SPATIAL AND TEMPORAL VARIATIONS OF THE HAITIAN K/T BOUNDARY RECORD: IMPLICATIONS CONCERNING THE EVENT OR EVENTS

Florentin. J-M. R. Maurrasse1, Marcos A. Lamolda2, Roque Aguado3, Danuta Peryt4 and Gautam Sen1

1 Department of Geology; Florida International University; Miami, Florida 33199; USA; e-mail: <maurrasse@fiu.edu>, <seng@fiu.edu>
2 Faculdad de Ciencias-UPV; Campus de Lejona; Apartado644; 48080 Bilbao; Spain
3 Depto. de Geologia; E.U Politecnica; c/Alfonso X El Sabio, 28; 23700 Linares; Spain
4 Instityt Paleobiologii PAN; ul. Twarda 51/55; PL- 00-818 Warszawa; Poland


Figure 1. K/T boundary localities in Haiti discussed in text: (1) Beloc sections adjacent to village (Beloc RD in Fig. 4); (2) Beloc stratotype and Platon Piton; (3) K/T section near Riviere Gosseline; (4) K/T section at Mme.Toussaint (Grand Goave).


Figure 2. Sketch of the measured stratotype section of the K-T boundary layer at Beloc. a, limestone bed; b, fine clay (2 mm thick) layer that also has greatest concentration of Ir; c, laminated sandy marl; d, white chalk lens; e, graded sandy marl; f, coarse spherule bearing marl lens; g, fine spherules in sandy marl; h, coarse, brown-colored spherule-rich smectite layer.
Evidence of physical disruptions caused by the postulated bolide impact [1] at the close of the Maastrichtian is clearly defined in the record of the K/T boundary (KTB) layer from different sites (Fig. 1) in the Southern Peninsula of Haiti [2,3]. Lithologic and biostratigraphic record [4, 5] of the KTB layer from the different sites also shows varying degrees of mixing, yielding faunal components within a time range consistent with bioevents characteristic of the traditional boundary zone, namely the uppermost part of the Abathomphalus mayaroensis Zone, part of the Guembelitria cretacea Zone, and the Parvularugoglobigerina eugubina Zone, respectively (Fig. 2). The nanno floras also show transitional taxa that concur with the foraminiferal data, and are indicative of the Micula murus and M. prinsii Zones as well as the CP1 of the Early Paleocene. [5]. The Boundary layer shows variation in thickness with a maximum of 75cm at the Beloc stratotype [4], and the topmost part of the main tektite layer is coincident with an iridium peak (Fig. 3). Geochemical analyses [6, 7, 8, and others] also demonstrated the tektite nature of the spherules, which can be chronologically related to the impact event recorded at Chicxulub, Yucatan, Mexico, 65 million years ago [6,8]. Faint primary sedimentary structures within the boundary layer are constant at all outcrops, although discrete spatial differences exist even within short distances (Fig. 4). In the areas adjacent to the stratotype (Platon Piton and Madame Toussaint) a volcanogenic layer occurs below the main tektite layer, which has been assigned to the Chicxulub event [1], and shows conspicuous, as well as cryptic, cross-lamination indicative of complex, multiphase subaqueous flow processes that affected sedimentation of the layers.


Figure 3. Iridium peak at the K/T boundary.
Note position of sample 205 (maximum Ir)
located at top of boundary layer in Fig. 2.		 At Platon Piton, the KTB layer consists predominately of tektites, and conforms to the main boundary layer. However, a 65 cm-thick, olive gray (5Y 5/1), volcanogenic layer occurs 7 meters below the KTB horizon. It includes a mixed foraminiferal assemblage indicative of the Latest Maastrichtian. Scarce radiolarian, Archaeodictyomitra lamellicostata, Amphipyndax pseudoconulus, Dictyomitra multicostata, Dictyomitra aff. koslovae, Cryptamphorella aff. conara, also indicate mixing of Campanian to Maastrichtian taxa. The internal fabric of the layer shows anisotropic distribution of the clasts supported by 2 to 30 % matrix similar to the altered tektite layer. Dominant minerals are ilmenite, and mostly dark green euhedral hornblende crystals and fragments, which constitute up to 42 % of the coarse residues; their composition and textural appearance are similar to amphibole phenocrysts found in andesites. Plagioclases make up 15 % of the coarse fraction, and their composition is within the range of plagioclases found in mafic and intermediate igneous rocks.

Figure 4. Lateral variation in boundary beds as they occur at localities 1-2 shown in Fig. 1.

Figure 5. Sub-spherical bi-pyramidal quartz crystal found associated with the volcanogenic layer. Geochemical composition is shown in insert, and SEM analytical results are shown in juxtaposition.

Sub-spherical quartz crystals (Fig. 5) also occur throughout the layer. Arguments can be made for a pyroclastic origin of this layer although such an origin is apparently inconsistent with the geologic history of that part of the Caribbean at that time, non-explosive tholeiitic volcanism occurred much earlier within the Late Cretaceous. Thus, the exact provenance of these eruptive materials remains to be determined. Based on inferred rate of sedimentation of the Beloc Formation, the volcanic event occurred between 300 and 400 kyrs prior to the recorded Chicxulub impact event at 65 M.Y [8].

The outcrop at Riviere Gosseline (Fig. 1) shows an unusual polymictic and extremely heterometric megabreccia layer intercalated within limestone facies of the Beloc Formation. It grades laterally into a large slump similar to an olistolite. The conspicuous tektite-rich unit characteristic of the stratotype area is absent, but a lamina (0.2 to 0,8 cm) occurs 63 cm below the megabreccia level and includes altered microspherules with tear drop shape characteristic of impact melt ejecta materials or microtektites as found in the stratotype. Stratigraphically the lamina is coeval with the lower part of the tektite-rich horizon at Beloc. Clasts in the megabreccia include rip up fragments of the Beloc Formation, as well as exotic rocks from the Macaya Formation, shallow-water algal limestones with rudists, andesitic fragments, broken crystals of plagioclase and brown amphibole. Smaller fragments often occur interstitially and the fine fraction may display cross lamination and graded bedding at irregular intervals within the megabreccia.

The outcrop at Madame Toussaint also shows a 60 cm-thick volcanic layer with mineralogical and microfaunal characteristics similar to those described at Platon Piton.The mixed volcaniclastic nature of the bed is also clearly defined in its carbonate content that is consistently lower than 5 %, in contrast to values of 25 to 40 % in the infrajacent and suprajacent marl and limestone layers. Lenticular structures and cross-lamination with varying size fractions are repetitive as seen in previous outcrops.

Spatial and temporal variability of the stratigraphic record including the KTB layer in the Southern Peninsula of Haiti can be attributed to multiple processes that caused varying degrees of mixing and heterogeneity at different sites. Persistent recurrent cross-laminated structures at all KTB sites within the circum Gulf of Mexico region [3; 9, 10, 11,12,13] and elsewhere are certainly primary traction structures that developed beyond the realm of a single basin, and therefore imply an ocean scale disturbance. It is evident that since all basin floors were affected by traction at all depths, they can be related to transient standing-wave oscillations throughout the water column [3] analog to mega seiche [14]. The heterogeneity of patterns observed are thus related to water movement and resuspension of sediment that diminished slowly from one oscillation to the next, as observed in smaller-scale modern seiches [15]. Hence, the rhythmic rocking motion of ocean waters that developed the structures should be a natural response not only to the actual direct disturbance of the water by the causing factor, but also by the large amplitude surface waves that rippled the earth’s crust [14] generated by the powerful shock of the bolide impact [1,16, 17, 18]. The varying magnitude and pattern of expression of the cross-laminae are the result of resuspended sediments [19], depending on grain size involved, the basin area natural sloshing period, and associated damping.

The cross-laminated volcanic beds are also indicative of complex sets of wave frequencies associated with oscillatory deep-water waves that affected the bottom due to a pre-KTB violent volcanic eruption and seismic event yet to be located.

References

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