region – and from the same approximate time period – are shown to have substantially different compositions from those found in the WORMIL area. Common tephra recognized in other project areas nearby include the Sidi Hakoma, Maka Sand, Wargolo, Cindery and

Moiti tuffs. The Sidi-Hakoma tuff, found at Hadar, Dikika and Gona, has been shown to correlate with the Tulu Bor tuff, a marker tuff from the Turkana basin (Brown, 1982).

The Sidi Hakoma tuff at Hadar has been dated to 3.35 Ma (Haileab and Brown, 1992); average analyses are consistently lower in Fe2O3 content than any of the tephra in the

WORMIL area (Figure 27). The Maka Sand tuff, found in the Middle Awash, has not been dated due to pervasive Miocene contamination (White et al., 1993), but is from the

same general time period as the others here discussed. This tuff is bimodal with respect to

Fe, but in a different range than is the Kilaytoli/Lokochot tuff; it has Al2O3 content

similar to that of the Mille tuff (Figure 27). The Wargolo tuff, defined in the Turkana

basin, has also been found in the Middle Awash (Brown et al., 1992); it has been dated to

~3.8 Ma (Haileab and Brown, 1992). Analyses of this tuff have consistently lower Al2O3 content than the coarse-grained tephra in our area, and consistently higher Fe2O3 content

than our fine-grained tephra. The Cindery tuff, which is bimodal like the Basalt-Rhyolite

tuff (Hall et al., 1984), is found in the Middle Awash; however, it has been dated to 3.8-

4.0 Ma (Haileab and Brown, 1992) and does not correlate with the bimodal tephra we see in the WORMIL area. The Moiti tuff, defined in the Turkana basin, has also been found in the Middle Awash (Brown et al., 1992); it has been dated to ~4.0 Ma (Haileab and

Brown, 1992). It exhibits bimodality similar to that of the Kilaytoli/Lokochot tuff (Figure

27), but it is considerably older, and thus cannot be correlative. None of the other tephra

layers in our study area correlates with another tuff from Dikika, Hadar, the Middle

Awash, or the Turkana basin for which data are available for comparison; they are generally of different ages than those determined for the material in the Western Mille area.

Figure 24. Plot of Fe2O3 v. Al2O3 for WORMIL tephra samples, as well as average values from analyses of tephra known elsewhere in the region.

Implications

The correlations demonstrated above are meaningful within two general frames of

reference. Within the smaller, Woranso-Mille project framework, the chemical

correlations provide confirmation of stratigraphic correlations in the Western Mille area;

they have answered questions and provided others to be answered in the future.

Correlation of the Kilaytoli and Lokochot tuffs, as well as the Waki and Lomogol tuffs,

provides a reference not only for researchers on the Woranso-Mille team, but for those

associated with other research projects in the region. Data have been added to the

collective databases for the Lokochot and Lomogol tuffs, and their extents have been

shown to include the Afar region, which had not previously been shown.

Within the broader context of the eastern African region, there is a possibility to

extend the Kilaytoli/Lokochot correlation further – and to suggest a source for the tephra

we have correlated. One possibility for the source of the Kilaytoli/Lokochot tuff has been

presented by Deino et al. (in review). There is a tephra layer known as the Crystal tuff

that is found ~500 km south of the WORMIL project area, in the central sector of the

MER (WoldeGabriel et al., 1990). It is exposed along both rift margins in this area, and

has been dated to 3.56 ± 0.03 Ma (WoldeGabriel et al., 1992; Deino et al., in review). On

the western margin, at a site called Guraghe, it is ~200-250 m thick, and at Munesa on the

eastern margin, ~75 km away, it reaches thicknesses of over 300 m (WoldeGabriel et al.,

1992). Coupled with the possible correlation of this tuff with one found in a drill core of

the Aluto caldera nearby (Figure 28), the sheer thickness of this tephra layer suggests that

its source was near where the exposures are found. It has been posited that the source was

a caldera that was destroyed by subsequent rifting, and is now covered over by the 57

volcanic products of that rifting (WoldeGabriel et al., 1992). The connection to the

Lokochot tuff lies in the possibility that the Crystal tuff is simply a different expression

of the same tephra layer – it is coarser-grained due to its proximity to its source, and

significantly thicker for the same reason. Compared with an average thickness of ~1-3 m

for the Kilaytoli tuff in the WORMIL area, and a typical thickness of ~2 m for the

Lokochot tuff in the Turkana basin (Brown and Feibel 1986), the variability in grainsize

and thickness support this hypothesis, as do the agreement of the dates for each tephra

layer.

Figure 25. Distribution of Lokochot/Kilaytoli and Crystal tuffs; DSDP cores 231 and 722 both contain layers correlated with the Lokochot tuff; Guraghe, Munesa and Aluto caldera are locations of the Crystal tuff, as mentioned above.

Given the felsic composition of the glass that makes up the Lokochot tuff, the

event that ejected this material was likely a Plinian-style eruption that would have sent a

column of material high into the atmosphere (Sarna-Wojcicki et al., 1981). When this

type of event occurs, material is dispersed by the prevalent winds in the area, and the variable dispersal of material may be reflected in air-fall deposits as grain size variation correlated with distance from the source. Since coarse grains settle out of a plume of volcanic material faster than finer grains, grain size decreases with distance from a tuff’s source (Sarna-Wojcicki et al., 1981). Most of the tephra we find in the Western Mille area are coarse-grained and pumice-rich, which suggests that their source or sources are relatively near. The finer mean particle sizes of the Kilaytoli and Waki tuffs suggest that they originated from more distant sources than the others.

Figure 26. Schematic diagram of distribution of pyroclastic material; notice correlation of thickness and grainsize with distance from source; after Johnston, 1997.

Tephra ejected from eruptions like those which produced the Lokochot tuff can be

transported thousands of kilometers from their source by winds in the various strata of the

atmosphere (Shane, 2000). The flux of material is determined by the volume erupted, the height achieved, and by the prevailing wind strength(s) (Feakins et al., 2007). The larger 59

the volume erupted, the higher the chances of material entering not only the troposphere

but the stratosphere as well. With this further dispersal of material, the chances are

improved that material may spread in more than one dominant direction, due to differing

prevalent wind directions in the different levels of the atmosphere (Shane, 2000).

Seasonal wind reversals in the troposphere, along with fairly consistent easterly winds in the stratosphere, for example, might explain the dispersal of material from an eruption in eastern Africa to both the east and the west during the summer months (Feakins et al.,

2007).

It has been estimated using known exposures that the erupted volume of the

Crystal tuff was in excess of 1100 km3 (WoldeGabriel et al., 1990), approximately 1000

times that erupted by Mount St. Helens in 1980 (Sarna-Wojcicki et al., 1981). This

relatively large erupted volume makes it likely that material would have entered the

stratosphere, thus enabling the dispersal of fine ash particles to both the southeast –

toward the Turkana basin – and to the northwest – toward the WORMIL project area, the

Gulf of Aden and the Arabian Sea. Adding to the Crystal tuff volume a conservative

estimate for the volume of the Kilaytoli/Lokochot tuff, based on known exposures and a

constant thickness of 1 m across the area between these locations, we get a total erupted

volume of ~2000 km3, a magnitude on the scale of the largest Yellowstone supervolcano

eruptions (Newhall and Dzurisin, 1988). Thus, the volcanic event that ejected the

Kilaytoli/Lokochot tuff, if correlative with the Crystal tuff, was truly massive and covered a great part of the region in at least a meter of pyroclastic material.

Geochemical data are available for sample BT-75 of the Crystal tuff, which has

been correlated with the Lokochot tuff on the basis of age (WoldeGabriel et al., 2000;

Deino et al., in review). Whole rock XRF analyses of this sample (WoldeGabriel, 1987)

exhibit geochemistry which is generally consistent with our analyses, though some

differences are evident. The values for Fe2O3 and K2O are intermediate between those for

the two modes of the Lokochot/Kilaytoli tuffs; this would make sense for a whole rock

analysis of a combination of the two modes. High Al2O3 and Na2O concentrations may be

explained by the fact that our analyses are of glass separates, while those of the Crystal

tuff include phenocrysts in the resultant bulk composition. Feldspars (26.3%) and biotite

(1.8%) are the dominant phenocrysts in this crystal-rich tuff (WoldeGabriel, 1987), so it

may be that they are the cause for the observed differences. For example, if there were a

high concentration of Albite (NaAlSi3O8) in the Crystal tuff, this would drive up the

composition with respect to Na and Al in a whole rock analysis, compared with an

analysis of only glass separates. These chemical data are not sufficiently similar to those

for the Lokochot tuff, nor for the Kilaytoli tuff, to suggest correlation, but the ages of the

different tephra layers agree, and the possibility remains that they are indeed different

expressions of the same tephra layer. A definitive correlation or the exclusion of this

possibility would require further sampling and analysis, including analysis of individual

grains of the Crystal tuff.

Future Work

At present, there are sites in the Western Mille area which have yet to be firmly

correlated with the others. Further sampling and chemical analysis will be necessary to

determine which of the tephra are exposed at Am-Ado. There have also been recent field

observations which introduce new questions. The recent realization that the Aralee Issie 61

tuff is geologically isolated from the rest of the Aralee Issie section raises questions about

the identity of this tephra – is it one of the other known tephra from the area, or a

different tephra layer altogether? It is possible that chemical analysis will help answer

this and other questions, but given the at times ambiguous results of these analyses – for example the similarity between samples ARI-08-3 and ARI-08-4 – it may be that further analysis will not elucidate this issue.

Conclusion

The confirmation of the new correlation of tephra in the WORMIL area has

implications for continued work in the area, in terms of geology as well as paleontology.

Depending on where fossiliferous horizons occur at a given site, the relative age of the

fossils can be inferred by their position in relation to one or more of the tephra layers that

have been dated. Now that the stratigraphy is more coherent across sites in the Western

Mille area, this should be a simpler task than it has been in the past. The correlation of the

Kilaytoli and Waki tuffs with tephra from other areas lends itself to comparison of the

fossil assemblages found in the different project areas in the region. Paleontologists

should now be able to compare specimens found in the WORMIL area with those found

in other parts of Ethiopia or Kenya from the same time period.

Appendix 1. Mesgid Dora Sections

A. Map of Mesgid Dora fossil localities; stars represent locations of measured sections shown in B below.

B. Mesgid Dora sections; tephra abbreviations and key same as Figure 3; section locations shown in A above.

Appendix 2. Sample Locations: GPS Coordinates.

Sample No. Description Latitude Longitude Elevation Collector Date AMA-08-1 Pumiceous Tuff 11˚ 31' 15.1'' 40˚ 28' 41.3'' 647 m JDA 3/3 AMA-08-2 Tuffaceous S.S. 11˚ 31' 12.7'' 40˚ 28' 44.0'' 642 m JDA 3/3 AMA-08-3 Pumiceous Tuff 11˚ 32' 02.1'' 40˚ 28' 24.8'' 673 m JDA 3/3 ARI-08-1 Pumiceous Tuff 11˚ 30' 57.6'' 40˚ 28' 49.6'' 637 m BZS 2/13 ARI-08-2 Non-pumiceous Tuff 11˚ 30' 57.6'' 40˚ 28' 51.0'' 634 m BZS 2/13 ARI-08-3 Pumiceous Tuff 11˚ 30' 57.4'' 40˚ 28' 51.6'' 633 m BZS 2/13 ARI-08-4 Tuff 11˚ 30' 55.9'' 40˚ 28' 53.4'' 629 m BZS 2/13 ARI-08-5 Non-pumiceous Tuff 11˚ 31' 11.4'' 40˚ 29' 03.1'' 645 m JDA 3/3 BDN-08-1 Non-pumiceous Tuff 11˚ 25' 04.8'' 40˚ 30' 59.6'' 653 m JDA 3/4 BUR-08-1 Altered Tuff 11˚ 28' 23.8'' 40˚ 32' 32.2'' 600 m BZS 2/19 DKL-08-1 Altered Tuff 11˚ 17' 03.9'' 40˚ 13' 13.6'' 916 m JDA 2/27 DKL-08-2 Tuffaceous S.S. 11˚ 17' 03.9'' 40˚ 13' 13.6'' 919 m JDA 2/27 DKL-08-3 Non-pumiceous Tuff 11˚ 17' 06.3'' 40˚ 13' 14.5'' 920 m JDA 2/27 EDR-08-1 Calcareous S.S. 11˚ 18' 31.6'' 40˚ 27' 40.1'' 657 m BZS 2/16 EDR-08-2 Tuff 11˚ 18' 31.6'' 40˚ 27' 40.1'' 656 m BZS 2/16 EH-08-1 Yellow Layer 11˚ 23' 12.5'' 40˚ 23' 53.1'' 714 m BZS 2/14 EH-08-2 Black Layer 11˚ 23' 12.5'' 40˚ 23' 53.1'' 716 m BZS 2/14 EH-08-3 Pumiceous Tuff 11˚ 23' 12.5'' 40˚ 23' 53.1'' 717 m BZS 2/14 EH-08-4 Non-pumiceous Tuff 11˚ 23' 12.5'' 40˚ 23' 53.1'' 725 m BZS 2/14 EH-08-5 Limestone 11˚ 22' 33.0'' 40˚ 23' 15.8'' 713 m BZS 2/14 FI-08-1 Non-pumiceous Tuff 11˚ 17' 55.0'' 40˚ 19' 18.5'' - BZS 2/15 KER-08-1 Altered Tuff 11˚ 28' 56.3'' 40˚ 27' 19.6'' 679 m BZS 2/18 KER-08-2 Pumiceous Tuff 11˚ 28' 50.9'' 40˚ 27' 21.7'' - YHS 2/28 LAD-08-1 Tuff 11˚ 20' 34.5'' 40˚ 31' 53.7'' - BZS 2/17 LDD-08-1 Calcareous S.S. 11˚ 25' 11.7'' 40˚ 34' 34.3'' 586 m BZS 2/20 LDD-08-2 Non-pumiceous Tuff 11˚ 25' 16.2'' 40˚ 33' 47.7'' 595 m BZS 2/20 MKM-08-1 Pumiceous Tuff 11˚ 30' 40.4'' 40˚ 30' 37.4'' 606 m JDA 2/28 MSD-08-1 Calcareous S.S. 11˚ 31' 04.4'' 40˚ 30' 01.8'' 639 m BZS 2/12 MSD-08-2 Pumiceous Tuff 11˚ 31' 09.0'' 40˚ 29' 53.5'' 627 m JDA 2/22 MSD-08-3 Bimodal Tuff 11˚ 31' 09.0'' 40˚ 29' 53.5'' 630 m JDA 2/22 MSD-08-4 Non-pumiceous Tuff 11˚ 31' 09.0'' 40˚ 29' 53.5'' 632 m JDA 2/22 MSD-08-5 Pumiceous Tuff 11˚ 31' 09.0'' 40˚ 29' 57.6'' 635 m JDA 2/22 MSD-08-6 Pumiceous Tuff 11˚ 31' 06.0'' 40˚ 30' 00.9'' 635 m JDA 2/22 MSD-08-7 Pumiceous Tuff 11˚ 30' 59.7'' 40˚ 30' 28.4'' - JDA 2/24 MSD-08-8 Altered Tuff 11˚ 30' 54.4'' 40˚ 30' 07.9'' 618 m JDA 2/24 MSD-08-9 Pumiceous Tuff 11˚ 30' 59.0'' 40˚ 29' 46.8'' 629 m JDA 2/28 MSD-08-10 Pumiceous Tuff 11˚ 30' 20.7'' 40˚ 30' 03.2'' 608 m JDA 2/28 MSD-08-11 Basaltic Tuff 11˚ 30' 20.7'' 40˚ 30' 03.2'' 609 m JDA 2/28 MSD-08-12 Pumiceous Tuff 11˚ 30' 42.8'' 40˚ 30' 02.1'' - JDA 3/1 MSD-08-13 Non-pumiceous Tuff 11˚ 31' 14.3'' 40˚ 30' 32.8'' - JDA 3/1 WMC-08-1 Non-pumiceous Tuff 11˚ 30' 13.8'' 40˚ 29' 32.7'' 620 m JDA 2/28 WMC-08-2 Pumiceous Tuff 11˚ 30' 04.7'' 40˚ 29' 28.9'' - JDA 3/3 WMC-08-3 Bimodal Tuff 11˚ 30' 04.7'' 40˚ 29' 28.9'' - JDA 3/3 WMC-08-4 Non-pumiceous Tuff 11˚ 30' 04.7'' 40˚ 29' 28.9'' 627 m JDA 3/3 WMC-08-5 Pumiceous Tuff 11˚ 30' 04.7'' 40˚ 29' 28.9'' - JDA 3/3

Appendix 3. Corrected EMPA Data.

Na2O MgO O Cl CaO K2O SiO2 Al2O3 TiO2 MnO Fe2O3 Sum

K80-295

41 3.321 0.026 5.505 0.163 0.210 2.462 74.811 9.772 0.298 0.122 4.362 101.052

43 3.458 0.034 4.305 0.123 0.194 3.038 75.702 10.704 0.221 0.114 2.990 100.884

44 3.788 0.023 3.524 0.144 0.157 4.044 75.810 10.764 0.156 0.116 3.010 101.537

45 4.902 0.031 3.332 0.130 0.190 4.676 74.825 10.946 0.144 0.116 2.846 102.139

46 4.452 0.029 2.776 0.105 0.188 4.704 76.041 11.114 0.239 0.147 3.066 102.862

47 4.772 0.034 3.360 0.152 0.179 4.133 75.230 10.747 0.170 0.103 3.256 102.134

48 2.113 0.047 5.211 0.156 0.178 2.917 74.872 9.782 0.201 0.136 4.168 99.781

49 4.087 0.035 5.854 0.215 0.162 3.752 74.597 10.090 0.185 0.139 4.287 103.402

50 2.933 0.043 5.845 0.154 0.193 3.000 74.401 9.836 0.349 0.100 4.225 101.079

51 3.198 0.019 6.937 0.171 0.199 3.440 74.084 10.029 0.269 0.119 4.286 102.752

WM-KSD-1

- 52 3.219 4.815 0.123 0.194 5.374 74.853 10.620 0.144 0.079 3.073 102.493 0.001 53 4.350 0.024 5.177 0.114 0.169 5.612 71.659 10.758 0.223 0.079 2.861 101.026

54 1.996 0.018 5.334 0.134 0.177 4.812 73.184 10.649 0.241 0.037 2.699 99.281

55 3.370 0.044 5.740 0.118 0.159 5.128 74.169 10.488 0.117 0.071 3.034 102.438

56 2.644 0.027 6.307 0.117 0.167 5.005 75.011 10.926 0.203 0.085 3.057 103.549

57 2.484 0.047 5.325 0.121 0.191 5.194 73.808 10.672 0.152 0.096 2.944 101.034

58 3.097 0.036 3.296 0.138 0.191 4.495 74.111 10.757 0.163 0.065 3.077 99.425

59 2.865 0.023 6.082 0.134 0.189 4.580 72.443 10.637 0.239 0.054 3.063 100.310

60 2.633 0.037 1.992 0.131 0.198 4.037 75.195 11.033 0.184 0.057 3.061 98.559

61 2.463 0.054 5.002 0.121 0.160 4.718 72.443 10.691 0.191 0.068 2.941 98.853

62 3.142 0.059 5.653 0.125 0.186 5.289 73.798 10.855 0.130 0.045 2.962 102.245

63 3.935 0.063 4.117 0.166 0.179 5.236 73.322 10.722 0.205 0.048 2.953 100.945

64 2.567 0.033 4.865 0.104 0.185 5.307 73.227 10.747 0.209 0.125 3.004 100.372

65 3.542 0.033 5.334 0.126 0.172 4.654 73.835 10.668 0.057 0.034 2.993 101.448

WM-KSD-3

66 3.130 0.105 2.483 0.150 0.223 3.587 75.314 9.912 0.286 0.190 4.444 99.825

68 3.295 0.006 4.039 0.128 0.222 4.188 73.685 10.514 0.148 0.094 3.323 99.644

69 1.773 0.021 3.728 0.166 0.188 3.680 74.591 9.706 0.327 0.111 4.070 98.360

71 3.076 0.018 5.387 0.173 0.234 4.746 74.226 9.919 0.284 0.088 4.290 102.442

73 2.426 0.021 5.004 0.197 0.173 3.897 72.410 9.941 0.329 0.208 4.134 98.739

74 3.732 0.031 3.957 0.196 0.193 4.750 73.357 10.320 0.144 0.134 4.151 100.967

75 2.753 0.009 4.122 0.209 0.189 4.626 74.523 9.972 0.187 0.131 4.045 100.764

76 3.596 0.034 2.713 0.156 0.199 5.232 72.495 9.878 0.227 0.114 4.223 98.868

77 1.950 0.025 3.524 0.153 0.184 4.849 73.594 9.839 0.161 0.120 3.422 97.821

80 3.276 0.012 4.316 0.117 0.153 4.581 74.326 10.614 0.130 0.094 2.972 100.592 65

81 3.221 0.030 5.563 0.141 0.152 4.845 74.802 10.514 0.165 0.060 2.947 102.438

82 3.027 0.013 4.806 0.189 0.222 5.072 73.503 10.106 0.231 0.145 4.418 101.732

84 3.352 0.048 3.853 0.156 0.198 5.238 73.114 9.955 0.282 0.148 4.342 100.685

85 2.859 0.054 5.945 0.147 0.188 4.727 73.487 9.903 0.299 0.114 4.341 102.064

86 2.592 0.027 4.437 0.110 0.172 4.855 74.490 10.829 0.196 0.114 2.970 100.792

87 3.883 0.015 3.204 0.111 0.194 3.957 74.215 10.725 0.129 0.034 2.954 99.423

88 2.392 0.012 4.926 0.115 0.184 4.462 73.122 10.593 0.146 0.120 3.047 99.116

89 3.324 0.023 4.052 0.119 0.191 4.093 75.088 10.201 0.133 0.065 3.165 100.454

90 1.988 0.027 4.940 0.150 0.185 4.865 74.213 10.718 0.177 0.091 2.950 100.304

91 2.066 0.024 4.854 0.171 0.172 4.580 73.595 9.918 0.238 0.145 4.354 100.118

ARI-08-5

93 1.279 0.016 6.987 0.128 0.170 3.729 73.373 10.575 0.294 0.108 2.990 99.649

95 2.689 0.022 3.873 0.133 0.182 6.045 72.855 10.713 0.216 0.119 3.037 99.884

96 3.476 0.020 3.535 0.145 0.168 4.862 72.002 10.699 0.140 0.100 3.117 98.265

97 1.998 0.039 4.506 0.148 0.195 4.912 73.636 9.863 0.282 0.162 4.492 100.234

98 3.064 0.031 5.575 0.107 0.165 5.140 72.916 10.767 0.194 0.102 3.074 101.136

99 2.489 0.016 5.295 0.180 0.234 5.178 72.616 9.982 0.252 0.136 4.297 100.675

100 1.562 0.022 6.982 0.093 0.226 4.953 73.545 10.048 0.238 0.100 3.658 101.427

101 1.919 0.028 5.923 0.149 0.196 5.237 73.020 9.970 0.239 0.173 4.148 101.003

102 2.301 0.072 5.706 0.204 0.146 4.015 72.988 9.411 0.233 0.142 4.800 100.018

103 3.092 0.038 4.575 0.147 0.154 4.480 73.487 10.572 0.199 0.122 3.114 99.982

104 3.214 0.037 3.965 0.099 0.189 5.277 74.193 10.629 0.243 0.125 2.973 100.946

105 3.312 0.016 4.398 0.122 0.211 5.552 74.129 10.506 0.162 0.085 2.891 101.384

106 2.798 0.017 3.655 0.095 0.212 4.441 74.044 10.425 0.225 0.182 3.636 99.730

107 2.450 0.036 4.784 0.107 0.160 5.646 74.498 10.793 0.037 0.125 2.937 101.572

108 3.106 0.025 2.827 0.114 0.166 5.221 74.078 10.563 0.286 0.077 3.088 99.551

109 2.063 0.041 4.566 0.157 0.203 4.378 73.385 9.924 0.273 0.111 4.236 99.338

110 3.575 0.034 3.345 0.129 0.192 4.653 73.899 10.609 0.164 0.137 3.129 99.866

111 2.102 0.028 4.186 0.129 0.196 5.027 74.497 10.620 0.174 0.060 3.094 100.112

ARI-08-2

112 2.211 0.038 4.369 0.147 0.157 4.334 74.364 9.931 0.239 0.176 4.188 100.153

113 2.380 0.015 5.216 0.070 0.209 5.496 73.347 10.199 0.261 0.142 3.785 101.120

115 1.901 0.032 5.459 0.120 0.172 4.756 74.363 9.463 0.190 0.190 4.571 101.217

116 2.676 0.033 4.855 0.124 0.153 4.847 73.096 10.161 0.193 0.165 3.746 100.049

117 2.617 0.020 6.105 0.111 0.122 5.264 74.335 10.020 0.219 0.162 3.948 102.924

118 2.448 0.022 6.465 0.165 0.183 5.330 72.531 9.511 0.231 0.091 4.546 101.521

119 0.861 0.027 5.579 0.186 0.157 5.005 72.658 9.570 0.144 0.142 4.517 98.847

121 1.776 0.027 6.355 0.108 0.165 5.843 72.731 10.157 0.199 0.213 4.115 101.689

122 3.297 0.012 4.850 0.140 0.123 5.706 73.591 9.626 0.284 0.188 4.489 102.305

123 2.786 0.024 5.159 0.167 0.138 5.353 73.222 9.950 0.248 0.148 4.283 101.478

124 3.680 0.031 4.159 0.090 0.156 6.177 72.590 10.119 0.239 0.168 3.870 101.280

125 2.836 0.041 5.442 0.183 0.174 4.449 72.972 9.539 0.207 0.156 4.610 100.611

126 1.794 0.019 3.877 0.094 0.224 5.164 73.522 10.251 0.233 0.162 3.700 99.041

127 1.766 0.027 5.078 0.186 0.135 4.130 72.947 9.299 0.237 0.134 4.756 98.694

412 2.050 0.020 5.564 0.080 0.219 4.758 74.212 10.226 0.262 0.166 3.930 101.487

413 2.424 0.027 5.576 0.130 0.208 5.701 73.616 9.943 0.184 0.163 4.104 102.078

414 2.391 0.010 5.335 0.162 0.158 5.279 74.274 9.719 0.251 0.203 4.669 102.452 - 415 2.127 6.491 0.144 0.134 4.615 72.548 9.538 0.290 0.143 4.732 100.761 0.001 416 0.847 0.039 7.480 0.184 0.099 5.321 72.160 9.296 0.111 0.184 4.731 100.452

WMC-08-4

128 3.990 0.007 4.986 0.083 0.157 4.319 74.291 10.347 0.244 0.219 3.736 102.380

129 3.014 0.051 6.578 0.160 0.121 5.655 73.653 9.736 0.274 0.139 4.605 103.988

130 3.140 0.024 3.617 0.103 0.200 5.322 73.950 10.103 0.175 0.136 3.755 100.526

131 2.779 0.034 6.403 0.190 0.116 5.547 72.988 9.652 0.179 0.136 4.540 102.565

132 5.684 0.029 3.461 0.085 0.179 4.100 75.524 10.339 0.288 0.097 3.818 103.604

133 3.719 0.025 4.808 0.119 0.170 3.495 74.828 9.768 0.346 0.162 4.102 101.541

134 4.181 0.027 7.211 0.179 0.177 5.054 73.908 9.401 0.182 0.145 4.536 105.001

135 3.278 0.025 5.909 0.119 0.203 4.793 72.389 10.331 0.191 0.148 3.702 101.088

136 3.187 0.034 6.633 0.114 0.159 4.369 72.856 9.952 0.164 0.097 3.826 101.391

137 3.055 0.018 4.426 0.096 0.216 4.118 73.428 10.155 0.232 0.188 3.969 99.901

405 2.426 0.039 4.909 0.080 0.258 3.455 74.340 10.122 0.149 0.152 3.856 99.786

406 2.311 0.020 5.329 0.180 0.170 3.764 73.886 9.550 0.085 0.195 4.677 100.167

407 3.255 0.001 5.781 0.189 0.177 4.835 74.292 9.763 0.277 0.143 4.422 103.136

408 2.352 0.022 3.763 0.112 0.180 6.641 73.677 10.059 0.206 0.166 3.843 101.022

409 2.261 0.026 4.104 0.138 0.127 4.659 75.562 10.158 0.211 0.189 4.221 101.656

410 1.902 0.017 5.441 0.147 0.179 5.703 73.796 9.734 0.295 0.126 4.168 101.509

ARI-08-1

138 2.559 0.152 4.805 0.074 0.662 4.885 72.259 12.608 0.288 0.088 1.914 100.294

139 3.406 0.183 3.456 0.062 0.703 4.626 72.497 12.728 0.136 0.063 2.078 99.936

140 2.823 0.165 3.458 0.057 0.706 5.978 71.423 12.788 0.190 0.077 1.636 99.300

141 3.472 0.179 2.208 0.077 0.714 5.909 71.832 12.894 0.253 0.054 2.008 99.600

142 2.709 0.153 4.413 0.053 0.663 5.476 71.254 12.999 0.215 0.020 1.854 99.809

143 3.721 0.167 4.079 0.052 0.690 4.803 71.322 12.673 0.141 0.100 1.708 99.455

144 2.817 0.161 5.027 0.072 0.743 5.228 71.982 12.792 0.253 0.026 1.900 101.000

145 3.295 0.163 5.504 0.060 0.718 5.420 71.058 12.749 0.149 0.066 1.982 101.164

146 2.932 0.183 4.283 0.085 0.663 5.844 72.003 12.964 0.173 0.037 1.939 101.105

147 3.191 0.140 2.458 0.059 0.635 5.704 72.775 12.869 0.189 0.094 1.873 99.987

MKM-08-1

314 1.705 0.163 6.649 0.070 0.726 6.001 70.554 12.851 0.260 0.075 1.810 100.864

315 3.170 0.132 5.343 0.062 0.672 6.817 71.199 12.886 0.164 0.028 1.789 102.262

316 2.763 0.154 3.977 0.040 0.701 5.712 71.777 12.861 0.185 0.069 1.814 100.052

317 2.562 0.166 5.142 0.054 0.711 6.438 71.985 12.927 0.226 0.042 1.878 102.131

318 4.353 0.186 3.551 0.067 0.660 5.786 70.752 12.794 0.243 0.053 1.966 100.410

319 2.464 0.161 4.704 0.071 0.643 5.998 71.276 12.776 0.228 0.083 1.987 100.390

320 3.274 0.138 4.073 0.067 0.691 6.696 72.087 12.626 0.220 0.064 1.966 101.902

321 2.957 0.175 4.558 0.058 0.709 5.760 71.115 12.813 0.172 0.075 1.857 100.249

322 2.181 0.164 4.196 0.090 0.676 6.083 71.982 12.725 0.206 0.055 2.064 100.423 - 323 3.393 4.317 0.056 -0.011 6.153 72.150 12.982 0.188 0.069 1.865 101.147 0.013

MSD-08-5

324 2.204 0.189 3.068 0.030 0.716 6.973 71.628 12.986 0.285 0.019 2.005 100.104

325 2.954 0.164 2.674 0.058 0.697 7.011 71.996 12.938 0.285 0.047 2.051 100.875

326 3.983 0.211 2.451 0.075 0.868 4.816 71.771 13.426 0.239 0.047 2.105 99.993

328 3.225 0.147 3.289 0.061 0.612 6.853 71.667 12.830 0.187 0.033 1.516 100.419

329 4.246 0.170 1.185 0.047 0.700 6.080 72.971 13.022 0.216 0.061 2.109 100.806 - 331 3.393 2.546 0.096 0.681 6.238 72.498 12.817 0.172 0.072 1.930 100.413 0.032 332 1.392 0.008 4.330 0.123 0.151 4.280 74.692 10.001 0.247 0.163 4.097 99.484

333 2.812 0.155 4.759 0.094 0.689 6.253 71.979 13.107 0.259 0.014 1.891 102.010

334 2.097 0.190 3.313 0.061 0.850 6.001 72.203 13.308 0.327 0.086 2.161 100.597

335 2.138 0.179 2.833 0.082 0.698 5.728 72.069 12.793 0.177 0.086 1.929 98.711

336 3.790 0.157 3.118 0.040 0.661 6.311 71.707 12.714 0.248 0.064 1.892 100.702

337 3.355 0.161 4.150 0.037 0.671 6.725 73.212 12.936 0.221 0.055 1.920 103.444

338 2.468 0.165 2.858 0.085 0.666 5.088 72.604 12.982 0.189 0.092 1.979 99.177

MSD-08-3B

339 4.139 0.138 2.920 0.051 0.770 4.640 74.505 11.860 0.243 0.061 2.449 101.776 - 340 2.013 5.680 0.022 9.917 0.709 51.164 13.347 2.737 0.235 13.656 99.016 0.463 341 2.365 5.504 0.232 0.023 9.605 0.766 52.187 13.221 2.850 0.202 14.029 100.984

343 2.187 5.143 1.292 0.019 10.213 0.487 52.974 16.827 1.983 0.181 8.670 99.977

344 2.323 5.823 0.230 0.008 9.937 0.737 50.979 13.339 2.779 0.205 13.466 99.827

345 2.198 0.129 4.147 0.055 0.709 5.246 71.386 12.720 0.135 0.058 2.138 98.921 - 346 2.265 5.787 0.016 9.858 0.806 50.623 13.255 2.853 0.194 13.348 98.608 0.399 - 347 2.120 5.452 0.012 9.818 0.870 51.101 13.541 2.714 0.238 13.497 98.800 0.564 348 10.968 0.020 0.440 0.014 0.042 0.074 68.873 19.815 0.084 0.036 0.344 100.709

349 2.140 5.494 0.726 0.039 9.748 0.745 50.711 13.369 2.685 0.232 13.800 99.689 - 350 2.009 5.481 0.036 9.742 0.753 51.059 13.362 2.895 0.249 13.401 98.475 0.512 - - 351 2.501 5.297 9.858 0.804 51.065 13.410 2.985 0.241 13.560 99.246 0.467 0.007 352 2.129 5.549 0.534 0.020 9.732 0.760 50.555 13.203 3.032 0.189 13.180 98.882

MSD-08-2

355 2.496 0.020 5.472 0.040 0.405 6.064 73.634 11.656 0.146 0.064 2.026 102.023

356 3.143 0.038 5.751 0.050 0.402 6.638 73.247 11.783 0.170 0.083 1.970 103.274

357 2.345 0.022 4.631 0.023 0.386 6.052 73.678 11.754 0.111 0.017 1.912 100.930

358 3.305 0.006 4.096 0.046 0.452 5.695 73.932 11.689 0.077 0.042 1.984 101.324

359 3.348 0.015 4.959 0.052 0.434 5.609 73.479 11.450 0.238 0.025 1.984 101.596

361 3.327 0.015 4.966 0.046 0.399 6.956 74.267 11.802 0.150 0.025 1.881 103.834

362 2.702 0.024 5.019 0.040 0.441 6.473 74.089 11.646 0.001 0.056 1.945 102.436

363 2.719 0.019 5.057 0.030 0.498 5.456 73.180 11.601 0.090 0.056 1.838 100.545

364 3.222 0.011 5.406 0.030 0.443 6.161 72.814 11.590 0.168 0.039 1.843 101.726

365 3.284 0.014 5.902 0.019 0.425 4.970 73.419 11.764 0.107 0.047 1.968 101.920

366 3.111 0.023 6.063 0.026 0.416 6.118 73.542 11.625 0.091 0.022 1.855 102.892

367 2.890 0.033 3.875 0.027 0.448 5.339 73.269 11.616 0.106 0.042 1.838 99.484

ARI-08-3

368 2.847 0.070 4.414 0.063 0.564 5.309 73.713 11.428 0.127 0.053 2.561 101.147

369 2.451 0.041 4.983 0.036 0.401 5.046 73.320 11.509 0.114 0.044 1.866 99.812

370 3.023 0.025 6.003 0.047 0.428 5.987 74.008 11.648 0.161 0.058 2.060 103.450

371 3.228 0.009 6.234 0.033 0.432 5.876 73.409 11.686 0.092 0.019 1.944 102.961

372 3.000 0.021 4.515 0.019 0.416 5.750 73.002 12.008 0.175 0.069 1.937 100.912

373 3.540 0.044 5.199 0.047 0.418 6.123 74.095 11.774 0.226 0.061 1.937 103.463

374 4.179 0.028 4.814 0.038 0.412 5.406 72.115 11.779 0.251 0.025 1.879 100.926

375 3.616 0.030 2.760 0.060 0.450 5.585 75.036 11.800 0.085 0.047 1.851 101.319

376 2.967 0.027 4.746 0.053 0.402 5.809 74.034 11.631 0.147 0.083 1.868 101.767

377 3.347 0.032 5.127 0.027 0.425 6.304 73.183 11.780 0.221 0.039 1.832 102.316

378 3.655 0.030 4.042 0.050 0.433 5.599 71.801 11.792 0.072 0.047 1.962 99.481

379 2.868 0.036 5.925 0.070 0.386 5.837 73.001 11.516 0.124 0.017 1.977 101.757

380 3.031 0.013 4.557 0.037 0.467 6.321 73.167 11.641 0.080 0.017 1.931 101.261

MSD-08-13

381 2.731 0.012 4.006 0.115 0.193 5.400 74.067 10.725 0.061 0.069 2.868 100.247

382 2.608 0.020 3.449 0.185 0.156 4.915 76.321 9.689 0.241 0.127 4.299 102.011

383 2.454 0.051 4.733 0.107 0.166 4.526 73.369 10.601 0.143 0.025 2.793 98.967

384 3.165 0.073 5.130 0.141 0.165 5.268 73.130 10.683 0.160 0.078 2.868 100.860

386 2.237 0.031 4.661 0.093 0.188 4.783 74.346 10.591 0.177 0.111 3.112 100.331

387 3.182 0.037 2.184 0.115 0.198 4.222 74.717 10.557 0.174 0.094 3.193 98.676

388 1.187 0.063 5.642 0.153 0.189 3.875 74.842 9.368 0.152 0.158 4.180 99.809

389 1.774 0.024 5.319 0.190 0.189 5.306 74.568 9.838 0.212 0.136 4.088 101.643

390 2.518 0.029 3.975 0.107 0.186 5.451 74.464 10.575 0.222 0.067 2.959 100.553

391 1.997 0.034 3.394 0.130 0.170 5.491 74.955 11.030 0.245 0.100 3.039 100.586

392 2.348 0.060 3.065 0.115 0.185 6.074 75.894 10.838 0.168 0.119 2.869 101.736

ARI-08-4

393 4.623 0.001 4.165 0.015 0.467 4.704 73.974 11.851 0.122 0.014 1.945 101.881

394 2.730 0.047 4.086 0.041 0.388 3.434 77.721 10.908 0.201 0.040 1.858 101.455

395 2.438 0.024 4.816 0.026 0.442 5.388 73.924 11.719 0.084 0.051 2.052 100.965

396 3.782 0.024 4.367 0.022 0.421 4.758 74.494 11.768 0.054 0.034 1.954 101.679 - 397 2.757 4.028 0.030 0.452 4.778 75.050 11.820 0.224 0.089 1.956 101.179 0.004 - 398 3.280 3.743 0.045 0.417 4.817 74.974 11.772 0.106 0.026 1.934 101.102 0.012 399 3.117 0.067 4.817 0.022 0.367 4.400 75.526 11.738 0.176 0.074 1.889 102.192

400 2.954 0.056 3.400 0.069 0.476 5.952 74.894 11.442 0.155 0.106 2.308 101.810

401 3.632 0.001 3.807 0.041 0.373 6.089 74.117 11.837 0.103 0.075 1.945 102.020

402 2.818 0.052 3.714 0.039 0.487 5.295 73.611 11.691 0.225 0.046 2.512 100.491

404 3.481 0.022 5.137 0.038 0.430 5.171 73.472 11.771 0.066 0.106 1.930 101.623

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