www.sciencemag.org/content/354/6314/878/suppl/DC1

Supplementary Material for

The formation of peak rings in large impact craters

Joanna Morgan,* Sean Gulick, Timothy Bralower, Elise Chenot, Gail Christeson, Philippe Claeys, Charles Cockell, Gareth S. Collins, Marco J. L. Coolen, Ludovic

Ferrière, Catalina Gebhardt, Kazuhisa Goto, Heather Jones, David A. Kring, Erwan Le Ber, Johanna Lofi, Xiao Long, Christopher Lowery, Claire Mellett, Rubén Ocampo-

Torres, Gordon R. Osinski, Ligia Perez-Cruz, Annemarie Pickersgill, Michael Poelchau, Auriol Rae, Cornelia Rasmussen, Mario Rebolledo-Vieyra, Ulrich Riller, Honami Sato,

Douglas R. Schmitt, Jan Smit, Sonia Tikoo, Naotaka Tomioka, Jaime Urrutia-Fucugauchi, Michael Whalen, Axel Wittmann, Kosei Yamaguchi, William Zylberman

*Corresponding author. Email: j.morgan@imperial.ac.uk

Published 18 November 2016, Science 354, 878 (2016)

DOI: 10.1126/science.aah6561

This PDF file includes:

Material and Methods Table S1 References

Supplementary Materials for

The formation of peak rings in large impact craters

Joanna Morgan, Sean Gulick, Timothy Bralower, Elise Chenot, Gail Christeson, Philippe Claeys, Charles Cockell, Gareth S. Collins, Marco J. L. Coolen, Ludovic Ferrière, Catalina Gebhardt, Kazuhisa Goto, Heather Jones, David A. Kring, Erwan Le Ber,

Johanna Lofi, Xiao Long, Christopher Lowery, Claire Mellett, Rubén Ocampo-Torres, Gordon R. Osinski, Ligia Perez-Cruz, Annemarie Pickersgill, Michael Pölchau, Auriol

Rae, Cornelia Rasmussen, Mario Rebolledo-Vieyra, Ulrich Riller, Honami Sato, Douglas R. Schmitt, Jan Smit, Sonia Tikoo, Naotaka Tomioka, Jaime Urrutia-Fucugauchi,

Michael Whalen, Axel Wittmann, Kosei Yamaguchi, William Zylberman.

correspondence to: j.morgan@ic.ac.uk

This PDF file includes:

Materials and Methods Tables S1

Materials and Methods

Numerical modeling

The Chicxulub impact was simulated using the iSALE2D-Dellen shock physics code (43-

44). Based on the SALE hydrocode (46), iSALE2D was developed to simulate impact

phenomena involving complex geological materials (43, 46-48) using a multi-material

Eulerian approach. Numerical model parameters were based on a recent suite of

Chicxulub impact simulations that produced a good match to geological and geophysical

constraints (17-19). A simplified target structure was used comprising 2.8-km (calcite)

sediments, 30-km (granite) crust overlying (dunite) mantle. This structure approximates

the pre-impact target stratigraphy in the Yucatan which, in onshore wells outside the

1

crater, consists of a 2.5- to 3-km thick sequence of Mesozoic sedimentary rocks formed

from carbonates and anhydrite, above Paleozoic basement (49-50). Marine seismic

reflection data suggest the Mesozoic sequence may thicken up to ~4 km offshore to the

northeast of the Chicxulub impact structure (13, 51). Crustal thickness was determined

from reflection and refraction data (11, 19). A geothermal gradient of 10 K/km was used

to 80-km depth.

The impactor parameters were: diameter 14.4 km, velocity 12 km/s, density = 2650

kg/m3. A vertical incidence impact angle was enforced by the cylindrical geometry of the

two-dimensional model. A spatial resolution of 200 m was used, corresponding to 36

cells across the impactor radius. While other impactor trajectory angle, mass and speed

combinations will produce a final crater of the same scale and structure, this low-

velocity, large-diameter vertical impact scenario is computationally expedient, while also

accounting, very approximately, for the reduced vertical velocity component in a more

typical, oblique incidence impact. In the absence of a material model for chondritic

asteroids, the impactor was also represented using the granite material model because

granite has a reference density equivalent to the average bulk density of stony asteroids

(52). Model results are not expected to be sensitive to the equation of state of the

impactor.

Equation-of-state tables for calcite (53), granite (54), and dunite (55), derived using the

Analytical Equation of State (ANEOS) package (56), were used to describe the

thermodynamic behavior of target and impactor materials. The strength model presented

2

in Collins et al. (48), with a modified failure strain equation (57), was used to describe

the response of materials to shear deformation. The strength model includes a transient

target weakening model that facilitates deep-seated gravitational collapse of the initial

bowl-shaped cavity (58). The physical explanation for this apparent target weakening is

still a matter of debate; in our simulation the assumed explanation is acoustic fluidization

(59), which is incorporated using the “block-model” approach (see 60, and references

therein). The relevant material strength parameters are given in Table S1. Simulations

were performed using the latest version of iSALE (44) and processed to examine the

provenance, shock state and kinematics of peak-ring materials (Fig. 1A-F).

When locating the drill hole on the numerical simulation (Fig. 1F), we have attempted to

match its position with the position of the drill hole on the seismic reflection profile (Fig.

2A). Site M0077A is located on the outer edge of the peak ring - not at its

topographically highest point. The range of shock pressures encountered by the peak-

ring rocks is fairly consistent across the peak ring, so the precise location of the drill hole

on Fig. 1F does not affect our conclusions.

Seismic reflection

Multichannel seismic line ChicxR3 (Fig. 1G) was processed through post-stack time

migration as described in Gulick et al. (13) and then depth converted using the ocean

bottom seismometer constrained velocities described in Christeson et al. (19).

Interpretation in this study follows the methodology from Gulick et al. (14) with the

difference that zones of similar seismic facies were distinguished based on interpreted

lithology. Cenozoic sedimentary rocks are interpreted above the regionally mappable top

3

of the K-Pg boundary. Mesozoic sedimentary rocks were distinguished by seismic facies

within the annular trough as impact derived material above and crystalline basement

rocks below exhibit a loss of coherent reflectivity. Peak ring rocks are defined by seismic

transparency, except for isolated lower frequency reflectors interpreted as melt zones, and

bounded toward the outer edge by mappable dipping reflectivity (e.g. 11).

Density and natural gamma ray (NGR) measurements

Density and NGR data were acquired on whole-round cores using a Geotek multi-sensor

core logger (MSCL), with density recorded at 2-cm intervals, and NGR at 10-cm

intervals. Core was allowed to equilibrate 6 hours to ambient temperature before MSCL

acquisition. A full calibration of the MSCL sensors was conducted at the start of the

expedition and calibration checks were then performed approximately once every 6 hours

for the gamma density and every week for the NGR.

The GRA densitometer on the MSCL operates by passing gamma rays from a 137Cs

source through a whole-round core and into a sodium iodide (NaI) detector located

directly behind the core (61). The input gamma ray peak has a principal energy of 0.662

MeV and is attenuated as it passes through the core. Attenuation of gamma rays, mainly

by Compton scattering, is related to electron density, and thereby related to material bulk

density by:

ρb = ρew/2ΣN

4

where ρb is bulk density in g/cc, ρe is electron density w is molecular weight and N =

atomic number of elements in the material. For the majority of elements, and for rock-

forming minerals, 2ΣN/w is ~1, whereas for hydrogen it is 1.9841. Therefore, for a

known sample thickness, the gamma ray count is proportional to density. The standard

sampling interval was set at 2 cm with count time set at 10 s. The resolution with this

setup is 0.5 cm.

NGR measurements record gamma radiation, which is emitted from rock primarily as a

result of the radioactive decay of 40K and the decay of isotopes in the 238U and 232Th

series. Measurement of natural gamma rays from the recovered core provides an

indication of the concentration of these elements. The sensor comprises 3 NaI(Tl)

detectors housed in 6 inch diameter lead shields. Emitted gamma rays hit the NaI(Tl)

crystals which produce a pulse of light which is detected by the photomultiplier tube

producing a small electrical current to give a voltage pulse, which is related to the energy

of the gamma emission. Multiple detectors are used in order to increase the recorded

signal level because natural rocks and sediments have very low natural radioactivity, so

combining data collected with multiple detectors improves the data quality. Natural

gamma total counts refer to the integration of all emission counts over the gamma ray

energy range between 0 and 3 MeV; total counts were measured for 1 minute every 10

cm of core. For IODP/ICDP Site M0077A cores, NGR measurements are provided in

counts per seconds (cps).

Full waveform sonic probe (QL40-FWS)

5

The ALT QL40‐FWS tool measures the time it takes for a sound pulse to travel from a

monopole 6 kHz piezoelectric transmitter to 4 receivers. The transmitter and receivers are

mounted on the same tool. The acoustic pulse generated by the transmitter travels in

various different forms through borehole fluid to the rock interface, where some of the

energy is critically refracted along the borehole wall. As a result of wavefront spreading

(Huygens principle), some of the refracted energy is transmitted back into the borehole

fluid adjacent to each of the 4 receivers (RX1 to RX4), located at 60 cm, 80 cm, 100 cm

and 120 cm from the transmitter, respectively. The sampling interval for the transmitter is

4 µs and the vertical measurement interval was set to 5 cm. The tool signal was checked

during acquisition in the steel pipe while running downhole. The sampling interval is 4

µs. Recorded waveforms are then examined, and waves arrival times (transit times of the

acoustic energy) are selected (picked). The excellent borehole conditions at IODP/ICDP

Site M0077A allowed the automatic picking of the first arrival (compressional P‐wave)

between RX1 and RX2 using the WellCAD software package. Locally mis-picked

waveforms were subsequently manually adjusted. By measuring the acoustic transit time

and knowing the distance between the receivers (20 cm), the P-wave sonic velocity of the

rock was calculated and given in kilometers per seconds (km/s).

Vertical Seismic Profile (VSP)

The VSP system consisted of two main components: 1) a seismic source, and 2) a digital

downhole seismic recording system. The pneumatic acoustic sources for EXP364 VSPs

were produced using a Sercel mini-generator-injector (mini-GI) airgun system. The mini-

GI was deployed and suspended directly from the L/B Myrtle at ~2 m below the sea

surface. Compressed air was produced using a Max-Air 90 STD (10.8 scfm) electric (220

6

VAC, single phase) compressor, and the airgun pressure was 2000 psi. Source timing was

controlled by a Real Time Systems HotShot portable controller. At each depth position,

5 shots were recorded on the 3-component wall locking geophone sondes. The depth

encoding was provided to the Sercel system to the nearest centimeter by an electronic

counting wheel on the winch head, and depths were confirmed through comparisons of

gamma ray logs. Velocity analysis used the one way transit time versus depth picks, and

velocities were determined using a local slope method (62).

Table S1 Numerical model parameters Parameter definition Crust &

Impactor Sediments Mantle

Reference density [kg m-3] 2630 2600 3310 Poisson’s ratio 0.3 0.3 0.25 Melt temperature (zero pressure)1 [K] 1673 1500 1373 Simon approximation parameter (𝑎𝑎) 1 [GPa] 6 6 1.52 Simon approximation parameter (𝑐𝑐) 1 3 3 4.05 Thermal softening parameter (𝜉𝜉)2 1.2 1.2 1.2 Intact strength (zero pressure) 2 [MPa] 10 5 10 Intact coefficient of friction2 2 1 1.2 Intact strength limit2 [GPa] 2.5 0.5 3.5 Damaged strength (zero pressure) 2 [MPa] 0.01 0.01 0.01 Damaged coefficient of friction2 0.6 0.6 0.6 Damaged strength limit2 [GPa] 2.5 0.5 3.5 Minimum failure strain at low pressure (𝜖𝜖𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓)3

10-4

Slope of failure strain vs. pressure (𝑘𝑘𝑝𝑝𝑝𝑝)3 [Pa-1] 10-11

Transition pressure for failure strain (𝑝𝑝𝑝𝑝)3 [MPa] 300 Vibrational particle velocity as a fraction of particle velocity4 0.1 Maximum vibrational particle velocity4 [m s-1] 200 Time after which no new vibrations are generated4 [s] 16 Decay time of acoustic vibrations4 [s] 166 Kinematic viscosity of acoustically fluidized material4 [m2 s-1] 288,000

1. Melt curve parameters (63) 2. Strength model parameters (48) 3. Failure strain model: 𝜖𝜖𝑓𝑓 = max (𝜖𝜖𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓,𝑘𝑘𝑝𝑝𝑝𝑝[𝑝𝑝 − 𝑝𝑝𝑝𝑝]) (57) 4. Acoustic fluidization model parameters (60); note the corresponding scaling constants are

𝛾𝛾𝜂𝜂 = 0.008, 𝛾𝛾𝛽𝛽 = 115.

7

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