Introduction ] [ 2. Geological background and methods ] [ 3.
Results ] [ 4. Cupido mexico ] [ 5. Published online in final form pdf on July 21, DOI A rich geobiological record of Cretaceous biotic and abiotic interactions around the proto-Gulf of Mexico has been preserved in the massive Cupido carbonate platform, i.
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This work documents lateral facies variation on a dip slope reef from a new outcrop in the upper part of the Cupido Formation in the state of Nuevo Leon, Mexico. Cupido mexico measured transect is correlated with a stratigraphic column logged in a nearby section. The preserved fossil biota represents marginal reef facies dominated by abundant rudist shells such as Douvillelia skeltoniToucasia sp.
Benthic foraminifers miliolids and textularids with associated dasycladalean algae such as Salpingorella sp. This facies is overlain by a thin cm stromatolite horizon at the upper end of the measured section. This locality represents a new paleobiological and taphonomic window into one of the most extensive carbonate platform system developed along the margin of the Gulf of Mexico during the Cretaceous.
Torres de la Cruz F. In response, massive carbonate platforms formed in low Cupido mexico and high-frequency eustatic cycles shallow carbonates cycles on the scale Cupido mexico s to s to 10s of s of yearscomposed of peritidal carbonates in the ancestral Gulf of Mexico from the Barremian to the Albian Lehmann et al. Cretaceous sedimentary rocks are well-represented in several states of northeastern Mexico, particularly in Nuevo Leon, where massive limestones from the Cupido Formation crown the uppermost part of the Cupido mexico Madre Oriental SMO and line up in superb scenic views around the area of Monterrey Fig.
Click on thumbnail to enlarge the image. The Cupido Formation developed as a reef-rimed carbonate platform composed of corals, stromatoporoids, sponges, rudists, green algae, and benthic foraminifera Wilson Although the large-scale platform paleo-configuration was proposed almost twenty Cupido mexico ago Goldhammer, little work has been devoted to lateral sedimentological and bathymetric variations at smaller scales.
Most previous works Conklin and Moore, have reported the great variability in thickness of this formation, ranging from a few hundred meters of thickness near Saltillo to approximately m near Monterrey both cities separated by an approximate distance of 60 km and up to m at Minas Viejas Wilson and Cupido mexico, located 40 km north of Monterrey.
After the breakup of Pangea and during the subsequent rifting and drifting stages, several basins developed in northeastern Mexico in a process that also generated the Jurassic Louann Salt deposits in Texas and the Campeche Salt basin. The Cupido mexico accommodation space was filled by thick carbonate systems. In this way, the thermal contraction of tectonic plateaus allowed the development Cupido mexico carbonate platforms in this region.
The Cupido platform, coeval with the Sligo platform in Texas Lehmann et al. Johnson, is part of one of most extensive carbonate systems extending over an area of approximately 80, km 2 Lehmann et al. As the main lithostratigraphic unit of the Barremian-Aptian carbonate platform, the Cupido Formation hereafter CFwas defined by Cupido mexico on the Based on chronostratigraphic data and facies association, Lehmann et al.
The CF originated as an extensive coastal lagoon with peritidal carbonate cycles between the basement of the Coahuila Block Fig.
This small locality exposes fossiliferous limestones with sub-horizontal stratification but lacks any close stratigraphic references and Cupido mexico a trend parallel to the land surface, precluding a good stratigraphic control. However, the abundance and size of fossils deserved a closer Cupido mexico. Even where massive grey strata were visible at the basal lateral side at the western side of the outcropstratification is fully-covered by vegetation, by Quaternary sediments and by coquinas composed of reworked fossiliferous material from the Cupido.
All measurements were taken through the hill scarp, without Cupido mexico stratigraphic control during fieldwork campaigns from February to In order to place this transect into the Cupido Formation, the outcrop has been correlated with a stratigraphic column that was logged on the west-facing hill less than one Cupido mexico northwest of the transect.
The measured section was located by 21 GPS Global Positioning System spots for reference; structural strike and dip data were taken for stratigraphic control Fig.
Based on this reference profile, it is assumed that the studied section Cupido mexico with the upper part of the Cupido and documents lateral facies variations along a dip slope bordered Cupido mexico one end by lagoonal facies and at the other by reef facies.
About 50 petrographic thin sections were made for petrographic analysis. Where possible, macrofossils identified in the field were collected, but the largest rudists and corals remained in dolomitized limestones in situ. Grey and brown thick-bedded to massive limestones lie on an overturned-fold structure with a NW-SE-orientation.
The geological open polygon on the Cupido mexico blue line derives from structural data of the geological section modified from Torres de la Cruz The PM locality is located Cupido mexico two hills as shown in the geologic map of Figure 4. The first Cupido mexico section was measured on the flat hill marked as I, and the second vertical section used as reference is located on the hill marked as II Fig.
The dominant lithology is composed of highly-recrystallized and fractured light-brown limestone Fig. C-Dmostly fractured and filled with calcite. The description of the reference transect II Figs. The reference section at the PM locality. B A south-facing panoramic view from the PM outcrop. C and D Sub-horizontal stratification on the reference outcrop II. According to lithology and fossil content the stratigraphic reference column at site II was sub-divided into lower, middle and upper sections Fig.
The lower section is characterized by the succession of thin bioturbated beds with bivalves and chert nodules. The middle section is dominated by bioturbation and calcite nodules.
The upper part, which laterally correlates with the PM outcrop ICupido mexico represented by fossiliferous limestone with rudists, stromatoporoids, corals and the local occurrence of calcareous algae. A-B The upper member is dominated by rudist and coral bindstones preserved in gray limestones. CD, E and F are examples of bioturbation horizons differentially preserved in limestones in the m of the middle section.
Bioturbation Cupido mexico vary in orientation, diameter and preservation. G and H Examples of nodular chert G and bioturbated limestones H found in the lower section of the vertical profile Cupido mexico II. At the PM outcrop site I light grey and brown cm-thick massive limestones with variable fossil content are the dominant lithology. The dip slope was divided into five distinctive zones that were based on the fossil content and associations and their relative position on the measured transect.
The most fossiliferous sampled area covers a m transect and it is found within the m long transect Fig.
A lineal distance of m covered by Cupido mexico sedimentation is found between Zone 1 and Zone 2. Zone 2 at m is the first sampling spot on the outcrop. Between Zone 2 at m and Zone 5 at m there are m of lineal distance of a massif limestone over a massive structure that lacks clear stratigraphic control and that was correlated laterally with the m stratigraphic column. The western margin of the dip slope is partially covered by colluvium and caliche. Pink dolostones and light and dark gray massive limestones characterize the middle and upper zones.
The basal Zone 1 is characterized by a cover of soil, caliche and conglomerates, and the local presence of diagenetic fossiliferous coquinas in situ of unknown age. Secondary sedimentary structures as stylolites, karren and dissolution fronts are evident in zone 1 Fig. These coquinas may be correlated with middle part Cupido mexico the stratigraphic column, described at the 0 m in the measured section, and may represent a lower stratigraphic stage than the rest of the Cupido mexico.
The Cupido mexico microfossils in thin sections correspond to benthic foraminifera and algae. The main macrofossils in Zone 2 at m are small rudists with benthic foraminifera and few calcareous algae as microfossils Fig.
Dolomitic limestone with abundant macrofossils dominates the middle section on Zones 3 at m and Zone 4 at m. This zone is characterized by large rudists Fig. C in close association with stromatoporoid fragments Fig. D and large corals Fig.
The petrographic lithologies of zones Cupido mexico of wackestones and packstones with green algae and benthic miliolids, but other bioclasts such as shells and echinoderm fragments are also common. Zone 5 at m in the measured transect is characterized Cupido mexico the larger rudist shells in low density per square meter. At the upper Cupido mexico of measured section beyond zone 5 small laterally-linked-stromatolites Fig. F usually known as LLS laterally-linked-stromatolites occur as a thin and discrete horizon.
A Typical karren in Cupido limestones from Zone 1. B Rudist wackestones in Zone 2. C Rudist shells in different geometrical planes from Zone 3.
D and E Stromatoporoid and coral fragments in Zone 4. F Small spheroidal stromatolites in Zone 5. Each image illustrates the most characteristic fossil in that specific zone.
The A-A' section corresponds to the section mapped on Figure 2while the right axis means the elevation above sea level. The preserved shells Cupido mexico found either parallel-oriented, but more commonly in erect positions Fig.
Typically rudist shells from zones 3 to 5 show different categories of preservation: These specimens are found as complete individuals in different orientations; more than 20 individuals can be counted every 20 cm 2.
Shells of Toucasia sp. D-F and are especially abundant at the margin of the outcrop; the size of Cupido mexico rudist ranges between 3 to 5 cm. The examples illustrated in Figure 9. E-F are very similar to shells of Pseudotoucasia. G and other less abundant rudist shells are part of the PM macrofossils Fig. Some shells are similar to Offneria sp. Gastropod shells up to 8 Cupido mexico in length from the middle and upper section Fig.