Post-impact heating of a crater lake

I. Gilmour1, D.W. Jolley2, J.S. Watson1, M.A. Gilmour1 and S.P. Kelley1

1. Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Milton Keynes MK7 6AA, UK 2. Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB9 2UE, UK

Impact hydrothermal systems

•  Candidate habitats for the origin and evolution of life –  Mars exploration focused on cratering environments with

evidence of a long-term history of aqueous processes •  Large impact events can generate a hydrothermal

system if the impact occurs on a water- or ice-rich target

•  Potential significance of impact-generated hydrothermal systems as habitats dependent on –  longevity –  continued availability of liquid H2O and nutrients –  hospitable environments for life in the form of post-impact

lakes and lacustrine sediments

Terrestrial impact crater lakes

•  Numerous terrestrial impact craters contain lakes and lacustrine sediments –  Research mainly focused on the paleoclimatic records

•  In craters where the lake formed immediately post-impact, basal lacustrine sediments may have been altered by the impact-generated heating or hydrothermal system enabling constraints to be placed on the extent and duration of heating

Boltysh Impact Crater •  25km complex crater •  Ukrainian Shield – impact on

land •  Ar/Ar age 65.17 ± 0.64 Ma

(Kelley & Gurov, 2002) •  Developed a lacustrine

depositional system in 600 m of accommodation space

•  Pre-dates Chicxulub by a few ka (Jolley et al. 2010)

•  Drilled in the 1960s & 70s •  Cores lost

Scien&fic  Drilling,  Spring  2008  

•  596m  cored  borehole  west  of  central  upli@  •  >95%  recovery  

•  596  -­‐  582m  –  allochthonous  impact  breccia  •  390m  Cenzoic  crater  fill  

•  582  –  490m  cyclic,  fining  upwards,  poorly  sorted  sands  and  sandy  muds  >  turbidity  currents  

•  490  –  190m  finely  laminated  organic  rich  shales  •  Lacustrine,  abundant  plant  macrofossils  

•  ~300m  abundant  ostracods  and  gastropods  (in  life  posi&on),  interbedded  with  gypsum  lamellae  >  shallow  evapora&ve  lake  

(Ames et al., 1998). This is consistent with differences between thelevel of alteration within the Kara, Popigai, and Puchezh-Katunki im-pact structures, Russia (Table 1), where the most intensive impact-generated hydrothermal alteration took place in the craters thatformed in shallow continental shelf or intra-continental shallow ba-sins (e.g., Kara and Puchezh-Katunki) (Naumov, 2002). The differencein the intensity of hydrothermal alteration of crater-fill impactitesbetween the Haughton and Ries impact structures is notable giventheir similar size (23 and 24 km, respectively) and the fact that theyboth occurred in a continental setting. Critically, the crater-fillsuevites at the Ries are overlain by !400 m of lacustrine crater-fillsediments and sedimentation appears to have commenced immedi-ately following impact (Arp, 1995). In contrast, at Haughton, there isno evidence preserved of a crater lake immediately post-impact(Osinski and Lee, 2005). This suggests that the presence/absence ofan overlying crater lake may play a critical role in determining thelevel of hydrothermal alteration of crater-fill impactites.

2.2.2. Interior of central upliftsIn many terrestrial impact structures, erosion has removed the

superficial crater-fill impactites. This is reflected in the largenumber of sites where hydrothermal alteration has only beendocumented in the more deep-seated lithologies of central uplifts(Table 1). As noted above, central uplifts are formed during themodification stage of complex impact crater formation and theiruplifted geotherms can contribute a heat source driving hydrother-mal systems. Central uplifts form in craters >2–4 km diameter onEarth, and >5–10 km on Mars (Melosh, 1989) and are comprisedof fault-bounded blocks of coherent to brecciated bedrock com-monly with injection dykes of impact melt-bearing or melt-freeimpact breccias. Mineralization within such lithologies is typicallydiscrete and restricted to vug and vein filling cavities and alongfractures (Fig. 2b). Deep drilling of a number of structures, suchas the !35 km diameter Manson (McCarville and Crossey, 1996)and !80 km diameter Puchezh-Katunki (Naumov, 2002) impactstructures, reveal a zoned alteration assemblage with inferredhydrothermal mineral crystallization temperatures that increaseboth with depth and towards the crater center (Fig. 1).

2.2.3. Outer margin of central upliftsStructural studies of complex impact structures have shown

that the outer margins of central uplifts are often highly fractured

and faulted because they represent an interference zone where theinwards-collapsing crater walls interact with the outwards-collapsing edge of the central uplift (Kenkmann and von Dalwigk,2000; Osinski and Spray, 2005). Not surprisingly, these zones com-monly represent sites of more intense hydrothermal alteration,particularly the infilling of fractures to form vein networks (Figs. 1and 2c) (Hode et al., 2003; Osinski et al., 2005). Observations fromHaughton suggest that these outer central uplift regions are buriedunder crater-fill impact melt rocks and breccias in fresh craters.

2.2.4. Ejecta depositsImpact ejecta deposits are characteristic features of fresh im-

pact craters on Earth and other planets. Such deposits are superfi-cial in nature, typically tens of meters thick for craters <100 km indiameter and as a result of erosion are rarely preserved on Earth.An important observation is that ejecta deposits appear to be com-prised of (at least) two distinct facies or layers in many craters onthe terrestrial planets (Osinski et al., 2011). The Ries structure inGermany is an excellent example, where a patchy layer of impactmelt-bearing breccia overlies melt-free lithic breccias (BunteBreccia). Importantly, the Bunte Breccia deposits were emplacedat ambient temperatures and no evidence of hydrothermal alter-ation has been documented (Hörz, 1982). The overlying impactmelt-bearing breccias, in contrast, were emplaced at temperatures>750–900 !C (Osinski et al., 2004).

A range of ‘‘secondary’’ minerals have been documented withinthe impact melt-bearing breccias, with montmorillonite clay andzeolite minerals being the dominant assemblages (Fig. 2d). Compli-cations with the origin of these assemblages arise due to the natureof the groundmass. In particular, there is evidence for two genera-tions of hydrous silicates with an early undetermined groundmass-forming phase, potentially formed through devitrification orautometamorphism of hydrous impact glasses (Osinski et al.,2004), and later cross-cutting veins of platy montmorillonite clay(Osinski, 2005a). Some favor a hydrothermal origin for at least someof these clays (Newsom et al., 1986; Osinski, 2005a), while others,based on stable isotope studies, suggest a low-temperature origin(<20 !C) (Muttik et al., 2010). However, these lower temperaturesare based on studies of bulk samples so that it is unclear what gen-eration of hydrous silicates were analyzed and/or whether this rep-resents a modern-day overprint of an originally higher temperatureassemblage. Regardless of these complications, it appears that the

Fig. 1. Distribution of impact-generated hydrothermal alteration deposits within and around a typical complex impact crater. The six settings are highlighted and numberedin the order in which they are discussed in the text.

G.R. Osinski et al. / Icarus xxx (2012) xxx–xxx 5

Please cite this article in press as: Osinski, G.R., et al. Impact-generated hydrothermal systems on Earth and Mars. Icarus (2012), http://dx.doi.org/10.1016/j.icarus.2012.08.030

Distribu&on  of  impact-­‐generated  hydrothermal  altera&on  deposits  within  and  around  a  typical  complex  impact  crater  (a@er  Osinski  et  al.  2012)  

Molecular  parameters  of  cooling  (thermal  matura&on)  

Hopane  in  sediment  (geological  configura&on)  

ββ22R  

βα22R   αβ22R   αβ22S  

x

ββ/(αβ+βα+αβ)

βα/(αβ+βα)

Thermal  maturity  parameters  

0 5 10TOC /%

540

546

552

558

564

570

576

582

Core

Dep

th /m

K/Pg0.1 0.3 0.5 0.7 0.9

βα/(αβ+βα)0 50100150B. Braunii

0.1 0.3 0.5 0.7 0.9ββ/(αβ+βα+ββ)

C 31ββ

C 31αβ22R

C 31βα

C 31ββ

C 31βα

C 31αβ22R

C 31αβ22S

C 31ββ

C 31βα

C 31αβ22R

C 31αβ22S

15 18 21 24 27δ18OVSMOW/‰

Previous estimates of duration of heating

•  ~1.5 – 4.5 ka for the 4 km diameter Kärdla crater (Jõeleht et al., 2005) •  ~5 ka for 24-km-diameter Haughton crater (Parnell et al. 2005) •  67 ka for 30-km-diameter crater in an early Martian environment (Abramov

and Kring, 2005) •  ~600 ka. and ~1.6 Ma for 23-km-diameter Lappajärvi (Schmieder and

Jourdan, 2013)

•  In comparing the longevity of the hydrothermal systems developed at the Ries and Haughton impact structures, Osinski (2012) concluded that crater lakes were critical in the development of longer-lived hydrothermal systems

•  Continuous sedimentation record at Boltysh in 600 m of accommodation space provide powerful stratigraphic constraints on timescales

Post-impact timescales

•  Palynology of early post-impact sediments

•  Early-mid successional community of ferns and angiosperms

•  Parallels with inter-lava flow durations

•  2 – 5 ka timescale between the basal lake sediments and fern-spike that marks K/Pg boundary (~581.6 m)

•  Need to constrain longer timescale

CLIMATIC OSCILLATIONS STALL K/PG RECOVERY

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576.5576.7576.9577.1577.3577.5577.7577.9578.1578.3578.5578.7578.9579.1579.3579.5579.7579.9580.1580.3580.5580.7580.9581.1581.3581.5581.7581.9582.1582.3582.5582.7582.9583.1583.3

0 20

Cup

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0 20

Pinac

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ndiff

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icac

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Ros

acea

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0 20 0 20 0 20 0 20 0 0 0 0 0 20 40 60

Nor

map

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0 20

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map

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0 20 40 60 80 100

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(incl. P

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0 20

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Gymnosperms Angiosperms - post Normapolles Normapolles Ferns

Fe

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Ph

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Boltyshpost impact

BarrenZone

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Fig. 2. Frequency plot of selected taxa summed by botanical affinity. These are shown as count data from aliquot mounts of standard dry weight rock, because of the low pollen frequencies in some samples. The significant increase in diversity and influx of Palmae pollen (mainly Arecipites spp.) at the onset of fern spore spike Phase 2 should be noted. The Platanaceae–Normapolles–Pinaceae association that succeeds Phase 2 is defined by the dominance of pollen from these families from 578.1 m.

Superimposed on a long-term reduction in moisture availability marked by increasing Normapolles dominance, declining ferns and Cupressaceae are shorter-term oscillations (Figs 3 and 4). Periods of higher moisture availability occur early in each oscillation (O1–O4, Figs 3 and 4), and correspond to low-diversity palynofloras. These pass into intervals of higher palynofloral diversity in the succeeding drier period. In the early, wetter period of each oscillation, diversity may have been suppressed by competition from Cupressaceae as the dominant plant in the true swamp community. In the succeeding drier periods lower moisture availability would have reduced the ecospace available to Cupressaceae, resulting in an open mosaic of plant communities with correspondingly greater diversity. This ecosystem fragmentation is evident not only from the response of the broadly thermophyllic Normapolles group (Batten 1981), but also in the post-Normapolles angiosperms and ferns. Ferns main-tained higher taxonomic diversities in the later, drier stages of oscillations O1, O3 and O4 (Fig. 4) while undergoing a significant fall in overall spore abundance (Fig. 3).

The K/Pg event occurred early in oscillation O1, amplifying the moisture availability and temperature (Tschudy & Tschudy 1986) and enhancing conditions for the dominance of ferns in the primary recovery vegetation. The subsequent reduction in moisture availabil-ity in the upper part of this oscillation modified the plant successional pathway. Transition to the higher diversity, angiosperm-dominated

mid-successional communities during periods of reduced moisture availability would have retarded the spread of true swamp late suc-cessional vegetation. In consequence, the apparent rate of recovery from the K/Pg event of Boltysh terrestrial ecosystems would have been retarded by oscillations unconnected with the K/Pg.

Duration of biotic reassembly

Constraining the duration of post K/Pg biotic reassembly in the Boltysh area is facilitated by the occurrence of the Dan-C2 negative CIE in sediments overlying the upper limit of oscillation O4 (Gilmour et al. 2012). Onset of the Dan-C2 negative CIE occurred at 65.98 Ma, between 0.20 and 0.32 myr after the K/Pg boundary (66.24 ± 0.06 Ma). The upper limit of oscillation O4 occurs 8 m beneath the base of the Dan-C2. The thickness of each successive oscillation was controlled by the efficiency of clastic sediment input via the marginal fluvio-deltaic system and by ejecta availability with increasing blanket denudation. These factors were probably compounded by decreasing fluvial discharge consequent on the overall warming and drying cli-mate evident prior to the Dan-C2 (Fig. 3, and Gilmour et al. 2012). Variability in clastic sediment input to the crater is evident from the crater fill facies distribution derived from the Russian drilling pro-gramme (Fig. 1), which identified turbidite fan retreat towards the crater margins prior to the Dan-C2. From the K/Pg boundary to the

at Open University on April 24, 2013http://jgs.lyellcollection.org/Downloaded from

5m  

Early  Successional  

Mid  Successional  

Late  Successional    

-38 -36 -34 -32 -30 -28 -26 -24 -22 -20δ13Corg (‰)

Age Model for Boltysh

Precessional  ~178  ka  

Obliquity  ~340  ka  

K  

Pg  ~250  ka  

-35 -30 -25 -20δ13CVPDB/‰

-50

0

50

100

150

200

250

300

350

400

Age

rela

tive

to o

nset

of C

IE /k

a

-1 0 1 2 3 4δ13CVPDB/‰

DSDP 527Boltysh

0 1 2 3δ13CVPDB/‰

ODP 1049C

0 1 2δ13CVPDB/‰

DSDP 528

-35 -30 -25 -20 -15δ13CVPDB /‰

Precession Obliquity

Comparison with marine Dan-C2 hyperthermal record

~30  -­‐  40  kyr  

Astrobiological Significance

•  Impact hydrothermal environments –  Spatial extent –  Continued availability of liquid H2O, energy and nutrients over

extended periods of time •  Majority of Martian impact craters have diameters of less

than 50 km –  many contain well-preserved lacustrine sedimentary deposits

•  Boltysh –  no evidence for timescales of heating as long as 600 ka –  estimate of ~30 – 40 ka. is longer than Haughton crater –  Haughton, no evidence preserved for a crater lake forming post-

impact –  Supports the suggestion that the presence an intra-crater lake

may play a crucial role in determining the extent and duration of impact-induced hydrothermal systems