Abstract Approximately 5 km of Cretaceous and Paleogene strata are exposed in the Serranfa del Lnlerior of northeastern Venezuela, and the depositional settings and paleoenvironmental conditions of these strata have been investigated, leading to paleogeographic reconstructions spanning approximately 90 my of passive-margin sedimentation. Exposed Lower Cretaceous strata are generally shallow marine in origin and vary between siljciclasUc shelf deposits and bioherm-dominated, impure carbonate platform deposits. Neocomian-Aptian shelfal and carbonate-platform facies are widespread and comprise the Barranqufn Formation. A major, Early Cretaceous siliciclasiic fiuvio-deltaic system emanated from southwest of the Serranfa del Interior and was the source of the commonly coarse-grained Lower Cretaceous strata. In Early Albian time, a short-lived transgressive/regressive cycle led to deposition of the shaley, deep-shelf deposits of the Garcfa Formation. The E) Cantil Formation was deposited on a Early to early Middle Albian carbonate platform that had significant and variable silicjclaslic contamination (particularly in the southern Serranfa del Interior). The carbonate platform started retrograding southward in Early Albian time and was eventually succeeded by deeper marine deposition of glauconitic sand and shale of the Cbimana Formation. After a brief, Middle Albian progradational event (upper Chimana Formation), regional transgression led to primarily pelagic deposition in the Querecual Formation. Upper Cretaceous strata are notably more homogeneous and of deeper marine origin than Lower Cretaceous strata, and consist primarily of organic-rich, calcareous siltstone and muddy, micritic limestone. These slope deposits of the Querecual and San Antonio Formations are the petroleum source rocks for the Eastern Venezuela Basin. Deep-water (>200 m) sedimentation continued almost continuously from Late Albian until mid-Maastrichtian time, with (he exception of a minor, Santonian- Early Campanian influx of sand at the base of the San Antonio Formation. A voluminous influx of submarine fan sediments occurred in Late Maastrichtian time during deposition of the San Juan Formation. After transgression and monotonous dark shale deposition in the Vidono Formation, renewed progradation in Early Eocene time led to deposition of the glauconitic submarine fan deposits of the Caratas Formation. Shallowing of the depositional surface locally led to shelfal carbonate deposition at the top of the Caratas Formation in Middle Eocene time (the Tinajitas limestone). Passive-margin sedimentation was finished by the close of the Eocene Epoch, and was followed by foredeep sedimentation and eventually by uplift and exposure of the passive-margin strata within the Serranfa del Interior.

ABSTRACT The Edwards (Balcones Fault Zone) Aquifer in central Texas is typically defined as having three segments: the San Antonio, the Barton Springs, and the Northern segment, which are separated by groundwater divides or points of discharge. The San Antonio segment of the Edwards Aquifer is defined as extending from east of Brackettville in the west to Hays County in the east. The San Antonio segment has been further delineated into two pools, the San Antonio Pool and the Uvalde Pool, for water management purposes. The San Antonio Pool is the larger of the two pools and is recharged by the Dry Frio, Frio, Sabinal, Medina, Cibolo, Guadalupe, and Blanco River watersheds, in addition to direct recharge and flow from the Uvalde Pool via the Knippa Gap. To a lesser extent, interformational flow between units stratigraphically above and below the Edwards Formation limestone also occurs. The most prominent points of discharge from the San Antonio Pool are Comal, San Marcos, and Hueco Springs. San Pedro and San Antonio Springs in Bexar County discharge during periods of high stage in the aquifer. There are limited numbers of additional springs in the Frio River watershed with limited discharge. Significant water is discharged from the Medina Lake and Diversion Lake (downstream from Medina Lake dam) system via conduits and surface flow to recharge paleo-alluvial deposits (Leona Gravel) in the Medina River floodplain. This discharge had previously been assumed to recharge the Edwards Aquifer, but it continues downgradient in the Leona Gravel and is lost to the aquifer.

Abstract The Anacacho Limestone represents an anomaly in the Gulfian-age rocks of Texas. Like the Austin Chalk that it unconformably overlies, the Anacacho is a limestone in a section dominated by terrigenous elastics and mudrocks; unlike the Austin Chalk (which is extensive throughout the margin of the Gulf Basin), the Anacacho is a small carbonate bank that extends less than 96 mi (160 km) along an east-west trend on the flanks of the Uvalde Salient. The formation thins perceptibly to the east toward San Antonio, where it is replaced by rocks of the Taylor Group. The formation reaches its maximum thickness on the flanks of the Uvalde Salient, and terminates abruptly at the western edge of the Anacacho Mountains. West of this termination the Anacacho is replaced by the Upson and San Miguel Formations. From the Nueces River, west of the Uvalde Salient, westward to the Anacacho Mountains, the limestone outcrop is continuous for approximately 28 mi (46 km). The width of the outcrop varies from 2.4 mi (4 km) to 9 mi (15 km). East of the Uvalde Salient, outcrops of the Anacacho Limestone are discontinuous and scattered. Much of the section is either covered by alluvium or is lost along faults of the Balcones Fault Zone (Bureau of Economic Geology, 1974). This section, from Blanco Creek eastward to San Antonio, is approximately 60 mi (100 km) in length. However, outcrops in this section are limited in length from a few miles to several hundred feet. Exposures are mostly along

The Tacaná Volcanic Complex represents the northernmost active volcano of the Central American Volcanic Arc. The genesis of this volcanic chain is related to the subduction of the Cocos plate beneath the Caribbean plate. The Tacaná Volcanic Complex is influenced by an important tectonic structure as it lies south of the active left-lateral strike-slip Motozintla fault related to the Motagua-Polochic fault zone. The geological evolution of the Tacaná Volcanic Complex and surrounding areas is grouped into six major sequences dating from the Mesozoic to Recent. The oldest basement rocks are Mesozoic schists and gneisses of low-grade metamorphism. These rocks are intruded by Tertiary granites, granodiorites, and tonalites ranging in age from 12 to 39 Ma, apparently separated by a gap of 9 m.y. The first intrusive phase occurred during late Eocene to early Oligocene, and the second during early to middle Miocene. These rocks are overlain by deposits from the Calderas San Rafael (ca. 2 Ma), Chanjale (ca. 1 Ma), and Sibinal (unknown age), grouped under the name Chanjale–San Rafael Sequence, of late Pliocene–Pleistocene age. The activity of these calderas produced thick block-and-ash flows, ignimbrites, lavas, and debris flows. The Tacaná Volcanic Complex began its formation during the late Pleistocene, nested in the preexisting San Rafael Caldera. The Tacaná Volcanic Complex formed through the emplacement of four volcanic centers. The first, Chichuj volcano, was formed by andesitic lava flows and pyroclastic deposits, after which it was destroyed by the collapse of the edifice. The second, Tacaná volcano, formed through the emission of basaltic-andesite lava flows, as well as andesitic and dacitic domes that produced extensive block-and-ash flows ∼38,000, 28,000, and 16,000 yr B.P. The Plan de las Ardillas structure (the third volcanic center) consists of an andesitic dome with two lava flows emplaced on the high slope of the Tacaná ∼30,000 yr B.P. Finally, the San Antonio volcanic center was built through the emission of lava flows, andesitic and dacitic domes, and it was destroyed by a Peléan eruption at 1950 yr B.P. that produced a block-and-ash flow deposit. The Tacaná Volcanic Complex was emplaced along a NE-SW trend beginning with Chichuj, followed by Tacaná, Las Ardillas, and San Antonio. This direction is roughly the same as the NE-SW Tacaná graben (as proposed in this work), together with other faults and fractures exposed in the region. The rocks of the Chanjale-San Rafael Sequence and the Tacaná Volcanic Complex have a calc-alkaline signature with medium K contents, negative anomalies of Nb, Ti, and P, and enrichment in light rare earth elements, typical of subduction zones.